Air Quality on PV [RE-wrenches]

[Bill Brooks]

Lynne,

I misunderstood your question about effects of pollution. It is very
difficult to quantify the reflective characteristics of pollution. Our
30-year solar resource data tends to agree quite well with measured data in
North Carolina, so I don't think the resource is being impacted to an
extreme. I would be surprised if it was ever more than 5%. North Carolina
has a tremendous amount of water vapor in the air, which is why flat-plate
collectors work so much better than concentrator systems. Our diffuse
(scattered) radiation can be 30% of the energy we get from the sun. This
also makes tracking systems a little less effective.

Living now in the land of real air pollution, I can attest that North
Carolina ain't got nearly the problem that Californy has. Temperature
effects still dominate system losses in the summer time. The problem is that
almost everyone overpredicts their system performance. Then when the system
doesn't live up to expectations, they start to blame other things like
pollution when it was something else.

Our system losses come from many sources:

Shading
Dirt
Wire Losses
Module Mismatch
Inverter Losses (much higher than most people predict)
Battery Losses
Charge controller losses
(did I say we have losses?)

Take the STC rating and multiply by 0.7 and that is a fair number for system
max AC power (spring and fall). Take STC rating (in kW) x 0.6 x solar
resource (5.0 kWh/m2/day--Raleigh, NC) x 365 days/year = Annual Energy
Generation for optimal tilt with little or no shading. These are
conservative estimates for grid-connected PV systems. If you are using
numbers substantially higher, you will always be disappointed with power
output. If you use these numbers you should be happy with your performance
unless the system has some maintenance problem.

Bill.


> -----Original Message-----
> From: Lynne A Carter [mailto:solarvil at netpath.net]
> Sent: Tuesday, April 10, 2001 7:11 PM
> To: RE-wrenches at topica.com
> Subject: Re: Air Quality on PV [RE-wrenches]
>
>
> Bill,
> How are you? I hope CA is treating you well. That is a wonderful site lots
> of neat info, thank you!   I used the calculator and we came up with the
> numbers we are offsetting. Ox lbs. 255, SO2 lbs. 460, CO2 lbs. 59,498 and
> got a net profit on the total mileage for all the company/personal cars,
> trucks and vans. That's fun.
> I did not see any information on effects of air quality on PV
> power ratings.
> Air Quality, in NC is very dirty air. We see humidity (water vapor in the
> air) but we also see air pollution. I am hoping to find a number that I
> might use to calculate the decreased photovoltaic electricity
> that dirty air
> may cause. Like a code "orange," "red" and maybe "purple" how
> much power am
> I loosing from the lack of good air quality? I may have missed this at the
> site it is quite large.  Let me know if I am wrong.
> Today its in the 90's and were seeing lots of haze the power production is
> down. Luckily, all this hot air brought in some wind and looks like a
> thunderstorm soon. It could be the photovoltaic arrays are
> responding to the
> temperature or the pollution or water vapor.
> We size systems a little larger to compensate for the summer temperatures
> and the pollution.  This year it could get very bad because of
> all the coal
> electric plants that are firing up.
>
> Lyn at solarvillage.com
> Solar Village Institute inc.
> PO Box 14
> Saxapahaw, NC  27340
> Tel. 336-376-9530
> Fax. 336-376-1809
>
>
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