Green shorts - Solar photovoltaics
Solar photovoltaics
Solar photovoltaics (PVs) convert energy from daylight into electricity using a semiconductor material such as silicon. Cells are made from silicon; when particles of
sunlight (photons) fall on the cells, they dislodge the outer electrons of their atoms. The generated current flows in one direction only. This ‘direct’ current can be
stored in batteries to power 12 volt appliances. However, batteries and an inverter can be used to convert the 12 volt direct current to 240 volt alternating current.
Alternatively, the panels can be connected to the grid. A grid-support system is one which charges batteries, and re-directs any surplus into the grid if the batteries are
full.
What is available?
There are a number of PV technologies, including polycrystalline, monocrystalline and thin-film. Solar PV cells can be arranged in panels on a building’s roof or walls, and
can often directly feed electricity into the building. With the latest PV technology, cells can also be integrated into the roof tiles themselves.
Groups of solar PV cells can be added together to provide increasing levels of power. This can range from small, kilowatt-sized solar panels for use in domestic households,
to larger arrays, which function as separate solar power plants feeding power directly into the electricity grid.
Solar energy is only produced during the day and also varies in output due to cloud cover. In the case of small-scale solar PV systems, batteries or other forms of
electricity storage can be used to store the electricity for periods when the output is low but the demand is high.
Is solar PV suitable for your home?
To tell if solar electricity is right for you, there are a few key questions to consider:
- Do you have a sunny place to put it? You'll need a roof or wall that faces within 90 degrees of south, and isn't overshadowed by trees or buildings. If the surface is
in shadow for parts of the day, your system will generate less energy.
- Is your roof strong enough? Solar panels are not light and the roof must be strong enough to take their weight, especially if the panel is placed on top of existing
tiles.
- Do you need planning permission? In England and Scotland, you don't need planning permission for most home solar electricity systems, as long as they're below a certain
size - but you should check with your local planning officer if your home is a listed building, or is in a conservation area.
What are the benefits?
With photovoltaics there are no emissions; however, large-scale use of lead-acid batteries would cause environmental problems in their manufacture and disposal, so
connection to the grid would be preferred unless in a remote location.
Can they work in temperate countries? Yes they can, and there is calculated to be enough south-facing roof space in the UK to provide all the country’s electricity needs
using PV.
A single panel can be used with a battery to power lights or animal fencing in a remote location, however, all or most of an average homes electricity can be catered for
with a large system.
There are government grants in the UK to help with professionally-installed, grid-connected systems; however, with current electricity prices at around 10p per kWh this will
give a payback time of 40+ years, though the system will save 1-2 tonnes of carbon per year.
Background information
Research paper (pdf) from Pennsylvania State University
Concludes that PVs take around 5 years to generate the same amount of electricity as is used in their manufacture.
Net energy analysis
for sustainable energy production from silicon based solar cells