re: are any photovoltaic modules designed and/or waranteed for low (2-3sun) concentrations? SOLAR.KnowledgePublications.com

re: are any photovoltaic modules designed and/or waranteed for low (2-3sun) concentrations?
8 jun 2001
we might lay 10 photowatt 75 watt panels (50.7"x21.88", #pv6010, $390
from www.jademountain.com) in a water trough under a 16'x24'x16' tall
linear parabolic reflector to make about 0.8x4x10x75 = 2400 w of peak
electrical power in december, or 10% less, if the reflector has south
glazing to make it usable winter floorspace for people.

the south glazing (if any) might be excel or ge clear polycarbonate,
which comes in 4'x24'x0.020" thick rolls. rimol greenhouse systems
(877) rimol-gh sells excel for $290+$10 ups per 49"x50' roll. ge
polymer shapes (800 445-0719 sells 4'x100' rolls of "lexan 8010"
for $381.30. a 4'x500' roll is $1507.

if the reflector and pump and controls cost $1k, the effective pv panel
cost becomes about $2/peak watt, and we get lots of hot water for showers
and space heating as well, on the order of 260k btu/day, ie 76 kwh/day.

the target might be a 30" uv polyethylene duct which folds flat to 48".
at 62 cents per linear foot, 36 feet would cost about $22, including
a 6' vertical portion at each end of the 24' trough for easy entry and
exit of wires and hoses. the panels are designed to be waterproof, but
the wiring might need some attention, eg some silicone caulk. 

to collect heat efficiently, we need to drain the trough at night.

suppose it's empty in the morning. the sun comes up, and the pv panel
temp rises to the hot water tank temp or 60 c, whichever is lower, which
opens a pv-powered 12v 11.6 w solenoid (eg grainger's 3a434 solenoid
with a 3424231 coil) to let tank water flow into the trough via a float
valve until the level exceeds the height of the underwater horizontal
pv panels. water flows into the trough and out of a spigot at the far
end and into a sump until the sump level float switch turns on a
5 gpm@4'head 12v hot water pump which returns the water to the tank.

when the sun goes down, the pv panel temp drops to the tank temp or
60 c, whichever is lower, the solenoid valve closes, the trough drains
into the sump, and the pump returns the remaining water to the tank
and stops for the night.

for meltdown protection, the pump might continue into the night if
the tank water temp is greater than 60 c, and if the pv panel temp
rises to 80 c or more, we might pull a pin with a mechanical solenoid
that releases the ground tie on the north edge of the reflector and
allows it to tip forward and shadow the target. if the reflector has
south glazing, the solenoid could release a shadecloth curtain that
falls down to cover the glazing. 

nick