Storage systems for renewable energies: Topic for today and tomorrow
Energy storage systems are vital in order to use renewable energies on a large scale because the fluctuating supply of renewable energy is subject to nature’s whim. The Renewable Energy Hamburg Cluster presents the four most important types of storage systems and two award-winning pilot projects.
Be it windy or calm, day or night, renewable energy depends on natural conditions that are sometimes available in abundance or sometimes not at all. Therefore, in order to generate further development, renewable energies must be stored on a large or small scale as required. It will be one of the main topics at WindEnergy Hamburg, the leading international trade fair for the wind energy industry that is being held from 27 to 30 September in Hamburg. "The goal has not yet been achieved. However, the industry is openly and intensively addressing the subject of storage and many solutions already exist," says Jan Rispens, Managing Director at the Renewable Energy Hamburg Cluster. The German federal government’s goal envisages that the share of renewable energy shall constitute at least 80 percent of the energy supply by 2050. In order to achieve this goal, in the future smaller storage systems will initially be required in order to support the grid locally, and when the share increases effective medium and long-term storage systems will also be needed. "Many wind or solar farms are still being built - therefore we need suitable storage solutions and also a suitable legal framework," Rispens adds.
What different types of storage systems are there?
Battery storage systems: Increasingly also suitable for larger power systems
Currently, batteries are mainly used in smaller power systems in single family homes or multi-family dwellings. Due to the low number of possible charge cycles, the total cost for batteries is still very high. Furthermore, the storage capacity is reduced as a result of often being charged and discharged. Therefore, their possible uses in power systems are restricted. New battery technologies already feature a higher number of possible charge cycles and a larger storage capacity. However, economical use in larger energy systems is currently still hindered by the comparatively high energy costs and the number of charge cycles, which remains low. Nevertheless, several large battery storage systems that support the local grid have recently been brought on line - the technology is developing rapidly.
Pumped storage systems: Technological sophistication
In pumped storage technology, water is pumped into a tank situated at a high level where it is stored. To date, it is the most technically proven and most used storage technology. When required water is released and electricity is generated by means of a turbine and a generator. However, there are some restricting factors regarding future expansion: Conservationists are concerned about the massive impact on the landscape. Furthermore, there are only very few potential new sites for pumped storage power stations in Germany due to the necessary topological features. In terms of technology, they can be flexibly controlled and are ready for operation quickly. Therefore, they can reliably provide different types of balancing energy. Balancing energy keeps the frequency constant in the power grid and ensures the stability of the power system.
Power-to-Heat: Converting power to heat
In this procedure excess power is converted to heat when the power grid is over supplied with renewable energy. The power-to-heat systems (PtH systems) not only serve grid stability but also the reduction of carbon dioxide emissions. Since this technology allows power from renewable energies to be integrated with relatively low investment costs, the PtH systems reduce the output of combined heat and power stations using fossil fuels in local and district heating systems and bring down CO2 emissions. These systems are a comparatively cost-effective technology and at the same time, they provide an option to stabilise the German power grid that is already economically attractive today and that will become increasingly important in the coming years. Excess power can be immediately stored in thermal storage systems, but it can also be used to drive electric thermal pumps that use it to collect ambient heat from the earth or from the air. The heat yield of the power used could clearly further increase in the future.
Power-to-Gas: Storing energy with power and water
In power-to-gas technology, water is converted to hydrogen using power and it is sometimes converted to methane in a further step. These gaseous substances can be fed into the existing natural gas grid and stored there. The power-to-gas procedure can provide a storage time of several months and a large storage capacity for surplus amounts of energy owing to its connection to the existing and very large natural gas grid. As a result of the identical properties and chemical structures of fossil and renewable methane, the natural gas grid can be used for transporting and storing large amounts of energy. A further possible benefit of the power-to-gas procedure can be found in the use of carbon dioxide that is produced by industry or in power stations (even biomass power stations). Transforming carbon dioxide and hydrogen into methane means that a procedure is available by which carbon dioxide can be effectively "recycled". However, this technology is still comparably expensive.
Two award-winning pilot projects as examples of Germany’s progress:
The SILYZER from Siemens AG:
The largest available and standardised PEM electrolysis system (PEM = Proton Exchange Membrane) – the SILYZER – won Siemens AG the German Renewables Award 2015 in the category "Product Innovation of the Year". With the aid of electrolysis, excess renewable electricity can be converted into hydrogen, which can then be stored as the need arises. Hydrogen is a versatile resource for the industry and the mobility sector in conjunction with fuel cells for later reconversion processes.
Further information at:
The SmartRegion Pellworm:
The importance of smart storage systems in local energy supply is underlined by the project SmartRegion Pellworm, winner of the "Project of the Year" category at the German Renewables Award 2015. Over several decades, Hansewerk AG and Schleswig-Holstein Netz GmbH have created a supply system on the North Sea island of Pellworm that is characterised by a high share of renewable energies. On the annual balance sheet, about three times the volume of electricity is generated from renewable energy sources as is consumed, aided by the utilisation of several innovative storage systems with battery storage systems as well as a redox flow battery that are controlled by smart control systems. The 37 km²-island is connected to the mainland by two undersea cables.
Further information about SmartRegion Pellworm at: