The honest starting point: most panels sold in the UK today are good, and the panel is rarely the thing that decides whether you are pleased with your system. The installer matters more.
That said, here is how to compare them.
The specifications worth reading
Wattage How much the panel produces under standard test conditions. Current domestic panels are commonly around 400 to 450W. Wattage tells you how many panels you need for a given system size.
Efficiency How much of the light hitting the panel becomes electricity. Currently around 20% to 24%. This only matters if roof space is your constraint. With plenty of roof, a less efficient panel at a better price per watt is usually the better buy.
Temperature coefficient How much output falls as the panel heats up. Lower is better. Matters less in Britain than in hot countries.
Degradation rate How much output is lost each year. See degradation.
Warranties Two separate things: a product warranty against the panel failing, and a performance warranty guaranteeing a minimum output after a given number of years. Check both. See warranties.
The comparison that actually matters
Price per watt installed, not price per panel.
A quote with fewer, higher-wattage panels may be better or worse value than one with more, lower-wattage panels. Divide the total price by the total watts and compare.
Then check whether the two quotes include the same things. A cheaper price per watt with scaffolding excluded is not cheaper.
Where panel choice does matter
If your roof is small Efficiency buys you capacity in a fixed area. Paying more per watt for a higher-efficiency panel can be the only way to get the system you want.
If you have shading Back-contact panels generally cope better with partial shading than conventional designs. Given how common shading is on British roofs, this is worth asking about. See panel technologies.
If appearance matters All-black panels cost a little more and produce marginally less. A legitimate choice; just know what you are paying for.
If the manufacturer’s UK presence is weak A warranty is only as good as the ability to claim on it. See below.
The warranty question nobody asks
A twenty-five year panel warranty assumes the manufacturer still exists in twenty-five years and still has a UK route to make a claim.
Solar manufacturing has seen a lot of companies disappear. Several manufacturers that were prominent enough to warrant their own review pages a decade ago have since collapsed, been delisted or left the market entirely.
So ask:
- Does the manufacturer have a UK office or a UK distributor?
- How would I claim, in practice, in year twelve?
- Does the installer’s workmanship warranty cover the labour of replacing a panel, or only the panel itself?
That last point catches people out. A free replacement panel still needs scaffolding and a day’s labour to fit.
Which brands you will be quoted
We do not recommend brands. We are not an installer and we do not sell equipment, so an endorsement from us would not mean anything.
What we can tell you is which manufacturers have a real UK presence and are likely to appear on your quotes. See which panel brands you will be quoted.
What to do
- Get quotes from up to 3 installers and see what they each propose
- Work out the price per watt for each
- Check the two warranties on each panel, and the manufacturer’s UK presence
- Ask why they chose that panel for your roof specifically
- If the answers are all reasonable, choose on the installer rather than the panel