There are a number of different rates of  VAT that apply:

 

0% for a new build domestic project. (where no property existed before).

 

5% when doing a domestic repair which includes replacing the panel.

 

5% for fitting a new system on an existing house when working for the house owner directly.

 

20% when working for a builder or developer.

 

20% when doing a domestic repair which does not include replacing the panel.