Subject: Re: Flat Panel Efficiency?

From: [email-masked] (Nick Pine)
Date: 14 Mar 1995 08:37:48 -0500

Jim Bulmer <[email-masked]> wrote:

>What efficiency can I expect from flat-panel solar collectors?

That depends on a lot of things, like the collection and ambient
temparatures and the number and type of glazings and collection surfaces,
whether selective or not.

>If I assume 1000 W/m^2 incident light, how
>many watts' worth of hot water will come out of the panel? 

500? There are lots of efficiency curves around page 315 of Duffie and
Beckman's book, _Solar Engineering of Thermal Processes," 2nd edition.
Water heaters are more efficient than air heaters, usually, from 60-80%
vs 40-60, altho the new unglazed Conserval air heater has an efficiency
of 80%, they say, heating cold air from the outside. The Conserval people
say that when you add glazing, efficiency goes down by at least 80%.

People sometimes lose sight of the fact that if a collector is cheap, or
replaces something with 0 efficiency that costs about the same or more, and
that has to be there anyway, eg vinyl siding, low efficiency can be fine.

As temperatures go up, efficiency goes down. Steve Baer talks about this,
saying that when people start experimenting, they are impressed with
high temperatures, which is an indication of INefficiency...

>How would the efficiency of a flat-panel collector
>compare with that of a parabolic trough of the same size?

Probably not so good, at low temperatures. Perhaps better at high temperatures.

Nick

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From: [email-masked] (Nick Pine)
Date: 14 Mar 1995 08:43:24 -0500

Nick Pine <[email-masked]> wrote:

>The Conserval people say that when you add glazing, efficiency goes down
>by at least 80%.

Oops. I meant it goes down by at least 20%.

Nick