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Batteries low cost energy storage

Published on August 4th, 2014 | by Tina Casey

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Sodium-β Batteries Could Transform Wind And Solar Into Baseload Generators

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August 4th, 2014 by
 
The cost of generating wind and solar power has been sinking like a stone, but the cost of storing all that energy for a rainy day has remained stubbornly high. With that in mind let’s take a look at a new advanced energy storage development announced by our friends over at Pacific Northwest National Laboratory.

PNNL has been working on bringing down the cost of sodium-β batteries (that’s β for beta). Sodium-β batteries are widely perceived to be the key to advanced energy storage for utility scale wind and solar energy power, but their relatively high cost has been an obstacle to widespread adoption.

low cost energy storage

New liquid metal alloy improves sodium-β batteries (courtesy of PNNL).

Sodium-β Batteries For Advanced Energy Storage

Sodium-β refers to a class of rechargeable metallic batteries, in which the two electrodes are separated by a ceramic membrane made of beta alumina. Initially used to construct industrial furnaces, by the 1960′s beta alumina was rediscovered as a conductive material with applications for advanced energy storage.

According to the Energy Department, there are two promising materials for the positive electrodes, sodium-sulfur or sodium-nickel-chloride (the later is the ZEBRA battery, for those of you familiar with the topic).

In terms of performance potential, sodium-β batteries could far outstrip lithium-ion batteries, the current gold standard. In addition to advanced energy storage for utility operations, sodium-β batteries could also play a role in mobile energy storage for electric vehicles.

The main problem is that under current technology, the molten state of the sodium-β electrode materials is maintained by a high operating temperature, up in the 350 C range. The high temperature is the main driver of expense for the batteries. It contributes to a relatively short lifespan, and it also requires the use of more expensive materials.

With that in mind, let’s take a look at PNNL’s solution for lowering the cost of sodium-β batteries, published online in Nature Communications.

A New Liquid Metal Alloy Electrode

PNNL’s solution is a new liquid metal alloy electrode. In addition to lowering the operating temperature of the battery, the new electrode is also expected to improve the useful life of the battery, reduce the risk of accidental fire, and contribute to lower manufacturing costs.

The new alloy addresses an unwanted side effect, which is the behavior of the molten sodium when it comes into contact with alumina at a lower temperature. Here’s how PNNL sums up the challenge:

Lowering the battery’s operating temperature creates several other technical challenges. Key among them is getting the negative sodium electrode to fully coat, or “wet,” the ceramic electrolyte. Molten sodium resists covering beta alumina’s surface when it’s below 400 degrees Celsius, causing sodium to curl up like a drop of oil in water and making the battery less efficient.

The PNNL workaround involved using a sodium alloy rather than pure sodium. After some experimentation the research team came up with a liquid sodium-cesium alloy (cesium is a soft, silvery metal).

The results seem pretty impressive. A battery tricked out with the sodium-cesium alloy was able to function effectively at 150 degrees C. Its power capacity was about the same as a conventional sodium-β battery, and it also retained its storage capacity, indicating the potential for lifecycle cost savings. Here’s the numbers according to PNNL:

After 100 charge and discharge cycles, a test battery with PNNL’s electrode maintained about 97 percent of its initial storage capacity, while a battery with the traditional, sodium-only electrode maintained 70 percent after 60 cycles.

As for the cost of materials, one of the pricey parts of a conventional sodium-β battery is its steel casing. The lower operating temperature enables the use of polymers, which are far cheaper.

Although cesium would raise costs, the use of polymers and other less expensive components, combined with a longer lifespan, could result in lower overall costs.

The next step for the team is to scale up their test battery to a more useful size.

Scaling Up For Wind And Solar Power

The new alloy is just one path that PNNL is exploring to develop a low cost, utility scale energy storage system based on sodium-β batteries. PNNL is also working to lower costs through another utility scale sodium-β battery research project that teams the lab with  a company called EaglePicher Technologies, LLC. Though perhaps best known for robotics, EaglePicher is also an advanced energy storage specialist and manufacturer.

In this project, EaglePicher and PNNL are working to shift the basic design of sodium-β batteries from a tubular shape in the electrolyte to a stacked, planar configuration.

 

Like the new alloy, the stacked design is aimed at lowering the operating temperature. The planar configuration also has the potential to operate more efficiently, leading to an estimated 30 percent increase in energy density, while contributing to lower manufacturing costs.

According to PNNL, cost-effective, utility scale sodium-β battery technology could be the means by which wind and solar become baseload generators.

