The home is already exporting energy, the car is plugged in, yet surplus-led charging is still waiting. Everything appears ready. But charging only starts when sufficient power is available at that moment.
With a small surplus, the number of phases used by the car can be decisive. The same sunny morning may be enough for a properly configured single-phase charge while a three-phase charge does not start at all.
Charging has a lower operating threshold
The charger controls the current the car may draw. Zaptec's guide to multi-charger home installations uses a minimum charging current of 6 A. Check separately what your car and configuration support. The manufacturer's guide provides the starting figures.
At a nominal phase voltage of 230 V, 6 A on one phase is about 1.38 kW. Across three phases at the same current, the total is 4.14 kW.
A 2 kW surplus may therefore be usable in a suitable single-phase system but remains below the three-phase minimum. In practice, starting may require some margin and delay; the charger need not switch on exactly at the theoretical threshold.
The home uses the roof's generation first
If the inverter shows 3 kW of generation while the home consumes 1.8 kW, just 1.2 kW of surplus remains for the car—below the single-phase threshold above.
If household consumption falls to 0.6 kW at the same generation, 2.4 kW remains. Sunshine has not changed, yet the charging opportunity has. Surplus tracking needs measurement that shows the power currently available.
That momentary remainder is what the car sees. Rated system size and annual generation answer other questions; surplus-only charging depends on instantaneous surplus.
Four hours can add up to a useful top-up
In our example, 1.5, 2, 3 and 2.5 kW remain after household use in four consecutive hours. Each hourly power value is treated as constant and the car stays plugged in.
| Hour | Surplus | Theoretical single-phase minimum: 1.38 kW | Theoretical three-phase minimum: 4.14 kW |
|---|---|---|---|
| First | 1.5 kW | Met | Not met |
| Second | 2 kW | Met | Not met |
| Third | 3 kW | Met | Not met |
| Fourth | 2.5 kW | Met | Not met |
The four hours contain 9 kWh of surplus in total. A suitably configured single-phase charge operating within the right current range could use energy from it. On three phases at equal current, surplus-only charging would not reach the theoretical minimum in any hour.
If the daily target is 8 kWh measured at the charger, the morning could theoretically cover it. Current steps, start delay, phase loading and the car's response all affect reality. The 9 kWh is an opportunity, not a guarantee.
Lower power has a useful role
The lower threshold helps when the car can wait and you want to use your own surplus. Several lower-power hours can still accumulate energy that matters for everyday journeys.
If departure is near, different operation may be needed. A controller that allows the grid to supply the shortfall can help. With 1 kW surplus, for example, reaching the theoretical 1.38 kW minimum would require 0.38 kW from the grid.
The question in both cases is the energy required within the available time and how much may come from the grid. Configure charging around that objective.
Plan Go 2 phase switching as part of the whole system
Go 2 phase switching requires a three-phase connection, an installation configured as three-phase, an online connection and suitable Zaptec control. It does not work in Standalone mode or with native OCPP authentication. Single-phase mode uses the phase connected to L1; switching back depends on the car. The Go 2 phase-switching guide explains the details. OCPP is a communications standard between a charger and external management system.
The desired operation needs both surplus measurement and the right phase count. Zaptec documents an external solar integration, but Hungary is not on the current country list for the factory Sense solar mode. Check the integration description and Sense country list.
Set start and stop conditions so operation remains predictable through brief fluctuations. A multi-hour trial reveals more than a momentary display.
Start with data from one morning
Choose a period when the car is at home and surplus often lies between 1.5 and 3 kW. Note the exact car and charger models, connection phase count and energy needed before departure.
A survey can then assess what lower-power hours could deliver and the measurement or control required. Your generation curve becomes the basis for the decision.
Put smaller amounts of surplus to work too
On our contact page, give the exact car and charger models and typical daytime surplus. We can help find the Zaptec solution that fits your system.
