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The Inside Story Of The World’s Biggest ‘Battery’ And The Future Of Renewable Energy

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Originally published on ClimateProgress.
by Ryan Koronowski

The largest battery in the world has sat quietly in George Washington National Forest along the Virginia-West Virginia border for nearly 30 years. A five-hour drive from the nation’s capital, it sits in the middle of the Appalachians, tucked behind the Blue Ridge Mountains.

Very few people in the urban areas that benefit from its power know of its existence, let alone its purpose. Talk to people that live and work a few miles away in Warm Springs, Virginia, and some will have a vague awareness but will readily admit that they don’t spare a thought for how electricity gets to their outlets. Dan Gessler, who works for Dominion Power, the company that operates the facility, put it simply: “I think the vast majority of the public doesn’t even know it exists, it’s up here in the middle of nowhere out in the mountains.”

The Bath County Hydro Pumped Storage Facility is not really a battery in the common sense of the term, but it is the largest pumped storage facility in the world. It stores a lot of energy, which helps 60 million people in 13 states (and DC) served by the regional transmission organization, PJM Interconnection. Quite often when someone in that huge area comes home from work and turns on the lights or switches on the TV, some of those electrons flowing down the power lines are coming from two lakes on a mountain in rural Virginia.

When Sean Fridley, the facility’s Station Manager, looks at the Upper Reservoir perched a thousand feet above his office, he doesn’t see drops of water. He sees a thousands-of-megawatts-deep block of power, a huge amount of stored potential energy — with more output than the Hoover Dam — that he can turn on with a flick of a switch.

“It’s one of the biggest engineering projects, ever,” Fridley said. “The machinery is huge.”

But can such a massive “battery” be drained by climate-fueled drought?

Another look at hydropower

A view of the power station from across the Lower Reservoir.

Most of the energy we use, at its root, relies on the sun. Solar power directly converts radiation to electricity, winds flow across the planet because of sun-warmed temperature differentials to spin huge turbines, and we burn biofuels that come from plants grown by the sun. Fossil fuels come from organic matter that grew on solar power, then died and got buried underground for millions of years to turn into a kind of stored power that can be burned to make other turbines spin.

Moving water has been generating electricity since the first hydroelectric dam came online in Wisconsin in 1882. The sun evaporates water on the surface, pulls it up into clouds, which precipitate down to watersheds. The water is then pulled down to sea level through rivers by gravity. Hydroelectric power takes this water and sends it through a machine that spins a turbine around, generating electricity. To ensure that there is enough water to reliably produce power, most hydro facilities dam a river to be able to release a steady amount of water over a long period of time, through droughts and floods.

Most people are familiar with the basics of conventional hydro — but what about hydro pumped storage? The first ones were in Europe, dating back to about ten years after the first hydroelectric dam. The idea is to produce electricity with the steadiness of hydroelectric power, but to utilize electricity that would otherwise be wasted to take the place of the normal evaporation, precipitation, and gravity that makes rivers flow. A pumped storage facility uses that excess power and pumps water uphill, where it can be used at a later time to power homes and businesses. Pumped storage facilities provide reliability to the grid and a place to put power that would otherwise be wasted.

Terry Nelson is Bath County’s Manager of Power Generation Operations & Maintenance. He helped build the facility back in the 80s, and described it this way: “Realistically, it’s a very simple station. You generate a lot of power but if you look at a coal station, we’re so much more simple. We don’t have coal dust, we don’t have high-pressure steam. It’s a nice place to work. It’s not that loud.”

Indeed, sitting around a conference table in the heart of the power station with some of the people who keep it running, a visitor can hear and feel a steady hum as another turbine comes online to meet the demand of power users. But it could easily be confused with a loud air conditioner, and eventually it fades from attention.

Why pumped storage?


Operating an electric grid is hard work. Coordinating power producers’ constantly-changing supply with power consumers’ constantly-changing demand requires serious planning, a lot of resources, and intelligent software to manage the second-by-second ebbs and flows throughout the system. A facility that can supply extra power when demand spikes, as well as usefully take in extra power when supply stays high while demand drops is extremely helpful.

