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Subject Index - Writing Style

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.

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.

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.  

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.


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.

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.


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.

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.


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.

decision maker


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.


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.

first-person pronouns

See personal pronouns.

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.

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.


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.

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.


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


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

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.

life cycle


"Lightbulb" is spelled as one word.


"Microgrid" is spelled as one word.


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

Our nation is a leader in renewable energy markets.

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.


Spell as one word. Don't hyphenate

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."


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

taxonomic names

See capitalization and italics.

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.

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.


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.

web terms

The following words are lowercase:

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

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

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