On Wed, 08 Mar 2006 11:41:40 GMT someone who may be Tony Bryer
wrote this:-

On Tue, 07 Mar 2006 20:33:24 -0400 Derek Broughton wrote :
OK, I'll accept those numbers. Anyone got a better figure on
the average cost of heating water?

The latest SAP 2005 algorithms for a 100m2 house, 110 litre factory
insulated cylinder give a required raw energy input for DHW of
3172kWh. Divide this by the boiler efficiency to get the actual
energy required.

And the efficiency of the pump and pipework. I doubt if the
conversion of gas into hot water is ever going to exceed 80%
efficiency over a year. That gives 3965kWh gas input. At 3p per kWh
that is 118.95 a year, at today's prices. A solar water heating
system should save at least 75% of this through the year, which is
£89.21 a year saved at today's prices.

If the water is heated by off-peak electricity, in theory 100%
efficient, at 4p per unit, then 3172kWh cost £126.88 at today's
prices.

I have no idea by how much the price of gas and electricity will go
up by over say 20 years, but it will go up. The price of sunshine
will remain the same though.

As for maintenance, an evacuated tube system may need a tube or two
replacing over 20 years, but that will probably be it.




--
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