Create TMY3 File

SAM's TMY3 creator is a tool for converting your own weather data into the TMY3 format.

Although it is possible to create your own TMY3 weather file outside of SAM, or to use your data in one of the other weather file formats, using the TMY3 Creator will help you avoid data formatting issues that can render a weather file unreadable by SAM's weather data processor. For example, the following problems will cause SAM's weather file reader to fail:

Incorrectly formatted dates or decimal values.

Data with the wrong units.

Empty columns or cells, even for a data element that the performance model does not use.

Note. The TMY3 Creator is not available for the wind power or geothermal co-production models because those models use resource data in different formats.

To open the TMY3 Creator:

Click Create TMY3 File.

The TMY3 Creator allows you to use your own weather data in SAM, and helps to ensure that the data is correctly formatted. Although SAM only uses some of the columns of data in a TMY3 file, the weather file reader will fail if any of the columns in the file contain incorrectly formatted data because it reads the weather file before the performance model simulations begin.

Using the TMY3 Creator involves three overall steps:

1. Open an existing, correctly formatted TMY3 file to use as a base file.

2. Type and paste data in the the tables in the TMY3 Creator window to replace data in the base file with your data.

3. Save the data to a new TMY3 file.

 

Notes.
 
Unless you have a complete set of weather data for your location that you can use with confidence, using your own data introduces uncertainty into your analysis, and may result in inaccurate results or simulation errors.
 
As an alternative to the TMY3 Creator, if you plan to use your weather data with the physical trough model or one of the photovoltaic models, you may want to create a weather file in the SMW format.

To use the TMY3 Creator, you must have the following:

A "base" TMY3 file, which is an existing file in TMY3 format that SAM modifies by replacing only the columns that SAM needs for simulations with your data. If you have a complete data set that includes all of the columns shown in the table below, then you can use any valid TMY3 file as a base file. If you do not have data for all of the categories listed in the table below, you may want to use a base file with data for the same or a nearby location with similar weather characteristics.

Hourly data (8,760 rows) for each of the data columns shown in the table below with no gaps. If you do not have data for one or more of the columns, you can choose to not replace data for those columns, and instead use data from the base file. This will result in a data set that SAM can read but with mismatched elements that may cause inaccurate results or errors in the simulation. In some cases, you maybe able to use a null value indicator such as 999 or -999 for columns or cells for which you have no data.

A Note about Excel and TMY3 Files.
 
Opening TMY3 files in Excel and saving them can cause the data in the files to become unreadable in SAM:
 
1. Excel adds commas to the header rows to match the number of columns in the data rows because it assumes that all rows in the file have the same number of columns.
 
2. Excel automatically changes date and number formats so that SAM's weather data processor can no longer recognize the data, for example changing 01/01/1987 to 1/1/1987.
 
To avoid these problems, do not open and save your TMY3 format files in Excel. To examine the data, use a program like DView (http://www.mistaya.ca/software/dview.htm) or a text editor. If you do use Excel to make changes to data in a TMY3 file, you can avoid the inadvertently changing the data format by using the TMY3 Creator to create a new file containing your modified data.

To prepare your data:

1.Identify a file in TMY3 format to use as the base file (see description above). This can be any of the following:

One of the TMY3 files included with SAM in the \weather folder of you SAM installation folder (c:\SAM\SAM 2014.1.14 in Windows). The TMY3 files have the .csv extension, for example, 723815TY.csv.

A TMY3 file for a location near your weather file location from the NSRDB database http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3/.

A valid TMY3 file that you created for a different location, and tested in SAM.

2.To facilitate copying and pasting data, create a spreadsheet with tables of data that match the two TMY3 Creator tables: One containing a row of header information (Site Identifier Code, Station Name, etc.), and the other containing columns of weather data. Organize the columns in your spreadsheet so that they are in the same order as those in the TMY3 Creator tables.

