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EV chargingHow solar aware EV charging actually works
Solar aware chargers do something genuinely clever: they watch your meter and match the car's draw to whatever the roof has spare. Here is the mechanism, and the hard floor that stops it working on a dull day.
Updated 4 August 2026 · written by the Clearline guidance team
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The mechanism, in one paragraph
A solar aware charger is fitted with a CT clamp, a sensor that clips around the incoming mains cable and measures the current flowing in or out of your property. That single reading tells the charger whether you are importing electricity from the grid or exporting it. From there the logic is simple: if you are exporting, the roof has spare capacity, so raise the car's charge current. If you are importing, the house needs that power, so back off.
It happens continuously, not once an hour. A cloud passes, the export reading drops, the charge current follows it down within seconds. The kettle goes on, the same thing happens. This is why a solar aware charger and a plain timer charger produce completely different results on the same roof.
The clamp reads the meter tail
A CT clamp on the incoming mains measures total import or export in real time. It does not need to know what your inverter is doing, only what is crossing the meter.
The charger converts surplus into current
Charge current is variable, on the Zappi anywhere from 6A to 32A. The unit translates the available surplus into a current the car will accept.
It tracks generation and consumption together
The target is a net export of roughly zero, so the charger keeps adjusting as the roof and the house both change through the day.
It pauses when there is not enough
Below the protocol minimum the charger cannot deliver anything meaningful, so surplus-only modes stop and wait rather than importing on your behalf.
The 1.4kW floor, and why it matters more than any feature
This is the single most important number in solar charging and it is rarely explained on a product page. The Mode 3 charging protocol has a minimum charge current of 6A, which at 230V works out at about 1.4kW. A car cannot be charged from less surplus than that. There is no trickle setting below it and no way around it, because the limit lives in the standard the car and the charger use to talk to each other.
So on a bright afternoon with 3kW of surplus, a surplus-only mode charges happily. On a grey morning producing 900W of surplus, nothing happens at all. The charger waits. Work it through in miles and the picture sharpens: a 7kW charger adds roughly 25 to 35 miles an hour, so 1.4kW is a fifth of that, which is around 5 to 7 miles of range an hour. Solar-only charging is a slow, patient business, and it suits people who leave the car on the drive during the day.
Solar-only charging suits a car that sits at home
If your car leaves at eight and returns at six, the roof produces its best surplus while the car is somewhere else. In that household the honest answer is an off-peak overnight tariff, with solar charging used at weekends. A charger that does both well is worth more than a charger that does surplus tracking brilliantly and tariffs badly.
The three-mode ladder, and what each mode really does
Most solar aware chargers offer a version of the same three settings. The naming differs, the behaviour does not.
| Behaviour | myenergi Zappi | Hypervolt Home 3 Pro | What happens |
|---|---|---|---|
| Full speed regardless | FAST | Boost | Charges at up to 7.4kW using solar plus imported grid power. Use when you need the car ready. |
| Solar first, topped up | ECO | Eco | Prioritises solar but tops up from the grid to hold the 1.4kW minimum, so charging continues through cloud. |
| Surplus only | ECO+ | Super Eco | Pauses charging when there is too much imported power and resumes only on surplus generation. Nothing comes off the grid. |
Mode names and behaviour from the myenergi Zappi v2.1 datasheet and published Hypervolt reviews, checked August 2026. Ohme markets solar charging as Solar Boost through its own CT and app.
The middle mode is the one most households end up using. It keeps the car charging rather than stopping and starting all afternoon, and it accepts a small amount of grid import as the price of continuity. The surplus-only mode is the purist's setting and it is the right one if your export rate is low and you would rather put every spare kWh into the car.
The export margin, and the fight between your car and your battery
If you have battery storage as well as an EV, both want the same surplus, and left alone they will squabble over it. The battery sees export and starts charging, the car sees the export disappear and backs off, then the battery fills and the export returns, and round it goes.
The fix is an export margin, a setting that tells the charger to wait until it sees a set level of export, say 50W, before it starts. That small buffer stops the charger and the battery chasing the same watt. myenergi states the Zappi works alongside battery storage systems and supports 100% self-generated charging from solar or wind. Getting the priority order right is a commissioning conversation, not a box you tick in an app, and it is worth raising before the kit goes on the wall.
