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Alphabet spinoff Malta raises $26M for technology to store power in molten salt (bloomberg.com)
244 points by lawrenceyan on Dec 20, 2018 | hide | past | favorite | 130 comments

Similar technology already in production in the UK: https://www.sunamp.com

They make a molten salt heat battery for homes and businesses. You store excess heat or electricity in the battery, and use it for central heating and hot water. Since you’re not trying to convert it back to electricity it’s very efficient. It basically replaces a large expensive water cylinder with a smallish box.

PS: I have no connection with or investment in Sunamp, I just think it’s a terrific idea. I am a potential customer, though!

This is not really the same. Malta seems to use a heat pump to produce reservoirs of both hot and cold material. This allows to produce electricity via a carnot process with very high efficiency (theoretically 100% because while the carnot process that produces electricity has an efficiency <1, the heat pump can have a carnot efficiency of >1). In practice they might get to 70% efficiency or so.

Sunamp.com seems to be just ohmic heating for thermal usage of excess electricity.

Are you sure sunamp is molten salt? To me, molten salt is to store energy at a very high temperature in insulated containers.

I thought sunamp is some kind of room temperature phase change material that does not require heavy insulation.

Was going to mention Sunamp.

It does use a PCM, and that is described as a salt so maybe it's where the confusion comes from.

It also has far better insulation than equivalent devices (hot water cylinders). Typically VIPs, although I've read a few reports about the casing being compromised recently and that wouldn't play nicely with the panel.

Yes, I glommed onto the use of “salt” in both cases and figured they were similar.

There are other alternative technologies to store energy as heat, in particular molten silicon:

- https://reneweconomy.com.au/mit-team-gains-ground-on-molten-...

- https://1414degrees.com.au/ (which looks like a competitor for malta)

I’m not at all sure, you’re almost certainly right.

(Not knowing much about the chemistry, I’m naively conflating the two)

Edit to add: Sunamp has non-zero heat loss, so it must be stored hot rather than room temperature, but it might not be very hot.

Sunamp is missing the “cold portion” of the system that Malta has set up, drastically decreasing energy efficiency by not being able to maximize the advantage of heat differentials in the Carnot process.

Most of the Concentrated Solar Power plants uses molten salt to store energy. First was installed in 1995 (Solar ttwo) in Spain. https://en.wikipedia.org/wiki/The_Solar_Project#Solar_Two

Torresol and other spanish companies have some experience with it.


Related: https://en.wikipedia.org/wiki/List_of_solar_thermal_power_st...

The neat little graph showing the rise in global yearly investments up to 2040 is amusing. Nassim Taleb has made me very wary of these things.

what's even the calculation behind a projection like that, it even has a little spike in 2035!

Well 2035 was the year they discovered the catalyst that made the reaction hold for months instead of hours. It took years to commercialize though.

Haha what reference is this? I have such an odd feeling I’ve heard this in dystopian sci fi

Hah I made it up! I do a bit of sci if writing though.


Take it with a grain of salt.

but... molten salt has no grains

Reading the article beyond the neat little graph tells you of California's plans. Governments and companies make long term investments in their own structure over multiple years. This is also the basis of the bond market.

The graph is projecting global yearly investments not just California. And even if it was just California I would be doubtful of a projection 20 years into the future.

I'm guessing it's because the scheduled restrictions on sales and use of ICE vehicles will really kick in around that time. So there will be a corresponding higher demand on the electric grid caused by a growing fleet of electric vehicles.

But obviously it's somewhat speculative.

Don’t phaseout dates set in the future create a spike in demand near the deadline?

Either people will be bored of ICEs for other reasons long before and make this a non event. Or, everyone will try to buy a new ICE in the year or two before they stop selling them. Automakers will use this as a justification for trying to move the deadline out. If that happens then the spike in electric drive will come at the next tradein time, not the deadline.

somewhat? it's _completely_ speculative!

The rather extreme losses associated with electricity > heat > heat engine > electricity seem like an absolute deal killer. Assuming they are at an extreme 50% round trip efficiency you need to be extremely cheap to have a hope of breaking even. Worse heat has fairly low energy density and cools over time so they can’t really scale the up or down that much.

