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re: cooling of pv modules (was calculating windload...)
22 dec 2002
george ghio wrote:
>> sharp 165 w, 32.5" (ns) x 62" (ew), with an extra 1/8" for tape between
>> ns edges and 1.625 (unistrut) + 0.25 (tape) between ew edges...
>
>this sounds as though you are butting your panels to the ns unistrut at
>the ends. is this correct?
>> >> 32'
>> >> p-----------p-----------p
>> >> | | | | | | | 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.
>> >> p-----------p-----------p
>> >> south
every panel would be surrounded by 1/4" foam tape squeezed to 1/8". ns edges
would have a piece of unistrut between them. ew edges would be panel-frame,
tape, panel-frame. each panel would bolt through the flange perpendicular to
the face in four places, to another panel on ew edges or unistrut on ns
(short) edges. the outermost north and south panel edges would only have
support from the unistrut below the edge. i haven't worked out deflections
and thermal expansions for hole sizes and spacings, but so far this looks
reasonable to me.
>...as the sun moves across the sky from east to west the reflected light
>will move across the panels from west to east causing unequal intensity
>of the suns rays moving across the panels...
they will still produce more power with the reflector. one part of this
scheme is to pair appropriate 24 v panels in series for the 48 v sun tie
inverter, ie those with similar illumination, on average. we can pair 30
panels in lots of ways. some are better than others, to maximize yearly
energy output.
>> >> ...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 north edge. maybe no separate pump...
>> >
>> >cost?
>>
>> that marginal cost would be low, for a 32'x2" pvc pipe
>> with some holes and a 32' gutter. if new, the extra 27'
>> of unistrut for the north poles would cost about $90,
>> and the cost of the tarp is about $50.
>
>so the pool is level with and right up under the panels? this being the
>only way that this could work without extra piping.
swimming pools have filter pumps.
>> >> 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.
>> >
>> >cost?
>>
>> more, about $60 for the poly-film pillow. the tank could be
>> a 4'x8'x8' epdm-lined plywood box in the basement. magic-aire's
>> $150 2'x2' all-copper shw 2347 duct heat exchanger can transfer
>> 45k btu/hour between 125 f water and 68 f air at 1400 cfm with
>> a 0.1" h20 pressure drop.
>
>...during the summer when the panels get hot enough to require cooling
>we will use the heated water to heat the house.
this would work better in wintertime, altho we might evaporate water from
a licl solution in summertime for ac and dehumidification and heat storage
for winter. in sun, panels are always warmer than outdoor air, and output
always increases with cooling, no matter how cold it is outdoors, but
we don't want ice.
>> >> 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.
>> >
>> >cost?
>>
>> my plumbing supply store sells the galvanized tanks for about
>> $150. seems high, compared to a whole water heater for $200.
>
>this requires that the hw tank be mounted at one corner of the panel
>frame because there seems to be no pipe to take the water any where else
>and the shower will be right under the hw tank because there is no pipe
>to take the water into the house.
the basement seems like a better place for the tanks, with
1 or 2 hoses buried along with the 240 v wire to the house.
>> >steel frame bolted to alloy framed panels...
>galvanic corrosion
plastic grommets.
>lets get down to the numbers
good...
>...25,000 for the whole box and dice to get 20% more out of your panels.
maybe less than 20%, with free heat, but it might have to cost more. the
rebaters are thinking about a new rule, "the customer must pay at least
20% of the final cost," which means a 5 kw system would have to cost at
least $31,250, to get the full $25k rebate. i suspect contractors won't
have a problem with that :-)
>out of this $25,000 we take $17,325 for the panels leaving $7,675 for
>the mounting and cooling of the 30 - 165w sharp panels.
>
>now as the panels cost $577.50 each and 6 panels is 20% of 30 panels and
>these extra 6 panels would cost $3,465 for an increase in energy of 20%
>with $4,210 left over to build the frame...
the contractor needs to add at least $31,250-$17,325 = $13,925 to the cost
of the 30 panels. hey, no problem :-)
nick
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