Storing Electricity: The Key to Managing EnergyPublished on 12.06.2016
10 min read
Storing is the only solution that can balance rising worldwide demand for electricity with an output that is increasingly dependent on intermittent energy sources like the sun and the wind. Outside of pumped-storage plants, electricity storage remains expensive. Certain technologies are still inefficient and are sometimes dependent on rare earth elements. Nevertheless, researchers around the world are hopeful about this Holy Grail of tomorrow’s energy landscape, and more and more promising innovations are emerging.
© EDF / HURET CHRISTOPHE - Aerial view of the Grand'Maison facility in the French Alps, which features a pumped-storage power plant for storing electricity.
In electric power production, supply and demand do not always match up at any given time. Night and day, power plants generate the same amount of electricity, although it is most in demand in the mornings and evenings, when people are at home, as well as during winter and fall, when heating and air conditioning are used the most. It isn’t possible to serve a sudden surge by restarting a -fired or nuclear power plant.
The challenge of electricity storage has become all the more pronounced with the rise of wind farms and solar plants, whose output depends on the weather. This makes it crucial to store the surplus electricity so that it can be reinjected into the grid when needed. Otherwise, power outages may ensue.
Electricity is simply the movement of electrons. It cannot be stored like oil or water - it has to be converted temporarily into another form of energy. Various imperfect technologies are competing with each other, and new avenues are emerging.
The Different Types of Storage Systems
The most widely used method is based on artificial reservoirs in the mountains that offer large-scale storage. In pumped-storage power plants, electricity is used to pump water from a lower to an upper reservoir, and when the water is released downwards, it generates electricity. The world's pumped-storage power plants have a total generating capacity of 140 GW and this capacity could increase by a factor of 4 to 15 by 20401. One of the largest facilities is in Bath County, Virginia (United States), which has a generating capacity of more than 3,000 MW. There are around six major facilities in France. The largest one, located at Grand’Maison in Isère, has a generating capacity of 1,790 MW, while the others vary from 300 to 900 MW.
Another large-scale electricity storage system involves compressing air that, once decompressed, releases energy (CAES – Compressed Air Energy Storage). In the United States and Germany, compressed air is stored in large caverns and decommissioned mines. Many other projects are under construction worldwide, with CAES already representing generation capacity of 400 MW. At €50 to €150 per kWh, pumped-storage power plants and compressed air energy storage are the least expensive technologies available, and together they account for 87% of electricity storage capacity worldwide. However, these types of storage are insufficient and cannot be built everywhere.
Batteries are another universal storage method, providing power for everything from small electronic devices to electric cars, and from homes to entire neighborhoods or cities. Batteries make mobile, decentralized storage possible. The electrochemical process costs between €500 and €1,200 per kWh based on the type of battery (sodium-sulfur or lithium-ion). Current costs are however rapidly decreasing as technological advances and the economies of scale associated with growth in production come into play.
Another technology that is starting to expand uses electricity to produce or , which can be stored to later release energy when burned or used in cells. These "power-to-gas" methods are rather expensive at close to €500 per kWh. Fuel cells or batteries may be used for local energy storage at the generation site and can even be used by consumers who have access to private power production systems in energy-positive buildings. The residential energy storage market is rapidly growing in Germany and Japan.
For occasional storage needs, inertia wheels can be used to store electricity in the form of . It is also possible to use capacitors or storage systems that convert electricity into magnetic energy. However, the process is very expensive at more than €10,000 per kWh.
Exponential Market Potential and Myriad Innovations
The electricity storage market is booming. The International Agency (IRENA) has estimated that 150 GW of battery storage and 325 GW of pumped storage will be needed by 2030 based on the assumption of a 45% market penetration rate for renewable energies.
Total global investment in electricity storage is expected to reach €277 billion between 2010 and 2030. On a regular basis, news releases from companies and researchers in the United States, Japan and Europe announce the development of batteries that charge faster or are more powerful. Pilot projects using hydrogen are also on the rise. Among the most innovative is a system for storing hydrogen in solid form being developed by French start-up McPhy Energy. The electricity storage industry, like the renewable energy and the electronics industries, suffers however from a serious handicap: it is dependent on rare earths, a set of 17 chemical elements with unique properties that are produced in very limited quantities in a small number of countries.
The market for lithium-ion batteries, for example, which have been adopted by most electronics and electric vehicle manufacturers, is expected to grow tenfold by 2020, but the batteries require lithium, the reserves of which are mainly found in South America (specifically Bolivia - in the high-plateau Salar de Uyuni salt flat -, Chile and Argentina), China and the United States. The availability of this metal is therefore essential and numerous laboratories are working on lithium, particularly in France.
Other rare earths such as neodymium, dysprosium, praseodymium, lanthanum and terbium are key in the manufacture of the permanent magnets that power electric vehicles and wind turbines. To give an idea, electric vehicles typically contain 12 to 25 kilograms of rare earth elements.
In all, 97% of rare earth production is concentrated in China, giving that country a powerful economic weapon. That said, the greatest risk is that these elements could run out, or at least at an economically viable cost, over the next 15 years. The best option is therefore to recycle them. Recycling techniques are already being used on an industrial scale.
- Association technique énergie environnement (in French only)