It might be possible if they where starting with heat, but feeding this from wind and solar just seems unlikely.

Think of it like this:

You produce energy at an amortized cost of $X /MW. You store energy efficiently (lithium batteries) at an amortized cost of $Y /MW back into the grid. You store energy inefficiently (Malta?) at an amortized cost of $Z /MW back into the grid.

If Z<< Y, then simply ramp up your input production and you are likely in the money. Also, I'm not sure what you mean by "Worse heat has fairly low energy density and cools over time"... energy density is not relevant at all when you have practically unlimited space to store power (GIANT) fields next to your solar/wind farms.

Solar farms are ~0.8 MW / acre that adds up fast. Many current nuclear powerplants are similar energy density when you consider all the space inside the fencing.

Energy density is more a problem of materials. If you start talking GW hours it’s ~1GW from a ~38 ft tall and 48 meter diameter tank, even at $1,000 per ton it adds up. On top of that you need steam turbines etc.

From the description, it sounds like a giant Peltier device, not a steam turbine (otherwise why would they care about having a cold tank?). Solar farms also have a ton of space in between turbines so I’m not sure that metric is relevant. Additionally, since this device uses very safe materials (salt and coolant), there’s no reason you couldn’t dig a really big hole and shove the device inside...it would also provide some nice natural thermal insulation. When it comes to storing energy far from urban areas, cost is a much higher priority than energy density.

It uses gas compression through staged compressors to make the hot side, and gas expansion through staged expanders for the cold side, which makes a loop.

Think of it like a scaled up, reversible refrigerator.

I'd like to know if they also have a 'medium temp' tank, since if they do, they can keep the temperatures of the hot and cold tanks constant, and just change the amount of molten salt in them. That in turn means the compressors can be fixed compression ratios, which will dramatically increase efficiency.

To follow up here, having read the paper, they have two 'medium temperature' tanks (for the hot and cold side materials, which are different). The turbines do indeed work at constant input and output temperature, and at constant flow velocity and therefore wattage.

The paper suggests changing the pressure of the working fluid to adjust load, but I suspect it is hard to design a turbine to be efficient at a wide range of working pressures, so instead they'll end up with many parallel turbines, and just switch some off to get less energy produced.

I think it not so bad because a system like this isn't really competing with primary producers (solar/wind), it's competing with peaking sources fueled by nat gas/oil/hydro/batteries. All of which have a higher cost per MWH. I think too you can do the equivalent of cogen by using the waste heat from the thermal cycle for commercial and industrial heating.

My take is thermal storage is going to become really important once we start taking coal and nat gas plants off line causing the daily power price curve to invert. Power goes from cheap at night, expensive during the afternoon to cheap in the morning and expensive in the early evening. Once that happens thermal storage becomes balance sheet economic.

Germany and California have both experienced negative electricity prices. The economics of this kind of battery could very well work with a low efficiency if it's cheap to build.

No, not really- negative prices are very short spikes. They aren't driven by fundamental oversupply, they're caused by fossil plants that are unable to ramp down their power output quickly enough to keep the grid in spec. The amount of storage required is very small, but the required power and speed are high.

The whole price advantage of thermal storage is in the amount of stored power. It's very cheap to build insulated tanks. It's expensive to build large turbines, pumps and heaters, the things you need for fast response. Thermal batteries are already kind of iffy compared to batteries (or rather, where batteries will be in 5+ years), so if you skew that price by several factors by going for high power, chemical batteries are definitely cheaper.

In a fully renewable grid, you'd need longer term storage like thermal batteries. 3 days is the most common figure. The electricity price would never go negative, even without batteries- renewables just turn off too quickly. You can just unplug solar panels if they're generating too much power.

Negative electricity prices are also driven by wind subsidies. Wind producers get 2.3 cents per kilowatt hour in tax credits. This means they make money even when the price of electricity is negative—-up to 2.3 cents a kilowatt hour.

Negative prices pretty much never happen in countries without subsidies.

It also isn't true that turning off any power station can't be done instantly. The station has to be able to cope with all its transmission lines suddenly being cut, which is a forced instant turnoff. It's more that the startup time is large, and they think that by losing money now, they'll still be running later when the power price is positive again.

