Solar Calculations

How much energy?

There are a number of factors which determine how much energy you can collect from the sun.

  • The time of year
  • The orientation of the collector(s)
  • The angle of the collector(s)
  • The size of collector(s)
  • The type of collector(s)

The amount of energy is generally expressed in kWh/m2/day. This is the amount of solar energy that strikes a square metre of the earth's surface in a single day. NASA1 has produced data which shows how much energy reaches the ground. This information is averaged out over ten years, so it takes into account our climate and therefore includes cloud cover.

In London, the annual average is 2.61 kwh/m2/day

In Edinburgh, the annual average is 2.26 kwh/m2/day

But that varies greatly, so there is much more gain during the summer months. The graph below shows the amount of energy gain based one metre square area, south facing, at an angle of 35 degrees.Tilt 35

1Data courtesy of NASA - Surface meteorology and Solar Energy Data Set

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