What Is a Solar Diverter for EV Charging?

A solar diverter is a device or feature that monitors your home's solar panel output in real time and automatically redirects surplus electricity into your EV's battery rather than letting it export to the grid. Without a diverter, any solar energy your panels generate that your home is not immediately using gets exported at a low export rate, or is simply lost if you are not on an export tariff. With a diverter, that surplus flows into your car instead, effectively giving you some free miles from energy you would otherwise not benefit from. If you have or are considering solar panels and drive an EV, this is one of the most practical ways to link the two systems, and some home chargers like the Zappi (from myenergi) have the feature built in. For more on home charging options and compatible cables, see our EV guides.

How does a solar diverter actually work?

A solar diverter uses a current transformer (CT) clamp fitted to your incoming electricity supply to measure what your home is consuming and what your panels are generating at any given moment. When generation exceeds consumption, there is surplus power that would otherwise flow out to the grid. The diverter detects this surplus and sends it to a connected load, in this case your EV charger, rather than allowing it to export. It does this dynamically, adjusting the charging rate up and down as your solar output fluctuates with cloud cover and time of day. The result is that the car charges at whatever rate the surplus allows, which can range from a trickle on a cloudy day to a steady charge on a bright summer afternoon.

Do all EV chargers support solar diversion?

No. Solar diversion capability is not standard across all home chargers. The most well-known charger with built-in solar diversion is the Zappi by myenergi, which has the feature as a core part of its design and works with any solar installation using a standard CT clamp. Some other chargers can achieve basic solar diversion through integration with a home energy management system, but the depth of integration varies. If solar diversion is important to you, checking that the specific charger supports it natively, or confirming it will integrate with your inverter or energy management platform, is an important step before purchase. Using an untethered charger with solar diversion still means you need your own Type 2 charging cable to connect to the car.

Do you need a battery storage system as well?

No. A solar diverter works independently of a home battery. It simply redirects surplus generation to the car in real time rather than storing it. If you do have a home battery (such as a Tesla Powerwall or a myenergi Libbi), the system can be configured to prioritise charging the home battery first, then the car, or whichever order makes most sense for your usage pattern. Without a home battery, the diverter still makes good use of surplus solar, and for many households the car is the largest flexible load in the home, making it the ideal recipient for that surplus energy. You do not need to invest in a home battery to benefit from solar EV charging.

How much difference does solar diversion make in the UK?

The honest answer is: it depends heavily on your solar array size, how much you drive, and the UK's notoriously variable weather. In summer, a reasonably sized array on a south-facing roof can generate more than a typical household uses during daylight hours, and diverting that surplus to an EV can add meaningful free range over the course of a week. In winter, UK solar generation drops significantly, and the car will rely more heavily on overnight grid charging. Speaking in generalities: if you drive modest daily mileages and have a reasonably sized array, solar diversion is a worthwhile addition to your setup. If you drive very high mileages or have limited south-facing roof space, it supplements but does not replace grid charging. Rather than trusting any specific figures, run the numbers with your actual solar generation data and current tariff to see how it applies to your situation.

Can you retrofit solar diversion to an existing charger?

It depends on the charger. Some chargers can be controlled via an API or integration with a home energy management system, which can approximate solar diversion behaviour. Others have no such capability. If you already have a charger installed and want to add solar diversion, the first step is to check what integrations your existing charger supports. If it cannot support diversion, replacing it with a Zappi or another compatible unit is the most reliable solution. An approved installer can advise on what is and is not possible with your existing setup, and whether any of the cabling or infrastructure from the original installation can be reused, which can reduce the cost of a swap.

Is solar diversion worth it if you are also on an off-peak overnight tariff?

Yes, the two approaches complement each other well. Overnight off-peak charging is excellent for keeping the battery topped up at a predictable low cost, while solar diversion during the day captures surplus generation that would otherwise be of limited value. Many EV owners run a smart charger that does both: scheduled to charge cheaply overnight and set to accept solar surplus during the day. If your tariff has an export rate that is reasonably competitive, you may occasionally choose to export rather than divert, but for most drivers the maths favours sending surplus solar to the car rather than the grid. Your charger's app or your home energy platform should allow you to configure the priority.

Frequently asked questions

Can I use solar diversion with a tethered charger?

Yes. Solar diversion is a function of the charger's control system, not whether the cable is tethered or attached separately. Both tethered and untethered versions of chargers like the Zappi support solar diversion modes. If you choose an untethered charger with solar diversion, you still need a Type 2 cable to connect the car, but the diversion feature works regardless.

Does solar diversion work with all inverter brands?

Solar diversion using a CT clamp works with virtually any inverter, because the clamp measures the property's import and export at the meter rather than reading the inverter directly. Some chargers also offer direct integration with specific inverter brands via Modbus or proprietary protocols for more precise control. Check the compatibility list for your specific charger and inverter if direct integration matters to you.

Will a solar diverter void my EV's warranty?

No. A solar diverter affects how the charger controls the charging rate, not what is happening inside the car's battery. The car simply receives AC power through the standard Type 2 inlet, as it would from any charger. From the vehicle's perspective, solar diversion is indistinguishable from any other AC charging session. EV warranties do not cover damage from using standard AC home chargers, provided they are properly installed.

Can solar diversion charge the car fast enough to be useful on a typical UK day?

On a bright summer day with a moderately sized array, surplus solar can sustain a useful charging rate for several hours. On an overcast day, the rate may be lower or intermittent. The car does not need to charge at full speed to be useful: even a few kilowatt-hours added during the day from surplus solar represents real free range. For most UK drivers with a typical overnight grid top-up as well, solar diversion is a bonus on good days rather than the sole charging strategy.

Is the Zappi the only charger with built-in solar diversion?

Zappi is the most widely known UK home charger with solar diversion built in as a core feature, and it has a strong track record. Other chargers from brands like Wallbox and some other European manufacturers also offer solar diversion modes, though availability in the UK and the depth of the feature varies. If you are comparing options, check the specific charger's documentation rather than assuming solar diversion works the same way across all brands.

What size solar array do I need to make EV solar diversion worthwhile?

There is no single answer, as it depends on your roof, orientation, shading, and how much you drive. A larger array generates more surplus, but even a smaller system will produce some surplus on sunny days that can usefully go to the car. The best approach is to review your actual generation data (or use your installer's modelling tools for a new system) and compare it with your typical daily mileage. Most EV and solar advisers would say that solar diversion becomes increasingly worthwhile as your array size grows relative to your home's daytime consumption.

Ready to set up home charging? If your charger is untethered, you will need a cable for both home and public AC use. Browse our Type 2 charging cables to find the right lead for your car, or use the cable finder on our home page to match by vehicle. Our guides section covers more on home charger choice, smart tariffs, and getting the most out of your EV setup.