EV Charging · Smart charging
Combining a home battery with Smappee smart charging can boost your self-sufficiency and make better use of your own solar power. But there's one thing to watch out for: your battery system usually has its own software trying to keep grid import/export close to zero, and Smappee's Solar charging (previously called "Surplus only") tries to do exactly the same thing. If both systems are reacting to the same signal at the same time, they can work against each other.
What you need to do about this depends on how your battery is connected:
- Hybrid system: the battery and solar panels share one inverter. Usually the case when the battery was installed together with the panels.
- Stand-alone system: the battery has its own separate inverter. Usually the case when a battery is retrofitted onto an existing solar installation.
Not sure which one you have? Your installer sets this during installation, but it can also be checked or changed afterwards (see below).
Hybrid inverter (one shared inverter)
Smappee can only measure AC current. Since the battery and solar panels share one inverter, we only see the combined current after the inverter, the sum of battery output and solar output. It's not possible for our measurement to tell the two apart.
With the flag enabled, when charging on Solar charging (Grid support at 0A), the EV will only start charging once the home battery is full, and will stop again once the solar panels no longer produce enough surplus. With any other charging mode, the battery is free to provide (part of) the charging power, just like it would for any other appliance in the house.
How does this work? (technical background)
Normally, Solar charging tries to keep grid power as close to zero as possible. With the flag enabled, a small amount of export (around 200W) is allowed instead. If that power is actually coming from the battery, the battery's own controller sees this export and reduces its output in response. This continues until the battery isn't contributing power anymore, so the EV ends up charging purely from solar surplus.
Your installer sets this flag during installation, but you can also check or change it afterwards in the app:
- Go to Settings > Smappee monitors
- Tap your energy monitor > Circuit configuration
- Tap Solar
- Toggle "Hybrid solar inverter" on or off (below the "Solar export" field)
Stand-alone inverter (retrofit, separate inverter)
If your battery has its own inverter, separate from the solar inverter, Smappee can measure the battery's output on its own. We highly recommend setting this up.
- Attach a CT clamp or Solid Core to the battery inverter's cable. Make sure the arrow on the CT (K → L) points towards the grid, a reversed CT gives you backwards readings.
- In the Smappee app, configure this circuit as a submeter of type Storage ("the energy that is stored in a battery").
Once set up: battery charging shows as a negative value, battery discharging shows as a positive value. You'll be able to see power going in and out of the battery at all times, and your calculated consumption is corrected so that charging the battery is no longer counted as household consumption.
Want the EV to be charged before the battery?
By default, solar surplus can go to either the EV or the battery. If you want surplus to go to the EV first, and only the leftover to the battery, ask your installer to change the physical wiring to the topology below, so that surplus is measured as export (and available to Solar charging) before it reaches the battery.
Note: if the charging station is set to Standard Charging (not a smart charging mode), it will still draw power from the battery until it's empty, regardless of this wiring priority.
Checking your grid and solar readings with a battery installed
A battery that's actively charging or discharging keeps shifting the net grid and solar values, which makes it hard to tell if the underlying readings are actually correct. If you need to verify grid or solar measurements on a site with a battery, temporarily switch the battery off first. With the battery out of the picture, the readings stabilise and are much easier to validate. Switch the battery back on once you're done checking.
Common symptoms explained
| What you see | Likely explanation |
|---|---|
| "Always On" consumption shows a negative value | Can be caused by the battery shifting the net baseline. Not a fault by itself. |
| Solar production shows values at night | Hybrid inverter: the reading is battery output, not solar. Expected behaviour, see above. |
| Household consumption looks unexpectedly high | A stand-alone battery that's charging is being counted as consumption, because it isn't configured as a Storage submeter yet (see above). |