Solar PV Voltage Drop Calculator
Calculate voltage drop for solar PV AC circuits from inverter to consumer unit
Solar PV Quick Facts
- AC side voltage drop calculated same as any power circuit - 5% limit applies
- DC side uses different calculation - consult inverter/panel specifications
- Typical domestic inverter output: 3.6kW (16A), 5kW (22A), 8kW (35A) single-phase
- Three-phase inverters distribute current across phases - lower per-phase drop
- MCS requires voltage drop compliance for accreditation and FIT/SEG payments
Values from BS 7671 Table 4D1B (PVC copper at 70°C)
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Common Solar PV Scenarios
3.6kW inverter - roof to garage CU (10m)
16A with 2.5mm² (18 mV/A/m). At 10m: (18 × 16 × 10) ÷ 1000 = 2.88V (1.25%) ✓
5kW inverter - loft to utility (15m)
22A with 4mm² (11 mV/A/m). At 15m: (11 × 22 × 15) ÷ 1000 = 3.63V (1.58%) ✓
8kW inverter - long run (25m)
35A with 6mm² (7.3 mV/A/m). At 25m: (7.3 × 35 × 25) ÷ 1000 = 6.39V (2.78%) ✓
10kW three-phase - barn installation (40m)
15A per phase with 4mm². At 40m 3Ø: (11 × 15 × 40 × 0.866) ÷ 1000 = 5.72V (1.43% on 400V) ✓
Battery inverter to CU (hybrid system)
Size for battery discharge current, not just PV. 5kW battery = 22A. Check both charge and discharge paths.
Related Renewable Energy Calculations
Installing a heat pump alongside your solar panels? Check voltage drop for that circuit too. For battery storage systems with high discharge currents, use our cable sizing calculator. See our main voltage drop calculator for all circuit types.
Solar PV AC Side Voltage Drop
The AC side of a solar PV system runs from the inverter output to the consumer unit connection point. This uses standard BS 7671 voltage drop calculations with the 5% limit for power circuits. The inverter converts DC from panels to AC at 230V (single-phase) or 400V (three-phase). Cable sizing considers maximum inverter output current.
Solar PV AC Cable Installation Costs (2024)
Typical UK costs for AC side cabling only. Full solar installation costs vary significantly.
| Installation Scenario | Materials | Labour | Total |
|---|---|---|---|
| Simple AC run (<10m) | £50-100 | £100-200 | £150-300 |
| Standard domestic (10-20m) | £80-180 | £150-300 | £230-480 |
| Long run or difficult route | £150-300 | £250-450 | £400-750 |
| Three-phase AC installation | £200-400 | £300-500 | £500-900 |
| Dedicated PV consumer unit | £150-300 | £200-350 | £350-650 |
Prices as of 2024. AC cable costs are typically a small part of total solar installation.
DC Side Considerations
DC cable from panels to inverter uses different calculations based on string voltage (typically 300-600V DC) and string current. DC voltage drop should be kept under 1-2% to maintain MPPT efficiency. This calculator covers AC side only - consult panel and inverter specifications for DC cable sizing, or use specialist PV design software.
MCS Compliance Requirements
The Microgeneration Certification Scheme (MCS) is required for Feed-in Tariff (legacy) and Smart Export Guarantee (SEG) payments. MCS standards require BS 7671 compliance including voltage drop limits. Installations must be by MCS-certified installers using approved equipment. Non-compliant installations may be refused grid connection or export payments.
G98/G99 Grid Connection
Systems up to 16A per phase (3.68kW single-phase, 11.04kW three-phase) can connect under G98 with simple notification to DNO. Larger systems require G99 application with network studies. The DNO may impose export limitations based on local network capacity. Voltage drop compliance is part of the overall installation assessment.
Frequently Asked Questions
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