[RE-wrenches] Real world PV production

Kelly Keilwitz, Whidbey Sun & Wind kelly at whidbeysunwind.com
Thu Jun 10 07:57:53 PDT 2010


Thanks, Don,
Performance predictions such as from PV Watts VASTLY underestimate PV  
production in our area. For example, PV Watts estimates 940 kWh/kW for  
a 4:12 pitch at 180˚, whereas such systems are actually producing up  
to 1300 kWh/kW (as measured by a renenue-grade production meter). We  
have to set the derating factor to nearly 100% in order for the  
predictions to match.

I assume that is partly due to coarse irradiance data (not accounting  
for higher irradiance for our location in the rain shadow of the  
Olympic Mountains), but also due to our clear, cool, windy summers,  
good natural washing, and (perhaps) dispersed distribution of  
irradiance.

I want to know if the opposite is true: Do performance predictions  
OVERESTIMATE PV production in areas with historically high irradiance,  
but significant soiling and temperature issues.

Thanks,
-Kelly

Kelly Keilwitz, P.E.
Whidbey Sun & Wind
Renewable Energy Systems
kelly at whidbeysunwind.com
360-678-7131

On Jun 9, 2010, at 8:59 AM, i2p wrote:

>
> On Jun 9, 2010, at 8:22:12 AM, "Kelly Keilwitz, Whidbey Sun & Wind" <kelly at whidbeysunwind.com 
> > wrote:
>
> Thanks, Joel
> How about PV systems away from the coast, in a hotter, dustier
> location, like Bakersfield, Fresno, Sacramento, Palm Springs,
> etc........?
>
> In central CA we do a little better. I casually monitor several  
> systems in this area and expect around 1500-1600 kwh/kw. per year.
>
> Don Loweburg
>

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