Sizing a grid-connect solar system

People living in houses use a lot of power. About 4000kWh per year is fairly standard for the average family house - or a little over 10kWh per day.

Of course, there is no reason you can't put a solar array of any size you like on a house. If you produce more electricity than you use, you simply export the surplus to the national grid, and get paid by the electricity companies. If you have a small array and produce less than you use, you just pay for the additional power.

Let's look at the size of array you would need to be carbon neutral however - to produce as much power as you use averaged over the course of the year.

A solar array of 1kW rated power typically produces between 750kWh and 1000kWh per year in the UK, depending on location. So in order to produce enough power to make a typical family home carbon neutral you need around 4-5kW of solar panels.

You can do the sums more accurately yourself - simply look at your electricity bill to see how much power you use over the course of a year (it will be given in units - one unit equals one kWh). Then look at the map to see how much power you can expect a solar array at your location to generate.

At about £4 per Watt, a 5 kW array gives no change from £20,000 - even before you add in additional costs for inverters, a mounting system, and installation. Making your household as energy efficient as possible will drastically reduce the amount of energy you need to produce to go carbon neutral. People living off-grid in boats and caravans often use about 400kWh or even less per year - but it's certainly possible to live a low-energy lifestyle even in a conventional house!