Ask The Builder: Questions To Ask Before Installing Solar Panels?

Ask The Builder: Questions To Ask Before Installing Solar Panels

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Here Are The Basics Of How Solar Panels Work

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Buying Advice For Solar Panels

Well-chosen solar panel systems 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 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 what 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.

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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 install (or the size of your system) will depend on how much electricity you need to generate and how much space you have on your roof.

It's essential to install the right size for your household. Too large a system may risk wasting energy that you can't use, although installing a solar battery and/or exporting energy to the grid can help.

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

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

3.6-4kWp systems are the most common in our survey

Nearly half of those who live in a bungalow with solar panels in our survey have this size, four in 10 in detached homes, and a quarter of respondents in semi-detached and terraced houses.

The next most popular solar panel system size for terraces and semis was 2.1-2.5kWp.

The size you need will depend on your household's electricity use, how often your home is occupied, and at what times of the day. Discuss all of these things with your surveyor so you can get the right-sized system for your needs and budget.

 Find out how much solar panels cost to install.

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. It’s key to the solar PV system. 

String inverters are the most common and cheapest. 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, that 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 options.

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

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

What do you want from your solar panels?

Once they're installed, your attitudes towards the main benefits of your solar panels might change, 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 so that it's guaranteed 'green energy

a long-term investment that's 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 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 their lower bills.

Find out whether solar panels are a good investment.

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

load 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 installed

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 itemized details of what you'll get for your money. Make sure you get a breakdown of how any claimed energy savings are calculated too.

Use our Which? The 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 if 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 of these solar panel 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.

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