Pumped storage hydropower (PSH) operates by storing electricity in the form of gravitational potential energy through pumping water from a lower to an upper reservoir. First built since the end of the 19th  century,  PSH is a mature and proven technology for long-duration energy storage. It has continuously evolved to suit the needs of changing power systems,  providing a suite of power systems flexibility services such as inertia,  frequency control,  voltage regulation, and black-start capability, which are vital to support the growing shares of variable renewable energy in grid systems. However,  it is often absent in discussions concerning the need and deployment of energy storage due to a lack of understanding and perceived geographic limitations.  A recent report by the International Forum for Pumped Storage Hydropower discusses some of the recent innovations in pumped hydropower storage with consideration of retrofitting and upgrading, as well as hybrid systems. REGlobal presents an extract of this report..

It is axiomatic that short and long term dispatchable energy storage is critical to society. In the past, it was in the form of fossil fuels, and in the future, it must be mostly carbon free over its whole life cycle. While many industrial societies have already had “energy transitions” in the form of the replacement of coal by oil and gas or nuclear energy,  there was only a change in the primary energy source while the system architecture remained unchanged. In these systems, energy storage did not have any important functionality, because a sufficiently high and permanently available reserve capacity was inherently provided by the fuel itself for the thermal power plants  (baseload capability with reliably available capacity)  and because the residual load was never below zero.

Energy storage was provided by nature in the primary resources of coal,  gas,  uranium or oil,  while electricity was generated according to demand by thermal power plants beholden to the Carnot cycle, meaning that energy storage took place before electric power generation by steam turbines. However, the production of renewable energy from wind and sun is detached from demand and it becomes necessary to store the energy after it is collected. This changes the sequence of storage and production and adds additional costs. Currently, policymakers too often assume that it will be possible to forego storage by focusing on grid expansion and the flexible control of production and use such as implied by published articles that propose compensating for the volatility of renewable energy by building controllable and highly flexible new thermal plants (e.g. gas power plants) and by promoting the use of demand-side management (disconnecting consumers in the industrial and private sectors).

Here we present a viable lower carbon approach to the main challenges of energy transition relating to system architecture: The provision for sufficient flexibility when feeding in significant amounts of renewable energy (RE) and ensuring system adequacy (reliably available capacity) during periods of low production from renewable sources can be met with Pumped Storage Hydroelectric systems as the primary system for long duration and medium response time,  with chemical batteries providing short term fast response.   

To this end, we have called for short technology profiles to be submitted that describe new approaches to energy storage with pumped storage hydropower as a base.  The goal of this report is to improve the understanding of innovative PSH technologies and to explore potential benefits and opportunities based on physics and evidence. Over twenty technology briefs were submitted by a wide range of organizations from industry, academia, and government laboratories. The reviewers went through several rounds and some papers were then withdrawn as the ideas were too early for presentation in this Forum, as such, 17 profiles were included in this report. Furthermore, we have asked for detailed costing and carbon accounting analysis to be provided, to which we received a range of responses with varying levels of detail. To compare innovations, an Estimated Technology Readiness Level (TRL) was added for each brief.

For the ideas that have made it through the initial peer review process, a short summary is provided here to promote discussions and help develop a path forward:

  • New approaches for PSH highlighted in this report span three board categories: furthering PSH potential (such as seawater PSH), retrofitting and upgrading PSH systems (such as utilizing abandoned mines), and developing hybrid systems (such as combined with thermal storage).
  • There is emerging research on retrofitting PSH at disused mines, underground caverns, non-powered dams and conventional hydro plants, representing vast untapped PSH potential. Environmental impacts are smaller than greenfield PSH developments with the underground lower reservoir and upper reservoir constructed on an existing brownfield site.
  • Location agnostic systems are made possible by modern tunnel boring machines to create underground water ways and power houses, or convert an existing abandoned mine.
  • Enhanced by latest technological advancements, such as the use of variable speed pump-turbines or hydraulic short circuit, it is possible to enhance the performance and flexibility services provided by existing PSH with viable costs.
  • Hybrid solutions such as PSH coupled with other energy storage technologies (e.g. batteries) and solar PV have to potential to provide a one-stop solution and enable access to revenue streams in electricity markets.
  • Thermal PSH is a new concept that seeks to maximise efficiency with heat storage, and suggests that deep excavated rock when exposed to the air absorbs considerable carbon dioxide from air, reducing system lifecycle carbon footprint.
  • Oceanside seawater PSH has great potential in many places around the world, especially when combined with reverse osmosis to provide freshwater with reduced costs and environmental impacts. In addition, given the large populations near coastlines, it is beneficial to use seawater as the main source for working fluid for PSH with the ocean as the lower reservoir. The system can also then readily provide freshwater by desalination where power turbine outflow dilutes brine output.
  • Financing a first-of-kind technology can be challenging, and it is likely the first project will be implemented under balance sheet financing, possibly by a state-owned utility in support of major PV installations.
  • To catalyse the path forward for development of traditional and new PSH systems, peer-reviewable detailed financial, environmental, and social impact factor cost accounting is needed to enable policy makers and investors to make rational decisions. Research institutions play an important role in helping to produce this analysis and peer review to ensure accuracy.
  • When comparing costs to those of chemical battery systems, full life-cycle costs over the entire lifespan of the system must be considered.
  • Business and policy barriers (feed in tariffs, tax breaks, levies) are as big as technology barriers in the deployment of these innovations. To incentivise the development of carbon-free energy storage systems and disincentivise the continued use of carbon-intensive fossil resources at hand, a Greenhouse Gas Emissions fee (GEF) could be deployed to represent the true cost of carbon emissions in all products produced domestically or imported, which would be collected to support a renewable energy research and development fund to combat global warming.
  • Education is fundamental for the continuous improvement in research and development, as well as increasing awareness on the need for carbon accounting in order to avoid disastrous climate change.

The complete report can be accessed by clicking here