The financial case for home EV charging is almost always straightforward: public fast charging costs two to four times as much per unit as home charging, and the cost of a 7kW wallbox installation is typically recovered within one to two years from the saving alone. What is less well understood is how an EV interacts with a solar panel system. If the car is plugged in during the day and charged via a solar divert, it absorbs surplus generation directly, reducing the electricity that would otherwise be exported at the lower Smart Export Guarantee rate. In this scenario, the EV can significantly reduce the financial case for a separate battery, because the car itself is acting as a large storage device during daylight hours.
This optimiser models the annual cost of home versus public charging for your mileage and vehicle, the saving from a time-of-use tariff with a low overnight rate, the contribution a solar system can make to EV charging demand, and whether adding an EV changes the optimal battery size for your solar installation. It also shows the home charger payback period, which for most drivers is under twelve months. All figures are illustrative. Squared Money is an introducer, not a lender or energy adviser.
At a Glance
- The home charger payback period is usually under a year. The annual saving from charging at home versus at public fast chargers typically exceeds £600 to £1,200 for drivers covering 7,000 to 12,000 miles per year. After the OZEV grant, a 7kW wallbox typically costs £500 to £900 installed. The optimiser calculates your payback precisely: the EV home charging optimiser.
- A time-of-use tariff with a low overnight rate can double the saving. Charging at 8p to 12p per kWh overnight rather than 24p more than halves the home charging cost and significantly increases the annual saving versus public charging. The saving over 8,000 miles can exceed £1,200 per year on a good overnight tariff.
- Day charging via solar divert typically covers 25% to 40% of EV demand. If the car is plugged in at home during the day and a solar divert system is fitted, surplus solar generation charges the car before being exported. This is free electricity that would otherwise earn only the SEG export rate: the EV home charging optimiser.
- Adding an EV can reduce the financial case for a separate battery. When the car charges from solar surplus during the day, it absorbs much of the excess generation a battery would otherwise need to capture. The optimiser shows whether a battery remains financially justified once the EV is factored in.
- The OZEV grant provides £350 toward home charger installation for eligible households. The grant is available for flats and for properties where the applicant can demonstrate they will use the charger at their home address. It is not available for detached houses under standard terms. Check current eligibility on the OZEV website before factoring it into your budget.
EV home charging optimiser
Model your annual home charging cost, public charging saving, and the financial case for a home charger. Add solar and battery details to see how an EV changes your energy system economics. All figures are illustrative.
Your electric vehicle
Efficiency: typical EVs achieve 2.8-3.5 mi/kWh in UK conditions. Larger SUVs sit toward the lower end; smaller hatchbacks toward the upper. Check your vehicle specification or real-world data. Public charging rate: slow/destination chargers are typically 40-60p/kWh; fast AC chargers 50-70p/kWh; rapid DC chargers 70-99p/kWh. Enter your typical blended rate.
Home charging
Home charger installation
OZEV grant applies (-£350)
Available for flats and some rental properties. Check current eligibility on gov.uk/electric-vehicle-chargepoint-grant.
Solar system (optional)
Understanding EV Charging Modes
Standard home charging
Charging at the standard unit rate, any time
The simplest approach: plug in when you arrive home and charge at your standard unit rate. A 7kW wallbox fully charges most EVs overnight. The saving versus public charging is significant: at 24p per kWh home versus 65p public, every 100 miles costs around £7 at home versus £19 at a fast public charger. No tariff change is needed. The wallbox is for convenience and speed of charge, not because it is required for home charging.
Time-of-use overnight tariff
Charging at a low off-peak rate overnight
Several electricity suppliers offer tariffs with a low overnight rate, typically between 7p and 15p per kWh, specifically designed for EV charging. The EV is set to charge during the cheap hours (usually midnight to 6am). The saving versus the standard unit rate is substantial: at 10p per kWh overnight versus 24p, the EV charging cost halves. These tariffs typically apply a higher rate during peak hours in exchange, so overall benefit depends on your household’s daytime electricity usage pattern.
Solar divert charging
Charging from surplus solar generation during the day
A solar divert device detects when the solar system is generating more electricity than the household is using and automatically starts charging the EV from the surplus. The electricity is free: it would otherwise be exported at the Smart Export Guarantee rate. Solar divert devices typically cost £250 to £500 fitted and are compatible with most wallboxes. The EV needs to be plugged in and available during daylight hours for this to work, making it most suitable for households where a car is at home during the day.
The EV as battery storage
Why day-charging reduces the case for a separate battery
When the EV charges from solar surplus during the day, it absorbs generation that a separate battery would otherwise need to capture. A 60kWh EV battery has far more capacity than any domestic storage battery, so it can absorb substantial surplus without filling. The financial implication is that if you already have an EV charging from solar during the day, the additional saving from a separate battery is smaller, and you may need a smaller battery than a solar-only household of the same profile. The optimiser models this interaction and shows whether a battery remains justified once the EV is factored in.
Related Tools and Guides
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Models the optimal battery size for your solar system without an EV. Use alongside this optimiser to compare the battery financial case with and without the EV’s solar absorption effect.
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Estimates annual generation, bill saving, and SEG income for your solar system based on roof orientation and self-consumption rate. Use this to confirm the system size input for this optimiser.
