2022 – Repurposing Existing Storages for Pumped Hydropower

Dr Mark Locke Senior Technical Director Dams and Hydropower GHD
Malcolm Barker Senior Technical Director Dams GHD
Mike Westerman Senior Technical Director Hydropower GHD

There are many attractions to repurposing existing water storages for pumped hydropower energy storage (PHES), including water availability, potentially lesser environmental disturbance and lower cost, and greater community acceptance. However, there are also significant challenges. This paper explores GHD’s experience with addressing these challenges including several case studies.

Existing reservoirs often involve old dams with legacy issues requiring significant upgrades to meet new standards. This is further complicated because the new operating regime may involve daily reservoir cycling over a significant portion of the dam height and the rapid drawdown may be a significant new loading condition on the existing dam. Rapid drawdown can lead to both upstream instability and concern of washout of fines from embankments.

PHES may be considered as part of the closure plan of mines or quarries, or for repurposing old mine voids. This can be an excellent re-use of a site, making use of the existing disturbed area and existing workforce in the region. Existing pits are often not sufficiently stable to resist the daily water level fluctuations, potentially requiring extensive stabilisation. Existing water storages on mine sites commonly were not designed to modern standards or experience extensive seepage requiring upgrades or liners. Tailings dams are sometimes considered for PHES reservoirs, commonly requiring a liner to separate the water from tailings, and a thorough knowledge of compressibility and liquefaction risk of the underlying tailings. Water quality management can also be a significant risk at mine sites, where legacy acid rock drainage or metal leaching can become concentrated within a closed cycle PHES system.

Robust facing systems such as concrete faced rockfill dams or modern asphaltic concrete have a high capital cost. To reduce capital costs, liners are commonly considered for PHES reservoirs, particularly when repurposing existing sites. Membrane liners such as HDPE, LLDPE, PVC and bitumen impregnated membranes are lower cost but have durability and rupture risks. EPDM appears to provide a potential option that can resist the demands of PHES operation at moderate cost. Detailing of appropriate liner systems and subgrade is essential.