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Published on January 13th, 2016 | by Christopher Arcus


We Don’t Need Storage Today To Integrate Renewables

January 13th, 2016 by  

Today, storage is not widely used. Despite moderate renewable energy integration, places like Denmark and Germany use very little storage. In countries like Uruguay, even higher levels of renewables are used with little storage.

How so?

To understand, we need to look at how the grid works.

A system operator balances generation vs demand. Operators look at day-ahead demand curves. The expected vs actual demand can be plotted. You can see plots of day-ahead and hour-ahead demand here:

The operator plans the day-ahead generation to match predicted demand and holds some in reserve for unplanned outages. The generation is a mix of sources. If the sources are variable renewables like wind or solar, the prediction is based on forecasts. For now, in the majority of the world, flexible sources exist to compensate for variable renewables. Why? Take a look at that graph. Reserves are higher than demand. The total available generation must be higher than the annual peak demand in summer. That means there are a large number of power plants idle most of the year. That’s why up to 40% renewables can be accommodated without any major changes.

We need to plan a major shift in energy infrastructure to renewables. What do we need to increase renewables integration? We need finance sources and approval streamlining. We need to reduce solar BOS costs.

We need better solar and wind forecasting to help match load and reduce reserves. Increased NREL funding can speed implementation of improved, taller wind turbines. Increases in transmission can reduce curtailment and allow connection from high-resource areas to load centers. Improved grid practices like “Energy Imbalance Markets” can allow neighboring ISOs to share power and resources more effectively and closer to real time, in 15-minute updates.

But what about those arguments about how solar and wind are not available for long times? 

Let’s suppose we assume a very crude model of demand vs generation. Assume there are 2 weeks with no solar or wind on average everywhere. About 4% of generation. Now assume those two weeks are powered by the mothballed and shutdown FF power plants. How much carbon emissions is that? That is an overly simplified and certainly incorrect scenario. But it illustrates the point. 

Existing FF power plants can be used as reserves at low capacity factor. We wouldn’t need 100% FF for those two weeks, either. We have dispatchable renewables like hydro, geothermal, and biomass.

Just as we do today, we can hold some wind and solar in reserve, as overcapacity. Added dispatchable renewables like geothermal, hydro, and biomass combine to meet demand. When you look at it that way, storage is useful, but not critical.

The vast majority of Tesla storage will be used for utilities to replace gas peakers.

It will be at least a decade before meaningful amounts of grid storage will be needed to implement renewables. 

I think we need to shift the conversation from what energy will look like in 35 years, to what it takes to integrate renewables right now.

Demand management and transmission will be used to integrate renewables before storage becomes a bottleneck, for example, so advancing those markets and associated infrastructure is important now.

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About the Author

has studied wind, electric vehicles, and environmental issues. An electrical engineer familiar with power and electronics, he has participated in the Automotive X Prize contest. He is an avid writer, specializing in electric vehicles, batteries, and wind energy.

  • heinbloed

    The cheapest battery in Germany costs € 300.-/3.2 kW and includes the power management system, manufacturer is Varta.

    The cheap price is available thanks to supports from the Bavarian state and only for citizens of Bavaria and limited to 10.000 applications, other makes and manufacturers are accepted as well off course:

    (in German)


    The Bavarian government claims that they’ll live in the dark when last atom power plant is being switched-off in 2022/23. Or somewhere near.

  • heinbloed

    2nd September 2015: Denmark’s first day without ‘conventional power plant’:


    Power storage in Denmark is mainly done with the aid of thermal storage (electric boilers in the district heating systems). Very few chemical batteries.

    Norway – the nation with the about highest power storage potential available in the existing hydro power plants – reassesses plans to extend the interconnectors. The alumina magnet Germany would take it all:


    Germany – without much power storage yet – has already the lowest power prices in Europe next to Scandinavia :

    (” Increasing prices …”)

    It is actually Norway and Sweden who are cheaper at the moment, Finland has blown itself out beyond any competitiveness with their atomic dreams.

    And Sweden’s Vattenfall can’t afford to keep the atom power plants open anymore:



    The Scandinavian power prices


    and the German power prices


    where peak load futures (2018 and 2019) dropped yesterday below € 30.-/MWh for the first time and fell further today:


    Just horrible what the atomic exit has resulted in: no more connectors to Norway 😉

    For a brief period today the peak load power future 2017 dropped today as well below € 30.-/MWh, see the EEX data link just above.

  • Ross

    Why would geothermal be used as dispatchable? I can understand biomass being used that way because there’s a fuel cost. Is geothermal not set to a base level of energy recovery equal to that coming in from the earth’s core?

    • Ronald Brakels

      Well, the capacity factor of geothermal is apparently around 70% which is what one would expect from something that is used mostly for baseload, with some load following thrown in. I don’t know much about conventional geothermal energy since we ain’t got none here, but I presume some plants are below the natural heat replacement rate and so operate in baseload mode, while others are above it and so load follow.

    • Bob_Wallace

      I can only see using geothermal as dispatchable in a situation where the heat source was inadequate to run 24/365. In that case running part time would allow for heat recovery.

      • Ross

        Yes. That’s the scenario that makes sense to me. Reading up a little on geothermal power sources they seem to also vary naturally. e.g. Geysers.

    • eveee

      Geothermal is like hydro. It can act as base load and like a flexible source that can adjust to variable sources like wind and solar. The flexibility has a value.

      The value is mostly associated with a reduction in the need for gas peaker plant expansion, a costly move.

      “Adjusting institutional procurement processes to recognize geothermal’s double-duty potential requires that the full value of geothermal be included in cost comparisons with other generation sources, and that all avoided costs resulting from geothermal either be credited to it as added value or subtracted from projects that impose system costs.”


      A simple analysis of comparative costs must be based on a system cost perspective. Translated, its cheaper to use geothermal for occasional ramping than to buy gas peakers that sit idle most of the time and also consume fuel when they run.

      • Ross

        So are we talking about an occasional increased draw of power from the geothermal source at a rate higher than energy is flowing in? I presume that the draw on the geothermal resource then has to be reduced for a period after using it to peak output.

        • eveee

          Sounds about right. There is a steam pressure source. Its created by injecting water into the rock. They cannot draw too much steam or the pressure drops. They can also lower output. Right now, most units cannot drop to zero output.

