PV - Photovoltaics
Energy from the sun
The sun provides an abundant, free source of clean energy in the form of natural light and warmth. It is possible to capture some of this free energy directly to convert sunlight into electricity using solar photovoltaic (PV) panels.
How does PV work?
Solar PV systems convert light into electrical power using a thin layer of semi-conducting material, usually silicon, encased between a sheet of glass and a polymer resin. They range in size from a few square centimetres, for example on calculators and watches to systems of hundreds of square metres made from interconnected modules that form an array. When exposed to daylight electrons in the semi-conducting material become energised. These electrons are then able to flow through the material generating a direct current (DC). The DC is carried through wiring to an inverter which converts the current to 240V alternating current (AC) so it can be connected to your home’s main electricity supply.
Benefits of PV
PV can be easily incorporated into most houses. The most common option is to use standard solar PV modules in a frame fixed to an existing pitched roof. In this arrangement the panels will slightly protrude from the roof tiles but are still in keeping with the shape of the house. As solar PV is made up of modules, typically around 1m x 1.5m, an array (the full solar PV installation) can be designed to accommodate virtually any size and shape of roof.
What does kWp and kWh mean?
Solar electricity systems are given a rating in kilowatts peak (kWp). This is essentially the rate at which it generates energy at peak performance for example at noon on a sunny day. The kWp of a domestic system will vary depending on the roof area available to accommodate the panels.
The total amount of electricity the system actually generates in a year is measured in kilowatt hours (kWh). This will depend on the system’s orientation, shading and how sunny your site is, as well as the size of the system (in kWp) installed.
A typical domestic system is between 1.5 and 4kWp. Each kWp should generate around 900 to 1000kWh per year if unshaded and facing due south with a tilt of around 30-50°. A solar roof array would typically generate 1200 to 3400kWh per year depending on size. By contrast an average home uses 4400kWh of electricity per year on lights and appliances. However, an energy efficient home using A rated appliances and lighting could conceivably use half this value.
To get the most from a PV system try to use electricity during the daytime, when the system will be generating the most.