If you have solar panels and an electric car, you’ve probably thought about charging from your own generation rather than the grid. Solar diversion is how you make that happen automatically — without watching the app and running out to plug in at exactly the right moment.
What solar diversion is
When your solar panels are producing more than your home is using, that surplus would normally go back to the grid. Depending on your export arrangement, you might receive a few pence per kilowatt-hour for it through the Smart Export Guarantee — but that’s a fraction of what you’d pay to import the same unit later in the day.
Solar diversion redirects that surplus into your EV instead. The charger monitors what the panels are generating and what the house is consuming in real time, then adjusts its output so it only draws on what’s left over. If generation drops — cloud passing over, for instance — the charger backs off. When the sun returns, it ramps back up. The house always takes priority; the car gets whatever remains.
How it works in practice
The charger uses a CT (current transformer) clamp on the incoming supply cable to monitor the flow of electricity in and out of the property at any given moment. When there’s more generation than demand — when the property is exporting — the charger ramps up to absorb that surplus. The aim is to keep grid import and export as close to zero as possible.
The myenergi Zappi is the charger most associated with this kind of diversion. Its “eco” and “eco+” modes work exactly this way, and it can receive CT clamp data wirelessly via the myenergi Harvi if running a cable between the meter and charger isn’t practical. Other chargers with solar diversion capability include the Ohme and certain Hypervolt models. The details of how each manages the control logic differ, but the underlying principle is the same.
The limitation worth knowing about
Most home EV chargers have a minimum charge rate. The Zappi, for example, won’t charge below 1.4kW — so if your solar surplus is less than that at any given moment, diversion won’t engage. On a partly cloudy day, or with a smaller solar array, there may be periods where the generation is there but not quite enough to trigger charging. It’s not a flaw in the technology — it’s a constraint of how AC charging works — but it’s useful to know if you’re expecting to charge solely from solar on overcast days.
Does diversion replace a smart tariff?
Not necessarily, and you don’t have to choose between them. The most effective setups combine both: divert surplus solar into the car during the day, then top up overnight with cheap grid electricity via a tariff like Octopus Go if the car still needs more. The Zappi handles this well, with separate modes for eco diversion and scheduled charging.
If you have a battery as well, it’s worth thinking through whether surplus solar should go to the car or the battery first — the answer depends on your usage patterns and how the system is wired. We covered the CT clamp placement detail that affects this in our guide to wiring EV chargers and battery systems.
If you’re in Bristol or South Gloucestershire and want to add solar diversion to an existing setup — or include it in a new installation — get in touch.
