Personally, as someone working in the industry for a number of years, im not convinced the payback period for solar justifies the initial spend.it will be hard to beat a condensing heat/hot water combi boiler or condensing boiler c/w high output pressurised cylinder combo.
Might be worth a mention -a brand new product nearly available - Domestic Micro Combined Heat & Power unit (CHP) from the Baxi group. it produces enough free electricity to power a house. Too early to comment, but may prove to be the next generation fad!