Abstract
In response to the Paris climate agreement, the Chinese government has taken actions to improve the energy structure by reducing the share of coal-fired thermal power and increasing the use of clean energy. However, due to the extreme shortage of large-scale energy storage facilities, the utilization efficiency of wind and solar power remains low. This paper proposes to use abandoned coal mine goafs serving as large-scale pumped hydro storage (PHS) reservoir. In this paper, suitability of coal mine goafs as PHS underground reservoirs was analyzed with respects to the storage capacity, usable capacity, and ventilation between goaf and outside. The storage capacity is 1.97 × 106 m3 for a typical mining area with an extent of 3 × 5 km2 and a coal seam thickness of 6 m. A typical goaf-PHS system with the energy type αw=0.74 has a performance of 82.8% in the case of annual operation, able to regulate solar-wind energy with an average value of 275 kW. The performance of the proposed goaf-PHS system was analyzed based on the reservoir estimation and meteorological information from a typical region in China. It has been found that using abandoned coal mine goafs to develop PHS plants is technically feasible in wind and solar-rich northwestern and southwestern China.
Highlights
China’s coal-heavy primary energy structure causes environmental pollution and massive carbon dioxide emission (Chen et al, 2019)
We proposed to use abandoned coal mine goafs serving as large-scale pumped hydro storage reservoirs
The suitability of goafs as pumped hydroelectric storage (PHS) underground reservoirs was analyzed with respect to the storage capacity, usable capacity, and ventilation between goafs and the outside
Summary
China’s coal-heavy primary energy structure causes environmental pollution and massive carbon dioxide emission (Chen et al, 2019). Aforementioned researches demonstrate the enormous potential capacity of underground coal mine goafs served as water reservoirs for PHS plants. Based on the above analysis, the pressure loss during water-air exchange in the goaf is negligible and the storage capacity of one goaf reservoir is temporarily set at 1.97 × 106 m3 and the usable coefficient is 0.8. The comprehensive system efficiency of the goaf-PHS is 73.6 and 77.5%, respectively, which are notably lower than that in yearly operation case, since the water flow is faster in daily regulation mode and more friction produces more energy loss. With a hypothesis of geological medium (residual coal and gangue) containing 1% pyrite, Pujades et al conducted numerical simulations and show that the pH value would decrease continuously to 3.1–3.3 in both surface reservoir and underground goaf reservoir (which is considered as a porous medium in the study) during 30 days of repeated pumpings and injections (Pujades et al, 2018). The environmental influence of goaf reservoirs should be a point of concern and a solvable problem when developing the hybrid-PHS plants using abandoned coal mine goafs
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