Dominion’s 3,000-Megawatt Battery

Bath County Pumped Storage Station: lower reservoir

The Bath County pumped-storage facility has worked out so well for Dominion that the utility wants to build a smaller version in Southwest Virginia.

Since its completion in 1985, the Bath County Pumped Storage Station has functioned like a giant battery, supplementing Dominion Energy Virginia’s base-load coal, nuclear and gas-fired plants with its variable output. When energy demand peaks in the early morning and evening, the Bath County facility drains water from an upper reservoir through tunnels to its hydroelectric turbines more than 1,000 feet below. Then in the evening, when demand is low, Dominion pumps water in the lower reservoir back up the mountain, in effect recharging its battery.

Bath County is capable of producing 3,000 megawatts of electricity for up to three hours at a time, making Dominion’s 60% ownership of the facility a critical component of the company’s total 19,900-megawatt generating fleet. That same flexibility will serve the company well as it integrates between 5,280 and 5,760 megawatts of intermittent solar power its system over the next two decades. Solar generates maximum power with the mid-day sun and none at night, scrambling the traditional supply-and-demand equation. Bath County will play a critical goal in keeping power output in concert with demand.

Indeed, Dominion is so enamored with its pump-storage facility that it wants another one. The utility is giving serious study to a site in Tazewell County that would be capable of generating up to 850 megawatts of electricity. Building a pumped-storage project there would cost roughly $2 billion.

Dominion is touting the Tazewell project as an economic boon for Southwest Virginia, a region whose economy is depressed from the long-term decline of the coal industry. A Tazewell pumped-storage facility would create more than 2,000 jobs during the construction phase, plus 50 permanent jobs, and would contribute $37 million to the regional economy, including $12 million in tax revenue.

With interest in the project high in Southwest Virginia, Dominion invited regional media to Bath County to see how pumped storage works. I tagged a long as the sole member of the Richmond media.

Bath County is a marvel. Most notably, the facility is the largest pumped-storage operation in the world. It produces more electricity than the Hoover dam. The earth-rock impoundment dam creating the upper reservoir reputedly is the eighth highest dam in the world. But the facility is so tucked away so deep in the mountains — it takes more than half an hour to get there from Hot Springs, location of another Bath County icon, the Homestead — that spa visitors have no idea it’s there.

The upper reservoir at the Bath County Pumped Storage Station.

The upper reservoir serves one function: to hold the water that pours through three gravity-fed tunnels at the rate of 2.2 million gallons per minute. Those tunnels split into six, and the water drives six 505-megawatt turbines. The depth of the upper reservoir, which sits at an elevation of roughly 3,000 feet, fluctuates dramatically throughout the day as the water level rises and drops.

This photo looks down at a sharp angle. The flat expanse is the rock-and-dirt impoundment dam, reputedly the world’s 8th highest dam.

Building the two reservoirs and three tunnels entailed excavation of 36.3 million cubic yards of material, quarrying 2.8 million cubic yards of rock, and pouring 1.1 million cubic yards of concrete. Dominion maintains an elaborate system of sensors and inspections to ensure that the the integrity of the structures is never compromised. Dominion staff walk the upper and lower dams weekly to look for seepage or other signs of failure. To keep the vegetation low, the company has contracted with a service to bring in goats. (Without question, the goats were the crowd-pleaser of the tour.)

The generating station, sitting at the base of the mountain, houses the turbines. The pressure created by thousand-foot columns of water with a lake above them is phenomenal.

Top-down view of the six turbines. The main structure of the unit is below ground. The component visible at the center of the photo is where the rotating brushes create magnetic fields.

The beauty of the Bath pumped-storage facility is that it can be dispatched quickly. The turbines can start generating electricity within six minutes. Within 15 minutes, they can begin pumping water back to the upper reservoir. That’s not the same flexibility provided by a real battery, which can dispatch electricity more or less instantaneously, but it is more nimble than any other conventional power source.

The hydroelectric technology is deemed low risk and high-efficiency — for five units of power consumed to pump water back up the mountain, the plant generates four units of power, making it 80% efficient. Pumped storage also has a long lifetime and low operating costs. Recent technological advances may make the Wise County facility even more responsive to fluctuations in demand than Bath. A July 2016 Department of Energy report, “Hydropower Vision: a New Chapter for America’s Renewable Electricity Source,” found that advanced pumped-storage capabilities such as adjustable-speed and closed-loop and modular designs can “further facilitate integration of variable generation, such as wind and solar, due to its ability to provide grid flexibility, reserve capacity and system inertia.”

