On Fri, 19 May 2006 13:11:06 +0100, David Hansen wrote:

... I said that it would make more sense to replace an
inefficient boiler with a high-efficiency one than install solar water
heating and keep the dinosaur. Do you agree?

That depends on the situation. For example, if someone was able to
run an old boiler for a few more years and then install a micro CHP
unit I suspect that would be better for the environment.

OK, but that would be an extremely unusual situation and, dare I
say?, a rather contrived example.

I was (and am) trying to establish a rule of thumb that you don't put in
solar water heating before you've addressed draughtproofing, insulation
and heating efficiency. This isn't an academic exercise: I know someone
who's just signed up for a (very expensive) solar system. His rambling old
5-bedroom house has draughty external doors, many draughty single-glazed
windows, at best 50mm loft insulation, probably no insulation in the
cavity walls, and a standard efficiency boiler with a programmer + room
thermostat as controls (single zone). He coukld have spent 1/10th the
money and resources and saved vastly more energy than the solar system is
going to produce.

Now this guy isn't your average SUV driver who thinks he's green
because his wife buys Ecover but an economist working for a radical
economic/ecological think-tank FFS! If he doesn't know better what hope is
there of getting Joe/Jo public to make ecologically-sensible decisions?

Don't get me wrong I'm all for renewables, and have no objection to people
with the money putting in solar systems (after they've got the other
factors right) even though it may not pay back economically. Likewise the
(proposed?) local regs in London requiring renewables in new developments.
As with condensing boilers as the technology becomes more widespread the
costs should come down furthering deployment of the technology, which is
IMHO A Good Thing.

BTW picking up on your mention of microCHP I looked into the MicroGen and
WhisperGen but they didn't seem to be available at the moment. There are
also issues of what to do with surplus electricity produced (I think this
came up here or on uk.environment recently?). Do you know of any
domestic-scale installations in the UK?