Abstract
In the current energy context, intermittent and non-dispatchable renewable energy sources, such as wind and solar photovoltaic (generation does not necessarily correspond to demand), require flexible solutions to store energy. Energy storage systems (ESS) are able to balance the intermittent and volatile generation outputs of variable renewable energies (VRE). ESS provide ancillary services such as: frequency, primary and voltage control to the power grid. In order to fulfil the power system control, ESS can switch within seconds for different operation modes. Many times, ESS imply environment impacts on landscape and society. To solve this problem, disused underground spaces, such as closed mines, can be used as underground reservoir for energy storage plants. In this paper, a comparative analysis between underground pumped storage hydropower (UPSH), compressed air energy storage (CAES) and suspended weight gravity energy storage (SWGES) with suspended weights in abandoned mine shafts is carried out. Pumped storage hydropower (PSH) is the most mature concept and account for 99% of bulk storage capacity worldwide. The results obtained show that in UPSH and CAES plants, the amount of stored energy depends mainly on the underground reservoir capacity, while in SWGES plants depends on the depth of the mine shafts and the mass. The energy stored in a SWGES plant (3.81 MWh cycle-1 with 600 m of usable depth assuming 3,000 tonne suspended weight) is much lower than UPSH and CAES plants.
Highlights
In 2017, electricity generation from renewable energy sources (RES) contributed 30.7% to total EU-28 gross electricity consumption [1]
The energy storage capacity of the underground pumped storage hydropower system depends on the reservoir capacity and net head [11], and it is given by Eq (1)
The stored energy in a suspended weight gravity energy storage (SWGES) plant is much lower than underground pumped storage hydropower (UPSH) or compressed air energy storage (CAES) plants
Summary
In 2017, electricity generation from renewable energy sources (RES) contributed 30.7% to total EU-28 gross electricity consumption [1]. The intermittent nature of some RES, such as wind and solar photovoltaic requires flexible ESS. An UPSH scheme, CAES plants and SWGES system are effectively a large storage battery. PSH is the most mature technology and account for 99% of bulk storage capacity worldwide [2], because allows large amounts of energy to be stored and generated. PSH plants imply environment impacts on landscape and society [3]. An alternative could be UPSH plants in disused mining structures. Some studies have considered the use of underground reservoirs [2, 3,4,5,6,7,8,9,10], until now there have been no known projects of this type under operation
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