A molten salt storage solution using sodium hydroxide
sifted.eu
sifted.eu
There are lots of cheap ways of storing heat... The capacity cost of thermal storage has not been the bottleneck for commercialization, but rather the round trip efficiency. This seems academically interesting, but I doubt it will be much more than that.
To a first order approximation, the cost of power from a storage system is going to be $/kWh_source_power/efficiency+ammortized cost of capital. No matter how cheap the second term is (and it can't be that cheap unless someone invents a 10x cheaper turbine), the first term tends to make storage uneconomical unless your RTE is above ~80%. This will get ~60% at best.
(of course, I could always be wrong)
Arguably batteries are ideal for the problem. However thermal storage systems like this one have good scaling to storage side of things: insulation is cheap, adding tanks is cheap. The basic turbine cost can supply wallplate stated power, the tankage gives duration and you can add as many tanks as you have room for.
Alongside simply supplying the energy, batteries are great for maintenance of supply frequency but I don't understand how they do reactive power. Turbine based systems do reactive power really well because of the rotational torque (I think) so represent a distinct role in electricity supply stability. (Its entirely possible batteries can do this too)
Finally, repurposing of steam turbine based generation sites means they have transmission systems, turbines on site and to hand: the capex component can be less.
We still need storage solutions like this for long term storage, though, as batteries are mainly used for load shifting and short term arbitrage right now, at 6 hours of discharge and less.
They can essentially do this instantly, i.e., substantially sub-wavelength of your line frequency (a PWM of 10 kHz isn't even high for an inverter, and 100 kHz is well within what's feasible for large systems operating at a couple hundred volts; 10 kHz would equate a light-speed delay of 30km, 100 kHz of just 3km, which gets into the territory of relativistic w.r.t. medium voltage rings in cities).
The issue with solar is not the storage from day to night, but the storage from summer to winter.
Hydro systems and pumped storage look useful in this but the extent of summer winter variance is very specific to latitude and much of the planet isn't as badly affected. Wear transmission losses, buy power from lower lattitudes
Batteries output DC. They need an inverter to be connected to the grid. The inverter needs to choose a phase angle at which to output current and voltage, through something that looks suspiciously like a boost converter. This doesn't have to be quite the same phase as the line, it can "lead" or "lag" in an attempt to push the line phase angle back to what it's supposed to be.
Has there been any effort to do this directly at power plants, so there isn't a round trip?
You have a heat source that generates the same heat 24/7 (e.g. nuclear reactor). You have solar panels that generate power only during the day. So you put the heat from the heat source into storage while solar is generating, then take it back out after the sun goes down.
You're not going from electricity to heat back to electricity, you're just not converting the original heat into electricity until later in the day.
But it doesn't help for gas turbines, coal, etc - it's even cheaper to just leave the gas/coal unburnt till needed.
And most renewables don't make heat to make steam to drive a turbine.
On paper to a layman, they look perfect for at least some applications. Very cheap and easy to build the "stacks", almost completely nontoxic/safe, and relatively easy to scale (I think they don't scale indefinitely with liquid tank size...that the plate surface area also matters?)
For flow batteries, the plate area controls the charge/discharge rate and the tank size controls the capacity. In theory you can scale the capacity as far as you can build tanks; I don't know whether there are practical considerations of "self-discharge" or electrolyte degradation.
Please do your homework before you speak.
For long duration storage, capital cost is much more important than round trip efficiency.
[0]Rough #. Carnot efficiency would define your max theoretical for a heat-engine process.
Efficiencies above 50% are claimed by some dual-cycle plants (gas turbines with steam generation), and with cogeneration utilising waste heat, higher yet, but the electrical generation component remains in the 40--50% range.
https://www.powermag.com/another-world-record-for-combined-c...
I'll note it's a manufacturer claim (e.g., "value never to be exceeded" --- most optimal possibly conditions likely).
What's the significance of LHV in this context?
Otherwise, what's a typical percentage difference between LHV and HHV efficiencies?
https://en.wikipedia.org/wiki/Heat_of_combustion
The difference for natural gas is about 10%.
