Solar heating and solar power

Maybe, and almost certainly not respectively. Solar-photovoltaic is not a realistic option, unless you live where it'd take over 5-20000 quid to install mains electricity. It's marginal in places with lots of sun, if you'r willing to neglect interest.

no

and no.

It _might_ be cost effective to install _and_operate_for_at_least_a_decade_ solar heating. You can put a system up and it will "save you money", but you're still paying for it. The break even really depends on if you can keep it operating reliably for a good long period, without needing to replace the collectors.

depends on the design. Good designs can pay back at 25% pa, overpriced commerical kit selling for thousands can never pay back. The thing to go for is flat panel space heating. It costs less than water heating, and harvests more heat easily.

no chance.

NT