Absorbed Radiation for Flat Plate PV Modules?

Hello,
As I understand it, the absorbed (aka useful or effective, maybe?) radiation for PV modules is calculated in different ways for the CEC, Sandia, and PVWatts models. These calculations come in after the incident irradiance is calculated and take into account AOI and spectral effects. Is there any way in SAM to view the hourly absorbed/useful/effective radiation, as opposed to just what is incident?

Thanks!
Sara

Dear Sara,

Here are the hourly variables that SAM reports that are relevant to your question. You can see these variables on the Results page tables and time series graphs.

For the flat-plate PV model, which includes the CEC and Sandia module models, the following output variables are available in the hourly results:

Global horizontal irradiance (kW/m2): The total horizontal radiation values from the weather file. SAM does not use this value if you choose the "Beam and Diffuse" option on the Array page.

Nominal incident beam irradiance (kW/m2): The beam radiation values from the weather file. This variable is misnamed in SAM 2012.11.30.

Nominal incident diffuse irradiance (kW/m2): The diffuse horizontal radiation valuse from the weather file. This variable is misnamed in SAM 2012.11.30. SAM does not use this value if you choose the "Total and Beam" option on the Array page.

Subarray [1..4] incident beam irradiance after shading and soiling (kW/m2): The beam radiation incident on the modules in Subarrays 1 through 4.

Subarray [1..4] Incident diffuse irradiance after shading and soiling (kW/m2): The diffuse radiation incident on the modules in Subarrays 1 through 4.

Input radiation (kWh): Equivalent to the energy absorbed by all of the modules in the system. This is the energy that is converted to electricity. For a system with one subarray, the module efficiency reported in the results for the subarray is equal to the subarray gross DC output divided by the input radiation.

For the PVWatts model, SAM reports the global, beam, and diffuse radiation values from the weather file, and the plane-of-array (POA) irradiance. The POA irradiance is the solar radiation incident on the array.

Best regards,
Paul.

Thanks! When I run SAM using the CEC and Sandia models for the same module (FS 270) I see that the hourly input radiation is the same in both cases. Based on your answer to a previous question in this forum about fresnel losses, I thought that the Sandia and CEC models would calculate incident angle losses differently from one another. Is this not the case? Or is there something else that one needs to do in SAM to switch between the two models (other than just changing the module from CEC database to Sandia)?

Hi Sara,

The flat-plate PV model uses the same radiation processing algorithm to calculate the radiation incident on the array, regardless of which module model you choose on the Module page. The Hourly Input Radiation value in the hourly results should not change with the module model option.

The module model options do use different algorithms to calculate the array's DC output from the incident radiation.

Best regards,
Paul.