[RE-wrenches] Real world PV production

[Kelly Keilwitz, Whidbey Sun & Wind]

Joel,
Thanks for the information. 35% loss due to to smog or soiling is a  
big hit and, I'm sure, an exception. Still, if the loss is even 20% it  
supports the concept that an array here on the cool, cloudy west side  
of the WA Cascades can perform on par with an equivalent array in a  
hot, dusty/smoggy location in CA.

I'd still like to hear of actual less-than-stellar production numbers  
recorded in such situations.

-Kelly



On Jun 10, 2010, at 9:02 AM, Joel Davidson wrote:

> PVWatts is a good general estimator when you fine-tune the derate  
> factor. For single crystal and multicrystalline arrays, I generally  
> use 0.65 for battery-based PV and inverter systems and 0.82 for  
> batteryless inverter systems. PVWatts annual results are l5% low for  
> Unisolar arrays because PVWatts uses the crystalline silicon  
> temperature coefficient.
>
> Even though PVWatts2 may seem more accurate, it does not factor in  
> unique local climate conditions like California coastal morning and  
> afternoon fog or inland persistent winter Tule fog. However, NREL's  
> climate data does include LA's "June gloom" see http://en.wikipedia.org/wiki/June_Gloom
>
> For flat roofs in snowy climates like the Unisolar project in  
> Rochester NY, I deduct 30% from PVWatt's November through March  
> estimates for a fairly accurate annual estimate. Powerlight (now  
> SunPower) also uses an additional 30% monthly derating for flat  
> roofs in snowy locations.
>
> PVWatts does not account for really dusty and dirty air locations.  
> Bill Brooks worked at PVUSA and is very knowledgeable about power  
> loss from soiling from agricultural dust in central California. Bill  
> also measured 35% power loss at the Long Beach CA harbor waste-to- 
> energy powerplant PV systems. That location and most LA county  
> freeways experience particulate pollution that not only reduces PV  
> production but causes permanent respiratory damage to children and  
> shorten the lives of elderly people, sort of like the canary in the  
> mine.
>
> Joel Davidson
> ----- Original Message -----
> From: Kelly Keilwitz, Whidbey Sun & Wind
> To: RE-wrenches
> Sent: Thursday, June 10, 2010 7:57 AM
> Subject: Re: [RE-wrenches] Real world PV production
>
> 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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