I have never been convinced about Solar Thermal.
Claims of up to 70% of your domestic hot water produced!
Ok lets say 50%
Cost of heating hot water is 5% of your heating cost,
My heating cost is around £1000 per annum,
5% of £1000 = £50, 50% of £50 =£25, there you go, that's how much you save.
If a basic system costs £2500 installed, then ROI is 100 years.....
You can play around with these figures a little, but think about it, how much hot water do you really use in your house, washing machine "cold fill", dishwasher "cold fill", so just shower or bath really, hmmmm