How Solar Panels Produce Electricity
When light reaches a solar panel, the light energy is absorbed by the semiconductor material in the panel. This releases electrons, which can then flow in an electric current.
Converting Solar Power to Electricity: Inverters
Solar panels produce direct current (DC) electricity. The electricity used by household lights and appliances is alternating current (AC). Inverters convert DC electricity to AC.
- Central inverter: Some solar energy systems connect the panels of a solar array in a series and send the combined output of the panels to a central inverter. A disadvantage of using a central inverter is that a panel with reduced output (caused by shading from vegetation or snow cover, for example) lowers the output of all the panels.
- Micro-inverters: In a system that uses micro-inverters, each panel in a solar array has its own small inverter. An advantage of a micro-inverter system is that reduced output from one panel doesn't affect the output of the other panels. This results in more overall power from the array, compared to a system using a central inverter.
Variables That Affect Solar Energy Output
Four main variables affect the solar energy output from a photovoltaic panel. These are time of year, time of day, available sunlight, and panel temperature.
- Time of Year (Month): This determines the sun's angle to the horizon. The more direct the sun's angle on the solar panel, the higher the panel's energy output will be. The best angle is in summer, when the sun is higher in the sky.
- Time of Day (Hour): This determines the sun's position as it rises and sets. As with time of year, the more direct the angle of the sun is on the solar panel, the higher the panel's energy output will be. The best angle is when the sun is directly overhead at noon.
- Available Sunlight: This determines how much sunlight reaches the solar panel, based on cloud cover, fog, rain, snow, etc.
- Solar Panel Temperature: This affects the efficiency of the solar panel. The higher the temperature, the lower the energy output.
The formula to calculate actual solar power output is as follows: Potential Solar Power Output (based on Date and Time) x Available Sunlight x Solar Panel Temperature = Actual Solar Power Output.
It works this way: Potential solar power output is the power generated when the panel is getting the full amount of potential sunlight available at a particular time of year and time of day. This is multiplied by a percentage of available sunlight, and is then multiplied by an adjustment for solar panel temperature. The result equals the actual solar power output.
Click image above to open an interactive Flash animation that lets you set the four main variables in real time, to see how they affect energy output. The formula for actual solar power output is also displayed.
Note: Many people believe that Minnesota is not a good place for generating solar energy, because of the cold climate, and because of the angle of the sun due to how far north we are. This is a misconception. Cold is good for photovoltaic activity, and the angle of the sun here is more than adequate for good generation of photovoltaic electricity.