Getting Off Stream
DEEP IN THE HILLS ACROSS the country are massive reservoirs of potential energy known as pumped storage hydropower, where water is lifted hundreds of feet up by the largest pumps in the land into isolated off-stream holding ponds, in order to have the water fall back down, a few hours later, day after day. Pumped storage spends energy to make energy, leveling out the supply and demand of the grid.
Pumped storage was developed in the 1960s, and continued with the construction of large-scale power plants, as a way to capture excess energy at periods of lower demand, usually at night, and release it during the day, when the need and value of the energy increases. It also serves as an instantly available back up, in case a major electrical producer, such as a nuclear power plant, suddenly shuts down. But today, as more variable sources of energy come online, like intermittent wind and solar, pumped storage becomes even more important as a reservoir to hold and release energy when the wind stops blowing, and the sun stops shining. There are currently dozens of projects proposed for development in the USA, though it will take years to permit and construct them.
In the meantime, these few dozen pumped storage facilities, many of which have been around for half a century, constitute 95% of the storage capacity of the electrical grid, nationwide. They continue to operate, in the background, like infrastructural leviathans, breathing in and out.
In pumped storage hydroelectric plants, the turbines that generate electricity from water flowing into them can be reversed and function as pumps, lifting the water back up to the reservoir. Otherwise, pumped storage is similar to a regular hydroelectric plant operating in connection with a dam and a reservoir along a river. Some of the 40 major pumped storage projects in the USA simply are hydropower plants with additional reversible generators that provide the option of moving water backwards on a river flooded by multiple dams and reservoirs, to manage water levels and supply, as well as produce power.
23 of the 40 major pumped storage projects in the country, however, use a specially built upper reservoir to hold water pumped up to it—a reservoir that is not on an existing waterway, and is thus off-stream—while its lower reservoir is usually created by a dam on an existing river. These off-stream reservoirs are like bubbles off of the otherwise contiguous hydrology of the nation.
Another form of pumped storage uses both an upper and a lower reservoir that are isolated from existing waterways (referred to in the industry as a closed-loop system). While this type of pumped storage is found in Europe and in other parts of the world, there are no closed-loop systems in the USA. This, however, is likely to change. Though there hasn’t been a major pumped storage project built in the USA since 1995, most of the several dozen proposed pumped storage projects currently under review are of the closed-loop type.
Visiting Pumped Storage
Visiting pumped storage sites is like going on a safari to see immobile land beasts in their native habitat. The genre is monolithic and simple, and in a way uniform and redundant. However, each site is unique, and expressive, in its way. Some are in remote places, relishing their obscurity, as many critical infrastructure sites do. Roads dead-end at security gates, where faceless queries are fielded through intercoms, with little opportunity to witness their wonders. Others engage grandly in public relations, building overlooks with interpretive signs, and visitor centers that rival science museums and attract school field trips. Though nearly identical in function, each site says different things about the region and context it is in, and about the relationship between the industry that supplies energy, and those it serves—the people who supply the demand.
Starting in the Northeast
The first pumped storage hydroelectric project built in the USA is the Rocky River Power Station on the Housatonic River in western Connecticut. The powerhouse opened in 1929, and continues to generate as much as a modest 31 megawatts to this day. The plant’s two generators can reverse, to pump water from the river up to a reservoir called Candlewood Lake, located 200 feet above the river’s elevation.
The reservoir was built between 1926 and 1928. Dams had to be constructed and 4,500 acres of trees were cleared to create the basin, which covers eight square miles. Hundreds of people, living and dead, were relocated, including 35 families in the small town of Jerusalem. When the Rocky River Station started pumping water into the basin, it created the largest lake in Connecticut. Today the lake is a popular recreation site, and is lined with homes and private property.
FirstLight operates another pumped storage project, 120 miles away in western Massachusetts, near the town of Northfield. Unlike at Rocky River, however, most of the facilities are out of sight, at least to visitors, and the 320-acre upper reservoir is off limits, atop Northfield Mountain.
The Northfield Mountain Pumped Storage Project took four years to build, and when it opened in 1972 it was one of the largest pumped storage facilities in the world. Today it is one of the ten largest pumped storage plants in the USA.
