Utility Grid
Only utility grid permitted as external energy source
The only permitted external energy source in the battery-backup grid is the utility grid. Even when using the Sunny Island, the battery-backup system does not support the operation with a generator (e.g. diesel generator).
Residual-current monitoring unit:
If an external residual-current device is required, install a residual-current device which trips at a residual current of 100 mA or higher (for details on selecting a residual-current device, see the Technical Information "Criteria for Selecting a Residual-Current Device" at www.SMA-Solar.com).
Special conditions for use of the battery-backup grid with Sunny Island in Belgium
The utility grid connected to the automatic transfer switching device must generally be a TN or TT system. In Belgium, the utility grid can be designed to function as an IT system that is, however, grounded to the neutral point of the source.
This results in a hybrid form of an IT and TT system. Compared with a TT system, this hybrid form is not equipped with a neutral conductor. With this installation, the following restriction applies when using the battery-backup system:
- If the utility grid functions as an IT system that is grounded to the neutral point of the source, the connected battery-backup system must be single-phase.
Characteristics of the battery-backup grid
Characteristic | Single-phase battery-backup grid with Sunny Island | Three-phase battery-backup grid with Sunny Island | Three-phase battery-backup grid with Sunny Tripower Smart Energy | Single-phase battery-backup grid with Sunny Boy Smart Energy | Three-phase battery-backup grid with Sunny Boy Smart Energy |
|---|---|---|---|---|---|
Utility grid | TN or TT | TN or TT | TN or TT | TN or TT | TN system |
Single-phase or three-phase | Three-phase | 3-phase | Single-phase | Three-phase | |
Behavior of the battery inverters in the event of grid failure | 1 Sunny Island supplies the battery-backup grid. | Three Sunny Island inverters switched in parallel on the DC side supply each line conductor with the corresponding phase. | Sunny Tripower Smart Energy supplies the battery-backup grid. | Sunny Boy Smart Energy supplies the battery-backup grid. | Sunny Boy Smart Energy supplies the battery-backup grid. |
Recognition of grid failure | Grid failure is only recognized on the line conductor which is connected to the battery inverter (e.g. L1). | Grid failure is recognized on all line conductors. | Grid failure is recognized on all line conductors. | Grid failure is recognized on the connecting phase. | Grid failure is recognized on the connecting phase. |
Supply of the loads in the event of grid failure | All connected single-phase loads are supplied (e.g. the loads connected to L1). | All loads are supplied. | The loads connected to the battery-backup grid are supplied. | All connected loads are supplied. | All connected single-phase loads are supplied. |
Grid feed-in by the PV inverters in the event of grid failure | Only single-phase PV inverters can feed energy into the grid. | Single-phase and three-phase PV inverters can feed energy into the grid. | Only the three-phase Sunny Tripower Smart Energy can provide a grid in the event of a grid failure and feed in. | Only the single-phase Sunny Boy Smart Energy can provide a grid and further single-phase PV or hybrid inverters can feed in additionally. | Only the single-phase Sunny Boy Smart Energy can provide a grid and further single-phase PV or hybrid inverters can feed in additionally. |
Phase coupling in the battery-backup grid | Phase coupling is possible in a three-phase grid. | Phase coupling is not possible. | Phase coupling is not necessary. | Phase coupling is not possible. | Phase coupling is possible. |
Rotating magnetic field in the battery-backup grid | No: even with phase coupling, the battery-backup grid remains single-phase. | Yes: three Sunny Island inverters form a three-phase battery backup grid with rotating magnetic field. | Yes: one Sunny Tripower Smart Energy provides a three-phase battery-backup grid with rotating magnetic field. | No: even with phase coupling, the battery-backup grid remains single-phase. | No: even with phase coupling, the battery-backup grid remains single-phase. |
Phase coupling
If three-phase loads are connected to a single-phase utility grid with phase coupling, SMA Solar Technology AG cannot rule out damage to the three-phase loads. With phase coupling, single-phase loads only must be connected to the battery-backup grid.
Designing the neutral conductor cross-section for the current of the single-phase inverter
To prevent overload of the neutral conductor, the cross-section of the neutral conductor must be designed to match the current of the single-phase inverter.
Battery-backup grid with or without all-pole disconnection
Type of grid disconnection | All-pole disconnection | Non-all-pole disconnection |
|---|---|---|
Operating principle | In the event of grid failure, a tie switch disconnects all line conductors and the neutral conductor from the utility grid. | In the event of grid failure, a tie switch disconnects all line conductors from the utility grid. The neutral conductor of the battery-backup grid remains permanently connected to the utility grid. |
Criterion for use | If the technical connection requirements of the grid operator or the locally applicable standards and directives call for all-pole disconnection, you must install the battery-backup system with all-pole disconnection. | If the technical connection requirements of the grid operator or the locally applicable standards and directives prohibit disconnection of the neutral conductor, you must install the battery-backup system without all-pole disconnection. |