1

Chapter 2

Pumped Hydroelectric Storage

Chi-Jen Yang

Duke University, Durham, North Carolina 27708, USA. Tel. +1 919 9459075. E-mail

address: cj.y@duke.edu

Contents

Introduction

Pros and Cons

Historical Developments

Prospects

4.1 Revival of Conventional Pumped Hydroelectricity Storage

4.2 Alternative and Novel Pumped Hydroelectricity Storage designs

4.3 Retrofits of existing PHS and conventional hydropower stations

References

Abstract

Pumped hydroelectric storage (PHS) is the most established technology for utility-scale

electricity storage and has been commercially deployed since the 1890s. Since the 2000s,

there have been revived interests in developing PHS facilities worldwide. Because most

low-carbon electricity resources (for example, wind, solar, and nuclear) cannot flexibly

adjust their output to match fluctuating power demands, there is an increasing need for

bulk electricity storage due to increasing adoption of renewable energy. This chapter

introduces the PHS technology, the pros and cons, its historical developments, and the

prospect.

Key Words:

Pumped Hydroelectric Storage; Closed-loop; Pump-back; Peak Shaving

1. Introduction:

Pumped hydroelectric storage (PHS) is the most widely adopted utility-scale electricity

storage technology. Furthermore, PHS provides the most mature and commercially

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available solution to bulk electricity storage. It serves to stabilize the electricity grid

through peak shaving, load balancing, frequency regulation, and reserve generation.

Japan currently has the largest installed PHS capacity in the world [1], followed by China

[2] and the United States [3]. China currently has the most aggressive plan to expand

PHS installation, with 14 GW under construction and many more planned. China is

expected to surpass Japan in installed PHS capacity by 2018. Table 1 shows the installed

PHS capacities in major countries [2, 3, 4, 5].

Table 1. Installed PHS capacities.

Country

Installed PHS Capacity

/(MW)

Japan 27 438

China 21 545

USA 20 858

Italy 7 071

Spain 6 889

Germany 6 388

France 5 894

India 5072

Austria 4 808

Korea, South 4 700

United Kingdom 2 828

Switzerland 2 687

Taiwan 2 608

Australia 2 542

Poland 1 745

Portugal 1 592

South Africa 1 580

Thailand 1 391

Belgium 1 307

Russia 1 246

Czech Republic 1 145

Luxembourg 1 096

Bulgaria 1 052

Iran 1 040

Slovakia 1 017

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Argentina 974

Norway 967

Ukraine 905

Lithuania 900

Philippines 709

Greece 699

Serbia 614

Morocco 465

Ireland 292

Croatia 282

Slovenia 185

Canada 174

Romania 53

Chile 31

Brazil 20

A PHS facility is typically equipped with pumps and generators connecting an upper and

a lower reservoir (Figure 1). 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 a higher price.

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Figure 1. PHS Diagram.

There are two main types of PHS facilities: (1) pure or off-stream PHS, which rely

entirely on water that were previously pumped into an upper reservoir as the source of

energy; (2) combined, hybrid, or pump-back PHS, which use both pumped water and

natural stream flow water to generate power [4]. Off-stream PHS is sometimes also

referred to as closed-loop systems. However, some may define closed-loop systems more

strictly as being entirely isolated from natural ecosystems. The U.S. Federal Energy

Regulatory Commission defines closed-loop pumped storage as projects that are not

continuously connected to a naturally-flowing water feature [5].

The efficiency of PHS varies quite significantly due to the long history of the technology

and the long life of a facility. The round-trip efficiency (electricity generated divided by

the electricity used to pump water) of facilities with older designs may be lower than

60%, while a state-of-the-art PHS system may achieve over 80% efficiency.

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2. Pros and Cons

By storing electricity, 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.

PHS facilities provide very large capacities of electricity, with low operation and

maintenance cost, and high reliability. The levelized storage cost for electricity using

PHS is usually much lower than other electricity storage technologies.

There are several drawbacks to PHS technology. 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 in civil construction, which can only

be recouped over decades.

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 [6]. 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.