3 days is silly. Extra capacity is very cheap, currently we have gas turbines filling this role but extra wind and solar never drop to zero and costs less than needing 5x as much storage.

Now as storage prices drop the equation changes, but not very quickly as their ineffecency means you still need extra capacity and that capacity reduces the need for storage.

Not just Germany and California. The central plains regions of Kansas/Oklahoma and parts of Texas are really high wind producers. We have negative prices from time to time and not just because of congestion. The marginal cost of energy is simply sometimes negative. This has an impact on all nodal prices in the market.

A lot of the fundamentals have actually already been researched and at least in academia, the various ideas have all been out there for quite a few decades now.

The main impetus has been in getting the funding to kickstart everything, and backing from Alphabet with strong financial support plus an intellectual talent from subsidiaries (Google, X, etc.) to pool from is the killer combination here in my opinion.

Have any links to share?


This is the paper the Malta team uses in their blog (https://blog.x.company/introducing-malta-81bceb559061) on explaining how the system works at large. It’s a pretty good summary.

And in case anyone is wondering, yes, it's the same Bob Laughlin that won the 1998 Nobel prize in physics for the theory behind the fractional quantum Hall effect.

I'm not an engineer, and the article doesn't state it, but there are probably benefits to the technology. For one thing I imagine the heat-content and thus energy storage density must be rather high, while the storage material is probably quite cheap. Water would have (a lot) lesser density, and most electrical batteries are way more expensive.

Additionally the molten salt may be good at insulating itself or at least easy to insulate against heat losses cheaply.

And maybe it can be fueled by energy forms other than electricity.

The main paper behind this actually dismisses insulation losses as minimal at scale.

It suggests burying the tanks, and using earth as insulation.

In a different section, it suggests putting hot and cold stuff in the same tank, which sounds incompatible though...

Maybe not both at the same time?

If energy is free or nearly free and it’s being wasted currently, then how much does the efficiency really matter?

First if you can’t charge every day then your capital costs are effectively much higher.

It’s only ‘free’ before you have a battery in place that can use it. With this buying at 3c/kWh and selling at 6c/kWh is losing money. If anything else can profit and scale by buying at 3.01c/kWh and selling at 6c/kWh then that’s going to win.

It may encourage energy to be generated unnecessarily, producing unnecessary CO2.

If there are other systems that are more efficient, then it probably does matter.

Solar can generate heat directly, using Concentrated Solar Power plants: https://en.wikipedia.org/wiki/Concentrated_solar_power

Those are horrifically expensive relative to PV and largely abandoned tech. A core issue is you can’t concentrate sunlight on a cloudy day making them even less dependable than PV. The Ivanpah Solar Power Facility even reverts to natural gas, this is while costing 4x what PV does.

PS: By abandoned the worldwide concentrating solar power installed over the last 20 years is ~1/2 the amount of PV added every month.

Spot on. I made a whole bunch of Solar Concentrator models and did a number of calculations on them. The work was probably flawed for very precise budgeting but order of magnitude should have been correct and even then it would not work, not even close.

The best I found was a moveable array of mirrors and stationary collectors but this too is fragile and a maintenance headache. Leaks of working fluid and mechanical problems would ruin the economics even if you could get the basics to work out in your favor.

There are plenty of CSP projects underway. See https://solarpaces.nrel.gov/by-status.

The list is ~25 locations even including 14MW power plants. Like: https://solarpaces.nrel.gov/dadri-iscc-plant but mostly it’s 50Mw. And that’s not what’s coming online this month or something they can take years to build.

By comparison 95,000+ MW of PV is installed every year. And PV has a much higher capacity factor so actual MW per year is even further in PV’s favor.

It seems to still be a viable solution in countries with a high percentage of sunny days throughout the year.


Compare the economics of loss here, to the economics of not storing the electricity, and so wasting it in other ways. Yes, there is a round-trip loss through the system. No, this is not always in economics, an insurmountable problem.

For instance, "the hump" which was the US air shipment of materiel to China, in order to bomb Japanese forces was obviously a major loss maker in energy terms. Some huge multiplier of fuel spent to send fuel, worse than 5:1. Was it "worth" it? Yes! the war effort demanded the loss be borne.

