For most of the 2010s the monocrystalline-versus-polycrystalline decision was a real one for UK commercial buyers. Mono cost 15-25 percent more and offered roughly 2-3 percentage points of additional efficiency. Whether the premium was worth the efficiency depended on roof area, electricity tariff, and capital availability. By 2026 the question is essentially settled: monocrystalline has won on every relevant dimension, polycrystalline is functionally obsolete in commercial procurement, and the real specification decision has moved up a level — within monocrystalline, which cell architecture (PERC, TOPCon, HJT, or ABC back-contact) and which Tier-1 manufacturer. This page covers why poly is gone, what the modern mono technology landscape looks like, and the bottom-line buyer recommendation.
How each technology is made
Monocrystalline. A single large cylindrical ingot of pure silicon is grown by the Czochralski process — a seed crystal is dipped into molten silicon and pulled slowly upward, with the molten silicon solidifying around the seed in a continuous single-crystal structure. The ingot is sliced into thin square wafers using diamond wire saws. Each wafer becomes one solar cell. The single-crystal structure means electrons move freely through the silicon, giving high cell efficiency. Cost is high because the Czochralski process is slow and energy-intensive.
Polycrystalline (also called multicrystalline). Molten silicon is poured into a square mould and allowed to cool. Multiple crystals form simultaneously and the resulting ingot has a multi-grain structure. The ingot is sliced into wafers the same way. The multi-grain structure has more boundaries that scatter electrons, giving lower cell efficiency. Cost is lower because the casting process is faster and uses less energy than Czochralski.
Efficiency — where the gap actually sits in 2026
The efficiency gap between mono and poly has widened dramatically since 2010 because mono technology has improved while poly has stagnated.
| Technology | Cell efficiency | Module efficiency | Watts per square metre |
|---|---|---|---|
| Polycrystalline (legacy budget) | 17-19% | 15-17% | 150-175 W/m2 |
| Monocrystalline PERC (legacy mainstream 2018-2023) | 21-22% | 20-22% | 200-220 W/m2 |
| Monocrystalline n-type TOPCon (2024+ mainstream) | 22-23.5% | 21.5-23% | 215-235 W/m2 |
| Monocrystalline HJT (2024+ premium) | 23-25% | 22-24% | 225-250 W/m2 |
| Monocrystalline ABC back-contact (2025+ premium-premium) | 24-25.5% | 23-24.5% | 235-255 W/m2 |
The mono-versus-poly module efficiency gap is now 4-6 percentage points — 21-23 percent for modern mono versus 15-17 percent for poly. On a roof-area-constrained commercial site the practical effect is substantial: a 1,000 m2 roof fits roughly 200 kW of modern mono versus 150 kW of poly. That 50 kW difference is worth 50,000-90,000 pounds of net present value over 25 years on UK 2026 commercial economics.
Cost per W has converged
The historical poly cost advantage has effectively disappeared by 2026. Several factors drove the convergence: mono manufacturing scaled massively from 2018 onwards (Longi, JA Solar, Trina, Jinko all shifted to mono-dominant production), poly volume shrank as commercial buyers migrated to mono, and the Chinese government incentive structure shifted to favour high-efficiency mono. The result is mono Tier-1 panels at 0.18-0.24 pounds per W in 2026 and poly at 0.16-0.20 — a 5-15 percent discount that no longer justifies the efficiency loss.
Total system cost per kW installed (panels plus inverter plus mounting plus install plus DNO plus commissioning) shows essentially zero difference between mono and poly in 2026. The poly panels are slightly cheaper, but the additional roof area means more mounting hardware and more labour, eating the panel-cost saving. On a complete-system basis poly is no longer cheaper per kW.
Why poly is essentially gone from UK commercial in 2026
Three things drove poly out of commercial procurement.
The cost gap closed. Mono volume scale-up brought mono price down to within 5-15 percent of poly. The gap is no longer big enough to justify accepting 4-6 percentage points of efficiency loss.
