• Solar panels (PV)

    Generate cheap, green electricity from sunlight. Solar panel electricity systems, also known as solar photovoltaics (PV), capture the sun’s energy using photovoltaic cells.

    The cells convert the sunlight into electricity, which can be used to run household appliances and lighting.

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  • Home integration

    Solar PV panels produce direct current (DC) which is converted to alternating current (AC) by an inverter so it can be used by appliances in the home.

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  • PV explained

    Photovoltaic (PV) cells are made from layers of semi-conducting material, usually silicon. When light shines on the cell it creates an electric field across the layers.

    The stronger the sunshine, the more electricity is produced. Groups of cells are mounted together in panels or modules that can be mounted on your roof.

The benefits of solar electricity

Solar panel electricity systems, also known as solar photovoltaics (PV), capture the sun’s energy using photovoltaic cells. These cells don’t need direct sunlight to work – they can still generate some electricity on a cloudy day. The cells convert the sunlight into electricity, which can be used to run household appliances and lighting.

  • Cut your electricity bills

    Sunlight is free, so once you’ve paid for the initial installation your electricity costs will be reduced.

  • Get paid for what you generate

    Through Feed-in-Tariffs, you get paid for the electricity you generate even if you use it.

  • Sell your electricity to the grid

    If your system is producing more electricity than you need, or when you can’t use it, you can sell the surplus back to the grid.

  • Cut your Carbon footprint

    Solar electricity is green, renewables energy and doesn’t release any harmful carbon dioxide] or other pollutants. A typical home solar PV system could save over a tonne of carbon dioxide per year – that’s more than 30 tonnes over its lifetime.

Costs, savings & earnings

  • 4kWp

    The average domestic solar PV system is 3.5 to 4kWp and costs around £7,000 (including VAT at 5%),

  • £5,500 - £9,500

    A typical cost including installation ranges from £5,500 to £9,500.

Costs

Costs have fallen significantly over the last year. They vary between installers and products, so we recommend getting quotes from at least three installers.

Other factors that affect PV installation costs are:

  • The more electricity the system can generate, the more it costs but the more it could save.
  • Larger systems are usually more cost-effective than smaller systems (up to 4kWp).
  • PV panels are all around the same price per kWp, but PV tiles cost much more than a typical system made up of panels.
  • Panels built into a roof are more expensive than those that sit on top.

Savings & income

A 4kWp system can generate around 3,700 kilowatt hours of electricity a year – roughly equivalent to a typical household’s electricity needs. It will save nearly two tonnes of carbon dioxide every year.

If your system is eligible for the Feed-In Tariff scheme it could generate savings and income of around £785 a year (based on a 4kWp solar PV system eligible for a generation tariff of 14.9p/kWh). You will get paid for both the electricity you generate and use, and what you don’t use and export to the grid. When applying for FITs you will need to show evidence of your property’s Energy Performance Certificate and this will affect what tariff you can get.

If you know your system size, you can get a tailored estimate for your system using our Solar Energy Calculator.

Please note that the Feed-in Tariff scheme is not available in Northern Ireland.

Green Deal finance & renewables

This technology is an eligible measure under the UK government’s Green Deal which is a financing mechanism that lets people pay for energy-efficiency improvements through savings on their energy bills.

Further information on Green Deal.

Maintenance

Solar PV needs little maintenance – you’ll just need to keep the panels relatively clean and make sure trees don’t begin to overshadow them. In the UK panels that are tilted at 15° or more have the additional benefit of being cleaned by rainfall to ensure optimal performance. Debris is more likely to accumulate if you have ground mounted panels.

If dust, debris, snow or bird droppings are a problem they should be removed with warm water (and perhaps some washing-up liquid or something similar – your installer can advise) and a brush or a high pressure hose (or telescopic cleaning pole) if the panels are difficult to reach. Always be careful if you are working above the ground or near the top of a ladder.

Alternatively, there are a number of specialist window cleaning companies who will clean solar PV panels for you at a cost (of around £30 based on our research in March 2012) depending on the size of your array and location. Many of these companies use a water fed pole system which does away with the need for a ladder.

Once fitted, your installer should leave written details of any maintenance checks that you should carry out from time to time to ensure everything is working properly. This should include details of the main inverter fault signals and key trouble-shooting guidance. Ideally your installer should demonstrate this to you at the point of handover. Keeping a close eye on your system and the amount of electricity it’s generating (alongside the weather conditions) will familiarise you with what to expect and alert you to when something might be wrong.

The panels should last 25 years or more, but the inverter is likely to need replacing some time during this period, at a current cost of around £1,000. Consult with your installer for exact maintenance requirements before you commit to installing a solar PV system.

How do solar panels work?

PV cells are made from layers of semi-conducting material, usually silicon. When light shines on the cell it creates an electric field across the layers. The stronger the sunshine, the more electricity is produced. Groups of cells are mounted together in panels or modules that can be mounted on your roof.

