Technical Assessment: Underground Pumped Hydroelectric Energy Storage

BBEnergy’s engineering experience and domain knowledge were showcased in a recent technical assessment carried out at one of our longstanding deep level gold mining clients. The client has to keep various non-operational deep level mining shafts (>1.5km deep) open to maintain acceptable underground water levels to accommodate the surrounding mining operations. The upkeep and staffing of these shafts are a large expense for the mine and therefore various opportunities to unlock more value from these are being investigated.

Underground Pumped Hydroelectric Energy Storage (UPHES) schemes store excess electricity by pumping water from a lower underground reservoir to an upper reservoir, converting it to potential energy. During Eskom’s peak tariff periods, water is released from the upper reservoir, spinning turbines to generate electricity. Although similar than conventional PHES schemes, in this application, the significantly higher heads accessible in unused deep level gold mines, will allow for higher generation capacity at lower water flow rates.

BBEnergy was appointed to carry out a technical assessment at two deep level gold mines, one having a depth of approximately 2km and the other approximately 1.5km. BBEnergy’s scope of work was to:

• Verify the technical viability of the proposed technology for the two sites,
• Verify the accuracy of the financial models, and
• Identify the best concept for further feasibility studies.

BBEnergy’s assessment started with underground site visits to determine the conditions of underground infrastructure:

• Availability of decommissioned haulages which can be used as storage reservoirs
• Capacity of existing pump chambers and feasibility for expanding them
• Condition and size of existing piping columns which can be re-used as penstocks

Based on the available infrastructure, the preferred shaft was selected and various options for the location of the respective water reservoirs were evaluated against each other. The tables below provide a summary of the achievable generation capacity, cost (CAPEX), generation hours per day and simple payback period:

Based on this evaluation, BBEnergy was able to provide recommendations to the Client which informed decisions on further detailed feasibility studies.