Which? tested 12 solar panel brands last month and ranked SunPower first for efficiency. The consumer group’s findings, released on 14 October, give UK homeowners a rare independent benchmark in a market flooded with technical specs and sales pitches.
As reported by Which?, SunPower’s Maxeon 6 panels convert 22.8% of sunlight into electricity, a figure that matters more in Manchester‘s drizzle than Arizona’s desert. The catch: they cost roughly £1,500 more than budget brands for a 4kW system.
What the Which? tests actually measure
The lab tested 12 panels for output at low light (200 W/m²) and high temperature (75°C), plus degradation over 25 years. SunPower lost just 0.25% efficiency per year, half the industry average. LG’s NeON R panels came second, with a 25-year product warranty that covers labour, not just parts. JA Solar’s JAM72D30 scored best for value: £0.48 per watt versus SunPower’s £0.72, according to Which? data.
For a typical 3-bed semi using 3,500 kWh/year, a 4kW system (10–12 panels) costs £5,000–£8,000 installed. The Energy Saving Trust estimates annual savings of £270–£410 on bills, plus £120–£180 from the Smart Export Guarantee (SEG) if you sell surplus. Payback: 10–14 years, depending on orientation and shading.
Grants, VAT and EPC reality
The 0% VAT on solar panels, introduced in April 2022 and extended to March 2027, cuts £500 from a typical install. But the bigger prize is an improved Energy Performance Certificate (EPC). Solar panels can lift a D-rated home to C, adding 2–3 points to the score. That matters from 2025, when landlords must hit EPC C for new tenancies under the government’s proposed regulations.
Ofgem’s SEG rates vary by supplier: Octopus pays 15p/kWh, EDF 5p/kWh. A 4kW system exporting 50% of generation earns roughly £150–£250 a year at Octopus rates. But the scheme is voluntary, suppliers can set their own tariffs or refuse to offer one. The government has not yet mandated minimum SEG rates, despite calls from Which? and Citizens Advice.
What this misses, the installer trap
Which? tests panels, not installers. Yet the Microgeneration Certification Scheme (MCS) database shows 1,200 registered solar installers in the UK. A bad install can halve output: shading from a chimney, wrong inverter sizing, or panels facing 45° east instead of south. The MCS guarantees workmanship, but only if you check the installer’s MCS number on the certification body’s website before signing.
Axiom’s advice: get three quotes from MCS-registered installers, ask for the panel’s datasheet (manufacturer’s efficiency at 200 W/m²), and check the warranty covers labour for at least 10 years. SunPower, LG and JA Solar all meet that threshold. Budget brands like Longi and Trina do not, though their panels cost 30% less.
The Which? test is a solid starting point. But the real decision comes down to your roof: orientation, pitch, shading, and whether you plan to stay 10 years or 20. If you move in five, payback won’t arrive. If you stay 20, SunPower’s premium pays off. For most homeowners, JA Solar at £0.48/watt with a 15-year warranty is the sensible middle ground, unless you live in a conservation area, where planning permission adds £500–£1,000 in fees.
Households on standard variable tariffs can check SEG rates via Ofgem’s comparison tool from 4 November. MCS-certified installers are listed at mcs-certified.com. Eligibility for 0% VAT requires the installer to issue a certificate, keep it with your EPC documents.
Frequently Asked Questions
Yes, but output drops 60–80% from June peak. In December, a 4kW system generates roughly 2–4 kWh per day, enough to run the fridge and lights, but not a heat pump. Which? tests confirm modern panels still produce at 200 W/m² light intensity, typical of overcast days.
No if you want SEG payments or 0% VAT, both require MCS-certified installation. DIY installs void most warranties and may breach building regulations. A professional install costs £5,000–£8,000 but protects your investment.
