A good quote for solar panel installation shows the system size in kWp and an annual output estimate. It also gives a total price and the installer’s MCS certification number. Therefore, compare quotes on cost per kW and on that output figure, not on the headline price alone.
Start with the output estimate
Every MCS-certified installer must give you an output estimate before you sign a contract. The rules sit in MCS standard MIS 3002. Take the installed kWp and multiply by a kWh per kWp value from the MCS table. Then multiply by a shade factor between 0 and 1.
The table value depends on your postcode zone, roof pitch and compass direction. Meanwhile, the shade factor is 1.00 when the horizon is clear and nothing blocks the sun. Trees, chimneys and neighbouring buildings pull it down.
The standard also requires a warning, because nobody can predict output with certainty. MCS limits the figure to guidance for the first year of generation and says you should not treat it as a guarantee. If your quote has no such wording, ask why.
Sense-check it with independent data
You can test the figure in minutes, since the data is free. Our kWh per kWp guide explains what the number means and how to read it. Then compare the installer’s value with an independent source.
For instance, the European Commission’s PVGIS tool gives a useful benchmark. In our PVGIS runs, a south-facing system at a 35 degree tilt produces about 1,042 kWh per kWp a year in Cardiff. The same setup gives about 1,014 kWh in Swansea and 1,023 kWh in Bristol.
Those cities sit close together, so their results land within about 3% of each other. You can read more about solar output in Cardiff, solar output in Swansea and solar output in Bristol on their city pages. Across all 24 cities we model, the spread runs from 853 to 1,156 kWh per kWp.
However, if a quote claims far more than the local PVGIS figure, ask the installer to show their working. MCS tables and PVGIS use different methods, so a small gap is normal. A large one deserves a question.
Compare the price per kW
Therefore, divide each quote’s total by its system size in kW. That one step makes quotes of different sizes comparable. A 5 kWp system will cost more than a 3 kWp one, but the cost per kW should be similar.
For a benchmark, use government data. The energy department reports a median installed cost of £1,595 per kW for systems up to 4 kW in 2025/26. For systems of 4 to 10 kW the median is £1,546 per kW. Those figures cover equipment, installation and connection, but not batteries.
At that median, a 4 kWp system comes to about £6,400. Energy Saving Trust gives a separate estimate of around £7,600 for a typical 4.5 kWp system. A quote well above both deserves a closer look. A quote far below them deserves one too, because it may leave something out.
Our payback guide shows how to turn a price and an output figure into your own payback estimate. Use it once you have two or three comparable quotes.
Check the installer, not only the price
Meanwhile, solar panels and batteries qualify for 0% VAT until 31 March 2027 when a contractor installs them, according to HMRC guidance. After that date the 5% rate returns under current rules. Check whether each quote states the VAT treatment.
Next, confirm the installer’s certification. MCS runs a Find an Installer search where you can look up a company by name or certification number. Each entry shows the certification body and the technologies the firm can fit. You usually need an MCS installation to claim payments under the Smart Export Guarantee.
Look at consumer protection as well, because a deposit is the main risk. The Renewable Energy Consumer Code says members should not ask for more than 25% of the final price as a deposit. Members must also avoid high-pressure sales tactics. Ask each firm which code it follows and check the claim yourself.
Read the small print
Compare the same items across all your quotes, for example the panel make and model. Look for the inverter, the mounting system and the warranty periods. Check whether scaffolding, the grid application and the MCS certificate sit inside the price.
Ask about the grid connection too. Under rule G98, a system up to 16A per phase can connect first. That is about 3.68 kW on a single-phase supply. The installer then tells the network operator within 28 days.
Larger systems fall under G99, which needs approval before installation. Your installer should say which route applies and handle the paperwork.
Planning is the other item to raise. Most roof systems in England count as permitted development, although listed buildings and some conservation areas differ. Our planning permission guide covers the rules, and a good installer will flag any issue on your property.
Finally, ask how the quote treats winter. Output drops sharply from November to February, and a flat annual figure hides that. Our guide to solar panel output in winter shows the monthly pattern.
If you want a heat pump later
Some households plan to add a heat pump after the solar. If that applies to you, tell each installer now, because it changes how much electricity you will use. Our upcoming guide on solar panels and heat pumps covers how the two work together.
Next steps
Before you collect quotes, run your own numbers in our solar yield calculator. It gives you a transparent estimate to hold the installers’ figures against. Then, when you are ready, request quotes from MCS-certified installers. Solar Yield passes your enquiry on and does not install anything itself.