So with this energy storage. Energy in the form of electricity is fleeting. If you don't convert it to a persisting potential energy form, it isn't there when you want it. Loss in the system is well understood by the engineers, financiers, planners.

Pumped Hydro has losses. Compressed Air has losses. Conversion to Ammonia or Hydrogen has losses. Winching concrete uphill in trains has losses.

Of all of these, thermal storage of energy in molten salt is perhaps the best understood. Its not unusual.

TL;DR short statements like "buuut the losses" are silly. This is not an absolute deal killer, it's an understood problem.

>Energy in the form of electricity is fleeting. If you don't convert it to a persisting potential energy form, it isn't there when you want it. Loss in the system is well understood by the engineers, financiers, planners.

This is true, but it only makes sense if you are talking about generation sources that can’t be controlled (e.g. solar, wind). It’s a complete waste if you’re just storing energy from something like natural gas plants, coal, etc. In the latter cases you are better off deferring generation of electricity you don’t need.

The cost moment to stop and start spinning metal is huge. These devices can't bid at 5min intervals let alone 30sec. They are precisely the ones which benefit from a method to store electricity, because making steam not exist means then spending time making it exist again, to spin the turbine. They bid into 30 minute supply price moments and then try to run at the highest contract bid price for as long as possible.

Gas turbines can start quickly but its said to be very expensive to do the startup. Its better to run them idle than have to cold start.

If the goal is to remove steam energy sources from coal and gas and oil, I get this. But if you have them, and you have efficiency from constant operating load, then rather than incurr start and stop cost, its better to store, even with wastage.

Back when I was a trainspotter, I used to hang at loco sheds and I asked a driver once why so many diesel locos ran idle doing nothing. he said that starting from cold was a pain. They costed it, and it worked out ok to run idle at their fuel cost, rather than have to restart. I think this is a similar moment.

So basically, I think you may have inverted the thing a bit. You can ignore free-energy inputs like wind and solar, but its wasteful so if you can't shed load in coal, its worth storing energy from solar and wind, meantime. If you have total excess energy from all sources, its worth storing it from anything which it is costly to stop-start, and you might as well store everything you can, to the capacity of storage.

Because wind and solar cannot guarantee supply in specific situations, storage can turn them into reliable power (albiet at lower intensity than the wallplate, because the storage either runs down too soon, or can't deliver as much peak)

Thats what I am reading anyway. This all feels like a classic complex linear programming optimisation problem for wiser people in power engineering economics.

Thanks - funny how diesel locomotives stay iddling for hours, yet our diesel cars now turn off when stopped for just a few seconds - due to idiotic CO2 related testing and legislation. Result, a horrible experience of noise and lurching, often every few minutes in traffic, less responsive so less safe, more engine ware, all for zero fuel actually saved.

Start-Stop in cars does save a considerable amount, which is a fact that can easily be verified, so you pretty much disqualified yourself there with "for zero fuel actually saved"...

The additional wear is not on the engine itself but on the starter components and those are simply designed for the additional load so that they can deal with the starts and stops.

A "considerable amount", huh? Can you please verify it for us and put a number on it? How much is it over the lifetime of a typical family car?

Okay, but once there are competing possible uses of "extra" electricity, it's going to have a price, and if the price is high enough, then high energy losses will result in some of the alternatives being uneconomical.

I think it's going to be hard to pick winners, even if you do some of the math.

Okay, but once there are competing possible uses of "extra" electricity, it's going to have a price, and if the price is high enough, then high energy losses will result in some of the alternatives being uneconomical.

The idea would be (for me at least, I am not neutral in this) to marginalise the coal and oil and gas generation to make it the most expensive form.

If you live in Poland, or Victoria (Australia) you have unlimited brown coal, which burns sulphurously filthy bad smoke, its the worst possible energy source we have right now but its the cheapest. It has already been seen to displace high quality low-ash black coal, because thats worth money in China and India for export. So I get your message: cheap beats clean.

