Pumped storage a technology first developed in the 1890s, plays an increasingly significant role in the renewable energy transition of today as wind and solar power evolve. The most important demand factor for pumped storage is the ambitious renewable-energy targets that are driving national municipal power grids to the brink of failure.
The only solution for the issue of variable power production and hence, the non-dispatchable nature of the IRES plan are electrical energy storages. PSH plants are arguably the most feasible large-scale energy storage technology out of all the currently available options.
The refurbishment of the current 140,000-MW global network of plants is the largest and most consistent demand for pumped-storage hydropower. Japan has over 27,000 MW of operational (and aging) pumped-storage capacity, the United States has 23,000 MW, and Europe has over 25,000 MW of operational (and aging) pumped-storage capacity. Repowering existing plants with newer turbines and generators that provide more energy by using less water.
Need for Enhancement of PSH Technology
The last pumped storage construction spree in the 1970s and 80s took a toll on the environment because of some notable misconceptions about ecology. Almost all currently operating large-scale PSH plants were required to construct at least one dam along the main stem rivers.
Contrary to popular belief, this led to excessive alterations of the adjoining ecology, especially freshwater aquatic life. Consequently, project developers are aiming to minimize such issues by focusing on new plant locations and sizes with minimal environmental impacts in this new wave of PSH development.
One major solution with this regard is already under construction and subject to further research and development – “Closed-loop” pumped storages.
Apart from the scientific aspect, there are numerous economical hindrances in the establishment of PSH projects. EES technologies can provide modules of the transmission network, as well as provide ancillary services and mitigate power wastage by consuming excess energy generation. Market regulations normally bar transmission assets from engaging in wholesale energy and ancillary distribution markets in order to protect grid operators and prevent the possibility of market abuse.
In the contemporary electric market, PSH plants have the ability to add value to ancillary services beyond the time shift of energy delivery. Although, the lack of energy policies regarding energy storage is becoming an obstacle in the utilization of the full potential of PSH plants.
Prospects of Innovation
Regarding the development of psh technology, there is an urgent need for new alternatives to counter the worldwide reservations against pumped storages.
Following are some currently existing ideas as well as prospective innovations practically possible in the near future.
Seawater
Pumped storage Hydropower plants can just as easily be operated using seawater! Although it sounds surprising, apart from some additional challenges, tidal waves can just as easily help in generating energy dedicated to an electrical energy storage system.
In 1999, the Yanbaru project of Okinawa demonstrated seawater pumped storage for the first time. Although decommissioned soon after that, there are new projects on the brink of initiation in Hawaii and Chile which would be raising seawater about a few hundred meters to use in their PSH projects. These projects are estimated to have about 300 MW maximum power generation capacity. [1]
Underground Reservoirs
The concept of underground reservoirs has been under consideration and research for a long while now. According to sources, this just might be a viable alternative for embankment dam reservoirs.
Many relevant projects are being proposed around the world, like in Norton (Ohio), Kentucky, etc. The Mount Hope project in New Jersey plans on utilizing a former iron mine as the lower reservoir. Several other projects subject to approval in Europe are planning on using base metal mines.
In the case of such projects, being built on existing topographies, the capital required and hence the cost-per-kilowatt estimate is lower as compared to surface projects.
This idea could become groundbreaking if abandoned coalmines prove to be adequate for storage.
Diagram with labels to visualize the concept of underground reservoirs
Abandoned Open Pit Mines
Mined out pits provided readily available water storage and elevation difference in well-understood geology. The existing infrastructure associated with the mine can help to reduce the development costs.
The development of pump hydropower in old mined out pits can also offset mine rehabilitation costs and ease the community burden of lost employment opportunities in mine closure.
Kidston Pumped Hydro is an example of a pumped hydropower project that is using Old Mining Pits as reservoirs.
Underwater reservoirs
The announcement claims of the four-year research project StEnSea (Storing Energy at Sea) being successful in the testing of underwater pumped storage reservoirs has led many to believe that the much-awaited revolution in PSH technology is just around the corner.
The basis of the concept describes a hollow sphere to be submerged and anchored at a great depth underwater. This would act as the lower reservoir, while the entire enveloping sea is the upper reservoir. Energy is generated when water gushes in via a reversible turbine integrated inside the sphere.
Similar to regular pumped storages, the turbine pumps the water out again during off-peak hours utilizing the excess electricity from the grid.
The quality of energy is based on the simple laws of pressure in liquids. The deeper the hollow sphere is placed underwater, the more densely it will be able to store energy. In other words, the quality/amount of energy stored is proportional to the height of the column of water above the sphere.
Some of the evident advantages of this breakthrough include:
- No terrain requirement,
- No mechanical structure needed,
- No limit to storage capacity on the vast seabed,
- Limited repercussions in case of mishap (little to no environmental damage,
- No losses to evaporation and surrounding,
- Limited transmission losses in case of power stations and settlements near the shore.
As for estimated produce, a sphere with a storing diameter of 30m placed 700m underwater would provide a 20MWh storage capacity with 5MW power generation. Furthermore, the cost analysis ensues that this could mean the energy would cost only a few euro cents per kWh!
Diagram with labels to visualize the concept of Underwater reservoirs
Decentralized systems
There are micro-pumped storage hydro plants options under consideration that can be built on streams and drinking water networks.
Such plants can aid in the decentralized integration of intermittent renewable energy sources (IRES) technologies like wind and solar power. They provide disseminated energy storage allowing for more variable production and distribution.
Switzerland is a prime example of a country planning to fully utilize this prospective potential. It is insinuated in a study that the total installed capacity of small pumped storage hydropower plants was due to increase by 3 to 9 times in the previous decade.
Home Use
There is quite a lot of research currently underway concerning the idea of nuclear hydropower projects for residential use. Pico hydro projects may be an option as closed-loop plants for domestic energy generation systems.
This could be made possible using small generators and cisterns – which prove effective in acting as covered reservoirs.
Research and Development Prospects
The biggest obstacle in the growth and development of pumped storage hydropower is the economic and financial policy factor.
Countries need to examine financial management to correctly compensate pumped storage hydropower for the entire array of useful services offered to the power grid.
Moreover, the International Hydropower Association (IHA) needs to work on developing systems that will enable owners/operators of pumped storage hydropower plants to evaluate the profitability of switching from fixed-speed to adjustable-speed technologies.
PSH capacity is expected to grow by nearly twenty per cent of the present capacity (26 GW) over the next five years, owing primarily to increased demand for system versatility to incorporate variable renewables in China, parts of Asia, Europe, and the Middle east. Due to recent project advances in China, Australia, and India, the projection has been updated upward from back in 2017.
Besides the rapid increase in global capacity, new alternative sub-branches of the technology are closely underway. The coming decades are expected to introduce a new era of 100% renewable energy generation and optimal PSH potential utilization.