          “If you are trying to store power in a reservoir, geothermal doesn’t fit that description,” Thomsen said. But the Ormat binary technology’s flexible mode ramp rate, using an injection valve, is 30 percent of the nominal power of the facility per minute. “The ramp rate is not the question. The technology is not as important as the economics. And if utilities demanded this, there would be even more innovation — if the price was right.”

          That indicates that power is varied by varying the injection rate.


      • Bob_Wallace

        Difference is, we can build as many gas peakers as we want and install them where we like. Geothermal is amount and site limited.

        I suspect we mostly use hydro as dispatchable generation because there’s not enough inflow to run full out 24/365. At least that’s the case of the dams which I’m familiar with. They’re run part time because they don’t have enough water supply to run all the time.

        • eveee

          Yes. The gas peakers can be placed at will. Pumped hydro will extend the length of time hydro can be used, because it will be less dependent on inflow with water pumped back up into the reservoir. There will still be some seasonal or climate induced changes that cannot be avoided.

          • bink

            peakers are being limited in their siting in urban areas.They are more polluting than their gas counterparts

          • eveee

            Yes. There are other limits to peakers, too. Sometimes they have gas pipeline limits. That happened on the East Coast during the polar vortex.
            You are pointing to CCGT being cleaner. ( and more efficient)

          • bink

            neither is setting any efficiency records but generally I expect the CCGT to be cleaner and more efficient if being used for baseload power

  • Brett

    Concerns about grid stability with increasing shares of intermittent srouces may have been founded in ignorance in the past, and therefore the fact that reliable data wasn’t available dictated caution. That isn’t the case today, there are thousands if not millions of data points that are showing that intermittent sources aren’t problematic, and are actually beneficial for mitigating the use of peaker plants.

    Storage is actually going to be the key in going from integrating renewables, to the dominance of renewables, as expanding storage will reduce the need for baseload generation from sources like gas, coal or nuclear.

    • eveee

      NRELs 2010 Futures Study for 80% renewable by 2050 estimated about 10% storage.


      There are a number of other renewables integration methods. Too often these others are overlooked compared to storage. The emphasis has to be balanced more properly. Storage has a place, but not so much now. TOU may help storage, and is needed to send proper price signals.


      Demand management is largely underutilized. Some utilities are fighting it.


      Storage is dropping in price and has a role right now, reducing grid power peaks and lowering costly generation expansion. DG solar is reducing power peaks also, and is eliminating day/night arbitrage as a source of storage income. So storage is shifting to other roles.

      • Brett

        The impact of storage in private residences and companies is a complete unknown at this point, but given the overwhelmingly positive response to the announcement of first-gen Tesla Power Walls and Power Packs (only one of many storage products available), the desire to mitigate TOU pricing in many jurisdictions could cause rapid proliferation of distributed storage, similar to DG solar. Power to the people!

        • eveee

          You bet. Storage is likely to be added in residential especially once TOU rates start.

        • JamesWimberley

          In countries where residential consumers cross-subsidise industrial ones like Germany and Australia, the economics of home storage are ridiculously good. This is likely to lead to under-investment in storage rather than underinvestment, until the distorted incentives are corrected. From a technical point of view, home storage is bound to be inefficient compared to grid storage, which can access a much wider range of options from lithium batteries to pumped hydro.

          • Brett

            I didn’t want to single out Australia, because everything I’d heard about their electricity costs seems so out of whack with everything I know, but now that I’m looking at some stats (albeit from 2011 – https://www.ovoenergy.com/guides/energy-guides/average-electricity-prices-kwh.html), it seems like the kwh price in Germany and other jurisdictions are also quite high.

            These per kWh rates seem so ridiculously high compared to where I live (Canada), that it seems like the LCC of owning a solar system with storage would be almost a no-brainer from an individual economic perspective.

            Grid storage would obviously be far superior in terms of efficiency, and more cost-effective as well, but I guess I’m looking at which economic behaviour is going to drive storage fastest, and looking at all these countries that either have little electrical infrastructure, or those prone to frequent brown-outs / black-outs (India comes to mind), storage demand could be very high indeed.

            Similar to how many countries leaped frogged telecommunications technology in North America by going straight to wireless and cellular infrastructure. It’s much more affordable when you don’t have enormous sunk costs in legacy infrastructure, like our electrical grid and nuclear plants.

          • Jenny Sommer

            What’s the cost of electricity in Germany and Australia vs Canada?

          • Ronald Brakels

            Well, I pay 30 US cents per kilowatt-hour for grid electricity in Australia. That’s the total cost. The marginal cost, what I pay for each extra kilowatt-hour is only 24 US cents a kilowatt-hour. The average marginal cost for grid electricity in Australia should be around 21 US cents a kilowatt-hour.

            Update: The Australian dollar is down by over 4% from the last time I checked it, adjust the electricity prices accordingly, or not if you think it will spring back up. (I mean, it’s not as if anything bad could happen to the economy of China, right?)

          • Brett

            According to this site: https://www.ovoenergy.com/guides/energy-guides/average-electricity-prices-kwh.html

            somewhere between 190% to 250% higher than Canada (again, its out of date info). It’s also price, not cost, so there are margins and taxes built it, but if I was asked to pay $0.35 per kwh, purchasing a 5kw system for $5k (http://www.ebay.ca/itm/New-5KW-Solar-Power-Generator-System-for-110v-220v-Home-Use-Shipped-By-Sea/131687731384?_trksid=p2141725.c100338.m3726&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20150313114020%26meid%3Dcde474d18ac4451da8628d348740bbc4%26pid%3D100338%26rk%3D3%26rkt%3D17%26sd%3D281892952178) would seem stupid not to do, the payback period would probably be well under 20 years, without any feed in tarriff at all.

          • Jenny Sommer

            It’s around $US 0.2/kWh in Germany.

            It’s nothing to worry about. The average German is using less than half the kWh compared to a US citizen… I guess Canada is more like the rest of North America?

          • heinbloed

            It is about nearly US $ 0.30/kWh (ca. €0.25 – €0.28/kWh) incl. VAT and surcharges and without grid/metering fees in Germany for households and small enterprises.

            If a second meter is used for night tariffs it becomes cheaper, the night tariff (heat pumps, direct el. heating) dropped between 6-10% last year.

          • Jenny Sommer
          • heinbloed

            Read your offer again:

            ” Arbeitspreis pro kWh = 25.36 Ct/kWh incl. VAT”

            (and excl. “Grundpreis” = grid and metering charges )

            That is US$ 0.301/kWh.

