6kW Solar Panel System: The Large Home Choice

System overview: - Panels: 16 × 375–400W monocrystalline - Total capacity: 6.0–6.4 kWp - Roof space needed: ~27 m² (16 panels at 1.7 m² each) - Weight on roof: ~320 kg total - Annual generation: 5,600–6,200 kWh - Inverter: 5–6kW string inverter, hybrid inverter, or 16 micro-inverters

Cost breakdown: - Panels (16): £3,200–£5,600 - Inverter: £700–£1,400 - Mounting system: £400–£750 - Wiring and components: £250–£500 - Scaffolding: £250–£600 - Labour: £1,500–£2,500 - Total installed: £8,000–£11,000 (0% VAT)

DNO notification: 6kW exceeds the 3.68kW G98 threshold, so G99 notification is required (your installer handles this). Approval is usually automatic within 2 weeks.

Source: MCS installer pricing 2026; ENA G99 requirements.

6kW without battery (50% self-consumption): - Self-consumed: 3,000 kWh × 24.5p = £735 - Exported: 3,000 kWh × 4.5p = £135 - Total annual savings: £870 - Cost: £9,500 average - Payback: ~10.9 years - 25-year net savings: £12,250

6kW with 13kWh battery (80% self-consumption): - Self-consumed: 4,800 kWh × 24.5p = £1,176 - Exported: 1,200 kWh × 4.5p = £54 - Total annual savings: £1,230 - Cost: £9,500 + £6,000 (battery) = £15,500 - Battery replacement (year 13): £4,000 - Payback: ~12.6 years - 25-year net savings: £8,750

6kW + battery + Octopus Flux: - Peak export at 15–24p during 16:00–19:00: +£200–£300/year - Overnight cheap charging at 7.5p: additional arbitrage - Effective total: £1,430–£1,530/year - Effective payback: 10–11 years

Source: Ofgem Q1 2026; Octopus Flux tariff.

| Metric | 4kW | 5kW | 6kW | |--------|-----|-----|-----| | Panels | 10 | 13 | 16 | | Roof space | 17m² | 22m² | 27m² | | Cost | £6,750 | £8,000 | £9,500 | | Annual output | 4,000 kWh | 5,000 kWh | 6,000 kWh | | Annual savings | £580 | £726 | £870 | | Payback | 11.6 yrs | 11.0 yrs | 10.9 yrs | | 25yr net | £7,750 | £10,150 | £12,250 |

Incremental cost from 5kW to 6kW: £1,500 for 3 extra panels Extra annual savings: £144 Payback on extra panels: 10.4 years

The marginal investment is worthwhile if you have the roof space. However, the 5kW to 6kW jump is slightly less compelling than 4kW to 5kW because self-consumption percentage drops as system size grows (you export more surplus).

Source: PVGIS; Ofgem; MCS pricing.

A 6kW system generates more surplus than most households can use directly. Without a battery, a large proportion is exported at low SEG rates (4.5p/kWh). A battery captures this surplus for evening use at 24.5p/kWh value.

Recommended battery sizes for 6kW: - 10kWh: Good for most households. Covers evening + overnight for average consumption. - 13.5kWh (Tesla Powerwall): Better for high-consumption homes. Covers extended evening use. - Two batteries (20kWh): For maximum self-consumption. Only worthwhile if consumption is very high.

The battery ROI improves with larger solar systems because there is more surplus to capture. A battery paired with a 6kW system saves more per year than the same battery with a 4kW system.

Source: Energy Saving Trust; battery sizing guidance.