China is gradually transforming its coal-reliant energy system as it moves towards a more sustainable future. With many coal reserves now exhausted, and with outdated mines that do not meet safe production requirements having been or set to close, it’s resulting in a growing number of abandoned mines.
Estimates suggest that such closed or abandoned facilities across the country could be in the region of 15,000, forming an underground space of approximately one million kilometres in length and 15.6 billion m3 in volume.
As Zhongbo Su et al discussed in their research published in the Journal of Energy Storage, many of these mines have complex geological conditions and phased shutdown plans, while research on the development and utilisation of them is somewhat lacking. How to safely and effectively reuse these abandoned underground spaces is now an important issue that needs to be addressed by the coal industry, and is also becoming a major discussion topic amongst scholars in China and abroad.
With China continuing to transform its power system with a commitment to carbon neutrality, efficient and stable energy storage technology will be critical to improve the reliability of variable renewable generation sources.
“Regulating power technology such as pumped storage, characterised by flexibility, cleanliness and high efficiency, will be crucial for the stable operation of the power system. As the most mature, economical and large-scale development option among China’s current peak-shaving power sources,” the authors state, “pumped storage power stations will usher in a golden period in the next decade.”
Underground pumped storage development is being seen as a way to utilise abandoned coal mines and coordinate the development of clean energy in high-potential communities. It will be able to:
- Complement renewable energy and abandoned mines in time and space.
- Reduce the impact of random renewable energy grid connections on the power system.
- Provide strategic space for the exploitation of new energy and smart grids.
- Help promote the low-carbon transformation of China’s energy system.
- Achieve the goal of coordinated development of green, low-carbon and recycling policies.
In their research, Zhongbo Su et al introduce a novel framework to evaluate the development potential for underground pumped storage power stations in the Yellow River Basin.
Flowing through nine provinces in China, the 5464km long Yellow River is the country’s second-longest river. It also acts as a corridor connecting the river source, upper, middle, lower reaches and estuaries, as well as being a significant source of China’s power transmission from west to east and coal transportation from north to south. With nine coal bases in the Yellow River Basin, there is a large amount of underground space left behind after coal mining. As the authors point out, the distribution of abandoned coal mines in the nine provinces of this river basin partially overlaps the geographical location of the wind/solar energy distribution belt in northern China.
The main advantages of using abandoned coal mines for water storage include:
- Shortening the construction period due to the geological data acquired at the early stage of coal mining.
- Significantly reducing construction costs due to existing available infrastructure.
- Providing favourable topographical conditions because of the natural altitude intercept in coal mines’ underground space.
- Offering a large total storage volume.
- Offering stable geotechnical conditions and a permanent environment for long-term hydraulic infrastructure.
- Reducing the evaporation of water resources within mines and offering groundwater resources for supplementation.
Although the potential feasibility of such facilities has increasingly attracted the attention of scholars, the authors say it remains unexplored. Systematic theoretical methods and technical specifications are described as being insufficient for their construction, while there is a lack of relevant supporting policies and legal systems currently in place.
Zhongbo Su et al say that evaluating the regional development potential of underground pumped storage in the Yellow River Basin will be of “guiding significance for promoting its construction”, and thereby alleviating the volatility problems of wind and solar power within the Chinese power system.
Lack of knowledge
The use of geomembrane lining systems for pumped storage hydropower reservoirs has been the focus of research by the US Department of Energy’s HydroWires initiative.
The first application of these in the US can be traced back to the 200MW Mount Elbert pumped storage powerplant in Colorado, which was constructed by the US Bureau of Reclamation in 1981. And the first one constructed using an exposed or uncovered geomembrane lining system is thought to be the 30MW Okinawa Yanbaru seawater demonstration pumped storage project in Japan, which was completed in 1999.
Newer facilities designed and constructed using either covered or exposed geomembrane lining systems include the 30MW Calheta/Pico da Urze in Madeira, the 344MW Kokhav Hayarden and 300MW Mount Gilboa projects in Israel, and the 350MW Abdelmoumen in Morocco. However, no new pumped storage facilities have been constructed in the US using geomembrane lining systems since the Mount Elbert power plant.
Acknowledging that there is a lack a body of knowledge in the design, construction, and performance of these systems in the US, this HydroWire report summarises the results of a scoping study performed to research the use of geomembrane lining systems for pumped storage hydropower reservoirs. It consisted of a literature review of pertinent and publicly available information about geomembrane lining materials and their use and applicability to these reservoirs.
