On Sun, 05 Mar 2006 13:26:11 +0000 someone who may be Peter Parry
wrote this:-

I want to use something on a barn conversion we might move to. Add more
insulation etc. is not an option as no loft etc. exists. The boiler is oil
fired but no indirect to HW tank so all HW is electric, E7 at night and full
price during the day. I can get to the tank from the roof line so I was
thinking solar HW would be helpful here.

You would be better replacing the existing system with one which
included hot water provision off the boiler.

It would certainly be worthwhile replacing the existing hot water
cylinder with a solar one, able to take heat from the boiler and
solar panels as necessary. With electric heating as a backup this
would give the best range of options. A heat bank is another option,
especially useful if there is a suitable source of fuel around, like
wood.

In the winter they can't provide enough energy,

Probably not, though it depends on the water usage and size of the
storage vessel, as well as the amount of light. However, that is not
really the point. What energy they do provide is energy that is not
provided in other ways.

in the summer you usually end up unable to use
all the energy collected as you simply don't use enough hot water.

That rather depends on the water usage and size of the storage
vessel.

failures in the panels, which are obviously
subject to a lot of temperature cycling, is not uncommon.

Assuming you are talking about flat plate panels, in a year they
cycle less than radiators. With evacuated tubes a tube may fail, but
this does not affect the other tubes.


--
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