            And not the $ US 0.20/kWh you came up with before.

          • Jenny Sommer

            That’s without the bonus.
            It’s effectively 19€ct for the first year….then you switch.
            That’s exactly what people should do for the next 4-5 years.
            It is about finding the sweet spot for your investment.

            At the moment you are looking at a payback time of 16yrs minimum even with 28ct grid power.
            Over 20 years in Austria with 18€ct grid power and no incentives for battery storage.
            What I won’t predict is battery replacement cost after 16-20yrs. That’s so far out, batteries and PVcells could be had for 1/4 of todays prices.

            If you have the money – invest! I’d be seriously interested in actual payback times/real live economics.
            Do you know anybody tracking the performance of his PV/storage system?

          • heinbloed

            You’re giving wrong answers, the OP asked what power costs in Germany. And not how the special offers are advertised.

            Most German end consumers have not switched their supplier ever.

            The question is relevant to many citizens in the USA since they can’t switch due to monopoly market situations.
            No special offers, just the question: is a battery-and-PV system worth it.

            “Buy a petrol generator and get 20 gallons for free. Next offer available next year.Maybe.”

          • Jenny Sommer

            The original statement by James was that the economics of home storage would be ridiculously good in Germany (and Australia).
            Do you think that is correct?

            Is it worth it when you can switch? You might want to buy your system a year or two years later when pices are down 30% and you have used up all switching opportunities…
            If you are smart you switch. If you are not smart you can either afford it or you might live somewhere in the city (or Plattenbau) where you couldn’t install a PV system if you could afford it.
            If you already got a PV system you could also see if installing more cells (or thermal storage) would be a smarter option.
            I read that over 70% have already switched once…most have switched.
            I set my calendar… Switching day, 10 minutes to save 200-250€.

          • heinbloed

            ” The original statement by James was that the economics of home storage would be ridiculously good in Germany (and Australia).
            Do you think that is correct? ”


            ” Is it worth it when you can switch?”

            A non-relevant question.

            ” I read that over 70% have already switched once ”

            Link please.

          • Jenny Sommer

            You are right. Cumulative change rate since 1998 is 40% (11/15).

            How much does the battery save over a kWh grid power?
            About 3-8ct?
            How much is the battery+installation?
            Is the cycle life relevant or won’t you use it up anyways?
            Opportunity cost?
            Ecological impact?

          • heinbloed

            ” Cumulative change rate since 1998 is 40% ”

            Link please.

          • Jenny Sommer
          • heinbloed


          • Jenny Sommer

            The cheapest rate without bonus, including everything is still under 22€ct.
            But why wouldn’t you switch and take the bonus when you can?

          • Steven F

            Germany has a feed in tariff to encourage renewables. The money for this tariff comes from a tax on electricity from the grid.
            In Australia the high electricity cost is very different. Around 2005 Australia utilities expected a lot of new demand which would require a lot of grid improvements. The utilities got approval to add a fee to pay for the upgrade. That fee accounts for most of the difference between Canada and Australia. The Fee in Australia is encouraging people to install solar. As a result the anticipated demand has not appeared. In fact demand is now decreasing and many of the grid improvements may no longer be needed.

          • TatuSaloranta

            I think many RE advocates seriously underestimate cost issues with chemical battery storage; perhaps due to mismatch between power and storage capacity ratings. While it is not unreasonable to consider total storage with power output close to maximum needed by the grid it is quite something to sustain that rate for multiple hours, much less for multiple days. Not necessarily technical problem, just very expensive. I mean, even for 1 hour of full capacity would cost more than equivalent RE generation — at least doubling up the needed RE investment.

            But multiple day “outages” (2 days or more) do occur with wind; and unfortunately these also tend to occur during winter when solar power in most industrialized countries can not help significantly.

            I think that the solution for 2-3 day minimal wind conditions needs to consider other chemical storage. Biomass is already used as sort of storage, and power-to-gas may work out acceptably — its lackluster efficiency is not a major problem if it is only needed for 1-2% of time. Storage, generation capacity and transfer (electricity interconnections and possibly gas transport, unless highly centralized) are obstacles to store there.

          • neroden

            Multiple day outages simply do not occur with solar outside the snowbelt; accordingly, I expect that overbuild of solar is likely to be the solution in most of the world. In the snowbelt, there is an unfortunate problem relating to clearing snow off solar panels; eventually someone will solve this, but we will probably also need some big transmission lines to bring power from the south.

            Really, with the ever-declining price of solar power, the only condition which requires storage is nighttime.

          • Bob_Wallace

            That’s not true. The tule fog can settle in and blanket the CA Central Valley for days. California forest fires can greatly reduce solar output for days and weeks.

            There will be problems we will have to solve. It should be several years before we’ll need to. There’s a lot of low hanging fossil fuel fruit to pick before we need to worry about the unusual situations.

          • TatuSaloranta

            In northern latitudes the problem is that there is very little production during winter; not that snow blocks sunlight (although that does take it from 10% to 0% of summer levels).
            You can check out seasonal irradiation levels, and it’s vary varied even outside of snowy zone — solar does not contribute much in Germany during winter, and even in Spain there is still strong seasonal variation. In Spain (and similar) one could perhaps overbuild, to get to steady enough state; but considering Europe as whole (for example), that will not work.

            As to outages: more than 24h very low production (say, below 20% of rating) occurs quite regularly in Scandinavia; but everywhere wind is variable enough so that it poses problem when penetration is high enough.
            Extending size of grid helps smooth things out; similarly, over-building helps in that there is certain level of capacity one can consider “base load” (if I recall correctly, with small adjustments it was close to 30%?)

            What I am arguing for is just that the use case of “deep storage”, which occurs only couple of times a year, is distinct from day/night, or intra-day variability, both of which are easier to resolve. I don’t think over-building alone can solve this; and I think that current residential/utility level batteries (lithium, lead) are too expensive to do most of it.
            What seems more realistic is that some of it can be handled by pumped hydro; and rest with biofueld, perhaps power-to-gas. Source energy for these can be variable.

            Such storage would seem more like national emergency storage that is done currently for oil products. Perhaps this is how it should be handled for electricity as well — it is a strategic national safety issue, after all.

          • heinbloed

            From how many battery owners have you heard this story?

