Definition
Basic
Pumped hydro is based on conventional hydroelectric technology. Facilities pump water from one reservoir into another at a higher elevation, typically using lower-priced off-peak electricity. When energy is required, the water in the higher elevation reservoir is released and runs through hydraulic turbines that generate electricity. One key advantage of this system is that the gravitational energy stored in the upper reservoir can be stored for long periods of time with virtually no energy loss.
Commodification
A pumped hydro facility is typically equipped with pumps/generators connecting an upper and a lower reservoir. The pumps utilize relatively cheap electricity from the power grid during off-peak hours to move water from the lower reservoir to the upper one to store energy. During periods of high electricity demand (peak-hours), water is released from the upper reservoir to generate power at higher price.
History
Origin
The earliest PHS in the world appeared in the Alpine regions of Switzerland, Austria, and Italy in the 1890s. The earliest designs use separate pump impellers and turbine generators. Since the 1950s, a single reversible pump-turbine has become the dominant design for PHS. The development of PHS remained relatively slow until the 1960s, when utilities in many countries began to envision a dominant role for nuclear power. Many PHS facilities were intended to complement to nuclear power for providing peaking power.
Popular Use
Some researchers believe development could reach upwards of 4.5 gigawatts per year, once the reality of large-scale renewables integration starts to happen in 2015 and beyond. This forecast may seem lofty, but really it comes down to building 20 – 40 facilities worldwide that average between 500 megawatts and 1 gigawatt.
Money Involved
Costs
In 1985, a 2,100 MW pumped hydro facility cost $1.7 billion, or approximately $800 per kW. Today, a new pumped hydro facility costs approximately $1,500 per kW, give or take. Once built, the cost per kWh of storage is relatively economical, approximately $125 per kWh.
Use
Primary
Most low-carbon electricity resources cannot flexibly adjust their output to match fluctuating power demands. For instance, nuclear power plants best operate continuously and their outputs cannot be ramped up and down quickly. Wind and sunshine are intermittent and therefore the operators of wind turbines and solar power devices have little control over the schedule of electricity output. Utility-scale electricity storage to maintain balance and prevent blackouts remains a significant challenge to a de-carbonized power system.
Pumped hydro storage provides the most proven and commercially viable solution to the aforementioned barrier. It serves to stabilize the electricity grid through peak shaving, load balancing, frequency control, and reserve generation.
Production
Construction
A pumped hydro storage facility is typically equipped with pumps/generators connecting an upper and a lower reservoir. The pumps utilize relatively cheap electricity from the power grid during off-peak hours to move water from the lower reservoir to the upper one to store energy. During periods of high electricity demand (peak-hours), water is released from the upper reservoir to generate power at higher price.
There are two main types of PHS facilities: pure or off-stream PHS, which rely entirely on water that were previously pumped into an upper reservoir as the source of energy; combined or pump-back PHS, which use both pumped water and natural stream flow water to generate power. Off-stream PHS is sometimes also referred to as closed-loop systems. However, some may define closed-loop more strictly as entirely isolated from natural ecosystem.
Challenges
Suitable Location
The deployment of PHS requires suitable terrains with significant elevation difference between the two reservoirs and significant amount of water resource. The construction of a PHS station typically takes many years, sometimes over a decade. Although the operation and maintenance cost is very low, there is a high upfront capital investment, which can only be recouped over decades.
Environment
Environmental impacts are also serious concerns and have caused many cancellations of proposed PHS projects. Conventional PHS construction sometimes involves damming a river to create a reservoir. Blocking natural water flows disrupt the aquatic ecosystem and the flooding of previously dry areas may destroy terrestrial wildlife habitats and significantly change the landscape.
Pumping may also increase the water temperature and stir up sediments at the bottom of the reservoirs and deteriorate water quality. PHS operation may also trap and kill fish. There are technologies to mitigate the ecological impacts. Fish deterrent systems could be installed to minimize fish entrapment and reduce fish kill. The water intake and outlet could be designed to minimize the turbulence. An oxygen injection system could also compensate for the potential oxygen loss due to warming of the water because of pumping.
In some cases, the PHS system may serve to stabilize water level and maintain water quality. The potential impacts of PHS projects are site-specific and must be evaluated on a case-by-case basis. Governments usually require an environmental impact assessment before approving a PHS project.
Possibilities
Power Systems
By storing electricity, pumped hydro storage (PHS) facilities can protect the power system from outages. Coupled with advanced power electronics, PHS systems can also reduce harmonic distortions, and eliminate voltage sags and surges. Among all kinds of power generators, those peak-load generators typically produce electricity at much higher costs than the base-load ones. PHS provides an alternative to peaking power by storing cheap base-load electricity and releasing it during peak hours.
Key Countries
Installed PHS Capacity
(in megawatts)
1. Japan - 25,183
2. United States - 21,886
3. China - 15,643
4. Italy - 7,544
5. Spain - 5,347
Prospects
Outlook
Many existing PHS facilities were built many decades ago and therefore were equipped with outdated and inefficient technology. There is a significant potential in increasing PHS capacity simply by renovating and upgrading the existing PHS facilities. In addition, many existing conventional hydropower stations could be re-engineered to add pump-back units and become combined PHS stations.
Miscellaneous
Further Information
Technology and automation group ABB has won an order worth $23 million from Eskom, South Africa's leading electric utility, to supply an electrical balance of plant solution for the Ingula pumped-storage hydropower plant.
Vietnam is expected to build a pumped-storage hydropower plant with total capacity of 1,500 megawatts in the country's northern mountainous province of Son La in 2013.
A Danish architectural firm is taking a well-known method of energy storage and applying it to renewable energy, turning unused land surrounded by water into Green Power Islands.
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