CALCULATIONS OF SOLAR ENERGY OUTPUT
How much energy can a photovoltaic module produce?
Electrical energy is generally measured in kilowatt-hours (kWh). Thus, if a module produces 100 Watts for 1 hours, it has produced 100 Watt-hours or 0.1 kWh. The amount of energy produced on a given day will depend on location, shading, and module orientation (direction and tilt).
In a good area for solar power, a properly oriented module which produces 100 Watts at noon on a clear day will produce an average of about 0.5 kWh/day in January and 0.8 kWh/day in May and June. (Fluctuations result from the amount of variation in direct sunlight on a typical day).
In a relatively "poor" area for solar power, the same module will still produce about 0.25 kWh/day in January and 0.6 kWh/day in July.
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
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 m² is 15.6%
Be aware that this nominal ratio is given for standard test conditions : radiation=1000 W/m², 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 from our consultant : solar radiation data - You have to find the global annual irradiation incident on your PV panels with your specific inclination (slope, tilt) and orientation (azimuth).
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 %)
- Temperature 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 (?)
The amount of sun your solar cells are exposed to (and hence how much energy they will generate) depends upon:
• The orientation and tilt of your installation (which will be optimised by your installer)
• Whether there are shadows cast over your cells (due to trees, buildings etc)
• The number of daylight hours (governed by where you live)
• The intensity of the sunlight (governed by where you live)
• The number of hours of full sun vs cloudy days (governed by where you live)