          • bink

            you can specifically scale a redox flow battery because the power and energy in the platform are decoupled. Batteries absorb energy and generate. Therefore the hours of service in a redox platform is only limited by the available energy no matter the source of power. The cost of doing so in a flow battery platform actually goes down as you add capacity. Unlike lithium you only scale the energy side by adding additional volumes of electrolyte or bigger tanks.

            The electrolyte as a percentage of the system cost is much lower that the power component. Include in that calculation no additional installation or balance of system considerations.

          • Jenny Sommer

            Do you believe a RE system backed up by RF batteries would be cheaper than Hinkley Point C?

          • bink

            Taken togehther the capex of the RE and battery would come in under the nuclear capex (kW cost). Since the solar energy is free its really amortization of fixed and capital costs. We would have to include energy purchases from the grid in any calculations but we can guarantee the lowest overnight pricing via pricing algorithm, On its surface no it would not be cheaper but in terms of cost effectiveness the economics bear out with the RE+storage

            The nuclear will provide baseload power and not much more in the way of load following, which by the way is not allowed in US.

            The RE storage facility will earn income from providing ancillary and energy services and reduce investment in additional capital, transmission ans distribution infrastructure

          • Jenny Sommer

            Home storage is uneconomical in Germany.
            You don’t need backup against blackouts and power isn’t that expensive if you are not too lazy to switch.

          • heinbloed

            Half of the power storage systems in Germany are installed without supports/subsidies.
            Because it is economical:


            ( last sentence)

          • Jenny Sommer

            Geh bitte
            Doesn’t make them economical. You can argue that the effect is a nice one for the grid but how do you figure it is economical for the owner?

          • heinbloed

            It is the owner who easily calculates the sums on a beer mat:

            purchased power cost € 0.20/kWh – € 0.28/kWh.
            From the battery it is cheaper, esp. when when a PV system is already existent.

          • heinbloed


            ” “For 2015 we estimate 12,500 new systems will be installed – with and without KfW support,” Hoehner said.”

            (that’s from May 2015)


            I think I’ve heard that 20,000 systems were installed with half of them supported.But check this.

          • Ronald Brakels

            Avoided transmission costs that result from home and business energy storage means it can be economically efficient to install it even if it costs considerably more than utility scale storage. For the vast majority of the world’s grid connected population it doesn’t make sense at the moment. But provided the cost continues to fall, it will make economic sense in an increasing number of areas for an increasing number of people. The combination of falling costs in home and business energy storage and in distributed solar make it worthwhile.

          • Matt

            I have to agree it likely will make sense, but mostly because of strange market signals. If you get zero for power you feed into the grid and pay $0.25 when you take a kwh out. Then “wonder of wonder” it can be to your personal benefit to have a battery.

          • Ronald Brakels

            New rooftop solar only gets roughly the average daytime wholesale electricity price as a feed-in tariff in Australia. None of the avoided transmission costs are included in the feed-in tariff. Why? Because apparently they are not sure how to work it out accurately and they decided to not to work it out at all to the benefit of fossil fuel generators. Gee, thanks guys. Your laziness is drowning children in Bangladesh. How do you sleep at night? What’s that? On huge bags of cash? You bastards.

    • Steven F

      it wasn’t all ignorance. In 1970s when a wind turbine turned on it directly connect the generator to the grid. That caused a brief period of frequency and voltage fluctuations on the grid. There were legitimate concerns among utilities that large wind farms would destabilize the grid. Today no wind turbine in the market directly connects the turbine to the grid. Instead the turbine is allowed to put out variable AC which is then converted to DC and then back to AC with electronics. The frequency and voltage output of modern turbines is very tighly controlled and will not impact the grids like turbines built in the 70s Many of the 10% to 20% renewable limits people have mentioned came from US government studies.

      • eveee

        Yes, grid stability issues with renewables is a myth.
        If anything, renewables are more stable than conventional sources.

        You are referring to Converter style wind turbines that go from AD to DC and back to AC. They are used more for offshore and are great for stability. Any source with an inverter is capable of fast, controllable response.
        The doubly fed induction generators, DFIG, still comprise the bulk of onshore generators. They also have voltage ride through features, and have voltage and frequency regulation.
        These features are becoming part of grid code that new wind turbines meet. These wind turbines can also be controlled from a remote location, allowing full system control.
        Overall, both kinds support and enhance grid stability.
        There is a great discussion re renewables and grid stability in IEEE Power and Energy Magazine Nov/Dec 2015.

  • Freddy D

    Remember that by 2030, the year California has committed to 50% renewable generation for example, storage technology, EV storage, demand management systems will be much further along. It may really be a non-issue by the time renewables get to 60, 70, 80%.

  • vensonata

    Perspective: The goals of the Ipcc are about 80% reduction of carbon based fuels by 2050. Most of us greenies tend to think about 0% carbon. We should realize that to get to 80% reduction is as easy as falling off a log compared to 100% reduction. That 20% fossil fuel back up is enormous. I would propose we aim for 95% reduction and the last 5% can be backed up by natural gas. It is used infrequently.

    Chemical battery storage has recently arrived and is rapidly moving towards viability on a large scale. The author refers to “a two week period without solar or wind”. That is a single period requiring 100% supply by fossil fuels. He is generous in the extreme to the naysayers of renewables. Periods like that do not last two weeks continuously but are dotted throughout the winter. Those periods of up to 3 days can be supplied by battery and recharged for the next small period. Throughout the winter there may be 4 or 5 occasions each of 2 or 3 days where renewable need supplement. That is a more realistic picture than a single 14 day run of no wind, no sun, on a one million sq mile grid area.

    • Brett

      Your caution is certainly reasonable, but it doesn’t hurt to shoot for the moon. The goal should be 100% reduction and if only 95% is reached, that’s still a vast improvement only 80%.

      Thirty-five years is a long time, looking at li-on battery pack costs, which have fallen precipitously in only the last 5 years, its not hard to imagine energy storage and solar wind becoming more cost competitive than any fossil fuel source. Obviously the curve will start to become more shallow as economies of scale are reached, but that’s only one existing and proven technology, and others may arise.

      From at least a North American standpoint, the compensating use of significant hydroelectric resources already installed in Canada and the US, coupled with chemical storage, could probably serve to meet energy needs during times when solar or wind aren’t sufficient to meet demand.

      • vensonata

        The only problem with hydro is it doesn’t ramp up. It provides about 7% of US needs but in a steady way. Hydro pump up could double that but 14% when you need 90% is not enough. That is why either gas peakers or a 3.5 day battery is required. Probably both will be required.

