Home Solar Calculator

Estimate how much of your electricity a solar and battery system could provide, and how much you could save each year.

What would you like to do?

Your solar system

Let's estimate your roof size

Which way does your sunniest roof face?

For battery, tariffs, and roof detail — switch to Detailed above.

Annual electricity use 3,500 kWh

UK average is ~3,500 kWh/year

Solar panels 3.80 kWp

Number of panels 10 panels

Orientation SE / SW (45°)

Roof pitch (tilt) 35°

Each panel is 475 Wp · typical UK roof is 30–40°

Battery storage

kWh

0 = no battery

Occupancy pattern

Affects how much solar you use directly vs export

Electricity tariff rates

Import (p/kWh)

Export/SEG (p/kWh)

Overnight rate (p/kWh)

Import = standard rate; overnight = off-peak tariff (e.g. Octopus Go); export = SEG rate

Electricity price inflation 3.0% / yr

Applied to import savings & arbitrage in payback model; export rate kept flat

Addition to house value £0

Deducted from effective cost in payback calculation; evidence varies — set to zero if unsure

Your estimate

Updated ✓

☀️ Use your postcode to estimate your solar potential.

Install cost	Yr 1 saving	Yr 5 saving	Payback
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How this tool works

Generation estimate

Annual solar generation is calculated using irradiance data from the MCS MGD003 dataset — the same data used by certified solar installers in the UK. The dataset provides annual yield figures (kWh per kWp) for 25 climate zones across the UK, at every combination of roof tilt (0–90°) and orientation (0–175° from south). Your postcode is matched to the nearest zone centre. The panel output assumes each panel is rated at 475 Wp; performance losses (wiring, inverter, temperature) are already embedded in the MCS irradiance figures.

Self-consumption & battery

What fraction of generated electricity is actually used in your home (rather than exported) depends on when you're home and whether you have a battery. These fractions come from the MCS MGD003 self-consumption lookup tables, which model three occupancy archetypes and a range of battery sizes against different generation and demand levels. A 90% cap on demand met is applied — it is not practically possible to cover all electricity from solar alone due to overnight and low-irradiance periods.

Financial estimate

Annual saving = (self-consumed kWh × import rate) + (exported kWh × export rate) + battery arbitrage saving. The import rate is what you currently pay per kWh; the export rate is what you receive under the Smart Export Guarantee (SEG) or similar tariff.

Battery arbitrage

A battery can earn additional value by charging from the grid overnight at a cheap off-peak rate (e.g. Octopus Go at ~7.5p/kWh) and discharging during the day instead of importing at the standard rate. The number of available arbitrage cycles = 365 minus the cycles already used for solar self-consumption. Solar self-consumption cycles are estimated from the uplift in the MCS self-consumption fraction between PV-only and PV-with-battery, divided by battery capacity (accounting for 90% round-trip efficiency). Each arbitrage cycle earns: battery capacity × 90% efficiency × (import rate − overnight rate). Arbitrage saving is set to zero if the overnight rate exceeds the effective discharge value.

Limitations

The MCS lookup tables cover generation and demand up to 5,999 kWh/year. Very large systems (typically >12 panels) or high-demand homes may approach this boundary; results in those cases are approximations. This tool does not account for shading, soiling, or system degradation over time. Always get a quote from an MCS-certified installer before making any purchasing decision.