The primary asset that pumped storage facilities bring to grid operators is reliability. Fridley, the station manager, said “the fact that we can start rapidly, we can put a lot of power on the system, we provide stability to the system — we provide lower risk to the grid.”

“If a large unit is lost, we can, within five to ten minutes, put a unit online. That’s 500 megawatts.” Other back-up power plants like natural gas combined-cycle plants take, at best, 20-30 minutes to start producing power. “Having that capability to quick-start a big unit, that’s very important to the system.”

The economic reality of a pumped storage facility is the fact that it allows large baseload systems like nuclear power to operate at night without inefficiently (and expensively) cycling down production. It’s hard to idle a nuclear reactor. It’s in no one’s best interest to operate existing coal plants inefficiently — so finding a way to use the power they do produce in a productive manner is a win all around. So in the middle of the night, electricity demand slows dramatically, and the extra power that might otherwise be wasted can be used very cheaply to charge pumped hydro facilities like Bath County. Wind turbines also spin whenever the wind blows, and facilities like this don’t care where the electrons come from, as long as the power is cheap. “You can take the power they’re producing at night to pump our water back up,” said Steve King, the plant’s power generation/technical support supervisor.

One day, it may be possible to use this extra energy (or extra intermittent wind and solar) to charge conventional battery systems. But right now, the world’slargest conventional batteries don’t even come close to the production or storage capacity achieved by a large pumped storage plant like Bath County. Given the current state of conventional batteries, it is much cheaper to pump water up a hill.

So how does it work?


Europe continues to invest heavily in pumped storage, with skyrocketing renewable output and decent capacity. There are 40 pumped storage facilities in the U.S., and Bath County is one of the youngest, even though it remains the largest in the world. Rocky Mountain Hydroelectric Plant in Georgia is the newest, commissioned in 1995. Development in the U.S. has been slow because the facilities are expensive, hard to site, and hard to build.

Design documents for a huge facility in the mountains between Virginia and West Virginia date back to the early 1970s, when regional power providers wanted to find something to do with their extra night-time power. There are not many places in the country that present this sort of unique geologic opportunity to easily pump water back and forth between two large reservoirs at different altitudes. The two valleys at the site were perfect for a hydro facility. The station got a license in 1975, and broke ground shortly thereafter. In 1985, $1.6 billion dollars later, the station went into operation.

The whole system is laid out over two reservoirs. The upper reservoir is smaller, fed by Little Back Creek and a 4 square mile watershed. This reservoir is an artificial lake created out of a valley, filled in by a dam made of an impervious core of 18 million cubic yards of clay and stone.

Over 1,000 feet downhill from this reservoir is a larger lake, fed by Back Creek and a larger 75 square mile watershed. The water flows out of this system into the Jackson River, then the James River, and then out to the mouth of the Chesapeake.

But before it does that, the 51 workers at the Bath County Pumped Storage Facility have work for it to do.

Partway down the wall of the upper reservoir, there are three tunnels, covered by “trash racks” — grates installed to keep debris and wildlife from entering. Because the water flows both ways, the grates largely self-clean themselves. The tunnels (known as “penstocks”) lead 1,262 feet down through the mountainside to the power station overlooking the lower reservoir. When power is needed in the morning, an enormous ball valve turns open at the bottom, and water flows down to the cavernous, ten-story power station. It flows down the penstock, past the open valve, and enters the top of the 19-foot diameter turbine blade housing. The water pressure is great enough that it begins to spin the blades of the 90-ton turbine. Quickly. It accelerates and within five minutes, a generator housed around the turbine is sending power along high-voltage transmission wires, supplying the grid with up to 462 megawatts of energy each. The water continues down into the lower reservoir, slowly filling it up. There are three penstocks, and each has two turbines.

On a hot day, the first turbine starts spinning by 10 or 11 a.m., and the last generator might stay on until 8 p.m. Billions of gallons of water flow from the Upper Reservoir (which can drop 105 feet) to the Lower Reservoir (which can rise 60 feet). However, just looking at the surface of the Lower Reservoir from the parking lot by the station, a gentle roiling near the station is all that is visible to suggest anything is happening. While there are fish and normal wildlife in the reservoirs, fishing and other recreational activity is forbidden because of the steep decline into the reservoir, as well as the dramatic change in water levels over the course of a day. Later in the day, as demand drops, the turbines switch off and the other main purpose of the facility takes center stage.