        • TatuSaloranta

          And that 3.5 day battery would be very, very expensive with current prices, or even with estimated cost improvements with no breakthrough within next or even 5 years. I doubt current style chemical batteries will be the backbone of handling multiple day outage.

          Unfortunately you are also correct wrt hydro storage: while somewhat economical, capacity is bound by geography. It can be used to solve intra-day problem, but not multiple days.

          This would leave power-to-gas chemical storage, which has poor efficiency. However: considering that this usage would be relatively small slice of total energy need, efficiency is probably not the main problem. Rather it would be storage and transfer. But assuming source is electricity from wind, solar, it can be transferred quite efficiently over time so that initial generation and storage can be more centralized.
          Generation from gas (or liquid) would require non-trivial plants as well.

          So choice would actually be between high-capacity electricity interconnectors, or gas pipelines (or some combination thereof). Given that former has much more use for general-purpose load balancing, it would seem better to have smallish number of electricity-to-gas-and-back hubs, with massive interconnections. For US these could be mostly located within existing (and future) grid edges, like that missing (Tres Amigos?) Texas interconnector.

          So my bet is that the real solution for that multi-day low production comes down to (1) over-capacity, (2) massive grid inteconnections, (3) power-to-gas.

          • Jenny Sommer

            There is ongoing research. Why shouldn’t some form of chemical storage fill the gap? Flow batteries? Maybe some massive storage solution like the hydraulic rock storage idea. With the remaining % p2g. The problem gets smaller the earlier you can predict it. Just start filling all storage when it is available. Dump overproduction into thermal/cold storage and you can later reduce peak demand.
            Even today a lot if industrial demand is curtailed.

          • TatuSaloranta

            It is not impossible, but the trajectory at this point is not promising for large-capacity storage. So it is good to not assume chemical batteries will definitely be the solution. Hopefully flow batteries will improve the situation — they can have significant cost advantage, and some of them even have low-toxicity materials.

            Batteries are great for some of storage needs, from frequency regulation to intra-day balancing.

          • vensonata

            The battery is possible. I have worked out the details. This is what is required:
            1. A 1000 cycle battery. High cycle batteries are misleading, their low price per kwh assumes you can actually access them. It is a huge jar of vitamins with an expiry date that means most will be wasted. A 1000 cycle battery will require 30 years at 33 cycles per year to use it up. It will cost no more than $50 per kwh. Giving electricity at 5cents per kwh. (cheaper is conceivable. I am using presently available tech)

            2. It is 40 twh of storage total…1%of the total U.S. grid, 3.65 days of electricity.
            It will cost 2 trillion dollars! Don’t panic. Divided by 30 that is 66 billion dollars per year, about the same as lottery ticket sales in the US. It increases the total grid cost by 16%. But will be zeroed by efficiency improvements of 16%.

          • Jens Stubbe

            Your calculations are done entirely without OPEX. The interest alone will drive the cost much higher. Also you assume a cost point that is roughly a third of today and you do not take into account that the cost of energy is constantly dropping. Utility scale solar has dropped 17% year on year as an example. It will be so much more reasonable to expect that the engineers that develop wind power and solar power has the ability to continue the progress they have proven.

            Over provision, larger capacity factors, stronger HVDC infrastructure, smart grid implementation, energy efficiency and Synfuels will be a much cheaper and faster way to reach 100% renewable grid and beyond.

            The current battery hype is misplaced and actually instigated by the proponents of Nuclear and fossils that always declare that a grid based upon intermittent electricity generation is unfeasible.

            In Denmark 52% of electricity generation was provided by wind in 2015. If you add solar, biomass and hydro the intermittent renewable percentage was higher. Still we have just about the cheapest electricity generation and certainly the most stable grid.

          • vensonata

            Cost point is $50 kwh. At scale it is possible. We are not talking high cycle lithium, we are talking low cycle tech. However, this chemical battery is purely to cater to rich Americans convenient lifestyles. Electricity is a poor way to store thermal energy. Behind the meter hot water thermal storage is about $3 kwh! compare to $50 for the battery. Most winter needs are thermal. In other words a 24 gallon tank can store 7 kwh equivalent to the powerwall for $100 rather than $3000.
            If Americans want to be frugal they will make both hot water and ice storage pervasive throughout the country by 2030. Overbuilding PV and Wind and battery storage will be greatly reduced.

          • Matt

            Most summer is AC, so thermal has massive ability to shift within the load with the day.

          • heinbloed

            The missing link:



            Consider that the US situation at the status quo has not many inner state-to-state connections and very few interconnectors abroad.
            A lot of publishers for the media have very little experience in the international trade/energy business.
            The colonist’s first thought was ‘independence’ what for many means freedom. This was and is the situation in most ex-colonies.
            Hence the gun, the barn, the battery and all of it ‘mine and this must be worth it’.
            A historical consequence,outdated in the modern humanistic world.

          • TatuSaloranta

            Low-cycle-rate battery is an interesting idea: if you could trade lower number of cycles to reduce cost, that would definitely be beneficial for “deep storage” — it could with even much lower max cycle counts: if major low-production events only occurred an average of, 5 times a year, would cover 20 years with just 100 cycles. I don’t know if this is a trade-off that is easy to do, but very interesting idea — different cycle rates for different use case (arbitrage/voltage-regulation, intra-day smoothing, day/night, longer term).

            Your second point is along what I wanted to highlight: cost is huge. And you are right, it needs to be built over time, amortized so it’s sizable but doable.
            In fact it is similar to one of my pet peeves in US: why are power lines NOT dug underground? Local utility always hides behind “it’s so expensive for vast areas” excuse — yet somehow much more sparsely populated Nordic countries have managed to do it _over time_.

          • bink

            Cycling has nothing to do with cost. Cycling has to do with inherent chemical degradation.

          • TatuSaloranta

            Cycling has correlation to cost, in that materials that degrade more slowly tend to be more expensive. As a result, higher the required lifetime in cycles, more expensive the system. If not, we would have batteries that never degrade, given that cost is not related to cycles at all as you claim.

            What I was wondering was just that what if instead of assuming relatively high cycling requirements one would be content with low number of, say, 100 cycles (before degradation reduced capacity). Would that allow use of significantly cheaper material, components, mechanism or overall design?

            It may be that there is no cost advantage. But if there was, then it would make sense to see how that could be taken advantage of.