Most PHS facilities have good safety records. Nevertheless, the upper reservoir failure of

Taum Sauk PHS station in the United States should be heeded as a reminder of its

potential danger. On December 14, 2005, the upper reservoir of Taum Suak was

overfilled, and the embankment was then overtopped and breached. The suddenly leased

water washed away over one square kilometer of forest, uprooted all the trees and

obliterated a house in its path. Although the Taum Sauk PHS station was later repaired

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and brought back to operation in 2010, the reservoir failure incident should provide

important lessons for future PHS design, construction and operation.

3. Historical Development

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 [7]. 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 nuclear power in providing peaking

power.

In the 1990s, the development of PHS significantly declined in many countries. Many

factors may have contributed to the decline. Low natural gas prices during this period

make gas turbines more competitive in providing peaking power than PHS.

The earliest PHS facilities were built in Italy and Switzerland in the 1890s [7]. Before the

1950s, most of the PHS facilities were located in Europe. The United States completed its

first PHS station in 1928. Japan built its first PHS in 1934 and China in 1968. Since the

1950s, the adoption of PHS has gradually spread all over the world. As of 2014, the U.S.

DOE Global Energy Storage Database recorded over three hundred operating PHS

stations with total capacity of 142 GW in 41 countries [8].

The design and site selection for PHS facilities are greatly influenced by national policies.

Japan, China, and the United States have the largest PHS capacities in the world. Table 2,

3, and 4 list the PHS facilities in Japan, China, and the United States. The distinctive

policies and regulatory regimes for PHS in Japan, China, and the United States offer

interesting contrasts and may reveal useful policy insights.

The buildup of PHS capacities in Japan has been relatively steady over several decades.

The Japanese power sector is mainly composed of vertically-integrated regional electric

power utilities, which build, own and operate the PHS facilities. The vertically integrated

power sector structure has provided a stable and predictable business environment that is

favorable to the investments in PHS. The path of PHS development PHS in Japan is an

epitome of PHS development worldwide. Before the early 1960s, PHS facilities were

rare and small, mostly of hybrid design. The deployment started to accelerate since the

1960s and continued throughout the 1990s. Since the 1970s, pure/off-stream PHS has

become the dominant design, which is likely a result of increased concerns for ecological

impacts of the hybrid systems. In addition to having the worlds largest PHS capacities, Japan is also the world leader in employing seawater PHS and variable-speed PHS.

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Table 2 PHS stations in Japan.

Plant Name

(Japanese)

Plant Name

(English) Location Type

Rating/

(MW)

Commission

Year

Ikejirigawa Nagano Prefecture Hybrid 2 1934 Omorikawa Kochi Prefecture Hybrid 12 1959 Morotsuka Miyazaki Prefecture Hybrid 50 1961 Hatakenagi No.1 Shizuoka Prefecture Hybrid 137 1962 Mio Nagano Prefecture Hybrid 36 1963 Ikehara Nara Prefecture Hybrid 350 1964 Ananaigawa Kochi Prefecture Hybrid 13 1964 Shiroyama Kanagawa Prefecture Pure 250 1965 Yagisawa Gunma Prefecture Hybrid 240 1965 Shinnaruhagawa Okayama Prefecture Hybrid 303 1968 Nagano Fukui Prefecture Hybrid 220 1968 Kagetaira Tokushima Prefecture Hybrid 47 1968 Azumi Nagano Prefecture Hybrid 623 1969 Takane No.1 Gifu Prefecture Hybrid 340 1969 Midono Nagano Prefecture Hybrid 245 1969 Kisen'yama Kyoto Pure 466 1970 Shintoyone Aichi Prefecture Hybrid 1 125 1972 Numappara Tochigi Prefecture Pure 675 1973 Okutataragi Hyogo Prefecture Pure 1 932 1974 Niikappu Hokkaido Hybrid 200 1974 Ohira Kumamoto Prefecture Pure 500 1975 Namwon Hiroshima Prefecture Pure 620 1976 Mazekawa No.1 Gifu Prefecture Hybrid 288 1976 Futai Dam Niigata Prefecture Pure 1 000 1978 Shin-Takasegawa Nagano Prefecture Hybrid 1 280 1979 Okuyoshino Nara Prefecture Pure 1 206 1980 Okuyahagi No.2 Aichi Prefecture Pure 780 1980 Okuyahagi No.1 Aichi Prefecture Pure 323 1980 Tamahara Gunma Prefecture Pure 1 200 1981 Motokawa Kochi Prefecture Pure 615 1982 Daini Numazawa Fukushima Prefecture Pure 460 1982 Takami Hokkaido Hybrid 200 1983

