People are often surprised to learn just how much solar energy is available in the UK and Eire. The map shows the light energy (in kilowatt hours or kWh) falling upon a square metre of horizontal ground each year. For comparison, according to the Global Solar Atlas, the annual Global Horizontal Irradiation in Rome is 1,596kWh/m2 or around 60% more.
A tilted surface can collect more energy than a horizontal surface, depending upon which direction it is facing. A surface tilted towards the South at 35 degrees will intercept around 11% more light energy than a horizontal surface. A home of 80 sq. m, built with modern levels of insulation will have an annual space heating demand of around 2,000 kWh, and a domestic hot water demand of 2,000 kWh, for a total heating demand of 4,000 kWh. Average electricity demand is estimated to be around 4,500 kWh/year.
A single roof pitch of the same house will intercept 54,000 kWh of light energy each year – more than six times the energy used.
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