Energy storage in underground coal mines in NW Spain: Assessment of an underground lower water reservoir and preliminary energy balance

Abstract

During the last decades, the Asturian Central Coal Basin (ACCB) has been a highly exploited coal mining area by means of underground mining and its network of tunnels extend among more than 30 mines. Parts of this infrastructure will soon become available for alternative uses since most of the coal mining facilities in Spain will fade out in 2018. Increasing penetration of renewable energy sources into the electrical grid, with intermittent and fluctuating supply, leads to excessive frequency variations, so the development of energy storage technologies are required, such as Pumped Storage Hydroelectricity (PSH). Reduced environmental impacts, deep, non-flooded shafts and abundance of water from underground runoff , make coal mines in ACCB suitable for the development of Underground Pumped-Storage Hydropower projects (UPSH). The network of tunnels of a mine facility has an unusual geometry for a water storage system. Although there are numerous studies for the construction of UPSH plants, until now there have been no known projects of this type under operation. Filling and emptying processes during the operation of the turbine-pump are complex due to the presence of two fluids interacting inside the tunnels, water and air. This paper explores the viability of a network of tunnels as an underground water reservoir. Two-phase three-dimensional CFD models have been developed in order to know the flow behavior in the tunnels. The pressure and velocity results that have been obtained in the simulations confirm that the use of underground mines as a lower reservoir of a UPSH is technically possible.

Low-enthalpy Geothermal Energy Potential of Mine Water from Closured Underground Coal Mines in Northern Spain

“…When the activity in the mines ceases, the pumping works are interrupted and the mining drifts are flooded [13][14][15]. The average time of inundation of an underground mine in the ACCB is about 4 years.…”

Transient Simulation of Underground Pumped Storage Hydropower Plants Operating in Pumping Mode

“…The idea of locating the lower water reservoir of a PSH scheme underground was proposed in 1901 by Reginald A. Fessenden [8]. Some studies of UPSH plants have been developed in recent years [2,6,[9][10][11][12][13][14]. However, there are no bibliographic evidence of UPSH plants under operation worldwide.…”

Comparing Subsurface Energy Storage Systems: Underground Pumped Storage Hydropower, Compressed Air Energy Storage and Suspended Weight Gravity Energy Storage

“…An alternative could be UPSH plants in disused mining structures. Although some studies have considered the use of underground reservoirs [2,[3][4][5][6][7][8][9][10], however until now there have been no known projects of this type under operation.…”