
It all depends what you need/want them to do............I run my caravan in summer on one 20w pv panel (£70) an 85w battery (£38), and a cheap controller (£22).........or at the other end of the scale, if you want a big array and all the ancillaries to give you the typical average electricity consumption of a UK home - £15-20,000...............

You'd expect to spend around £4 per watt, or £4.50 per watt fitted.......