To create a TMY3 weather file:

1.Open the file or files containing your weather data in a spreadsheet program or any software that allows you to copy columns of 8,760 rows to your computer's clipboard.

2.Start SAM, and create a new case for the technology you want to use with your weather data.

3.On the Location and Resource page, click Create TMY3 file.

4.In the TMY3 Creator window, click Open base TMY3 file, and navigate to the folder containing the base file.

5.Type values in the header fields as appropriate. See below descriptions of the fields.

If you have organized the data in your spreadsheet as a table with columns in the same order as they are in the TMY3 Creator: Select and copy the entire table in the spreadsheet (without column headings), click the first column in the TMY3 Creator table, and click Paste to populate the entire table.

6.In your weather data file, copy the column of global horizontal radiation data. Be sure to copy all 8,760 rows of data, but do not include the row header. The column should contain 8,760 rows of numbers.

7.In the TMY3 Creator window, click the GHI (W/m2) column heading. SAM should highlight the entire column in dark gray.

8.Click Paste.

9.Repeat the copy and paste procedure for each column until you have pasted all of your data into the table.

Alternatively, you can copy and paste the entire 9 x 8760 table as described under Step 6 above.

10.Click Save as TMY3 file (at the bottom of the window).

Save the file in a folder that you have included in the weather file search list, or to a folder that you plan to add to the list. See Weather File Folders for details.

11.Click the close button at the top right of the window, or click Cancel and Discard Data to close the TMY3 Creator.

12.Click Refresh list. SAM may take a moment or two to refresh the location list.

13.In the Location list, select the new TMY3 file. You should find it toward the end of the list.

14.Click View Hourly Data to open the time series data viewer and visually inspect the data.

After creating and loading your weather file, run some test simulations and examine the time series results to see if there are any problems with the data. You can view graphs of the data with the weather data viewer.

Header Data

Site Identifier Code

A six-digit number identifying the location. If you do not have a station code, use a dummy value like 999999.

Station Name

A text description identifying the location. The station name must contain at least one character.

Station State

A two-letter text abbreviation for the location's state. If you do not have a state abbreviation, use a dummy value like NA.

Site Time Zone (GMT)

The location's time zone offset from Greenwich Mean Time (GMT) with no daylight savings adjustment. A positive value indicates a time zone east of the Prime Meridian. Decimals indicate fractions of hours. A negative value indicates a time zone west of the prime meridian. For example, Chicago is -6; India is 5.5.

Site Latitude (DD)

Location's latitude in decimal degrees. A positive value between zero and 90 indicates a latitude north of the equator. A negative value between 0 and -90 indicates a latitude south of the equator. For example, Durban (South Africa) is -29.97; New York City is 40.71.

Site Longitude (DD)

Location's longitude in decimal degrees. A positive value between zero and 180 indicates a longitude east of the Prime Meridian. A negative value between zero and -180 indicates a longitude west of the Prime Meridian. For example, Durban (South Africa) is 30.95; New York City is -74.01.

Site Elevation (m)

Location's height above sea level in meters.

Hourly Data

GHI (W/m2)

Global horizontal irradiance: Total amount of direct and diffuse solar radiation received on a horizontal surface Watts per square meter.

DNI (W/m2)

Direct normal irradiance: Amount of solar radiation received within a limited field of view centered on the sun in Watts per square meter.

DHI (W/m2)

Diffuse horizontal irradiance: Amount of solar radiation received from the sky, excluding the solar disk on a horizontal surface in Watts per square meter.

Dry-bulb (C)

Average dry bulb temperature for the hour in degrees Celsius..

Dew-point (C)

Average dew point temperature for the hour in degrees Celsius.

RHum (%)

Average relative humidity for the hour.

Pressure (mbar)

Station pressure or measured atmospheric pressure in millibars corrected for temperature and humidity for the hour.

Wspd (m/s)

Average speed of the wind for the hour in meters per second.

Albedo (unitless)

Ratio of reflected solar radiation to global horizontal radiation. Use -99 for null.