          • bink

            Your premise is wrong. The cost of the battery is the cost of the battery. The type of battery chemistry and its use in a application is the biggest factor in degradation.

            In other words you can’t alter the potential of the battery chemistry itself only through application use or software.

            Similar as to what is already occurring in long duration installations to extend battery life (50-70% dod).

            Why you would not want to use the full capacity of something you paid for in the scenario you present is beyond me.

            Vanadium batteries don.t degrade and are being sold based on length of contract or 20 year calendar life with unlimited cycling.

          • TatuSaloranta

            Where did you get the idea that change would be through use or software? I said nothing of the sort. Obviously it would be the actual materials and/or construction of the battery using cheaper materials, which could be allowed decay faster, allowing one to build a cheaper battery when not requiring high number of charge/discharge cycles. In extreme case of biofuels, for example, you “charge” it once (synthesize) and “discharge” once, when burning into energy.

            It may well be that such trade-off does not exist with current materials. That does not mean that thought-exercise would be useless. Engineering is all about choosing trade-offs: and trading between cost and various other aspects is amongst simplest ones. Engineers do not try to maximize or optimize all properties; trade-offs are at heart of best designs.

          • bink

            You are so not informed on this subject matter of battery chemistry, What you state is misinformation. The battery degradation is inherent to the material being used. There is nothing you can do chemically to change that nor should you want to because the cost of material is the same, Like I already stated you can limit battery cycling via software or application use such as which is occurring w/ the Powerwall,

            The 10 kWh powerwall has 52 cycles of deep discharge annually but the same battery would be able to perform weekly cycles using software to limit the depth of discharge to say, 50%.

            You need to read more carefully I never stated you said anything about software I did to give context to my post.

          • TatuSaloranta

            You seem unable to read or understand written text so it is pointless to try to discuss anything. I did not say anything about degradation being separate from material — of course it is. That was EXACTLY MY POINT. And the cost of DIFFERENT MATERIALS is often different. Obviously.
            And different batteries are constructed using different materials internally, to get different properties and cost.
            It is amusing to hear you seemingly claim that all batteries are the same. I can’t even begin to outline how wrong that is; educate yourself at


            Finally: Powerwall has NOTHING to do with what I was talking about — this was about long-term storage at utility level. Why on earth would you think home-user would want such a thing? Discussion had nothing to do with home user aspect.

          • bink

            insults? no one who knows me would say that i think all batteries are the same, just the opposite. So I never claimed that. Show me where? . . I dont need to go to wiki I am in the business of energy storage development and integration You are someone who states theory as fact. degradation separate from material you are confused sir. I never said that The inherent potential is what it is. You can either exploit the potential or limit it through use or software is all I was saying. Do you have experience with grid storage? I do. As an integrator we provide the battery control scheme for the interconnection and services

          • bink

            By the way the 10 kWh powerwall, once a week cycling isn’t some special cheaper chemistry. The battery is designed to allow a deeper dod probably (90-100%) by design which is why cycling is limited. Compare this to the 7 kWh daily battery which is probably limited to 50% dod to extend the cycle life. We don’t know but it could be and probably is the same chemistry

          • Bob_Wallace

            Several real solutions. I suspect we’ll end up using a mix.

            We’ve got 80,000 existing dams in the US, we only use about 2,500 for generation. At least 10% of the others should be useful for pump-up hydro.

            Add to that several thousand abandoned rock quarries and open pit mines. Over 1,000 rock quarries on federal land alone. There’s a rock quarry just outside Chicago that’s being turned into PuHS right now.

            There are flow batteries. Large amounts of energy can be stored (hopefully) in the form of inexpensive chemicals in simple tanks.

            And there’s dispatchable generation. Coal and gas plant run on biofuel. We’ve already converted coal plants to biomass burners. Landfill and sewer gas can run turbines. Paid off coal and gas plants will have covered their capital costs and fixed operating expenses should be low. Fire them up when supply is stretched and run them 24 hours a day until wind and solar are back to strength.

          • TatuSaloranta

            Yes, multiple solutions are needed. Flow batteries do show promise, and perhaps they could take the role many suggest for longer-term battery storage.

            I also think that the last point is important. Not sure if just biomass could work (perhaps, haven’t tried the numbers?); or perhaps power-to-gas, directly from wind/solar was needed.

            All in all, I am mostly saying that the cost aspect is easy to underrate. And especially so since the difference between storage power rating (maximum power it can deliver) and actual stored energy are so often confused.
            What I mean by that is that there are many news where a new 1 MW storage solution is highlighted — without considering that energy storage may be limited to something relatively low; even just 1MWH. Such systems work well for many uses, but would help much less for day-over-day balancing.

          • Bob_Wallace

            Southern Company is/was converting a coal plant to biomass. Using trees from a plantation which used to grow trees for paper production.

            If we need dispatchable generation for the last 2%, 1%, 0.01% we could grow it. Perhaps not the most “perfect” solution, but one we could use until perfect rides into town.

          • Calamity_Jean

            “If we need dispatchable generation for the last 2%, 1%, 0.01% we could grow it.”

            Since this would happen maybe three times per century, and there would be some energy production, why not just declare an emergency and shut down non-essential activity?

          • Otis11

            Or have flexible pricing – increase the price of electricity temporarily and demand for ‘luxury’ electricity usage will decrease. Maybe even enough to keep ‘non-essential’ but profitable usage online! (Good for the economy to keep things running)

          • Calamity_Jean

            Whatever works, I always say.

          • bink

            Bob, from my perspective we have too much overgeneration in must parts of the country and the incentive to build to drive utility shareholder profit is the main reason.

            Storage has demonstrated in the PJM it can provide reliability as a function of dispatch.

            People tend to forget storage absorbs energy that would otherwise dissipate on the grid during low consumption hours.

            This is power that is already produced so the infrastructure costs are already sunk in the power plant that generated the power in the first place. This is a cost savings and lowers carbon emissions even further.

            Also storage helps lower power production and pollution from these power plants because they again are providing a lot of the services your baseload and intermediate and peaker power plants would provide such as; load following, regulation, Var, voltage support, reactive power, peak energy.

            As I have stated before not all batteries are equal so in some cases this may not be the reality

          • bink

            This article is limited in its scope around the discussion of energy storage. My company is a energy storage integrator and developer. So a lot of what you theorize about is fallacy and not true.

