Group: alt.energy.renewable
From: nicksanspam@ece.villanova.edu
Date: Thursday, March 13, 2008 7:19 AM
Subject: Re: Solve the problems or declare defeat

Morris Dovey wrote:

>... overcast doesn't prevent a good panel from producing real heat.

Au contraire. This is simple physics. On a cold enough day, the glazing
loss can cool 70 F room air more than an overcast sun can warm it. For
instance, in 10% sun (25 Btu/h-ft^2), a collector with R2 glazing with
80% solar transmission (eg twinwall polycarbonate) will lose heat if
(70-T)1ft^2/R2 > 0.8x25, ie T < 30 F.

Nick