Solar radiation

• To obtain maximum energy from the irradiance, the PV module must always be facing the sun.
• In northern hemisphere the modules will be positioned facing due south.
• Theoretically the module should be tilted equal to the latitude of the site location.
• However in practice, in the latitude from 0 to 15 deg, the module will generally be tilted at 10 degree to the horizontal.
• Solar irradiation reaching the top of the atmosphere is called solar constant Gc=1367 W/m^2
• Solar irradiation at sea level on earth is 1000 W/m^2
• Daily irradiation is commonly referred as peak sun hour (PSH). The number of PSH for the day is the number of hours for which energy at the rate of 1000 W/m^2 would give an equivalent amount of energy to the total energy for that day. 
• Unit for PSH is (kWh/m^2)/(kW/m^2) or hour. 
• The energy in SI unit is Joule. To convert M/J^2 to peak sun hour, use the following formula:

                                                        

• Air mass (AM) is the path length the sun's array has to travel through the atmosphere to reach earth surface.