Alphabet (Google) turns to molten salt to store clean energy

A concentrating solar power plant. Source: Climate Central

Climate Central

Using giant vats of molten salt and antifreeze under the codename “Malta,” Google’s parent company Alphabet is joining Tesla and smaller companies that are developing ways to store wind and solar power affordably to expand renewables and combat climate change.

Alphabet’s X research lab is developing a cutting-edge molten salt technology that aims to store wind and solar power for longer periods of time and for less cost than the giant lithium-ion batteries Tesla and other companies are designing.

Electricity storage could help electric companies use more wind power. Source: Climate Central
Electricity storage could help electric companies use more wind power. Source: Climate Central

Electricity storage is considered critical to the expansion of renewables in the U.S. to help fight climate change and wean the U.S. away from electric power plants that use fossil fuel.

The amount of electricity wind turbines and solar panels produce depends on the weather, so the flow of power from them isn’t constant. Some of it is wasted when people aren’t using much electricity.

Storage allows wind and solar power to be used when it’s needed most, not just when the sun is shining or the wind is blowing. That way, stored renewables can be used instead of special power plants that run on natural gas when people are using a lot of electricity.

A growing number of states, including New York and California, have climate goals that require some percentage of the state’s electricity to come from storage. Today, electric companies that use power storage mostly rely on big batteries that weigh several tons each.

Tesla has been developing large-scale lithium-ion batteries for several years. It’s batteries are being used by a number of electric companies in California, and they may also be combined with a proposed offshore wind farm announced this week in Massachusetts.

But big batteries aren’t the only way to store electricity.

“There is a plurality of contenders (for power storage technologies) including pumped hydro, compressed air, flywheels, and batteries,” said Donald Sadoway, an MIT materials chemist whose research focuses on energy use and efficiency. “Electricity storage is hugely complex and will be satisfied not by a single solution.”

Pumped hydro-power is considered energy storage because water stored in a reservoir generates electricity when it flows out through an electric turbine. Compressed air works in a similar way, generating electricity as it is released from an air tank. Flywheels capture rotational energy in a spinning mechanical device, which slows down and releases energy when power is needed.

Malta stores wind and solar power by converting electricity to thermal energy. Heat is stored in molten salt, and cold is stored in a vat of liquid antifreeze solution. When the power is needed, the hot and cold energy are converted back into electricity by a heat engine.

A concentrating solar power plant. Source: Climate Central
A concentrating solar power plant. Source: Climate Central

Electricity in the system is produced most efficiently when there is a wider temperature difference between the hot and cold vats. Exotic materials are often needed to maintain high temperatures, but Malta appears to be using common materials instead, said Craig Turchi, a scientist at the National Renewable Energy Laboratory’s Thermal Systems Research and Development Group.

Similar hot-cold storage technology has been developed using hot water instead of molten salt, but the salt appears to be more energy efficient, said Turchi, who is unaffiliated with X.

According to X, salt-based thermal energy storage has the potential to be many times cheaper than battery storage because most of the materials necessary — steel tanks, salt and antifreeze — are inexpensive and abundant. The company says its Malta technology may be recharged thousands of times and last for up to 40 years, several times longer than today’s batteries.

Sadoway, who is also unaffiliated with X, said it’s too soon to say how Malta would compete on cost compared to other electricity storage technology because the company hasn’t provided any cost data publicly. “Thermal storage competes well with lithium-ion on service lifetime and on safety,” he said.

X declined to comment.

Turchi said he and other NREL scientists will be “rooting” for X to work out the details of the Malta project. “Our solar thermal power group is heavily vested in thermal energy storage technologies and we are always on watch for new developments,” he said.

Source: Climate Central. Reproduced with permission.


18 responses to “Alphabet (Google) turns to molten salt to store clean energy”

  1. Andy Saunders Avatar
    Andy Saunders

    “the hot and cold energy are converted back into electricity by a heat engine”

    And so the Carnot Efficiency loses a large fraction of the energy stored. Doesn’t seem feasible.

    1. Ian Avatar

      We have the solution to our energy woes and its simple: wind , solar, connectivity, battery and water storage. Why p1ss around with anything else?

      1. Keith Avatar

        So you have renable energy sources, and list 2 energy storage technologies, but not everyone is enthused about adding more hydro dams, and lithium battery is more energy dence making it better for transportation, but cost is more important for grid level energy storage that case less about the density of storage.

