Re: In terms of watts per dollar...
Unlike some parts of the world, UK generated electricity does not roll the meter backwards. Much of what is generated is not used because people are at work and thus they cant take advantage of it. I have solar panels and a Nissan Leaf but find that only now can I generate power late enough into the evening to charge some of the car while still making electricity.
As for not being able to generate enough heat via thermal panels for 24/7 usage then no you cant, but with enough panels and enough hot water storage then you could cut it down quite a bit. Bear in mind the ideal solution is a PV-T panel but due to the way the UK market works (pushing people to MCS and their "approved" installers) means that we will not see PV-T any time soon. 16 panels turned into 16 PV-T panels could mean that you end up with too much hot water during peak times.
Biting the hand that feeds IT
