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<div class="moz-cite-prefix">On 6/3/2013 11:28 AM, RT wrote:<br>
</div>
<blockquote cite="mid:op.wx3zyaqt0ciq73@rt-acernb" type="cite">On
Mon, 03 Jun 2013 09:24:34 -0400, Topher
<a class="moz-txt-link-rfc2396E" href="mailto:topher@greenfret.com"><topher@greenfret.com></a> wrote:
<br>
<br>
<blockquote type="cite">On 6/2/2013 7:08 PM, RT wrote:
<br>
<blockquote type="cite"> he did mention "concentrating
photovoltaic (CPV)" systems that were
<br>
becoming viable which utilise Fresnel lenses to concentrate
sunlight
<br>
so that solar arrays could be reduced to the size of [his]
thumbnail.
<br>
</blockquote>
<br>
I don't think I want one on my roof though. My current plans
are for
<br>
about 2000 watts of cells. That's 8000 watts or so of heat that
needs
<br>
to be dissipated. I come back to the thing I have been saying
for years. If you aren't
<br>
making solar CHEAPER, you aren't helping.
<br>
</blockquote>
<br>
I'm not a gizmologist so I've not looked into CPV systems but I do
know that the efficiency of PV cells in general drops as the
temperatures to which they are subjected, increases.
<br>
</blockquote>
Yes.<br>
<blockquote cite="mid:op.wx3zyaqt0ciq73@rt-acernb" type="cite">As
such I would imagine that the people developing CPV systems have
addressed temperature issues.
<br>
</blockquote>
Not sure that follows, but even at the theoretical efficiency limit
of PV, there is going to a *lot* of waste heat in a system like
that.<br>
<br>
<blockquote cite="mid:op.wx3zyaqt0ciq73@rt-acernb" type="cite">If I
were doing it, I'd certainly be looking at how to utilise the
"waste" heat for some beneficial task, say like heating or
pre-heating for a DHWH system.
<br>
</blockquote>
Presumably. Not a simple engineering problem though. 8,000 Watts =
7,500 BTUs / sec = 90 gallons per sec (at 10 degree rise).<br>
<blockquote cite="mid:op.wx3zyaqt0ciq73@rt-acernb" type="cite">
<br>
Also, I'm pretty sure that I remember my neighbour saying that CPV
systems are typically designed as tracking systems, my guess is
that they'd be dual-axis tracking to maximise efficiency. If
that's the case, it's unlikley that there'd be any contact between
the PV array and the roof so I doubt there'd be any heat related
issues WRT the roof.
<br>
</blockquote>
The CPV I have seen were all large commercial operations. So it is
not clear that it helps homeowners at all. The reason to use a roof
in the first place is that it is already shading. Moving the PV
somewhere else doubles the shading. tracking is <i>already</i>
more expensive than just adding more panels.<br>
<br>
<blockquote cite="mid:op.wx3zyaqt0ciq73@rt-acernb" type="cite">From
what I've seen the major cost of any solar power plant has been
the cost of the PV panels.
<br>
</blockquote>
Not anymore (at least for small systems). For the most recent
estimate I saw, balance of system was <i>twice</i> the cost of the
panels. YMMV.<br>
<br>
<blockquote cite="mid:op.wx3zyaqt0ciq73@rt-acernb" type="cite">I
don't recall their being particularly pricey so I don't expect
that the addition of Fresnel lenses to a PV In array would be much
of a factor in increasing cost.
<br>
</blockquote>
The problem is not just the cost of the lenses. In order to get the
same output as a 20 meter^2 PV panel array, you need 20 meter^2 of
Fresnel lenses; and some means of holding it very steady in the
wind, a precise distance away from the collector; plus be able to
move the whole unit (including the cooling system), very precisely
throughout the day, every day.<br>
<br>
Gizmological, as you say.<br>
<br>
Thank You Kindly,<br>
<br>
Corwyn<br>
<pre class="moz-signature" cols="72">--
Topher Belknap
Green Fret Consulting
Kermit didn't know the half of it...
<a class="moz-txt-link-freetext" href="http://www.GreenFret.com/">http://www.GreenFret.com/</a>
<a class="moz-txt-link-abbreviated" href="mailto:topher@greenfret.com">topher@greenfret.com</a>
</pre>
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