        1. Ian Avatar

          Huh, what are you saying? Are you advocating for heat storage? Andy Saunders above points out the Carnot cycle is not an efficient one, That would be a similar problem using steam. When it comes to electricity storage round trip efficiency RTE is all important. For the moment ,neglecting construction and maintenance costs, and arbitrage for the sake of simplicity: lithium batteries about 83% RTE, PHES 70 to 80%. For lithium batteries you might charge the storage with $100 worth of electricity, when you draw it out again you get $83 back. Gas storage RTE 50% put $100 in and get $50 back. Who knows what thermal storage RTE will be. If it’s in the range of batteries and Pumped hydro then it’s probably worth while. In the case of solar thermal, or geothermal, then sure, thermal storage is a good thing, simply because the heat is the driving force of the generator anyway, and storing it for a better market opportunity makes sense. Storing heat or cold at the user end is also worthwhile, again the reason is that heating or cooling is the final product and storing it can take advantage of the lowest price electricity or intermittently available electricity. The problem is electricity storage : putting it in a storage device and then retrieving it again later.

          The thing I like about lithium batteries is that you can put them in a vehicle and get double duty out of them. 1 for transportation and 2 for electricity storage. (. That’s in a Vehicle to Grid world). Electric vehicles need enough battery storage to give a marketable range but rarely are used to the full extent of their range. In Australia the average daily use is 40km whilst the range of an EV might be over 200km. If the battery is 50 KWH and 8KWH is used on average 42 KWH are available for other purposes.

          We need to decarbonise transportation urgently, perhaps more urgently than we need storage options for grid electricity. Electrifying and extending public transport is good and necessary but private transportation can and should be electrified.

          Converting the electricity grid to renewables is almost a fait accompli, but transportation now needs a hand up.

          1. Keith Avatar

            If your concerend about carbon dioxide, tranportation is a small percentage of anthropogenic sources. Im more concerend about cost of energy. If a technology can lower the total cost of renewable energy ondemand, then that is great. Im not advocating for any paticular tech. Just recognize that some solutions wont work for every location, and it might be better to reserve lithium for transportation and if possible use a cheper tech for grid storage.

    2. Mike Shurtleff Avatar
      Mike Shurtleff

      Depends on cost. No cost numbers given.
      Turn-around efficiency is just part of cost. Wind on the USA Great Plains is now 3c/kWh if you ignore the PTC. If your storage has a 75% turn-around efficiency, you lose 25% of your energy by the time it comes back out.
      3c/kWh = 3c/1000 Wh going in
      3c/750 Wh = 4c/1000 Wh = 4c/kWh coming out
      Then you also need to account for the cost of your store amortized over the lifetime kWhours used. Lithium ion batteries will get down to at least $100/kWh over 5,000 cycles, so: 10,000c/kWh / 5,000 = 2c/kWh cost of storage (ignoring turn around efficiency, which is usually in the high 90% range for lithium ion).
      Let’s say this thermal storage can come in at 1c/kWh cost of storage (because materials are very cheap and cycle-life is many thousands). That would mean cost of storing 3c/kWh Wind would now be 3c + 1c (efficiency) + 1c (battery structure) = (3c + 2c)/kWh = 5c/kWh total with 2c/kWh of that being your total storage cost.
      Thing to notice is in-efficient storage adds a lot of cost if the electricity is expensive to begin with, but adds much less cost if electricity is low-cost to begin with.
      Alphabet is not being stupid. This could turn out to be a very cost effective way to store electricity. Donald Sadoway is being a very fair and unbiased observer. Cool guy.

      One thing not being mentioned here is water. Does this Alphabet thermal battery use water and steam generation to extract electricity back out. I’m guessing this is a closed cycle setup. Water use by thermal plants is already becoming limiting in some areas. Water availability is actually a problem. Energy is no longer a big problem, thanks to progress in Wind, Solar, and Storage.

      Another possible path up the mountain?! Great!!!

      1. Andy Saunders Avatar
        Andy Saunders

        Yeah but no but yeah but no but…

        You’re underestimating the inefficiency. And also you shouldn’t just compare costs, but also alternatives. Let’s say there’s a pumped-hydro alternative, which have typical round-trip energy losses of say 85% (there are plenty with better than that, and batteries were well over 90%). So assuming your 3c/kwh wind power input, the cost of 1kwh of output power is 3/0.85 = 3.53c.

        Assuming the molten salt is at say 1000F (pretty high – likely would increase your capital cost significantly and cause LCOE to rise) then you get 70% carnot efficiency, which means a likely actual efficiency of more like 65% or less. Which gives a running cost of 3/0.65 = 4.62c, or 30% greater than pumped storage.

        1. Mike Shurtleff Avatar
          Mike Shurtleff

          I’m just saying this is within the realm of realistic alternatives, that’s all. I’m not particularly enamored of thermal storage. I am not saying thermal is better.

          I’ve compared alternatives and am well aware of low-cost of hydro and high efficiency of lithium-ion batteries. These are already being used and thermal must be able to compete with them. Yes, comparison is needed.

          “So assuming your 3c/kwh wind power input, the cost of 1kwh of output power is 3/0.85 = 3.53c.”
          No, you’re missing the cost of your storage system. I’m guessing only a few cents for pumped hydro. Still that makes it similar to thermal, EXCEPT pumped hydro can be used for seasonal storage, longer term storage than thermal.

