PV Gap

Jeffrey Said:

How are solar panels rated? When a panel is listed as 11kW, how long does it take to produce that amount?

We Answered:

When we test the power of a solar panel, we put it under a 'fake Sun' that gives 1,000W m^-2 of light of wavelengths that make it through the atmosphere. This is roughly what you get at the equator when it's fully sunny.

Then we put wires on either side of the cell, put voltages across it and measure the currents out. We find out where the max power point (power = current x voltage) is and then we make sure any resistive load fits to that point.


So the 11 kW you're stated is the _power_ it generates at any one time. To convert that into _energy_ you have to multiply it by time. So at full power for an hour it would generate 11 kWh (a kWh is a 'unit' of electricity), or in one second it would generate 11 kJ or 11,000 Joules.

One way of thinking of power and energy is like driving a car; power is how fast energy is going past, it's your 'speed'. Energy is how much has gone past, it's your 'distance'.



The amount of power you'll generate in a year depends on where you are - you need to find an average insolation map for your area which tells you the sunlight you get.

As a rule of thumb, you multiply your kW figure by 750 to see how many units of electricity you'll generate in northern England in a year, 900 in south England, 1100 in S Germany and 2200 in the Californian desert.

So in a year, an 11kW system should generate about 8,200kWh in the UK, 12,000kWh in Germany or 22,000kWh in the desert.