Three people operate the night shift, using cheaper, low-demand power from the grid to pump the water that flowed down all day into the Lower Reservoir back up the tunnels to the Upper Reservoir. Some days they can get it all back up. Many days they cannot — when demand is high, when there is not enough water in the area due to drought, when demand is higher than normal at night. They usually try to catch up over the weekend when demand is lower.

Over the last 28 years, power output is essentially unchanged, but the pace within the power station has picked up. The grid cycles them up and down more frequently, so that now the turbines come on and offline 4,500 times per year. There is more electricity demand than there was in the 80s, and more demand peaks mean more times when a turbine needs to turn on and off. Technological upgrades allow for more precise management of the whole system.

The facility has 3,030 megawatts of capacity (3.03 gigawatts), meaning that when the upper reservoir is full and all 6 turbines are spinning, it can produce that much power to the grid. The average generation is 2,772 megawatts — as water exits the Upper Reservoir, the pressure of water (the head, or weight of water) turning the turbines decreases, meaning that the facility starts to produce less power when there is less water.

“So as you run it down and deplete that, you’re going to get less generation output,” said Fridley, the station manager. “As the day progresses on, as we empty this upper reservoir out, then that is going to deplete.”

Climate Change and Hydropower

Lower Reservoir, with the station to the left. Outflow from the penstocks visible on left.

The usual concerns about how climate change will impact the power grid involve storms that knock down infrastructure, flooding that shorts out or damages equipment, or heat waves that buckle metal or drive up electricity demand for cooling. Drought, however, is the worst enemy of the hydroelectric dam. Normally, a pumped storage facility contains so much water and is self-contained enough that drought would not trouble it. But recently, concerns about water levels have caused some concern for even the largest pumped storage facility in the world.

Fridley explained that “We have the capability of storing 24,000 megawatt-hours up on the mountain on any given day. And if we have drought conditions that eat into that, we’re just reduced on power output. It’s as simple as that, it’s simple physics. The plan is to just let it dig into the power. Because there’s really nothing else you can do. If there’s no water, you can’t make electricity… We have not got to that point yet, but we’ve had some close calls.”

The creeks that feed Bath County can vary from peaks of over 400 cubic feet per second (cfs) during floods, to lows of 8-12 cfs in the summer when there’s a drought.

“The concern is when we get into drought periods,” said Nelson, the station’s power generation manager. “Last year was one of our worst years we’ve had in a long time, and that is a concern because if you get through the summer and you lose enough water you can’t fill the upper reservoir.”

“It depends on how bad you got it, continued Nelson. “If you can’t fill it totally full, it doesn’t really hurt you that much because we don’t normally use all of it — we don’t normally fill it up all the way overnight and then bring it all down the next day. But as it gets worse, it could come a point that you really couldn’t fill it to the point that you lose some of the storage so you lose some of the power capability.”

Times of high demand can help to drop the levels of the Upper Reservoir dangerously low. “A few years ago we had that real hot week,” said Nelson. “We actually pumped on the high load of the day, I guess so we’d have energy for the next day. So that was the only time I’ve ever seen us do that. Everybody else was generating full and we were pumping.”

Steve King, the plant’s technical support supervisor, explained how the reservoir was built with drought in mind. The excavation provided a “conservation pool” as an extra amount of water to get through the drier summer months. “In recent years we’ve come awful close to depleting that conservation pool.” 2012 brought “abnormally dry” drought conditions to most of Virginia and much of the country.

What happens when water levels get low? Though Bath County sells its power to PJM, and buys it back from them as well, it is regulated by the Federal Energy Regulatory Commission (FERC). Nelson said, “we have agreements with FERC where when we get into drought situations, we don’t have to let as much water out. There still comes a point that you could, in theory, run out.”

Everyone noted that drought was not an issue this year — there had been plenty of rain. Because this is not a flood control facility (like many dams are), all water that comes in has to come back out. Some years, however, that inflow is low enough that all it’s doing is replacing water lost to evaporation and to natural seepage through the dam.

