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How to calculate the annual solar energy output of a photovoltaic system

The global formula to estimate the electricity generated in output of a photovoltaic system is :

          E = A * r * H * PR

E = Energy (kWh)
A = Total solar panel Area (m˛)
r = solar panel yield (%) 
H = Annual average solar radiation on tilted panels (shadings not included)
PR = Performance ratio, coefficient for losses (range between 0.5 and 0.9, default value = 0.75)


 r is the yield of the solar panel given by the ratio : electrical power (in kWp) of one solar panel divided by the area of one panel
Example : the solar panel yield of a PV module of 250 Wp with an area of 1.6 m˛ is 15.6%
Be aware that this nominal ratio is given for standard test conditions (STC) : radiation=1000 W/m˛, cell temperature=25 °C, Wind speed=1 m/s, AM=1.5 The unit of the nominal power of the photovoltaic panel in these conditions is called "Watt-peak" (Wp or kWp=1000 Wp or MWp=1000000 Wp).

H You can find this global radiation value here : solar radiation data
You have to find the global annual irradiation incident on your PV panels with your specific inclination (slope, tilt) and orientation (azimut).

PR : PR (Performance Ratio) is a very important value to evaluate the quality of a photovoltaic installation because it gives the performance of the installation independently of the orientation, inclination of the panel. It includes all losses.

Example of losses details that gives the PR value (depend on the site, the technology, and sizing of the system) :
- Inverter losses (4% to 15 %)
- Température losses (5% to 18%)
- DC cables losses (1 to 3 %)
- AC cables losses (1 to 3 %)
- Shadings 0 % to 80% !!! (specific to each site)
- Losses weak radiation 3% to 7%
- Losses due to dust, snow... (2%)
- Other Losses (?)


Download :
Excel file to compute the annual solar electrical energy output of a photovoltaic system :
PV-power-calculation-basic.xls

Of course in order to simulate the energy production of a PV system with a better accuracy and to get monthly, hourly or instantaneous electric values, you have to use tools and softwares listed in www.photovoltaic-software.com.


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