Posted by John W. Hall on November 3, 2005, 12:17 am
I note that some recent PV panels are very thin, e.g. as used on some
of the solar vehicles in the recent contest in Australia. Since the
efficiency of most PV cells is rather low, I assume the incident
energy that is not converted to electricity appears as heat. Which, in
excess, is perhaps damaging to the cells.
Would it be beneficial to have a flat water-heating panel on which the
front surface is covered by these PV materials? This would reduce the
heat stress on the PV material and provide water heating, while
requiring less area than using separate PV & thermal areas.
I suspect this has been done, or at least contemplated somewhere, but
have not seen any references to it.
Cochrane, Alberta, Canada.
"Helping People Prosper in the Information Age"
Posted by Iain McClatchie on November 3, 2005, 2:04 am
I've asked the Heliodyne people about this, because I think it's
a good idea, too. Lots of applications are area-limited for solar.
Issues (in the context of glazed flat-plate collectors with PV):
1) If the water system fails (pump, controller, sensors, as well as
the collector), the PV panel gets *much* hotter.
2) PV panels/cells are designed to selectively reflect the unused
wavelengths, which could be changed but requires more of a
relationship between the PV and thermal supplier.
3) Hot water around electrical bits => corrosion.
Posted by nicksanspam on November 3, 2005, 8:45 am
The Missouri/Rollo 2005 DOE Solar Decathlon team custom-made a copper roof
with 1/2" copper pipes in round grooves underneath and Unsolar PVs adhered
to the upper surface.
Posted by Christian Kaiser on November 3, 2005, 10:21 am
But then, there's some contradiction.
PV panels are most efficient at low temperatures, PT at high ones... My PT
panels go up to 110 deg C on a clear day, even 140 deg C if the system shuts
down, which is not at all the best operating temperature of the PV cells. So
this is a compromise only if the area is too small.
Posted by Nick Pine on November 3, 2005, 12:37 pm
Operating at 50-55 C is a good compromise. Lower if you want more electricity.
Higher if you want more hot water. This might change with the season.