Hi Graham,

I have looked extensively at solar water heating. I could bore you to
death with figures and calculations but my opinion is that at todays
prices you will never see payback on a commercially installed system.
I have looked at DIYing it and worked out a payback of 20 years (not
counting running and maintenance costs) and that is comparing it to oil
which is comparatively expensive.
As a commercialy installedl system (even with a grant) is much more
expensive than DIY then your payback time is even greater than that.
I should also mention I am in central Scotland so I guess you might
have more sun than me and perhaps a better payback...

As energy prices increase, the payback time gets better so my advice to
you is to revisit this in a few years.

You didn't mention your motivation for looking at this. If
environmental then it maybe makes sense but I don't know the energy
costs in the manufacture of these.

You also didn't mention how many people you are looking to heat water
for or if this is a retrofit or part of a new build. Payback is better
on a larger system and installation cheaper on a new build.

Alan.