            We are providing services for a 100 MW solar + 50 MW battery array in the southwest U.S. Our 150 MW solar + storage facility is displacing a, 40 and 60 MW solar arrays, a 40 MW aeroderivitive gas turbine (GT) and a 177 MW hard frame combustion turbine (CT) under an avoided cost rate case.

            Avoided cost means we have a number of hurdles to clear in order to get approval to build from the PRC.

            One of those is we have to be equal or cheaper in cost than what is being proposed. Another is we have to provide the same amount or greater (energy) capacity.

            We have accomplished both of those in regards to the project.

            We have proposed to provide several services:

            Ancillary- renewable integration, balancing (regulation, load following), fast response frequency regulation, voltage support, Var, spinning and non spinning reserve

            Energy-renewable and non renewable bulk energy, and 40 MW of peak demand energy

            We are providing frequency regulation and voltage support 24/7 350 (forced outage) days of the year

            Essentially we are a baseload power plant because we are providing a continuous output from the facility from morning to night.

            We could not accomplish this without the use of the vanadium redox battery technology.

            The batteries ability to provide unlimited cycling, the capability to charge and discharge at the same time and being able to fluidly switch between power and energy applications is the key.

            And before you dismiss all of this. We were invited by the state in question to present to a group of stakeholders for a statewide workshop on renewable energy and storage.

            An audience which included 2 DOE national labs, power companies (NextERA being one) and national and international energy consulting groups

            The co-developer, a large multinational whose Director of North America flew in from Korea specifically to speak and show their companies support with committed funding for the project.

            This will be the largest facility of its kind to date, globally. And the only one of this size providing the services described above

            Yes we are taking grid power from a nearby wind farm and the grid at night to charge. But we are not relying on that for the 24hr voltage and (frequency) regulation services. We are keeping some of the solar power in reserve for that.

            The night charging is so that we can provide cpacity to load follow in the morning while the sun rises as factories and business start up. throughout the day we are taking solar power feeding directly into the battery for the continuous output, not filling the gaps.

          • bink

            Bob did you just remove my posts? especially when I thought I was being respectful in them and just sticking to the facts as I saw them. I had been reading these posts for two days now and did not post. I only tried to address what I saw as gross misinformation. Go figure

          • Bob_Wallace

            Nope. Removed none of your posts.

            There are no posts from you in the Pending, Spam or Deleted folders (at least in the last six weeks, I didn’t look back further).

            If any of your posts are missing I have no idea why. Or how. Anything a mod deletes goes into the Deleted file and stays there for 30 days until Disqus sweeps it out. Even post you might delete yourself would go to the Deleted files.

            So either 1) you never made them or 2) Disqus vaporized them (server problem?).

            Actually, there’s a third possibility. Disqus does some sort of strange time warp stuff at times. If you access the discussion via an email link you might not see all the comments made. I’ve seen that happen both on CT and other Disqus using sites.

            Try finding the article on the CT site and then opening it. See if your comments display then.

            Let me know.

          • bink

            I think they all reapprared. thanks for the info though

          • Bob_Wallace

            OK, then that’s on Disqus.

    • Bob_Wallace

      The “last 5%” from biofuels. Biofuels give us the same storage and dispatchability as fossil fuels.

      Done correctly, biofuels can sequester some carbon as they grow. Plants have roots that grow underground. Some, like switchgrass, have massive, deep-growing root systems.

      • vensonata

        Yes Bob, thanks for that. It was staring me in the face. 5% bio fuels instead of natural gas. So easy, what was I thinking?

    • JonathanMaddox

      There are other storage technologies in advanced stages of development which are potentially going to be considerably less expensive at scale than today’s battery chemistries. They include Sadoway’s liquid metal batteries (Ambri), Danielle Fong’s compressed air with liquid water thermal storage (Lightsail), reversible heat pump storage, James Macnaghten’s reversible heat-pump thermal storage (Isentropic), Toby Peters’ cryogenic, liquid-nitrogen heat pump storage (Higview Power), and finally, potentially enormously, there’s power-to-gas: fuel synthesis from excess electric energy in the seasons of high production, making hay while the sun shines. I can’t name a name because there’s a cast of thousands working on this, starting at the Baden-Württemberg Centre for Solar and Hydrogen Research and the Fraunhofer Institute and extending through utilities and startups across Germany, several other European countries and the USA.

      And, as Bob says, there’s biofuel.

      • vensonata

        One problem with flow batteries as with lithium; their lovely prices per kwh are based on high cycle life. A flow battery with 10,000 cycles or 20,000 cycles can give you electricity at 2 or 3 cents kwh. But only if you can cycle everyday for 30 to 60 years! If you want a large battery that will only cycle 30 times per year you will never access your theoretical stored kwh. Think of an ultracapacitor with 1 million cycles…at $1000 kwh you will never compete with a battery because it will take you 1000 years to squeeze the juice out. In other words high cycle batteries have been eagerly awaited because of the illusion of low cost. But it only works with little batteries that cycle at least once a day. We need a big, cheap, low cycle battery. A really cheap lead acid pig of a battery that has 500 cycles would answer a nation sized battery better than a sleek, elegant modern high cycle battery…if you get my drift.

        • bink

          Vensonata, your theory is not based on fact. The cyclability of the battery has to do with degradation or the lack of thereof that is inherent in the battery chemistry.

          That degradation or cycle life can be exasperated by application use as in the case of lithium batteries.

          So it would stand to reason that the unit manufacturing costs are sunk based on sizing not cycling.

          As far as using up all that cyclability. Using lithium in a utility grid, commercial or industrial application you are likely to use up its useful life with a battery swap-out by the end of the contract term.

          With a Vanadium Redox Flow Battery (VRFB) pumps and propellers will be swapped out on a 5 year schedule but the electrolyte is indefinite. This would allow for an life expectancy that matches utility assets (transformers, capacitors, voltage regulators, etc.) that it would replace or defer.

          Also, the VRFB has unlimited cyclability so my company when consulting on a project where we provide the battery integration would never propose a VRFB for a front of the meter singular application.

          It needs to be used as much as possible. The fact that it can seamlessly switch back and forth between power and energy applications means that it will cycle many times in a day.

          The vendor we use will come and pick up the battery at the end of the contract and recycle 90% of it (no disposal fee).

          So you can see once they have a good amount of contracts terminating the cost of raw materials is almost non existent.

