Stop accepting P-type PERC

What’s actually different?

Every solar panel works the same basic way: sunlight hits a silicon wafer, knocks electrons loose, and the panel captures that movement as electricity. The bit that changes between PERC and TOPCon is what the silicon is treated with, and how the back of the cell is built to stop electrons escaping before you can use them.

P-type PERC stands for Passivated Emitter and Rear Cell. It uses silicon treated with boron (P-type), with a fairly simple aluminium layer across the back. That layer does its job, but it lets a meaningful chunk of electrons recombine and turn into wasted heat instead of usable current. PERC was a genuine step forward when it launched, and it’s the reason solar panels got noticeably better through the 2010s. It’s just no longer the newest idea in the room.

N-type TOPCon stands for Tunnel Oxide Passivated Contact. It uses silicon treated with phosphorus (N-type), which is naturally less prone to a defect called light-induced degradation, plus an ultra-thin oxide layer on the back that acts like a one-way valve for electrons — letting current out while blocking the recombination that PERC loses energy to. Fewer electrons wasted means more of the sunlight hitting your roof actually turns into electricity you can use.

The numbers installers hope you won’t ask about

Efficiency is only one part of the story. What actually decides whether a panel is a good bet for 25 years on a UK roof is a combination of four figures. Here’s how the two technologies stack up, alongside the premium options you’ll sometimes see quoted too.

Figures reflect typical 2026 commercial module ranges for UK-supplied residential panels. Individual models vary within these bands.

Twenty-five years is a long time to be on the losing side of a graph

Degradation sounds like a small number until you let it run for a couple of decades. A panel that loses 0.6% of its output every year is losing nearly twice as much ground as one losing 0.35% — and that gap compounds, year after year, for the entire life of your roof.

That’s on top of TOPCon starting from a higher efficiency figure in year one. Put the two together and a TOPCon system isn’t just marginally ahead at the ribbon-cutting — it pulls further ahead every year you own it.

Why this matters more here than it does in Spain

Britain doesn’t get the same blast of direct sun as southern Europe, but it makes up for it with a lot of hazy, overcast daylight — and the odd properly hot roof in a July heatwave. Both of those situations are exactly where the temperature coefficient and low-light behaviour of a cell start to matter.

The temperature coefficient tells you how much output a panel loses for every degree its surface warms above 25°C. A dark roof on a warm day can easily run 20–30°C hotter than the air temperature around it, so this isn’t an abstract lab number — it’s happening on your actual roof most summer afternoons. TOPCon’s lower coefficient means it holds onto more of its output exactly when a PERC panel is starting to lose the most ground.

The same logic runs in reverse on a grey January afternoon. TOPCon’s cell structure is more efficient at converting the diffuse, indirect daylight that makes up a big share of UK generation, not just the direct sun PERC was originally optimised for.

So why do some installers still quote PERC?

Not usually out of malice. There are a few honest reasons a PERC panel might still turn up on a 2026 quote:

Clearing old stock. Distributors occasionally have a pallet of older panels to move, and it’s cheaper for an installer to sell those on than write off the loss.

Habit. Some smaller installers haven’t updated their default supplier catalogue in a while, and simply keep quoting what they’ve always quoted.

Margin. PERC is cheaper to manufacture. On a fixed headline price, swapping in a cheaper panel quietly improves the installer’s margin without you necessarily noticing, unless you ask what’s actually in the box.

None of that makes PERC dangerous or a scam — it’s still a perfectly functional panel. It just means the burden is on you to ask the question, because plenty of installers won’t volunteer the answer unprompted.

Is TOPCon actually worth paying more for in 2026?

This is the bit that’s changed the most. For years, TOPCon carried a genuine price premium, and “PERC because it’s cheaper” was a fair argument for a tight budget. Through 2025 and into 2026, that’s largely stopped being true. Tier 1 manufacturers — Jinko, JA Solar, Trina, LONGi and others — have scaled up TOPCon production so heavily that it now sits at close to price parity with PERC on a per-watt basis. Several manufacturers have already wound their PERC lines down or converted them to TOPCon outright.

For a typical UK home, that means a fully installed 4kW system still lands in the familiar £6,500–£8,500 bracket most buyers are already expecting, regardless of whether it’s fitted with TOPCon or PERC panels. If your quote shows a big price gap between the two, it’s worth asking your installer to explain exactly where that difference is coming from — it’s no longer simply “the cost of the cell.” For the full breakdown of what a 2026 UK system costs across every system size, our solar panel cost and technology guide covers it in detail.

The 0% VAT relief on qualifying residential solar installations, in place until 31 March 2027, applies equally to both panel types too — so tax isn’t a reason to pick one over the other either. You can read HMRC’s own guidance on VAT on energy-saving materials if you want the detail straight from source.

The panels UK installers are actually fitting in 2026

N-type TOPCon has become the default across almost every mainstream UK residential installer. These are the models that keep coming up on real quotes right now:

Curious how the three biggest names actually compare on paper? Our Jinko vs JA Solar vs Trina Solar breakdown goes through it panel by panel, and our pick of the best solar panels for UK homes this year ranks the current line-up in full.

Before you sign anything — a short checklist

None of this requires becoming a solar engineer overnight. A few direct questions will tell you everything you need to know about what’s actually being quoted.

• 1

  Ask for the exact panel model and datasheet, not just “monocrystalline” — PERC and TOPCon panels are both monocrystalline, so that word alone tells you nothing.

• 2

  Confirm in writing whether the cell technology is N-type TOPCon, HJT or P-type PERC. It should be printed on the datasheet, not just described verbally.

• 3

  Check the panel against the MCS Certified Products database and confirm it’s listed as a Bloomberg NEF Tier 1 manufacturer — a bankability signal that reputable brands are happy to confirm.

• 4

  Make sure your installer, not just the panel, is MCS certified — you’ll need this for the Smart Export Guarantee and most grant eligibility, and it’s worth checking they’re also signed up to a consumer code like RECC.

• 5

  Get the degradation rate and temperature coefficient figures in writing rather than relying on a verbal “it’s a good panel.”

Useful places to check: the MCS Certified Products database, the Renewable Energy Consumer Code (RECC), and the government’s own solar deployment statistics if you want to see how fast the UK market is actually moving.

Quick questions, straight answers