On Earth, Solar average full exposure received by 1 m² of panels exposed in sunlight is 1 kW, While in space the solar constant is from 1,367 kW/m². Despite its name the solar constant is not really constant as the solar activity is not itself constant.
Losses during the crossing of the light atmosphere is such that the energy that comes down to Earth is lowest and average order 1 kW/m² to true noon. It is this value that is commonly used for calculations. In the laboratory to determine the performance of a cell or a solar panel, an artificial solar energy source 1 kW/m² is also used. In the end, energy that arrives on the ground depends on the inclination of the Sun so the thickness of the atmosphere to cross and its cloud.
While this matter can be studied more in detail on the website of the Institute of solar energy (INES), the number of hours of equivalent full sun particularly concerns the producer of photovoltaic electricity.
Indeed, a solar panel is only exceptionally exactly facing the Sun as the earth rotates continuously and that the angle of the Sun relative to the Panel constantly evolves. During a day without cloud the electrical production of the Panel varies the position of the Sun also permanently and is never at its maximum except in the brief passage of the midday. The production at the end of day is therefore a sum of partial productions. Weather covered, so in the absence of Sun, the ambient brightness, While the Sun is hidden, allows a small electricity, and these small collective output eventually make of the kWh. End of the year from the total electrical production gets the number of equivalent hours sunlight of the year has nothing to do with the number of hours of sunshine and the weather meaning.
Hours of sunshine
The number of hours of sunlight seen by weather services or climatologists is not of the same nature. Or there is the Sun either there is not. Rouen is located on the line of 1750 hours of sunshine per year, While the number of hours of equivalent full sun is close to 1100 hours.
It should also take account of the ground albedo, i.e. of its power of reflection of light. When a facility is surrounded by snow for example, so a very reflective environment, the production of an installation increases because it retrieves a small part of the light reflected by the snow surrounding. But this variable is not easy to quantify and lies, in fact, included in the number of hours of equivalent full sun.
Prior to equip itself with photovoltaic panels
Prior to equip itself with photovoltaic panels, It is interesting to know what you can learn at the geographical location concerned. For this, the European Community has put online a free software that enables every citizen of the Union wherever it is located in the community to know annual electricity in kWh production which it will benefit.
After a few tries to get familiar with this software, We discover that in Liège can be obtained 840 kWh/KWP/year, Hamburg 870, Colmar 940, Rouen 950, Munich 950, Arcachon 1100, Chamonix 1110, La Rochelle 1140, Agen 1150, Montélimar 1280, Perpignan 1290, Eraklion Crete 1310, Madrid 1400, Cannes 1465, Seville 1470, Malta 1480, Faro Portugal 1550