Photovoltaic electricity is possible if

• the roof orientation is between south-east and south-west the best being straight South
• the tilt angle is between 0° (flat) and 90° (façade), with the best being 30° (like a roof)
• there is little shadow during the day i.e. no tall trees or high buildings to shade the array from direct sunlight for any appreciable part of the day

Effect of latitude

The strength of the solar radiation is dependent upon the distance it travels in the earth’s atmosphere; at midday, when the sun is at its highest, the distance is shortest so the sun is most intense and as the sun sets the distance increases and the intensity decreases. The output of the solar cells decreases too so there is a diurnal variation of electricity production. Latitude determines the number of annual sunshine hours and the annual irradiation which in France varies form 1 500 kWh/m2 in Nice and 900 kWh/m2 in Lille.

Effect of climate

Whilst on a sunny day solar radiation can be directly received, on a cloudy day less radiation is received because it is scattered by water droplets in the clouds. The difference between a very cloudy day and a very sunny day can be almost a factor of 10.

However, half of the electricity produced during a full year in France comes from direct sun rays, the other half from the “diffused light” which is present even on a cloudy day.

Environmental impact

The major impact is associated with the preparation of the solar cells themselves and this can be minimised through recycling of waste materials. The other impact is visual in that the photovoltaic modules, like solar water modules, will be visible on roofs of buildings, but, when properly integrated, it can also strongly improve the aesthetics of the building.

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