For example, I can use 10 watts of electricity to remove 10 watts of heat from a cold place and add 20 watts of heat to a hot place.
Later, I can apply the same in reverse. I can move 20 watts of heat from the same hot place, heating the cold place by 10 watts, while generating 10 watts of electricity.
The use of the phrase "efficiency" while discussing ideal heat pumps is misleading - no energy is ever wasted or lost, the law merely limits the ratio of electrical Vs heat energy you get in/out.
The process is not thermodynamically reversible in the sense that there's a net energy expenditure either way. No free lunches.
What a heat pump can do is to move a greater amount of energy than it uses to move it. Measurements of this include COP (coefficient of performance), EER (energy efficiency ratio), and SEER or ESEER ((European) seasonal energy ratio).
The COP is a direct measure of energy moved divided by energy input, and ranges from about 2--4, with typical ground-loop heat pumps achieving scores around 3--3.5. That is they move three times the heat energy that they run under. It's as if a furnace output three times more heat energy than fuel input.
In your example, we'd first want to correct power (watts) to energy (watt-hours or joules). But 10 watt-hours of electricity would move about 30 watt-hours worth of heat, for a typical heat pump. If you're heating, you'd dump the additional 10 watt-hours into the heated space, if you were cooling, you'd want the heat pump's own heat to be directed to the external environment.
Discussion of heat gained/wasted with heat pumps is ... complicated. Note that effectiveness in moving heat decreases as the differential being moved against increases. That is, if you're trying to cool a space in an environment that's already warm, you're pumping heat "uphill". Similarly, if you're trying to warm a space from a cold environment, there's not much external heat to extract.
Ground-loop heat pumps benefit by the fact that ground temperatures tend to be more moderate than outdoor ambient air temperatures, so the temperature gradients are more favourable and predictable.
That's a very large amount of bricks and a potentially dangerously high temperature but still...
Pottery kiln manufacturers might be able to design this? Kilns go to higher temp than this and are used indoors.
If talking about individual houses, not condos, most economic solution is a two-stage water heating powered by a wood pellet or gas burner, where the second stage has a 3-5 ton water tank as a heat storage, so that the burner doesn't need to run continiously. This is a proven, simple, maintainable and safe solution.
We're talking ~50-150kW thermal power here. Solar can not reach that. Several cubic meters of almost-boiling water is hazardous enough.
Keeping a highly corrosive liquid at 700C in your own home.. no, thanks.
But there’s a much easier, more economical way to use solar power for heating in cold climates: heat pumps! PV panels give you electricity and then you get 2-3X the power for heating. There are economies of scale in the supply chain, low CapEx, and not a lot of plumbing.
They pump heat into the ground in the summer for air conditioning and pump it back out in the winter for heating.
You don't need to be "much", you need to ideally match the TCO of other fuels (or come close, if you care more about reducing fossil fuel use and CO2, which is arguably more important than TCO. People obsess about heating costs but then run out and buy $60,000 luxury cars to do an hour+ commute each day in.)
Our 6.6kW array can provide roughly 1/3 the electricity we need to heat all of our 1875 adobe home, which is poorly insulated at best. If this was closer to passivhaus standards, I imagine it could get close to 100%.
Also hot firebricks was my proposed solution. Water has comparatively low energy density and I wouldn't want the corrosive liquid either.
I understand that there isn't a ton of sun in winter months but maybe you could over provision your PV, store summer or fall solar energy and top up with whatever you can get from the sun in the winter?
Burners scale badly to lower power. Also, automatic pellet feeders are prone to breaking down, which you absolutely do not want to happen when it's -15C on the outside.
Thus a thermal buffer is needed.
> Also hot firebricks was my proposed solution. Water has comparatively low energy density
Water actually has about four times more energy density than bricks.
> I understand that there isn't a ton of sun in winter months but maybe you could over provision your PV
Prohibitevily expensive in both money and area needed
> store summer or fall solar energy
Impossible. Where and how would you store enough?
Say you’re living up north in Norway. Plenty of sun in summer, very little of it in winter plus guaranteed heat and electricity demand in winter.
