Thermochemical energy storage: an interesting way to store heat
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- Опубликовано: 2 окт 2024
- In this video, we take a look at thermochemical energy storage (TCES), which makes use of reversible chemical processes to store heat for later use.
(AKIO TV) MMXXIV
/ actual_akiotv
IMPORTANT INFORMATION:
Turns out the heat capacity of air is actually 1000kJ/kg K, not 700. I was fooled by Google search which gave the wrong answer. That means the energy we stored was a bit over 8 Wh, which means the energy density was over 900MJ/m3 and the efficiency over 30%, so better than the video shows
The salt in my setup is never dried completely. Di- and mono hydrates of calcium chloride melt at 170+ C, which my setup cannot achieve.
Therefore the setup only dries to the dihydrate state of calcium chloride, meaning some water is still in there in the "dry" state, even if the drying setup is left to run for an infinite time.
I forgot to measure the volume directly. The 32mL was based on the density of CaCl2 hexahydrate (1.7g/mL). In reality, the volume would have been slightly greater due to the air gaps between the grains. I considered it fair to use this "smaller" value though, since likely I could have run the setup for longer without overhydration, and could have started with dryer salt, which would have increased the energy content, so this sort of compensates. Not a very scientific way of thinking of course, but realise this wasn't a scientific experiment, but a demo for a YT video, take the values I measured with a grain of salt and look at actual research for obtaining values :)
My camera had some issues which caused some glitches in the video. Your graphics card or monitor is not broken.
Thanks for watching!
Given that premise, it would have been better to just explain it using already available data and some slides. Trying to derive the data using terrible methodology became a distraction from the point you were trying to make. You also didn't bring up the efficiency of the process until around ⅔ of the way through the video despite it being a key factor in deciding how valuable a process is.
Some channels you might want to check out for different ways of presenting and/or demonstrating something like this are Practical Engineering, Undecided, AvE, Cody's Lab, Minute Physics, The Thought Emporium, and Nile Red. There are many others, but I think that's a decent variety of styles.
I think the styles of The Thought Emporium and Nile Red would most fit you, but the others touch on topics it seems you would be interested in and might provide some inspiration for how you would want to produce your content
Oh, also Applied Science
@@blackoak4978 First of all, I know most of these channels, they're great.
So although some things were off, I wouldn't call the method "terrible". The numbers are, as far as I can tell fairly accurate, and match up quite well with what research shows. The biggest problem is the wrong value for the heat capacity of air, but I only discovered that after the video was up. (and what a stupid mistake it was)
I felt in general the accuracy of the test doesn't change the conclusion of the video much. If anything, the errors here make TCES seem a bit worse than it is. If it had been 40% energy denser, or less dense, the general point would still be kind of the same: not quite dense enough to be revolutionary, but perhaps better than sensible or latent heat storage.
Of course I could have opted for a different way of doing this. For instance, I could have just used existing values, but IMO, that's a bit boring and gets the point across less well. Otherwise, I could have done the demo without measuring values, so that people could have seen it in action, but then used existing data for analysis. That is something I considered doing, and almost did, but I decided against it, because I think doing the measurements on camera adds extra value, because it allows people to think/learn about calculating heat energy in an air flow, etc. It also contained the (IMHO) important lesson not to just blindly trust a power meter (or any measuring equipment for that matter). Basically, although things didn't go perfectly, I think there's stuff in there people can learn from, which includes the mistakes.
Finally about the efficiency, first of all it's not quite as critical as it seems. Systems like this are generally charged from "leftovers" such as excess power generation, direct solar heat, or even industrial waste heat. Say your storage system can store 30%, then that means you can recover 30% (a significant part) of the energy that would otherwise not be used at all. 30% is low, but turning a solar panel completely off, or dissipating all heat through some cooling tower is clearly worse, and so even with a low efficiency it can be a significant improvement. This is the reason why I didn't discuss efficiency earlier in the video, because it's not as important as with other energy storage systems.
That doesn't take away the fact that efficiency is very important nonetheless. I tried to find information on this, but I could not find a practical test result for the charging efficiency of a salt hydrate system. If you happen to find it, please do send it to me because I'm very much interested in this. This is actually one of the other considerations I used when I decided to test this myself, I wanted an efficiency figure, which I could not find elsewhere. I figured, given my rather simple drying setup, I could at least obtain a worst-case efficiency figure, which is better than nothing. The number I got (25-30%) with a very basic setup, makes me optimistic about what would be possible given a bit more design effort, so I do want to try it again some time soon, with better thermal insulation.
If you place the heat storage inside the environment where the heat will be needed, leaking heat ceases to be much of a problem. ALso look up Zeolite... used in some dishwasher drying cycles already
I guess it depends when you're charging it. If the charging is done when heat is also needed for something then there is indeed no loss.
