NREL Style Guide Full Text

Explore the full text of the NREL Style Guide. 

508 compliance

As a leading, respected national laboratory, NREL must ensure that its publications and content are accessible to all people. Specifically, we must ensure that everything is “508 compliant.”

What It Means

In 1998, Congress amended the Rehabilitation Act of 1972 to require federal agencies to make their electronic and information technology accessible to people with disabilities. For example, individuals using assistive technology (such as JAWS, a computer screen reader program) can read a document that is 508 compliant.

What It Involves

All graphs, graphics, animations, fact sheets, and so on must be accessible. Further, videos, animations, and audio files must be 508 compliant. These media types require text versions.

Working with a communications representative will ensure that your content goes through the proper process and is 508 compliant before publishing.

**Don’t Forget To Add Alt Text!**

A key part of ensuring 508 compliance involves adding alt text for every figure and photo in technical reports, fact sheets, articles, webpages, social media, and so on. Alt text provides a semantic meaning or description of the image. It can also be read by search engines. 

Keep It Simple

Imagine if, instead of reading a document, you had to listen to it being read to you. By keeping this in mind, you can write alt text that is clear and descriptive. To help, see the following examples of alt text—one for a photo and one for an illustration. For more complicated figures or graphs, try to provide a high-level overview of what is being shown (versus describing every detail).


Photo of an eagle flying out of a cage with sky above, the ground below, and wind turbines in the background.

Alt text: Eagle flying out of a cage with wind turbines in the background.


An illustration showing spar-buoy, barge, and tension-line floating offshore wind turbines in the ocean, with the wind turbines above the surface of the water and the foundations anchoring them to the seabed.

Alt text: Illustration of spar-buoy, barge, and tension-line floating offshore wind turbines in the ocean, with foundations anchoring them to the seabed.

For more information on accessibility and alt text, review NREL’s Communication Standards.

Subject: Government Terms, Publication Formatting, Publication Policies and Services

a and an

Use "a" before any acronym or word that begins with a consonant sound. Use "an" before any acronym or word that begins with a vowel sound. An acronym is pronounced as a word (for example, a HEPA filter); an initialism is pronounced as its letters (for example, an NGO). The first sound of the word or letters indicates whether to use "a" or "an." Examples: a light-water reactor, an LWR; a Human Resources Office memo, an HRO memo; a nongovernmental organization, an NGO; a National Renewable Energy Laboratory subcontract, an NREL subcontract.

Subject: Grammar and Usage

abbreviations and acronyms

An abbreviation is a shortened form of a word used in place of the full word (e.g., Inc.). An acronym is a word formed from the first letters of each of the words in a phrase or name (e.g., NREL or DOE). Abbreviations and acronyms are treated similarly in NREL publications. 

  1. Using Abbreviations and Acronyms Sparingly
    Avoid using a given acronym unless you use it extensively in a publication. In a short report, do not use an acronym for a phrase you use five or fewer times. In a long report, do not use an acronym for a phrase you use fewer than 10 times. In a webpage, do not use an acronym for a phrase you use fewer than three times.

    Some two-letter abbreviations and acronyms are acceptable (e.g., AC and DC, or MW). Avoid other two-letter acronyms that are less universally used (e.g., EE and RE).

    If you use many acronyms in a report, add a list of acronyms at the beginning of the report. For an example, see this sample report.

  2. Spelling out Acronyms
    In general, each time you use an acronym for the first time in the body of a report or on a given webpage, spell it out and put the acronym in parentheses after the full name. However, you do not need to spell out most common abbreviations and acronyms (e.g., AC, DC, cm, m, Hz, kW, MW, GW, and rpm) in most technical reports.

  3. Abbreviating Measurement Units
    Spell out a technical abbreviation in full in text when you use it without numerals. For example, write "a few centimeters" rather than "a few cm."

    Abbreviate units of measurement when they are used with a numeral or numeric value (e.g., 900 W/m2, 43 cm, or 60 Hz). With a few exceptions (such as %, °, $, and ¢), use a space to separate them from numerals.

  4. Abbreviating Plurals
    Use a small s (no apostrophe) for plurals of most abbreviations. For plurals of units of measurement, omit the s (e.g., 15 cm, 6 m, 5 million Btu, 75 dB, 40 W).

  5. Abbreviating Equations and References
    You can abbreviate "equation" and "reference" when you use them with numbers, but spell them out at the beginning of a sentence.

    See Eq. 1-1, Eq. 2-7, and Ref. 10.
    Equation 2-1 shows the relation.

  6. Abbreviating in Journals
    For a journal article, consult the publisher's or professional society's guidelines for abbreviations, if they are available. For abbreviations of journal titles, please see the Woodward Library website.

Subject: Data and Measurement, Writing Style


An abstract usually accompanies a journal article or conference paper. It is an important indexing and research tool. Abstracts are usually 200 to 250 words in length and the content summarizes and highlights the major points of the journal article, conference paper, or report. It may also include a brief description of the purpose, scope, and methods used to reach the conclusions.

Some journals and conferences ask that you submit an abstract that briefly describes the paper’s purpose and contents before your submission is accepted. Check with the journal or conference sponsor for guidance on abstract requirements such as length.

Abstracts for NREL Publications

The U.S. Department of Energy’s Office of Scientific and Technical Information requires an abstract of 200 words or fewer for its citation record posting. This abstract is also typically included in the metadata of the final publication PDF and should briefly describe the context, purpose, and nature of the work and summarize major results or conclusions.

Subject: Publication Formatting

academic degrees

Avoid the use of academic degrees unless it's absolutely necessary to establish credentials. If so, use the following abbreviations with periods included after a name and set them off with commas: Ph.D., B.A., M.A., and LL.D. Use them only on first reference. Also, use an apostrophe in bachelor's degree, a master's, etc., but there is no possessive in Bachelor of Arts or Master of Science, for example.

When possible, avoid using Dr. before the names of individuals who hold doctoral degrees, such as Ph.D. Instead, when necessary or appropriate, write out the name of the person’s degree.

Katerina Melnyk, who has a doctorate in computational science, was principal investigator.

Maxwell Garcia, Ph.D., is joining the IPO directorate.

The academic subject of the degree should be lowercase, except for proper nouns.

She has a Master of Science in theoretical physics.

He completed a bachelor's degree in English literature at Harvard University.

Subject: Writing Style


You may acknowledge the reviews, funding, and other assistance of individuals and groups in NREL technical reports and papers. Acknowledgments can go in a preface or foreword in a technical report, or they can be on a separate page if they are extensive. They also often follow the main text in professional journal articles. Journals usually contain examples or instructions for authors.

Subject: Publication Formatting

active voice and passive voice

Try to write more active-voice sentences than passive-voice sentences. In other words, the subject of most of your sentences should be the "actor" or "agent" (who did it?) rather than the thing "acted upon."

Active voice: We tested the apparatus.
Passive voice: The apparatus was tested by us.

Research shows that active voice helps even highly educated readers absorb information more quickly. Passive voice is no longer considered to be more scholarly or scientific than active voice. Active voice also lends clarity and vigor to technical writing. But sometimes passive voice is appropriate, especially when it's more important to emphasize what was done than who did it. Passive voice can add variety to your writing, too. See also personal pronouns.  

Subject: Writing Style


Use U.S. Postal Service abbreviations (such as CO for Colorado and DC for District of Columbia) for states in bibliographies, references, and full addresses (those that include streets or post office boxes).

P.O. Box 123
Denver, CO 80101
In text, when you refer to a state with a city or by itself (for example, "The state energy office is stepping up solar retrofit activities in Massachusetts."), spell out the name of the state in full, except for the District of Columbia (D.C.). See also states and countries.

Subject: Geography

affect and effect

"Affect" is usually a verb, and "effect" is usually a noun.

affect (verb):

The new deposition process affected the efficiency of the device.

effect (noun):

We measured the effect of the new process on the efficiency of the device.

These words can be confusing because "affect" can sometimes be a noun (when it denotes an emotion), and "effect" can be a verb (when it means "to bring about").

Subject: Grammar and Usage

air conditioning

"Air conditioning" is two words when used as a noun and hyphenated when used as an adjective.

Air conditioning is energy-intensive.
The efficiency of the air-conditioning system can be improved.

Subject: Writing Style

air-source heat pump

Subject: Technology-Related Terms

Alliance for Sustainable Energy, the Alliance

The Alliance for Sustainable Energy LLC, equally owned and governed by Midwest Research Institute and Battelle, is the manager and operator of NREL (effective Oct. 1, 2008).

The appropriate term on second and subsequent references is "Alliance" as opposed to the acronym "ASE." Because many companies and groups have ASE as their acronym, this usage will help distinguish the Alliance. Also, because it is used as a proper second reference and not a generic term, the Alliance will remain capitalized for that usage.

Subject: Government Terms

American Recovery and Reinvestment Act of 2009

After spelling out the full name on first reference, you may use "Recovery Act" in subsequent references instead of the acronym "ARRA." But when using "Recovery Act," do not identify it in parentheses after the full name like you would with the acronym.

Subject: Government Terms


Ampersands can be used in acronyms, left navigation, right navigation, and in a website's top banner (but not in the heading). Ampersands can also be used as the official name of a company or initiative, for example, PG&E or Leadership in Energy & Environmental Design. Do not use "&" to mean "and" in other situations.

Subject: Writing Style


You can include detailed background or technical information, derivations, equations, or data tables in one or more appendices. Large, detailed tables are often placed in an appendix. If you have more than one appendix, title them with letters (Appendix A, B, C, etc.). If you have only one appendix, title it "Appendix" rather than "Appendix A." Name figures and tables in appendices so they reflect the title (Figure A-1, Table B-2, etc.). In the case of only one appendix, use the “A-1” convention for figures and tables. 

Subject: Publication Formatting

assure, ensure, and insure

"Assure" means to make sure or give confidence. "Ensure" means to guarantee. "Insure" means to provide or obtain insurance.

The manufacturer assured the group the equipment would work properly.
Ensure the lid is fitted properly before starting the experiment.
The laboratory must insure the new equipment before it can be used.

Subject: Grammar and Usage

author-date citations

This is the preferred style for NREL reports and papers. Do not use a comma between the author's last name and the year: (Smith 2000). See also references.

Subject: Publication Formatting, Writing Style


"Bandgap" is one word.

Subject: Technology-Related Terms


"Baseload" is one word when used as a noun or adjective.

Subject: Technology-Related Terms

because and since

"Because" indicates a cause-and-effect relationship. "Since" indicates a time relationship.

Because the equipment malfunctioned, the experiment failed.
Since we began using the new procedures, there have been no more malfunctions.

Subject: Grammar and Usage


A bibliography, which is different from a reference list, is a list of works that are related to your subject or publication but not cited, either by author or by number, in the text. Alphabetize works in bibliographies according to the last name of the first author. You may use NREL's reference style in listing the works if you don't have other guidelines (e.g., from a journal). Some bibliographies are titled "For Further Reading." Compile your in-text citations of literature and other sources in a list of references.

Subject: Publication Formatting

black start

When used as a noun, “black start” is two words. Hyphenate “black-start” when it is used as a modifier. Avoid using as a verb if possible.

This building is capable of black start.
This building has black-start capabilities.

Subject: Technology-Related Terms


BOS stands for balance of systems (not system).

Subject: Technology-Related Terms

British thermal units

The abbreviation for "British thermal unit" is Btu. "Btu" is used for both singular and plural cases.

Subject: Data and Measurement


Bullets are printed to the left of items in a list. You must have at least two items in a bulleted list.

