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Dual-Use Solar Panels
After not paying attention to solar technologies for a
long time, I have come to Home Power magazine to get
caught up with the current state of the art. I am
surprised that there isn’t any mention of combined
photovoltaic and solar hot water panels! It would seem
a natural fit to have the PV in front getting hot and
producing electricity, with a water jacket behind drawing
off the heat for use indoors. From the sounds of what
I’ve read so far, the PV is more efficient at cooler
temperatures. Scavenging the heat may increase the
output of the panels, and perhaps offset the draw of the
pumps to circulate the hot water. The hassle of a
rooftop installation would be well repaid with such a
dual reward technology. Is there potential in this
concept, or has it been shown to be folly? Best Regards,
Steve Jacobson
Hi Steve. “Folly” is probably not the right word for it.
“Problematic” might better describe it. It does seem like
a perfect marriage, and it has been tried. First there is
the potential problem of mixing water and electricity. It
doesn’t seem too hard to overcome that problem with
good isolation.
Then, there is the added complexity, size, and weight. I
think complexity is the biggie, though. If something goes
wrong with the water heater, which is the relatively
cheaper portion, you have to replace the whole thing,
including the more expensive electrical portion. If
something goes wrong with the PV part, what you have
left is a very inefficient water heater. If the water portion
quits working, you end up actually increasing the
temperature of the PV due to the insulating properties
of the water jacket.
The conventional thinking is that PV works well enough
with adequate air space on either side. And silicon PV
materials are not the best way to heat water—copper
plates and tubes in solar H2O collectors work much
more efficiently. The conclusion is that it is more
efficient and less problematic to use separate collectors
for each process.
All that said, I personally have long been interested in
this very idea, and look forward to seeing if the industry
or experimenters come up with something that works
well.
Michael Welch • Home Power
Another factor that Michael doesn’t mention (and a
huge factor, the biggest really) is temperature. PVs like
it cool and solar DHW needs to be hot to be effective. If
a dual collector gets hot enough to provide DHW, it’s far
too hot for the PVs to be effective. If the dual collector is
cool enough for the PVs, the DHW is tepid at best.
Richard Perez • Home Power
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