Underground pumped hydro storage: Flatland Large-scale Electricity Supply

Abstract

Dutch energy policy foresees a considerable role for such variable electricity sources as photovoltaic and wind energy. This thesis makes it clear that no adequate measures have been taken to account for the variability of these sources. The approach taken by the Dutch government is to extend cross-border connections, to shift demand away from peak hours and to use batteries in electric vehicles and households for energy storage. The thesis argues that the outcome of this approach is uncertain. Especially after 2023 problems with balancing demand and supply will increase, with often no other option than to use gas-fired power plants to prevent a black-out. The thesis makes it plausible that this is detrimental to the attainment of CO2 emission targets set by the Dutch government. This also means that wind turbines and photovoltaic panels have to be switched off when there is a surplus, which is detrimental to their economy. The thesis assesses other storage technologies and concludes that none is able to balance the Dutch grid adequately in the near future. Pumped hydro storage (PHS) is worldwide the dominant and most efficient technology for balancing the grid. Low-cost (or surplus) power is used to pump water up into a reservoir at elevated heights. During high demand and high prices water is released, passing through a turbine connected to a power generator. The thesis describes recent developments in PHS, including turbine technology and the changing role of PHS in the grid. The Netherlands is almost flat and lacks natural locations suitable for PHS. The only option is constructing an artificial height difference. The thesis proposes to construct a reservoir in caverns some 1,400 meters sub-surface in the Dutch region South Limburg. The idea is to circulate water between a small basin at the surface (50 ha) and the deep caverns. An underground PHS (U-PHS) project is proposed with a maximum power of 1,400 MW and a storage capacity of 8.4 GWh, which is essential to balance all wind and solar power currently planned in the Netherlands. The round trip efficiency of U-PHS is circa 80%. The details of the geological requirements, design, construction and planning are set out in the thesis. Construction will cost € 1,800 million, including all excavation costs, electro-mechanical equipment, pumps, turbines, and ground level installations. Construction will take 6 years. A cost-benefit analysis makes it clear that this project is viable and can be successfully financed through a public private partnership. Finally, the social implications of this project are discussed, including its favourable effects on employment, and the role of U-PHS in a more distant future. It is concluded that an U-PHS project is feasible. Its technology is proven, its economy is sound and its finance is within reach. It can play an important role in both the transition towards sustainable electricity and establishing the Netherlands as main European energy hub. Underground pumped hydro is also a smart way of using the underground to preserve the surface of the earth - wherever in the world.