The following guidelines apply to bulleted lists: 

  • Make bulleted lists parallel in construction (i.e., begin all the items in the list with the same part of speech, such as a verb or a noun, and make sure they are either all phrases or all complete sentences).
  • Use numbered or lettered lists instead of bullets if you want to refer to the list items elsewhere in the text.
  • Begin each item with a capital letter.
  • Follow these rules for punctuation: 
    • If all items are complete sentences, include a period after each bullet. 
    • If all items are single words or short phrases, include a period after the final bullet only. 
    • Do not use semicolons or commas after bullets. 
  • Use bulleted lists sparingly to:  
    • Highlight important items  
    • Draw attention to main points  
    • Help readers find information. 

The example below shows the ending punctuation rule applied for a multilevel list. In general, think of the punctuation as closing out a “thought,” akin to finishing a sentence.

NREL technical reports are divided into: 

  • Front matter 
    • Title page 
    • Disclaimer 
    • Foreword 
    • Preface 
    • Acknowledgments 
    • List of acronyms
    • Executive summary 
    • Table of contents 
    • Lists of figures and tables.
  • Body text, organized into sections
  • Back matter
    • Glossary
    • Reference list
    • Bibliography
    • Appendices. 

Report Formatting
In text, the first level of bullet is indented 0.25 in., and text begins at the 0.5-in. mark. This level is bulleted with a solid dot. Second-level bullets are open dots, and third-level bullets are em dashes (—). Each subsequent level of bullet is sequentially indented 0.5 in. In lists with items that are more than one line, each bulleted item is followed by a 6-pt. space. 

On the Web 
For web content (and for PowerPoint slides and figures), terminal punctuation for a bulleted list is optional when there is no lead-in sentence.Use best judgment and remember that consistency is key. When formatting bullets on the web, there should be a space between the text above the bullets and the first bullet. To facilitate scanning, consider adding a blank line between each bulleted item when the bulleted text is long. Do not use bullets with lists of links.

Subject: Publication Formatting


1. Proper Nouns

Capitalize proper names. These include the names of government programs, official projects, formal groups, organizations, companies, titles when they precede a name (use lowercase in titles that follow the name), specific geographic areas or features, and ethnic groups.

When referring to NREL, "National Renewable Energy Laboratory" is capitalized, but "the lab," "the laboratory," and "national laboratories" are not.

the Alcohol Fuels Program
the Ethanol Project
the Human Resources Office
the U.S. Bureau of Mines
Solarex Corp.
President Carter
Christine Johnson, president and chief executive officer
the Southwest
Lake Powell
the Colorado River
African, Asian, Black, Caucasian, Hispanic, or Native Americans

One exception to this rule is companies and products with stylized lowercase or "camel cap" names (e.g., eBay, iPhone). In these cases, use the company’s or product’s preferred capitalization.

2. Figure Captions, Table Titles, and Section Headings

Figure captions: Capitalize only the first word and proper nouns in figure captions. No period needed (unless there are multiple full sentences).

Figure 1. Results for the electrochromic window developed at NREL

Table titles and section headings: Capitalize the main words of table titles and headings and subheadings, including the second word in a hyphenated term (e.g., "PV Program Five-Year Plan"). No period needed.

Table 1. Number and Frequency of Defects in Six Samples

Testing the 7.6-m Blades
Results for E. Coli
Development of Method To Detect Anomalies

Do not capitalize:

  • Articles (e.g., "a," "an," and "the") unless they begin the title or heading
  • Conjunctions of three or fewer letters (e.g., "and," "or," "nor," "yet," "so," and "but")
  • Prepositions of three or fewer letters (e.g., "for," "of," "on," and "up").

Do capitalize:

  • Conjunctions (e.g., "than") and prepositions of four or more letters (e.g., “from,” “with,” “above,” “after,” “down,” “inside,” “over,” and “into”)
  • "To" as an infinitive (but lowercase as a preposition, e.g., “Scientists Travel to Chile To Engage Utilities”)
  • Verbs, including "is" and "are."

For journal/conference submissions or other non-NREL publications, follow the style recommended by the professional society or publisher.

3. Titles

Capitalize titles when they precede the person's name. Lowercase titles and names of groups when they follow the name.

Chief Operating Officer Mark Wilson
Mary Jones, the president of the company
John Smith, the chair of the committee

4. Trade Names

Capitalize trade or brand names, and include a trademark, copyright, or other symbol only when it's an Alliance-registered trademark. Include the symbol the first time you use the trade name in body text (not in a title, acronym list, or section header); thereafter, you may omit the symbol. Also use superscript for trademark symbols. See the trademark symbols entry for a list of Alliance trademarks.

5. Taxonomic Names

When writing about botanical and zoological divisions, capitalize the names of all divisions higher than species: genera, families, orders, classes, and phyla. Italicize genera, species, and varieties.

Clostridium thermocellum
Escherichia coli

After you first mention them (and spell them out), you can abbreviate most generic names followed by species names.

C. thermocellum
E. coli

See also captions, fiscal year, geographic regions, headings and subheadings, states and countries, and tables.

Subject: Grammar and Usage, Writing Style


Each substantive photo and image should be accompanied by a caption. Capitalize the first word in a caption and use lowercase thereafter, except for proper nouns and capitalized abbreviations. You don't need a period at the end of a caption unless there is additional text below the caption such as a figure note or the caption includes multiple complete sentences.

For information about figure captions, see figures.

See also photo, image, and video credits.

Subject: Publication Formatting

chemical terms

Do not use a hyphen in most chemical expressions, even when the terms are used as modifiers.

carbon dioxide levels
hydrogen ion activity

Use a hyphen after prefixes when that's the standard for certain chemical formulas.

L(+)-2, 3-butanediol

Use a hyphen to indicate mixtures or combinations.


Subject: Technology-Related Terms


See references and citations for guidance on author-date and numbered citations.

Subject: Publication Formatting


"Cleantech" is spelled as one word. It is not hyphenated, and the "t" is not capitalized. The word "cleantech" is typically used in reference to investments in sustainable technologies, including renewable energy and energy efficiency. Don't use as a shortened form of "clean technology" in other references.

Subject: Technology-Related Terms

close-spaced sublimation

The term is "close-spaced sublimation," not "closed-space sublimation."

Subject: Technology-Related Terms


Subject: Technology-Related Terms


Colons formally introduce a list or series, a question, or an amplification.

We test three types of collectors: flat plates, evacuated tubes, and parabolic troughs.

When the colon is followed by a complete sentence, capitalize the first letter of the first word after the colon.

The relationship between the two is inverse: When volume increases, pressure decreases.

Colons also often separate the parts of a ratio.

We added enough water to obtain a 3:1 dilution.

However, commas, not colons, usually follow words such as "that is," "namely," and "for example." You don't need a colon after a verb or preposition that precedes or introduces a list ("includes," "to," "with," "between," etc.). Use a colon when a noun (such as "the following") introduces a list in the text.

Subject: Punctuation


1. When To Use Commas

Use a comma to separate items in a series, including the next-to-last word in the series.

We develop solar thermal, wind, biomass, and photovoltaic energy technologies.

Use a comma to separate the parts of a compound sentence linked by a coordinating conjunction (such as "and," "but," "or," and "nor") when each part has its own subject and verb (unless they're very short).

I laughed at the unintentional joke, but she frowned.

Use commas to set off nonessential or nonrestrictive (parenthetical) words, phrases, and clauses from the rest of the sentence. In other words, the commas signal that the information between them is something extra and not essential to the meaning of the sentence.

The subsystem, which takes a day to install, will be delivered in two weeks.

Use commas to enclose the name of a state when it follows a city and a year when it follows the month and day.

The test systems in Gardner, Massachusetts, are performing well.
The next test sites will be in Golden, Colorado, and Chapel Hill, North Carolina.
On April 11, 1998, the committee members completed five of the six objectives.

2. When Not To Use Commas

Do not use a comma to separate compound subjects or compound verbs.

Theorists and nonspecialists alike agree on the importance of the discovery. (There is no comma between the two parts of this compound subject.)
The researchers rolled out the thin metal sheet and formed it into coils. (There is no comma between the two parts of this compound verb.)

Do not use commas to set off words or phrases that are restrictive (i.e., essential to the meaning of a sentence).

Only the sensors that were attached to the outer edge failed. (The words are essential to the meaning of the sentence.)
The system will work efficiently only if it includes storage. (The words are essential to the meaning.)

See also which and that.

Subject: Punctuation

compose and comprise

"Composed of" is correct; "comprised of" is incorrect. See the examples below.

The United States is composed of 50 states.
The parts constitute the whole.
The whole comprises its parts.

The department comprises four groups; each group is composed of five to seven scientists, technicians, and support staff.

Subject: Grammar and Usage

concentrating solar power

Concentrating solar power (CSP) captures the sun’s heat and uses the thermal energy to produce electricity (e.g., via a steam turbine).

Subject: Technology-Related Terms

Congress and congressional

Capitalize "U.S. Congress" and "Congress" when referring to the U.S. Senate and House of Representatives. Lowercase "congressional" unless it is part of a proper name.

The U.S. Congress is reviewing congressional salaries. A full list is available in the Congressional Record.

Subject: Government Terms


See table of contents. For a list of all the content a report may include, see report contents.

Subject: Publication Formatting

contiguous United States, continental United States, and CONUS

"Contiguous" means sharing a common border; "continental" means belonging to a continent. In its strictest sense, “contiguous United States” refers to the lower 48 states in North America (including the District of Columbia), and "continental United States" refers to 49 states (including Alaska and the District of Columbia). However, the terms are often confused and used inconsistently. Best to specify the meaning on first use of the phrase.

Follow the acronym rules if using CONUS, but specify which states the phrase covers on first mention.

Subject: Writing Style

cooperative research and development agreement

Use lowercase for "cooperative research and development agreement" because it's not a proper noun. On second reference, you can use the acronym "CRADA."

Subject: Government Terms


Subject: Technology-Related Terms


CPV (concentrating photovoltaics) uses lenses to intensify the sunlight striking PV cells, which enhances the cells' electricity production.

Subject: Technology-Related Terms

criterion, datum, memorandum, phenomenon, and their plurals

"Criterion" is a singular noun (one criterion), and "criteria" is the plural (two or more criteria). "Data" is the plural of "datum." The plural of "memorandum" can be either "memoranda" or "memorandums." "Phenomenon" is singular, and "phenomena" is plural.

Subject: Data and Measurement, Grammar and Usage


Follow the general rule for prefixes and do not use a hyphen:


Exceptions: Cyber Monday (n.) and cyber (adj.) as a separate modifier, e.g., cyber shopping and cyber liability insurance.

See the Associated Press Stylebook for more guidelines.

Subject: Websites, Writing Style


Use dashes (often called "long dashes" or "em dashes") to enclose and set off parenthetical (nonessential but often illustrative) information in a sentence. Also use dashes to set off a list of items separated by commas. Do not add spaces around the dash.

The polymer components of the cell walls—cellulose, hemicellulose, and lignin—provide the feedstocks for these chemicals.

Use an em dash to signal that an important point is going to be made or that a change in the construction of the sentence follows.

The presentation concluded with a discussion of the two project factors that concern contractors the most—cost and time.

The major omission in the project assessment was the delay caused by the circuit failures—everyone knew about it, but no one mentioned it to the reviewers.

You can usually use commas, colons, and semicolons in place of dashes, but dashes add special emphasis.

Use shorter dashes known as "en dashes" (rather than a hyphen or em dash) to indicate a range or to substitute for the word "to."