Considering all the other advances in utility scale energy storage and new smart grid technology, it really is only a matter of time before wind and solar become just as steady and reliable as any mainstream fossil fuel.

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About the Author

Tina Casey specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.



  • Offgridman

    Questions, questions, questions.
    While only briefly mentioned it was said that these could be competition for lithium in vehicle usage. I guess because of a higher density storage of energy for size, but they are going to have to get way beyond the tested 100 cycles for either grid or vehicle storage.
    Which leads me to wondering about the operating temperatures. Are the higher temperatures a result of extra energy put in to keep them warm so they will function correctly? Like the lithium batteries have to be cooled or warmed for optimum performance? Or is the heat a result of the action of the charge /discharge cycle? And if the latter could it mean that using these in a car (once the size and number of cycles is resolved) that the heat being released could help to keep the cabin space warm in northern or winter environments rather than having to pull energy out of the batteries to run heaters for the cabin space? I guess conversely this leads to the question that if using these in southern or summer climates would you have to get extra energy out of the batteries to keep the occupants comfortable if the heat from the batteries would adversely effect the cabin temperature?
    Thoughts anyone?

  • Hans

    Why would you want to be a base load generator? With enough cheap storage you can become a peak load generator, which is much more profitable, and much more useful for the grid.

  • loebner

    It seems to me that the best storage medium is heat. Isetropic.co.uk uses a heat pump system to heat gravel. It was described here in cleantechnica. Apparently the efficiency is equal to pumped hydro.

    Concentrated solar thermal uses molten salts. It can provide power for about 6 hours after sunset, I believe. I don’t understand why they don’t use simple resistive heating. Note that resistive heating is almost 100% efficient. (The reason that it’s an expensive way to heat a house is that the electricity is expensive, not that it’s inefficient.)

    • Steve Grinwis

      Heat engines requires maintenance, and don’t last infinitely long. Expect a decent heat engine to last 20 years, with escalating maintenance costs before needing a refurb.

      Expect batteries at $200 / kWh to outperform heat engines on cost, due their insanely high efficiency, especially at low charge / discharge rates, and ever lengthening lifespan. Stationary applications aren’t like cars. You can deal with more than 80% capacity loss, and cycle them for a solid 20 years I’d expect.

      • loebner

        I don’t understand what is your objection to heat engines. Don’t forget that coal, natural gas, geothermal, nuclear, etc. all use heat engines. The *only* difference is the source of heat.

        1. Heat engines are already used with concentrated solar.

        2. What do you consider “insanely high efficiency”?

        3. There is no way that one can deal with an 80% capacity loss. From what I understand, the goal is 99.9% charge/discharge efficiency. If the battery looses .001 each daily cycle, after 1000 cycles (3 years?) the efficiency degrades to 0.367 = (.999^1000)

        One can heat the storage medium an infinite number of times. One simply has to swap out the engine after 30 years. No big deal.

        • Steve Grinwis

          You are applying an exponential degradation, when it’s linear with charge cycles. The battery in my car is rated for 4500 cycles to 80 capacity. So 9000 cycles to 60 capacity.

          The batteries will last longer than current state of the art stirling engines, which must operate at very high temperature to get efficiency. Even then, they fail to reach the efficiency of the most advanced diesel engines, while falling far short on power density and cost.

          Perhaps stirling engines will one day run our grid. But not today or any day soon.

      • Bob_Wallace

        “Expect batteries at $200 / kWh to outperform heat engines on cost, due their insanely high efficiency,….”

        How about $91-116/kWh with 70% efficiency? Or $60/kWh?

        Eos Energy Storage’s Zinc Air Battery.

        Those are the projected prices at commercial manufacturing volumes (100 MW/year). The company projects the potential to take costs as low as $60/kWh at higher manufacturing volumes (300 MW/yr).

        https://mail-attachment.googleusercontent.com/attachment/u/0/?ui=2&ik=467aed4e36&view=att&th=146d003f811b2b85&attid=0.1&disp=inline&safe=1&zw&sadnir=2&sadssc=1&saduie=AG9B_P-ZZd7cpEZTnyIRVV47fHad&sadet=1407508446349&sads=4sYu9H-drTiwebY8735neAsNim4

    • Bob_Wallace

      It’s an unproven idea. Many of us are waiting for proof that Isetropic can make their idea work and for a competitive price.

      If they can compete with PuHS they have a winner. Their system is so much easier to site, quicker to bring on line, and can be distributed around the grid.