The efficiency gap widened. Mono moved from PERC (22 percent module efficiency in 2020) through TOPCon (23 percent in 2024) to HJT and ABC (24-25 percent in 2026). Poly stayed at 15-17 percent. The gap doubled over six years.
Tier-1 manufacturers stopped making poly commercial product. By 2026 essentially no major Tier-1 manufacturer (JA Solar, Trina, Longi, Jinko, REC, Maxeon, Q CELLS, Aiko) lists a polycrystalline commercial product line. The remaining poly market is served by Tier-2 and Tier-3 brands selling into price-sensitive emerging markets. UK commercial procurement specs Tier-1, and Tier-1 means mono.
For UK commercial buyers the practical answer is simple: do not specify poly in 2026. We have not delivered a polycrystalline commercial install since 2022 and the market has continued to move further in that direction.
The new mono technology choice — PERC vs TOPCon vs HJT vs ABC
Within monocrystalline the meaningful 2026 specification decision is between four cell architectures.
PERC (Passivated Emitter Rear Cell). The dominant technology 2017-2023. P-type silicon with a passivation layer on the rear. Module efficiency 20-22 percent. Most legacy installs from this period are PERC. Still available from budget Tier-1 brands but largely superseded.
TOPCon (Tunnel Oxide Passivated Contact). The mainstream 2024-2026 technology. N-type silicon with a thin oxide tunnel layer. Module efficiency 21.5-23 percent. Better temperature coefficient than PERC. Better PID resistance. Default specification on the bulk of our 2026 installs. JA Solar, Trina, Longi, Jinko all major TOPCon producers.
HJT (Heterojunction). Premium 2024-2026 technology. Combines crystalline silicon with thin-film amorphous silicon layers. Module efficiency 22-24 percent. Excellent temperature coefficient (-0.24 to -0.26 percent per C). Lower degradation rate. REC, Meyer Burger, and several others manufacture HJT. Premium pricing 15-30 percent above TOPCon.
ABC back-contact. Premium-premium 2025-2026 technology. All electrical contacts on the rear side of the cell, eliminating front-side busbars. Module efficiency 23-25 percent — the highest commercial product available. Maxeon and Aiko are the main producers. Pricing 30-50 percent above TOPCon.
Temperature behaviour
UK summer cell temperatures regularly reach 55-65 C on rooftop installations. Panel power output drops as cell temperature rises above 25 C STC reference, and the rate of drop (the temperature coefficient) varies by technology.
- Polycrystalline: -0.39 to -0.41 percent per C → 12-16 percent power loss at 60 C
- Monocrystalline PERC: -0.32 to -0.36 percent per C → 11-13 percent loss at 60 C
- Monocrystalline TOPCon: -0.28 to -0.30 percent per C → 9-11 percent loss at 60 C
- Monocrystalline HJT: -0.24 to -0.26 percent per C → 8-9 percent loss at 60 C
- Monocrystalline ABC: -0.26 to -0.28 percent per C → 9-10 percent loss at 60 C
On a hot summer week at peak generation, modern n-type TOPCon mono delivers 3-5 percent more energy than legacy poly thanks to its better temperature behaviour. Combined with the 4-6 percentage point STC efficiency advantage, real-world summer-yield gap between mono and poly is typically 10-15 percent on top of the nameplate gap.
Aesthetic and listed-building implications
Monocrystalline panels are uniformly black. With all-black framing (some manufacturers offer black-anodised aluminium) and black backsheet (premium specifications), the modules become almost-uniformly black surfaces — visually quiet, premium-looking, suitable for high-spec corporate office buildings, listed buildings, and conservation areas.
Polycrystalline panels have a mottled blue colour from the multi-grain crystal structure. The blue look is visually busier, dates the installation as 2010-2015 era, and is associated with budget specifications. Heritage planning officers in conservation areas and on listed buildings will essentially never approve blue poly panels — black mono is required as a starting point on heritage applications. See our listed building solar panels page for the full heritage approval framework.
