Home Battery

Many photovoltaic systems are now combined with a home battery. The battery stores excess solar energy and makes it available again when needed.

evcc has a number of functions to optimize the interaction between the electric car and the home battery. If the battery or hybrid inverter is configured, evcc knows the charge level of the home battery and can take this into account when regulating the charging of the electric car.

Where does the solar energy go first?

Home batteries react very quickly to available surplus and absorb this energy. In the standard case, the home battery would therefore be fully charged first before any free surplus flows into the electric car.

If you have a larger storage unit, it may also make sense to start charging the electric car earlier. You can configure this behavior on the Battery page, which you can open from the navigation bar.

Here you set the charge level up to which the home battery should be charged with priority and from when the electric car can use the surplus. With the lower limit you determine how much energy is reserved for home consumption (1) and in which area the vehicle has priority (2).

Example: You set the limit to 50%. This means that solar energy flows into the home battery first. If the battery reaches a charge level of 50%, charging points that are in Solar mode are released. The charging power is regulated so that the home battery maintains its charge level. If the surplus exceeds the maximum charging power of the battery, the vehicle will be charged before reaching the limit. If no vehicle is connected or fully charged, excess energy continues to flow into the battery.

Battery-supported vehicle charging

In Solar mode, evcc tries to control the charge so that only solar energy is used directly. Discharging the home battery is avoided. With the Battery-supported vehicle charging function, you can explicitly release part of your home battery for charging the electric car.

The upper limit determines which part (3) of the stored energy can flow into the electric car.

Example: You release the area above 75% for Battery-supported charging. Your home battery has already filled up to 100% during the day. You plug in your electric car in Solar mode. In addition to the available surplus, the released upper 25% of the home battery is now also used to charge the electric car. If there is no surplus available and the charge level of the home battery has fallen to 75%, charging is stopped.

This feature is particularly useful if you have a storage unit whose capacity can cover more than your usual household consumption. It then enables you to charge the car in the evenings, for example, when there is little sun left.

Efficiency and conversion losses: Generally, it is recommended to charge the car directly with solar energy if possible. Taking the detour through the home battery always results in conversion losses, which, depending on the system, can amount to 5-10%.

Automatic start

In solar mode, the charging process only starts when there is a surplus available. If you plug in your car when there is no surplus available, the charging process will not start. Not even if there is enough released energy in the home battery.

You can change this behavior with the “start automatically …” option. If you set the value here to ”… when over 90%”, for example, the charging process will start when the home battery has reached this level. As in the previous example, the charging ends when the charge level of the home battery has dropped to the set limit (here 75%).

Battery Boost

Battery boost supports Solar and Min+Solar mode with power from the home battery. In addition to the power available from the photovoltaic system the maximum available power from the home battery is used. To bring the home battery to its maximum output power, a small grid consumption is required.

Activating the boost is a two-step process. First, select a Battery Boost limit in the settings of the charging point. This enables the feature and defines how far the home battery may be drained.

A boost button then appears next to the charging progress indicator of the charging point. Click it to start boosting for the current charging session. The green fill of the button shows how much boost energy is left before the home battery reaches the limit. Clicking the button again stops the boost. It also ends when the car is unplugged or the mode is changed.

Example: This is useful if the car leaves the charging station in near future and there will be an excess of solar power in the upcoming hours. In doing so the energy in the car is maximized, while the home battery will recharge while the car is away.

The above-mentioned priority settings are overridden for this charging session.

Multiple batteries

Of course, you can also configure multiple batteries in evcc. In the user interface, an average charge level is calculated from the respective charge level and the battery capacity. This value is the basis for the control functions described above.

Example: You have a 5 kWh storage unit that is 50% charged. In addition, you have a 10 kWh storage unit with a charge level of 80%. This results in an average value of 70%, since 10.5 kWh (2.5 kWh + 8 kWh) of 15 kWh (5 kWh + 10 kWh) are filled.

You can view the individual charge levels on the Battery page.

Active battery control

The functions described above are compatible with all battery systems. evcc simply adjusts the charging control of the electric car depending on the charge level of the home battery. In some cases, however, this control is not sufficient and it is necessary to control the battery directly. Many newer battery or hybrid inverters offer an interface for this.

Discharge Lock

Scenario 1: You have to go to an appointment spontaneously and want to charge your car quickly. However, you do not want the home battery to be completely discharged as a result.

Scenario 2: You have a dynamic electricity tariff and want to charge your car at night because energy is particularly cheap then. However, the home battery will try to cover the charging demand as long as it has energy left. The cheap night-time electricity is only used once the home battery is empty.

If your system supports active battery control, you can activate the “Prevent discharge in fast mode and planned charging” option on the Battery page. This puts the home battery into a locked state when a fast charging process is active. This can be triggered by fast mode, smart grid charging, charging planning or minimum charging.

The blocking state applies for the period of fast charging. The home battery is not discharged during this time.

Grid Charging

Scenario: You have a dynamic electricity tariff and want to charge your home battery with cheap electricity at night. For example, because the surplus generated during the day is not enough.

Similar to CO₂- and price-optimized charging for vehicles, you can also charge the home battery with cheap electricity. If your inverter supports this function, the Grid charging section appears on the Battery page. You can set a limit here. If the current electricity price falls below this limit, the home battery will be charged from the grid and simultaneously locked to prevent discharging.

Optionally, you can set a maximum charge level up to which the battery is charged from the grid. When the battery reaches this value, grid charging is automatically stopped. The Maximum charge (maxsoc) option can be found in your battery system’s device configuration.

Under PV, Battery, Grid, Meter you can see on the Active battery control tag whether your system supports battery control and if maxsoc is available.