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Matanoagawa Tottori Prefecture Pure 1 200 1986 Tenzan Saga Prefecture Pure 600 1986 Imaichi Tochigi Prefecture Pure 1 050 1988 Shimogo Fukushima Prefecture Pure 1 000 1988 Okawachi Hyogo Prefecture Pure 1 280 1992 Okumino Gifu Prefecture Pure 1 500 1994 Shiobara Tochigi Prefecture Pure 900 1994 Futai Dam No.2 Niigata Prefecture Pure 600 1996 Kazunogawa Yamanashi Prefecture Pure 1 200 1999

Okinawa Seawater

Pumped Hydro Okinawa Prefecture Pure 30 1999

Kannagawa Gunma Prefecture Pure 940 2005 Omarugawa Miyazaki Prefecture Pure 1 200 2007 Shumarinai Hokkaido Hybrid 1 2013 Kyogoku Hokkaido Pure 200 2014

China is a latecomer in the worldwide PHS deployment, but it is catching up quickly.

With the largest PHS capacities planned and under construction, China will soon

overtake Japan as the host of the largest PHS capacities in the world. Most of the PHS

facilities in China are relative new, with large capacity and off-steam design.

Chinas regulatory regime for PHS has been through great changes in the past two decades. Before 2004, most of the PHS facilities in China were built by local

governments and local grid companies with diverse pricing models. In 2002, China

restructured its power sector by separating them into 2 state-owned grid companies and 5

power generation corporations. In 2004, the National Development and Reform

Commission promulgated a regulation which specified that PHS stations are transmission

facilities and should be constructed and managed by the grid companies, and that the

construction and operation costs of PHS should be incorporated into the operation costs

of the grid companies [9]. The decision to treat PHS as transmission facilities has

contributed to the rapid expansion of PHS in China.

Table 3 PHS stations in China.

Plant Name

(Chinese)

Plant Name

(English) Province Type

Rating/

(MW)

Commission

Year

9

Gangnan Hebei Hybrid 11 1968

Miyun Beijing Hybrid 22 1975

Panjiakou Hebei Hybrid 270 1992

Cuntangkou Sichuan Pure 2 1992

Guangzhou Phase 1 Guangdong Pure 1,200 1994

Shisanling Beijing Pure 800 1997

Yangzhuoyong Tibet Pure 90 1997

Xikou Zhejiang Pure 80 1998

Tianhuangping Zhejiang Pure 1 800 2000

Guangzhou Phase 2 Guangdong Pure 1 200 2000

Xianghongdian Anhui Hybrid 80 2000

Tiantang Hubei Pure 70 2001

Shahe Jiangsu Pure 100 2002

Huilong Henan Pure 120 2005

TONGBAI Zhejiang Pure 1 200 2006

Hakusan Jilin Hybrid 300 2006

Taian Shandong Pure 1 000 2007

Langyashan Anhui Pure 600 2007

Xilongchi Shanxi Pure 1 200 2008

Yixing Jiangsu Pure 1 000 2008

Zhanghewan Hebei Pure 1 000 2008

Huizhou Guangdong Pure 2 400 2009

Heimifeng Phase 1 Hunan Pure 1 200 2009

Bailianhe Hubei Pure 1 200 2010

Baoquan Henan Pure 1 200 2011

Pushihe Liaoning Pure 1 200 2012

Xiangshuijian Anhui Pure 1 000 2012

Xianyou Fujian Pure 1 200 2013

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Most of the PHS facilities in the United States were built in the 1970s and 1980s. Since

the 1990s, the construction of PHS slowed down in the United States. Environmental

concerns caused the cancellation of several PHS projects and significantly prolonged the

permitting process. Power sector restructure also contributed to this slowdown. During

the 1990s, the United States started to restructure the power sector by separating

generation from transmission. The nature of energy storage falls into the gray area

between generation and transmission [10]. Because the net electricity output of PHS

operation is negative, a PHS facility usually cannot qualify as a power generator.

