Wind speed in wind modeling, PV and CSP plus file converting from PVGIS

Hi Mona,

1. For the wind power model, SAM uses a wind shear model to calculate the wind speed at hub height given the measurement height of the wind resource data, so you do not need to adjust the wind resource data. For example, if you have wind speed data measured at 100 meters, and the turbine hub height is 110 meters, SAM adjusts the wind speed to 110 meters. Note that SAM only performs the wind shear adjustment when the difference between the measurement height and the hub height is less than 35 meters.

2. SAM's photovoltaic (PV) and concentrating solar power (CSP) models use wind speed data to calculate PV cell temperature and heat losses (CSP). SAM assumes that wind speed data in the solar resource files is measured at 2 meters, near the typical height of ground mounted PV arrays or CSP collectors. The C++ code for these calculations is available in the SAM open source repositories on GitHub: github.com/NREL/SAM.

3. You can find a description of the SAM CSV file format for solar resource data and SRW format for wind resource data in SAM's Help system. We've also posted a PDF version of those descriptions on the SAM website at sam.nrel.gov/weather-data/weather-data-publications.

SAM's Solar Resource File Converter macro should convert files in the PVGIS5 format to SAM CSV. If you could post a copy of the file you are trying to convert, I will see if I can see what is causing the error. It is possible that the PVGIS format has changed since we wrote the conversion macro.

Best regards,
Paul.

Hi Mona,

Thank you for attaching your file.

This appears to be a time series file from PVGIS V5. This file contains global horizontal irradiance (GHI), ambient dry-bulb temperature, and wind speed. SAM's photovoltaic model requires data for two components of solar radiation (direct normal irradiance, diffuse horizontal irradiance), so the data is not suitable to use with SAM.

The PVGIS website does provide access to solar resource data in the EPW format that can be used directly in SAM without conversion. You can download these from the "TMY" tab on the PVGIS download page by clicking the "EPW" button. (SAM's Solar Resource File Converter macro will convert files you download by clicking the "CSV" button to the SAM CSV format.)



However, these files do contain typical meteorological year (TMY) data rather than data for a particular year. TMY files combine data from months in different years to construct a "typical" file that represents the solar resource over a historical period.

Best regards,
Paul.

Hi Fabian,

The PVGIS APIs do provide data other than the TMY files we mention at sam.nrel.gov/weather-data.

The last time I investigated this, I discovered that the single-year data provided by the PVGIS API does not have all of the required information to create a weather file SAM can use.

For example, hourly radiation data from re.jrc.ec.europa.eu/pvg_tools/en/tools.html#HR returns hourly data for specific years, but that data only includes meteorological data for wind speed and ambient temperature so it is not suitable for CSP models that require information about atmospheric pressure and humidity. Those files also do not include a time zone, so you have to add that manually or get it from a different API.

A time series request like re.jrc.ec.europa.eu/pvgis5/seriescalc.php?lat=-4.441931&lon=15.266293&peakpower=1&loss=0&angle=0&aspect=0&startyear=2007&endyear=2015 returns multiple years of data, but only includes GHI, ambient temperature and wind speed, so it is not suitable for SAM's solar models that require two solar irradiance components. That data also does not return a time zone.

This information is about a year old, so may be out of date. If you discover anything different please let me know.

Best regards,
Paul.