How to buy solar panels How to buy solar photovoltaics

Solar PV costs and savings

Prices for PV systems will vary depending on the size and type of the system, as well as the structure of the building where the panels will be installed. 

An average PV system of 3kWp costs about £10,000, with solar tiles working out more expensive than conventional solar panels.

The more electricity the system can generate, the higher the savings – but the bigger the initial cost. A 2kWp system could cut up to £200 from your annual electricity bill, depending on your consumption and how you maximise use of the electricity produced by the panels. In addition to the savings on your bill, you'll get paid under the feed-in tariff schemes. Our guide to the feed-in tariff has more information on how you can earn cash by making your own energy.

Which? investigation into sales of solar panels

We've investigated how well firms assess properties during the initial sales visit. In 2011, we posed as a potential customer and invited 12 firms to a house rigged with secret cameras to see whether they were complying with the consumer code they signed up to. 

Identities have been disguised to protect our researchers.

Our footage shows that two companies breached code by offering a discount valid for 24 hours only and offering a 'first come, first served' discount in exchange for providing regular meter readings ('monitoring') – activities specifically banned in the code. One salesman failed to mention ongoing costs, despite prompting, and another admitted he wasn't a surveyor -  the consumer would have to make a decision based on a (likely inaccurate) quote made by a salesperson, before getting a professional evaluation from a surveyor.

Which? investigation in detail

Solar electricity has attracted much interest since the government introduced the feed-in tariff, which pays the consumer for every unit of electricity the solar system generates. The payments are guaranteed for 25 years and, in the right conditions, this means that you are very likely to recoup your initial outlay in less than 25 years and make a profit after that. To qualify for the generous scheme, you have to use products and installers certified under the Microgeneration Certification Scheme (MCS).

Posing as a consumer considering solar PV, we invited 12 certified companies to quote for solar PV. We wanted to see if each surveyor would assess the house properly and estimate payback time and profit from the feed-in tariff accurately. We also wanted to see the quality of advice given and if all the important details, such as the need to replace the inverter within the 25-year period, were mentioned.  

What we found

Of the 12 solar photovoltaic companies, we found many issues.

• Two used pressure-sell tactics, which are banned under the code.
• Five did not go inside the loft to check suitability for installation of solar PV.
• Five sent a salesperson not a surveyor but still gave a quote, estimate or price.
• Seven didn't take into account the fact that part of the roof was in shade, so putting solar panels there was questionable.
• Eight did not ask questions about energy usage or lifestyle.
• Eight underestimated the time time it would take for the system to pay itself. We found that the methodology companies have to use under building regulations to estimate payback and savings is flawed and can lead to inaccurate predictions. Whilst we are calling for this to be improved, it is worth taking these values with caution.
• 10 failed to mention that the inverter (which is an essential part of a PV system and turns the current generated into useable AC current) would need replacing earlier, even when prompted about maintenance requirements and ongoing costs.

Frequently asked solar PV questions

How do I know whether my home is suitable for solar PV panels?

Solar PV panels are worth considering if you have a mainly south-facing roof with little or no shade, and you aren't thinking of moving house anytime soon. Although a south-facing roof would lead to the best power output, a south-west or south-east-facing roof should be fine, but you'd get less power out of the system.

The Energy Saving Trust has a handy solar energy calculator that allows you to estimate the payback time and profit you can make from the feed-in tariff. How much electricity you will generate (and therefore how much profit) will depend on:

• the tilt angle of your roof and its orientation
• where you live: the south-west gets more sun than the north, which could impact the amount of electricity your system will generate, although not too significantly.

The Met Office website has useful solar radiation maps. The higher the radiation figure, the more electricity your PV system will produce.

The table below shows the percentage of the maximum output you will get from a solar PV system with different orientation (south, west, east) and tilt angles. Most roofs in the UK are angled at between 30 degrees and 45 degrees. Installation is not recommended on roofs facing north. 

