An ideal combination: high-power and high-energy
- Highly flexible management of wind power
- Expansion of existing community wind farm project
- Hybrid system combines lithium-ion and vanadium redox flow batteries
- Rapid availability and long-term storage
While debate rages in Germany about reorganizing the country's transition to alternative forms of energy, an energy storage project on the North Sea coast is quietly setting new standards. A flexible Bosch hybrid battery stores wind power when grids are overloaded. It is one of the largest of its kind in Europe.
The best of both worlds: from mid-July, a custom-made hybrid system comprising two high-performance battery types will be saving the electricity generated at a community wind farm in the municipality of Braderup, in the far north of Germany. For this project, Bosch will be supplying a compound battery made up of lithium-ion and vanadium redox flow components, along with the controls for the complete system. This compound battery stores electrical energy when the power grids on the windy coast are overloaded and cannot transport any more electricity. "With this concept, we are expanding the range of possible applications for our storage systems," says Cordelia Thielitz, who heads the stationary storage business area at Bosch. "What's more, storage systems of this kind make it possible to cut back on the expansion of power grids, which has been the source of conflict in many places."
Making wind power available, whatever the weather
As advanced as this new concept is, the purpose of the storage system remains exactly the same as ever: it should be possible to feed wind power into the grid at all times – regardless of whether gales are battering the coast or there is scarcely a puff of breeze. If too much wind power is being generated, the hybrid storage system absorbs the excess and feeds it into the grid later. This means that renewable energy sources, which are subject to strong fluctuations in supply, can be integrated more effectively into the existing power grid. Until now, it has sometimes been necessary to turn turbines out of the wind when grids are overloaded.
Double battery in Braderup
The wind blows irregularly over the village of Braderup in northern Germany. Sometimes there are squalls, and sometimes the wind is weaker, but more constant. To store the electricity generated in both cases, the system uses two different batteries.
One is a lithium-ion energy storage unit with a capacity of two megawatt hours and an output of two megawatts. Bosch buys the lithium ion batteries from the Japanese manufacturer Sony.
The other is a vanadium redox flow battery with a capacity of one megawatt hour and a peak output of 325 kilowatts. Bosch buys the vanadium redox flow battery from the Nuremberg-based Vanadis Power GmbH. In this area, Bosch cooperates closely with Vanadis's affiliate in the United States, UniEnergy Technologies.
Bosch designs and supplies the complete system, and operates it using its specially developed electronic controls and the corresponding software. The wind farm and battery are connected to the power grid run by Schleswig-Holstein Netz AG. The required 10-kilometer underground cable has already been laid.
200 private investors as clients
The client for the battery project is Energiespeicher Nord GmbH & Co. KG, a joint venture founded in 2013 by Robert Bosch GmbH and the community wind farm Braderup-Tinningstedt GmbH & Co. KG. The community wind farm has 200 private investors, and its six wind turbines were put up at the turn of the year. The flat region on the North Sea coast is one of the windiest in Germany. "We combine the strong points of the two battery types and put them to use for our needs," says Jan Martin Hansen, one of the two general managers of Energiespeicher Nord GmbH & Co. KG. "Depending on wind strength and state of charge, the electronics allocate the power being generated to the battery type that is best suited to the task." Hansen also called on the German government to change the legal framework conditions to make innovative battery storage systems a viable prospect.
The other general manager is Bosch's Cordelia Thielitz, who explains the joint venture's approach as follows: "Lithium-ion batteries are sometimes called "high-power batteries" because of their ability to absorb and release large amounts of electrical energy over a short period of time, while vanadium redox flow, or "high-energy" batteries store large amounts of energy very efficiently over long periods of time. We use both technologies in a roughly equal share in Braderup. The resulting storage facility is an important milestone on the road to the renewable energy supply of the future. We want to demonstrate that wind-turbine power generation does not have to be shut down when the grid is overloaded. This advance brings the goal of a renewable, efficient, and more distributed energy system several steps closer."