Is there someplace I could read up on this? I could see using and citing it later.
Figuring out the cost per kWh of battery storage has been a pain in my neck. Mostly people just say the capital cost.
Amortized capital cost would be a function of upfront cost, lifetime (years), cycles (and per cycle efficiency over time), capacity factor (e.g. average drawdown of the batteries per cycle), and discount rate.
If one has a software background, it might be easier to just to simulate 10 years of cycles to figure out how many kWhs come out of the battery bank per year. Adjust by a discount factor (cycles today pay more in real dollars than cycles in 10 years), and divide the upfront cost by that number.
NaOH, in large quantities, is an unforgiving material. As I've read my way into carbon-capture technology, I was saddened to find it there, too. HF also comes to mind in this direction (but is in another league). There's a correlation between those properties that make them useful and those that make them dangerous.
The most powerful counterexample to this notion that comes to mind, though, is water. What a spectacular chemical, one that is so useful we have built ourselves from it, yet we can also swim in it for hours without concern for any adverse effect beyond temporarily-wrinkly skin. (While it's less-relevant for thermal solar, it's darn good at heat-capacity, too! :) )
It doesn't have any enduring toxicity. It won't get into your bones or your genetics. It's not bioaccumulative.
It’s dangerous because you’re also partially made of significant amounts of fats (and other things), which gets very very painful and can make it somewhat difficult to continue living when they get turned to soap while still part of you.
In the production of soap, it is used to break down the fats used rather than being part of the soap.
It involves the addition of an unnamed chemical compound functioning as a reducing anode straight into the fuel, which is a fairly awesome thing I wasn't aware was possible.
Yes, that's what it looks like: https://www.freepatentsonline.com/y2020/0105424.html
It’s not too surprising that a particular implementation that has various benefits compared to the existing state of the art would be patentable.
That's actually what the company is researching - this is a side-track. Their patent specifically calls out reactors...
That's my understanding of the problem, anyway.
Solar thermal plants can be used to generate energy, but they're not great at storing it for dispatch at later times. Even the link you provided has thermal storage as a component of the system-- you need to figure out how to dispatch electricity at night.
What's proposed is a cheaper storage solution, and they state it can still provide power after 10 hours.
> Even the link you provided has thermal storage as a component of the system-- you need to figure out how to dispatch electricity at night.
This is referring to the thermal storage of the molten salt tower.
What I'm getting at is why is solar PV -> electricity -> thermal storage preferable to solar mirrors -> thermal storage. Is solar PV less expensive than mirrors?
NaOH doesn't boil until over 1300 C. The temperature range from melting to boiling is over 1000 C.
"The liquid metal battery is comprised of a liquid calcium alloy anode, a molten salt electrolyte and a cathode comprised of solid particles of antimony"
molten salt loses approx. 50% of it's energy after 14 days, while hexametaphosphate for example, when kept as salt, can be stored probably for decades.
Hexametaphosphate can be produced from cheap monophosphate salt by heating it in solution to 700c and can be kept in room temperature until it is utilized. The energy density of hexametaphosphate is around ~ 80kWh , which higher or the same as most molten salt heat storages available.
Disclaimer: My company (Enzymit) develops enzymes that use polyphosphates, rather than ATP as an energy source to catalyze many types of reactions.
Are there a lot of regions where neither solar nor wind is viable but (their new version of) nuclear is?
Are they using rare-earth based catalysts to control some chemical reaction? It's corrosive so will always break down parts, so have they extended the life by 10x or 1,000,000x ? Storing heat in this medium leads to thermal losses I'm not seeing a mock-up of how it's proposed that this is minimised. Surely trying to store high-energy corrosive materials at high-temp is dangerous even at this modular scale?
Naively this sounds like their solution to "saving the world" is "boiling acid" which is at least novel...
... blah blah blah blah blah. UNTIL NOW.
Okay, with that off my chest, this technology seems on the surface pretty cool and I certainly hope it works out.
Well, I just spent an hour bringing a pound of salt to a nice boil. The I tossed in my phone, which was at 10% battery. It did not recharge.