      • loebner

        I’m not sure what you consider “unproven.” Compression heats a gas, for example diesel engines. Expansion cools gas, for example air conditioners. Stirling and other heat engines use a temperature differential. The isentropic scheme is a Brayton cycle.

        • Bob_Wallace

          There are zero Isetropic systems operating on the grid today. It’s an idea still awaiting proof.

          Working involves more than simply functioning. The technology has to prove to be useful and affordable.

          We know that CAES works to store electricity. We have two CAES sites connected to the grid and they have been operating for a long time. But they aren’t affordable enough to consider large scale deployment.

  • JamesWimberley

    Where do PNNL claim that this a battery can be made cheap enough to make wind and solar into baseload generators? What they actually say is that it “could allow more utilities to store large amounts of renewable energy
    and make the nation’s power system more reliable and resilient.” To me, “large amounts” translates into “an hour a day”.

    Tina: there is no requirement for “baseload generators” to oensure reliible supply. It’s a myth, a projection of an inefficiency in traditional coal and nuclear generators (John Quiggin). Demand varies greatly over the 24 hours. To meet it efficiently, you need flexible generators and storage. In the merit order, wind and solar will always come first as they have no marginal cost. You can call them baseload if you like, but it’s not really helpful. But their output is inconveniently variable from the weather, so the gaps – which arise independently of demand peaks – will have to be filled with more expensive despatchables. Batteries are a despatchable.

  • Steve Grinwis

    What I’m reading here is mostly:

    Unfeasible battery made slightly more feasible.

    Hopefully it’s s step towards awesome stationary batteries, but I’m not holding my breath.

    • Calamity_Jean

      I hafta ask how much stationary (as opposed to vehicular) storage will even be needed. Batteries will need to get pretty darn cheap before they are cheaper than transmitting power from one place to another, even with line losses. I can see needing batteries to cover brief variations in power (a few minutes), but needing to store large amounts of power for hours isn’t likely to happen until the grid is 90% renewable or more. Even then, it might be more economical to keep a few natural gas burning generators in working order, and fuel them with biogas. Weather-related changes to wind and solar are quite predictable an hour in advance. It seems simpler to me to just ring up another location and say, “Send me more juice.”

      • JamesWimberley

        Pumped storage was originally built, on a very large scale in Japan, to provide backup against outages in large and lumpy conventional and nuclear power stations. It’s all still there.

        Calamity_Jean’s point is partly reinforced by the practical impossibility of inter-seasonal storage. If you have enough wind and and solar for your peak demand (winter in Europe, summer in the US), you will have a large surplus in other seasons. The storage requirement is to cover the longest likely weather-driven break in your peak season. Fraunhofer thinks this is 2 weeks in Germany. a lot. They are thinking gas too.

        • Calamity_Jean

          Two weeks of not-much-wind and not-much-sun? Yow. Yeah, they’re gonna need biogas. Another smart move might be to go to their southern neighbors (Spain, southern France, Italy, Greece) and offer to help finance installation of lots of solar power. Tell them that in winter when those southern lands don’t need so much power Germany will buy it. Any places that agree, Germany puts in transmission lines to move the electricity north.

          Have you seen anything about the University of Delaware/PGM study on 100% renewables for the northeastern US? They figured they’d sell the winter excess for heating, to compete with gas or oil furnaces. http://www.udel.edu/udaily/2013/dec/renewable-energy-121012.html

          • JamesWimberley

            The grandiose Desertec scheme, a German initiative, to cover North African deserts with CSP plants to feed Europe has fizzled. The costs don’t add up. Morocco. etc are gradually going solar (pv not CSP), but for domestic consumption. The flow across the existing 700 MW Gibraltar interconnect may be reversed. Meanwhile Spain and France are more than doubling interconnection capacity through the Pyrenees to 3.4 GW. So your vision is happening, but on a small scale.

          • Calamity_Jean

            I was inspired by the summer/winter interchange between California and Oregon/Washington. In summer the Pacific Northwest sends power to California to help run the air conditioners, in winter California sends power north for home heating. Neither area has quite enough generating capacity to cover their peak demand season, and both have excess capacity for their off-peak season. Fortunately for both, the seasons are different.

            I take it that the Gibraltar interconnect currently sends power south. I never thought Desertec would work; too freaking expensive. Maybe 50 years from now, if humanity isn’t extinct.