Water is pumped in and out of the Connecticut River at an unmarked intake/outfall. Filling the reservoir takes 11 hours, and draining it takes eight hours, using all four pump/turbines in the power station. This generates as much as 1,168 megawatts of power on the way down, but consumes around 30% more than that on the way up.
Like many other pumped storage plants of this era, Northfield Mountain was constructed to balance the power grid for a nearby nuclear power plant, in this case Vermont Yankee, a few miles up the Connecticut River, just over the state line, in Vermont.
25 miles further west as the crow flies into the Berkshire Mountains is Bear Swamp, the third of three pumped storage projects in New England. Like Northfield Mountain, the upper storage reservoir at Bear Swamp was constructed on a hill several hundred feet above a dammed river, in this case the Deerfield River, which serves as the lower reservoir.
The Deerfield River is a very hard working river. Though only 70 miles long, it drops more than 1,000 feet through the hilly northern Berkshires, and has ten dams along its course, each producing electricity, and, for decades, its waters cooled a nuclear power plant, which has since been removed. It is also a hard playing river, with busy recreational rafting and kayaking taking advantage of the controlled releases from its dams, starting below the Fife Dam, which forms the lower reservoir for the Bear Swamp Pumped Storage Project.
A restricted access road across the top of the dam leads to the Jack Cockwell Station, the powerhouse for the project, which is located underground, below the upper reservoir atop Rowe Mountain. Construction started in 1968, and was completed in 1974. The plant has two pump/turbines that together generate 600 megawatts, enough to power around 60,000 homes, at least for the few hours that it takes to drain the reservoir.
75 miles west of the Berkshires, and past the Hudson River Valley, lies Schoharie Creek, and the Blenheim-Gilboa Pumped Storage Project, one of two pumped storage projects in New York State. The Blenheim-Gilboa Pumped Storage Project has an upper storage reservoir 1,000 feet above the creek on Brown Mountain, and uses a dammed portion of Schoharie Creek as a lower reservoir.
The plant is owned and operated by the New York Power Authority (NYPA), which operates a visitor center nearby, inside a transformed and repurposed barn, with elaborate interactive displays that describe the project in detail.
The New York Power Authority also operates the other pumped storage plant in the state, the Lewiston Pumped Storage Project, next to the Niagara River. It is part of the larger Niagara Power Project, which includes the Robert Moses Generating Station, one of the largest hydroelectric plants in the nation.
The Niagara Power Project, in turn, is part of the New York Power Authority’s statewide electrical production and distribution system, which is described in the NYPA’s Power Vista, a visitor attraction that rivals those at Niagara Falls, four miles upstream.
The Lewiston Pump-Generating Plant lies between the upper reservoir and the lower reservoir, known as the forebay. In addition to being the source for the pumped storage operation, the forebay, which holds two billion gallons of water and is nearly a mile long, also feeds the adjacent Robert Moses Power Plant, a 2,000- megawatt hydropower plant directly on the river. The forebay is fed by a conduit which draws water at intakes above Niagara Falls, and runs under the city like a submerged river, for four miles.
Though not clearly marked, it is possible to visit the actual upper reservoir, by walking up its side, next to a soccer field. What the reservoir lacks in elevation above the power station (less than 100 feet, far less than most pumped power facilities) it makes up for in area—1,900 acres, and in volume—20 billion gallons.
Along the western edge of its six miles of shoreline are the short penstocks at the top of the 1,000-foot-long pumped power station, which functions like a dam in the wall of the reservoir, inside of which are 12 reversible pump/turbines, spinning one way, or the other, adding 240 megawatts to the grid during the day, when demand for power is high.
90 miles south, along the Allegheny River in western Pennsylvania, is the Seneca Pumped Storage Project, one of two pumped storage operations in that state. The plant was built next to the preexisting Kinzua Dam, a large flood control dam built by the Army Corps of Engineers in the early 1960s, that backs up the river into a reservoir 24 miles long, flooding all the way to the Seneca Indian Reservation in New York State.
The pumped storage plant is contained in a powerhouse below the dam, discharging into the river at the stilling basin at the bottom of the dam. Inside are two reversible pump/turbines, and a third non-reversible turbine. The plant opened in 1970, and generates 450 megawatts at its peak.