25–45 cm2
2–5 runs per hour
See sections 3.1–3.6
Jan. 16–Feb. 3, 2011.

In date spans, do not use "from" in conjunction with an en dash (e.g., "from Jan. 16–Feb. 3"). The correct form is "from Jan. 16 to Feb. 3" or "Jan. 16–Feb. 3."

Do not use an en dash (or hyphen) to mean "and"; the word "between" is followed by the word "and" (not "to"): between 25 and 30.

Subject: Punctuation

data in tables

Place a zero to the left of the decimal in any number less than 1 in text and tables (e.g., 0.5, 0.039). Align columns of data vertically on the decimals. When the units of measurement for the data are different, alignment is not necessary (but be sure to specify the units).

Subject: Data and Measurement


“Dataset” is spelled as one word.

Subject: Data and Measurement

decision maker

Subject: Writing Style

degree symbol

Do not include a space before or after the degree symbol.


Repeat the degree symbol in ranges.

32°C–36°C (temperature)
60°–90° (angles)

Express kelvins as K rather than as °K; leave a space before the K.

85 K

Subject: Data and Measurement

dish/engine systems

Use a slash rather than a hyphen.

Subject: Technology-Related Terms


Express thousands of dollars using a comma.


Express millions and billions of dollars this way.

$3 million
$1.2 billion

Do not use a hyphen to join a number and words such as “million” or “billion,” even when used as a unit modifier.

$4 million prize
$200 billion budget

In technical reports and papers, use a dollar sign to express costs less than $1.

$0.06 per kilowatt-hour

Subject: Data and Measurement


When you want to leave out part of text material you are quoting, use ellipsis marks (three dots with a space on each side) to indicate the omission.

A participle is "a word having the characteristics of both verb and adjective ... [that] shows such verbal features as tense and voice. ..."

If the words before the ellipses form a grammatically correct sentence, put a period at the end of the sentence and follow it by ellipses. In most cases, however, you don't have to use ellipses at the beginning or end of quotes, just within them. When you add a word or words to the quote, to make it clear, enclose the added word or words in brackets to show that it is not part of the original quotation.

When you quote whole paragraphs but omit text between any two of them, center three asterisks, with spaces between them (* * *), between the paragraphs quoted. See also quotation marks.

Subject: Punctuation


Email is acceptable in all references for "electronic mail." Use a hyphen with other e- terms: e-book, e-business, e-commerce, e-fuel.

I sent an email to everyone involved with the project.
The email blast was sent to everyone who made a purchase from the e-business.

Subject: Writing Style

energy efficient

Hyphenate “energy efficient” only when used as a modifier:

NREL supports the development of energy-efficient technologies.

The window replacement helped her home become more energy efficient.
Never hyphenate “energy efficiency.”

Energy efficiency strategies in buildings include insulation, daylighting, and plug load management.

Subject: Punctuation


ENERGY STAR is always in capitals. Use ENERGY STAR® the first time it is used on a page; thereafter, use ENERGY STAR. The ® should be superscript, and there's no space between the ® and ENERGY STAR.

Subject: Government Terms

enhanced geothermal system

The preferred term is "enhanced geothermal system." It is also sometimes referred to as an "engineered geothermal system."

Subject: Technology-Related Terms


Make sure that all the terms in your equations are defined and used consistently both in the text and in subsequent equations, figures, and tables.

The conductive heat flow equation is:

dQ/dt = AKdT/dx

dQ/dt = the time rate of heat transfer
A = the area of an end contact
K = the thermal conductivity
dT/dx = the thermal gradient.

Subject: Data and Measurement


Because it's vague, use "etc." (et cetera) sparingly. Don't add it to the end of a list beginning with "for example," or the abbreviation "e.g.," because each word in your list is an example of your subject or topic, but "etc." is not, so you don't need it.

Subject: Writing Style

executive summary

If you include a summary in a report, place it before the table of contents page. If your report is brief, a summary is not usually necessary. If your report is long, or if you think some readers will want one, you can include an executive summary.

An executive summary can be up to 5% to 10% of the length of your paper. It should be written so that it can be read independently of the full report, as executive summaries are frequently published as a separate document. Its content should include a brief statement of the problem or proposal covered in the report, background information, concise analysis, and the main conclusions. Furthermore, it should be written in plain language, where technical language is defined or examples/further context are provided, making it easy for nontechnical readers to understand.

Figures or tables in the executive summary should be labeled using the format Figure ES-1, Table ES-1.

Subject: Publication Formatting


Subject: Technology-Related Terms


Use a capital letter with "federal" for corporate or governmental bodies that use the word as part of their formal names.

Federal Trade Commission, Federal Communications Commission

Use lowercase when the word is used to distinguish something from state, county, city, etc. entities.

federal government, federal court, federal judge

Subject: Government Terms


Figures can include line drawings, graphs, charts, diagrams, schematics, flowcharts, illustrations, and photographs. Be sure that computer-generated figures are clear and readable, so they can be reproduced easily. Make sure the data in your figures correspond to the data in your text and tables.

Number figures in a simple sequence (e.g., Figure 1, Figure 2). In long reports, papers, or book chapters, you may include section or chapter numbers in the figure numbers (e.g., Figure 1-1, Figure 1-2, Figure 2-1, and so on).

Use 10-pt. Arial bold for captions. The caption is centered under the illustration. For data charts and graphs, use 9-pt. Arial for source lines below the figure. See also captions.

A graphic that uses colored lines to represent numbers for generation of concentrating solar power, solar photovoltaics, biomass, wind, and all renewable resources.

Figure 1. Renewables as a percentage of total installed capacity worldwide

No period is needed after a caption if it is an incomplete sentence (see Figure 1 above). If one or more full sentences follow the incomplete sentence (as a continuing caption or subcaption), each caption (including the opening incomplete sentence) should have a period. Don’t bold subcaptions. See Figure 2-1 below for an example.

Figure 2-1. Photoconductivity spectra of a composite CIS thin film.
Inset: The probable energy band diagram.

As required, appropriate credit and Image Gallery information should be provided for figure images. See photo and image credits. Place credit information after the caption.

Figure 2. A Trombe wall at the Zion National Park Visitor Center. Photo by Thomas Wood, NREL 12345

Subject: Publication Formatting

first-person pronouns

See personal pronouns.

Subject: Grammar and Usage, Writing Style

fiscal year

Spell out "fiscal year" (e.g., Fiscal Year 2024) the first time you use it; after that, you can abbreviate it using two capitals followed by a space before the full year (e.g., FY 2024). FY24 may be used to save space in charts and graphs. On the web, always spell out fiscal year.

Subject: Dates


Use Times New Roman for the text of NREL technical papers and reports. Use Arial for figures, tables, and headings.

Subject: Publication Formatting


You can use footnotes to place detailed explanatory or supplementary information at the bottom of a page; use in-text references to cite others' works. Use superscript numerals for footnote numbering. You can also place explanations, details, contradictions, and examples in the text rather than in footnotes. Footnote numbers are printed outside commas and periods but inside colons, semicolons, and dashes.

The experiment took place in April,1 and it was evaluated in May.2
We discussed these three stages of writing7: prewriting, writing, and revising.

Mark the footnotes to tables in NREL reports with superscript letters: a, b, c, etc.

Subject: Publication Formatting


The foreword to a book or formal report contains introductory remarks written, and usually signed, by someone other than the author or authors. Brief introductory remarks written by authors are contained in a preface.

Subject: Publication Formatting


Use words instead of numerals for simple fractions in text.

a third of the way
one-fifth its actual size
three-fourths of the participants

Write out complex fractions with numerals separated by a solidus.

5-1/2 days afterward
2-1/2 times greater

Display complex, built-up fractions by centering them vertically between two parts of a paragraph.

Example of an equation centered and placed vertically between two parts of a paragraph.

Place a zero to the left of the decimal in fractions less than 1.


See also equations.

Subject: Data and Measurement

front matter and back matter

NREL reports can include front and back matter in the following order:

Front Matter

  1. Title page
  2. Disclaimer
  3. Foreword
  4. Preface
  5. Acknowledgments
  6. Nomenclature
  7. Executive summary
  8. Table of contents
  9. Lists of figures and tables

Back Matter

  1. Glossary
  2. Reference list
  3. Bibliography
  4. Appendices

Paginate front matter with small Roman numerals (i, ii, iii) rather than Arabic numbers. Count the title page as page i, but don't print the number on it. All technical reports should contain a title page, a disclaimer, and a table of contents. Many outreach publications, such as DOE/NREL program overviews, contain only a contents list and brief acknowledgments in the front matter.

Subject: Publication Formatting


Subject: Technology-Related Terms

geographic information system

Do not capitalize "geographic information system" unless used as part of a proper noun. It's also "geographic," not "geographical." Our acronym style guidelines apply as well.

Subject: Writing Style

geographic regions

Don't capitalize words that describe general areas of the country or areas of a state.

the eastern United States
southwestern Nebraska
northern New Mexico

Capitalize directional words when they designate specific or widely known regions; if in doubt, use lowercase.

Southern California
West Texas
the Midwestern states
the South Side of Chicago

Subject: Geography

geopressured geothermal resource

Subject: Technology-Related Terms

Geothermal Electric Technology Evaluation Model

Subject: Technology-Related Terms

geothermal heat pump

Subject: Technology-Related Terms

glossary and nomenclature

If you use many mathematical or Greek symbols or technical terms in your report or paper, consider defining them in a glossary or nomenclature. Arrange the list alphabetically, and group Greek letters and definitions alphabetically in a separate list. Nomenclatures are usually in the front of a report, before the contents page. Glossaries usually go in the back, before the references.

Subject: Publication Formatting

Google Earth and Google Maps

When using satellite images from Google Earth and terrain images from Google Maps, include attribution to Google, which is included in Google images with copyright notices such as "© 2009 Google, Map Data © 2009 Tele Atlas." The Google logo and attribution text can be removed if they are added elsewhere within the image content.

In print, if attribution cannot be placed on the image or map, separate attribution text must be provided directly adjacent to it.

In video, attribution must appear on-screen for the duration of the time the map or image is shown; including attribution in end credits only does not suffice.

If the Google Earth image is altered (e.g., text or graphics are added), the image is legal only if Google Earth software is used to make the alteration and correct attribution is included. Any other alteration of the image using any other software is strictly prohibited.

Derivative works cannot be created. For example, NREL cannot combine multiple static map images to show a larger map.

Subject: Publication Policies and Services

headings and subheadings

Here is a standard format for six levels of report subheadings:

First-Level Headings: Arial Bold 18 pt. blue

Second-Level Headings: Arial Bold 14 pt. blue

Third-Level Headings: Arial Bold Italic 12 pt. blue

Fourth-Level Headings: Arial Italic 12 pt. blue

Fifth-Level Headings: Times New Roman Bold 12 pt. black

Sixth-Level Headings: Times New Roman Bold Italic 12 pt. black

Seventh-Level Headings: Times New Roman Italic 12 pt. black

You can number headings and subheadings (e.g., 1.0, 1.1, 1.2, 2.0) if that will help readers with a long report. Print text in 12-point Times New Roman.

Subject: Publication Formatting

heat mining

Subject: Technology-Related Terms

high-performance computing

“High-performance computing” should be hyphenated. The abbreviation HPC can be used to refer to high-performance computing but should not be used to mean high-performance computer. However, the term "supercomputer" may be used in place of high-performance computer.

Subject: Punctuation, Technology-Related Terms

hybrid electric vehicle

This phrase contains no hyphens.

