TOPCon vs PERC Solar Panels: What the Spec Sheet Actually Tells You
If you have been getting solar quotes in the past twelve months, you have almost certainly heard "TOPCon" more than once. Most installers are now defaulting to TOPCon panels, and several manufacturers have wound down PERC production lines entirely. Here is what the technology difference actually means — and when it matters for a UK install.
What PERC and TOPCon actually are
Both are silicon solar cell technologies, but they differ in how they handle the recombination of electrons at the cell's rear surface — the main cause of efficiency loss in a standard cell.
PERC (Passivated Emitter and Rear Cell) adds a dielectric passivation layer to the rear of the cell, reducing recombination. It has been the industry standard since around 2016 and is a mature, well-understood P-type (boron-doped) technology.
TOPCon (Tunnel Oxide Passivated Contact) takes the rear passivation concept further, using an ultra-thin tunnel oxide layer and a polysilicon layer to reduce recombination losses more aggressively. It is an N-type (phosphorus-doped) technology, which matters for a specific reason covered below.
The efficiency difference is real but smaller than it sounds
Commercial TOPCon panels typically achieve module efficiencies of 22–23%, compared to 20–21.5% for current PERC. That sounds significant, but on a typical 30m² south-facing roof, the difference in annual output between a 22% TOPCon panel and a 20.5% PERC panel is around 100–150kWh per year — roughly 5–7% more generation.
If your roof space is constrained, this matters: you can fit more watts into the same area. If you have a large unshaded roof and just need to hit a target output, PERC gets you there with more panels and lower cost per watt.
Degradation is where TOPCon wins clearly
N-type cells degrade more slowly than P-type. TOPCon panels typically carry performance warranties guaranteeing less than 0.4% degradation per year, versus 0.5–0.55% for standard PERC. Over 25 years, that is a meaningful difference: a 400W TOPCon panel will likely be producing around 10% more than an equivalent-wattage PERC panel at the end of its warranted life.
This is not marketing. The lower degradation rate is rooted in the N-type cell's resistance to light-induced degradation (LID) and light and elevated temperature-induced degradation (LeTID) — both of which disproportionately affect P-type PERC cells in the first years of operation.
Low-light performance
N-type cells also perform better under diffuse light conditions — overcast skies, early morning, late afternoon. In the UK, where roughly 60% of days have significant cloud cover, this is not a trivial advantage. The difference in low-irradiance performance (typically expressed as efficiency at 200 W/m² versus rated conditions of 1000 W/m²) is usually 1–2 percentage points in favour of TOPCon.
Is the price premium justified?
As of early 2026, TOPCon panels typically cost 5–12% more per watt than equivalent PERC panels from the same manufacturer. The price gap has narrowed significantly — in 2022 it was closer to 20–25%. For most homeowners, the combination of lower degradation and better low-light performance tips the calculation in TOPCon's favour, even before the efficiency argument.
The case for PERC is primarily cost. If you are on a tight budget, a quality PERC panel from a reputable manufacturer (Jinko, Longi, Canadian Solar) still represents a sound investment. If you are optimising for 25-year yield and have a constrained roof, TOPCon is now the clear choice.
What this means for the comparison engine
The solar panels on SmartSolarHomes are scored on degradation warranty, low-light performance coefficient, efficiency, and manufacturer warranty terms — all of which reflect these technology differences. TOPCon panels score well on the first two criteria by design; whether that overall score translates to the right choice for your roof depends on your specific constraints.