Two households have the same size solar installation and similar electric cars. One car is parked at home on weekdays, while the other only returns after work. Although both roofs generate the same amount, the solar energy available for direct EV charging can be very different.
When planning solar charging, a good first step is therefore to place the car's routine alongside the generation curve. This shows which periods you can actually use and where a controller that follows measured surplus could help.
Start with what remains after the home has taken its share
If the solar panels are generating 5 kW at midday, cooking, cooling and every other appliance running at the time also use part of that output. Only what remains is available to the car.
It helps to know both how much energy the home imports from the grid and how much it exports. The inverter display shows generation, but planning a charge also requires you to know how much of that generation remains as surplus for use on site. If the system includes a home battery, it belongs in the same energy balance.
Surplus power, measured in kW, can change from moment to moment. The energy accumulated over time is measured in kWh. Together, the two figures show what charging can deliver.
Three sunny hours, two different routines
Consider a simplified example. The figures are hourly averages treated as constant within each hour; household consumption does not yet include the car.
| Period | Generation | Household use | Remaining surplus |
|---|---|---|---|
| 11:00–12:00 | 4.8 kW | 1.3 kW | 3.5 kW |
| 12:00–13:00 | 5.6 kW | 2.2 kW | 3.4 kW |
| 13:00–14:00 | 4.2 kW | 0.9 kW | 3.3 kW |
Someone in the first household works from home, so the car stays plugged in throughout. If single-phase charging can follow these power levels, a theoretical 10.2 kWh of surplus could pass through the charger to the car.
The second car does not arrive until 13:00. Of the same midday surplus, it can use only the final hour's 3.3 kWh. The two routines therefore produce a difference of 6.9 kWh even though the solar installation has not changed.
In practice, the controller, the car and phase loading may reduce the amount you can use. These figures refer to energy measured at the charger; less may be stored in the battery.
The difference is what still needs to be supplied
Suppose each car needs 18 kWh per day, measured at the charger. After the midday period, the first still needs 7.8 kWh and the second 14.7 kWh. That must come from later solar generation or from the grid.
That is enough information to guide a decision. Surplus tracking can be useful when a car is regularly at home. If it is usually away during the day, a weekend or work-from-home day may be the better opportunity to match charging to solar surplus.
Annual solar generation alone cannot tell you this. The amount you can use directly on any given day depends on whether the car is at home when surplus really exists.
A schedule is simple; surplus tracking adapts
The Zaptec app lets you set a start and end time for charging, so you can charge during a known daytime window. The manufacturer's scheduling guide explains the steps.
A fixed schedule, however, knows nothing about passing clouds or the next peak in kitchen demand. Charging that follows surplus needs three things: measurement data, a controller that can interpret it and a controllable charger. The system can then adjust the power drawn as the day changes.
During the first hour of our example, from 11:00 to 12:00, charging continuously at 7.4 kW would draw 7.4 kWh. With only 3.5 kWh of surplus available, another 3.9 kWh would have to come from the grid. Simply charging during daylight does not determine how much of the energy is your own solar generation.
Choose a specific control solution for your Zaptec system
Zaptec describes API and OCPP connections for solar integration with Go and Go 2. External control can manage the charger through these software interfaces. Current control through the API requires an online installation operating in Default Charging mode. The Zaptec integration guide sets out the prerequisites.
For example, evcc offers a documented external connection for Zaptec Go and requires a sponsor token. The evcc Zaptec Go documentation is a useful setup reference. The selected meter, permissions and control tasks must be checked as parts of the complete system.
As at 14 September 2026, Hungary is not included among the countries supported by the factory solar mode in Zaptec Sense. In Hungary, planning should therefore be based on an integration that can actually be implemented. You can check support on the Sense country list.
Find a daytime window you can genuinely use
Choose a day when the car will definitely remain at home. Compare generation and household consumption over the same period, then set out how much energy you need before departure.
This will show whether a simple daytime schedule is enough or whether you would prefer automatic tracking of changing surplus. It will also reveal how much grid energy is still needed.
Choose a charger around your solar installation and routine
On our contact page, tell us the inverter and car models and when the car is normally parked at home. We can then help you choose the Zaptec model and integration you need.