Subject: Technology-Related Terms

hyphens, compound words, and unit modifiers

Hyphenation rules can be intimidating, but remember that the ultimate goal is to provide as much clarity and consistency as possible. If you can’t find the proper hyphenation in this style guide, consult the AP Stylebook, followed by Merriam-Webster.

1. Verb Phrases: Verb, Noun, and Adjective Forms

Verb phrases that contain an adverb (e.g., build up, set up, start up, and break down) are usually written as two words. The noun and adjective forms of these words are usually one word, although there are exceptions.

We observed the slow buildup of biofouling on the blades.
The algae began to build up.

We helped with the setup.
To set up the experiment, begin with fresh samples.

The startup costs were more than we estimated.
The project is expected to start up next year

I think I'm having another breakdown.
It's time to break down the tent.

2. Compound Words Containing Prefixes and Suffixes

In most cases, you don't need a hyphen between prefixes or suffixes and the root words.


threefold, hundredfold
(also 100-fold)

Sometimes hyphens are needed when the root word begins with the same letter that the prefix ends in.


Use a hyphen between prefixes and proper nouns (but not common nouns) or dates whether they're used as nouns or modifiers.


Use two hyphens when adding a prefix to a word that already contains a prefix, even when there is no hyphen after the prefix in the original word.


Finally, these prefixes usually require a hyphen: "ex," "self," and "quasi."

3. Unit Modifiers With and Without Hyphens

Use a hyphen to indicate that words have been combined into a unit modifier, which is a descriptive expression composed of two or more words that form one new meaning. For example, in the term "flat-plate collector," "flat-plate" is the unit modifier. Here are some examples of unit modifiers that usually include hyphens:

low-level radiation
last-minute addition
high-temperature process
fatigue-induced wear
nine-story building
cost-effective solution

To see how adding the hyphen can prevent confusion, consider these examples:

The scientists tested a new defect causing gas.
The scientists tested a new defect-causing gas.

In the first example, the scientists might seem to have tested a defect; in the second example, it's clear that they tested a gas.

You don't need a hyphen in common unit modifiers that are not ambiguous or confusing.

high school students
solar radiation resource
solar thermal electric systems

Don't use a hyphen when both words of a unit modifier are capitalized.

Biofuels Program objectives
Pacific Ocean exploration
World Cup qualifier

Leave out the hyphens if you rewrite a sentence so the words in the unit modifier come after the noun they describe

We purchased state-of-the-art lab equipment.
We purchased lab equipment that reflects the state of the art.

They made some last-minute adjustments.
They made some adjustments at the last minute.

Don't use a hyphen with a unit modifier containing an adverb ending in "-ly."

heavily skewed results
frequently missed deadlines
commonly seen mistakes

Don’t use a hyphen with two-word Latin phrases when the phrases are used as modifiers.

candidates for in situ testing at wind farms
at the atomistic scale, ab initio models provide detailed descriptions

When you use numbers in unit modifiers, retain all the necessary hyphens. However, do not use a hyphen to join a number and words such as “million” or “billion.”

2-ft-diameter tubes
13-cm-wide substrate
$4 million prize

Or rewrite the sentence to omit the hyphens.

tubes that are 2 ft in diameter
a substrate that is 13 cm wide

Use suspended hyphens when your compound modifier is interrupted by another word, such as part of a list.

light-, medium-, and heavy-duty vehicles
5- and 10-m blades

Suspended hyphens can also be used for different prefixes on the same root word (micro- and mesoscale), but the preferred style is to write out each word fully (microscale and mesoscale). Use your best judgment, considering both the context and audience.

4. Common Hyphenated Terms

Certain words and phrases are always hyphenated, regardless of context. Examples include:

decision-making (but decision maker)

Subject: Grammar and Usage

III-V solar cell

This term refers to a cell composed of semiconducting materials from Group III (e.g., gallium) and Group V (e.g., arsenic) elements of the periodic table.

Subject: Technology-Related Terms

Inc. and LLC

Official company names can use the abbreviation “Inc.” or the initialism “LLC” without first defining these terms. Do not use commas around either term.

Alliance for Sustainable Energy LLC
Apple Inc.

Subject: Writing Style

inclusive language

The way we communicate reflects our priorities as a laboratory; using inclusive language is respectful and promotes equity. Following are brief discussions of common topics related to inclusivity—please use this as a starting point as you examine the words that you use and their impact. 


The race and ethnicity entry covers capitalization, hyphenation, and word choice. Beyond that, be mindful of terms and phrases with racist histories—these can be prevalent in both scientific writing and everyday language.

"master/slave” (replace with “parent/child” or “primary/secondary”)
“whitelisting/blacklisting,” (replace with “allow list/deny list” or similar)
“brown bag” (replace with “lunch and learn”)

All written, audio, and visual products at NREL must comply with Section 508, which allows assistive technology (e.g., a screen reader) to relay information to a person. Visit the 508 compliance entry to learn more about captions, alt text, and clear navigation of PDFs, webpages, and more. 

Also, take care to avoid using unintentionally ableist language. Examples like “blind to,” “fall on deaf ears,” “crippled by,” and so on imply that people with these disabilities are ignorant or helpless. Instead, reword your sentences to be specific and clear with what you are trying to convey.


Whenever possible, use words that apply to any gender, such as “moderator” rather than “chairman” or “manufactured” rather than “man-made.” In addition, honor the pronouns that a person has chosen to describe themself. Note that the nongendered “they” is appropriate in reference to a single person or a group of people; further, “they” is preferred over “he/she,” which often feels cumbersome in text and is less comprehensive.  

The AP Stylebook has entries on inclusive storytelling and gender-neutral language. 

Sexuality, Age, Religion, and Socioeconomic Status 

Be mindful in your writing to not assume victimhood or inadvertently apply stereotypes. For example, rather than “poverty-stricken,” use “low-income.” Instead of “elderly,” use “older adults.” Avoid “the” descriptors (e.g., “the homeless,” “the poor”) because they are usually dehumanizing. Also, when considering identity-based descriptors such as sexuality, age, or religion, consider whether the descriptor is appropriate to include. If it is not relevant to the story, there are often more neutral ways of describing a person or group. 

Inclusiveness Check 

Microsoft Word offers an inclusiveness check as part of its proofing options. However, similar to how spell-checkers do not replace review by an editor, this inclusiveness check does not replace common sense regarding eliminating biases and promoting respect. To turn on this inclusiveness check, go to File > Options > Proofing, click on the “Settings” button next to “Writing Style,” and check all the boxes under the “Inclusiveness” heading. 

Screenshot of inclusive language instructions

Other Resources

There are many resources available about inclusive language and promoting diversity and equity in your writing. Following are a few that may be helpful:

Centers for Disease Control and Prevention. 2022. “Preferred Terms for Select Population Groups & Communities.”

Ferguson, Jackie, Kaela Kovach-Galton, and Roxanne Bellamy. 2020. Say This, Not That: Activating Workplace Diversity Through Inclusive Language Practice. The Diversity Movement.

Google. 2021. “Striving for a more inclusive workplace? Start by examining your language.”

Inclusive Naming Initiative. 2023. “Frequently Asked Questions.”

Lawrence Livermore National Laboratory. 2022. Pronouns Matter Everyday. LLNL-BR-831843.

Linguistic Society of America. 2016. “Guidelines for Inclusive Language.”

Questions can be directed to the Editorial Board or the Office of Diversity and Inclusion.


Subject: Grammar and Usage


An initialism is similar to an acronym, but it is pronounced by its letters.

National Fire Protection Association (NFPA)
public utility commissions (PUCs)
chemical vapor deposition (CVD)
compact vacuum insulation (CVI)
chlorofluorocarbons (CFCs)

Use a small s (no apostrophe) for plurals of most initialisms (e.g., PUCs and CFCs, not PUC's or CFC's).

Avoid the use of initialisms unless they are used extensively in a document. In short reports, spell out initialisms that are used fewer than five times. In long reports, spell out initialisms that are used fewer than 10 times. If initialisms are used, spell them out on first use, and put the initialism in parentheses after the full name.

To avoid confusion, try not to use too many in any sentence or paragraph. Include a glossary or list of acronyms if your publication contains a lot of them.

On the Web
The above guidelines apply to web content as well. However, if you use an initialism, spell it out or define it the first time you use it on each webpage. On the web, spell out initialisms that are used fewer than three times.

Subject: Writing Style

International and Non-English Speaking Audiences

If your audience is international, consider following an international style guide such as the United Nations Editorial Manual. If your text is in English, consider using British English. Use plain language. Keep sentences short. Write in active voice when possible. Avoid idioms and colloquialisms. Be aware of differences in style for currencies, dates, units, and addresses.

If you choose to translate content and are trying to reach a wider audience, select a standard dialect of Arabic, Chinese, an Indian language, or Spanish. Your NREL communications representative can help you choose both the appropriate translation for your audience and a contractor to provide the translation. If you translate content, have it reviewed by a person fluent in that language. NREL has a list of bilingual staff members who can help read, write, and translate many languages. Your NREL communications representative can provide you that list.

Subject: Writing Style


Lowercase "internet," except for the specific phrase "Internet of Things" (abbreviated IoT).

Subject: Websites, Writing Style


Introductions usually contain background information on the research being reported, the general nature and context of the work, and its results (the "big picture"). Earlier related work can also be described.

Subject: Publication Formatting


Inverters convert direct current to alternating current.

Subject: Technology-Related Terms

it's and its

Even though "it's" has an apostrophe, it isn't a possessive pronoun. "It's" is a contraction, a short form of two words, like "isn't." "It's" always means "it is." "Its" is the possessive form of "it." Like "his," "hers," and "ours," the possessive "its" never needs an apostrophe.

It's a shame that the company lost its biggest investor.

Subject: Grammar and Usage


1. Using Italics for Emphasis

Use italics (sparingly) to emphasize a word or phrase or bring attention to it.

Never operate this equipment when it has a yellow danger tag.

2. Using Italics for Foreign Words and Phrases

Italicize such foreign words and phrases as terra incognita, in vivo, and inter alia; however, if the word or phrase is commonly used in your field (e.g., in situ, et al., ad hoc, ab initio), you may omit the italics.

3. Using Italics for Hyphenated Prefixes

Italicize hyphenated prefixes (such as cis-, trans-, o-, m-, and p-) to chemical formulas.

trans -1, 2-dibenzoylethylene
trans -glycol

4. Using Italics To Cite Published Documents

Use italics for the names of books, journals, newspapers, magazines, and reports.

Clean Energy Innovators: NREL People Working to Change the World 
Applied Physics Letters
The Denver Post

In print, the titles of journal and magazine articles are listed in regular roman type within quotation marks. On the web, omit the quotation marks.

"Solar Chimney Theory: Basic Precepts"

5. Using Italics in Taxonomic Names

Unless you're discussing a genus in a general way, use italics to refer to specific genera, species, and varieties.

Clostridium thermocellum
C. thermocellum

Subject: Writing Style

Kalina cycle

Subject: Technology-Related Terms

kilowatt (kW)

Subject: Data and Measurement

kilowatt-hour (kWh)

Subject: Data and Measurement

laboratory and lab

Only capitalize "laboratory" or "lab" when used with a laboratory's full name. Lowercase in all other references.

The National Renewable Energy Laboratory is a U.S. Department of Energy national laboratory. The laboratory is known for its research and development in renewable energy and energy efficiency.

Subject: Writing Style

life cycle

Subject: Writing Style


"Lightbulb" is spelled as one word.

