Solar, battery and EV calculator
Estimate annual solar, battery and EV energy balances from entered generation and allocations.
After you calculate
See your solar, battery and EV results
Add your solar generation, battery use, charging needs and system costs, then calculate to see your results.
Annual system benefit
Shown after calculationSimple system payback
Shown after calculationGrid purchases
Solar and battery flows
Full calculation
Uses your entered generation, charging pattern, tariffs and system costs.
Understand your estimate
How it works
Estimate annual energy flows for a home with solar, a battery and an electric vehicle. Start with the same year of household demand, EV charging and solar generation. Household demand must exclude the EV so charging is not counted twice.
Split solar used directly by the home from solar used directly by the EV. Then enter battery energy delivered to each after losses. These are separate paths: energy used directly should not also appear as battery delivery.
Use meter records or an installer report for the allocations. Annual totals alone do not show when energy is available. Solar and battery use must happen when the home or EV can use it. The calculator checks that the annual amounts fit, but does not schedule them.
A few good questions
Before youget started.
Understand this calculator, the figures to enter and the limits of your estimate.
Sources
- Energy price cap unit rates and standing chargesChecked on 9 October 2026
- European Commission: PVGIS reproducible yield calculationsChecked on 13 October 2026
- Australian Government: solar and battery financial benefitsChecked on 14 October 2026
- Last checked
- 14 October 2026
- Rates as of
- 1 October 2026
EnergySums
Solar, battery and EV calculator
United Kingdom · How it works
- Guide updated
- 14 October 2026
- Rates as of
- 1 October 2026
| Item | Value |
|---|---|
| Guide updated | 14 October 2026 |
| Rates as of | 1 October 2026 |
How it works
Estimate annual energy flows for a home with solar, a battery and an electric vehicle. Start with the same year of household demand, EV charging and solar generation. Household demand must exclude the EV so charging is not counted twice.
Split solar used directly by the home from solar used directly by the EV. Then enter battery energy delivered to each after losses. These are separate paths: energy used directly should not also appear as battery delivery.
Use meter records or an installer report for the allocations. Annual totals alone do not show when energy is available. Solar and battery use must happen when the home or EV can use it. The calculator checks that the annual amounts fit, but does not schedule them.
Formula
Battery charging = delivered household and EV energy ÷ round-trip efficiency. Export = generation − direct household use − direct EV use − battery charging. Remaining imports = demand − direct solar − battery delivery. Annual system benefit = avoided purchases + export receipts − maintenance.
Use a percentage as a fraction once: for example, 50% means 50 ÷ 100 = 0.5. Use 0.5 in the energy formula; do not divide it by 100 again.
Energy prices are entered in pence or cents per kWh unless the field names another unit. Divide by 100 to obtain pounds or dollars. Fixed supply charges are excluded unless explicitly entered. Use tax-inclusive bill prices for personal scenarios.
Read the energy balance before payback. Generation is shared between direct use, battery charging and export. Demand not met by direct solar or battery delivery remains a grid import. Battery losses mean charging energy is larger than delivered energy.
Worked example
These illustrative inputs are separate from your saved answers. Prices, use and performance are held constant for this worked scenario; they are not personal defaults.
Inputs used in this worked example.