          “…which means a likely actual efficiency of more like 65% or less.”
          Very reasonable.

          “…30% greater than pumped storage.”
          Yes, likely a little more than pumped hydro storage when you’ve properly accounted for storage system cost, as well. Still cost difference is not that great, especially when you consider some areas do not have geography for pumped hydro. Not an option there.

          I am only pointing out it is another reasonable path up the mountain and may even be cost competitive in some areas …or not. We’ll see.

  2. Sid Abma Avatar

    Coal can make a comeback with the technology of Carbon Capture Utilization. This technology transforms over 90% of the CO2 in combusted coal exhaust into useful-saleable products for less than $20/tonne. It will create a LOT of full time jobs in a number of sectors.
    Waste is not a waste if it has a purpose and Sidel Global has given a purpose to this exhaust. There is many more particles in the exhaust that can be recovered and utilized. Even the coal ash has a number of uses.
    Coal can be combusted as clean as natural gas.

    1. Ian Avatar

      Most research into CC has been abandoned everywhere because they found it a high cost – low feasibility dead end.
      Solar and wind are far more cost effective ways of generating electricity….with or without storage.

    2. Ren Stimpy Avatar
      Ren Stimpy

      What products would it produce, at what cost each, and exactly how toxic would those products be? How could it compete with long-established markets for those products? Please let us know all the devil’s details on how coal can “make a comeback” and how more of coal’s “particles in the exhaust” can be recovered and utilized and be competitive in long-established markets. We’re waiting with bated breath for a fantastic story.

      1. Mike Shurtleff Avatar
        Mike Shurtleff

        Coal is simply no longer economically competitive, even without considering external costs. All the crap Sid is talking about is uneconomic add on bs. It still will not compete in cost. DOA

    3. Miles Harding Avatar
      Miles Harding

      Shame on you for believing the crap from this company.

      The story is in what they don’t say!. It always comes down to a matter of scale and proportion. A comercially useful coal fired power staton produces a vast amount of CO2 and plants are not equipped to deal with it in high concentration, so the scale of emissions vastly exceeds the greenhouse operation’s capacity to absorb it. The heat may be more useful, but this is hardly a greenhouse friendly option.

      If you want to see how build a large scale greenhouse, you would be far better advised to look to Sundrop farms, who have an excellent operation that doesn’t require the output of a coal power station. The atmosphere’s 400ppm is sufficient CO2 to grow a lot of tomatoes.

    4. Mike Shurtleff Avatar
      Mike Shurtleff

      “Coal can make a comeback with the technology of Carbon Capture Utilization.”
      No, it cannot. Wind, Solar, and NG are all lower cost than new coal. So called “clean coal” with Carbon Capture is even more expensive. Ian is right, CC efforts are being abandoned.

      “Waste is not a waste if it has a purpose…”
      Not true in coal’s case because it’s still not economically competitive if you do all that.

      “Coal can be combusted as clean as natural gas.”
      …or we could just use NG at lower cost.

    5. Barri Mundee Avatar
      Barri Mundee

      You seem to be flogging a very dead horse Sid. Please feel free to correct me but I understand that CCS requires about a third of the coal plant’s output and that will not make the energy produced competitive. The energy industry is not allocating much investment funds into CCS either.

      1. Sid Abma Avatar

        Hi Barri
        We are doing CCU not CCS. Our CCU System requires no heat energy from the power plant and only a small amount of electricity. Our process happens in an atmospheric reactor. We use an amine that is produced from an agriculturally grown plant and an earth based product.
        CCS costs $70 tonne to remove the CO2 and as you stated they require 30% of the power plants created steam to “strip” the CO2 out so that it can then be compressed and pumped through a pipeline and then pumped again into the earth, where it has to be monitored forever to ensure that it will not leak out.
        Our System cost millions to install not billions.

  3. Ian Avatar

    Why doesn’t Alphabet spend its money on building a lithium battery factory to get the manufacturing going in a very big way. Germany is building its own ‘gigafactory’ but this will only be complete in 2028. This really is not good enough. We need two hundred gigafactories to wean off oil. We need big companies and governments to shoulder this moonshot. We have one beautiful earth and F all time to save her. A inventory of gigafactories required may be a start. Here are the calcs: 1 gigafactory = 500 000 EV cars. Australia1 million new cars registered a year = 2 gigafactories, USA 17.8 million new cars 40 gigafactories , China 20 million new cars 40 gigafactories, europe 15 million new cars 30 gigafactories. South America 4 million new cars 8 gigafactories. If the world builds 20 gigafactories a year the job will be complete in 10 years. Revenue in oil is Stellar and revenue in its replacement will be just as Stellar.

  4. Brunel Avatar

    Google should build UHVDC transmission lines from Arizona to Canada. AC transmission is very lossy – why lose all those electrons?

Get up to 3 quotes from pre-vetted solar (and battery) installers.