For most of the last decade, buying solar modules meant choosing a wattage and a brand. In 2026 the cell technology matters again, because the market has reordered itself: p-type PERC has moved from default to legacy, and the choice is now between three n-type routes with genuinely different behaviour in the field.
This guide is for buyers specifying modules for commercial and utility projects – the people who have to defend a choice to a project owner, not to a homeowner. It deliberately spends less time on efficiency than most comparisons do, because efficiency is the number that matters least.
Where the market actually is in 2026
Industry shipment trackers now put p-type PERC below a quarter of global supply and falling fast, with several manufacturers having closed or converted those lines. TOPCon has become the volume default, holding roughly two-thirds of shipments. HJT remains a premium niche at around ten per cent, and back-contact (BC / xBC) has moved from novelty to a real, if smaller, segment.
The practical consequence for a buyer is simple: specifying PERC for a new project is now a decision that needs a reason. It is still available, and for clearance inventory at a distressed price it can be rational. But it is no longer the neutral default, and it will not be the technology your warranty and replacement market supports in ten years.
Efficiency is the least interesting number on the datasheet
Commercial TOPCon modules ship in the low twenty-three per cent range for module efficiency. HJT and BC sit perhaps half a point to a point higher at the top end. PERC sits lower again. That is a real difference, but on a project where land or roof area is not the binding constraint, an efficiency gap of one point mostly moves the bill of materials, not the business case.
Efficiency earns its premium in two situations: where the available area is fixed and you are trying to maximise installed capacity, and where the balance-of-system cost per watt falls because fewer modules are needed for the same array. If neither applies, buy on the other specifications below.
Temperature coefficient: the spec that matters in hot climates
Modules are rated at 25 degrees cell temperature and almost never operate there. A rooftop array on a summer afternoon runs far hotter, and the power lost to heat is governed by the temperature coefficient – the percentage of output lost per degree above the rating point.
- p-type PERC – roughly minus 0.35 to minus 0.42 per cent per degree.
- TOPCon – roughly minus 0.30 to minus 0.33.
- HJT – roughly minus 0.24 to minus 0.27, the best of the three.
Worked through on a hot roof, the spread between PERC and HJT is several per cent of instantaneous output during exactly the hours when a commercial load is highest. Over a twenty-five year production profile in a hot climate, this specification is worth more than the efficiency gap. If your project is in a hot region, price the temperature coefficient, not the nameplate.
Degradation and the first-year drop
Two numbers here, and buyers routinely conflate them.
- First-year light-induced degradation (LID) – p-type cells suffer a permanent output loss in the first hours of exposure, typically one to three per cent, before the long-term degradation clock even starts. n-type architectures based on phosphorus-doped silicon largely avoid the boron-oxygen mechanism behind it.
- Annual degradation – n-type products are typically warranted around 0.4 per cent per year; p-type PERC more commonly 0.45 to 0.6.
Ask for both, and ask whether the performance warranty is written on a linear or a stepped basis. A linear warranty that still guarantees the mid-eighties per cent range at year twenty-five is the market norm for tier-one n-type product.
Bifaciality: when the rear side actually pays
Bifacial modules are now standard on ground-mount and increasingly on commercial flat roofs, but the rear-side contribution only materialises under the right conditions. Bifaciality factors run roughly 65-75 per cent for bifacial PERC, 70-80 for TOPCon, and 90-92 for HJT. What converts that factor into real energy is the albedo of the surface beneath the array and the height and spacing of the rows.
Over pale gravel, sand or a white membrane roof, the rear side contributes meaningfully. Over dark soil, low-mounted rows, or tightly packed rooftop arrays, it contributes very little – and you should not pay a premium for it. Where the rear side does matter – agrivoltaics, floating solar, high-clearance trackers – HJT’s bifaciality advantage becomes a genuine differentiator.
The question TOPCon buyers should now ask: UV-induced degradation
Independent reliability testing has flagged UV-induced degradation as a specific concern for some TOPCon constructions, with reported losses under accelerated UV exposure varying widely between bills of materials – from negligible to well into the teens, with a median measured in the low single digits. Some manufacturers have addressed it through encapsulant and passivation changes; others have not.
This is not an argument against TOPCon, which is the correct default for most projects. It is an argument for asking a specific question before you buy: what UV testing has this exact bill of materials been through, and what was the result? Ask for the report, not the marketing claim.
Reliability spread is now wider than the technology gap
The most useful finding from recent independent module scorecards is uncomfortable: a large majority of manufacturers had at least one failure across the test programme. The spread within a technology now exceeds the spread between technologies. A well-made p-type module from a disciplined manufacturer will outperform a carelessly made n-type module.
Which means technology selection is the second question, not the first. The first is manufacturer quality and bankability – and that is why we treat the datasheet review in our module buying guide as a prerequisite to this one.
What to specify
Reference table
Swipe horizontally to view all columns →
| Parameter | What to put in the specification | Where it decides the outcome |
|---|---|---|
| Cell technology | TOPCon as default; HJT where heat or bifacial gain dominates; BC where area is constrained | Project type and climate |
| Efficiency | Specify only if area is the binding constraint | BOM count and area use |
| Temperature coefficient | Maximum acceptable value, stated in the PO | Hot-climate summer yield |
| Degradation | First-year LID and annual rate, linear warranty | 25-year energy model |
| Bifaciality | Only where albedo and mounting justify it | Ground-mount and high-clearance arrays |
| UV testing | Request the UV exposure report for the exact BOM | Long-term TOPCon stability |
| Manufacturer | Independent reliability scorecard history | Outweighs the technology choice |
Specifying for a live project
Send the project location, mounting type and area constraint with your enquiry and the technology choice usually resolves itself. Browse the configurations we supply on the solar modules page, and if you are sizing the array and storage together, the sequence in our commercial sizing guide starts from the load profile. For a project-specific recommendation, use the contact page.
BUYER CHECKLIST
Buyer considerations for this scope
What differs for the project, not the datasheet headline?
Degradation rate, temperature coefficient, bifacial gain, low-light behaviour and the warranty terms behind them. A small efficiency difference is usually worth less over the life of the array than the degradation and warranty terms that come with it.
Is it available in the quantity and power class you need?
Availability is confirmed per enquiry, and where a project needs mixed power classes in one container that should be stated up front. A technology choice that cannot be delivered in the required bin is not a choice at all.
What should be held constant across two quotes?
The wattage bin, the warranty terms, the degradation curve, and the balance-of-system cost that follows from module size and weight. Comparing headline watt-price across different bins is the most common way to choose the more expensive option.
PRACTICAL ANSWERS
Questions buyers ask about this
Is efficiency the number to compare?
It is the least interesting number on the datasheet. On a roof, watts per square metre and the temperature coefficient decide what you actually get; on ground-mount, cost per watt and the balance-of-system saving from higher power decide it.
What does the temperature coefficient change?
How much output is lost as the cell heats up. In hot climates the difference between a strong and a weak coefficient is worth more than a fraction of a percent of nameplate efficiency.
How should we read the degradation figures?
Look at the first-year drop and the linear rate after it, not just the year-25 figure. Two modules with the same year-25 guarantee can differ meaningfully in the early years, which is when the project cash flow is tightest.
Which technology should we buy in 2026?
TOPCon is the volume default and the safest on supply and price. HJT suits high-temperature and high-value roofs. PERC still makes sense on price-driven ground-mount where the extra efficiency does not pay back.
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