Energy storage for stabilising the low-voltage electricity grid
An industrial energy storage facility, a joint project between Tauron Dystrybucja, Apator and the AGH University of Kraków, has been installed in Ochotnica Dolna (Małopolskie Province). The local council, which is also a partner in the project, has for years been working to improve energy security by increasing the share of RES.
Energy storage facilities
Ochotnica Dolna
Over the past few years, photovoltaic installations have been gradually set up across the Ochotnica Dolna municipality, with PV panels being installed on the roofs of detached houses. Currently, almost 35% of buildings across the entire municipality have photovoltaic panels, and the energy they generate is used to meet the energy needs of residents. Ochotnica Dolna has one of the highest densities of prosumer photovoltaic installations in Poland. Because most of these are single-phase installations connected asymmetrically across individual phases, and due to the local grid's characteristics (a lack of large energy consumers and long low-voltage supply lines), RES installations create various power-quality problems for the operator – particularly during generation periods.
The main issues relating to power quality are phase voltage imbalance and voltage levels exceeding permissible limits during energy generation. Voltage surges cause prosumer systems to shut down, which in turn reduces the return on investment. To improve the situation, it is necessary to balance phase voltages and reduce the grid voltage level when it exceeds the permissible value.
The proposed solution to help stabilise the electricity grid is the installation of an energy storage facility in the municipality. Its purpose will be to improve voltage parameters. In addition to Apator and Tauron Dystrybucja, the project was supported by researchers from the AGH University.
Thanks to the energy storage facility's converter application and a custom-developed control algorithm, the storage battery will charge during periods of RES generation – but only from those phases where the voltage exceeds the limit. Subsequently, during the evening peak-demand period and at night, the facility will discharge into the grid, ensuring it is ready to store RES-generated energy the following day.
As part of the project, the energy storage system's operation will be verified in the following modes:
Symmetrisation of phase voltages at the point of connection to the electricity grid (PPE) by transferring active power between individual phases, with a limit on phase power asymmetry dependent on the capacity of the AC/DC converter’s DC circuit
Stabilisation of voltages at the PPE by regulating the active power of battery charging/discharging independently for each phase of the supply voltage
Voltage stabilisation by regulating reactive power with a limitation on asymmetry following the maximum permissible charging/discharging of the battery
Where phase voltages are within standard limits – maintaining the battery charge level within ranges that ensure voltage stabilisation via active power, potentially depending on the time of day (hour)
Compensation of higher current harmonics, taking into account an additional current measurement circuit
Energy storage systems represent a new area of activity within the Apator Group linked to the energy transition. These solutions form an important part of the offering related to environmental protection, sustainability and a modern approach to energy.