Solar electricity: introduction

“I’d put my money on the sun and solar energy. What a source of power! I hope we don’t have to wait until oil and coal run out before we tackle that.” – Thomas Edison, 1931

What is solar electricity?

Solar electricity is the generation of electricity from the power of the sun, via photovoltaic (PV) cells. It is different from solar water heating, where water passes through panels to be heated directly, and no electricity is generated.

sun-roof

Solar PV is not just for the tropics; even with our clouds, an average of over 1000kWh/m² of solar radiation falls on the UK, which is about 60% of the solar radiation found at the equator.

Photovoltaic cells are made from silicon; when particles of sunlight (photons) fall on the cells, they dislodge the outer electrons of the silicon atoms, and push them along to the next atom; a chain of moving electrons is produced, and if a wire is attached to the panels, these electrons can be pushed down it to supply a useable electric current. This current is measured in amps, and to give some idea of the scale involved, one amp of current involves the movement of 6 million million million electrons per second.

inverter

Inverter with display for you to monitor the performance of your system.

The solar electricity produced this way (and also from batteries) flows in one direction only, and so is called direct current, whereas electricity from the UK national grid is alternating current, as the flow of electrons changes direction 50 times per second. Direct current can be stored in batteries to power 12 volt appliances. However, these are more expensive and less readily available than ordinary domestic 240 volt appliances, so 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 through a solar grid inverter with a meter to record how much electricity has been generated, whether it’s used in the home or exported . A grid-support system is one where batteries are also included to store surplus electricity that would have been exported into the grid. This can then be used to buffer loads taken from the grid later in the day – the loads are shared between the batteries and the grid to reduce grid consumption. Battery damage is prevented by a battery management system (BMS) to prevent both over-discharge and over-charging.

solar-tracking

A tracking system used with these panels allows them to follow the sun throughout the day.

What are the benefits of solar electricity?

As a renewable source of energy, the main environmental benefits of PV are based on the fact that it doesn’t cause the problems that other types of electricity generation do.

Burning fossil fuels in conventional power stations releases nitric oxides, nitrogen dioxide and sulphur dioxide, causing acid rain which damages forests, wildlife and human health; it also releases carbon monoxide, nitrous oxides, lead, particulates and hydrocarbons, which cause damage to plants, ecosystems, and human health – especially respiratory problems. Also, burning fossil fuels releases over 35 billion tonnes of CO2 into the atmosphere each year. CO2 is the most important of the ‘greenhouse gases’ responsible for global warming. Fossil fuel generation of electricity results in ten times the carbon emissions of solar PV per unit generated.

solar-thermal-electric

Installing both solar electric (left) and solar hot water (right) panels on a roof.

With PV solar electricity there are no emissions in use, no environmentally-damaging extraction and transport of coal and oil to feed power stations, and no radioactive waste, or the potential leaks and disasters associated with nuclear power stations. However, there are also environmental problems caused by the extraction of materials, manufacturing and waste associated with solar PV. These problems are less serious than the impact of fossil fuel extraction and burning, or the catastrophic nuclear disasters that seem to happen every 10-20 years. The application of technology will reduce the impact of PV in ways that are not possible for fossil fuels or nuclear.

PV modules generate between 9 and 34 times the amount of electricity in their lifetime as is used in their manufacture.

Roof installation video from our solar electricity online course.

Large-scale use of lead-acid batteries cause environmental problems in their manufacture and disposal, so connection to the grid would be better environmentally, unless in a remote location. Batteries do mean that you are autonomous though, and not subject to power cuts. The use of second hand traction batteries can extend the battery life for up to another 20 years if correctly maintained and used with correctly sized system and so can improve your knowledge and skill base considerably.

Solar PV can democratise and decentralise our energy supply. Some technologies can only be controlled by the state or the corporate sector – like coal- or oil-fired or nuclear power stations. PV generation (although not the manufacture of the panels, yet) can be controlled by individuals and communities, along with other sources of energy such as wind, hydro or wood. Ivan Illich called these kinds of technologies ‘convivial‘. We don’t think that control of something as important as our energy supply should be concentrated in the state or a few giant corporations.

solar-transport

PV systems aren’t just for houses – here are some examples of PV used on the move.