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Models when cumulative energy savings overtake total loan interest. Use the annual saving figure from this optimiser to model the charger installation payback if financed.
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Home improvement loans for energy efficiency upgrades
Covers all the main energy efficiency improvements including solar panels and battery storage, with loan type guidance. Relevant if you are planning a combined EV charger, solar, and battery installation.
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Checking won’t harm your credit scoreFrequently Asked Questions
Do I need a 7kW wallbox or will a standard socket do?
A standard 3-pin socket charges at around 2.3kW, which adds approximately 8 to 10 miles of range per hour. For a typical EV with a 60kWh battery and a daily commute of 20 to 40 miles, this is often sufficient: 10 hours of overnight charging replaces a full day’s driving. The per-unit electricity cost is identical whether you use a standard socket or a wallbox. The wallbox is primarily a convenience and safety upgrade rather than a cost necessity. The case for a wallbox is strongest for higher-mileage drivers who need to restore significant range overnight, drivers of larger EVs with bigger batteries that take many hours to charge from a standard socket, and households where the main fuse board is some distance from the parking location.
For solar divert charging, a wallbox is required: standard socket chargers do not have the communication capability to integrate with solar divert devices. The solar divert device signals to the wallbox to start or stop charging and to adjust the charge rate based on surplus generation. This means if solar divert charging is your intended approach, the wallbox cost is a prerequisite for the solar saving to materialise.
What is the OZEV grant and do I qualify?
The Office for Zero Emission Vehicles provides a grant of £350 toward the cost of a home EV chargepoint installation for eligible applicants. The grant is available to people living in flats (whether renting or owning) and to people living in rental properties. It is not available to homeowners of detached or semi-detached houses as a standard entitlement, though separate grant schemes exist for landlords installing chargers in rental properties. The grant is applied directly by the OZEV-approved installer and deducted from the installation invoice, so you do not need to apply separately.
Eligibility conditions include: the vehicle must be on the eligible vehicle list, the charger must be installed at the applicant’s home address, and the installer must be OZEV-approved. The scheme terms change periodically, and the most current eligibility criteria and list of approved installers are on the gov.uk electric vehicle chargepoint grant page. If you do not qualify for the OZEV grant, the payback calculation in this optimiser is still typically well under two years for most drivers, so the financial case does not depend on the grant being available.
How much of my EV charging can realistically come from solar?
The proportion depends on how much of the time the car is at home and plugged in during daylight hours, the size of the solar system, and seasonal variation. A household where the car is parked at home all day most of the time, with a 4kWp system generating around 3,700 kWh per year, and where a solar divert is fitted, might realistically cover 25% to 40% of EV charging demand from solar. A household where the car is only at home overnight covers close to zero from solar without a battery to bridge the generation to the evening charge.
The optimiser uses a conservative 30% capture rate for day-charging households, which assumes the car is available to charge for roughly a third of the solar generation hours on average across the year. This figure varies by season: in summer the car may cover a higher proportion because generation is higher; in winter very little solar will be available regardless. The monthly profile section in the solar battery size calculator shows this seasonal variation in more detail for households also considering battery storage.
Should I get solar, a battery, and an EV charger at the same time?
Combining all three in a single installation has practical advantages: the installer can optimise the system as a whole, cabling and inverter sizing can be planned together, and there is usually a cost saving versus three separate installations. The financial case for combining them depends on each element individually. The solar case is assessed in the solar panel savings calculator. The battery case, once the EV’s daytime absorption effect is accounted for, may support a smaller battery than a solar-only household. The charger case is almost always strong for regular drivers. The combined installation does not guarantee the best outcome for each component individually.
The most important sequencing consideration is that if you are planning a time-of-use tariff for overnight EV charging, the tariff terms need to be compatible with both the EV charger’s smart scheduling and any battery storage system. Some time-of-use tariffs allow both the EV and the battery to charge at the overnight rate; others restrict overnight cheap charging to one device. Confirm the tariff compatibility before choosing your installation and battery specification. Our guide to home improvement loans for energy efficiency upgrades covers the loan options for combined solar, battery, and charger installations.
Squaring Up
The home charger payback case is one of the clearest in the home improvement space: the annual saving versus public charging is large relative to the installation cost, and the payback is typically measured in months rather than years. The more interesting question is how the charger interacts with solar and battery storage. Day charging via solar divert is the most financially efficient EV charging approach, but it changes the economics of battery storage by reducing the surplus available to store. The optimiser shows the combined picture rather than evaluating each element in isolation.
The time-of-use tariff case is compelling for night-charging households and is sometimes overlooked. The difference between 24p and 10p per kWh across an EV’s annual consumption is worth several hundred pounds per year with no capital cost beyond switching tariffs. For households not on a time-of-use tariff, this is often the highest-return first step before any hardware investment.
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Checking won’t harm your credit score Check eligibilityThis tool is for illustrative purposes only and does not constitute financial or energy advice. All charging cost estimates are based on illustrative rates and will differ from actual costs, which depend on your tariff, vehicle, usage pattern, and driving conditions. Vehicle efficiency figures are illustrative: check your vehicle specification for actual energy consumption. OZEV grant eligibility conditions change over time: verify current terms on gov.uk. Solar contribution estimates assume a conservative 30% daytime capture rate for households with a solar divert device and are illustrative only. Your home may be at risk if you do not keep up repayments on a secured loan.