Decide the pecking order first
Most households want the house served first, the battery second and the car third, because the car has all night and a cheap tariff to fall back on. Some want the car first because the battery is small. There is no universal right answer, only the one that matches how you actually use the car.
What you need for any of this to work
- A working solar array. Surplus tracking with no generation is just an expensive timer.
- A CT clamp fitted at the right place. It has to sit on the incoming mains so it sees the whole property, not on a single circuit.
- A charger that supports it. The Zappi ships with a clip-on grid sensor, and the Hypervolt Home 3 Pro includes its solar CT clamp in the box.
- Realistic expectations about the season. The surplus that fills a car in June is not there in December, and any honest model shows you both.
Want to know how many of your miles could realistically come off your own roof? The free remote design call models it against your array, your usage and your driving.
Get your free quote →Solar charging against an off-peak tariff
It is worth being blunt about the competition. Solar surplus is free at the point of use, but a good overnight EV rate is currently very cheap indeed, and the gap between the two is smaller than people assume. Our tariff guidance carries the current windows and rates with the dates they were checked, and charging an EV from your own solar works through the seasonal arithmetic in detail.
The households that do best use both. Solar covers the daytime and the weekends, the off-peak window covers everything else, and the charger switches between them without anyone thinking about it. Every county page on this site carries a local calculator that models the combination for your area, and you can find yours through the coverage map.
Clearline gives independent guidance and does not install. Installations, including CT clamp placement and commissioning, are carried out by an MCS-certified installation team for your area.
Solar charging questions, answered
What is a CT clamp on an EV charger?
It is a current sensor that clips around your incoming mains cable and measures how much electricity is flowing into or out of the property. The charger uses that reading to tell whether you are importing from the grid or exporting surplus solar, then raises or lowers the car's charge current to match. It is the component that makes solar aware charging possible.
Can I charge my car from solar only?
Yes, in surplus-only modes such as the Zappi's ECO+ or the Hypervolt's Super Eco, which pause charging when the house is importing and resume only on surplus generation. The limit is that you need at least about 1.4kW of surplus before anything happens at all. That makes solar-only charging realistic for a car parked at home during the day, and impractical for one that commutes.
Why does my charger stop when the sun goes behind a cloud?
Because the surplus has fallen below the 1.4kW minimum the charging protocol allows. The Mode 3 standard sets a floor of 6A, roughly 1.4kW at 230V, so there is no way to charge more slowly than that. In a solar-first mode the charger tops up from the grid to hold that minimum, and in a surplus-only mode it simply waits.
What does Eco+ mode do on a Zappi?
ECO+ pauses charging when there is too much imported power and resumes only when there is surplus generation, so the car is charged from your own roof rather than the grid. It varies the charge current continuously between 6A and 32A based on the CT clamp reading. It is the setting to use when you want no grid electricity going into the car at all.
Can my EV charger and my home battery share the same solar?
They can, but they need a priority order or they compete for the same surplus and end up cycling each other. An export margin setting, which delays charging until a set level of export such as 50W is seen, stops the charger fighting the battery. myenergi states the Zappi works alongside battery storage systems.
Is solar charging better than a cheap overnight tariff?
Not automatically. Solar surplus costs you nothing at the point of use but is only available in daylight and only in useful quantities on brighter days, whereas off-peak EV rates are available every night regardless of weather. Most households get the best result from both, using solar in the day and the off-peak window at night, which any decent smart charger will manage automatically.
See the numbers next: Tesla Powerwall 3, installed, or what a battery costs.
Figures and specifications in this guide are sourced below and were checked on the date shown. Rates and product specifications change; we confirm the current picture on your free design call.
Sources
- myenergi Zappi v2.1 datasheet Rev 2.1.5, ECO, ECO+ and FAST modes, 6A to 32A variable current, supplied clip-on grid sensor myenergi.com
- myenergi Zappi product page, 100% self-generated charging and compatibility with battery storage myenergi.com
- myenergi support forum, the 1.4kW minimum charge rate and the export margin setting myenergi.info
- Hypervolt Home 3 Pro solar modes, Boost, Eco and Super Eco bestchargers.co.uk
- Hypervolt Home 3 Pro included solar CT clamp teslacharger.co.uk
- Ohme Solar Boost and solar compatible charging via CT and app ohme-ev.com
- 7kW range added per hour, used to derive the miles per hour available at the 1.4kW minimum proev.co.uk
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