Water enters the plant from an intake built onto the upstream side of the dam, and can be used to generate power directly, or pumped 800 feet upwards to the circular upper reservoir, generally at night, when power demand and cost is lowest. During the day, when demand for electricity increases and its value goes up, the water flows out of the upper reservoir though the same vertical tunnels, to the power station. The water then leaves the station and flows down the Allegheny River unobstructed, all the way to Pittsburgh, 195 miles downstream, where it joins the Monongahela and becomes the Ohio River.
At the other end of Pennsylvania, 60 miles west of Philadelphia, is the Muddy Run Pumped Storage Project, which uses a dammed section of the Susquehanna River as its lower reservoir. When it opened in 1968 it was the largest pumped storage plant in the world.
The upper reservoir is a rambling 1,000-acre lake, 400 feet above the elevation of the river, with some recreational activity allowed along its shores, but only on the water that is isolated from the rest of the reservoir by another dam.
At the southern end of the upper reservoir a canal leads to four large intake towers atop four 25-foot-diameter shafts that bifurcate underground to connect to the eight pump/turbines in the plant, each of which generates 134 megawatts, giving the plant a total output capacity of 1,072 megawatts.
The plant uses a section of the Susquehanna formed by the Conowingo Dam, the last dam on the river before it enters Chesapeake Bay. This section of river also serves as the cooling water for the Peach Bottom Nuclear Power Plant, one of the first commercial nuclear plants in the nation. Muddy Run was under construction when Peach Bottom’s first reactor went online in 1966, and two larger reactors opened in 1974.
100 miles north, just over the state line into New Jersey, is the last of the eight pumped storage projects in the northeastern USA, the Yards Creek Project, a 450-megawatt pumped storage operation in the Appalachian Mountains in northwestern New Jersey.
It has an upper and lower reservoir separated by 3,600 horizontal feet, and 700 feet in elevation. An 18-foot-diameter pipe carrying the water up and down slope emerges from underground halfway down the hillside, and splits into three penstocks that connect to three pump/turbines in the plant.
Despite the large population in the Midwest there is only one pumped storage facility there: the Ludington Pumped Storage Plant, on the eastern shore of Lake Michigan. It helps stabilize the electrical grid in the Upper Midwest, which is heavily dependent on nuclear plants (five of them are along the shores of Lake Michigan itself). When Ludington opened in 1973, after four years of construction, it was the largest pumped storage plant in the world.
The upper reservoir, built on a bluff above the shore, is two miles long, 842 acres in size, 110 feet deep, and holds 25 billion gallons of water, 17 billion gallons of which are considered usable, causing a 67-foot change in water level in the reservoir. Levels in its lower reservoir, Lake Michigan, 360 feet below, are unaffected.
Between the upper and lower reservoirs are six penstocks, each 1,300 feet long and 28 feet wide, just beneath the surface of the 170-foot-tall dike that forms the walls of the upper reservoir. At the bottom, on the shore of the lake, is the powerhouse, with six reversible pump/turbines, each with the capacity of generating 387 megawatts, adding up to 2,322 megawatts total, enough to power a city of 1.6 million people (for a few hours).
Goin’ South
Things do not always go well at pumped storage facilities, though, as was the case at the Taum Sauk project, in southeastern Missouri. The facility opened in 1963, after three years of construction by its owner-operator, Ameren, Missouri’s largest utility company. The project consisted of a 55-acre upper reservoir on Proffit Mountain, connected by a 7,000-foot-long tunnel to a power plant, located on a dammed creek, 760 feet lower in elevation.
The upper reservoir was unique, as it was created by building a 120-foot-tall continuous earth-fill dam, resembling a giant above ground pool, which its operators often kept filled to the brim, sometimes just a few feet from the top of the dam.
Early on a December morning in 2005, the reservoir overflowed, and without a spillway, its wall eroded and collapsed. 1.5 billion gallons of water spewed down the hill, scouring the ground of all trees and soil, down to bedrock. The water cascaded through Johnson’s Shut-Ins State Park, at the base of hill, then followed the creek bed back to the lower reservoir. The dam at the lower reservoir held, and prevented the flood from reaching the town of Lesterville, where it likely would have done significant damage.
The superintendent of Johnson’s Shut-Ins State Park was at home with his wife and three children when the flood flowed through the park for 12 minutes, and washed their house away, but they all survived.
