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

"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.

It would take a not especially well designed system to waste 17% or 23%
on electricity. What you dont mention here is that using a solar panel
to provide power means more embodied energy used in manufacturing the
thing, plus more cost to pay back.


"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."

no, but you start from a position further back, due to embodied energy
in the panel. Youre also further back financially.


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.

correct

However, if you do it for a whole range of other reasons then the
investment makes perfect sense.

it doesnt, for one simple reason: you can spend less, invest less
embodied energy, and receive greater returns with solar space heating.


NT