Synergy’s investigation into pumped hydro

Executive summary

Synergy has completed its investigation into the technical feasibility of pumped hydroelectric storage (Pumped Hydro) within the South West Interconnected System (SWIS). The investigation found that pumped hydro is technically feasible as an option for long duration storage in several sites across the SWIS. However, the construction of a pumped hydro facility would face community, environmental and financial constraints, lengthy construction timeframes and technical risks. Consequently, Synergy will not do any further work on pumped hydro at this time and continue its efforts on construction of the wind and battery projects required to retire the state-owned coal fleet by 2030. 

The private sector may still wish to pursue their own pumped hydro investigations, and new market mechanisms are being implemented to encourage investment in new storage facilities to service WA’s main grid.

Pumped hydro

A pumped hydro scheme consists of two reservoirs located at different elevations, connected by a pipe or tunnel containing a pump/turbine unit and generator. When electricity demand is low but renewable electricity generation is high, excess electricity is taken from the grid and used to pump water from the lower reservoir to the upper reservoir, storing potential energy. During periods of high electricity demand or low renewable energy supply, water is released from the upper reservoir and flows downhill through turbines. The gravitational force causes the turbines to spin, which generates electricity.

Pumped hydro is a form of energy storage known as Long Duration Energy Storage (LDES). LDES can be used to decarbonise an electricity grid by storing energy from renewables when demand is low which can then be discharged for extended periods when wind or solar output is low. LDES can provide energy for longer periods of time than existing development options for batteries.

Purpose of the investigation

The State Government has committed to the retirement of all state-owned coal-fired power stations by 2030. These will be replaced with 810MW of renewable energy and 4,400MWh of battery storage. 

To complement the Government’s additional investment in replacement capacity, Synergy embarked on an investigation of pumped hydro in recognition of the anticipated new demand for renewable energy post 2030. This investigation is, to date, the most comprehensive investigation of pumped hydro opportunities in the SWIS.

The investigation

In 2022, Synergy engaged GHD as an engineering consultant to undertake an analysis of
opportunities for pumped hydro in the SWIS. A high-level scan was conducted which identified 80 potential sites within the SWIS for pumped hydro.

Potential sites were then filtered for topographical or geological issues and locations in national parks or nature reserves. A filtered list of 60 opportunities was subject to additional screening and ranking, which removed remote sites due to required infrastructure, sites that would be unable to meet a minimum storage requirement, and sites considered not suitable due to potential impacts on drinking water.

At the completion of the analysis, five shortlisted sites were found to be technically suitable for pumped hydro - Collie (Wellington Dam and a site subject to a mining lease), Yarloop, Conjurunup and Harvey.

Key findings

The investigation found that although pumped hydro is technically feasible within the SWIS, it presents significant delivery challenges, including potential impacts on state forests, Indigenous cultural heritage, biodiversity, landholders and local communities. All sites had potential impacts on critically endangered flora and fauna including foraging sites for black cockatoos. The report also found that the efficacy of pumped hydro will likely be impacted by declining rainfall and an increasing reliance on desalination for water supply in the south-west area of Western Australia.

The results of the investigation highlighted that building a pumped hydro project in the SWIS will require substantial financial commitment due to long development and construction timeframes, technical risks and capital costs.

Indicative capital costs for the five shortlisted sites ranged from $2 billion to $3 billion for the smallest option and up to $4 billion to $9 billion for a significantly larger asset. The investigation noted that these capital costs may be justified by the long operational life (~50 years) of a pumped hydro scheme. However, Synergy notes other pumped hydro schemes have experienced unexpected and significant cost escalations and delays.

Mine void pumped hydro

The investigation included a review of opportunities for pumped hydro in existing mining pits
recognising the potential for lower environmental impact through repurposing of these sites. The investigation found there are limited opportunities to develop a mine void pumped hydro scheme due to the requirement for construction of a supporting reservoir, which typically requires clearing of state forests or undisturbed areas. The investigation also found that many mine sites are remotely located with inadequate infrastructure to meet SWIS requirements.

Mining pits generally have the lowest environmental and social impacts of the short-listed sites. However, mine pits are subject to relatively high development costs, subject to private commercial interests, and present numerous technical risks including stability of mine walls and risks of dynamic liquefaction in the event of a significant seismic event. Mine pits also require clearing of native vegetation for the upper reservoir environmental approvals and rehabilitation of the broader mining area.

Next steps

In view of the above analysis, considering the associated development timelines and costs, Synergy will not be progressing any further consideration of pumped hydro technology at this time. However, the private sector may still pursue pumped hydro opportunities. Additionally, new market mechanisms are being implemented that will encourage investment in LDES technologies as required by the electricity system.