Ameren was declared liable for the accident, as operators knew the water level sensors were unreliable. The company was fined $15 million by the federal government, and have paid more than $200 million in settlements. In 2010 a rebuilt reservoir atop Proffit Mountain went online. Instead of an earth-filled dam, this one was made by the more sturdy roller compaction method, and includes a spillway. It cost $500 million, much of which was covered by insurance.
There are more than a dozen other pumped storage projects in southern states, with the largest cluster around northern Georgia and northern South Carolina. Some of them are part of large regional water management systems, like the Tennessee Valley Authority (TVA). One such system, the Keowee-Toxaway Hydroelectric Project, has two pumped storage projects within it, and is associated with a major nuclear power project as well.
The Keowee-Toxaway Hydroelectric Project is a series of reservoirs, dams, and hydro plants built in the early 1970s, to provide regional flood control and power production, and stable cooling water for the Oconee Nuclear Power Plant. The plant, with three reactors, was the largest nuclear power plant in the world when it opened in 1973.
The Keowee-Toxaway project flooded more than 40 square miles of territory, forming two large reservoirs, the rambling 20-mile-long Lake Keowee, which is heavily developed, and the 7,500-acre Lake Jocasee, which is mostly undeveloped and serves as a storage and flood control reservoir for Duke’s system. The dam that forms Lake Jocassee has four pump/turbines in it, which pump water up from Lake Keowee, and generate 774 megawatts of power when it flows back down.
Lake Jocassee is also the lower reservoir for a larger pumped storage project, called Bad Creek, which opened in 1991—one of the most recently constructed pumped storage projects in the USA. The Bad Creek Hydro Pumped Storage Station pumps water up 1,200 feet from Lake Jocassee to a 370-acre upper storage reservoir, built and operated by Duke Energy. The four pump/turbines in the underground power station produce as much as 1,065 megawatts for a few hours, when water runs back down to Lake Jocassee.
The completion of the dam forming Lake Jocassee in 1970, and flood waters rising behind it, are depicted in the opening sequence of the 1971 film Deliverance, an influential film that laments the loss of landscapes to hydroelectric projects in the South (among other things).
There are four pumped storage hydroelectric plants in Georgia, three of which are in dams on existing rivers, and are relatively small. Only one, the Rocky Mountain Hydroelectric Plant, uses an isolated specially constructed off-stream storage reservoir. It is the largest in the state, and the most recent major pumped storage operation to be built in the USA.
Rocky Mountain is located in the southern Appalachian Mountains, in the northwest corner of the state. Construction of the project started in 1977, but stopped in the 1980s, due to financing issues. It was finally finished and opened in 1995, after a total cost of more than one billion dollars.
The project consists of an oblong upper reservoir constructed near the top of Rocky Mountain and a lower reservoir with a power plant, containing three pump/turbines, capable of producing 385 megawatts each, for a total of 1,140 megawatts—making it the seventh largest pumped storage plant in the nation.
The lower reservoir and the land around it offers fee-based recreational activities, such as camping, boating, hunting, and fishing, though these activities are contained within two auxiliary ponds, keeping people away from the lower reservoir, where the powerhouse is. Most of the 5,000 acres owned by the utility company, Oglethorpe Power, are off limits to the public.
The Raccoon Mountain Pumped Storage Project is a few miles west of Chattanooga, Tennessee. It is the largest hydroelectric plant built by the Tennessee Valley Authority, which is saying a lot, as the TVA has 30 of them, and was a pioneer in large-scale dam construction. Raccoon Mountain was built between 1970 and 1979, and has a generating capacity of 1,650 megawatts, making it the third largest pumped storage project in the nation.
The TVA is part of the federal government, and the grounds of the Raccoon Mountain operation are welcoming and more open to the public than most. Visitors can circle the upper reservoir by car, driving along the top of the 280-foot-high, mile-and-a-half-long dam, the largest earthen dam built by the TVA.
There are hiking and biking trails, and an overlook providing a view of the intake structure in the upper reservoir. Even the electrical substation for the facility has an interpretive plaque and a viewing bench, and is likely one of the few electrical substations anywhere in the country designed with aesthetic considerations, and to be part of a park.
A visitor center next to the upper reservoir has informative displays inside and out, and a balcony that overlooks the Tennessee River Gorge and Nickajack Lake, the dammed segment of the river that serves as the lower reservoir for the project. The visitor center is at the top of an elevator shaft, and a 1,000-foot-long vertical corridor for the cables carrying the electricity from the plant.
Roads lead to the intake/outfall down below, at the river side, and the public is encouraged to visit, picnic, and fish outside the powerhouse service tunnels, where there are displays and equipment on view to enjoy as well.
The powerhouse inside the base of the mountain has four pump/turbines, each of which can generate as much as 413 megawatts. Water flowing down from the upper reservoir can generate power for 22 hours, and it takes 28 hours to pump it back up to fill the reservoir.
The TVA was established in 1933, as part of the New Deal, and was the largest regional development project in the nation’s history. It is still the largest public utility in the country, with dozens of power plants, transformed waterways, and transmission lines covering several southern states.
The largest pumped storage facility in the country is the Bath County Pumped Storage Station in the Allegheny Mountains, on the state line between Virginia and West Virginia. On the surface, it looks like other pumped storage projects, with a medium-sized 265-acre upper reservoir, connected by buried penstocks to a power station, located on the shore of lower reservoir, made by damming a creek.
The difference is inside the power plant, which has six pump/turbines, each with a capacity exceeding 500 megawatts, more than twice a typical size, enabling the plant to produce as much as 3,003 megawatts, making it the tenth largest electrical generating station in the USA, of any kind. It was the largest pumped storage facility in the world until 2021, when a 3,600-megawatt plant opened in China.
The upper reservoir is 1,200 feet above the power station, and its water level sinks 100 feet over the ten hours it takes to drain through the turbines into the lower reservoir. It takes 11 hours to pump the water back up. The plant is 80% efficient, meaning 20% more power is used to pump the water back up. Construction started in the late 1970s, and the plant opened in 1985, costing more than four billion in today’s dollars.
The grounds, including the upper and lower reservoirs, are off limits to the public, and information about it onsite is limited to a small kiosk outside the security station at its main entrance. The tattered site map indicates a visitor center on the property, which closed long ago. Two ponds were constructed below the lower reservoir to provide recreation for the public, as required by the plant’s construction and federal operating permit. Camping and fishing is permitted, though it requires a small fee.
Way Out West
The west has some pumped storage projects, too, including three in the mountains of Colorado; one built into the Grand Coulee project on the Columbia River in Washington State; and three small ones in Arizona, two of which are built into the continuous line of dam/reservoirs along the Salt River, part of the Salt River Project, which supplies Phoenix with electricity.
And then there is California, where the hydrology has been altered so fundamentally, with pumps moving water from one end of the state to the other, into and out of reservoirs, and over mountain ranges, through a network of thousands of miles of canals, that the whole place is an engineered plumbing project. Within this constructed hydraulic system there are, officially at least, seven pumped storage energy projects, all of which have unique and superlative qualities.
At the top of the state is a pumped storage project that is part of the Oroville-Thermalito Complex, in Northern California, a 12-mile-wide engineered waterworks extending from the Oroville Dam in the east to the Thermalito Afterbay in the west.
The Oroville-Thermalito Complex starts at the Oroville Dam, which captures the flow of the Feather River, as well as tributaries that trickle in from other dams higher up the watershed into the Sierra, forming Lake Oroville, the second largest reservoir in the state, after Lake Shasta. The dam is 770 feet high, and is the tallest in the nation. It took seven years to build, and was dedicated in 1968.
Though the primary function for the Oroville Dam and reservoir is to supply water and control flooding, it also generates electricity. The Edward Hyatt Power Plant, inside a 400-foot-long underground chamber carved inside the rock on the south side of the dam, produces up to 819 megawatts of power. Three of the six generating units have the ability to reverse, pumping water more than 600 feet from the base of the dam, back into Lake Oroville.
Water leaves and enters the plant at the base of the dam in the diversion pool tailrace. This pool runs for three miles, from the base of the dam to the diversion dam, which allows some water to re-enter the channel of the Feather River. The rest is diverted through the Thermalito Power Canal to the Thermalito Forebay, and eventually to the Thermalito Dam, five miles further west.
