Photo Voltaic Systems


How solar PV cells work

Photovoltaic (PV) cells convert sunlight into electricity. In most PV cells, light energy (photons) excite the electrons in the atoms of a semi-conducting material (for example silicon). The energised electrons then generate an electrical voltage.

The amount of electricity a solar PV system generates depends on the intensity of the sunlight it’s exposed to. Solar PV also generates electricity on cloudy days, but less so than with direct sunlight. Solar PV panels generate no electricity at night.

Solar PV cells are usually quite small, so you need to join lots together to create a PV panel. These panels can then be grouped together into solar PV arrays.

Key solar PV system components

PV systems usually include:

  • PV panels, cables, and mounting or fixing hardware
  • an inverter (that converts direct current from the PV panels into alternating current) and controller
  • special electricity meters to record the electricity generated, exported to the grid
  • and, for off-grid situations, batteries, back-up generators, and other specialist components.

Energy output of solar PV systems

Each solar PV panel is rated on its peak electrical output. For example, a panel with a 75 watts (W) peak rating (75 Wp) will have an output of 75 W under test conditions. A well placed panel usually generates 2.5 to 5 times its rated power output. So a 1 kWp panel can produce 2.5 kWh (kilowatt hours) to 5 kWh per day, or between 880 kWh and 1750 kWh per year.

Panels are usually available from 5 Wp to 300 Wp. A typical domestic solar PV system would be 1,500 Wp to 3,000 Wp, so you’ll have to buy a number of panels and connect them in an array to get the energy output that you need.

Where to place PV panels

Solar PV panels are suitable in both rural and urban conditions. Panels are usually installed on roofs but you can also place them on facades, conservatory roofs, sun shades, garages or specially built stands on the ground.

Make sure your site:

  • faces north
  • is free from shade and exposed to good sun all year
  • has enough space - a typical 1 kW panel needs around 8m2.