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re: cooling of pv modules (was calculating windload...)
1 jan 2003
george ghio   wrote:

>> >> >what is the selling price for this system from the ground up keeping 
>> >> >in mind that the cost includes the entire frame
>> >> exactly $31,250, $17,325 for panels plus $13,925 for everything else. 

or possibly more... $31,250 is the minimum sale price required to collect
the maximum $25k rebate, under the proposed rule that the rebate can be
no more than 80% of the cost... 0.8p = 25k makes p = $31,250. this could
also be economically attractive with a 10% tax-free return, ie a $42.2k
price with a $25k rebate.

>> >total cost of $31,250 to get 8577.8 kwh 

with no shiny tarp...

>> ...$6,250 for a 0.2x8577.8 = $1715.66 (27.4%) yearly tax-free return.
>well out here you would get $7500 cash back on installation but i think 
>that a $25000 rebate on a $21600 investment would be nice 

me too, but it looks like the maximum rebate for a $21.6k system would be
0.8x21.6k = $17,280.

>> >compared to 
>> >
>> >total cost of $21,600 to get 9249.6 kwh from a single axis frame...

how much with the inverters and grid-tie connection?

>>...can you park 2 cars underneath?
>if you like

the roof would be waterproof? good...

>> how many watts of what kind of panels at what angle, with how much sun?
>36 165w sharp ne-q5e2u panels at the angle and sun you specified. but of 
>course most people would adjust the angle for the season to gain even 
>better performance.

the rebate is $5/w up to 5 kw. it will only pay for 30 165w panels...
>> you might want to adjust the size and economics to fit this rebate
>> program, which is only offered within about 50 miles of philadelphia.
>what! they dont pay if you install more panels?


>the rebate here cuts off at $7500 but you can put up more panesl if you like.

you can install more here if you like, at your own expense.

>> >this price is based on my panelrack design that allows for the mounting 
>> >of 6 panels for $330 + 25 dollars for each extra panel. this comes to 
>> >$1080 au pluse a further $420 au for the additional concrete footings 
>> >and pipe for the base. this converted to us dollars at the exchange rate 
>> >of .56 as of this morning is $840 us.
>> would this include the inverters and grid-tie wiring?

george, george, george. what's the complete price for a _complete system_?

>>...come here and build 50 of them. i'm trying to avoid concrete...
>...a rather large wind loading and no foundations.

by boca code, the basic structure needs to withstand 12.6'x32'x13.3psf
= 5,363 pounds of force, so each of the 6 4.5' ground stakes (t-posts)
needs to withstand a 5,363/6 = 894 lb sliding force. at an average 6.3'
elevation, a 33.8k ft-lb overturning moment will try to uproot 3 stakes
and bury the other 3 deeper. with 22' between them, each post needs to
withstand 38.4k/22/3 = 582 lb of insertion and withdrawal force.

after consulting with three structural engineering profs ("gee, why don't
you test them?"), i'm planning to test the ground stakes for these forces.
my 3 greenhouses have been doing fine for the last several years with 3'
ground stakes. given the weight of the structure (including snow load)
and our clay soil, i'm more concerned about insertion force. we might end
up with some horizontal steel on the ground and a portable structure with
no permanent footprint and less installation labor.

> said that water cooling could be done cheaper than more panels.
>you have yet to prove it.

we've done that, using your evidence. the cooling system you described
would cost less than 11% more panels, ie $2,800. the tarp would add
something like 11% more for another $50 or so. it makes economic sense
to do this stuff, even though the rebate only pays for panels. 


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