Although their crucial load-balancing and ancillary services to the grid and reduces the

needs for transmission upgrades, PHS facilities are not recognized as parts of the

transmission infrastructure [11]. This confusion in business models has deterred the

development of PHS in the United States.

Table 4 PHS stations in the United States.

Plant Name County State

Type

Rating/

(MW)

Commission

Year

Rocky River Litchfield CT Hybrid 31 1928

Flatiron Larimer CO Hybrid 9 1954

Hiwassee Dam Cherokee NC Hybrid 95 1956

Lewiston Niagara Niagara NY Hybrid 240 1962

Taum Sauk Reynolds MO Pure 408 1963

Yards Creek Warren NJ Pure 453 1965

Cabin Creek Clear Creek CO Pure 300 1967

W R Gianelli Merced CA Pure 424 1967

Muddy Run Lancaster PA Pure 1 072 1967

ONeill Merced CA Pure 25 1968

Thermalito Butte CA Hybrid 83 1968

Edward C Hyatt Butte CA Hybrid 293 1968

Salina Mayes OK Pure 288 1970

FirstEnergy Seneca Warren PA Pure 469 1970

Smith Mountain Franklin VA Hybrid 247 1970

Mormon Flat Maricopa AZ Hybrid 54 1971

Horse Mesa Maricopa AZ Hybrid 100 1972

Degray Clark AR Hybrid 28 1972

Northfield Mountain Franklin MA Pure 940 1973

Ludington Mason MI Pure 1 979 1973

Blenheim Gilboa Schoharie NY Pure 1 000 1973

Jocassee Pickens SC Pure 612 1974

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Bear Swamp Berkshire MA Pure 600 1974

Castaic Los Angeles CA Hybrid 1 275 1976

Carters Murray GA Hybrid 250 1977

Fairfield Pumped Storage Fairfield SC Pure 511 1978

Raccoon Mountain Hamilton TN Pure 1 714 1979

Wallace Dam Hancock GA Hybrid 209 1980

Grand Coulee Grant WA Hybrid 314 1980

Harry Truman Benton MO Pure 161 1981

Mount Elbert Lake CO Pure 200 1983

Helms Pumped Storage Fresno CA Pure 1 053 1984

Clarence Cannon Ralls MO Hybrid 31 1984

Bath County Bath VA Pure 2 862 1985

J S Eastwood Fresno CA Pure 200 1987

Bad Creek Oconee SC Pure 1 065 1991

Waddell Maricopa AZ Pure 40 1993

North Hollywood Los Angeles CA Hybrid 5 1993

Rocky Mountain Floyd GA Pure 848 1995

Richard B Russell Elbert GA Hybrid 328 2002

Lake Hodges San Diego CA Pure 42 2012

The diverged paths of PHS development in Japan, China, and the United States have

shown that the national regulatory and institutional environments have tremendous

impacts on the deployment of PHS. PHS facilities are large facilities that require huge

upfront capital investments, and the paybacks are spread over many decades. If a

government wishes to facilitate the development of PHS, it needs to provide a stable and

predictable regulatory environment, and a reasonable pricing scheme that allow the PHS

facilities to be compensated for their services to the transmission grid.

4. Prospects

In recent years, due to increasing concern for global warming and the call to de-carbonize

electricity, there has been increasing commercial interest in PHS [12]. Developers are

actively pursuing new PHS projects around the world.

4.1 Revival of conventional PHS

More than 100 new PHS plants with about 74 GW capacities worldwide are expected to

be in operation by 2020 [13]. China has the most aggressive plan. In 2014, the Chinese

government announced its plan to more than quadruple its current PHS installations to a

total capacity of 100 GW by 2025 [14]. Driven by the need to accommodating rapid

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growth of intermittent renewable electricity, Europe is also witnessing a renaissance of

PHS, particularly in Spain, Switzerland, and Austria, with 27 GW new PHS capacity

expected by 2020 [15]. Although Japan already has the highest density of PHS

installation in the world, Japanese power companies are continuing to develop more PHS

plants. The United States is also experiencing a revival of PHS development. In 2014, the

U.S. Federal Energy Regulatory Commission issued licenses to construct and operate two

new PHS facilities (1.3 GW Eagle Mountain PHS and 400MW Iowa River PHS).