          • Bob_Wallace

            Morocco intends to sell electricity to Europe. Both solar and wind, IIRC.
            I suspect Desertec died more due to the unrest and political upheaval in North Africa than anything else. Looks like it’s being replaced by eHighway 2050, a beefed up European grid. It may be that the southern European countries can supply all the solar that Europe needs.

            I wouldn’t be surprised if North Africa gets back in the game well before 2050. If one has a lot of very sunny desert then selling electricity to northern Europe in the winter would seem to be a natural.

      • Steve Grinwis

        And what happens when the other location is tapped out?

        Seems easier to have 100% dispatchable storage on site. I don’t know how this is going to play out, and you are correct, we’re a long way from requiring dispatchable storage in my area. But we’re a lot closer than most of the U.S.

        • Calamity_Jean

          When the other location is tapped out, call a different other location.

          Storage is so expensive that it’s worth going to a lot of trouble to avoid it. When storage gets to be price-competitive with transmission, I’ll change my mind. Until then, storage is a red herring meant to stall renewables. It won’t really be needed until all the coal and nuke plants are long gone, and the last few gas generators are about to be dismantled.

          • Steve Grinwis

            It’s not as expensive as you are suggesting… It’s pretty much break even for the consumer market now, and current consumer prices.

            I pay a lot more money for peak vs offpeak power. $0.18 vs $0.06. As a home owner, if I can avoid those fees and charge my battery off peak, I can save a lot of money, $0.12 / kWh

            I can buy 1 kWh of battery for $400, and cycle it every day for 10 years (totally possible with today’s batteries). That saves me $438. If you only allow 80% DoD, then it’s $350. Now, I know I don’t have a smart controller or such for that price, but you can amortize the controller over the entire battery bank, and I’m only trying to show order of magnitude costs anyways.

            I could save even more if I cycle the battery past the 80% capacity point over it’s life, and run it for 20 years.

            Once Musk lowers the price of batteries to $200 / kWh in three years with the advent of the gigafactory, storage for consumers will be cost competitive with peak prices, about $0.06 / kWh + controller costs.

          • Calamity_Jean

            That’s quite a difference between peak and non-peak prices. Where I live I don’t have time-of-day pricing, so I didn’t think of that. It really makes a difference in the economic viability of batteries whether they are on the utility or the customer side of the meter.

          • Steve Grinwis

            Those prices are actually designed to shield the consumer from the real swings in prices, which range from $0.03 / kWh to $0.40 on hot summer days.

          • Bob_Wallace

            “(Massive storage) won’t really be needed until all the coal and nuke plants are long gone, and the last few gas generators are about to be dismantled.”

            That seems about right to me. As we add EVs to the grid we increase the acceptable penetration level of wind and solar from ~35% to something closer to 50%. That means that coal can go away. Even overbuilding/curtailing wind and solar makes more sense than new expensive thermal plants.

          • Steve Grinwis

            “Need” and “Will add” are very different things. The ability to defer all my usage to off peak is a non-trivial savings. At some point, that’ll make sense economically, even on the grid.

          • Bob_Wallace

            We’re most likely going to see a shrinkage of peak hours and a rise in offpeak prices. PV solar is going to wipe out much of the daily peak with only a small penetration. EVs charging at night will provide enough load to stop pricing at or below zero.

            In some places grid expansion may well lower the late afternoon/evening peak. And/or more solar may free up existing hydro from sunshine hours, allowing it to run faster later in the day.

            Then there’s load shifting.

            Overall, I see electricity price ranges dropping.

          • Steve Grinwis

            In Germany, they have oversupply which is knocking down prices, but when it all settles out, won’t it effectively mean evening price peaks?

          • Bob_Wallace

            Yes, the late afternoon/evening peak is still not addressed but the peak hours are shortened.

            And it may be possible to move some load back into solar hours as well as preserve some hydro for the later day peak.

            For example, while there is plenty of cheap solar cool down houses, refers and freezers. Heat up water heaters for those people who shower after work. The more load we can squeeze out of the late day peak, the cheaper to supply it.

          • bink

            Bob are you not aware that there are places in this country that have 10-12 hour peaks (most of Brooklyn, Queens and Hawaii) All a bunch of EV’s will do is create a 1st peak early in the morning or extend the evening peak making that electricity more expensive.

          • Bob_Wallace

            Solar will most likely knock those 10-12 hour price peaks down to shorter hours as has happened in Germany. On sunny days Germany now has two shorter peaks. (Below)

            EVs should become dispatchable load. (I’m not talking this year or next year, but once we have a significant number on line.)

