On Fri, 19 Oct 2007 09:08:17 +0000 (UTC) someone who may be Ed
Sirett wrote this:-

I think that's just what it is in Greece: you buy a package with a
collector and plumbing all connected up and stick it on your (flat) roof.
Cheap as chips over there and AFAIK not a gov't subsidy in sight.

But that's probably one of those simple thermosyphon type kits which are
used in 'hot' countries that never have weather below 0C.
We need something that frost proof so it has to be indirect and use a
frost protected working fluid.

That is one option. Another option is to use a controller which will
circulate water enough to keep the sensitive parts of the collector
from freezing. This could be say five minutes an hour. This does
reduce the temperature of the store a little, but it may be an
appropriate option in some circumstances.

Another option is to let it freeze, the approach taken by Solartwin.
It is unlikely to remain frozen for long during the day.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54