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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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...
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.
PS: By abandoned the worldwide concentrating solar power installed over the last 20 years is ~1/2 the amount of PV added every month.
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.
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.
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.
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.
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.
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.
I think it's going to be hard to pick winners, even if you do some of the math.
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.
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.
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.
"Electric heaters are 100% efficient" should really be "Electric heaters are only 33% as good as this other way of doing it".
It might be possible if they where starting with heat, but feeding this from wind and solar just seems unlikely.