Solar + EV Combined Savings

How Solar + EV Combined Savings works

This tool calculates the monetary value of using home solar electricity to charge an electric vehicle instead of drawing from the grid. It takes four inputs: average daily solar generation (kWh), the percentage of that solar energy consumed by the EV, the grid electricity rate (£/kWh), and the number of days per year the system operates. The result is an annual saving figure representing avoided grid purchases.

The formula

The calculation follows three steps. First, compute daily EV consumption from solar: Daily EV kWh = Solar kWh/day × (EV share % ÷ 100). Second, scale to annual: Annual EV kWh = Daily EV kWh × Days per year. Third, value at the grid rate: Annual saving (£) = Annual EV kWh × Grid rate (£/kWh). The secondary outputs include total solar kWh delivered to the EV and the daily saving.

Where this method is most accurate

The formula assumes solar generation remains at the average daily level across all counted days and that the EV consumes the specified percentage consistently. Real solar output varies with season, weather, and shading; real EV charging depends on driving patterns and battery state. The calculation is most reliable when inputs reflect long-term averages—for example, annual mean solar yield rather than a single sunny week—and when the EV charges during daylight hours when solar generation occurs.

What this tool does not do

This calculator does not model battery storage, time-of-use tariffs, export payments for surplus solar, or variations in solar yield across seasons. It does not account for the capital cost or depreciation of the solar installation, nor does it estimate the carbon emissions saved. The tool provides no vehicle-specific advice on charging schedules or whether a particular EV model is suitable for solar charging. All outputs are arithmetic projections based on user-supplied inputs, not guarantees of future savings.

Disclaimer

This calculator is an educational tool that performs transparent arithmetic on user-entered values. It offers no financial, tax, or vehicle advice and makes no claim about the suitability of solar panels or electric vehicles for any individual. Actual savings will differ due to weather, electricity tariff structures, export schemes, installation costs, and driving habits. Users are responsible for verifying all inputs and for consulting qualified professionals before making energy or automotive decisions.