The drawback of the Bath facility is that it can operate at full capacity, 3,000 megawatts, only three hours out of the day. When operating for extended periods, up to 11 hours, it can generate only 362 megawatts. And it can take up to 12 hours to restore the upper reservoir to its full capacity. Still, as long as Dominion has to balance supply and demand on its grid — a job that will get trickier as more intermittent solar production comes on line — and as long as there is a wide differential in the price of electricity at different times of the day, the Bath pumped-storage station will play a pivotal role in keeping the lights on in Virginia at a reasonable cost.

Whether the economics of the proposed Tazewell facility pencils out as nicely as at Bath remains to be seen. Tazewell would produce only a third of the power and construction would cost a bit more than Bath did three to four decades ago. Moreover, Dominion officials expect it will take a full decade to walk the project through the regulatory process and build the hydro plant. But unlike some infrastructure projects Dominion has been pushing recently, Tazewell would have three things going for it. One, it will have strong political support in Southwest Virginia. Second, compared to lengthy pipelines and transmission lines, the visual impact on neighbors will be negligible. And third, hydro power is not a fossil fuel, so it should win the blessing of environmentalists.

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24 responses to “Dominion’s 3,000-Megawatt Battery”

  1. Yes, it’s a giant storage device, like a battery. Having the ability to time-shift a big chunk of electricity over and over again is valuable to an electric utility. It’s a big potential source of revenue, especially in the regional wholesale energy market. But will that revenue exceed the cost — the amortization and servicing of the up front investment — and by how much (especially when compared with alternative investments)? Building the Tazewell project is an economic decision and, at its core, a simple one.

  2. A more interesting question is, should this huge storage device be built at ratepayer expense and “rate-based,” and all net gains or losses go to ratepayers — or should Dominion build this with shareholder funds and operate the unit for its own account? There’s a good case to be made either way; but Virginia is long past the day when it made sense to build generation, or seek SCC and GA approval for it, as though Dominion was a stand-alone electric utility with no wholesale market to buy or sell in.

  3. LarrytheG Avatar

    Enviro’s won’t like it: ”
    Reservoirs are a major source of global greenhouse gases, scientists say (WaPo)

    but if you’re gonna run it with solar – it’s totally backasswards from it’s original concept:

    This is no more a justifiable use of taxpayers nor ratepayers monies than Nukes would be…

    sounds like a PR diversion.. though I’m sure the tour was worth it!

  4. Pumped storage facilities are imposing in their scale. There is something about huge projects that require moving millions of cubic yards of soil and rock that give humans an impression of having power over nature and our own destiny.

    They were well suited for the purpose of using excess night-time generation from “must run” nuclear units and shifting it to the much higher value daytime peaks. Today, what were once cheap nuclear units can be expensive and cheap solar facilities produce an excess of generation during the daytime. Our needs are now reversed from the days that spawned the pump storage projects in the 70s and 80s.

    New pumped storage is at least three times more expensive than the legacy facilities. Its slow reaction rate, moderate efficiency, and the need to locate it far from load centers make it poorly suited to the needs of a modern grid.

    In ten years, rapidly responsive utility-scale batteries will be 75% cheaper than they are today. Batteries already provide a variety of ancillary services such as voltage and frequency control, backup power, as well as load shifting capability. If they are widely distributed, they will greatly contribute to the reliability and resiliency of the grid. Current batteries can discharge over five hours, instead of just three for the pumped storage units, and this is increasing as batteries evolve.

    In ten years, batteries in electric vehicles combined with a responsive charging network can accept excess generation and use it for fuel or for discharge to the grid during peak usage. These batteries, which are already paid for as part of the vehicle, can add to an inexpensive and flexible network of storage devices.

    We would be better off retiring our existing nuclear units after 60 years of operation and save the $4-5 billion that will be required to retrofit them for another 20 years of operation. The Bath County facility can be pumped up using the gas-fired combined cycle units so they can run at their optimum capacity and still provide value as newer, cheaper generating options are added to the grid.

