Buying advice for solar panels

Well-chosen solar panel systems can provide a reliable source of renewable electricity for decades, helping to cut your carbon footprint. Buying an inappropriate system could leave you out of pocket. 

Use our expert advice to help you decide what's most suitable for your home and features to look out for. Plus read owners' tips on what to consider before you buy.

We also show you how to spot a dodgy company and how to choose a decent solar panel installer.

Read more: what owners think of solar panel brands.

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Types of solar panels

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

Options include:

• monocrystalline
• polycrystalline
• hybrid
• thin film.

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

Bifacial solar panels (where they can generate electricity from both sides of the panel) also exist. 

Find out what's right for you in our guide to How solar PV systems work.

How many solar panels do I need?

How many solar panels you need (or the size of your system) will depend on how much electricity you need it to generate and how much space you have on your roof.

It's important not to buy too large a system, because you can't meet 100% of your electricity needs with solar PV (though installing a solar battery can help).

Solar panel system sizes are measured in kilowatt peaks (kWp). This is the maximum output of your system.

The most common system size, from our survey of more than 1,000 solar panel owners, was between 3.6-4kWp.*

Which? members can log-in to see the most common system size for bungalows, terrace, semi-detached and detached homes. Or join Which? to access all of our content.

Make sure the surveyor takes into account your household's electricity use, when you're at home and out, so you can get the right-sized system for your needs and budget.

 Find out how much solar panels cost.

Choosing a solar panel inverter

The inverter converts the direct current produced by the panels into usable alternating current. It’s key to the solar PV system. 

String inverters are most common and cheapest. They connect solar panels in series. If one of your panels failed or started to be shadowed 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.

Inverters are often fitted in the loft so they're not too far from your solar panels and energy loss in cables in minimised. 

But inverters can be affected by the heat, so your garage might be a better bet if your loft gets very hot in summer.

What do you want from your solar panels?

This might feel like something you'll find out once they're installed, but it's worth considering upfront. Solar panel owners we've spoken to have had some quite different motivations:

• wanting to charge their electric vehicle from solar panel electricity
• a long-term investment and futureproofing 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 money-making opportunity. Some owners who bought recently told us that they don't expect to benefit financially from their system, though a future owner of their house might!

Find out whether solar panels are a good investment.

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 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.

Compare their quotes and what they include. Make sure you get a breakdown of how any claimed energy savings are calculated too.

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

It's a good idea to use an MCS-accredited installation company that installs MCS-certified products. This is sometimes a pre-requisite for government support schemes. You can check on the Microgeneration Certification (MCS) website.

Also check 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 panels sales tactics

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

It's also very 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 or 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, and to Which? on 029 2267 0000.

* Online survey in June 2021 of 1,116 Which? Connect members with solar panels.