            If nothing else, utilities will probably move to TOU billing and EV owners will charge when rates are lowest. More likely time of charge will be handed over to grid operators (car companies and utilities are already cooperating on standards).

            The end result will be load much better matched to supply and the minimization of storage.

            Imagine the second German graph post EVs. Charging when cost is below the horizontal line will mean more market for wind and solar. That will make more supply available during the mini-peaks, which will lower those prices.

          • bink

            but Bob where in Brooklyn and Queens are you going to put solar? and solar does not always coincide with peak in many places, take evening peak for instance or sometmes day

          • Bob_Wallace

            How about outside Ocala? Or around Denton? Then send some NE hydro and offshore wind back when the NE is oversupplied and the southern areas in need of some power.

            Evening peak. Was I not adequately clear when I mentioned more than once that there will still be an evening peak after solar (likely) eats away most of the midday peak? That and the morning residual peak are storage’s likely market. Look at the German graphs again.

            BTW, offshore wind is likely to play hell with the current daytime peak.

          • bink

            Florida is closed system, one way in and one way out. does not make any sense to send power from NE when storage can take that instate overcapacity from nite and provide local.

            like i said solar does not always coincide with peak that is why you shift with storage

          • Bob_Wallace

            Hello?

            Put the panels in south Georgia until Florida comes to its senses. What are you not grasping about transmitting electricity?

            Transmission or storage? That will be a question of economics.

          • bink

            that issue is settled , Bob get your head out of the sand there are numerous utility studies that have been done in regards to central plants for peak or reserves versus storage for those applications. Storage wins

          • Bob_Wallace

            How about you summarize those studies and link them?

          • bink

            Bob, MAYBE I will but the fact that ConEdison is choosing to provide incentives for behind the meter storage in lieu of a $1billion dollar substation should tell you something. You know utilities are not going to do something as an alternative unless they are convinced there is a savings so don’t argue the point

          • bink

            Duke energy 37% reserves, FP&L 47% (winter) and you are talking about additional generation over a thousand miles away, Ha!!! Energy Storage is a dispatchable resource

          • Calamity_Jean

            At least partly on rooftops.

            “…where in Brooklyn and Queens are you going to put solar?”

            Somebody (sorry I forgot who) took aerial photos of New York City and concluded that about 3/4 of the roofs were suitable for putting PV on, and if that was done, NYC would generate about half of it’s own electricity. I don’t know whether NYC gets any hydropower now, but if it does, then the rooftop power would allow the hydro to be cut off during the day and saved for use during the predawn and sunset to bedtime peaks.

          • Calamity_Jean

            Oh, good.

            “More likely time of charge [for EVs] will be handed over to grid operators (car companies and utilities are already cooperating on standards).”

            Balancing the load by turning EV charging on and off makes everybody’s life easier. Plus, of course, EV charging is storage, mobile storage.

          • bink

            ConEdison is addressing those 10-12 hour peaks by a storage RFI on the customer side of the meter and foregoing the installation of a $1 billion dollar substation. This can peak can be addressed by a flow battery below $300 per kWh

          • Hans

            This can be addressed by additional transmission capacity in the east-west direction that crosses different time zones, orientating PV modules west, and/or intra-day storage.

          • Steve Grinwis

            A 6 time zone transmission capacity of any size will cross 1000′s of KM’s, and extend your ability to deliver peak.

            1 kWh delivered that distance would be more expensive than storing it in a battery, for sure.

          • Hans

            You only have to improve the connection between exisitng grids, rather than create a new transmission across the time zones. Look for example at the UK which is connected to the Central European timezone by HVDC cables to France and the Netherlands.

          • Steve Grinwis

            There is no free lunch. If you want to move a 100 MW across 6000 km, the grids between here and there are going to require upgrades. And that’s not enough to even start to solve the problem. We’d need the ability to move 12000 MW from BC to Ontario to flatten the evening peek.

            You don’t get it for free by handwaving and saying ‘Only interconnects’.

            If it was that easy to pull large amounts of power across huge distances, we’d be doing more of it. We don’t, and that’s because transmission is expensive.

            It might still be cheaper, but expect a price tag in the billions.

          • Bob_Wallace

            It will be billions, many billions, however we go. I suspect the final solution will be a combo of increased transmission and additional storage.
            The larger we make our grids, the more we can smooth out variability. Shipping some solar from Florida to California in the morning and some solar from California to Florida in the late afternoon may make more sense than building extra storage on each coast. Moving wind and hydro south at night and southern solar north during the day may make sense.

