Why GHI and Energy Yield is different for MET file with and without time-shift corrected .MET file?

[Sunoor]

Hi,

I am conducting research on PVsyst performance on different Meteo datasets. I selected a very simple Solar PV array with zero degree tilt.

I downloaded the meteorological data from NSRDB for year Houston 2020 with 30 min temporal resolution. 

I uploaded the data through the PVsyst custom file method. It suggested me a -14 min shift. So I performed two simulations: i) Simulation with Time shift ii) Simulation without timeshift.

I am not able to understand why does PVsyst model produce difference in Annual GHI, Energy Yield and PR?

 

	Without Timeshift	With Time Shift (-14min)
Annual GHI	1800 kWh/m2	1702 kWh/m2
PR	89.43%	88.64%
Annual Energy	17381 kWh	16Test_Houston_Project.VC0- WITHOUT Timeshift.pdfTest_Houston_Project.VC1-WITH Timeshift.pdf290 kWh
Simulation Variant	VC0	VC1

 

 

The most surprising result for me is the annual GHI, since PV array was at the zero degree tilt, the amount of annual GHI shall not be different in the timeshifted case. 

Regards

[Caroline F.]

Hi, 

 

i have some similar results. it would be interesting why these parameters change