5kW Solar Panel System: Cost, Output & Savings

System overview: - Panels: 13 × 385–400W monocrystalline - Total capacity: 5.0–5.2 kWp - Roof space needed: ~22 m² (13 panels at 1.7 m² each) - Weight on roof: ~260 kg total - Annual generation: 4,700–5,200 kWh - Inverter: 5kW string inverter, hybrid inverter, or 13 micro-inverters

Cost breakdown: - Panels (13): £2,600–£4,500 - Inverter: £600–£1,200 - Mounting system: £350–£650 - Wiring and components: £200–£450 - Scaffolding: £200–£500 - Labour: £1,200–£2,200 - Total installed: £6,500–£9,500 (0% VAT)

DNO notification: Systems over 3.68kW (single phase) require G99 notification to the Distribution Network Operator, which takes 4–8 weeks. Your installer handles this. Under 3.68kW, the simpler G98 process applies.

Source: MCS installer pricing 2026; ENA G98/G99 requirements.

Direct comparison:

| Metric | 4kW (10 panels) | 5kW (13 panels) | Difference | |--------|-----------------|-----------------|------------| | Cost | £6,750 | £8,000 | +£1,250 | | Annual output | 4,000 kWh | 5,000 kWh | +1,000 kWh | | Annual savings | £580 | £726 | +£146 | | Payback | 11.6 yrs | 11.0 yrs | 0.6 yrs faster | | 25yr net | £7,750 | £10,150 | +£2,400 more |

The extra £1,250 for 3 more panels delivers: - 1,000 kWh more per year - £146 more in annual savings - Payback on the extra panels: 8.6 years - 25-year extra profit: £2,400

Verdict: If your roof fits 13 panels, the 5kW system is better value than 4kW. The marginal cost per extra panel is lower, and the ROI on the additional investment is excellent.

Source: PVGIS; Ofgem Q1 2026.

A 5kW system generates more surplus than a 4kW, making a battery more valuable:

5kW without battery (50% self-consumption): - Self-consumed: 2,500 kWh × 24.5p = £613 - Exported: 2,500 kWh × 4.5p = £113 - Total: £726/year

5kW with 10kWh battery (80% self-consumption): - Self-consumed: 4,000 kWh × 24.5p = £980 - Exported: 1,000 kWh × 4.5p = £45 - Total: £1,025/year - Battery adds: £299/year - Battery cost: £4,500 - Battery payback: 15 years standalone (but improves with smart tariff)

5kW + battery + Octopus Flux: - Peak export income (16:00–19:00): +£150–£250/year - Overnight cheap charging: additional arbitrage savings - Effective total: £1,175–£1,275/year - Battery payback with smart tariff: 9–12 years

Source: Ofgem; Octopus Flux tariff.

Systems over 3.68kW (single phase) require G99 notification rather than the simpler G98 process:

G98 (under 3.68kW): Simple notification — installer submits a form, connection is automatic. No waiting period.

G99 (3.68kW–50kW): Application process — installer submits to your DNO, who has 11 working days to respond. Most applications are approved automatically, but the DNO may require a study if the local network is congested.

What this means for a 5kW system: - Your installer submits the G99 application 4–8 weeks before installation - In most areas, approval is automatic within 2 weeks - Rarely, the DNO may request a connection study (takes 45 days, free of charge) - Very rarely, the DNO may require a network upgrade before connection (costs vary — your installer should warn you if this is likely)

In practice: G99 causes a slight delay but is rarely a problem. Your installer handles all paperwork.

Source: ENA Engineering Recommendation G99; DNO application guidance.