    Output from renewables would be fully utilized whenever it is generated. Variation and shortfalls would be covered by batteries, the most efficient peakers, and output from the Bath facility. Of course, total electricity use would gradually decline as cost-effective energy efficiency gradually soaked up demand as population and economic activity continued to grow.

    So why is Dominion working so hard on a PR campaign for a new pumped-storage facility? Just as with the pipeline, this is not about creating the best energy system. Rather, it is about creating the greatest revenue stream. The Bath facility will likely be mostly removed from the rate base in the early 2020s. Adding another $2 billion dollars to the rate base a few years later would look mighty good to Dominion. Especially, since the GA legislation has set a very low bar for its economic justification.

    Using a written off Bath County facility and low-cost batteries is not nearly as attractive in terms of utility revenues. Of course, the Bath pumped-storage facility can still be useful if it is part of the justification for adding $5 billion in nuclear retrofits to the rate base.

    The Dominion Energy executives are very adept at promoting projects that serve the shareholders. This pumped-storage project is likely to skin the ratepayers, just as the ACP does. Let’s hope for an accurate and even-handed accounting of the costs and benefits from the SCC and see if the GA can stay out of it if the answer they desire is not delivered.

    As for Jim’s big three:
    1) Southwest Virginia would appreciate taking money from other parts of the state to aid in its rehabilitation. But I do not believe they are are a powerful enough political force to overcome other areas of the state if they got wise to the fact that this will cost them money (but maybe its payback for support for other dubious projects),

    2) A large pumped-storage facility located well outside of Dominion’s service territory would require lengthy transmission lines, which create visual, economic and environmental consequences,

    3) this would not please the environmentalists or the ratepayers. This project is not a hydro generating station, it is a pumped hydro storage facility, that will most likely be pumped up using fossil-fired generators that are not too good at rapidly following variations in load.

    1. Mark Heslep Avatar
      Mark Heslep

      “In ten years, rapidly responsive utility-scale batteries will be 75% cheaper than they are today. ”

      By far the largest utility battery installation in the world is the recent installation in S. Australia. The Australian facility is 129 MWh, which is 1.4% the storage capacity of Bath PuHS (9 GWh). Batteries with a daily cycle typically need replacement every 10 years. Bath is 32 yo, and might conservatively last three times that age.

      1. Reed Fawell 3rd Avatar
        Reed Fawell 3rd

        Here’s extract from US Department of Energy, dept. Energy Efficiency and Renewable Energy, published in 2001 (this being within early ‘W’ Bush Administration:

        “Here’s a look at the expected future direction of solar technology.

        All buildings will be built to combine energy-efficient design and construction practices and renewable energy technologies for a net-zero energy building. In effect, the building will conserve enough and produce its own energy supply to create a new generation of cost-effective buildings that have zero net annual need for non-renewable energy.

        Photo-voltaics research and development will continue intense interest in new materials, cell designs, and novel approaches to solar material and product development. It is a future where the clothes you wear and your mode of transportation can produce power that is clean and safe.

        Technology road maps for the future outline the research and development path to full competitiveness of concentrating solar power (CSP) with conventional power generation technologies within a decade. The potential of solar power in the Southwest United States is comparable in scale to the hydro-power resource of the Northwest. A desert area 10 miles by 15 miles could provide 20,000 megawatts of power, while the electricity needs of the entire United States could theoretically be met by a photo-voltaic array within an area 100 miles on a side. Concentrating solar power, or solar thermal electricity, could harness the sun’s heat energy to provide large-scale, domestically secure, and environmentally friendly electricity.

        The price of photo-voltaic power will be competitive with traditional sources of electricity within 10 years. Solar electricity will be used to electrolyze water, producing hydrogen for fuel cells for transportation and buildings.”

        See: timeline.pdf

        Like TooManyTaxes said: Don’t believe what “the experts” tell you.

  5. Steve Haner Avatar
    Steve Haner

    I am told that deep in the Integrated Resource Plan documents filed by Dominion there are reports that indicate the Bath facility is not – not – being used to full capacity, and its utilization has dropped noticeably over time. If there is unused capacity there, that is the biggest reason to question a new facility (even further away from the service territory.) It is something the SCC would zero in on quickly (which is why the SWVA legislation deemed the project to be in the public interest – a magic phrase which dictates the outcome to the SCC.) That was one of those pesky questions that nobody asked during the 2017 session – is Bath really being used to full capacity?

