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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?

CREDIT: (Credit: Hydro Equipment Association)

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.

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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?

A turbine generator, spun by millions of gallons of water.

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.

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