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Solar Irradiance figures

Select Country:

Select Town/City:
Solar Panel direction:

City of London
Average Solar Insolation figures

Measured in kWh/m2/day onto a horizontal surface:

Jan Feb Mar Apr May Jun
Jul Aug Sep Oct Nov Dec

Click on the images below to see irradiance figures for different angles:

Vertical Surface

Optimal Year Round
  38° angle
Adjusted throughout the Year
Best Winter Performance
  23° angle
Best Summer Performance
  53° angle
Flat Surface

Solar Energy Calculator

Using the calculator

  1. Use the application on the right to retrieve the solar irradiance figures that best match your location and the orientation of your panel.
    Tip: If your panel is horizontally mounted, then just select any direction in the 3rd drop down box "Solar Panel direction".
  2. Change the values in the boxes below for:
    Size of Panel
    Daily Solar Insolation (sun hours)
    Size of your Batter (Amp hous).

Change the values in the boxes

Size of Panel/Array Watts
Daily Solar Insolation (sun hours)

Output = 24 Ah / day (amp hours per day)

This will charge a Ah battery in
4.6 days (from empty to full)

Interpreting the figures

Think of Daily Solar Insolation as the average number of "sun hours" per day for each month.

To estimate the number Amp hours (Ah) of electricity a panel can produce in a given month the calculator (above) uses the following equation

Panel Rating (Watts)xSun Hours
  = Average Daily Output (Ah)


Let's say a value of 4 is given for July, it is equivalent to your solar panel receiving full, direct sunlight, for 4 hours each day.

Thus If you have a 100W solar panel, then in July it will produce 4 x 100 = 400Wh (Watt hours) of electricity per day.

To convert this to Ah (Amp hours) you can divide it by 17V (the voltage the panel produces at maximum power output).

So a 100W panel will make
  =   23.5Ah
approximately 24Ah of electricity per day, on average, with 4 sun hours of irradiance.

Figures provided by: Solar Electricity Handbook