The Thermalito Dam has a powerhouse with four turbines that generate up to 120 megawatts when it lets the water spill into the Thermalito Afterbay. Three of the turbines in the Thermalito Dam are reversible, and pump water out of the afterbay, raising the level through the entire system for ten miles, back to the Hyatt Plant, which can lift water back up to the Oroville Reservoir, thus regulating water levels throughout the Oroville Thermalito Complex.
The Thermalito Afterbay, the far end of this pumped storage project, is a large shallow off-stream terminal reservoir, covering 4,300 acres, created by a low dam that is 42,000 feet long along its south and west sides, and runs for four miles flat up against Highway 99.
170 miles south, near Los Banos, on the west side of the Central Valley, is the San Luis Reservoir, an even larger pumped storage reservoir—in fact the largest off-stream reservoir in the nation, covering 12,700 acres, with a capacity of more than 650 billion gallons.
The San Luis Reservoir serves as the upper reservoir for a pumped storage hydroelectric project, but its primary function is to store water for federal and state irrigation and drinking water projects. It is the main component of the San Luis Complex, which consists of two reservoirs and two pump/generator plants, and links two statewide aqueduct systems.
Water is pumped into the reservoir by the William R. Gianelli Pumping-Generating Plant at the base of the dam. It lifts water 300 feet into the reservoir, and generates as much as 424 megawatts of power when water flows back down through the plant, into a canal connected to the lower reservoir, called the O’Neill Forebay.
The O’Neill Forebay is fed by two canals, one state, and one federal. The state canal is the California Aqueduct, which brings water from the Delta in Northern California, to Central and Southern California. The California Aqueduct enters the forebay from the north, and leaves from the south, with gates that regulate its flow in and out.
The federal canal feeding the forebay is the Bureau of Reclamation’s Delta-Mendota Canal, which brings water from the Delta in Northern California to the farms throughout the Central Valley. The forebay has a small pumping-generating plant that lifts water 50 feet up out of the Delta-Mendota Canal, and generates 25 megawatts when it lets water back into it, though it is only occasionally used for this.
A hundred miles due east, deep in the Sierra, is the Balsam Meadow Pumped Storage Project, one of two pumped storage hydroelectric projects in the Southern Sierra. It uses a preexisting reservoir as a lower reservoir, a small upper reservoir, and a powerhouse between them.
The upper reservoir, also known as the Balsam Forebay, is filled by water pumped up to it from the lower reservoir, known as Shaver Lake, and by water flowing down from another reservoir above it.
The upper reservoir’s intake/outfall for the pumped storage project is at the top of a 7,500-foot-long tunnel bored through solid rock. At the other end, down below, is the Eastwood Powerhouse, in a cavity carved out of solid granite, 1,000 feet underground. The powerhouse has just one pump/turbine unit, with the capacity of generating 200 megawatts. Construction started in 1983 and ended in 1987, when the upper reservoir was filled.
Balsam Meadow was the last part of the larger Big Creek Hydroelectric Project, which was developed between 1913 and 1987 to provide power for Los Angeles. Owned and operated by Southern California Edison, one of a few major energy utilities in California, Big Creek has six reservoirs, nine power plants, and miles of underground tunnels connecting them. It generates a total of 1,000 megawatts, which comprises 90% of the company’s hydroelectric generation, and 20% of its total electrical generation.
20 miles east is the second of two pumped storage projects in the Southern Sierra, the Helms Pumped Storage Project. It is located at the end of the roads into the mountains, on the edge of the John Muir Wilderness Area, 8,100 feet above sea level. Owned and operated by Pacific Gas and Electric (PG&E), it is the fifth largest pumped storage project in the country.
The project uses similarly sized upper and lower reservoirs, three miles apart, connected by a tunnel, with an underground powerhouse near the lower reservoir, capable of producing more than 1,200 megawatts.
Both the upper reservoir, known as the Courtright Reservoir, and the lower reservoir, known as the Wishon Reservoir, predated the pumped storage project. They were built in the late 1950s, as part of a string of hydropower plants along the North Fork of the Kings River known as the Haas-Kings River Project. The pumped storage component was started in the late 1970s, linking the reservoirs by blasting a four-mile-long diagonal tunnel between them, and building an underground pump/turbine plant at the lower end of the tunnel, near the level of the lower reservoir. The project was finally completed in 1984.