Bottom-line buyer recommendation for UK commercial 2026
Specify monocrystalline. Within monocrystalline:
- Default mainstream (most commercial installs): Tier-1 n-type TOPCon at 21.5-23 percent module efficiency. JA Solar JAM72D40 series, Trina Vertex N, Longi Hi-MO 7, Jinko Tiger Neo. Cost-efficient, future-proof.
- Premium (long-life buildings, ESG-led, listed): HJT at 22-24 percent. REC Alpha Pure-RX or Meyer Burger. Better temperature behaviour, longer warranty, premium aesthetic.
- Premium-premium (40-year asset life, space-constrained): ABC back-contact at 23-25 percent. Maxeon 6 (40-year warranty) or Aiko ABC. Highest efficiency available, premium aesthetic.
Skip polycrystalline. The cost saving has gone, the efficiency gap has widened, and Tier-1 manufacturers have stopped making it. Specifying poly in 2026 means buying obsolete technology with no real economic justification.
Authority and reference sources
BloombergNEF Tier-1 list at BloombergNEF. MCS certified products at MCS. IEC standards at IEC. UK Government solar PV resources at gov.uk solar.
Related decision pages
For the full Tier-1 manufacturer comparison see solar panel manufacturers UK. For Tier-1 framework see tier-1 solar panels UK. For panel efficiency in detail see solar panel efficiency UK. For degradation behaviour see solar panel degradation. For warranty positioning see commercial solar warranty. For inverter selection see best commercial solar inverters and string vs microinverter. For finance see cost and payback calculator.
Common questions
Should I be considering polycrystalline panels for a 2026 commercial install?
No. Polycrystalline solar panels are essentially obsolete for UK commercial in 2026. The cost gap that historically justified poly has closed, the efficiency gap has widened from 2-3 percent to 4-6 percent, and almost no Tier-1 manufacturer makes commercial poly product any more. Specifying poly in 2026 means buying yesterday technology at no real saving with materially worse roof-area economics. The real choice in 2026 is which monocrystalline cell architecture — PERC, TOPCon, or HJT — and which Tier-1 manufacturer.
What is the actual efficiency difference between mono and poly?
Modern monocrystalline n-type TOPCon panels run 21.5-23 percent module efficiency. Modern HJT runs 22-25 percent. ABC back-contact (Aiko, Maxeon) runs 23-24 percent. Polycrystalline panels still on the budget market run 17-19 percent. The gap is 4-6 percentage points which translates to 25-35 percent more roof area required for the same kW capacity using poly. On a roof-area-constrained commercial site, mono delivers 25-35 percent more capacity than poly.
Is mono more expensive than poly?
In 2026, no. Mono and poly have converged on cost per W. The historical 15-25 percent poly discount has effectively disappeared because mono manufacturing has scaled and poly volume has shrunk. Tier-1 mono panels in 2026 sell at 0.18-0.24 pounds per W; budget poly at 0.16-0.20 pounds per W — a 5-15 percent discount that does not justify the efficiency loss when roof area, mounting cost, and inverter cost are factored in. On a complete-system basis (panels plus mounting plus inverter plus install) per kW installed, the cost difference between mono and poly is essentially zero.
What is the temperature coefficient difference?
Solar panel power output drops as cell temperature rises above 25C STC reference. Monocrystalline panels typically have a temperature coefficient of -0.30 to -0.32 percent per degree C. Polycrystalline is around -0.39 to -0.41 percent per C. On a hot UK summer day with cell temperatures reaching 55-65 C, the temperature loss is roughly 9-12 percent for mono versus 12-16 percent for poly. The 3-4 percentage point summer-yield advantage is meaningful on the longest-day generation peaks.
What about appearance — does it matter?
Modern monocrystalline panels are uniformly black with all-black framing and black backsheet options on premium specifications. Polycrystalline panels have a distinctive mottled blue colour from the multi-grain crystal structure. The poly look is dated and is associated with budget installations from the 2010s. For listed buildings and conservation areas, all-black monocrystalline is essentially mandatory — heritage planning officers will refuse blue poly panels almost universally. For ESG-led corporate projects the all-black mono aesthetic is preferred for the visual case.