What can I do?

You may think that PV is fine for the tropics, but can they work in temperate countries? Well, the UK receives on average around 800kW of solar energy per square metre per year, which represents around a quarter of the annual requirement of a typical family. There’s enough south-facing roof space in the UK to provide all the country’s electricity needs using PV.

Solar can be put to a range of different uses – a single panel can be used with a battery to power lights or animal fencing in a remote location, or you can attempt to supply all or most of your electricity with a large system.

solar-tiles

Solar roof tiles on a roof in Nottingham.

The first thing to do is find out how much electricity (in kilowatt-hours, kWh) you use in a year (check your bills – a kWh is a unit of electricity on your bill), and think about ways to reduce your usage: switch lights off when you leave the room; don’t leave appliances on standby; use a laptop (c. 18 watts) instead of a desktop (c. 180 watts); use Savaplugs and low-energy lighting and appliances; don’t overfill kettles; think about solar hot water and a wood-burning stove, and whether you need so much electrical gear at all.

A typical UK family will use about 3000-4000kWh per year, but if you are single with no children and / or reduce your electricity consumption, that figure might be 2000kWh per year. Taking the annual amount of sunshine into consideration, this will require a 2.4kW system. But any size system will help save money and carbon emissions.

solar-flat-roof

2kW installation on a flat roof in London.

There are currently no financial incentives for new installations, but with huge reductions in the cost of parts over the last 10 years, it’s eminently sensible to fit your own system. As you extend your grid solar system there will be a point where you’re exporting more than half of your power. As rules continue to change about whether and how much you get paid for the power you export to the grid, this could be the time to fit a diverter that monitors any potential export and instead of letting this happen, diverts the power that would have been exported into a dedicated load, like your immersion heater, storage heater, or electric vehicle; see video:

Installing a grid diverter to prevent export to the grid.

One of our course tutors (in the days before feed-in tariffs) installed panels and an inverter costing £3000, metered the electricity they produced, and compared the results to putting £3000 in the bank and paying his electricity bills from that. After 18 years the money in the bank was gone, but his PV system had paid for itself 6 years previously, and was still generating electricity. So payback times can be very project-specific, and can often be cost-effective even without government incentives.

The cost can’t (easily) be reduced by self-build (like solar hot water), because the manufacturing process is too high-tech, but you could self-install if you have the know-how. Of course you could use PV in combination with a wind turbine to take advantage of all weather conditions.

solar-scaffold

Installation using a scaffold tower on a terraced house in London.

Other factors to consider with solar electricity are: is your roof south-facing? Is it big enough? (if not, panels could be located on a frame in the garden or on a flat roof) Is it shaded? (If just one of your panels is partially shaded, it can affect all the panels in your system). If you’re using batteries they need to be deep-cycle (able to be continuously drained and re-charged) with a charge controller to prevent overcharging.

See our further info section for everything you need to think about if you’re considering a solar PV installation, and if you want to have a go at installing a system yourself, have a look at our book, Wind & Solar Electricity, and/or our online course.


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The specialist(s) below will respond to queries on this topic. Please comment in the box at the bottom of the page.

Andy Reynolds is a carpenter / joiner and woodsman who has tutored courses and authored books with us. He has lived on a smallholding in Lincolnshire since the early 80s, renovated a house, built a holiday cottage and got off-grid. He records his adventures with educational videos on his YouTube channel.

 

David Thorpe of One Planet Life is the author of The Solar Energy Pocket Reference Book, The Earthscan Expert Guide to Solar Technology, The One Planet Life, and Guides to Photovoltaics and Low Carbon Vehicle Fuels, and is a former manager of the publications department at CAT. He runs consultancy and workshops on aspects of solar PV system design, commissioning and cost.


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