Following an extremely windy Christmas 2016, the Deutsche Energie-Agentur (dena) – the German Energy Agency – is recommending improvements in the general framework for pumped-storage plants. When there is a large surplus of electricity from fluctuating sources such as wind and solar power, pumped-storage plants could make a significant contribution to the security of supply by storing the surplus energy in large quantities, and then releasing it when electricity supplies are lower. It would be worthwhile developing the general framework for electricity storage now, in order to ensure its economical operation in the future. For example, under the so-called end user ruling, inappropriate charges are imposed on pumped-storage plants.
‘Pumped-storage plants and other storage technologies are indispensable for the integration of volatile renewable energy sources,’ says Andreas Kuhlmann, dena’s Chief Executive. ‘They act as a buffer to even out fluctuations in the electricity supply and in demand. They also make a significant contribution to network stability overall. To enable us to make full use this key technology for the energy transition, we must create a favourable general framework right now, and also, if possible, stimulate investment in new plants. It makes no sense, for instance, to classify storage facilities as end users and impose excessive and unfair reallocation charges and levies. Unfortunately, in the latest amendments to the Energy Industry Act and the Renewable Energy Sources Act, this was not given due consideration. Electricity storage should be defined in the Energy Industry Act as a separate element and exempted from all end user charges.’
Pumped-storage plants ensure guaranteed output and can provide important ancillary services. These include: making an operating reserve available, through which unforeseen fluctuations in the network can be evened out in the short term; providing reactive power to keep the voltage stable; so-called black start capability – that is, the ability to begin operating without electricity; and their usefulness in congestion management in electricity grids during redispatch – that is, adjustment of the generating capacity of power plants.
Example, December 2016: pumped-storage relieves pressure on electricity grid and stores surplus electricity
The 2016 Christmas period was one of low demand for electricity and high wind energy supply. At times, prices on the European Energy Exchange, EEX, were negative. Some of the electricity was stored temporarily in German pumped-storage plants. However, this led to relatively high electricity exports. For example, on Christmas Eve the proportion of wind power in net electricity generation amounted to 52.5 per cent at 7 pm, while the proportion of electricity from pumped-storage plants, because of low electricity prices, was only 0.3 per cent. This is shown by data from the transmission system operators and the European Energy Exchange.
Four days later, on 28 December at the same time, the wind had dropped considerably. Demand and electricity prices rose again and wind turbines contributed just 5.6 per cent of the net electricity generated. By contrast, pumped-storage plants supplied 6.5 per cent of the electricity during this period. The Christmas period shows, for example, how pumped-storage plants help to even out and overcome large fluctuations in input and phases of low generation of renewable energy.
Energy transition needs various storage options
In general, besides pumped storage, there are various storage technologies, such as battery storage or power to gas. These differ primarily in their stage of development, their associated costs and their performance and capacity. Storage systems such as flywheels or capacitors can compensate for fluctuations in electricity only for a matter of seconds or minutes. Batteries, on the other hand, are suitable for timescales from minutes to hours, while pumped storage is regarded in terms of days.
Long-term storage systems that can provide electricity for days or weeks will be available mainly through chemical storage in the future, but these are still being tested. An example of these is power-to-gas technology, by which gases such as hydrogen or methane are produced with the help of renewable electricity. ‘The electric power system will require short- and long-term electricity storage on a large scale during the course of the energy transition,’ stresses Andreas Kuhlmann.
dena’s Platform for Pumped-Storage Plants
To devise solutions for the practical integration of pumped-storage plants into the energy system, dena has established the Platform for Pumped-Storage Plants. Partners include power plant operators, plant constructors, energy suppliers and grid operators. dena’s initiative brings together important companies from various industries and combines their know-how. High on the agenda are the negotiation of joint positions on the future role of pumped-storage plants in the energy system, the identification of challenges, statements on current issues, events and opportunities for dialogue.
Further information on pumped-storage plants and the dena platform can be found at www.pumpspeicher.info.
dena is also giving expert advice on the importance of pumped-storage plants for the energy industry at the discussions on the Atdorf pumped storage project, taking place from 10 to 28 January at Wehr in the District of Waldshut, Baden-Württemberg.