Key findings from the report were that:
- There are a number of suitable geomembrane materials available in the marketplace. However, the selection of a given one is subject to a variety of factors, and there is not one material that can be considered superior in all factors.
- Important considerations in the design and construction of a geomembrane lining system also include the cover and protection of the geomembrane lining, drainage and collection of water that leaks through the geomembrane lining, and support of the geomembrane lining material.
- Detailed design of a geomembrane lining system cannot be completed until a geomembrane lining manufacturer has been selected. For design-bid-build type projects, the owner and engineer will need to decide whether to select the manufacturer during preparation of the overall project design, or leave final design details and selection of the manufacturer to the contractor. For design-build and engineer-procure-construct projects, selection of the lining system and geomembrane lining system may be left to the design-build or EPC teams.
- No pumped storage specific design guidelines for geomembrane lining systems or specific regulations on their use in the US could be identified in the literature search conducted for this study.
Areas identified for further investigation and study include:
- Expanding the assessment to include all lining systems such as dense asphalt concrete, concrete facings and clay.
- Performing a market assessment.
- Engaging the Federal regulatory Energy Commission and other agencies to better understand regulatory issues.
- Developing a cost model for pricing geomembrane lining systems for pumped storage applications.
- Developing a preliminary reference design and cost assessment.
Boosterpump
Interest in upgrading existing hydropower plants to pumped storage facilities is on the rise due to the need for energy storage in the ongoing energy transition.
According to research published in Renewable Energy, the boosterpump concept offers a possible solution for overcoming any limitations when reconstructing existing hydropower plants to pumped storage. Studies have shown that it is technically feasible for both the 50MW Roskrepp and the 300MW Vinje hydropower plants in southern Norway.
Commissioned in 1979 and in need of major refurbishment, Roskrepp has one vertical Francis unit and an average annual production of 105GWh, utilising the head between the upstream Roskreppfjorden and the downstream Øyarvatn reservoirs. Reconstruction into a pumped storage plant is of interest owing to the large upstream and downstream reservoirs, the short operation time of the power plant, and an operational restriction on drawdown of the lower reservoir during summer.
Vinje was commissioned in 1964 and has three Francis turbines, each having a nominal discharge of 50m³/sec. This project utilises the head between Våmarvatn and Vinjevatn. Once again, reconstruction of Vinje into a pumped storage project is of interest due to the large upstream and downstream reservoirs, and the short operation time of the power plant. In addition, one of the units is currently experiencing challenges related to vibration from one of the runners, and so changing the runner may be combined with an upgrade to a reversible pump turbine.
Research carried out by the Norwegian University of Science and Technology, Statkraft Energi and Tidetec presents technical solutions on a feasibility level. It explains that the booster pump makes it possible to reconstruct the turbine and rehabilitate the generator unit with the same fixed speed for both turbine and pumping. It can be placed in the existing tailrace surge tank and is connected and disconnected to the waterway with gates. The proposed arrangement claims to solve all challenges related to start, stop, load changes and pump trip by introducing a water volume between the reversible pump turbine and boosterpump through a system of overflow weirs.
The technology is currently considered to be at TRL 4-5, and to lift to a higher level, experimental testing of the full system in relevant conditions is necessary. Before full-scale application can be realised, more research and development are required. Further work on this topic is encouraged to develop solutions that are more technically optimised and that can cut costs to make them more economically attractive.
According to the authors, Kaspar Vereidea, Livia Pitorac, Rachel Zeringue and Arne Kollandsru, the boosterpump is a promising solution to allow for the construction of more pumped storage, a necessary requirement for the renewable energy transition.
Plan ahead
Earlier in the year, the President of the International Hydropower Association, Malcolm Turnbull, wrote an open letter to the UK Prime Minister Rishi Sunak, welcoming the government’s decision to promote the development of long duration storage through a cap and floor scheme.
Turnbull reiterated how 7GW of shovel-ready pumped storage projects, with over 135GWh of storage capacity in the UK, will be “absolutely critical” for a least cost transition to zero emission energy.
Governments must plan ahead for their electricity storage to ensure projects are underway as soon as possible, Turnbull said. He also spoke about how he had to confront such issues during his time as Prime Minister of Australia. In 2016, a statewide electricity blackout in South Australia was caused by rapid renewable expansion with little thought given to firming. Consequently, Turnbull’s government put storage and pumped hydro on the agenda and started work on Snowy Hydro 2.0, which will be the largest pumped storage project in the world upon completion.
