Monocrystalline vs Polycrystalline: Which Is Better?

| Feature | Monocrystalline | Polycrystalline | |---------|----------------|----------------| | Efficiency | 20–22% | 15–17% | | Appearance | Uniform dark black | Speckled blue | | Low-light performance | Better | Worse | | Degradation rate | 0.3–0.4%/year | 0.5–0.7%/year | | Output after 25 years | 85–90% | 80–83% | | Cost per panel (400W) | £200–£350 | £150–£250 | | Cost per watt | ~£0.50–0.88 | ~£0.43–0.71 | | Roof space needed (4kW) | ~17 m² | ~22 m² | | Typical warranty | 25 years | 25 years | | Temperature coefficient | –0.35%/°C | –0.40%/°C | | UK market share (2026) | ~95% | ~5% |

The efficiency gap is significant: For the same 4kW system, monocrystalline needs 17m² of roof space vs 22m² for polycrystalline. On small UK roofs, this difference determines whether you fit 10 or 8 panels.

The price gap has nearly closed: In 2026, mono costs only £30–£50 more per panel than poly. This premium is recovered within 2 years through higher output.

Source: Panel manufacturer specifications; UK distributor pricing.

Very few situations favour polycrystalline in 2026:

• Very large roofs where space is unlimited (e.g., agricultural buildings) — poly's lower per-panel cost saves money when you can simply install more panels
• Budget-constrained projects where saving £300–£500 across a 10-panel system is critical
• Replacing existing poly panels — matching the existing aesthetic (blue) if adding to an older system

In all other cases: choose monocrystalline. The marginal cost saving of poly is not worth the efficiency, lifespan, and low-light performance sacrifices.

Most UK MCS installers no longer stock polycrystalline. If your installer quotes poly, ask why — it may indicate they are using old or clearance stock.

Source: UK installer product catalogues; manufacturer production data.

Monocrystalline: - Made from a SINGLE silicon crystal grown using the Czochralski process - Uniform crystal structure = consistent electron flow = higher efficiency - Cut into thin wafers and assembled into cells - Dark, uniform colour comes from the single-crystal structure - Manufacturing: more energy-intensive but produces more efficient cells

Polycrystalline: - Made from MULTIPLE silicon crystals melted together in a mould - Irregular crystal boundaries = less efficient electron flow - Visible crystal grain pattern creates the speckled blue appearance - Manufacturing: simpler and cheaper, but lower-quality cells - The multiple crystal boundaries create 'recombination zones' where electrons lose energy

Why the efficiency difference exists: In monocrystalline, electrons flow freely through the uniform crystal. In polycrystalline, electrons encounter grain boundaries (where different crystals meet), losing energy at each boundary. This fundamental physics difference cannot be designed away — mono will always be more efficient than poly.

Source: Solar cell physics; NREL photovoltaic fundamentals.

4kW system comparison over 25 years:

| Metric | Monocrystalline | Polycrystalline | |--------|----------------|----------------| | System cost | £6,750 | £6,250 | | Panels needed | 10 × 400W | 12 × 340W | | Year 1 output | 4,000 kWh | 4,000 kWh | | Year 25 output | 3,560 kWh (89%) | 3,300 kWh (83%) | | 25-year total output | 95,000 kWh | 90,000 kWh | | 25-year savings | £14,500 | £13,700 | | Net profit | £7,750 | £7,450 | | ROI | 115% | 119% |

Interesting finding: The ROI percentage is actually similar because poly costs less upfront. But mono generates £800 MORE in total electricity over 25 years. The higher absolute savings make mono the better choice — especially on limited roof space where you cannot fit 12 poly panels.

The definitive answer for UK homes: choose monocrystalline. It is the industry standard, delivers higher lifetime output, and the price difference has become negligible.

Source: LCOE calculations; degradation data from NREL.