You should also consider both the age and the robustness of your roof – solar PV panels are not light. Solar PV systems are most efficient if you use the electricity they produce during the day. Shade could be a big problem with solar panels so no panels should be installed where there is shade from trees, chimneys, walls or other obstructions.

What size of solar PV system is right for my home?

The right size for your home will mainly depend on the roof space available and how much electricity you use. We recommend that you do not buy too large a system as you cannot meet 100% of your demand with solar PV. Make sure the surveyor understands your electricity use so that the system is sized correctly. As a guide, an average 3kWp system would cost about £10,000.

Do I need planning permission?

Contact your council to see whether you need to apply for planning permission for your solar panel. You won’t need planning permission for most domestic solar panels, as long as they respect certain size criteria, but exceptions apply for listed buildings, buildings in conservation areas and world heritage sites. The EST has more information on planning permission.

Is the cost of solar PV coming down?

It is not very clear at the moment if the cost of solar modules are falling by as much as stated by industry. The intention of the feed-in tariff has been that as solar PV takes off, their cost will drop. And this is why the rate of the feed-in tariff is planned to decrease over time to compensate for the falling cost of solar systems. The Department of Energy and Climate Change has said that there has been a rapid fall in the global module costs of solar PV since the introduction of the FIT in April 2010. Greg Barker, the minister for Energy and Climate Change, also said that 'as solar PV technology has developed, its costs have reduced, and are now believed to be around 30% lower than originally projected'. 

However, a Which? investigation into solar PV in 2011 found costs averaging £6,000 per kilowatt with the lowest quote for £3,900/kW and the highest £9,900/kW. In this particular case, it does not seem to indicate a great drop in cost at that time. However, it is now believed that the installed price of a 3kWp system is about £10,000 with some installers saying it is £8,800.

In Germany, who had a very successful feed-in tariff, it was certainly true that cost went down. It is unclear as yet as if the UK will follow a similar trend as this will very much depend on the uptake of solar PV here. Higher manpower cost have been blamed for higher costs in the UK. 

Which? wants to see that the industry is passing on these falls in costs to consumers and there has been more signed recently of prices dropping. 

Are there any maintenance or ongoing costs to consider?

Solar PV systems are relatively simple and have no moving parts, so they don't need much maintenance. However, within 25 years you’ll need to replace the inverter, which costs about £1,000 (some installers say it costs less). Although when installed on an ideal roof slope the panels are self-cleaning, it is a good idea to have the solar panels cleaned occasionally. How often you clean them will depend on the slope of your roof and on how much dirt, such as bird droppings and leaves, they accumulate. 

What’s the best way of finding a reputable installation company?

Use the MCS website to ensure that your installer is MCS-certified, otherwise you can't take part in the feed-in tariff scheme. To find installers recommended by other Which? members, use Which? Local. Request a site visit with a technical survey, not a sales visit, and get at least three quotes. Ask for recommendations and addresses of installations in your local area that you could go and see.

What if the firm gives me a ‘hard sell’?

Companies that offer large on-the spot discounts or use other pressure-selling techniques deprive you of the chance to compare quotes and take time to think about their offer. You can report such firms to the REAL Assurance Scheme by calling 020 7981 0850, and to Which? on 01992 822800.

How can I ensure the installation process goes well?

Make sure you don't end up with panels overhanging the roof. Where panels are fitted just above the existing roof, it is good practice that at least 10cm should be left between the last panel and the roof edge to allow for access and to minimise the risk of wind blowing the panels off the roof. Use our checklist below to ensure you get a thorough survey, and ask your installer before they draw up the plans how much space they're leaving between the panel and the roof edge.

Solar PV buyers' checklist

Which? has produced a downloadable solar PV installation checklist which highlights the things you need to consider before having solar PV installed. 

The checklist includes tips and advice on what you should do, and the questions to ask, before, during and after a visit from a solar PV installer.

More on this...

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• Cut the cost: Our guide to ‘free’ solar panel schemes