Energy storage system in Ruse city

After the installation of the solar power plant in Ruse, our customer decided to increase the level of autonomy of his home by lithium-ion batteries. The idea consists using solar energy not only during the day but also at nighttime.

The second reason for installing the the energy storage system is frequent interruptions and low-voltage mains power, sometimes not more than 190 volts. Therefore, the storage system should be charged not only by the solar power plant, but also by the grid or by a diesel generator, giving users a stable 230 volts.

To solve the problem we have decided to apply Tesvolt storage with the leading solution by balancing of voltages between the cells in each module.

Tesvolt storage units are equipped with Sunny Island battery inverters of varying power. A three-phase network required three such inverters from which we started fitting.

We placed the inverters at a comfortable height, observing the necessary distances to provide effective ventilation. Each of the inverters has a rated output of 6,000 watts.

The battery inverters convert the alternating current from the photovoltaic inverter or that from the external grid into direct current for battery charging. When using the energy already stored, the conversion is opposite from direct current in to alternating. Thus, the battery inverters create their AC power grid.

Sunny Island inverters have been designed for 48 volt power storage configurations, and this implies large system currents. In this case, the maximum DC current for each inverter reaches 140 amps, so we use copper cables with a cross section of 75 mm².

Six such cables from the battery inverters enter in to a DC-swith with fuses and then are connected in parallel to the energy storage system.

Two cables with a cross section of 120 mm² are provided from the DC switch. Thus minimal energy losses at high currents are obtained.

The inverter, which forms the first phase of the alternating current, is set to master in order to synchronize the other two inverters. The «ABC» phase sequence must coincide with that of the external network to ensure overall synchronization.

Then we installed two TS 40 racks and placed in it 16 TESVOLT battery modules with 4.8 kW·h each, thus achieving a total power supply of 76.8 kW·h.

The peak power of the connected photovoltaic system is 21.78 kW. Therefore, ratio of the storage energy capacity to the installed plant capacity we achieved is about 3.5:1.

By using special connector rails, we have connected the battery modules in parallel. The nominal voltage of the entire storage system in this case has a value of safe 48 volt, the same as for each module. The TESVOLT modules also allow serial connection for configuration of high-voltage power storage.

We connected data cables to exchange information between the modules and the control unit. The balance of the voltages between the battery modules and between the cells in each one increases the reliability and service life of the storage system.

Turning on the system — a solemn moment. We close the powerful DC disconnectors and start all devices.

The TESVOLT control unit has completed the self-diagnosis process and has ’seen’ all the battery modules. The charge level (SOC) is 19% and battery health (SOH) is 100%.

One power unit (APU) controls up to 16 rechargeable modules, forming a cluster. The required amount of clusters can be integrated into a multi-cluster storage system.

After starting the system at full power, we carefully checked all modules and connections with a thermal imaging camera. It is essential to make sure that all batteries are at the same temperature and that the contact surfaces are not overheated.

The thermal imaging process is not a problem. All compounds are shown with moderate and uniform heating. Batteries also have the same temperature.

Special software allows remote control of the parameters of both the battery and the individual cells in the module.

A movie about our work

Pictures of the system