Energy Storage: the key to renewables success

For some years now, scientists have been proposing the exhaustion of fossil fuels. The idea of finding a way to make renewables as primary and not aleatory energy source is becoming increasingly popular. Energy storage is one way to go. As defined by the European Association for Energy Storage (EASE), “Energy Storage is a facility used for the intake and stocking of electricity in different suitable energy forms. The release of this energy, at a controlled time, can be in forms that include electricity, gas, thermal energy and other energy carriers”. The energy system is always evolving and growing in complexity; it means new challenges for a future energy system more interlinked and efficient. Energy storage is one of the important elements contributing to the development of a low-carbon electricity system also providing a backup for intermittent renewable energy. Storage exists on all levels of the energy chain, from local to strategic, and its full potential in the new energy system seems to be unexploited.

In a longer term scenario, energy storage technologies can contribute to increasing the penetration of renewables – in particular, intermittent renewables. EU energy policies have understood these technologies importance and also the need to support this sector. Still a lot has to be done. For this purpose, in 2011, the European Commission created EASE, as a result of a shared vision of the roles, technologies and potential applications of energy storage within the framework of the EU Energy and Climate Policy. EASE is a part of the Strategic Energy Technology-Plan (SET-Plan) designed to accelerate and develop a new research and innovation approach in the energy system transformation. The SET-Plan includes Wind, Solar Energy, Smart Grids, Green Cars, Smart Cities and Efficient Buildings initiatives, emphasizing the importance of future electricity markets and introducing a new concept of “Prosumer,” producer/consumer.

Despite being designed to open up and integrate the energy market, the Directive 2009/72/EC, which establishes common rules for the internal electricity market, for the generation, transmission and distribution of electricity, never mentions the concept of electricity storage. The means how the European electricity market is regulated, and the nature of the electricity market are critical policy issues determining the scope for energy storage to contribute effectively to energy security and emissions reduction. Now, the European electricity market remains fragmented.

The European Union has energy rules set at the European level, but in practice, it has 28 national regulatory frameworks. It cannot continue. National markets are characterised by the presence of strong incumbents and have tended to encourage regulators to prevent competition from abroad. There cannot exist a real internal market until such interconnection is built or reinforced. The inconsistent operational and regulatory approaches, in particular, the small incentive for energy storage in many European electricity markets does not permit a full liberalisation and transparency – also true for the different forms of renewable energy support mechanism across the EU. The need of equal chances for all the energy storage services ensuring non-discriminatory access to networks is evident. The current market design and national policies do not yet set the right incentives and provide insufficient predictability for potential investors. Europe has to reset its energy policy in the direction of a European Energy Union. If it continues the present path, the inevitable challenge of shifting to a low-carbon economy will be made harder by the economic, social and environmental costs of too many fragmented national energy markets.


The energy storage market is going through continued innovations. Several technologies for storing energy already exist, and they can be classified into five general groups: chemical, electrochemical, electrical, mechanical and thermal. Some of these are both in the research and development (R&D) or demonstration & deployment (D&D) stages, waiting to evolve further to become commercially viable on a larger scale. The growth of this market technology would make renewable energy more efficient and integrated into the electrical system. There is a need to increase the capacity of batteries, capacitors, or other devices, which allow keeping a reserve of energy likely if required.

It is possible to store electricity in different ways, not only using batteries. By electrolyzing, water produced hydrogen, that can then be stored and eventually re-electrified (e.g. via fuel cells). Compressed air energy storage (CAES) is another way to store energy generated at one time to be used at another. Again, thermal energy storage technologies allow us temporarily to reserve energy produced in the form of heat or cold for use at a different time. Modern solar thermal power plants produce all of their energy when the sun is shining during the day. The excess energy is often stored in these facilities – in the form of a molten salt or other materials – and used until the evening to generate steam to drive a turbine to produce electricity. Typical storage tools are batteries. The most commonly used are lead-based, lithium based, nickel-based and sodium-based batteries.


In Europe, there are a large number of energy storage facilities operating or under construction. In Austria, hydroelectric power provides approximately 55% of electricity with an installed capacity of 11,853 MW of which 3,500 MW is Pumped Hydro Storage (PHS). This huge capacity is due to its geographical characteristics with existing storage lakes reducing the building required. Obervermuntwerk II is an example of Pumped Storage Hydro Plant under construction. Once in operation in 2018, the Obervermuntwerk II pumped-storage power station will have an output of 360 MW and will be Illwerke’s second-largest power station. In 2011, a new pumped storage plant in the area of the existing Limberg I pumped storage power plant went into operation doubling the output capacity of the Kaprun power plant group from 353 MW to 833 MW. A new Pumped Storage Plant is currently undergoing approval procedure, Limberg III, as an extension of the pumped storage power plant Kaprun-Oberstufe. Following Limberg II, the project strengthens the power plant group in Kaprun as the green battery of Europe.

Denmark has salt caverns suitable for the development of Compressed Air Energy Storage, and it has been considered in energy planning models.

Germany has the largest number of Pumped Hydro Storage plants with 23 operational plants and is the second European country after Spain in installed capacity with 7 GW. Future solutions might be in artificial structures like remaining quarries of opencast mining structures or chalkstone quarries. Compressed air energy storage (CAES) could also be a future storage option. Currently, only one CAES with a power of 290 MW is installed in Germany, whose regulation facilitates energy storage installation with a new law (EnWG §118) that exempts new energy storage facilities (installed before 2019) of paying connection taxes for ten years.

Ireland has one of the best wind resources in Europe. Recently, AES UK & Ireland announced the completion of the Kilroot Advancion Energy Storage Array, located in Kilroot Power Station in Carrickfergus, Northern Ireland. The Array provides 10 megawatts (MW) of interconnected energy storage and is the largest and most advanced energy storage system in the area.

The EU needs to tackle energy issues by implementing a policy that encourages a competitive market. However, a regulatory framework is necessary to ensure a level playing field for all energy. To invest in new storage technologies to keep the advantages of the energy produced by renewable sources, getting over the problem of their discontinuity is the only way to exploit a source of infinite energy.

Alice Masili

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