Buying advice for solar panels

Well-chosen solar panels can provide a reliable source of renewable electricity for decades, helping to slash your electricity bills and cut your carbon footprint. 

But buying an inappropriate solar PV system for your home could leave you out of pocket. 

Use our expert advice to help you decide what's most suitable for your home and the features to look out for before you buy.

Read more: what owners think of their solar panel brands.

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Types of solar panels

The most common type of solar panel system used for domestic homes is PV – or photovoltaic – panels. They collect energy from the sun in photovoltaic cells, which is then passed through an inverter to generate electricity.

Each photovoltaic cell is made up of a series of layers of conductive material. Silicon is the most common.

Before you invite any solar panel firms to give you a quote, consider what type of solar PV you want. 

Monocrystalline:

• The most popular, most efficient and most expensive option.
• Very space efficient, so they need the smallest amount of roof space.
• Made from a very pure form of silicon.
• High power output.
• Very long lasting – current life expectancy is around 50 years.
• Perform better than other types in low levels of sunlight.
• Dark black in colour.

Polycrystalline:

• A less efficient but cheaper option.
• Made of multiple layers of silicon crystals, which makes them quicker and cheaper to produce.
• Last the same length of time as monocrystalline panels – currently estimated to be around 50 years.
• Don’t cope very well in extreme heat.
• Blue-ish in colour.

Thin film:

• Usually the cheapest option.
• Less efficient than mono or polycrystalline panels.
• Lightweight and flexible, so they can be used in alternative ways – such as on caravans and boats.
• Maintain their efficiency in weak or low light, and in high heat.
• Long lasting.  

Hybrid (PV-T):

• Combines photovoltaic cells with solar thermal panels, so that the same panel can generate heat and electricity.
• The technology is still very new, so needs specialist installation with higher costs.
• The thermal portion of a PV-T panel doesn’t reach as high temperatures as an independent solar thermal panel, so you’ll still need a primary heating system.

Solar panels are typically fitted on top of your existing roof, but you can also choose solar tiles and slates, which blend in better. However, these are pricey and may only be practical if you're replacing your roof at the same time.

Bifacial solar panels also exist, which can generate electricity from both sides of the panel.

Find out whether solar panels are worth it for you.

How many solar panels do I need?

The number of solar panels you install (or the size of your system) will depend on how much electricity you need to generate and the amount of space available on your roof.

It's important to install the right size for your household. Too large a system may be a waste of money if you generate energy that you can’t use, although installing a solar battery and/or exporting energy to the grid can help make the most of any excess.

Solar panel system sizes are normally expressed in kilowatt peaks (kWp), which is the maximum output of the system.

Household solar panel systems are typically up to 4kWp.

Is your home suitable for solar panels?

You’ll need to consider the following to know whether solar panels will work for your home:

• Location: Southern areas of the UK receive around 20% more solar energy than those furthest north.
• Roof slope: A 30-40 degree slope is ideal. The average UK home is 30 degrees – use this in a calculation if you’re not sure.
• Shading: A roof with 20% shading or less is best. Shading can heavily affect energy output – a roof that’s more than 80% shaded can reduce output by as much as 50%.
• Roof direction: A south-facing roof is optimal. An east or west-facing roof will produce 15% less energy, and a north-facing roof around 30% less.
• System size: The average size is around 4kWp, which requires at least 20 square metres of roof space. Adjust this down, if your roof is smaller; or up, if you want to cover the energy usage of a larger household.

To get a good idea of the potential savings of panels based on your home, you can enter this information into the Energy Saving Trust’s solar energy calculator.

 Find out more about solar panel installation and how much solar panels cost.

Do solar panels work without direct sunlight?

Yes. Solar panels can still produce electricity in winter, or on days when it's cloudy.

That's because they use particles of light – or photons – to generate electricity. These are found in both direct and indirect sunlight.

But solar panels work best when the sun is shining on them, and they can't produce electricity at night.

Choosing a solar panel inverter

To actually use the electricity generated by your solar panels, you need an inverter. This converts the direct current produced by the panels into usable alternating current.

String inverters are the most common and cheapest option. They connect solar panels in series. If one of your panels fails or starts to be overshadowed by a growing tree, it could impact your whole system.

Micro-inverters 'separate' the panels so, if one panel fails, the whole system won't be affected. It should also be easier to spot problems through the power-monitoring system. These are more expensive.

Inverters are often fitted in the loft so that they're not too far from your solar panels and energy loss in cables is minimised. But they can be affected by the heat, so if your loft tends to get very hot in summer, a garage might be a better bet, if you have one.

What do you want from your solar panels?

Once they're installed, you may discover unforeseen benefits in your solar panels, but it's worth considering what you are expecting upfront. 

Solar panel owners we've spoken to have had some quite different motivations:

• Wanting to charge their electric vehicle from solar panel electricity so that it's guaranteed 'green energy'
• A long-term investment that's future-proofing against electricity price rises
• Trying to reduce their carbon footprint
• Wanting to be less reliant on grid electricity (and its price changes).

In the past, solar panels were sometimes seen as a moneymaking opportunity. Some of the owners who bought solar panels recently told us that while they don't expect to benefit financially from their system and weren't driven by that as a motivation, a future owner of their house might well profit from lower bills.

Read more: are solar panels worth it?

What to know before you buy: solar panel owners' tips

Download our free checklist for everything you should consider before you buy solar panels.

It has tips and advice on what you should do, plus the questions to ask before, during and after a visit from a solar PV installer.

Which? members can log in to see useful tips from current solar panel owners. If you're not a member, join Which? to unlock these.

Finding a good solar panel installer

We recommend that you get at least three quotes from different installers. This will help give you an idea of the going rate for the type of system you want in your area. 

Also check our solar panel prices for an initial guide.

As with any building work, compare their quotes and make sure they include itemised details of what you'll get for your money. Make sure you get a breakdown of how any claimed energy savings are calculated too. Query any projections that seem too good to be true.

Use our Which? Trusted Traders search tool below to find reliable solar panel installers near you.

Be sure to use an MCS-accredited installation company that installs MCS-certified products. This is often a pre-requisite for government support schemes, and is required if you want to benefit from Smart Export Guarantee (SEG) payments. You can check an installer is verified on the Microgeneration Certification (MCS) website.

Also, find out whether your installer is a member of the Renewable Energy Consumer Code (RECC). This means that they have agreed to abide by high consumer protection standards. RECC also runs a dispute-resolution process if you have a complaint against an installer registered with it.

Beware these solar panel sales tactics

At Which? we often hear concerns from people approached by solar panel companies out of the blue, who put them under pressure to buy quickly. 

It's also common to get cold calls about add-ons to your existing solar panel system, which you may not need. 

Many solar panel firms are signed up to a consumer code that bans pressure-selling tactics. But you may still come across unscrupulous tactics. Here's what to watch out for:

• Time-limited or 'one-off' discounts
• Receiving a quote from a salesperson, rather than a specialist surveyor
• Being put under pressure to make an immediate decision
• No information about ongoing costs, such as maintenance
• A very low price (which might not include all necessary parts and services)
• Very optimistic savings figures or extremely short payback-time estimates 

A reputable firm will give you the time to consider your options and their quote, and they will be willing to help provide the information you need to help make your decision. 

You can report pressure selling to the Renewable Energy Consumer Code by calling 020 7981 0850.