Should I charge my EV at night or at midday when solar output is high?

The deciding factor is storage. Without a home battery, surplus solar generated while the car is away is exported to the grid, often at a relatively low rate, whereas with a battery that surplus is captured and held for when it is needed, including overnight EV charging³. A battery also allows charging on cheap electricity from a supplier, typically on certain tariffs at night or in the middle of the day⁴.

In practice, most households with solar and an EV run a hybrid: direct solar charging whenever the car is home in daylight, and off-peak grid charging for everything else. The sections below set out how each route works, what it costs in terms of foregone export, and how the setup changes between a PV-only home and one with panels plus a battery.

Midday solar charging versus night charging: the short answer

The two options are not competing ways of doing the same thing. Midday charging uses generation the household already owns; night charging buys electricity at a time when it is cheaper. A household with panels and a car at home during the day gets the first for nothing beyond the capital cost of the array. A household with the car away at work all day gets the second, and the solar it generates goes elsewhere.

The Energy Saving Trust's position is that an attractive overnight rate for charging will often be the best option, which reflects the fact that most cars are parked at home overnight and most solar generation happens while they are not². That is a statement about typical patterns, not a rule. Where the car is on the drive at midday, direct solar use avoids a purchase entirely, and no tariff can beat avoiding a purchase.

What complicates the comparison is export. Solar that is not used on site is exported, and the rate paid for export is generally lower than the rate charged for importing at night. That gap is the whole argument for a battery, and it is why the choice between midday and night charging is really a question about whether the household can store what it makes.

Charging from solar at midday: how the power flows

During daylight hours, a solar array first powers the home, then supplies energy to charge the EV, and finally stores any excess in the battery or exports it to the grid for credit⁸. That order matters: the car is third in the queue behind the house and, where fitted, the battery. Solar charging software can be set to charge the EV with 100% solar energy or a mix of solar and grid energy⁹, and a charger can follow the surplus solar power dynamically¹⁰, so a household drawing more than the array is generating is importing the difference, whatever the inverter is doing.

Standard charge points do not manage this. They draw electricity from the home supply without distinguishing between solar-generated power and grid electricity, so a car plugged in at midday will charge at its set rate and pull whatever the panels cannot cover from the grid³. Solar-aware chargers behave differently: they monitor real-time solar electricity production, adjust charging speed accordingly, and switch between solar and grid supply depending on availability³. Some have modes that use only the surplus solar the house is not consuming and would otherwise export¹.

The practical consequence is that midday charging is a variable-rate activity. Output rises and falls with cloud and season, and a charger that follows it will spend part of the session at low power. That is fine for a car parked all afternoon and poor for one that needs a full battery by two o'clock.

Charging at night from a home battery: how it works

At night, a system with storage prioritises stored battery energy to power the home and charge the EV, and if the battery is depleted it switches to grid power⁸. The battery itself can be filled two ways: from surplus solar during the day, or from cheap electricity bought from a supplier, typically on certain tariffs at night or in the middle of the day⁴.

That dual input is what makes the setup flexible. A home battery stores free electricity generated by solar panels during the day so it can be used by the household at night¹¹, and it can also charge at lower electricity prices overnight or at certain times during the day and discharge at peak hours⁹. The same unit therefore serves the summer solar case and the winter tariff case.

The Energy Saving Trust's battery guidance is blunt about the alternative: without storage, unused solar electricity is wasted or exported to the grid, often at a relatively low rate³. A battery converts that low-value export into avoided import, which is worth more. It also opens special export tariffs and lowers EV charging costs when combined with an overnight EV tariff¹⁰.

Why an energy storage system is the deciding factor

Everything above turns on storage. A PV-only household has one lever, which is timing: run the car when the sun is out. A PV-plus-battery household has two, because it can move solar generation from midday to night and can also buy cheap units to top up.

The scale of the difference is set by the export rate against the import rate. Solar exported at a low rate and bought back at a night rate is a loss on every unit; solar stored and discharged into the car is a unit not bought at all. That is the arithmetic behind the Energy Saving Trust's framing of a battery as the thing that captures surplus for overnight EV charging³.

Storage also changes what the car itself is for. A battery storage system allows a household to store extra electricity until it is needed, for example at night or during overcast or rainy weather¹², and solar PV can be paired with battery storage to hold excess electricity for when it is most needed¹³. The household can then choose when to use it, such as during peak hours when supply is expensive¹⁴.

The dependence that remains is on the grid for whatever the array and battery cannot cover, and on the manufacturer for the battery's controls, app and warranty. A battery is a managed product with firmware and a monitoring platform, not a passive tank.

Off-peak night tariffs versus free solar: what each costs you

EV tariffs are typically two-rate tariffs where it is cheaper to use energy at night, so vehicles can be charged more cheaply overnight¹⁵. The windows vary. Economy 7 gives a lower tariff per kWh between the night-time hours of 22:00 and 08:30⁵. Octopus Go, described as the original EV tariff, gives five hours of cheaper energy every night⁶. EV tariffs generally work similarly to domestic Economy 7 tariffs, with a lower unit rate for seven hours during the night¹⁶.

Against that, self-generated solar has no unit price at all. The comparison a household actually faces is between the export rate it gives up by using solar on site and the night rate it would otherwise pay. Where the night rate is low and the export rate is comparable, the gap narrows; where export is paid at a low rate, self-consumption wins clearly.

Economy 10 offers a different shape again: ten set hours of cheaper off-peak electricity, made up of three hours in the afternoon, two in the evening and five through the night¹⁷. That afternoon block is unusual among off-peak products and overlaps with solar generation, which makes it a poor fit for a household already self-consuming at midday and a reasonable one for a household without panels.

Matching your setup to the choice: PV only, PV plus battery

A PV-only household should expect to charge in daylight or not at all on solar. The array requires only daylight, not direct sunlight, to generate electricity¹⁸, so an overcast midday still produces something, but output in winter drops considerably and grid top-ups become more necessary³. In summer, a reasonably sized system can cover a significant portion of a typical household's EV charging needs³. The rest of the year, the car is on the grid.

A PV-plus-battery household can run the same pattern in summer and switch to stored or off-peak power in winter. The battery can be charged with cheap electricity from a supplier, typically on certain tariffs at night or in the middle of the day⁴, which covers the shortfall without any change to the car or the charger.

Two practical points apply to both. First, charging speed: a slow charger will normally fully charge a partly charged car in around four hours¹⁹, while a 3kW, 5kW or 7kW charger generally takes between six and 12 hours to go from 20 to 80 per cent²⁰. Overnight windows are sized for that. Second, smart charge points are pre-set not to charge during peak demand hours, between 8am and 11am and 4pm and 10pm on weekdays⁷, which leaves the solar-rich middle of the day clear for charging.

Where the choice breaks down

Three limits are worth stating plainly. The first is seasonal: winter output falls and grid top-ups become more necessary³, so a solar-only household is a grid household for part of the year whatever its summer performance. The second is timing: solar-aware charging only helps if the car is present, and a standard charger will draw from the grid regardless of what the panels are doing³. The third is control: the battery, the charger and the tariff are all managed products, and the household's independence runs through a manufacturer's app and a supplier's tariff terms.