In short
- Surplus means export with the battery nearly full; export alone is not enough.
- Values a few seconds old let automations follow clouds; values five minutes old make them switch at the wrong time.
- Add a delay before switching on and a margin before switching off, or the load will flicker.
A typical Growatt hybrid in Load First fills the battery first and exports the rest. On a good day the battery is full early in the afternoon, and from then on every spare kilowatt goes to the grid. If your export tariff is low, using that energy at home is worth much more.
What counts as surplus
Export alone is a misleading signal. In the morning the inverter may export for a moment while the battery is still charging hard. Real surplus is export while the battery is nearly full. A simple rule: grid power negative by more than the load you want to start, and battery state of charge above 95%.
Why speed matters
A passing cloud can cut solar production by half in seconds. With values from the Growatt cloud, several minutes old, an automation keeps a 2 kW water heater running long after the surplus has gone, and you buy that energy from the grid. With values every few seconds, read locally, the automation switches off almost as fast as the cloud arrives.
Three automations that work
| Load | Switch on when | Switch off when |
|---|---|---|
| Water heater (2 kW) | Export above 2 kW for 2 minutes, battery above 95% | Import above 300 W for 1 minute |
| Car charger | Export above 1.4 kW for 3 minutes | Import above 500 W, or battery under 80% |
| Heat pump boost | Export above 1 kW for 5 minutes, battery above 90% | Battery under 85% |
The delay before switching on avoids reacting to a single bright moment. The gap between the on and off thresholds keeps the load from flickering. Start with these numbers and adjust after a week of data.
Order of priority
If you have several loads, start the cheapest to stop first. The water heater can be interrupted without harm; a car charger usually tolerates it too; a heat pump prefers fewer starts. Give each its own threshold, so the second one only starts when the first is already running and export is still there.
The sensors you need
With Growatt Monitor, Home Assistant gets sensor.growatt_monitor_grid_power (negative when exporting), sensor.growatt_monitor_battery_soc and sensor.growatt_monitor_pv_power, refreshed every few seconds on your own network. That is all the automations above require. The box only reads the inverter; your priority settings stay as they are.
Common questions
Can I do this with the Growatt cloud integration?
You can try, but its values are several minutes old. On a cloudy day the loads will run on grid power a good part of the time.
Will this change how my battery charges?
No. In Load First, the battery still charges first. The automations only use what would otherwise be exported.
Do I need a smart relay for the water heater?
Yes, a relay or a smart plug rated for the heater’s power, installed by someone qualified if it is hard-wired.
