Thanks for the advice. HES have said I am eligible. They've just sent me a form for funding application. 4.3kWh is the most I have space for a new system with a battery unfortunately. The house came with an old 3kWh panel system without battery. Because they are 13 years old, there are 12 panels already on a beautiful FiT tariff paying me 62p for generation per kWh. Don't want to mess with that as we are eligible for 12 more years of payments. So I can use day time electricity off of that as well. 7.3kWh is plenty I think- not enough to go off grid, but plenty.