Total peak output: 2,325 kilowatts
The storage facility, which is to be situated on former farmland, has a total output of 2,325 kilowatts and a total capacity of 3,000 kilowatt hours. "Arithmetically, that is enough to cover the electricity needs of 40 average single-family homes for seven days and nights," says Johannes Kostka, the Bosch associate who is the project's commercial manager. The vanadium redox flow battery will be installed in a building measuring 150 square meters, while the lithium-ion batteries are housed in large steel containers covering an area of around 350 square meters. The total area of the installation, including building services and parking spaces, is approximately 2,500 square meters. The double battery at Braderup is one of the largest of its kind in Europe.
Offering flexibility
As a leading global supplier of technology and services, Bosch is responsible for developing the control electronics, looking after system integration, and testing different operating variants in Braderup. This includes marketing the batteries in the frequency regulation market, taking part of the energy and using it for the wind farm's own consumption, trading on the electricity exchange, and stabilizing the power grid. "The hybrid storage facility is very flexible," says Felix Maus, technical project manager at Bosch. "On the one hand, it stores electricity for use or sale. On the other, it can balance out short-term fluctuations in demand or energy production in order to keep the power grid stable. Remember that production and demand must be in equilibrium at all times. Another problem in the power grid is voltage fluctuations, which can damage grid installations. To prevent this, the storage facility's power electronics are capable of feeding so-called reactive power into the grid."
Jan Martin Hansen adds: "When the battery is installed, we can supply renewable energy even when the wind is not blowing. Having solved this major problem, our community wind farm will become a reliable partner that can deliver a continuous supply of renewably generated electricity."
Background information 1: Overburdened power grids and climate protection
When Energiespeicher Nord GmbH & Co. KG was founded in 2013, it was against the background of rising global demand for energy. At the same time, a fundamental change is underway in some parts of the world, with countries moving away from large, centralized power plants burning fossil fuels such as coal, oil, and gas and toward renewable energy sources such as wind and solar. Because the energy supplied by these renewables is subject to constant fluctuations, however, the issue of energy storage becomes vitally important. This is one of the many fields in which Bosch is contributing to the energy systems of the future.
Germany plans to cover around half its electricity needs with renewables by 2030. The coalition government in Berlin is currently discussing 'expansion corridors' for increasing renewables capacity. In the long term, renewable energy sources are to contribute a greater share of overall power supply, rising to between 40 and 45 percent by 2025 and to between 55 and 60 percent by 2035. That means lower CO2 emissions and greater climate protection. Energy storage facilities can reduce the number of new power lines that have to be built along the windy North Sea coast. On the one hand, the power can be used right where it is generated. On the other, the storage facilities allow excess production to be transported south when the grids are not overloaded. In short: storage facilities prevent congestion in grids.
Background information 2: How a vanadium redox flow battery works
A redox flow battery stores electrical energy in the form of chemical compounds dissolved in a liquid, which is known as an electrolyte. Driven by pumps, two electrolytes circulate in two separate loops. They only come in contact with each other in a small cell separated by an extremely fine membrane, through which positively charged hydrogen particles – the protons – can move from one side to the other. During charging, one of the two electrolyte solutions becomes positively charged while the other becomes negatively charged. When the battery is subsequently discharged, the charged particles return to their original electrolyte, releasing the stored electrical energy. A redox flow battery can be easily expanded by adding further tanks for more electrolyte solution. On account of the special properties of the electrolyte, the batteries retain their full capacity for up to 20 years, even with frequent charging and discharging – irrespective of how deeply they are discharged in each case.
Background information 3: How a lithium-ion battery works:
When a lithium-ion battery is charged and discharged, charged lithium particles (lithium ions) move back and forth between negative and positive electrodes. When a full battery is discharged, electrons are released and perform work in an external electric circuit: a current flows. When a battery is charged – for example, with the electricity from a wind farm – this process is reversed: the lithium ions absorb electrons and store them until the next discharge. This process can be repeated many times.
The special properties of lithium-ion batteries – such as their high charge and discharge speeds, high capacity, and high energy density – are due mainly to the electrode materials. The negative electrode is made of graphite, while the positive electrode is made of crystalline material, such as manganese, cobalt, aluminum, nickel, or iron. These metal ions form a tunnel structure in which lithium ions are stored during charging and from which they are released again during discharging.