If you legislate for the cost of dirty cheap power, then storage losses are a lot more tenable, compared to the remediation cost. BTW economists actually do cost the deaths per gigawatt. Dirty Coal has a really high death rate both mining it, and burning it. Kids die of Asthma at far higher rates, in economies which burn coal for power. The economic costs of killing children, quite apart from the social costs, are huge. Actuarially speaking, you don't want to do this because you alienate future income from those kids grown up, earning money. Its a third-party damage problem which makes it easy for the brown coal generator to ignore, but when the kids of the coal miners and power station workers die, (and that happens) it gets a bit more direct.

Victoria had underground brown coal fires burning for YEARS.

>. The economic costs of killing children, quite apart from the social costs, are huge.

Citation needed. Considering the economic side only, most places I've seen this cited around $3 - $30 Million per person killed, and compared to many emissions reduction tech, killing people is cheap.

I don’t know what Malta specifically is doing. The project mentioned elsewhere in here[1] is actually a thermal plant design — it uses mirrors to build a solar furnace and the salt acts as a buffering stage before the heat gets transferred to a conventional steam turbine setup. This eliminates one of the conversion steps.

1. https://en.wikipedia.org/wiki/The_Solar_Project

Pneumatic energy storage and pumped water storage both have very low efficiency but also low cost, so there are plenty of techs in this space that are being explored.

The question is whether wind and solar can be made cheap-enough to be worth overbuilding them five times over to feed into inefficient energy storage, or if we should just stick to batteries or hydrogen.

Pumped storage has ~80% round-trip efficiency. It's as good as lithium batteries. The biggest limitation is that there's not much room for growth. Most good sites for pumped storage have already been built.

In the developed world, flooding cities to make hydro stations is very unpopular...

Generating heat from electricity is nearly 100% efficient, so the round trip is probably a lot higher than you think. Plus, we're dealt with some pretty competent engineers here. I'm pretty sure they ran through the napkin calculations more than once on the targets they need to hit.

An electric heater's efficiency is "100%", but there are known ways to get much more than 100 percent for typical use cases. For example, heating your house with a heat pump can easily be 300% efficient, since you are also cooling down the outdoors.

"Electric heaters are 100% efficient" should really be "Electric heaters are only 33% as good as this other way of doing it".

Just a question: why does a sub from Google need to raise money?

I would question the confidence if a super big company starts something and is like: uh you know. We collect money from someone else.

For these industry-disruptor things you need some degree of support from the industry you're disrupting (i.e. you need to sell to utility companies that have strong business relationships with the large generation technology providers in the space). In practice this means raising money from, or partnering with, the right people that can leverage industry connections.

It is easier to get the right investors and partners if you are not controlled by Alphabet, because investors and partners have more assurances of the governance leverage they get for their money/effort. If you are Sergey's pet project, you are very vulnerable to mood swings on his (or Google's) behalf.

For partnerships in an industry with powerful entrenched interests? An analogous example is the Amazon/Buffett/JP Morgan partnership in healthcare.

So just rich people being rich?

It makes a lot of sense -- it's possible that this ends up being a very viable, scaled business with low margins. If the margins are lower than Alphabet enjoys as a whole, and if there isn't an argument for synergies with existing Alphabet businesses, it could simultaneously be a very good opportunity but also not accretive for Alphabet share holders. Part of the restructuring of Alphabet/Google and the hiring of Ruth Porat was to be more disciplined about not doing everything possible with shareholder money. $24M here, $24M there, sooner or later you're talking about real money.

It’s a good way to verify that your moonshot project is viable, and not just a hobby of somebody who, some time ago, managed to convince management an idea is worth working on.

The money itself pretty much has no value.

The big thing is strategic partnership and support from industry. If you look at who’s invested into Malta from the companies they list in the article, everyone one of them is highly relevant to some part of the business model / supply chain of Malta, with each company generally being at the top of their respective industries.

Same question - $26M is a small amount for Alphabet.

$26M from Alphabet for a power storage company is not "smart money", it's just a pile of cash. See my other comment sibling to yours.

Oh lord, can't you pick less conflicting names? Why don't I just name my company Jeff Bezos LLC?

Google and their ilk picking these childish cutesy names ("Project Loon", "Project Fi", "Malta") is incredibly grating and needlessly detracts from their objectives. Do it once and maybe it's clever. Do it as a rule, and it's hard to take the work seriously. Not to mention, do any of these so-called "projects" outside of Google's core competencies do well once they meet with the real world?

