The sun is a source of free energy which can be used to produce electricity as well as heat. The production of solar electricity relies on active solar technology. The most commonly encountered system for solar electricity production is solar photovoltaic. Other systems, such as concentrating solar thermal plants, whose primary output is heat, can also be used by producing steam to generate electricity using a turbine.
Solar Photovoltaic systems
When light energy is absorbed by a material known as a semiconductor, an electrical charge is created, this property of the material is known as the photoelectric effect. Silicon is the most common semiconductor used by PV cell manufacturers.
There are two main types of PV system : 1. Grid-connected PV system and 2. Stand-alone PV system. These are detailed below.
1. Grid-connected PV system
A grid-connected PV system is one which connects to the electricity grid. The electricity produced by the PV system is “exported” to the grid. The main advantage of using a grid-connected PV system is that the grid can be used as what is effectively an electricity storage system, where the electricity is “stored” and then “re-purchased”. A grid-tied sytem of this type is of interest when a payment is available for the electricity being exported to the grid, to offset the cost re-purchasing of electricity exported to the grid. Grid-connected PV systems do not need physical storage systems (batteries) and so the investment cost is reduced.
In a typical grid-connected PV system, the electricity is fed from the PV modules into an inverter. The inverter converts the electricity produced by the PV system (which is DC) into AC electricity for export to the electricity grid. The inverter is usually connected to either the main circuit breaker or fuse box, or else connected directly to the incoming cables from the grid. If the PV system is not supplying sufficient electricity to power the loads in the building (e.g., at night, when there is no solar energy available), then the electricity from the grid is used. When the electricity supplied by the PV system is greater than the loads in the building, then the electricity can be exported to the electricity grid. In cases where there is a payment available for exporting electricity, this can be an attractive option.
2. Stand-alone PV system
Stand-alone PV systems are used in areas that are not easily accessible or have no access to an electric grid. A stand-alone system is independent of the electricity grid, with the energy produced normally being stored in batteries. A typical stand-alone system would consist of a PV module or modules, batteries, and a charge controller. An inverter may also be included in the system to convert the direct current generated by the PV modules to the alternating current form required by normal appliances.
