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Pumped hydro Storage Plants: one of the cheapest sources of electricity

Hydropower plants can be operated to provide base-load power as well as peak-load supply through pumped-storage, says Jesús Sancho, ME Managing Director for ACCIONA

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Jesús Sancho, ME Managing Director for ACCIONA
Jesús Sancho, ME Managing Director for ACCIONA

Water is the most important resource on Earth and without it, we wouldn’t survive. For reasons of survival, since the dawn of time, humans have had to come up with ways of making the most out of their natural resources.

Historically, the human being has been improving different techniques of obtaining energy from water to create what we call hydropower. Hydropower, which is the generation of power by harnessing energy from moving water, is one of the main sources of renewable and clean energy in the world and is the most important source for energy storage.

It is estimated that storage hydropower represents 99% of the world’s operational electricity storage. In recent years, there have been significant global developments in hydropower.

The total installed capacity has grown by 39% from 2005 to 2015, with an average growth of about 4% per year. The rise has been concentrated in emerging markets. In 2016, hydropower installed capacity reached 1,064 gigawatts (GW) globally, generating 71% of all renewable electricity and 16.4% of the world’s electricity from all sources.

Sustainability

Nevertheless, dam construction must continue to evolve and progress. For that to happen, companies like ACCIONA that specialise in this work (with 14 hydroelectric Power Plants built so far worldwide) must invest in innovation, developing new tools or working techniques that lead to quicker, more efficient construction. 

Sustainability is another value to be kept at the forefront in the area of construction, especially for dams.

Water has helped to power our lives for more than a century. While wind and solar power continue to grow, water can also play an important role bringing more renewable resources into the power grid. One way is by storing energy through a technology known as pumped storage hydropower. In a conventional hydropower plant, the water from the reservoir flows through the plant, exits and is carried downstream.

However, in a pumped-storage plant the water runs through a closed circuit and is moved between two reservoirs:

  • Upper reservoir: Like in a conventional hydropower plant, a dam creates the upper reservoir. The water in this reservoir flows through the hydropower turbine to create electricity usually during the day.
  • Lower reservoir: It stores the water exiting the hydropower plant and rather than re-entering the river and flowing downstream it is accumulated here to be pumped up again at a convenient time usually during the night.

Using a reversible turbine, the plant can pump water back to the upper reservoir. This is done in off-peak hours. Essentially, the second reservoir refills the upper reservoir. By pumping water back to the upper reservoir, the plant has the water needed to generate electricity during periods of peak consumption.

Hydropower is one of the most flexible and sustainable renewable energy sources. It can be operated to provide base-load power as well as peak-load supply through pumped-storage, which is the most dominant form of energy storage on the electric grid today.

However, estimates indicate the availability of approximately 10,000TWh/year of unutilised hydropower potential worldwide. In 2015, pumped storage hydropower installed capacity worldwide was approximately 145GW.

East Asia uses this technology the most with an installed capacity of about 58GW. Japan’s installed capacity is 28GW and China’s is 23GW. The Middle East’s pumped storage installed capacity is 1.7GW.

Despite the wide adoption of other renewable energy sources such as solar and wind, hydroelectricity maintains its position as the cheapest source of electricity globally according to the International Renewable Energy Agency (IRENA).

The global weighted average levelized cost of electricity from new projects commissioned in 2017 was US$0.05/kWh from hydropower, compared with US$0.06 for onshore wind, $0.07 for bioenergy and geothermal projects and $0.10for utility-scale solar photovoltaic.

However, its potential has never been exploited in the GCC. As part of the Dubai Clean Energy Strategy 2050, launched by His Highness Sheikh Mohammed bin Rashid Al Maktoum, the UAE Vice President and Prime Minister and the Ruler of Dubai, UAE have launched several projects, including the hydroelectric pumped storage power station at Hatta (Dubai), the Hydroelectric PSHPP project.

Pumped hydro storage

This project will be the first of its kind in the Arabian Gulf, with a total capacity of 250MW by hydroelectricity from water stored in the Hatta Dam and a lifespan of up to 80 years. 

The hydroelectric power station will generate electricity by making use of the water stored in the Hatta Dam, which can store up to 1,716 million gallons and an upper reservoir that will be built in the mountain that can store up to 880 million additional gallons.

The upper reservoir will be 300 metres above the dam level. During off-peak hours of the grid, the reversible turbines will work as pumps to return water from the lower dam to the upper reservoir.

During peak-load hours, the turbines will make use of the water stored in the upper reservoir and use it to generate electricity and connect it to DEWA’s grid. The efficiency of power production will reach 90% with a 90-second response to demand for electricity.

The topic of energy storage has gained prominence in recent years and plays a key role in the design of modern electricity grids. Developments in other energy storage technologies may one day challenge pumped storage hydro’s near-monopoly on low-cost electricity storage. But for now, pumped hydro is still the only technology offering economically viable large-scale storage.

Keeping in mind this context, if there is one thing that will not disappear with the passage of time, it is the human effort to achieve greater quality of life, in which access to basic resources, such as water, is guaranteed in an increasingly populated world. This means that the great engineering works, like dams, will continue to be what they have been for centuries - essential infrastructures for society.

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