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DC-coupled battery storage systems
DC power grids in industry are becoming increasingly important, because DC grids can significantly increase energy efficiency and sustainability. In order to make optimum use of these advantages, the grids must be stable and securely supplied. Battery energy storage systems (BESS) make a significant contribution to this.
The challenge
Security of supply in the All Electric Society Factory
As one of the first industrial buildings in Germany, we have equipped our new building in Blomberg – the All Electric Society Factory – with a DC power grid so that we are able to reap its benefits. Naturally, we paid special attention to security of supply, in combination with maximum energy efficiency. Integrating a battery storage system that is connected directly to the DC grid was therefore an obvious decision.
One of the advantages of a DC-coupled BESS is the efficiency compared to conventional AC systems. Since there is no need to convert the direct current (DC) into alternating current (AC) and back again, conversion losses are avoided. This results in more efficient use of the stored energy, maximizes the available power, and makes using battery storage systems in DC grids an attractive option.
Cost-efficient electricity generation from renewable energies also plays a crucial role in the All Electric Society Factory. It offers the opportunity of strategically redesigning their own energy consumption in order to protect themselves against increasing electricity costs and to safeguard supply. Having a battery storage system also gives you the freedom to buy electricity when it is cheap and use it when needed.
Battery storage systems are flexible because they can store and release electrical energy with high power and have response times in the millisecond range. With their modular design, they can be scaled and adapted flexibly – right up to large-format, industrial storage systems. Analysis methods enable precise monitoring and control of the energy content and the performance of the batteries. The acquired data can be used in smart grids to ensure the optimized feed-in, storage, and use of energy. This not only contributes to grid stability, but also enables the more efficient integration of renewable energies.
A DC power grid optimizes the entire energy chain, from generation, through distribution, right through to consumption. Energy storage systems are indispensable here.
Tobias Lüke from Phoenix Contact Power Supplies GmbH and Roman Alberti from Voltfang GmbH
Cooperation as a success factor
Phoenix Contact cooperating with Voltfang
Voltfang GmbH, based in Aachen, Germany, develops methods for recycling e-mobility batteries. Second-life batteries and batteries from overproduction that were designed for e-mobility, usually have a higher load capacity than batteries that have been developed for stationary use. Voltfang takes advantage of this and focuses on reusing high-performance batteries that are designed for high-level cycle stability. With optimized operating strategies and intelligent energy management, the service life of these batteries is maximized and the efficiency for stationary applications is ensured. The Voltfang energy management system in conjunction with PLCnext Technology enables users to install all the application functions such as peak shaving, self-consumption optimization, dynamic electricity tariffs, and flexibility marketing and to optimize the economic operation of their energy systems. In addition, the Aachen-based company focuses on coupling battery storage systems to DC power grids. This laid the foundation for a successful collaboration.
The solution
From the idea to operation in practice: A battery storage system completes the All Electric Society Factory
The result of the collaboration between Phoenix Contact and Voltfang is a solution with a storage capacity of 300 kWh. Voltfang used re-qualified battery modules from electric vehicles for the energy storage system, which is situated in front of the All Electric Society Factory. By extending their useful life in this stationary storage application, these batteries have been given a new lease of life before they have to be recycled. The CHARX DC power module, which provide the 270 kW system with power in both directions of energy flow, are used as the interface between the DC grid and the battery. In addition to control cabinet components such as terminal blocks, safety components, relays, and fuse-links, the 24 V DC auxiliary voltage supply of the Quint series including UPS from Phoenix Contact was installed.
The components are supplied by the battery. As a result, the system has the ability to blackstart the entire DC grid and can therefore also take on the backup power function in the building’s energy system. The system is housed in a 20-foot container and is protected against surge voltages by the products of the VAL MB series from Phoenix Contact. The DC BESS is integrated into the DC grid management system via the PLCnext Technology platform from Phoenix Contact. The Voltfang EMS regulates the parameters for charging and discharging using a simplified control algorithm exclusively via the system voltage of the DC network. This compensates for voltage fluctuations and stabilizes the grid. Depending on the energy application, the higher-level energy management system specifies the characteristic curve that is to be used by the battery energy storage system for the control function. In normal operation, the storage system acts as a grid stabilizer. This system architecture enables error-resistant and scalable operation by minimizing communication between the individual subsystems in the power grid. With this pilot project, the companies have created a modular, scalable, sustainable, and, at the same time, efficient energy storage system, which is already being used in other DC grids in industrial applications on a similar scale due to its higher efficiency and lower material usage compared to AC coupling.
