The car leaves on a longer journey tomorrow morning. It is at home this afternoon, when the solar panels may generate, and your contract may offer a cheaper grid period later. At first the choice looks simple: use as much solar generation as possible.
Add one more figure: what would that energy be worth if exported instead? You can then compare using your own electricity during the day with buying from the grid later. The morning departure sets the deadline.
A daily decision needs two prices
For grid charging, consider what you pay. For solar surplus, consider what you give up by putting it into the car. If export would earn revenue, using the energy on site forgoes that amount.
This is not a separate bill item but part of the comparison. It avoids treating the same solar energy as both free charging and expected export income.
A full return-on-investment calculation for solar needs far more data. Here we consider only one day's surplus from an existing system. Your own contract determines whether import and export can be compared this way.
The task: 30 kWh by morning
In our example, the charger needs to deliver 30 kWh before departure. We assume 18 kWh of usable solar surplus in the afternoon, with the car plugged in and able to accept it.
Every price is invented: export is valued at 12 Ft/kWh, late-evening grid energy at 58 Ft/kWh and a cheaper night period at 28 Ft/kWh. The example treats purchase and export value separately; it is not a Hungarian settlement method or current offer.
| Daily charging plan | Grid purchase | Foregone export income | Combined comparison value |
|---|---|---|---|
| All 30 kWh late evening | 1740 Ft | 0 Ft | 1740 Ft |
| All 30 kWh overnight | 840 Ft | 0 Ft | 840 Ft |
| 18 kWh solar, 12 kWh overnight | 336 Ft | 216 Ft | 552 Ft |
In the mixed plan, 12 kWh from the grid costs 336 Ft and using the solar energy for the car forgoes 216 Ft of export income. Together that is 552 Ft: under our assumptions, 288 Ft less than the all-night figure of 840 Ft.
What does this mean on a real day?
In the example, it makes sense to use the daytime surplus and leave only 12 kWh for the cheaper night period. The required energy then comes partly from solar and partly from the grid.
The order can change. If night energy were 8 Ft/kWh, 30 kWh from the grid would cost 240 Ft. Using 18 kWh during the day and buying 12 kWh overnight would represent 216 + 96, or 312 Ft, in the comparison.
In that second example, exporting by day and charging from the grid at night is cheaper. The real prices decide; other household energy needs may also affect the choice.
Charging must finish by morning
Forecast generation only becomes charging if the car actually accepts it. If only 10 kWh rather than 18 kWh reaches the charger, another 20 kWh remains.
At a constant 7 kW, that takes nearly 2 hours 52 minutes. A two-hour overnight window is too short, so expand the plan in time. Always calculate the real charging time alongside the expected cheap period.
The calculations use energy delivered through the charger. How much reaches the battery, and whether it produces the desired departure level, also depends on the car.
Zaptec can be part of the coordinated system
With documented Go and Go 2 solar integrations, a suitable external controller can regulate charging. API current control requires an online installation in Default Charging mode. See the manufacturer's integration guide.
As at 14 September 2026, Hungary is not on the list of countries supported by Zaptec's factory Sense-based solar mode. A Hungarian system needs an external energy manager that is actually supported, including its measurement connection. The factory list is on the Zaptec Sense page.
When configuring automation, establish what calculates prices, what monitors household capacity and what sets charging current. Test the chosen operation while also checking that the required energy will be ready by morning.
Make one concrete daily plan
Choose an upcoming departure. Note the energy needed, expected daytime surplus and the two comparable prices in your contract. In the afternoon, use the charger's measured energy to see what remains.
You will know when solar is worthwhile, how much grid charging to add and how much time to allow.
Let's find a charging solution for your daily energy need
On our contact page, give the car and inverter models and the car's usual daytime parking hours. We can help you review a suitable Zaptec system and integration options.