    The 2007 statute, which of course has been chopped into chutney by the General Assembly over the past few years, did include a provision that profits from off-system sales were to be divided between the company and ratepayers. If the purpose of this is to make it possible to sell excess power to PJM, and the ratepayers will share in the benefit, that would be worth knowing. I have not heard that discussed.

    1. Capacity factor is a tough issue for pumped storage facilities. If it is used at its full capacity, i.e. pumped up for 12 hours then discharged at full power for 3 hours, then its capacity factor would be 3/24 or 12.5% in the best of circumstances.

      However, I can see how it would be used less now than it was earlier in its service life. Nuclear generation is comparatively more expensive now than it was when the facility was built. Plus, you take a 20% loss for pumping up the reservoir. PJM is awash in cheap energy now and it will only get worse as new gas plants, not justified by load growth, come on line. The output for the pumped storage facility will not be as competitive on the market as it once was. The new proposed facility, with its considerably higher cost, will be even less so. And soon, the energy surplus will need to be shifted from the daytime, rather than nighttime.

      All of Dominion’s generation is sold to PJM. Energy is purchased at wholesale rates for retail sales. During the 2016 IRP hearing, it became clear that Dominion was artificially limiting the use of cheaper solar in order to build excess combined cycle units to sell into the PJM market.

      Then Dominion realized that their only source of load growth, data centers, wanted only renewable generation and they shifted dramatically to solar in this year’s plan.

      With greater penetration of renewables in PJM, a portion of high demand periods is being met by lower cost energy, making it harder to sell the pumped storage output during the shoulder months in spring and fall.

      I don’t see how this new project can pencil out. The only hope would be to create another false narrative, as has been done with the pipeline. I don’t know how long the GA can keep raising energy costs to families and businesses in the state to benefit Dominion.

      As I have said many times, it doesn’t have to be like this. With revised regulations, Dominion can do things that are good for its customers and make money too. Staying with old habits will only harm their customers and ultimately their shareholders. Dominion has capable leadership and many tools at its disposal to do it better.

      1. Steve Haner Avatar
        Steve Haner

        I found a couple of charts in the back of the ’17 IRP that seem to indicate the facility being used to about 75+ percent capacity in recent years, and the same charts in an earlier version showed it well over 80 percent capacity in that earlier reporting period. If I’m reading it right it also shows the facility rated at 1800 or so MW, not 3000…….

        Until eleven ago I was blissfully ignorant on these issues. I was part of the working group on the 2017 re-reg bill and that started my education, which continues. I would be interested in more details on the model you envision, but my instinct would be to insist there still be an independent oversight agency (SCC) with a strong mandate to review everything on a reasonable and prudent standard. That is what the GA has taken away. I think the ratepayers and company can work most things out in that arena, but in the General Assembly David seldom beats Goliath.

        1. The facility is rated at 3000 MW, 1800 MW is Dominion’s share of it. The remainder, I think, is owned by the consortium of Virginia Co-ops. But it is Dominion’s energy that pumps it up, I believe.

          I agree with you about getting the SCC back into their full power to regulate the utilities. In the two states where I worked with utilities, I never saw the type of interference from the state legislature that exists in Virginia.

          The shift to a more modern energy and regulatory system that is occurring in other states first comes from the governor and legislature. The regulators and utilities are unlikely to do it on their own. Both are tradition-bound and slow to change. Some other force has to shake things up and change the way they see things, then they adapt for a more successful future.

  6. Jim, I wanted to go there to see it too. We also of course have Smith Mountain Lake as another pumped storage facility, and there may be few smaller ones.

  7. LarrytheG Avatar

    pump-storage uses more energy than it generates. should I repeat that?

    what pump storage does is use nuke or coal baseload to pump water from the bottom back to the top. You do this when you have more baseload capacity than there is demand for -usually in the wee hours of late night and early morning. Basically it stores extra power than can be used when there is peak demand.

    It made sense to use the extra baseload at night to pump back up than to use gas – which used to be about 7 times more expensive than it is now.

    but now gas is cheaper than nukes or coal

    but gas could be used directly to meet peak loads – cheaper than if it were used to pump water up then get generation back from that at a loss than if you just used the gas directly.

    so it does not sound like it makes economic sense to use gas to recharge pump-storage.

    the only way it makes economic sense is if you cannot dial back the baseload to save fuel.. you have that excess generation that will go to waste – that’s the literal dirty little secret of coal/nuke baseload.

