If I own a 3kW electric line, do I have to buy 3kWp photovoltaic installation or can I choose a different power?

First of all it is necessary to know your consumptions per year. If you need 3000kW/h (that’s the average consumption of an average family), you need to do this little calculation:

3000kW/h : 1.300 (average annual production of a photovoltaic installation) = 2.30 kWp.

In this case, the ideal installation is one of 3kWp.