Other hydro dams are also dealing with extra water. The Tennessee Valley Authority (TVA) operates one pumped storage facility and 49 other dams, and Tennessee this year has faced flooding. This means that hydroelectric dams have plenty of water to produce plenty of electricity, which lowers prices. It does also mean that the people who control the water flow, like TVA General Manager of River Scheduling Chuck Bach, have to let some spill, which floods farmlands and buildings along the river. To anticipate what’s coming, they model out up to 15 days in advance.

Rupak Thapaliya, of the Hydropower Reform Coalition, a group concerned about the ecological implications of hydropower, points out that one smart thing that the federal government, as well as state utilities and power companies, could do is to not assume the future is going to be like the past. He said the existing federal process of relicensing hydroelectric dams does not consider climate change, and that climate modeling should be an integral part of the process. Looking at environmental impacts in the past can be helpful in some contexts but since relying on past performance alone ignores how different things will be in the future, it does not show the full picture. Looking at climate models in various parts of the country and how they can manage water, he said, can only help the developers, so everyone should insist on the best information. Better climate models also help facility managers look beyond a 15 day forecast to anticipate flooding and drought conditions.

At least one pumped storage facility in Japan solves the drought problem by using seawater instead of freshwater, and locating its “Lower Reservoir” in the Pacific. Though it has several additional technical differences with a normal freshwater facility, being connected to the ocean does mean that it will never run out of water.

But what about freshwater hydro? One thing facilities like Bath County could do to address the potentially catastrophic drought conditions driven by climate change is to enable some serious cutting of carbon emissions.

What’s next?


With wind and solar now competing with nuclear power, the time when wind power could make legitimate business sense to help power the pumped storage facility at night could be closer than many think. Though Gessler said he did not know of any plans for Dominion to construct a wind farm specifically for Bath County, he did say, “I have heard that Bath County could become the battery for wind farms.”

Right now, the facility buys power from PJM, which does have renewable generators but most of its baseline power is nuclear and coal. A look at PJM’s interactive map of renewable energy shows a wide swath of wind farms throughout the Appalachians. “It’s really a business decision — they’re going to use the cheapest power they can to pump the water back up, but from their perspective here, it doesn’t matter what they use to pump it,” Gessler said. If storage facilities like Bath County make investments in renewable power plants more feasible because extra power generated by, say, wind turbines at night could go to good, profitable use, that means lower fossil fuel use and carbon emissions.

The ideal power source for recharging hydroelectric power pumped storage facilities would be cheap renewable sources that rely on intermittent fuel like sun and wind. If for some reason that power could not easily be used by the grid during high-demand times, perhaps it could power one penstock at a facility like Bath County. Excess wind blowing at night could be blended right into the baseline electricity already recharging facilities like Bath County.

The potential for pumped storage to theoretically be used to enable massive renewable expansion is there. So are the barriers. These facilities, even ones a quarter as ambitious as Bath County, can be very expensive. They also cannot exist in very many places due to the specific geographic and geologic necessities of having two reservoirs at very different altitudes while still close together.

Legislation recently passed by both houses of Congress and signed by the President could make things easier for them. The Hydropower Regulatory Efficiency Act and The Bureau of Reclamation Small Conduit Hydropower Development and Rural Jobs Act both attempt to streamline the process of developing hydropower on new and existing dams — only 3 percent of all dams in the country are used to produce power. Rupak Thapaliya, of the ecologically-concerned Hydropower Reform Coalition, said “this bill gets the balance right.” Specifically for pumped storage, FERC is now required to examine a 2-year streamlined licensing process for closed-loop pumped storage facilities, and there has been an uptick in applications.

As the burning of fossil fuels drives climate change across the planet, the adoption of renewable, low-carbon energy has taken on serious urgency. Renewable energy supplies 13 percent of the current electricity mix, and while wind and solar are growing quickly, hydropower still produces the lion’s share. Because wind and solar will see the most growth over the next few decades, the success of renewables is pinned on how easy it is to store their power, and pumped storage is an option and can be a model for scaling this task up to where it needs to be. With luck, it will happen before stations like Bath County — and ones out west — run out of water due to droughts spiked by climate change.

Jeff Spross assembled and narrated the video at the top of this post.

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