Unisolar Roofing [RE-wrenches]

[Doug Pratt]

Wow Bill!  This is great stuff!  Can you quote your "top secret" source? Where'd
this % of loss chart come from?  What kind of modules, what latitude, etc?

On the lower chart, this is telling us kWh of AC power production, per year, for
every kW of PV at standard test conditions?  Did I understand that correctly?

-Doug Pratt


Bill Brooks wrote:

> I realize that ASCII can be cruel, but hopefully you can read this. This is
> top secret so make sure you spread it around ;-). This chart tells us the
> impact of fixed orientation on annual energy production for a
> grid-connected, net-metered PV system. Do not use this for off-grid since we
> cannot predict array utilization nearly as well. The interesting thing about
> this chart is that it clearly shows that annual energy producting is not
> very sensitive to fairly wide variations in orientation (4:12 to 12:12, SE
> to SW only has about 5% loss from ideal). Moral of the story is don't tilt
> your modules on rooftop PV systems because it looks like hell, costs more to
> install, and often doesn't buy much as far as performance.
>
> Roof pitch      Flat    4:12    7:12    12:12   21:12   Vertical
> South           0.89    0.97    1.00    0.97    0.89    0.58
> SSE,SSW 0.89    0.97    0.99    0.96    0.88    0.59
> SE, SW  0.89    0.95    0.96    0.93    0.85    0.60
> ESE,WSW 0.89    0.92    0.91    0.87    0.79    0.57
> E, W            0.89    0.88    0.84    0.78    0.70    0.52
>
> Okay all you Wrenches out there, on the chart below are some real-life
> numbers you should be using for grid-connect PV systems that are properly
> oriented. This should generate some good controversy because nobody I know
> states numbers this low. However, these are real-life conservative numbers.
> A well installed system with minimal shading should be able to consistently
> produce this much electricity or more in a year. If it doesn't, there is
> something wrong with it (equipment or installation). The new California
> Buydown guidelines require a meter come June 1, 2001, so sharpen your pencil
> because customers are now going to need energy estimates. This means you
> need to do a detailed shading analysis with a Solar Pathfinder, use the
> chart above to adjust for orientation, and multiply that number by your
> location below and you're done! Piece of cake.
>
> CITY                    kWh/kWstc
> Arcata          1092
> Shasta          1345
> San Francisco   1379
> Sacramento              1455
> Fresno          1505
> Santa Maria             1422
> Barstow         1646
> Los Angeles             1406
> San Diego               1406
>
> Anybody want to comment?
>
> Bill.
>

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