Subject: Writing Style


You can use bulleted or numbered lists in NREL publications or webpages. Here's an example of a numbered list:

  1. Include at least two items in a bulleted or numbered list.

  2. Use numbered lists for procedural steps and for items referred to elsewhere in text (for example, "as described in Step 2").

  3. Use parallel construction in lists; that is, make all the listed items similar. Use sentences or phrases throughout, and begin each item with a verb or a noun consistently.

    1. Use lowercase letters to mark subordinate items in your list.

    2. Make sure you have at least two subordinate items under each main item.

    3. Indent them like this.

  4. Use punctuation in lists when the items are complete sentences; otherwise, place a period after the last item only.

You can also list a few items or procedures in paragraph format and number them (1) one, (2) two, (3) three, etc. See bullets for more formatting information.

On the Web

All of the above guidelines apply to the web. When formatting lists on the web, there should be a blank line between the text above the list and the first item listed. To facilitate scanning, consider adding a blank line between each listed item when the text for each one is long.

Subject: Publication Formatting


Subject: Technology-Related Terms


Please visit the NREL Brand Lab for guidance on the proper use of the NREL logo, a library of downloadable logo files, and guidance on NREL branding.



Subject: Technology-Related Terms

mathematical symbols

Leave a space on either side of mathematical symbols used as operation signs.

Tin - Tamb

°C × 1.8

The solidus (a/b) or division sign is an exception. Do not leave a space between numerals and the symbols for degrees, dollars, and percent (32°, $100, 17%). (However, leave a space between numerals and symbols of measurement such as cm and Å.) Do not leave a space between symbols such as >, <, and ≥ and the numeral unless they are the operation signs in an equation.

Subject: Data and Measurement

megawatt (MW)

Subject: Data and Measurement

megawatt-hour (MWh)

Subject: Data and Measurement

metric conversions

For quick online conversions of English units of measurement to metric units, see the Digital Dutch WWW Unit Converter website or IFP Reference Conversions on the French Property website.

Subject: Data and Measurement


"Microgrid" is spelled as one word.

Subject: Writing Style

microseismic events

Subject: Technology-Related Terms

misplaced modifiers

Modifiers in the wrong place can make a sentence confusing.

After identifying the correct material, the test procedure took about 5 minutes.

In this example, it isn't clear who or what identified the correct material. This might be better: After identifying the correct material, we conducted the 5-minute test procedure.

After being lost under a pile of old reports for 5 years, she finally found the manuscript.

What, or who, was lost—the manuscript, the woman, or the reader? Try to keep modifiers as close as possible to the people and things they describe. Strunk and White, authors of The Elements of Style, say this: "Modifiers should come, if possible, next to the word they modify." This is especially true for sentences containing introductory prepositional phrases or clauses followed by a comma.

Subject: Grammar and Usage

months and years

Capitalize the months in all uses. When a month is used with a specific date, abbreviate only Jan., Feb., Aug., Sept., Oct., Nov., and Dec. (Jan. 9, 2008). Also abbreviate these months in tables; however, omit the period. Spell out months when used alone or just with the year, and omit commas when the month and year appear together (October 2001).

Use a lowercase s (no apostrophe) to show the plural of a decade expressed with numerals (e.g., the 1990s).

Subject: Dates

multijunction solar cell

This term is preferred over "tandem solar cell."

Subject: Technology-Related Terms

multiplication symbols

Be as consistent as possible in using multiplication symbols in your paper or report. As appropriate, choose one symbol (× or ·), or omit the symbol and use proximity or parentheses: ab, (ab) (cd), etc.

Subject: Data and Measurement


Always use lowercase for the word "nation" when referring to the United States.

Our nation is a leader in renewable energy markets.

Subject: Writing Style

net zero

When used as a noun, “net zero” is two words. It is also two words when referencing the Net Zero Labs program. Hyphenate “net-zero” when it is used as a modifier.

NREL is eliminating its carbon footprint through the Net Zero Labs initiative.
We are close to achieving our emissions goal of net zero.
The goal is to achieve net-zero emissions.

Subject: Government Terms, Technology-Related Terms, Writing Style

non-SI (English) units of measurement

Use non-SI (Systeme International d'Unites) or nonmetric units of measurement (English or Imperial units) instead of metric units only when they are the industry standard. Otherwise, state metric units first, followed by English equivalents in parentheses.

38.1 m (125 ft)

Subject: Data and Measurement


Spell as one word. Don't hyphenate

Subject: Writing Style

noncondensable gases

Subject: Technology-Related Terms

nonrestrictive phrases and clauses

A nonrestrictive phrase or clause is one that adds information but is not essential to the meaning of the sentence.

The principal investigator, who has studied thin films for 10 years, will chair the panel discussion.

The passive solar features, which were suggested by NREL staff, reduced the agency's energy bills by 30%.

Nonrestrictive or nonessential phrases and clauses are enclosed between two commas when the phrase or clause is within a sentence, and they usually begin with "which" rather than "that." See also restrictive phrases and clauses and which and that.

Subject: Grammar and Usage

noun and adjective strings

Try not to string too many nouns and adjectives together in a sentence. An "agency personnel communications interface display" could also be called a "display of the communications of the agency's personnel." Better yet, it could just be called the "staff bulletin board."

Subject: Grammar and Usage, Writing Style


To give your writing more flow and vigor, try changing some of the nouns (especially those ending in -tion and -ment) to verbs (e.g., determine, complete, accomplish, achieve, measure, convert, characterize, combine) and other parts of speech. Doing this will move your readers along more quickly and make it easier for them to understand your text. In these examples, we changed some of the nouns in the first sentences to verbs and other parts of speech.

Contraction of the tree stems occurred with rapidity.
The tree stems contracted rapidly.

The frequent result of this process is the combination of the molecules.
This process frequently causes the molecules to combine.

The application of fertilizer has the result of stimulation of the yield.
Applying fertilizer stimulates the yield.

Which sentences were easiest to read and understand?

Subject: Grammar and Usage

NREL attribution statement

The NREL attribution statement, which recognizes NREL's affiliation with the U.S. Department of Energy and the Alliance for Sustainable Energy, is required on all NREL publications. In addition, note that a period is used on the "sentence" version of the statement.

Subject: Government Terms, Technology-Related Terms


1. Units of Measurement and Mathematical Expressions

Use numerals with units of measurement and time.

2-1/2 hours87 years
4.5 months6 liters
36 cm25 kW

With units of time, you can spell out numbers less than 10 if you do so consistently (this applies mainly to outreach products rather than technical reports and papers).

five-year plan
two-hour test
three-week turnaround

Use numerals to imply arithmetical values or manipulation.

a factor of 3
multiplied by 2
a ratio of 4:5
values of 1 and 48

Express measurement errors as:

6.0 nm ± 0.2 nm.

Leave a space between the number and the unit of measurement (0.2 nm) and put spaces around the operation sign. When the measurement error appears by itself, omit the space between the sign and the number.

The measurement error is ±0.2 nm.

2. Aligning Numbers

Align numbers that share a common unit of measurement on the decimals in columns of tables. Put a zero before the decimal in numbers smaller than one.


If all the numbers in a column do not share the same unit of measurement, you may center the numbers in the column and specify the unit of measurement.

3. Fractions and Decimals

You can spell out and hyphenate simple fractions (this is preferred in text) or express them, like more complex fractions, in numerals with a solidus.

one-fifth or 1/5
1/64 (but not 1/64th)

Use a hyphen to separate the integral and fractional parts of a mixed number, or convert the fraction to a decimal.

2-1/2 cm in diameter
2.5-cm-diameter solar cell

For numbers of 1 million or more, use the numeral (and a decimal, if necessary) and the words million, billion, etc.

1.1 million households
3.5 billion people
$2.5 million in funding

4. Precision and Numbers

Measurement uncertainty analysis calls for precision in measurements to a significant digit to the right of a decimal point, such as two or three digits (hundredths or thousandths). If you're not absolutely sure, check with an expert before changing the number of digits to the right of the decimal, or rounding the numbers. See also standard errors.

5. Punctuating Numbers

Use a comma to separate groups of three digits in numbers.


6. Ranges of Numbers

To show ranges, use an en dash (which is a little shorter than an em or long dash) with no spaces. Alternatively, if you write out a range, make sure you use the word "to" when you use "of" or "from" before the range. To express a range between some number and another number, always use the word "and" (not "to") with the word "between."

from 32°C to 40°C
6–12 cm
from 66 to 80 V
10–20 m2
between 8 and 12 m (not "between 8 to 12 m")
$3 million–$4 million

Note that some symbols, such as ° and %, are repeated in a range.

7. Scientific Notation

Express multiples of SI (metric) units in powers of 10 with the appropriate prefixes and technical abbreviations.

mm (millimeters, 10-3 m)
MJ (megajoules, 106 J)

Use standard scientific notation to express very small and very large numbers.

2.5 × 10-3
3.56 × 106

Avoid using M to mean "thousands" and MM to mean "millions"; use a capital M for "mega," or millions, as in MW for "megawatts."

8. Spelling out Numbers

Except with units of measurement and time (in technical reports), spell out numbers less than 10.

eight experimental runs
three species of yeast

Spell out all numbers at the beginning of a sentence.

Fifteen trials later, the results were the same.
Thirty-five participants attended the seminar.

In general, spell out numbers at the beginning of a bulleted item, but use best judgment depending on the context (e.g., a list of sentence fragments using numbers with many digits).

The electrical safety point of contact recorded the following during their field walk:
  • Seven staff occupied the laboratory while performing electrical work.
  • Twenty-five staff observed from a nearby corridor.
The photovoltaic cost benchmark data encompass:
  • 30 states
  • 1.6 million individual PV systems
  • 81% of all U.S. residential and nonresidential systems.

When a sentence contains one or more numbers greater than nine that are related to a smaller number, use numerals for all of them.

The results were the same in 3, 12, and 18 trials.
The contractor tested 8 devices in May, 12 in June, and 9 in July.

Spell out the first of two adjacent numbers unless the first one requires three or more words.

ten 5-kW arrays
thirty-two 4-cm2 devices
135 16-cm collectors

See also fractions.

Subject: Data and Measurement

over and under

In cases involving quantity, use "more than" rather than "over," and use "fewer than" or "less than" rather than "under." In cases involving temperature, use "higher than" or "lower than" or "warmer than" or "cooler than." In cases involving weight, use "heavier than" or "lighter than."

More than 500 people attended the conference, about 100 fewer than last year.

Subject: Grammar and Usage


Paginate the front matter of NREL reports with lowercase Roman numerals, up through the lists of figures and tables. The title page is usually page "i," although that number isn't printed on the page. Paginate the main body of your report with Arabic numerals. You may insert a blank page before Page 1 to make sure it will be a right-hand (odd-numbered) page, but don't insert blank pages after that. All subsequent sections can begin on the left or on the right, as they fall. Center the page numbers on each page.

If you include appendices at the end, you may continue to paginate them sequentially with numerals or use A-1, A-2, A-3, B-1, B-2, and so on, for the page numbers.

Subject: Publication Formatting


Use parallel construction in sentences as well as in lists. Express all similar sentence elements (subjects, verbs, verbals, objects) in a similar way.

Not Parallel Structure:
The lever was moved completely forward, going slightly to the right, and then it went backward halfway in order to complete the procedure.

We are not only responsible to our chief customer but also the taxpayers.

Parallel Structure:
To complete the procedure, push the lever all the way forward, slide it slightly to the right, and then pull it halfway back.

