PV System Facts
Solar electric systems capture the sun’s energy using photovoltaic (PV) cells. The cells then convert the sunlight (by means of the photo electric effect) into electricity. PV cells are panels you can attach to your roof or walls. Each cell is made from one or two layers of semiconducting material, usually silicon. When light shines on the cell it creates an electric field across the layers. The stronger the sunshine, the more electricity is produced. The strength of a PV cell is measured in watt peak (Wp) – that’s the amount of energy the cell generates in full sunlight.
The direct current (DC) from the PV cells is either connected and fed directly into the national grid or to DC batteries for storage before use. To avoid over charging of the batteries, the inward flow of direct current is controlled by means of a device called a charge controller. Before the current is used in homes and commercial environments, the direct current is converted to alternating current (AC) with a device called an inverter. Please note that some manufacturers produce combined inverter and charge controller devices all in one unit.
In some applications, it is not necessary to convert from direct to alternating current using an inverter. For example, LED solar street lights common in Africa and Asia do not need this device. The LED bulbs are highly energy efficient and operate using direct current. Similarly, DC fridges and freezers commonly used in the marine industry and in solar applications operate directly off direct current. Solar bore-hole pumps also operate without the use of an inverter.