This is because we’d expect most to do well in a snapshot test. Besides, models change all the time, and ones we’d tested might not be available any more, or be superseded by the time you’re reading this. So instead of performing short-term tests that are likely to be inconclusive and out of date, we sent independent expert solar auditors into factories. They checked every stage of the manufacturing process – from how individual cells are checked and connected, to how well panels are scrutinised for defects before they leave the factories. Our gallery, below, shows you each stage. Solar panel production
1. Connecting solar cells Individual solar cells are sorted by power. They’re soldered together into strings to form a solar panel (or module). Usually a panel is made up of 60 cells. They’re checked for tiny cracks or other defects using electromagnetism testing. Damaged cells should be rejected.
2. Lamination The cells are placed between layers that protect them. The layers are fed into a laminating machine, like an oven, and melted into one. This needs to done carefully so air bubbles don’t form and damage the panel’s electrical insulation. If humidity gets in, lifespan could be reduced.
3. Finishing A frame is then put round the panel to protect it. Tightness is key. A junction box is attached to connect the panel to the inverter using cables. The connection between the solar panel and the inverter must be waterproof and not too tight, so as not to apply too much pressure on the panel and damage the cells.
4. Quality control A flash test, with a sunlight simulator, helps determine the panel’s capacity. The panels are then sorted by how much power they can produce, and priced accordingly. Further quality controls may be carried out, for example, to find breakages or so-called hotspots.
Solar PV: what owners really think We asked 1,265 solar PV owners about their solar panels in June 2017. Owners rated how satisfied they are with their panels, and whether they’d recommend them to others. We used those results to calculate customer scores for seven popular brands. Canadian Solar has the highest customer score Canadian Solar has the highest customer score (85%), followed by Panasonic and LG (both 83%). Solar PV brands rated by owners Brand Customer score Canadian Solar 85% Panasonic 83% LG 83% Sanyo 81% Sharp 80% Solarworld 77% Suntech 75%
Table notes: Based on an online survey of 1,265 Which? members with solar PV panels in June 2017. Customer scores are only calculated for brands which received 30 or more responses. Sample sizes: Canadian Solar (34), Panasonic (39), LG (35), Sanyo (97), Sharp (107), Solarworld (46), Suntech (31). Buying solar panels If you install a solar photovoltaic system, you produce your own electricity – and get paid for it. Solar panels should last for at least 25 years, so getting the right kit and installation is key to long-term free electricity. Get a good brand of panels by checking the results of our expert factory audit, as you’ll know they’ve gone through rigorous checks. You should also read our expert tips on how to make the most of your solar panels.