We are responsible not only to our chief customer but also to the taxpayers.

Subject: Grammar and Usage


Use parentheses as appropriate for explanatory material in text and as shown in the examples that follow.

1. Parentheses in Equations

In equations, use parentheses, brackets, and braces in this sequence (which may be repeated as needed).

{[( )]}

2. Parentheses with Measurements

Use parentheses around English measurements that follow SI (metric) measurements.

3.1 m/s (7 mph)

3. Parentheses in Citations

When you use parentheses in text, such as for author-date references or for parenthetical (added) information, place a comma after the parentheses rather than before them.

In earlier research (Jones 1989), we showed how quantities of lipids could be increased by this method.

4. Nested Parentheses in Text

In body copy, use parentheses, brackets, and braces in this sequence, which may be repeated as needed: ([{ }]).

(The data presented here [originally derived from Mason {1998}] should not be used for location-specific analyses.)

Subject: Punctuation

percent, %, and percentage

Use the symbol % with numerals; use the word "percent" when you spell out numbers at the beginning of a sentence. To determine whether "percent" or % is singular or plural, look at the noun following it. If the next noun is a plural, use a plural verb; if it's singular, use a singular verb.

The maximum glucose yield was 60%.
Six percent of the pipes were rusty.
More than 10% of that amount was allocated to planning.

When there is no number, use the word "percentage," unless people in your field use a different terminology, such as "percent difference."

This table shows the percentages of government buildings having solar roofs, by state.

Subject: Data and Measurement


Periods are used in some abbreviations (e.g., i.e., a.m., p.m.) and not in others (ac, dc, rpm). Most acronyms do not have periods. When you end a sentence with "etc." (although this is seldom necessary) or another abbreviation that already includes a period, do not add another one.

This paper describes the program's purpose, objectives, schedule of deliverables, etc.
(Better: This paper describes the program's purpose, objectives, and schedule of deliverables.)

Subject: Punctuation

personal pronouns

First-person pronouns may be used in technical communications when appropriate, and some scientific and technical associations (such as the American Institute of Physics) encourage technical writers to do so. Common first-person pronouns include "we," "our," and "us." Personal pronouns can prevent confusion by clearly and concisely showing who performed an experiment or procedure.

We tested several hundred isolates that were able to ferment glucose.

We deposited a thin film of doped cadmium on the substrate.

Which of the following two sentences is easier to read and understand quickly?

It was determined that the workshop was a success.

We agreed that the workshop was a success.

See also active voice and passive voice.

Subject: Grammar and Usage

phone numbers

Do not use parentheses around area codes in phone numbers. Parentheses previously were used to set off the three-digit code in a phone number because it wasn't always necessary when dialing the number. However, they are required in most instances now.

Use hyphens to separate the digits in phone numbers.



Subject: Geography

photo, image, and video credits

If you use a photo, image, or video from the NREL Image Gallery, an NREL staff member, or a paid or external source, you must provide appropriate credit. See the entries on captions and sources for more information, as well as the copyrighted material page on the publishing site.

For Publications

Accordion TitleAccordion Content
Internal Sources

When the photo or image source is an NREL staff member or an NREL contract photographer, use the source's name along with the NREL affiliation. Present the credit in italics, and do not use a period at the end.

Use "by" for NREL sources ("from" is for external sources).

Illustration by Ray David, NREL
Photo by Pat Corkery, NREL

If the photo, image, or video is from the Image Gallery, you must also include the image number in the credit.

Illustration by Ray David, NREL 12345
Photo by Pat Corkery, NREL 54321

Use the following format if an NREL illustration contains material from an external source.

Illustration by Ray David, NREL 19500. Photos from Warren Gretz (NREL 10929) and Iberdola Renewables Inc. (NREL 15185)
External Sources

If you use a photo or image from an external source (whether paid or free), use the source's name (if available) and affiliation. If there is an NREL image number, do not replace "NREL" with the source's affiliation; the image number is always an NREL reference.

Present the credit in italics, and do not use a period at the end.

Use "from" for all external sources (not "by" or "courtesy of").

Photo from John Williams, Western Area Power Administration
Illustration from SunPower Corp.
Photo from Kathy Boyer, Triangle Clean Cities Coalition, NREL 18520
Photo from Margaret Smith, DOE, NREL 18215

If the photo, image, or video is included in the Image Gallery, you must also include the image number in the credit.

Photo from Xcel Energy, NREL 12345

If the photo, image, or video is from Getty Images or a similar source, you must also include the number in the credit.

Photo from Getty Images 12345678
Placement in Publications

If a caption is used with the photo or image, the credit should immediately follow it.

A picture of three people drawing equations on a glass window representing analysis work at NREL.
NREL analysts develop models, tools, and reports that help provide insight and objective information on renewable energy technologies. Photo by Pat Corkery, NREL 16560

If the photo or image is used for illustrative purposes and does not include a caption, the credit should appear directly beneath the photo.

A picture of three people drawing equations on a glass window representing analysis work at NREL.
Photo by Pat Corkery, NREL 16560

For NREL technical reports, use the “NREL_Figure_Caption” style for the caption itself, and then the “NREL_Figure_Note” for the in-text citation or other notes.

Photo of a sunset over the ocean and mountains
Figure 1. Caption text
Image from Smith et al. (2022)
Additional Guidance

For photo collages, pages with many photos with no captions, or full-page photos, credits can be placed on the same page or a different page, wherever they best fit the design.

For document covers, credits can be placed elsewhere in the document (typically inside the front cover). Reference the page containing the photos you are crediting.

If images are combined to create new graphics and the original images are still recognizable, the original images must be credited. For example, if two Getty Images photos are merged with NREL photos into a collage and used on a document cover, the credit should read: Cover images, clockwise from bottom: Getty Images 12345, Getty Images 67891, NREL 12345, NREL 67891

Placement in PowerPoint

Microsoft stock images are available through PowerPoint. You may use them in NREL publications, but do not move images out of Microsoft Office for other uses (e.g., a webpage). In general, NREL photos from the Image Gallery are recommended first, Getty Images second, and PowerPoint stock images last.

To credit these Microsoft stock images, use: Photo from Microsoft stock images

To credit other images used in a PowerPoint presentation, follow the guidance above for publication photo credits, and ensure the credit is listed somewhere on the slide itself (typically the bottom right corner). Do not list the photo credit in the notes section of the slide or at the end of the deck.

Press Enter to add more content

For the Web

For photos, images, and video on the web, include the credit after the caption and italicize it.

Use "from" for external sources and "by" for NREL sources. Do not use "courtesy of."

The National Wind Technology Center at NREL is located south of Boulder, Colorado. Photo from Joe Smith
The National Wind Technology Center at NREL is located south of Boulder, Colorado. Photo by Jennifer Josey, NREL

Don't include image numbers in the credit. Instead, the photo image file name should include the image number so it can be easily located in the Image Gallery if needed.

Subject: Publication Formatting

photovoltaics and photovoltaic

"Photovoltaics" is a singular noun. "Photovoltaic" is an adjective. The acronym PV can be a noun or an adjective, but do not pluralize it.

Subject: Technology-Related Terms


"Policymaker" and "policymaking" are both spelled as one word.

Subject: Writing Style


Brief introductory remarks and acknowledgments go in the report's preface. The preface comes after the title page and disclaimer page. (See front matter.) A preface written by someone other than the authors of the report is usually called a "foreword."

Subject: Publication Formatting


See hyphens, compound words, and unit modifiers and scientific notation.

Subject: Grammar and Usage


Use the standard SI unit for pressure or stress, which is the pascal (Pa) or the bar. Non-SI units include psi (pounds per square inch), millimeters of mercury, torr, and atmospheres, and they are still in relatively widespread use.

Subject: Data and Measurement

principal and principle

"Principal" often means "chief" or "main," such as the principal investigator in a research project or the principal of a high school. "Principle" often refers to a belief, value, or rule.

Subject: Grammar and Usage

quotation marks

Use quotation marks for direct quotes and the titles of articles, papers, and book chapters. In print, use "curly" or "fancy" quotation marks; on the web, use "straight" quotation marks. 

"Let's meet again in 6 months," the chairman said, "to discuss our progress."
She presented a paper titled "Materials Research in Silvered Polymer Reflectors."

Place commas (and periods) inside quotation marks; place semicolons, question marks, dashes, and exclamation points outside quotation marks unless they're part of the quotation.

"The results are in," he said.
"Can you hear me?" she asked.
Did he really say "I don't believe you"?

Use single quotation marks to indicate a quotation within material that is already enclosed in double quotation marks.

"Explain what you mean by 'confidence,'" she said.

When quotations are longer than two or three lines of text, begin them on the next line and indent them on each side (block quotations). You do not need quotation marks around block quotations, and you can use standard double quotation marks for quotes within block quotations. In in-text quotations, place reference numbers, superscripts, and author-date citations outside quotation marks (but before the final punctuation of a sentence). Place them after the final punctuation of the last sentence in a block quotation.

Subject: Punctuation

race and ethnicity

As a laboratory that strives for diversity of perspectives and inclusivity, our word choices, style, and tone must be carefully considered, particularly when it comes to topics related to race and ethnicity.

Capitalize Black when referring to African Americans or, more broadly, in any racial, ethnic, or cultural sense; do not capitalize white. Do not use the terms “Black(s)” or “white(s)” as singular or stand-alone nouns referring to a person or people. In the plural form, “Black people,” “white people,” “Black scientists,” and “white scientists” are preferable when clearly relevant.

NREL's Black Employee Resource Group focuses on developing and supporting a vibrant community for NREL staff that identify as Black or of African descent.

Capitalize “Indigenous” in reference to original inhabitants of a place, aligning with long-standing capitalization of other racial and ethnic identifiers such as Latino, Asian American, and Native American. (Note that no hyphen is used in dual heritage terms such as “Asian American” and “Mexican American.”) Capitalize “Elder” when referring to a Tribal or religious leader, but lowercase it when used to identify someone by age or when used generally.

The research team visited Indigenous communities throughout the Midwest to gather insights from local Elders.

The terms “Tribal” and “Tribe” should be capitalized, even when they are not part of an entity’s official name. Capitalize the word “nation” when part of a formal name.

the Kenaitze Indian Tribe
a citizen of the Navajo Nation
NREL researchers invited input from many Tribal councils.

In Alaska, the Indigenous groups are collectively known as Alaska Natives. Both “American Indians” and “Native Americans” are acceptable terms when referring to two or more people of different Tribal affiliations. “First Nation” is the preferred term for native Tribes in Canada. “Indian” is used to describe the peoples and cultures of the South Asian nation of India and should not be used as shorthand for American Indians, unless that is how a particular group prefers to be referenced.

NREL staff worked with Alaska Natives and First Nation Tribes to design specialized heating equipment.

For additional details, refer to the AP Stylebook's race-related coverage.

Subject: Grammar and Usage

Rankine cycle

Subject: Technology-Related Terms


In general, use a colon to indicate a ratio.

We prepared a 3:1 dilution.

However, some industries (such as the American automotive industry) use a solidus to express a ratio.

The engine is designed to have an optimum air/fuel ratio.

Subject: Data and Measurement

references and citations

For NREL publications, use the Chicago Manual of Style when you document references and use in-text citations. NREL prefers author-date citations (e.g., Smith et al. 2021) with a full references list at the end of the document, rather than numbered footnotes or endnotes.

Reference formatting can get tedious, but keep in mind that the ultimate goal is to clearly present relevant information so that readers can easily locate the sources used. Do the best that you can with the information you have.

