On Wed, 23 Nov 2005 12:41:15 +0000 someone who may be Peter Parry
wrote this:-

These do at least put some figures on the likely effects of these
units (something the manufacturers studiously avoid doing).

Incorrect.

Solartwin make quite a lot of one of the reports you mentioned.

http://www.solartwin.com/questions_a...s.htm#evidence

"Where's the evidence of this 20%?

"A recent UK government-funded study of eight solar water heating
systems at Milton Keynes confirmed what has long been suspected:
that the environmental benefits of solar can be substantially
improved by eliminating mains electricity. ( Side by side testing of
eight solar water heating systems 2001 DTI/Pub URN 01/1292)

"In this study, flat plate solar hot water systems negated an
average of 17% of their potential global warming benefits (i.e. CO2
savings) by using mains electricity.

"For partial-vacuum tubes ("solar tubes"), their loss averaged even
higher, at 23%.

"In other words, if you run mains-powered solar for ten years, its
electricity consumption deletes its CO2 saving by about two years.

"Solartwin’s environment-centred solar water heating design brief
specifies a solar electric pump. So your CO2 savings won’t retreat
two steps after advancing ten."

As the installed cost of commercially fitted solar panels is in the
region of GBP3,000 to GBP5,000 or more it is not surprise that the
manufacturers so carefully avoid any mention of how much energy the
things actually (don't) produce and the fact they can never pay for
themselves as the payback period is considerably greater than the
system life.

Solar water heating is much like double glazing. If you do it just
to save money then you are not going to do very well out of it.
However, if you do it for a whole range of other reasons then the
investment makes perfect sense.




--
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