All Installations Are Not Created Equal

The program that is used by the California Solar Initiative to generate it’s design factor, rebate information and Annual kWh output is PV Watts.  Let’s examine the default inputs to PV Watts.

PV Watts uses the following derate factors. It assumes that all modules and all installations have these conservative derates: 

PV module nameplate DC rating 0.95
Mismatch 0.98
Diodes and connections 0.995
DC wiring 0.98
AC wiring 0.99
Soiling 0.95
System availability 0.98

How can you increase your system output above the predicted kWh output of the CSI EPBB calculator.

1.  Buy a module that doesn’t have a minus 5% derate.  This saves 5%.

2.  Have your installer use large enough wire that your voltage drop is .5 and not 2. This save 1.5%

3.  Have your installer use large enough wire that your AC voltage drop is .5 instead of 1%  This saves .5%

4.  Wash your modules once a month.  This saves 5%.

5.  Make sure you have an installation company that ensures 99.9% uptime.  This saves nearly 2%.

Net result:  14%.

In the solar business, 14% more power output is pretty substantial.  Then, you check out the temperature coefficient of the modules.  Just like golf, the lower the temperature coefficient, the better.  I guess you get what you pay for. 

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