If you have solar panels and want to make better use of your surplus generation, you have two main routes: a traditional solar diverter (which redirects excess electricity into a hot water cylinder or other load) or a solar-compatible smart EV charger (which puts surplus directly into your car). Both solve the same fundamental problem — stopping surplus from being exported at a low rate — but they do very different things with it. This guide explains which option makes more sense for EV owners.
Key Takeaways
- A traditional solar diverter (such as the myenergi eddi) diverts surplus electricity to heat water or other resistive loads. It does not charge your EV.
- A solar-compatible smart EV charger (such as the myenergi Zappi) diverts surplus directly into your car’s battery instead.
- For EV owners, a solar-compatible charger is almost always more valuable than a hot water diverter — you get transport fuel from free solar generation.
- The Zappi’s ECO+ mode charges your EV from solar surplus only, automatically adjusting the rate as generation varies.
- The Zappi costs £200–£400 more than a standard smart charger — typically recouped within 12–18 months for solar households.
- Both devices can coexist in the myenergi ecosystem, serving different loads simultaneously.
What is a solar diverter?
A solar diverter monitors your property’s electricity flow and detects when you are generating more than you are using. Instead of allowing that surplus to export to the grid at the Smart Export Guarantee rate (often 5–15p/kWh), it redirects the excess to an immersion heater, underfloor heating coil, or other resistive load.
The most widely known solar diverter in the UK is the myenergi eddi, which is designed specifically to divert surplus into a hot water cylinder. The principle is simple: rather than heating water with a gas boiler or grid electricity, you heat it for free using otherwise-wasted solar.
Limitations of a traditional solar diverter for EV owners
A hot water diverter has a ceiling. Once your hot water tank is fully heated, surplus generation has nowhere to go and is exported. For an EV driver, this ceiling is reached quickly on a sunny day, and the surplus energy that could have added 20–30 miles of range disappears at grid export rates instead.
What is a solar-compatible smart EV charger?
A solar-compatible EV charger does the same thing as a solar diverter, but the load is your EV’s battery rather than a water cylinder. The charger monitors your solar generation and grid import/export balance in real time, and adjusts the charging rate to match available surplus.
The myenergi Zappi is the dominant product in this category in the UK. It operates in three modes:
| Mode | Behaviour |
|---|---|
| ECO+ | Charges from solar surplus only. Pauses automatically when surplus drops below the minimum 6A (1.4kW). Car charges only when the sun is generating enough. |
| ECO | Charges from surplus supplemented by a minimum grid draw of 6A. Ensures constant charging even on patchy days. |
| FAST | Charges at full rated speed (7.4kW) from the grid, regardless of solar output. Useful when you need range quickly. |
In ECO+ mode, the Zappi is effectively a solar diverter for your car. It steps the charge rate up and down in real time as cloud cover comes and goes, using every available unit of surplus generation.
The key comparison: hot water vs EV range
The financial case for directing surplus into your car rather than your hot water cylinder depends on which is more valuable to you. A rough comparison:
- Water heating via diverter: displaces approximately 0.2–0.3 kWh of gas or electric heating per litre of hot water heated. Roughly 1–2p per kWh of gas displaced.
- EV charging via Zappi ECO+: displaces grid electricity at your import rate (typically 20–35p/kWh in 2026). Each kWh of solar put into your car avoids buying grid electricity at full price.
For EV owners on grid electricity at current rates, every unit of solar diverted into the car is worth three to five times more than the same unit used to heat water. The car wins financially, almost every time.
Can you have both?
Yes. In the myenergi ecosystem, a Zappi (EV charger) and an eddi (hot water diverter) can operate simultaneously, with a priority hierarchy set in the myenergi app. You can configure the system to:
- Fill the EV first (highest priority)
- Then heat water if surplus remains
- Export anything left over at the Smart Export Guarantee rate
This setup maximises the value of every unit you generate without any manual intervention.
What if I don’t have a Zappi?
The Zappi is the most capable standalone solar-diverting EV charger in the UK, but it is not the only option. The Ohme Home Pro can also respond to solar signals via its smart scheduling features, though it works differently — it integrates with tariff data and solar output information rather than using CT clamps to divert surplus directly.
For most solar EV charging use cases, the Zappi remains the most direct, hardware-level solution. The solar charger comparison at BestChargers includes current pricing and a side-by-side of the main compatible models.
Cost comparison
| Product | Typical installed cost | Primary function |
|---|---|---|
| Standard smart EV charger (e.g. Pod Point Solo 3S) | ~£800 | Smart grid charging only |
| myenergi Zappi (7.4kW) | ~£950–£1,200 | Solar diversion + smart grid charging |
| myenergi eddi (hot water diverter) | ~£400–£600 installed | Hot water diversion from solar surplus |
| Zappi + eddi combined | ~£1,350–£1,700 installed | EV + hot water diversion |
For a solar EV owner, paying the premium for a Zappi over a standard charger is generally worthwhile. The payback on the price difference (roughly £200–£400 extra) comes from avoided grid electricity imports — at 25–30p/kWh, even 1,000 kWh of extra solar self-consumption per year covers the premium in one to two years.
Frequently Asked Questions
Do I need a solar diverter if I have a Zappi? Not necessarily for EV charging — the Zappi handles surplus diversion to your car. However, if you also want to heat hot water from surplus solar on days when your car is already charged, an eddi diverter running alongside the Zappi makes sense. The two can run together with priority settings in the myenergi app.
Does the Zappi work without solar panels? Yes. Without solar, the Zappi works as a standard smart home EV charger — scheduling charging to off-peak tariff hours and allowing remote control via the app. The solar diversion features only activate when CT clamps detect a solar generation signal.
Can any EV use a Zappi for solar charging? Yes. The Zappi is compatible with all EVs that can charge from a Type 2 outlet (the standard for home charging in the UK). The car simply accepts charge as it would from any other charger; the Zappi controls the rate from the supply side based on solar surplus.