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re: cooling of pv modules (was calculating windload...)
21 dec 2002
george ghio   wrote:

>ok a silvery tarp and a pump and now we are going to use the wast heat

good idea, if possible. maybe not, for the first one. i'd like to build
about 50 "solar garages" in the next year. 

>so where is the panel frame?

in my backyard. i'd bolt together a 32'x14' frame like this

|   |   |   |   |   |   |         using about 400' of 1.625"x2.4375" 
|   |   |   |   |   |   |         steel unistrut with the inner beams 
|---+---+---+---+---+---| 14'     doubled in each direction.
|   |   |   |   |   |   |         
|   |   |   |   |   |   |         the next one might have 25% less steel.

>the tarp frame? how is the tarp kept tight? 

the south posts (p) would be 9' tall. the north ones would be 18', ie 9'
above the level or 2% tilted array. the tarp would be tied to the posts
with light enough twine to let it blow loose before the structure tipped
over in a great wind. a few bungee cords might be nice.

>the pipe and fittings that go with the pump?

commensurate with the price of the $20 bilge pump.

>the water recovery and the waste heat recovery?

if the water evaporates, there would be no "recovery."
the water supply would be the pv roof, and maybe
a nearby house roof. i can think of 3 applications 
for "waste heat recovery": 

1. swimming pool heating, which might only involve
a pipe full of holes near the north edge and a gutter
below the south edge. maybe no separate pump...

2. space heating, with an insulated unpressurized tank
for thermal storage and a water-air heat exchanger, eg
a hydronic floor or a fan-coil unit. 

3. making hot water for showers, an extension of (2)
with a 42 gallon bare galvanized pressurized tank
inside the unpressurized tank to act as a preheater. 

>the control for the pump?

just wire it up to a panel, basically. a differential
thermostat could improve performance. one of harry
thomason's patents suggested raising the differential
from 5 to 25 c in summertime to reduce pump power, 
but these pumps only use 12 watts, and that would
reduce the pv output by more than 12 watts...

>temperature sensing for the panels? the anti freeze?

draindown, with a $6 freezestat to avoid making ice.

>the nuts and bolts? 

i've got about 500 pounds of unistrut nuts and bolts.
>what will it cost?

about the same as the rebate, $25k for 5 kw, including labor.


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