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Energy question of the week: Why is energy storage so important?

11. October 2010, 10.20, Jan Oliver Löfken, 4 Comment/s
Whether driving a car, switching on a light, or turning up the heating – we take it for granted that there'll be sufficient energy for us to use at that very moment. But this only works if two basics are in place. Firstly, energy needs to be transported quickly and reliably to the consumer in the required form. Second, energy storage guarantees straightforward access and acts as an 'energy buffer' to fill the gaps in distribution. So, what kinds of storage do we get our everyday energy from?

Fossil and renewable fuels – coal, gas, oil, biofuels and hydrogen – contain chemically-stored energy, which they release when burnt. Almost every type of mobility and the vast majority of our electricity and heat depend on these chemical energy stores. Even when we run or cycle, our bodies use biochemical processes to convert the energy-rich molecules they create from food into muscle movements. The advantage of all these substances is that they store energy in a high-density form, are ideal for transport, and quickly and efficiently use an engine or muscle 'machine' to convert the stored energy into movement, power or heat.

The power grid needs more storage

However, electricity is the form of energy most easily converted into heat, movement or light and it can be distributed via the power grid with minimal losses. But electrical energy cannot be stored directly where it is needed. The interconnected cables of the power grid are incapable of storing even one kilowatt-hour of energy. This is why electric power providers keep production and consumption pretty much in balance. With increasing numbers of wind farms and solar energy plants, where the power output fluctuates with the weather, this is becoming increasingly difficult. In addition to implementing a 'smart grid' in the future, this problem can be addressed by the provision of additional energy storage capacity.

Zehn-Kilowatt-Versuchanlage für die Untersuchung unterschiedlicher Wärmespeicher bis 400 Grad Celsius. Im Vordergrund (rechts) ist der Thermoölkreislauf zu erkennen, der für die Wärmezufuhr beziehungsweise -abfuhr beim Laden und Entladen des Speichers benötigt wird. Der Speicherbehälter (im Hintergrund links) ist ein 100 Liter-Zylinder mit externer Isolierung und kann mit unterschiedlichen Speichermedien betrieben werden. Bild: DLR.

A 10-kilowatt testing plant, used to investigate various different thermal storage techniques at temperatures of up to 400 degrees Celsius. Credit: DLR.

The possibilities of potential energy

It is at this point that storage systems that make use of what is referred to as 'potential energy' come into play. Energy is stored by pumping water from a low-lying reservoir into a reservoir at a higher level, using surplus electricity. This is done in pumped-storage plants in the Alps, for example. When the water is later allowed to flow back down – when additional power is required – its energy is used to drive turbines. The potential energy of the water in the reservoir situated at a higher location is converted back into electric power as the turbines turn the generators. "These pumped-storage plants offer excellent efficiency, but this technique will be difficult to expand any further," says Stefan Zunft, from the DLR Institute for Technical Thermodynamics in Stuttgart, Germany. This is just one reason why DLR energy research focuses on the development of new storage technologies. In the next blog post, we will tell you more about promising and unusual ideas for energy storage.

The DLR Energy question of the week in 'The future of energy' Year of Science

The Federal Ministry of Education and Research (BMBF) has given the Year of Science 2010 the motto 'The future of energy'. For this reason the science journalist Jan Oliver Löfken will this year answer a question on the subject of energy in his blog each week. Do you have a question about how our energy supply might look in the future? Or do you want to know, for example, how a wave power plant works and how it can efficiently generate electricity? Then send us your question by email. Science journalist Jan Oliver Löfken will investigate the answers and publish them each week in this blog.

Top image: Ceramic spheres can be used in solid-material energy storage. Credit: DLR.


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