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Battery coupling

Solar and battery systems can be wired in two topologies, and Tensor Cloud simulates both. You select the coupling type in the asset settings.

  • AC-coupled: The solar system and the battery each have a dedicated inverter and are connected on the AC side of the site meter. This is the default topology, and the usual choice when a battery is added to an existing solar plant.
  • DC-coupled: The solar system and the battery share a single site inverter and are connected on a common DC bus. This is a common choice for new-build projects.

Differences in the simulation​

  • Charging path: In a DC-coupled plant, solar power charges the battery directly on the DC bus, without passing through an inverter. This includes solar power above the site inverter's capacity, which would otherwise be clipped; the simulation prioritizes this charging path. In an AC-coupled plant, solar power above the solar inverter's capacity is clipped before it reaches the battery and cannot be recovered. Solar power above the meter limit or a curtailment order can still be stored, and the simulation charges from it first. Solar energy is converted twice on its way into the battery.
  • Shared or dedicated inverter: In an AC-coupled plant, the battery has its own inverter, so its full rated power is available whenever there is headroom at the meter. In a DC-coupled plant, solar export, battery discharge, and grid charging all pass through the site inverter and are limited by its capacity and efficiency. Capacity offered to the FCR market is scaled by the site inverter's efficiency, but not limited by its capacity. A DC-coupled battery can also offer FCR in slots with solar generation, using solar to cover the expected FCR discharge; an AC-coupled battery offers FCR only in slots without solar generation.
  • Meaning of battery settings: For an AC-coupled asset, the battery power capacity and roundtrip efficiency are AC-side values that include the battery inverter. For a DC-coupled asset, they are DC-side values: nameplate DC power and cell-only efficiency. Losses in the converter between the battery and the DC bus are not modelled separately. Reusing values from an AC-coupled configuration double-counts inverter losses and overstates the power available to the markets; small differences like these change dispatch decisions in every interval and compound over a multi-decade simulation.

How results are reported​

Each result is reported at the physical point where it occurs:

  • Site meter: values are always AC, measured at the meter, with the same meaning in both topologies.
  • Battery and solar generation: values are measured at the component, DC for a DC-coupled asset and AC for an AC-coupled one. Chart labels indicate AC or DC accordingly.