Following are examples of commonly cited publication types:

NREL Technical Report
Last, First, First Last, and First Last. Year. Report Title. Golden, CO: National Renewable Energy Laboratory. NREL/TP-XXXX-XXXX. URL.

Other Technical Reports
Last, First, First Last, and First Last. Year. Report Title. City, State: Publisher. Pub # if available. URL.

Journal Article
Last, First, First Last, and First Last. Year. “Article Title.” Journal Name Volume # (Issue #): Page #. URL or DOI.

Conference Paper/Presentation
Last, First, First Last, and First Last. Year. “Paper Title.” Presented at [conference name/location/dates as available]. [Author organization, location, and publication number if available.] URL or DOI.

Webpage (with authors)
Last, First, First Last, and First Last. Year. “Website Title.” Website name or publisher. Accessed date (e.g., “Accessed January 1, 2021”). URL.

Webpage (no authors)
Website name or publisher. Year. “Website Title.” Accessed date. URL.

News Article (online or in print)
Last, First, First Last, and First Last. Year. “Article Title.” News Outlet. Full publish date or access date if publish date not available. URL if available.

Fact Sheet
Last, First, First Last, and First Last. Year. “Fact Sheet Title.” City, State: Publisher. URL.

Last, First, First Last, and First Last. Year. Book Title. City, State: Publisher.

Book Chapter
Last, First, First Last, and First Last. Year. “Chapter Title.” In Book Title. Edited by First Last (if applicable), page numbers. City, State: Publisher.

Thesis or Dissertation
Last, First. Year. “Title.” Ph.D. dissertation/Master’s thesis, University Name.

Personal Communication
Often, mentioning the person’s name in the text is sufficient (“According to John Smith, CEO of XYZ…).

Last, First. Year. Personal Communication. Title, Organization Affiliation.

Last First, First Last, and First Last. Year. Patent Title. Patent number (include country code, the word “Patent,” and patent number with retained commas—for example, US Patent 3,597,875), filed [month, day, year], and issued [month, day, year].

Government Documents
For information on how to cite government documents, including bills and resolutions, court decisions, and congressional hearings, see Bowdoin College’s Quick Guide for Government Documents.

Guidance for how to cite datasets can be found within individual dataset entries in the NREL Data Catalog.

Datasets external to NREL can be cited like webpages.

In the references list, include up to 10 author names. If there are more than 10 authors, then list the first seven followed by “et al.” For in-text citations, include up to three names (Smith, Johnson, and Cook 2021). If there are more than three authors, list the first author’s name followed by “et al.” (Smith et al. 2021). Note that “et al.” does not need to be italicized.

If there is more than one reference entry with the same first author in a group of four or more authors and the same publication year, use “a,” “b,” etc. after the year to distinguish the references in the in-text citations.

If there is no year for a published work, use “n.d.” (which stands for “no date”) in place of the year. 

Place works that you use or recommend for further reading (but do not cite in the text) in a bibliography.

If you are preparing a manuscript for a publisher other than NREL, follow that publisher's preferred reference style. The best place to find this information is on the publisher’s website, typically under an “Information for Authors” section.

See the NREL Library website for information about  Zotero and EndNote citation tools

Subject: Publication Formatting

renewable energy certificate

Don't capitalize "renewable energy certificate." It's not a proper noun. Also, this is the term preferred over "renewable energy credit" or "green tags."

Subject: Government Terms

renewable portfolio standard

Only capitalize "renewable portfolio standard" when a state name precedes it.

Renewable energy certificates have been proposed under California Renewable Portfolio Standards.

Subject: Government Terms, Technology-Related Terms

report contents

Report contents may include (in order):

  1. A report cover
  2. A title page
  3. A disclaimer
  4. A foreword
  5. A preface
  6. Acknowledgments
  7. A nomenclature, list of abbreviations, or list of acronyms
  8. An executive summary
  9. A table of contents
  10. A list of figures
  11. A list of tables
  12. Body text
  13. A glossary
  14. references
  15. A bibliography
  16. Appendices.

See also front matter and back matter.

Subject: Publication Formatting

report covers

NREL uses standard covers for most technical reports and papers and subcontract reports. Covers contain the laboratory's name, address, and logo as well as an NREL report number and date of publication. You may spell out an author's first name with or without a middle initial or use initials for the first and middle name.

Subject: Publication Formatting

Research Support Facility

Use "Research Support Facility" (RSF), regardless of which phase or wing is cited.

The Research Support Facility is designed to be a model for sustainable, high-performance building design.

Construction on the first phase of the Research Support Facility, which is 222,000 square feet, was completed in summer 2010.

Subject: Government Terms

restrictive phrases and clauses

Do not use commas around restrictive phrases and clauses. They are essential to the meaning of the sentence, in contrast to nonrestrictive phrases and clauses, which simply add information that is not essential.

This is the house that Jack built.

See also which and that.

Subject: Grammar and Usage


Subject: Technology-Related Terms

scientific notation

Standard scientific notation represents a number as a factor multiplied by a power of 10; 3,560,000 is expressed as 3.56 × 106. This is useful for very large and very small numbers, especially in non-SI units. You can also use certain standard prefixes, many of which are listed here with their abbreviations.





























































We recommend choosing a prefix that permits the numerical value to fall between 0.1 and 1,000 (62 kW rather than 62,000 W).

Subject: Data and Measurement


Semicolons indicate a stronger or more important break in the flow of words than the break indicated by a comma. Use a semicolon in compound sentences that are NOT linked by a conjunction (such as "and," "but," "or," "nor," and "yet"). Place a semicolon before conjunctive adverbs (such as "however," "hence," "therefore," "nevertheless," and "consequently") in most complex sentences containing two or more clauses. When a sentence contains items in a series, you may use a semicolon between the items if one or more of the items contains commas.

1. Using Semicolons in Compound Sentences without Conjunctions

When clauses in a sentence are closely related in meaning, a semicolon is an appropriate dividing punctuation mark. Note that the words "and," "but," "or," and "nor" do not follow semicolons.

It was difficult to reproduce the experiment; the material Smith and Jones used was not widely available. Of the 13 samples, only one did not degrade; others deteriorated an average of 8%.

2. Using Semicolons with Conjunctive Adverbs

"Yet" and "so" are usually preceded by commas in a complex sentence. But use a semicolon before such conjunctive adverbs as "then," "however," "thus," "therefore," "hence," "accordingly," "moreover," "nevertheless," "consequently," "besides," "indeed," and "subsequently"; place a comma after the adverb.

The contractor's representative was out, so I left a message.

We used the Schartz-Metterklume method in the experiment; however, the problems with this method are well known.

Energy requirements are often expressed in quads, or quadrillion Btu; therefore, this report describes the number of quads supplied annually by each option.

Use a semicolon before "i.e." ("that is") and "e.g." ("for example") and a comma after them when a clause (with a subject and verb) follows them; use a comma when a phrase or list follows.

3. Using Semicolons in a Series

When items in a series contain internal punctuation (e.g., commas) or are very long, you can separate them with semicolons. In those cases, a conjunction can follow the last semicolon.

The contaminants in the sample were TCE, 150 ppb; toluene, 220 ppb; and benzene, 265 ppb.

Promising new technologies demonstrated at the exposition included advanced wind turbines; polycrystalline, thick-film, and thin-film solar cells; fast-growing energy crops; and fuel cells.

The vendor assured us that the replacement parts, which were essential in this installation, were on order; that the parts would be delivered as soon as they arrived; and that the delay in shipment was unavoidable.

Subject: Punctuation

SI (metric) system

NREL follows national policies and those of scientific societies by using the SI (Systeme International d'Unites, International System of Units) or metric system in expressing technical measurements. English units may follow metric ones or may be used alone in special cases, when that is appropriate for a publication's audience. See also the National Institute of Standards and Technology.

Subject: Data and Measurement

slash (solidus)

The solidus (or slash, slant, shilling mark, or virgule) is a versatile symbol that has mathematical as well as textual functions.

1. Using a Solidus in Fractions

Use a solidus to express a quotient in text when you do not need to use a displayed equation.

These structures yield photoluminescence lifetimes that are related to bulk
lifetime by the expression 1/t = 1/tB + 2 S/D.

Use a solidus in superscript and subscript fractions.


2. Using a Solidus in Text

In text, use a solidus to indicate some junctions, interfaces, and components.

gas-liquid interface
1-butyl acetate/acetic acid/water (3:1:1)

With abbreviated units of measurement, the solidus stands for "per."

2 g/cm2
355 W/m2

But spell out "per" when you spell out the units of measurement.

several cubic meters per second
a few cents per kilowatt-hour

Subject: Data and Measurement, Punctuation

Smart Grid and smart grid

Use capital letters for "Smart Grid" when referring to the overall goal or concept and lowercase letters for "smart grid" when referring to current implementations or when used as an adjective.

Subject: Technology-Related Terms

solar cell interfaces

Use a slash rather than a hyphen to designate solar cell interfaces or layers.


Subject: Technology-Related Terms

solar conversion efficiency

Define in outreach publications as "the percentage of sunlight striking a solar cell that is converted into electricity." A definition is often unnecessary in technical publications.

Subject: Technology-Related Terms

solar electricity

This term is interchangeable with "photovoltaic power," "PV power," or "PV electricity."

Subject: Technology-Related Terms


Include the sources of all figures and tables that were originally published by others, especially those outside NREL. If figures or tables come from a copyrighted publication, you may need permission to reproduce them. Add the source at the end of a figure caption or in a note following a table.

Source: Hansen, W.L.; Pearton, S.J.; Haller, E.E. (1984). Appl Phys. Lett. 44:606.

Write out the source in full, as in the example, if it is not in your reference list or bibliography. If it is in the reference list, use one of these styles.

Source: Hansen, Pearton, and Haller 1984.
Source: Ref. 19. (for numbered references)

Subject: Publication Formatting, Publication Policies and Services


Use only one space between a period and the beginning of the next sentence.

Subject: Publication Formatting


If you can't find a word or phrase in this style guide, consult the following reference guides in this order: (1) The Associated Press Stylebook and (2) Merriam-Webster's Collegiate Dictionary, Eleventh Edition.

For spelling out numbers, see numbers.

Subject: Grammar and Usage

standard errors

Express standard measurement errors as shown below.

6.0 nm ± 0.2 nm

Subject: Data and Measurement

state implementation plan

Capitalize "state implementation plan" only when a state or organization name precedes it.

The Connecticut Department of Environmental Protection incorporated emission reduction strategies into its U.S. Environmental Protection Agency State Implementation Plan for air quality.

Subject: Government Terms

states and countries

1. States

In text, consistently spell out states' names rather than using U.S. Postal Service abbreviations.

California (rather than CA)
Colorado (rather than CO)
Wyoming (rather than WY)

You may use D.C. for the District of Columbia in text, in both formal and informal publications. When you include addresses or state names in full addresses (containing streets and cities), contact lists, reference lists, and bibliographies, however, you may use the following abbreviations:

AL, AK, AZ, AR, CA, CO, CT, DC, DE, FL, GA, HI, ID, IL, IN, IA, KS, KY, LA, ME, MD, MA, MI, MN, MS, MO, MT, NE, NV, NH, NJ, NM, NY, NC, ND, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VT, VA, WA, WV, WI, WY (PR, VI).

2. Countries

Do not abbreviate the names of countries (including the United States) when they are used as nouns. Use "U.S." as the adjective form.

the United States
U.S. Department of Energy program
U.S. population

Subject: Geography

statistical terms

When referring to statistical or graphical terms, use a hyphen but no italics. Also, do not use capital letters.