The pumped storage operation was built primarily to provide grid stability in conjunction with the Diablo Canyon Nuclear Power Plant, which PG&E was building at the same time. That plant, 170 miles away on the Central Coast, and featured in the 1979 film The China Syndrome, is now the state’s only operating nuclear power plant.
South of the Grapevine, at the northern fringe of Los Angeles, next to Interstate 5, is Pyramid Lake, the upper reservoir for the fourth largest pumped storage project in the nation.
Poised at the top of Southern California, Pyramid Lake is filled from above, and below. The California Aqueduct, part of the California State Water Project, carries water from Northern California, pumping it over the Tehachapi Mountains. Emerging from the tunnel at the southern side of the Tehachapi, the aqueduct splits in two, with one portion heading east through the Antelope Valley, and the rest heading west, then south, into Pyramid Lake.
Water flows out of Pyramid Lake through the Angeles Tunnel, a seven-mile-long underground conduit, 30 feet in diameter, into penstocks that feed the Castaic Power Plant, which generates more than 1,550 megawatts at its peak from the plummeting water. Water emerging from the plant enters the Elderberry Forebay, which connects to the adjacent Castaic Lake, the official terminus of the west branch of the California Aqueduct, and a major reservoir of Los Angeles’ drinking water.
When the six primary turbines at the Castaic Plant reverse, usually at night when demand for power is at its lowest, they pump water backwards through the penstocks, up more than 1,000 feet in elevation and more than seven miles through the Angeles Tunnel, back into Pyramid Lake.
There is one last pumped storage project in the state, the Lake Hodges Pumped Storage Project, in the hills east of Encinitas, at the southern end of the sprawl of Southern California. Though it is small in output, producing only 40 megawatts at its peak, it is the most recently constructed pumped storage project in the nation, going online in 2012.
The lower reservoir is Lake Hodges, a dammed portion of the San Dieguito River. The dam was completed in 1918, and the reservoir was sustained only through runoff and rainfall. As San Diego grew, it became dependent on Colorado River water and Northern California water, brought to the region by pipelines and aqueducts.
As concern mounted about being cut off from imported water by an earthquake or system failure, the county established the Emergency and Carryover Storage Project, which included the construction of the Olivenhain Reservoir, to provide more local storage for the region. The new reservoir would in turn feed Lake Hodges, less than a mile away.
The Olivenhain Reservoir was completed in 2003, and is fed by imported water from the Second San Diego Aqueduct, coming from the north. An underground pipeline, ten feet wide and a mile long, was completed in 2008, connecting the Olivenhain Reservoir to Lake Hodges. A few years later the small pumping/generating station on the shore of Lake Hodges went online, capable of pumping water back uphill to the Olivenhain Reservoir. Like some other pumped storage projects in California, and along rivers around the USA, it exists more for water supply management than for electrical generation.
Battery Earth
Pumped storage has been likened to an electric battery, holding potential energy that can be converted to kinetic energy to produce electricity when needed. And though California has more pumped storage than any other state, its energy storage capacity, like that of the nation as well, needs to be substantially developed to meet the demands of a changing, sustainable grid.
To meet this demand, dozens of pumped storage projects have been proposed all over the country, nearly all of them fully off-stream (also referred to as closed-loop), which lessens their environmental impact. Still, only a few have passed the permit process so far, such as the Gordon Butte Pumped Storage Hydro Project near Martinsdale, Montana, and the Swan Lake Energy Storage Project in Klamath Falls, Oregon, which was permitted in 2019, and may go online in 2026, producing 400 megawatts.
Non-continuous energy production like solar and wind is going online right now, however, and energy storage will be required more quickly than pumped storage can be built, it seems. So the race is on to build utility-scale lithium battery storage arrays, so long as the material readily exists to create them. California has the largest of these battery arrays in the country, but they are being built quickly elsewhere as well.
At Moss Landing, California, on Monterey Bay, next to the looming gas-fired power plant that was once the largest power plant in the state, two new and expanding battery storage systems make it the largest utility-scale battery site in the nation, at the moment, with a 400-megawatt output. It is soon to be surpassed by another, near the town of Mojave, California, where the Sanborn-Edwards Solar Project is building a battery storage project capable of providing as much as 700 megawatts of power. For a few hours at a time, at least. ♦
