Solar Electricity Technology

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.

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 suppying 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 is an attractive option. Obviously it depends on the level of payment being offered.

For further information on grid-connected PV installations, go to Solar Electricity and the grid.

Stand alone PV systems are not connected to the grid. Stand alone systems are set up so that you use the electricity produced by the PV system directly. In order to take full advantage of the electricity produced, it needs to be stored. For this reason, a stand alone system will commonly include battery storage. For further considerations on battery storage, including storage for electricity storage from a wind turbine please see: Should I choose to add batteries instead of getting gridconnected?

Stand-alone PV systems are very useful where there is no electrical grid connection (e.g. in the developing world) and also for applications such as street lighting, traffic signs etc. For further information on the applications of stand-alone solar PV systems, and PV systems in general, go to Solar Electricity Applications.

Concentrating solar thermal systems for electricity generation

Concentrating solar thermal systems for electricity are used to convert solar heat into electricity (as opposed than photovoltaics which directly converts light energy into electricity). A system of concentrators focus a large amount of solar heat energy onto a small area. As a result, this small area is heated to a very high temperature and the heat is used to drive a steam turbine (or similar heat engine) which is connected to an electrical generator.

Concentrating solar thermal systems for electricity generation are encountered at large scales, i.e. sizeable installations for power generation occupying large spaces.
This type of technology is suitable in very hot climates and examples are most common in Meditteranean Europe, Spain and in Northern Africa.

For more information, go to Solar R & D Information and Resources.