We sell crystalline photovoltaic (PV) solar modules. Several modules wired together make a panel, or array, although you frequently hear “solar panel” when people actually mean solar module.
PV solar modules produce electricity from light, not from heat. We do not use thermal solar modules, which are used to heat water or air.
Our solar modules work through the photovoltaic effect, which causes a flow of electrons within the silica sealed inside the module. When these electrons are excited by particles of light striking the silica, they begin to travel through electrical circuits. These circuits are attached to the face of the silica cells, in order to reach an opposite charge and neutralize themselves. This flow of electrons from positive to negative is, by definition, DC electricity.
In Africa, most PV systems use this DC electricity to charge batteries or to pump water. Most solar modules in Europe, Japan and North America are used to feed electricity back to the utility grid or network. This is called “grid-tie” solar and usually only occurs where there is a strong government subsidy to send power back to the grid.
Solar is universal and will work virtually anywhere there is light; however, some locations are better than others. Irradiance, which is a measure of the sun’s light available at the surface of the earth, peaks at about 1000 watts per square meter. Because the typical crystalline solar cell has an efficiency rate of around 14-16%, we can expect to generate about 140-160W per square meter of solar cells placed in full sun. Insolation is a measure of the available energy from the sun and is expressed in terms of “full sun hours” (i.e. 4 full sun hours = 4 hours of sunlight at an irradiance level of 1000 watts per square meter). Obviously, different parts of the world receive more sunlight than others, so they will have more “full sun hours” per day. Use our Solar Insolation Map to get a general idea of the average full sun hours per day for your location.
The current and power output of photovoltaic modules are approximately proportional to sunlight intensity. At a given intensity, a module’s output current and operating voltage is determined by the characteristics of the load. If that load is a battery, the battery’s internal resistance will dictate the module’s operating voltage. A module which is rated at 17 volts will put out less than its rated power when used in a battery system. This is because the working voltage will be between 12 and 15 volts. As wattage (power) is the product of volts times amps, the module output will be reduced. For example: a 50 watt module working at 13.0 volts will produce 39.0 watts (13.0 volts x 3.0 amps = 39.0 watts). This is important to remember when sizing a PV system. Maximum Power Point Trackers (MPPT) are a good solution to help recover some of that lost power – learn more about solar controllers.
Modules should be installed in completely un-shaded areas – remember that the cells are wired in series and even partial shading can cut your module’s power in half. Pole mounted modules are popular in Africa, but if your array exceeds four modules you will probably want to use a ground or roof mount. You can buy a ready-made mounting structure at African Energy or have it made locally. Remember that north of the equator your modules should tilt at 15 degrees south, and in the south, face north. Tilt your modules at no less than 15 degrees, and up to your actual latitude. The 15- degree minimum tilt ensures that water and dust run off the module. You can also adjust to latitude minus 15 degrees in the summer and latitude plus 15 degrees in the winter, but never below 15 degrees.