The power of a PV cell is measured in kilowatts peak (kWp). That’s the rate at which it generates energy at peak performance in full direct sunlight during the summer. PV cells come in a variety of shapes and sizes. Most PV systems are made up of panels that fit on top of an existing roof, but you can also fit solar tiles.

Solar inverters

Solar inverters, also called grid-tied inverters, convert the direct current (DC) electricity produced by your solar PV panels to alternating current (AC) electricity that can be used in your home and exported back to the grid.

Solar invertors also:

  • ensure compliance with regulations about feeding electricity into the grid, for example by immediately disconnecting if there is a power cut
  • maximise electricity production by constantly varying its resistance (load).

Solar inverters are very efficient, usually 93–96% depending on the make and model – never 100% because they use some of the input DC power to run, generally around 10-25W. Their efficiency can be improved by an electronic technique known as Maximum Power Point Tracking (MPPT).

The point of maximum power output of a solar PV cell is dictated by a combination of current or voltage. Where it is will vary constantly according to light levels, shading, temperature and the characteristics of the solar PV panel. A MPPT system continually searches for this point to extract the maximum power available from the cell. Multiple MPPT systems can maximise yield even if part of the array is shaded. Find out more about MPPT at the YouGen blog.

Inverter sizing

There are many different makes and sizes of inverters on the market. The key characteristics are:

  • Maximum amount of DC electricity (expressed as max DC power in Watts)  the maximum number of watts the inverter has been designed to convert
  • Maximum input voltage – this is the maximum voltage the inverter can manage before its electronics are damaged
  • Initial input voltage (sometime called start-up voltage) – the minimum number of volts the solar PV panels need to produce for the inverter to start working
  • Maximum power point (mpp) voltage rang – the voltage range at which the inverter is working most efficiently.

Many solar PV systems in the UK have an inverter with a power rating that is smaller than the array. For a 3kWp array, this equates to an inverter size of between 2.4kW and 3.3kW (often expressed in watts: 2400W to 3300W). This is because the panels are not likely to be generating at their rated efficiency for long periods of time, and to ensure that the initial input voltage and maximum power point voltage range are reached as often as possible.

Inverter manufacturers often provide guidance to installers on solar inverter sizing, typically through providing system sizing software. As each inverter is manufactured to cope with a pre-determined maximum input voltage, the final choice of inverter will also be influenced by what is available on the market, particularly if your installer prefers to work with a limited number of makes.

Types of solar inverter

Grid-tied Micro-Inverters

Grid-tied inverters can either be linked to a number of solar PV panels (referred to as string or central inverters) or be linked to one or two solar PV panels – these are called micro-inverters.

Micro-inverters get around the need for all panels to have the same characteristics and be operating under the same conditions by having an inverter installed to the back of each panel. This means when the performance of a panel is affected, for example by natural shading or from obstructions from leaves or debris, it will not affect the overall performance of the system, as would a string invertor – particularly one without MPPT.

Micro-inverters also include MPPT which micro-inverter manufacturers claim works more effectively than it does in string inverters where something as small as an antenna could reduce the performance of the whole system.

String inverters

Standard string inverter warranties are usually between 5 and 10 years; as this is less than the warranties on solar PV panels it would seem sensible to budget for at least one string inverter replacement during the lifetime of your solar PV system. If you have micro-inverters installed instead this may not be necessary.

A string inverter works most efficiently when all the solar PV panels have the same characteristics and are operating under the same conditions. If it is known from the start that some of the panels are not likely to be operating under the same conditions – for example, they are not all orientated in the same direction or some of them will be shaded for a part of the day – this would be a good reason to install two or more inverters as part of the system. An alternative would be to install an inverter that has been designed to cope with more than one string of solar PV panels operating in different conditions.

Benefits of micro-inverters

Benefits claimed for micro-inverters include:

  • Performance of the solar PV array is optimised and reports claim the system could have improved energy harvest of between 5% and 20% over the lifetime of the system
  • Improved energy harvest should result in increased income
  • The potential for enhanced monitoring as the performance of each individual panel can be monitored separately.
  • Greater reliability – if one micro-inverter fails, it will not affect the whole system
  • Installation of micro-inverters is cheaper and easier as wiring is simpler and no high voltage DC equipment is required, which also makes them safer to install.
  • It may be easier to increase system size by adding new panels.
  • Increased lifetime – the single most common cause of failure in a solar PV system is the string invertor, which normally requires replacement at least once over the lifetime of the array. The latest micro-inverters have fewer life-limited components, and manufacturers claim a lifetime of 25 years to match the panels
  • The cost per watt is more for micro-inverters but is offset by a simpler installation and increased energy harvested.

Drawbacks of micro-inverters

The claimed drawbacks of micro-inverters include:

  • Still a relatively new technology and there are only a small number of manufacturers.
  • More expensive than string inverters
  • Potentially costly to replace as roof access required
  • Only useful in situations where shading is a significant issue
  • Lack of expertise should things go wrong – relatively small market thus reliance on small pool of installers and manufacturers
  • Some DNOs are still not sure about them (see the test requirements above).

We recommend that you check with your DNO before having micro-inverters installed.

Purchasing & Installation

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