Plug-in Solar Payback & Self-Use Calculator
See how much electricity a balcony, wall or garden plug-in solar kit could generate at your postcode, how much your home is likely to use directly, and what that means for annual savings and payback.
What this calculator does differently
Models self-use, not just generation
A small solar system can export a meaningful share of its output if the home is using little electricity at the same time. The result therefore compares hour-by-hour modelled output with the daytime demand you enter instead of treating every generated kWh as a full-price saving.
Models the inverter limit separately
If panel DC capacity is greater than the microinverter output, the model caps each hourly production value at the inverter rating. That shows both the low-light benefit of extra panel capacity and the modelled energy lost when peak production reaches the inverter limit.
How the estimate is produced
- Location: your Great Britain postcode is converted to latitude and longitude using Postcodes.io.
- Solar profile: the server requests PVGIS 5.3 hourly solar-production data for your orientation and angle. A representative hourly profile is scaled to the PVGIS long-term annual production estimate.
- Local shading: the additional shading percentage you enter reduces each hourly production value after the PVGIS model.
- Inverter cap: each hour is limited to the maximum AC output you entered, allowing the model to estimate clipping.
- Self-use: each hour of delivered solar is compared with your entered daytime household demand. Generation above that assumed demand is treated as export.
- Financial value: self-used electricity is valued at the import unit rate avoided. Export is worth zero unless you explicitly enter a confirmed export value.
Great Britain rules and product checks
The government framework taking effect from 27 August 2026 enables compliant plug-in solar products designed to connect through a standard UK mains plug. The framework is specifically for plug-in solar without batteries. The interim technical framework limits maximum apparent power supplied to the mains installation to 800 VA.
Rules, technical standards and consumer guidance can change. This website does not certify that a product complies with the applicable specification and does not assess the condition of your electrical installation, mounting structure, balcony, wall, fire safety, planning position, tenancy, lease or insurance cover.
Common questions
Why is export set to zero?
We do not assume that a plug-in solar user will receive an export payment. If you have written confirmation of a tariff or arrangement that pays for exported electricity from your particular system, you can enter that value and test it separately.
Is 800W always better than 400W or 600W?
Not necessarily. A larger system can generate more electricity, but if your daytime demand is low, more of that output may be exported rather than replacing electricity you would otherwise buy. The comparison table shows the additional annual value under the same location and household assumptions; it does not recommend a product.
What if my panels total more watts than the inverter?
The model keeps the panel DC rating and inverter output separate. Extra panel capacity can increase output in weaker light, while the inverter can still cap stronger production. The result reports both delivered generation and modelled clipping.