Another application for construction and operation license (for the 1 GW Parker Noll

PHS) is currently under review. In addition, there are over 40 proposed PHS projects

currently conducting feasibility studies with issued preliminary permits. With the mature

technology and high volume of commercial development activities, PHS will certainly

remain the most dominant energy storage technology in the foreseeable future.

4.2 Alternative and novel PHS designs

Variable Speed PHS: Most existing PHS facilities are equipped with fixed-speed pump

turbine. While those fixed-speed PHS facilities may provide economical bulk electricity

storage, they can only provide frequency regulation during its generating mode, but not in

pumping mode. With the increasing adoption of variable power sources such as wind and

solar, there is an increasing demand for frequency regulation. New variable speed

technology allows PHS facilities to regulate frequency at both pumping and generating

modes. Japan has pioneered the variable-speed PHS technology and has successfully

operated such systems at the Okawachi PHS station for over twenty years [16, 17].

European countries are actively introducing variable speed PHS in recent years in order

to accommodate more variable renewable electricity in their power portfolios [18].

Seawater PHS: In addition to the worldwide revived interests in developing conventional

PHS projects, many developers are also proposing new approaches. Japan has pioneered

seawater PHS. The Okinawa seawater PHS station, which has commenced operation in

1999, is the worlds first seawater PHS system [19]. The Okinawa PHS station uses the open sea as the lower reservoir together with a constructed upper reservoir at 150 meters

above sea level. New seawater projects have been proposed in Ireland, Greece, Belgium,

and the Netherlands [20, 21, 22, 23]. The energy islands concept proposed by the Dutch

consulting company DNV KEMA has an unusual approach; they plan to use the open sea

as the upper reservoir, and construct the lower reservoir by dredging and building a ring

of dikes at a depth of 50 m below sea level.

Underground PHS: Researchers since the 1970s [24], have proposed the possibility of

utilizing underground caverns as lower reservoirs for PHS projects but so far none have

been built [25]. The commercial interests in developing underground PHS have

resurfaced in recent years in the United States. Several U.S. developers have received

13

preliminary permits to study the feasibility of building underground PHS facilities at their

identified sites. A British company Quarry Battery is also working on developing

underground PHS facilities with abandoned quarries [26].

Compressed Air PHS: A promising innovative design (Figure 2) is to replace the upper

reservoir in PHS with a pressurized water container [27]. The air within the pressure

vessel becomes pressurized when water is pumped into the vessel. Instead of storing

potential energy in elevated water, the proposed compressed air pumped hydro system

stores the energy in compressed air. This innovative design could potentially free PHS

from the geographic requirements and make it feasible at almost any location with

flexible and scalable capacity. This concept is discussed in more detail in chapter 7.

Figure 2. Diagram of compressed air PHS

Undersea PHS: Another innovative concept (Figure 3) is to utilize the water pressure at

the bottom of the sea to store electricity from off-shore wind turbines [28]. The system

places submerged pressure vessels (hollow concrete tank) on the sea floor. It uses

electricity to pump water out of the tank to store energy, and generate electricity when

seawater is filling into the tank through the generator. This concept is further discussed in

chapter 6.

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Figure 3. Diagram of undersea PHS

4.3 Retrofits of existing PHS and conventional hydropower stations

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. Upgrades

to old PHS facilities typically include replacing outdated pumps/turbines, impellers, and

control systems with new advanced equipment. Many existing PHS station may increase

the capacity by 15% to 20% and efficiency by 5% to 10% [7]. In addition, many existing

conventional hydropower stations could be re-engineered to add a lower reservoir and

pump-back units to pump the water back to the upper reservoir during off-peak hours,

and become combined PHS stations for use with intermittent energy from renewable

sources such as wind turbines and solar panels.

Although PHS may be an essential enabling technology for de-carbonizing electricity, the

political will to mitigate carbon dioxide and to remove regulatory barriers for PHS is far

from certain. The price of natural gas is also a key determinant in the future of PHS.

Because PHS is essentially a peak-load technology, which competes directly with gas-

15

fired power, low natural gas price may render PHS uncompetitive. The vision of de-

carbonizing electricity and how PHS fits into it, will likely vary from country to country.

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