Battery systems

Energy Management

Energy flow: PV system with battery system

Battery systems can store energy from the PV system, release energy to consumers and - for certain types of battery charging - also absorb energy from the grid. The charge controller, which is based on the following logic or prioritization, controls the energy flows:

  1. Direct consumption
    Consumption is directly covered by PV energy

  2. Battery discharge
    Consumption is covered by the batteries

    1. Up to the power limit of the battery system.
    2. Until the minimum SOC of the batteries is reached.

  3. Mains cover
    Consumption is covered from the grid

  4. Battery charge
    Surplus PV energy is used to charge the battery.

    1. Up to the power limit of the battery system.
    2. Until the maximum SOC of the batteries is reached.

  5. Grid feed-in
    Surplus PV energy is fed into the grid.

  6. Maintenance charge


    Batteries are only charged with energy from the mains if charging methods are used to maintain the batteries (boost, full and equalisation charging) and PV energy is not available in sufficient quantities.

The energy from the PV system, battery system and grid is added up. The producers are therefore also used to cover consumption at the same time, if necessary.

During the day: PV generates more than pulling loads, the battery is not full.

During the day: PV generates more than consumer pull, battery is full

During the day: PV generates less than load pull, battery is not empty.

During the day: PV generates less than load pull, battery is empty

At night: PV produces nothing, consumers pull less than Batt-WR can afford, battery is not empty.

At night: PV produces nothing, consumers pull more than battery WR can achieve, battery is not empty.

At night: PV does not produce anything, pull loads, battery is empty.

Energy from the battery system is never fed into the grid.

Type of coupling

In principle, battery systems can be divided into AC- and DC-coupled topologies.

Battery system in AC coupling

In AC-coupled systems, the PV module and battery components are coupled after the DC/AC inverter. So there is an inverter (DC/AC) for the PV system and a bidirectional inverter (AC/DC and DC/AC) for the batteries. These systems are the most flexible in design, are easy to retrofit into existing systems and may also be able to draw energy from the grid (e.g. for battery maintenance charges).

In DC-coupled systems, the PV module and battery are brought to the same voltage level and connected on the DC side. Two types of wiring are particularly common here:

  • DC generator coupling
    Here the battery system is connected directly into the DC line between the PV generator and the MPP tracker of the PV inverter. The battery system also needs an MPP tracker to process the variable voltage of the PV generator. The advantage is the simple possibility of retrofitting these systems into existing PV systems.

    Battery system with DC generator coupling

  • DC-link coupling
    Here the battery system is connected to the DC link of the PV inverter, i.e. between the MPP tracker (with connected boost converter) and the DC/AC converter stage. This has the advantage that the battery system does not require its own MPP tracker. However, these systems cannot easily be integrated into existing PV systems.

    Battery system in DC-link coupling

Connection to the power grid

In practice, it must be ensured that the connection of the loads, the PV system and the battery system to the various phases of the power grid is such that energy can be exchanged.

In PV*SOL® it is assumed that all consumers, PV and battery inverters are connected properly. Consumers that are not connected to the battery system, e.g. because they are connected on another phase, should also not be simulated. On the consumption side, only the consumption is entered that is to be and can be covered by the PV system and/or the battery system.

See also