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Solar PV systems: is my roof suitable for solar panels?

We look at what you need to know before installing solar panels, with the help of our accredited Which? Trusted traders.
Man wearing a harness installing solar panels on a roof with a drill

Installing a solar system to create clean, carbon-free energy can free you from dependence on major electricity suppliers. So how does it work? In its simplest terms, solar panels gather sunlight, and the system converts that into electricity you can use in your home.

But how do you know if you can have solar panels fitted on your property? Which? Trusted Traders has endorsed solar panel installers in your area, who will come round for a consultation. Before you speak to an installer, there are a few points to bear in mind.

Ownership of the roof

You need to have the freehold of the property to install panels on the roof. If you are in a leasehold property, you will need the permission of the freeholder to make any alterations to the outside.

Planning permission

You do not usually need planning permission to install solar panels, unless you have a flat roof and they will be raised up on a frame. However, all installations need to comply with building regulations (see below).

Weight of the panels

Solar panels are heavy, and will put stress on your roof joists. Your installer needs to check whether your roof is strong enough to bear their weight. If the existing structure is not strong enough, then it will need to be reinforced before panels are installed.

Building regulations

All alternations to your property need to comply with building regulations. This is usually handled through a competent-person scheme – installers that are a member of an electrical trade body such as NICEIC or ELECSA will submit the alteration on your behalf.

So assuming you can install solar panels (and it will be possible on most roofs), a more complex question is should you invest in a solar PV system? This depends upon whether your roof layout will allow a solar PV system to generate sufficient power to make the installation worthwhile. See our article on the installation calculation for more details, or read on for more about the different factors that installers take into account around efficiency.

Efficiency factors for solar panels

You can check the amount of sunlight available, known as the insolation figure, with an online calculator. But as a rough guide, the following areas will affect the efficiency of your solar panel system:

Roof direction

Ideally you want solar panels on a roof that faces as close to due south as possible, to make the most of the available sunshine. But don’t despair if your property faces east/west. Tom Smith, Director at Go Green Systems Ltd, told us that an east/west split can work almost as well on occasion.

Angle or pitch of the roof

The ideal angle for solar panels is 30 degrees, but installers can deal with anything between 15 and 50 degrees. If you have a flat roof, then installers can mount the panels on a frame to get them at the best angle.

Size of the roof

You’ll need a space equivalent to a car-parking space for the panels themselves. The larger the space available, the more panels can be installed, which can generate more power.

You also need space inside the building for the inverter, which converts the current. The inverter must be surrounded by cold air, so it requires a space of approximately 1 metre wide by 1.5 metres high. If you have a large attic space, or a garage, that works well.

Most three-bed semis will have a viable roof area, big enough to install a 3 or 4kW system. A small terraced house might not have enough roof space to make an installation worthwhile, but your installer will be able to advise you – fewer occupants will require less energy, so it could still work.

Geographical location

There is more sun in the south of England, but it’s perfectly possible to have solar installations throughout the UK. Solar panels are more efficient than ever before, traders report installing solar systems in northern Scotland. Longer daylight hours in the summer go some way to compensate for the sunshine levels in Scotland. Areas in northern England can be more challenging because of the lower air quality.

Shading – obstructions to the sunlight

Anything that causes an obstruction to sunlight reaching the panels on the roof – such as trees, aerials or other buildings - reduces the amount of power they will generate. This is known as shading. Most properties do have some sort of shading, and your installer should factor this into the calculation of the amount of power your panels will generate.

When designing your installation, your installer will create a ‘sun-path’ diagram. This must identify objects within 10 metres of your panels that cause shading. These nearby causes of shading can seriously reduce the amount of power generated if you don’t compensate for them with specific equipment, such as micro-inverters or Solar Edge technology, which get the best performance from each pane. Your installer will be able to advise you what works best

Finding a contractor

Paul Lukehurst recommends looking out for a well-established contractors or companies that are a member of the Solar Trade Association or Which? Trusted Traders. Check that they have a good track record, and check references before signing a contract. We’d recommend getting at least three quotes.

Solar installers are covered by the Renewable Energy Consumer Code, which covers how customers must be treated. The Code specifies that:

  • sales people must not give false or misleading information about their business, products, services or facilities being offered
  • company representatives must not make any statement that is likely to mislead the consumer in any way
  • Code members and their representatives must not use any selling techniques designed to pressurise customers into making an immediate decision.  

If you feel anyone is breaking the code, you can report these firms to the Renewable Energy Consumer Code by calling 020 7981 0850, and to Which? on 01992 822800.

Sales visit and technical survey

Once you’ve found contractors to work with, the next stage is a home visit, where in addition to a full explanation of the products available to you, the sales person should:

  • check your roof measurements (to ensure systems will fit)
  • check the roof structure (for strength)
  • complete a shading analysis.

Before entering a contract, installers should give you a full explanation of how they will fit the mounting system to your property. A good installation company can bring along their own installation images to aid explanation, rather than industry standard or manufacturers’ images.

Check the Which? reviews of solar panel brands to find out the Best Buys.

Which? has more advice on buying solar panels, including an investigation into selling techniques.

Solar panel installation tips

Solar panels are full of photovoltaic (PV) cells. Light particles (photons) knock electrons free from atoms within these cells, generating a flow of direct current (DC) energy. The panels are connected to a piece of equipment called an inverter, which converts the DC electricity to an AC current that can be used by you or sold into the grid.

Installation of the panels is a precise process, as installers need to simultaneously work to Microgeneration Certification Scheme (MCS) requirements, Eurocodes, building regulations and manufacturer’s installation instructions. The MCS regulates the industry on behalf of Ofgem, and your solar PV system will only qualify for the feed-in tariff it is fitted to their standards.

Panel manufacturers stipulate zones where the mounting rails and clips should be positioned on the panel to avoid the panel flexing in the wind. If installers ignore this, then warranties are void. It is worth asking your installer to show you they are complying with the manufacturer’s instructions before making the final payment.

Cables must go through a flashing detail into the roof, not simply be pushed under tiles or fixed over the verge. They should also be secured away from other surfaces to prevent abrasion.

Which? has created this video guide to show you the installation process.

As well as the panels, installers will supply and fit the inverter, which converts the electricity for domestic use, plus a fuse board, isolator and total-generation meter next to your existing meter, to ensure the safety of the installation and measure how much electricity your system generates.

It’s worth fitting a performance-monitoring system at the same time as the main installation, as it’s much more expensive to add it on later.

Once the installation is compete, ask the installer to help you fill out the Feed-in Tariff application form, as not all installers will offer.

Maintaining your PV system

Solar PV systems are normally completely hassle-free when installed correctly. The self-cleaning coating and rainfall keep them clean. But you should keep an eye on their performance to check they’re still working. Elements of the system are consumer electronics, and can be unreliable.

The best way to ensure peak performance is with a monitoring system. Your installer will have a range for you to choose from. Paul Lukehurst from Poweri Systems Ltd said: ‘Solar Edge tech can be put on each panel to optimise performance. If there’s some dirt or shading, it makes sure it is still working as well as possible, and if there are any problems it will let you know. It costs about £30 per panel at the installation point.’

But if you’re looking at installing a monitoring system retrospectively, Paul would recommend a simpler OWL system, which costs about £75 overall, in order to avoid expensive installation costs.

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