This calculator uses standard UK solar industry assumptions. Here's how each figure is worked out:
- Annual usage: Your monthly bill ÷ £0.30 (average UK unit rate) × 12 gives your estimated annual kWh usage.
- System size: Based on covering your usage at approx. 850 kWh generated per kW installed per year (UK average), capped between 2 kW and 10 kW.
- Orientation factor: South-facing roofs capture the most sun (100%). East/West captures about 85%. North-facing is around 60%.
- Shading factor: No shading = 100% of potential. Heavy shading can reduce output by 30%.
- Self-consumption: Without a battery, ~70% of generated energy is used in-home. With a battery, ~85%, as evening usage is covered.
- Savings: Generated energy × self-consumption rate × £0.30/kWh electricity price.
- Installation cost: Estimated at £1,500 per kW (minimum £4,000). Battery adds ~£4,000. VAT on solar panels is 0% for most UK homes.
- COâ‚‚: UK grid average of 0.2 kg COâ‚‚ saved per kWh of solar generated.
- Panel count: Estimated assuming 400W panels (typical modern panel).