Subject: Data and Measurement


Print captions to figures and photos in a bold font. Subcaptions are supplementary information that follows a period after the main caption. Subcaptions are not printed in bold.

Figure 2-1. Photoconductivity spectra of a composite CIS thin film.
                     Inset: The probable energy band diagram.

But follow the publisher's guidelines for journal articles and conference papers.

Subject: Publication Formatting

systems integrator

The correct term is "systems integrator," not "system integrator."

Subject: Technology-Related Terms

table of contents

A table of contents is required in most technical reports. In NREL reports, the table of contents follows the rest of the front matter. Lists of figures and tables follow the contents page(s). Each main section of the report is listed in the table of contents with the page it begins on; some authors also like to list subsections. Nothing that comes before the table of contents (front matter) is listed, but references, bibliography, and appendices (back matter) are listed. Publications for general audiences probably should include a contents list if the publication is more than 10 pages long.

Subject: Publication Formatting


In small or average-sized tables, place a horizontal line (as wide as the table) under the title, under the column headings, and below the table (between the table and sources or notes, if any). Delete vertical lines and extra horizontal lines. If the table is very large, shading every other line with a light color or inserting horizontal lines every three or four rows can help readers locate data.

Table 1. Photovoltaic Power Production in
Three Applications
Application 1986 1987 1988 1989 1990
Grid-Connected PV 0.5 0.2 0.6 0.4 0.4
Central Station PV 3.8 4.7 5.5 5.9 6.4
Consumer Products 0.5 0.6 0.8 2.5 2.2

Number tables in simple sequence or by section in long reports (Table 1, Table 2 or Table 1-1, Table 1-2, and so on). Center the table title (in title case) over the table (unlike a figure caption, which is sentence case and goes under the figure) and print the title in 10-pt. Arial bold; supplementary material in the title is not in bold. If possible, print tables in Arial, rather than Times New Roman. Define abbreviations in notes to the table if they are not obvious. Table notes are denoted by lowercase superscript letters (a, b, c) rather than footnote numbers or asterisks.

Subject: Publication Formatting

taxonomic names

See capitalization and italics.

Subject: Writing Style

technical abbreviations

Unless your profession, technical field, or scientific discipline specifies something different, use the abbreviations in NREL's list of technical abbreviations or the National Institute of Science and Technology's Guide.

Subject: Data and Measurement, Technology-Related Terms


Hyphenate. Don't spell as one word.

Subject: Technology-Related Terms


Use a degree symbol (°) with temperatures expressed in the Celsius and Fahrenheit scales but not with kelvins (just use K). Don't leave a space between the number and the letter for °C and °F, but leave a space between the number and K.

0 K

Subject: Data and Measurement

that and which

See which and that.

Subject: Grammar and Usage


Use lowercase a.m. and p.m. (with periods) to denote "ante meridiem" and "post meridiem" (before and after noon). Use a colon to separate hours from minutes except for the top of the hour.

  • 11 a.m. (not 11:00 a.m.)
  • 3:30 p.m.

Subject: Grammar and Usage

title page

Most NREL technical reports contain a standard title page inside the cover.

Subject: Publication Formatting

trademark symbols

Trademark notice symbols (® or ™) are to be used for the Alliance-owned trademarks listed below. Trademark notice symbols should be used on the first reference in body copy only. Preferred capitalization is as listed.

Do not use trademark notice symbols with third-party products or services.

Alliance-owned registered trademarks include:

  • ADVISOR®                                                                                                   
  • Alliance®                                                                                                                                                            
  • Alliance for Sustainable Energy®                                                                  
  • Alliance for Sustainable Energy LLC® (logo/design mark)
  • BuildingSync®                                                                                                                                               
  • Colorado Center for Renewable Energy Economic Development® (logo/design mark)               
  • CREED®                                                                                                                                                            
  • HOMER®
  • JISEA Joint Institute for Strategic Energy Analysis® (logo/design mark)
  • OpenEI®                                                                                                                                                           
  • OpenStudio®                                                                                                                                 
  • PVWatts®
  • REopt®
  • REopt Renewable Energy Integration and Optimization® (logo/design mark)
  • REopt Lite®
  • REopt Lite® (logo/design mark)

The Alliance also has authorization from the Department of Energy to assert trademark rights to each name and tagline listed below. Preferred capitalization is as listed. The common law TM trademark notice symbol ™ should be used instead of the ® trademark registration notice symbol.

  • BEopt™
  • Building Agent™
  • CatCost™
  • Clean Energy Cybersecurity Accelerator™ (CECA)
  • ComStock™
  • CORE™ (Continuously Optimized Reliable Energy)
  • dGen™
  • Distant Observer™
  • DRIVE™
  • Engage™
  • EsterCycle™
  • FASTSim™
  • foresee™
  • H2FillS™
  • HIVE™
  • iiESI™
  • iiESI International Institute for Energy Systems Integration™ (logo/design mark)
  • LaDa™
  • MADE3D™
  • MHKiT™
  • nSnare™
  • OCHRE™
  • Open-OA™
  • OpenPATH™
  • PolyID™
  • RdTools™
  • ReEDS™
  • ResStock™
  • SolarAPP™
  • SolarAPP+™
  • SolarPILOT™
  • SPA™ (Solar Position Algorithm)
  • SwitchGlaze™
  • System Advisor Model™ (SAM)
  • Technology Performance Exchange™
  • TEMPO™
  • TPEx™
  • URBANopt™
  • VSHOT™

Following is a list of expired and/or abandoned trademarks that no longer use ™ or ® notice symbols.

  • ADVISOR 2002
  • ENERGY-10
  • EVI-Equity
  • EVI-RoadTrip
  • IMBY
  • New Iglu™
  • SolTRACE
  • VIBE

Following is a list of commonly used government-owned trademarks that should use the trademark notice symbols, as indicated. This list is for reference and is not intended to be all-inclusive. There are many other government-owned trademarks not listed.

  • CECA™
  • Clean Energy Cybersecurity Accelerator™
  • EnergyPlus®
  • H2@SCALE™
  • H-MAT®
  • Home Energy Score™
  • HydroGEN Advancing Water Splitting Materials™
  • HyBlend
  • IDAES®
  • ORISE®
  • Powering the Blue Economy™
  • SEED Platform
  • Solar Decathlon®

Subject: Government Terms


See International and Non-English Speaking Audiences.


U.S. Department of Energy

This is the preferred term for printed and outreach materials. When spelling it out, "U.S." should precede "Department of Energy" to distinguish it from other state and international departments. However, "U.S." should not be included with the acronym "DOE." Do not include "the" before "DOE."

On first reference, "Energy Department" may be used in communications to the press.

If the possessive is used with the term, the apostrophe should go after "U.S. Department of Energy" and with the "DOE" acronym as well. However, if you can write it in a way that avoids use of the possessive, that is preferred.

The U.S. Department of Energy's (DOE's) priorities include combating the climate crisis, creating clean energy union jobs, and promoting energy justice.

Subject: Government Terms

unit modifiers

See hyphens, compound words, and unit modifiers.

Subject: Grammar and Usage

United Kingdom and U.K.

Spell out "United Kingdom" when it is used as a noun. The abbreviation "U.K." is acceptable when it is used as an adjective.

Interest in renewable energy in the United Kingdom has increased in recent years.

New U.K. targets for reductions in carbon emissions have increased interest in renewable energy.

Subject: Writing Style

United States and U.S.

Spell out "United States" when it is used as a noun. The abbreviation "U.S." is acceptable when it is used as an adjective.

The United States is a leader in renewable energy markets.

The global markets for renewable energy are stronger than the U.S. markets.

Subject: Writing Style

units of measurement

Use numerals with units of measurement and time in technical papers and reports, even when the number is less than 10. In some outreach publications, you may spell out numbers less than 10, especially with units of time.

Except with $, °, and %, leave a space between the numeral and the unit. Include a hyphen between a numeral and an abbreviated unit when the value is used as an adjective.

Do not include a period after a unit symbol except at the end of a sentence. The exception to this rule is inches (which are abbreviated “in.”).

 2 kW7 cm216.8%
 3 m8-hour days300 Btu
 5 years$2 billion45°
 4 in.a 15-MW turbine65°C

Avoid nonstandard abbreviations such as sec or cc, and instead use standard abbreviations such as s and cm3. Unless your profession, technical field, or scientific discipline specifies something different, use the abbreviations in NREL's list of technical abbreviations or the National Institute of Standards and Technology (NIST) guide.

Use a center dot to indicate multiplication of units (such as N∙m for Newton-meters), and use a slash or negative exponent to indicate division. For example, 344 meters per second can be written as 344 m·s−1 or 344 m/s.

Format variables in italic type and units in roman type:

Correct: t = 3 s, where t is time and s is seconds
Incorrect: t = 3 s, where t is time and s is seconds
Do not mix information with unit symbols or names:

Correct: the water content is 20 mL/kg
Incorrect: 20 mL of water/kg
Avoid mixing symbols and names; for example, use kg/m instead of kilogram/m.

When expressing a range, repeat the unit symbol if it is closed-up with the numeral ($, °, %):

60°–90° (example of angular measurements)

Refer to the NIST style conventions checklist for additional style tips and examples.

Subject: Data and Measurement


Uniform resource locators, or URLs, are essentially web addresses.

On websites, URLs should be embedded in text.

More information is available on the NREL website.
NREL plays a critical role in CSP research.

In print, URLs should not be embedded in text. If a URL extends beyond one line of text, add a break at a solidus. Also, in general, you do not need to include the http:// prefix on most URLs. But test it before removing it. Shorten URLs as much as possible (e.g., remove unnecessary trailing such as /index.html) while ensuring functionality.

Subject: Websites, Writing Style


Subject: Data and Measurement

web terms

The following words are lowercase:

  • web
  • webpage
  • webcast
  • webinar
  • webmaster
  • website.

"World Wide Web" is a proper noun and should be capitalized.

Subject: Websites, Writing Style

website content

For website content guidance, see Content and Writing for We use the NREL Style Guide in conjunction with these guidelines and standards. Some specific NREL style guidelines, which are different from print style, for the web include:

Abbreviations and acronyms



Fiscal year



Photo credit


Subject: Websites, Writing Style

which and that

Standard American English uses "which" for nonrestrictive or nondefining phrases and clauses and "that" for restrictive or defining phrases and clauses. The word "which" usually signals the approach of added, nonessential information. When a phrase or clause is not essential to the meaning of a sentence, use the relative pronoun "which" and enclose the phrase or clause in commas. See also nonrestrictive phrases and clauses and restrictive phrases and clauses.

This paper, which she has been working on for three weeks, discusses string theory.

When a phrase or clause is essential to the meaning of a sentence (that is, the sentence would not make much sense without it), use "that" and leave out the commas.

The paper that he completed recently will be presented in New York; the paper that he finished last summer will be presented in Philadelphia.

Subject: Grammar and Usage

work-for-others agreement

Use lowercase for "work-for-others agreement" because it's not a proper noun. The acronym "WFO" refers only to work for others; therefore, when using the acronym, "WFO agreement" is correct.

Subject: Government Terms


For numbers less than one, place a zero before the decimal.


Subject: Data and Measurement

zero energy building

Use the term to indicate an energy-efficient building where, on a source energy basis, the actual annual delivered energy is less than or equal to the on-site renewable exported energy. Similar terms include zero energy campus, zero energy portfolio, and zero energy community.

Subject: Technology-Related Terms