If governments are not building long-duration storage projects themselves, they must provide the right framework to enable the rapid deployment of pumped storage, he goes on to say. As most electricity markets are designed to pay for generation, Turnbull says there are no obvious financial incentives to build the long-duration storage that a renewable energy system requires. Without such incentives, he adds, “there is a real risk that decarbonisation will stall, just as it needs to accelerate”.
To get the most out of such a policy mechanism, Turnbull recommends that the UK government:
- Delivers the scheme quickly so that the first application window opens by early 2025 and is focused on mature projects. This will get shovel-ready projects up and running and boost investor confidence.
- Guarantees that additional application windows will be held.
- Introduces soft targets for long-duration energy storage to instil investor confidence.
- Considers long-term contract visibility alongside comprehensive reform of the electricity market to ensure better renumeration for grid services and future pumped storage projects.
“Taken all together, these policies would also provide a blueprint for other countries that are considering how to ensure a reliable and affordable decarbonised electricity grid,” Turnbull concluded in his letter. “You can count on the International Hydropower Association as a strong ally in this critical work.”
Scottish plans
Plans have been unveiled to develop what could be the UK’s most efficient pumped storage project. Glen Earrach Energy Limited (GEE) is working on the 2GW facility in Scotland that will utilise the geography of Loch Ness and deliver up to 30GWh of clean energy.
“International experts have identified Glen Earrach Energy’s pumped storage hydro project as the most efficient in the UK, possibly even Europe,” says GEE Director, Roderick MacLeod.
The project’s efficiency is attributed to the substantial height difference between the upper and lower reservoirs, optimising power generation while minimising the impact on Loch Ness water levels. Central grid proximity to existing wind farms also increases the potential efficiency of the project.
GEE has started consultations with local communities, businesses, and government agencies to integrate the project into the environment and the community. The company is working with a consortium of advisors and experts, including AECOM, Alpiq, Frontier Economics, and LCP-Delta, and has submitted a scoping request to the Scottish Government’s Energy Consents Unit.
Also in Scotland, Drax is progressing plans to build a new 600MW underground plant adjacent to its existing Cruachan facility. Seismic surveys are being taken to provide crucial geological data about the rock in which the new plant would be housed.
“The expansion of Cruachan will be one of the most significant engineering projects in Scotland for many decades,” Steve Marshall, Development Manager, said. “The start of these seismic surveys of the mountain is a real milestone moment for the project, and everyone at Drax is excited to see the development take another step forward. These surveys will further complement borehole drilling works undertaken in 2022 and 2023 at the site.”
The seismic surveys involve drilling holes into the rock and laying small explosive charges, which are detonated to produce a powerful sound wave within the rock mass. It is expected that the sound wave will penetrate up to 60m below the ground surface before its reflected signal fades away. Sensitive equipment called geophones mounted on the ground measures the progress of the sound waves to provide information about fractures, fissures, or potential weak spots in the rock.
In other news, Holcim is playing a key role in the Kidston pumped storage hydropower project, set to become operational during 2025 in Queensland, Australia. Located 280km north-west of Townsville on the site of a decommissioned gold mine, Kidston is the world’s first pumped hydro power project to use 100% recycled aggregates in all its concrete. This initiative has been in development since 2018, with Holcim Australia collaborating with McConnell Dowell and John Holland JV.
Holcim has prioritised sustainability on the project by using 100% recycled aggregates in all supplied concrete for both surface works and underground in the 2km access tunnel to the pumphouse. The project also makes use of mining waste, processed on-site, to replace the need for new quarry extraction.
The Kidston project is a significant step towards Australia’s 2050 net-zero target and will help Queensland meet its renewable energy goals of 70% by 2032 and 80% by 2035. Once operational, it will generate enough power for towns with a combined population of 400,000 for eight hours daily.
Pumped storage potential has also come under the spotlight in Africa. In April, the World Bank issued a solicitation for an analytical study to evaluate the conceptual role and economic viability of pumped hydropower storage in the Southern Africa Power Pool. The study aims to identify the costs, benefits, and value of pumped storage in enhancing energy security, climate resilience, and facilitating a low-carbon transition in the region.
This article first appeared in International Water Power magazine.
