What is Solar PV?
The production of electric power through solar cells is known as solar photovoltaics or solar PV. Solar PV panels, or modules, consist of many photovoltaic cells that are made up of thin layers of semi-conducting material, normally crystalline silicon, which produce electricity when exposed to light. Solar PV differs from solar thermal in that PV enables property owners to generate electricity while solar thermal provides hot water.
How Does Solar PV Work?
During manufacture, the silicon material is chemically treated to alter its electrical properties. This means that when light hits the cell, an electric field is created across the layers and produces a current flow. The greater the intensity of light, the more electricity is produced.
Solar PV panels are linked to each other in series and then connected to the building’s main consumer unit or fuse board via a device called an inverter. This device converts the panel output from direct current (DC) to the alternating current (AC) form compatible with mains electricity. The inverter constantly monitors the grid voltage and frequency to ensure that its output matches. As well as allowing household devices to use this solar power just like normal mains electricity, this also allows excess electricity to be exported onto the grid at times when the instantaneous demand from the building is less than the power produced by the panels. This ensures that all the electricity produced is used and achieves a maximum reduction in carbon dioxide emissions. The main components of a solar PV installation are shown in the following diagram.
How Important is the Location?
The location of the solar PV is very important because of its sensitivity to the intensity of light. Solar PV modules need to receive the maximum possible amount of light and should therefore be installed on a south-facing roof. Due south is preferable as efficiency drops off in correlation to the angle of deviation from a due south orientation.
The angle of tilt of the modules is also important with the ideal range in the UK being between 35° and 40°, depending on latitude. Please refer to the table below.
It’s not advisable to install solar PV modules where trees or surrounding buildings will cast shadows on the array as any shadow affects the performance of the entire array and not just the modules in shadow.
How Much Electricity Can Solar PV Produce?
The output of photovoltaic panels is generally specified in kilowatts (kW) or kilowatts peak (kWp). The panel area required to produce an output of 1 kWp varies with panel technology, but a typical 1 kWp monocrystalline panel would have an area of around 7m2 and produce an annual electricity output of 830 kWh. This output would result in a reduction in carbon dioxide emissions of 471 kg.
How Does this Relate to the Feed-in Tariff?
Based on a 3kWp array with optimal due south orientation etc. this can be expected to generate approximately 2,490kWh/yr or kilowatt hours per year. Assuming an electricity price of 12p/kWh and that most of the electricity generated is consumed on site, this would mean a saving of up to £299 on the electricity bill. On top of this saving, the feed-in tariff provides an income of 41.3p/kWh for every kWh produced where the array is installed on an existing property, whether it is consumed or exported to the national grid. This means an income of £1,078 per year. If electricity prices rise, the savings increase and the payback time on the original investment shortens.
PV systems registered with the scheme from 1st April 2010 to 31st March 2012 will benefit as follows:
Any system up to 4kW on a new build property = 37.8p per kWh pay-back
Any system up to 4kW on an existing property = 43.3p per kWh pay-back
Any system 4-10kW new build or retrofitted = 37.8p per kWh pay-back
Any system 10-100kW new build or retrofitted = 32.9p per kWh pay-back
PV panels produce no noise, have no moving parts and can be made to blend unobtrusively into the surrounding structure. With an average lifespan of thirty years, no direct impact on the environment, minimal maintenance requirements and an income for all the electricity generated through feed-in tariffs guaranteed for 25 years, solar PV looks set to become a much more common sight on homes as well as commercial and public buildings over the next few years.