Creating a function to monitor PV module output as a function of cell efficiency

Hi Paul,

This is very helpful thank you. I believe I see where the equations are:
dcpwr += dcpwr*(Gamma/100.0)*(TcellC - 25.0); 
where the initial dcpwr is:
dcpwr = dceff*(input.poaIrr)*Area;
this corresponds to simple efficiency model equation in the tech guide:
Pmp = GηmAm (γmp,ref/100) (Tc −25)

So it looks like my model is in line. The only difference I made is to calculate an hourly 'effective' efficiency based on panels nominal efficiency,the ambient and cell temp and irradiance at each hour. In ampl code it looks like this:eff_val{t in PV_TYPES, h in HOURS} =pv_eff_ref[t] * (1 + temperature_coeff[t]*(temperature[h] - reference_temp))* (I[h] / reference_irradiance);the hourly DC output is then: (eff_val*Area of the panel*Number of panels*Irradiance)/1000
My hourly DC values seem to be longer than SAMs which makes some sense but I think the discrepancy is more than it should be. The other concern I have is that I'm not using the solar data correctly. How does the simple efficiency model use the solar data to determine hourly solar resource? Right now I'm just using DHI values from tmy data file for medly Florida, along with the temperature. Should I be incorporating the other solar values or doing a calculation for more accurate solar resource data?

Thanks!
Michael
 

Hi Michael,

SAM calculates the plane-of-array (POA) irradiance based on the irradiance data in the weather file (DNI and DHI by default), sun position, and array orientation. These equations are described in Chapter 6 of the SAM PV techncial manual I referenced above.

The source code for these calculations is in lib_irradproc.cpp: github.com/NREL/ssc/blob/patch/shared/lib_irradproc.cpp

Best regards,
Paul.