    There are times late at night when the nukes and coal are still burning fuel and cant be dialed back so using that excess generation to “re-charge” a pump-storage facility makes sense.

    The suggestion is that pump-storage could be mated with solar but it really does not make sense.

    First solar generates typically during the periods of high demand and does not generate during period of low demand.

    Second – the nuke and coal baseload plants are still going to be operating with excess generation that will be wasted if it cannot be used for pump-storage.

    Third – we probably have twice as much or more excess generation capacity at night than is needed for the existing pump-storage.

    From that point of view having another pump-storage facility to use what is being wasted might make sense but an obvious question is why are we burning so much baseload to start with such that a good amount of it is just not needed at night anyhow? I suspect that answer is not a simple one and probably involves reliability.

    None of the above has much to do with solar.. there really is no reasonable, cost-effective role for solar in a pump-storage scenario.

    Dominion knows this but they are counting on the fact that most ordinary folks don’t know and thus will accept the premise and Dominion is more than willing to do it even if it doesn’t make much economic sense – as long as the General Assembly is willing to let them make a profit at it.

    Dominion’s first responsibility is to their investors..and as long as they can claim that the cost of their electricity is less than others.. life is good even if Pump-storage for solar is largely a dog and pony PR effort.

    Jim should challenge DOminion to explain exactly how solar “works” for pump-storage… I and others will certainly be interested in hearing it.

    1. Larry,

      I’m not sure if you had a chance to read what I posted above. My point was that in 15 years, when the licenses begin to be renewed for our existing nuclear units, it will not be economic to do that. Dominion says it will cost $4 billion now. Given the history of nuclear units, it will probably cost twice that much when the time comes. I assumed $5 billion, to give Dominion the benefit of the doubt. It does not makes economic sense to invest that much for just 20 years of output.

      Certainly by that time, some sort of carbon pricing and regulations will be in effect, probably much sooner. Dominion expects that when CPP-like carbon limits arrive, Mt. Storm will be limited to 40% of its potential output. Older, less efficient coal units will probably be retired.

      While this is going on, increasingly cheaper renewables will meet much of the intermediate load and some of the peak. Output from these cheap sources might cut into the baseload requirements, causing the curtailment of combined-cycle units that have replaced the old nukes and coal plants as the primary source to meet base load requirements.

      It is much more economic to have these units run at full capacity as much as they can. They do not vary their output nearly as easily as simple combustion turbines do, and lose efficiency when they cut off the steam turbine. They will become the new “must run” units. Even though natural gas prices will increase, it will be cheaper to run these units as much as possible since ratepayers are paying for them anyway.

      Batteries and gas turbines will pick up the variations and the peaks.

      Energy efficiency will lower total demand at a lower cost than adding any new generation and the old nukes and coal plants can be retired without any threat to reliability.

      Solar can be connected to pumped storage, but it is much more efficient to use solar energy where it is generated (especially if it is distributed), avoiding the line losses to ship it to a remote pumped storage facility.

      The Bath County plant can be used as a storage source to keep the combined-cycle plants running at full capacity during times of excess generation, allowing them to generate in the most economical way possible. By that time, the facility will be fully written off (thus inexpensive) and no longer needed to justify continued operation of the nukes. This frees up 3000 MW of storage. A new pumped storage facility that is three times as expensive the Bath facility, will not be needed. It will not be able to compete economically with far cheaper batteries, and modern gas-fired peakers.

      Families, businesses and Virginia’s economy wins big in this scenario. Under current regulations, Dominion does not because it has failed to add a lot of expensive new projects to the rate base. We must create a new regulatory scheme to give them a good reason to help us create a modern energy system and the confidence that they can prosper in it.

      1. LarrytheG Avatar

        Tom. I usually read most all of what you post and they often are thought-provoking….

        but I still don’t see much of a role for solar with respect to pump storage because when solar is generating is pump-storage… unless they can pump up at the same time they are generating . Even then… when the upper pool is expended and needs to be replenished from below -it’s at night when solar is not generating so the power to run the pumps (still) has to come from the coal/nuke baseload plants.

        Perhpas you meant this and I did not comprehend: that if you run the pump-storage generation at night to make up for solar not generating – then during the day , use solar to replenish the upper pool so it can then generate again that night.