Indeed, the tech world seems to be full of people totally oblivious to branding - anything that's short and snappy and sounds vaguely familiar is 'great', no matter the real world or rest of the world.

Actually Google seems to be one of the worst at choosing googlable names ('Alphabet').

I agree. Why do they have to pick a whole name of a country at the beginning?

As if "America Inc" or "Canada Inc" would be able to operate

What are you referring to?

It's got the same name as a whole country..

Yeah, I'm wondering. Isn't this trademark infringement? EDIT: Definitely trademarked: EU001566702

Trademarked in what industry? Trademarks are not universal, they are only in particular industries.

Blog post from the Malta team on their graduation from X with their molten salt battery grid energy storage play.


From the blog post:

> Malta’s solution is to store electricity as heat in high temperature molten salt and cold in a low temperature liquid for days, or even weeks, until it’s needed. The key insight behind Malta is that electricity can be stored as heat in high temperature molten salt and cold in a low temperature liquid for days, or even weeks, until it’s needed.

The key insight is an oft forgotten energy storage fundamental called ‘tautology’.

Not sure if you noticed, but the phrase "Key insight" links to a scientific paper:


Yes, and to be clear, I’m interested (enamoured, even) in heat, by my long-running interest in air-cooled engines (VW, BMW, Porsche), and am fascinated with what’s going on here. My citation above was really a cheap shot at bad copy.

How can energy be stored as cold? Cold is by definition the absence of energy.

Temperature differences are what drive heat engines, i.e. you need a hot and a cold(er) reservoir. A nice demonstration of this is a handheld Stirling engine, which you can power by placing ice at the bottom (since it’s colder than the surrounding environment).

Okay, but technically you're storing the energy in the environment, not in the cold reservoir. Maybe a distinction not worth making.

0 - you must play the game

1 - you can never win

2 - you can only break even on a very cold day << f.n.

3 - it never ever gets that cold


f.n. >> the maximum efficiency of the work that can be extracted from a heat cycle is dependent on the relative difference between the hot end and the cold end and absolute zero. The closer you can get the cold end to zero relative to the hot, the higher the efficiency. The energy of a heat engine comes from the potential. If everything is equally hot there is no potential energy just as much as if everything is equally cold. If there is a gradient, you can do work.

This is extremely exciting technology! Any energy science aficionado worth their salt knows that molten salt can have very high energy density.

The paper says that at around 600C, nearly all materials have the same energy density.

Molten salt was chosen because it is a liquid, cheap, safe, and stable.

The paper also considers using rocks, but they're tricky to pump...

Do you have to keep the salt molten?

I believe it melts when it gets hot.

Not sure if you need to keep it hot enough to stay molten...

By the way, this is not new tech! What excited me here is the prospect of bringing these batteries into large scale production. Imo, this is the kind of thing that could transform how we heat and cool homes and other buildings. But right now it's quite niche and hard to access.

Here's Wikipedia: https://en.m.wikipedia.org/wiki/Molten-salt_battery?wprov=sf...

You should take it with a grain of salt, tho.

How can you even distinguish one grain from another once the molten situation kicks in?

Does anyone have any information about what kind of heat pump they are using (e.g. multi-stage hydrocarbon, supercritical CO2, etc)? Making a heat pump which can handle a difference of 175+ C and a high side of 200+ C may be straightforward in theory, but it is a non-trivial engineering challenge. I am unaware of any commercial off-the-shelf device which can meet these specs. I'm guessing this is what they need based upon the description. I happen to be in the market for a heat pump like this for my own research, so I am highly interested if anyone has any information.

My memories of thermodynamics theory are old and full of gaps, but from what I remember both steps, if performed at "normal” temperatures, necessarily produce a waste of energy. The first step, i.e. using electricity to drive a heat pump, is efficient only if the temperature differential between the cold body and the hot one is small. On the other side, conversion of thermal energy into electricity is efficient only if the temperature differential is large. How does Malta overcome this problem?

Your memories are wrong...

An ideal heat pump is fully reversible with no energy loss.

