How the Solar Savings Calculator Works (UK)

This site is designed to do one thing well: give you a fast, assumption-driven estimate of how much a solar PV system could save you each year, what you might earn from exports, and roughly how long it could take to pay back the upfront cost.

The two buckets: self-consumed vs exported electricity

A solar system produces electricity over the year (measured in kWh). That electricity typically ends up in one of two places:

• Self-consumed: electricity you use in your home (this reduces what you buy from your supplier).
• Exported: electricity you don’t use in the moment, sent back to the grid (often paid via an export tariff).

How annual savings are calculated

Your self-consumed electricity is valued at your electricity unit rate (p/kWh). If you self-consume 1,000 kWh and your unit rate is 26p/kWh, then your savings from self-consumption are roughly:

• 1,000 kWh × £0.26 = £260/year (estimate)

How export income is calculated

Exported electricity is valued at your export rate (p/kWh). If you export 1,500 kWh at 15p/kWh, export income is roughly:

• 1,500 kWh × £0.15 = £225/year (estimate)

Total annual benefit and payback time

Total annual benefit is the sum of savings + export income. Payback is the upfront cost divided by the annual benefit:

• Payback years = (Solar cost + Battery cost if included) ÷ (Annual savings + Annual export income)

The battery toggle (simple by design)

Batteries can increase how much solar you use at home by storing excess generation for later. That often improves annual savings (because self-consumed solar is usually “worth” more than exported solar). But batteries also increase upfront cost.

In this calculator, the battery toggle works by adding:

• A battery cost to your upfront total
• An “uplift” to your self-consumption (set as a simple percentage-point increase)

It’s intentionally transparent. You can make it conservative by using a smaller uplift and/or higher battery cost.

What affects real-world results

• Roof orientation & shading: can materially reduce annual generation.
• Household usage patterns: daytime usage tends to increase self-consumption.
• Installer pricing & warranties: quotes vary; compare like-for-like.
• Tariff changes: unit and export rates can change over time.
• System sizing: oversizing can increase exports (sometimes lowering savings efficiency).

How to use this calculator well

1. Run a conservative scenario (lower generation, lower self-consumption, modest export rate).
2. Run an expected scenario (your best guess).
3. Run an optimistic scenario (better usage shifting, higher rates).

Next: Battery vs no battery · What affects payback · Typical UK solar costs