        But that’s a 180 degree difference in concept from the current pump-storage concept …

        what say you?

        1. Don’t understand your comment to TomH, “don’t see much of a role for solar with respect to pump storage because when solar is generating is pump-storage.” Not necessarily. The point is, you use the “battery” when you can sell the power from it most profitably; you charge the “battery” when it’s cheapest to buy power. Today, power generally is cheapest at night when loads are lowest, but in places like California where solar is abundant, the time of cheapest grid power can be in the daytime, when solar is maxed out and exceeds even the daytime load. There is no “right” time for pumped storage to be used except what economics dictates. Even if you charge the battery at night, if the grid has lots of solar, the most profitable time to release that stored power will be just after sunset, when the solar output drops off but the evening load has not yet declined. So — solar and pumped storage do interact.

          1. LarrytheG Avatar

            Okay – so here’s the deal. Can you use pump-storage to generate during the day at peak demand and recharge it at night from coal/nukes – with solar?

            And what I mean by that is – if solar is generating during the day – and putting out at peak demand – would you choose to use it instead to recharge the pump storage -at the same time you’re generating peak storage also?

            Why would you do that instead of using all the solar available to respond to peak demand especially since you lose 20% of the solar in the conversation to pump storage.

            What I was asking was – WHAT IF – you changed the way you used the pump storage – to no longer recharge it at night – and generate during the day – ..

            but instead – to use the pump-storage generation at night to replace the solar not running and then next day let solar recharge the pump storage – essentially using the pump storage as a real “battery”?

            So it’s a totally reversed concept where solar melds with the pump storage and coal/nuke baseload no longer are used in conjunction with pump-storage.

            Does the above make any better sense?

            The fly in the ointment is how do you transform the grid to one where you only use “just enough” nukes/coal baseload so that you do not have any “left over” at night?

            And that’s where gas comes in. Gas becomes the “in-between’ fuel that you use when you do not have “enough” solar or “enough” pump-storage capacity…

            what say you?

    2. Mark Heslep Avatar
      Mark Heslep

      “but now gas is cheaper than nukes or coal”

      Not quite cheaper then old existing nuclear supplying Dominion. N. Anna, Surry have O&M less than 2 cents per kWh. And the costs of N Anna and Surry are going to stay there; we don’t know about gas.

      1. LarrytheG Avatar

        Didn’t realize the costs were that low – although most industry/EIA charts show higher numbers..

        ideally – what we’d want is to generate no more baseload than is the absolute minimum amount needed – and cover the demand over that – with dispatch generation. In that scenario solar is useful if it can be used in place of gas – but beyond that solar is not compatible with fuels that cannot dynamically vary – coal and nukes.

        but if you change the way that pump storage is used – from a recharge at night from baseload to a recharge during the day from solar – then pump-storage becomes a de-facto battery to store solar generated during the day to then use at night when solar is not available.

        that’s a concept.. I’m quite sure the actual “doing” would be a big deal change to the utility – and it may be moot anyhow because pump-storage is relatively rare … and will remain so because it takes specific terrain conditions AND very lightly settled and no major roads, .. those places just do not exist in more than one or two for the State of Virginia.

        Pump-storage won’t become the universal battery for Solar.. Pump storage has a niche – and that’s about it.

      2. The O&M costs are only a portion of the costs of operating a nuclear plant. That is a misleading number.

        It is especially misleading, because we are discussing a scenario that is 10-15 years into the future, when North Anna and Surry will add over $4 billion in capital costs, according to Dominion.

  8. “Pump-storage uses more energy than it generates. should I repeat that?

    Not sure where you got that. The Bath County facility consumes the equivalent of about 20% of the electricity it produces.

    1. Jim,

      One hundred percent of the energy for the pumped storage plant is produced by fossil or nuclear generation, 80% of that is recovered when the flow is reversed from top to bottom. There is no net generation from a pumped storage facility. Its purpose is to use lower cost generation that must run anyway and sell it back during peak periods when the price is higher. This price difference makes up for the 20% in energy losses for pumping up the reservoir.

      1. I went back to check my notes, and you are right. I have corrected the article. For every five units of outside power, Bath generates 4 units of power, making it 80% efficient. (Sorry Larry, you, too, were right, and I was wrong.)

        1. LarrytheG Avatar

          so… now that you see the “light” – is your opinion different about pump-storage?

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