          • vensonata

            Well, I am all for it. It is true that cycle life and cost per kwh are not intrinsically linked. But at the moment they are. Battery sellers base their prices on the cost per kwh that the market will bear, not necessarily how much it cost to manufacture the battery. But strangely enough, at this time, those two prices…the cost to manufacture and the final cost per kwh do have a rough correlation. If you can give me a 10,000 cycle battery that is still between 50-100 dollars per kwh, then we can have a reasonably priced “nation sized battery”. But we will still not access those kwh even in a century. But if a battery maker can pull it off, more power to them.

          • bink

            you are wrong. They do not start out pricing per kWh. Like any other manufacturing operation cost of goods, etc are determined plus a profit margin. That has nothing to do with life cycle cost of system that is a different calculation and number

          • bink

            that would be levelized cost of system

          • vensonata

            But see how it does work out about the same. But you can’t tell me that manufacture’s won’t be looking at their competitors price per kwh, because the customer will be looking at that, and comparison shopping on that basis.

          • bink

            That is not a game anyone is playing. You have to start with your cost to manufacture (including marketing etc) otherwise you risk underpricing and you are out of business quick. I am sure they are all starting at a margin of at least 12%. If you are smart you do the first couple of deals at cost to drive those sales.

            As I have been saying for quite sometime now. Revenue opportunity will determine the success of the projects and the technology developers.

            Recent suspension of RegD regulation services in the PJM is evidence of that. With a pending cap of 300 MW during the shoulder periods many lithium battery service providers will be hurting.

            The reason for the cap is excursion’s 6 hours of the day because after each dispatch period the signal is zeroed out causing the PJM signal to move in the opposite direction.

            The zero signal is to allow the batteries to recharge, so the services are really limited.

            What saddens me is that PJM developed limited policy solely around one technology that is a one trick pony.

            If they could have demonstrated the capacity to participate in the energy, capacity and demand response markets their projects could remain financially viable or serve as an incentive to keep developing.

      • bink

        Sorry, but Sadoway liquid metal batteries (Ambri) had to switch gears. And, I don’t think too many utilities would willingly want to have a 600 degree fire hazard next to millions of dollars of substation assets full of oil

  • JamesWimberley

    Sound. As with range for EVs, intermittency anxiety for wind and solar is a real issue blown up out of proportion.

    Niggle: “Increased NREL funding can speed implementation of improved, taller wind turbines.” Height above 80m makes little difference to the capacity factor of a wind turbine. The large recent gains in wind CFs- Bernard Chabot calls it the “silent wind revolution” – come from an increase in the ratio of rotor diameter to generator rating, trading higher peak output for longer output.

    The wind turbine manufacturers (Vestas, GE, Siemens, Gamesa, etc) are large and technically very capable. They need little help from the NREL. The one area in wind that calls for radical innovation is offshore floating platforms.

    • Freddy D

      Haha – yes, last I checked NREL doesn’t sell wind turbines. NREL has tons of R&D opprtunuties: cheaper hydrogen electrolysis, artificial leaf, economical direct air carbon capture, balance of solar system radical cost reductions, and storage storage storage at low low cost and many more very important topics.

    • eveee

      Are you sure height doesn’t increase wind CF? NREL seems to think otherwise and it does seem to make sense. Wind speed increases with tower height.


      Recent improvements in MidWest wind PPAs are attributed to both larger rotors designed for lower wind speeds and higher towers. IMO, its both.


      • JamesWimberley

        My claim was more modest: height should not improve the CF once you reach a zone of laminar flow clear of ground obstructions like trees and houses. I never said it doesn’t improve output. If you want bigger rotors, you must increase height anyway to maintain the minimum ground clearance.

        • eveee

          Wind speed keeps increasing CF even over 100m. Thats what the NREL paper says.

          • Bob_Wallace

            Here are 110 meter and 140 meter wind maps for the US. Getting up higher finds more wind.

    • Jens Stubbe

      GE and Siemens are large – Vestas is a quite small company and Gamesa even smaller. Vestas are going to test a 3.65MW turbine with 166 meter hub height. Even though you are very correct about the recent evolution in capacity factor can be attributed to increased rotor diameters relative to rated power there are a number of other strategies that also will increase capacity factor.

      The most important of these strategies are to tap into steadier and stronger winds with higher hub heights.

      Regarding offshore look at this link. http://www.floatingpowerplant.com/

      At the moment offshore in Denmark (90% of all offshore turbines in the world are Danish) is approximately 50% more expensive than onshore. The development is currently slowed because we are ruled once again by the party that elevated Lomborg into fame.

  • Frank

    I suspect, but don’t know, and would like to, whether battery systems can reduce the amout of over generation(reserve) needed because of their ability to ramp up in a couple of miliseconds instead of 15 minutes, because if they can, they should be able to make money without even cycling the batteries. An electrical insurance policy if you will.

    • evfan

      Yes, battery systems can reduce the amount of spinning reserves needed, and it is IMO one of the best uses of battery storage.

      The problem is the size of batteries needed and the cost. Which is why articles like this tend to focus on benefits that can be achieved with renewables.

      Over time all of this will happen. We will end up with more batteries and more renewables.

      • eveee

        Yea. Curiously, storage may happen with EVs much quicker than anticipated. Why not. They have ample storage.

      • bink

        Correction; batteries can provide spinning reserves. I am parsing here but I felt the need to make the point but you are also correct.

        I do have a problem with your statement about size and cost as it relates to actual facility footprint and operational expenses.

        The physical footprint for a 20 MW storage array would be smaller than a comparable 20 MW GT or CT.

        And because it is modular it provides flexibility in siting at specific locations where most needed providing dual use purposes for deferring transmission distribution asset, reducing line losses while reducing load and power production.

        A CT spinning reserve unit is not loaded (synchronized with the grid) it still has about a 3 min ramp at 20 MW’s a minute. that is 60 MW,s out of balance in that time. A battery (1000 MW min ramp) can arrest that instantaneously (milliseconds) even if the battery is idle and had to start its ready to ramp in 10-20 seconds.

        The economics of using a dual use battery more than mitigates the initial capex.

        If you consider the pollution (from load following), low efficiency, high variable and fixed costs and limited flexibility associated with the CT the battery economics look much better.

        Most don’t consider the last part “limited flexibility”

    • heinbloed



      You would have to distinguish between small scale end consumer’s batteries and medium to large (utility) sized batteries.

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