- Electricity price
- My bill rate
- Electricity unit price
- 30 p / kWh
- Export unit price
- 5 p / kWh
- Annual household electricity excluding EV
- 4000 kWh / year
- Annual metered EV charging electricity
- 2000 kWh / year
- Annual solar generation
- 6000 kWh / year
- Whole-system round-trip efficiency
- 75 %
- Solar used directly by household
- 2000 kWh / year
- Solar used directly by EV
- 500 kWh / year
- Solar-charged battery delivered to household
- 1200 kWh / year
- Solar-charged battery delivered to EV
- 300 kWh / year
- Combined installed price
- 8000 GBP
- Annual extra maintenance
- 0 GBP
- Price conversion
- 100 pence or cents per currency unit
| Item | Value |
|---|---|
| Electricity price | My bill rate |
| Electricity unit price | 30 p / kWh |
| Export unit price | 5 p / kWh |
| Annual household electricity excluding EV | 4000 kWh / year |
| Annual metered EV charging electricity | 2000 kWh / year |
| Annual solar generation | 6000 kWh / year |
| Whole-system round-trip efficiency | 75 % |
| Solar used directly by household | 2000 kWh / year |
| Solar used directly by EV | 500 kWh / year |
| Solar-charged battery delivered to household | 1200 kWh / year |
| Solar-charged battery delivered to EV | 300 kWh / year |
| Combined installed price | 8000 GBP |
| Annual extra maintenance | 0 GBP |
| Price conversion | 100 pence or cents per currency unit |
- System benefit / year
- £1,275.00
- Net energy cost / year
- £525.00
- Simple system payback
- 6.275 years
| Item | Value |
|---|---|
| System benefit / year | £1,275.00 |
| Net energy cost / year | £525.00 |
| Simple system payback | 6.275 years |
- Battery charging
- 1,500 delivered kWh ÷ (75 ÷ 100)= 2,000 kWh
- Remaining exports
- 6,000 generated kWh − 2,500 direct-use kWh − 2,000 charging kWh= 1,500 kWh
- Net annual energy cost
- (2,000 grid kWh × (30 p/kWh ÷ 100 p/GBP)) − (1,500 export kWh × (5 p/kWh ÷ 100 p/GBP)) + 0 GBP maintenance= £525.00
- Annual benefit
- 1,800 GBP baseline cost − 525 GBP system net cost= £1,275.00
| Calculation | Formula with saved values | Result |
|---|---|---|
| Battery charging | 1,500 delivered kWh ÷ (75 ÷ 100) | 2,000 kWh |
| Remaining exports | 6,000 generated kWh − 2,500 direct-use kWh − 2,000 charging kWh | 1,500 kWh |
| Net annual energy cost | (2,000 grid kWh × (30 p/kWh ÷ 100 p/GBP)) − (1,500 export kWh × (5 p/kWh ÷ 100 p/GBP)) + 0 GBP maintenance | £525.00 |
| Annual benefit | 1,800 GBP baseline cost − 525 GBP system net cost | £1,275.00 |
Assumptions and limits
The annual balance does not simulate charging schedules. Direct solar and battery delivery must each coincide with consumption. Metered EV charging already includes charger losses.
Battery delivery cannot exceed household or EV demand; its required charging plus direct use cannot exceed solar generation.
Annual scenarios hold prices and usage constant. Simple payback excludes financing, replacement, degradation and future price changes. There is no finite payback when the annual saving is zero or negative.
The combined installed price and extra maintenance should cover the same system described by the energy inputs. Check the quote scope rather than mixing costs for one setup with energy flows for another.
The tool does not infer solar output from roof size or battery delivery from storage capacity. Those figures need matching records or an assessment. Invalid edits preserve the last valid result with a warning.
Country rules
Use the UK or Australian version that matches your home and the price units shown. Published electricity uses the dated Ofgem or Australian network record for the selected country. Your actual import tariff may differ.
Enter the export payment from your own tariff, and use tax-inclusive import prices for the energy being avoided. Fixed supply charges are excluded. The page does not fetch live prices or apply an automatic incentive. Check the linked source dates and the prices on your contract.
When to ask a professional
Ask a qualified solar and battery installer to review the allocations, losses and equipment compatibility. Bring generation records, household and EV readings, tariff details and the combined quote.
Ask them to check whether the proposed charging and household schedules can use the stated energy. Installation and safety require a separate professional assessment. The annual calculation does not certify the design, guarantee savings or replace the maker instructions and local requirements.
Questions and answers
| Question | Answer |
|---|---|
| Where should I find my inputs? | Use metered usage, published equipment documentation or an installer assessment that matches the conditions being compared. Do not use a nameplate maximum as measured average consumption. |
| Does this predict my future bill? | No. It estimates the entered scenario using its selected prices and performance. Weather, behaviour, price changes and equipment condition can change actual costs. |
| Can I use my own prices? | Yes. Use prices from your bill or quote, including applicable tax. Keep units consistent. Existing fixed supply charges are excluded unless the form explicitly asks for them. |
| Are the worked-example inputs defaults? | No. The worked example is a hand-checked illustration, not typical property data. Enter your own equipment and usage information. |
Sources
| Source | Checked | Reference URL |
|---|---|---|
| Energy price cap unit rates and standing charges | 9 October 2026 | https://www.ofgem.gov.uk/information-consumers/energy-advice-households/get-energy-price-cap-standing-charges-and-unit-rates-region |
| European Commission: PVGIS reproducible yield calculations | 13 October 2026 | https://joint-research-centre.ec.europa.eu/photovoltaic-geographical-information-system-pvgis/using-pvgis-5/api-non-interactive-service_en |
| Australian Government: solar and battery financial benefits | 14 October 2026 | https://www.energy.gov.au/solar/financial-benefits-solar/how-solar-pays-itself-and-batteries-reduce-bills |