Maybe, but I clearly remember that it is not possible to have a reversible process wich only transfers heat from a colder body to a warmer one. The third law also gives quantitative bounds to the reversibility of such processes.

Heat pumps with efficiency above 1 rely on heat transfer between external bodies (e.g. from a subterranean water source to the atmosphere forhome heating systems), but this does not seem to be the system described by Malta.

You are thinking of the carnot limit.

>It provides an upper limit on the efficiency that any classical thermodynamic engine can achieve during the conversion of heat into work

The word 'efficiency' here is misleading... If one reverses the process, converting work back into heat, you get back all the original energy in an ideal machine (and real machines, for example gas turbines, are within ~15% of ideal for the temperature & pressure change between input and output)

Thanks for the clarification. I still have issues understanding the intermediate stage, where the world is entirely and reversibly converted into a temperature differential. I might have to go back to drawing T-S diagrams.

> Now X designs projects with two primary goals: to become a standalone Alphabet division or spin out into an independent company.

The difference being that Alphabet retains 100% vs retaining X%? Presumably they're spinning out whenever the capital required would be much more than they want to put in, or the tech seems promising but perhaps not as profitable as they would like?

Maybe they want strategic investors who bring more than just capital.

I have been thinking of ways a "new nuclear" company could have a business plan that gives them an exit in case they run into regulatory or other roadblocks and molten salt handling was one of the ones that seemed most promising.

(Too bad there doesn't seem to be any non-nuclear market for Brayton cycle turbines.)

I'm pretty naive about this stuff, but wouldn't an easy solution for storing energy to be, just use energy to lift something very heavy into the air, and then extract energy when it's lowered?

That's an avenue that's also being pursued, but it's not obviously superior to other storage plans. You've got lots of moving parts under high load, you need enough structural support to ensure that the top-heavy structure is stable.

It also doesn't contain a huge amount of energy - 1 ton of liquid NaCl contains about 700MJ of usable energy, you'd have to lift 700 tons of material 100m to contain the same in gravitational potential.

That is one of the ideas being explored:


Dinorwig Power Station in the UK pumps water to store 9.1Gwh https://en.wikipedia.org/wiki/Dinorwig_Power_Station

Has anyone looked at waste heat recovery for these sorts of things? If you already have a heat engine on premises I could see industrial applications for energy efficiency.

On a related note - could someone please develop a mass-produced stirling engine for low-temp differential residential use??

I’ve dreamed of this too, as it would be very easy to deploy. However I think someone mentioned that low differential sterling systems just don’t have much power in them period. I’m not sure though.

Where are the molten salts coming from?

Typical mixtures use eg potassium nitrate, sodium nitrate, and calcium nitrate. Salts are one of the most produced substances on earth. For instance, potassium nitrate is in virtually every fertilizer. I couldn't find how much is used annually, but it's made from potash, and US reserves of that are ~270 million tons[1]. At 40 to 110 kWh/ton[2] that's a minimum of 10.8 billion kWh (10.8 TWh), or a full day of storage.

[1]: https://minerals.usgs.gov/minerals/pubs/commodity/potash/mcs...

[2]: https://www.solarthermalworld.org/content/molten-salt-storag...

This is interesting from a sustainability model. Both lower tech to manufacturer and I'd assume less damaging to the environment than a lithium mine.

This design also needs almost double the amount of hexane...

Not so environmentally friendly...

Neither are used up though, and probably won't devalue with time, so the financial cost of them is just interest payments, and the environmental cost is zero.

I believe they're sourced from John McAfee

loving all these armchair scientists thinking they've found "the" flaw in a company they read one article about

To be fair, for every 1000 claimed energy breakthroughs, 1 succeeds. Being skeptical of any claim before it scales in the market is somewhat rational.

Molten salt nuclear reactor technology documentary


I believe the molten salt technology used for thermal energy storage is not directly related to molten salt nuclear reactors:

https://en.wikipedia.org/wiki/Thermal_energy_storage#Molten_... (sodium nitrate, potassium nitrate and calcium nitrate)


Many years ago when you could visit Dounreay nuclear power station I remember leaning they used liquid sodium as the main coolant. It was used to transfer heat our of the reactor from what I recall.

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