            Installing <100% the amount of storage needed for 'worst case' in each region but sharing storage across regions may make more sense and help pay for more transmission. No need to have "100% of needed" gas peakers for deep backup in every region. Share their output.

          • Hans the Elder

            My handwaving was a reply to your handwaving ;-)

            A little more handwaving:

            Let’s say there are three regions: A,B and C.

            And at some time region A has a oversupply of solar electricity. If region B has a peak demand during that time it will use the solar electricity from region A. This will replace conventional production so there will be no big difference in the use of the internal grid of region B. If there is no peak demand in region B it will pass on the solar electricity to region C. In this case region B uses only a part of its’ capacity for itself so there is also no problem in this case also.

            This is all a bit qualitative, and much depends on the penetration level of renewables, but it illustrates that you can get a long way with only an improvement of the connections between grids.

            This happens already in Europe. Historically each country organised its electricity production and transmission on its’ own, and international connections were only there for back-up with the opening of the internal EU market electricity started being traded all over the continent and the international connections became the bottle-neck. There is now an ongoing effort to make new international connections between countries.

            Free lunches do not exist, but in same cases one can get a fairly cheap lunch.

            There are several reasons why connections between grids were not there in the past:

            Handling large grids with many suppliers and consumer requires IT-technology that were not there when the grids developed.

            Connecting two AC grids means either completely synchronising the phase and frequency, which is not that easy, or using HVDC connections. The HVDC technology is fairly new.

            In the US you have the additional hurdles that the grids have been neglected for years now, and that your utilities are slow bureaucratic vertically integrated monopolies whose interests do not always coincide with that of consumers.

            Moreover, I advice that the US utilities are broken up in separate production, transmission, distribution and retail companies.

          • Bob_Wallace

            Europe, most of it, is connected. Power sales run back and forth across the continent and even down to Morocco.

            I suspect strengthening transmission is going to be cheaper than building lots of storage. And with better transmission storage can be shared/distributed. Furthermore, transmission lasts a long, long time making the overall cost lower.

          • bink

            what is so expensive ? back up your statement with numbers

          • Calamity_Jean

            Well, pumped storage, the only kind that exists in the US at present, costs just under $5,600 per kWh on average, according to the EIA: http://www.eia.gov/oiaf/beck_plantcosts/pdf/updatedplantcosts.pdf (PDF; see pp. 154 &156-157). Anything else must cost more, or it would be used instead of pumped storage.

          • Bob_Wallace

            (Whack the ‘h’. It should read $5,600 per kW.)

            Eagle Mountain, a closed loop PuHS, was recently given the go-ahead. Estimated cost between $1,500 and $2,000 per kW of installed generating capacity.

            http://www.cpuc.ca.gov/NR/rdonlyres/3D7E0901-53DB-48F8-B0F0-BCDAFF07097B/0/EagleCrestPresentationatCPUCPumpedStorageWorkshop1162014.pdf

          • Calamity_Jean

            Yeah, I miss-typed from force of habit. $2000 per kW is pretty cheap, how did they get the cost down so far?

          • Bob_Wallace

            Part of the reason is that they are using an existing open pit mine so they don’t have to dig the big hole. (I’m not clear on whether one or both reservoirs were already dug.)

            If we go forward with PuHS then using existing favorable sites is the way to hold costs low. We have about 1,000 abandoned rock quarries on federal land, there must be many more on private and state lands. We’ve got thousands of existing dams that could be converted.

            PuHS, like flow batteries, offer the ability to store deep backup for low cost. Make the reservoirs larger or storage tanks larger and power for those periods when wind and solar aren’t keeping up with demand for multiple days can be covered.

          • Bob_Wallace

            You can edit out the typo….

          • Calamity_Jean

            I know, but that makes your response to it look stupid. I thought that would be rude. I do go back and edit if I notice a typo within a minute or two, but after that I don’t think it’s right to change it.

          • Bob_Wallace

            You can always stick something like “eta: Corrected kWh to kW” at the bottom.

            Don’t worry about making me look stupid. I do that without anyone’s assistance…..

          • Calamity_Jean

            That’s news to me.

          • Bob_Wallace

            I’m pretty sure Disqus has always given us the ability to edit….

          • Calamity_Jean

            Not that! This: “…making me look stupid. I do that without anyone’s assistance…..”

          • Bob_Wallace

            ;o)

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