I knew about zeolites, but didn't realise some dishwashers use it haha. It appears they have an energy density disadvantage compared to salt hydrates, but they don't suffer from the same physical degradation which is nice.
@@AKIOTV , yes it's a different mechanism (zeolite vs cc) , some bosch dishwasher have the zeolite system. I may experiment with the CC too. I wonder how corrosive it is. For simple thermal storage inside my space I used a ceramics kiln filled with Basaltic rock... I liked the largish rocks because of the air spaces.. makes it easier to get hot air flow in and out. The Kiln , having a lid is nice. Very cheap high temp solution. If I were in the I.K I would just use some old night storage heaters... but we don't have them here in the USA , at least not cheap used ones. Thought about using low temperature water for heat storage, it takes up more volume and could freeze etc, all systems have pros and cons. The Kiln is very simple if one is safe about the very high temperatures. The nice thing about the Thermal (and electrical)chemical storage systems is they can store and be used way down the line...since they can be activated when needed....For daily (nightime release) the thermal kiln storage will save cycles and need for larger lithium batteries, much cheaper... for "edge cases" (many dark days in a row) Then I will go to my Lifepo4 and or a generator to charge batteries and recover the generator waste heat. Heat pumps as the normal heat source.
You can use a hygroscopic liquid that heats up when mixed with water.
This water can then be evaporated, for example, in a solar heater.
Of course, this method is completely unsuitable for use in vehicles, but for heating a house it is an almost ideal heat accumulator.
I suppose if you let it dry in ambient temperatures it would still store that heat. It would take longer but, it wouldn't use an external power to heat it to dry. Good project!
@@GTN3 You do need an increased temperature, at room temperature it will keep absorbing water until it dissolves in it. You leave this stuff in open air and the next day you'll have a puddle of brine.
Interesting as always, nicely simplified 👍👍
Nothing beats british accent...!!! That´s a baby Roger Moore right there...!!! great results too...!!!
haha
That's a really interesting way to store energy. Nicely explained as always!
I would need 20 MWh for heating. Let's be optimistic ( global warming ) and use 2MWh. I would need 10 m^3 of CaCl + water That is a lot. Now considering realistic scenario, I would need 100 m^3 of CaCl + 50 m^3 of water ( to use purified water ) + losses and non ideal conditions..... more like 200 m^3 space needed. That is a lot. I made a ist of possible material candidates. After like 20 different compounds, I realized the best choice is probably simple iron powder oxidation and reduction ( realistic space and price requirements )
@@jozsab1 The water doesn't need to be stored though, you can use vapor from the air, or a moisture pit if you have an extremely dry climate.
I'm not entirely familiar with iron oxide. Maybe interesting to look at for a video some day.
0:30 "Dear god..."
If you're thinking about performing a similar experiment with zeolite, then keep in mind that it will only heat up if it's completely dry. If you dry it in room temperature, and add water, the exothermic reaction will NOT happen.
@@barabolak I may try zeolite some time. Would be interesting to see the difference. I suspect the same setup would work, although I might add better insulation to the dryer.
Here's what chat GPT has to say about safety of this reaction:
When water is added to calcium chloride (CaCl₂), an exothermic reaction occurs, meaning it releases heat. This reaction itself does not produce toxic fumes. Calcium chloride dissolves in water by dissociating into calcium ions (Ca²⁺) and chloride ions (Cl⁻), and the release of heat is due to the hydration of these ions.
However, depending on the purity of the calcium chloride, there may be some minor concerns:
Impurities: Commercial calcium chloride can contain impurities that might release some gases or vapors. For example, if it contains magnesium chloride or other substances, they might interact with water differently.
Aerosols: The heat generated can cause rapid boiling of water, potentially creating steam or fine aerosol particles. While these aerosols are not inherently toxic, breathing them in could irritate your respiratory system, especially if they contain impurities.
To stay safe, it's best to perform the reaction in a well-ventilated area, and if you're working with large quantities or unknown purities, wearing a mask or ensuring proper ventilation is a good precaution.
I wonder if we can use it twice: to charge it you need heat. My smart solar mppt can get above 50 C when the sun shines, and then must be cooled to be no more than 40.
So actually the right storage would be something that reacts around 40 degrees, automatically regulating the solar charger.
And then at night hopefully you can put it in a hot water bottle for in bed. Of course, we need it to be bigger than this.
@@bloepje 50C is on the low side for calcium chloride, but a different salt might do the job.
In general, using waste heat to charge TCES systems is widely considered. For example you could also use waste heat from industrial plants etc. to dry salt at a large scale. Any form of waste heat is usable, so long as the temperature is high enough to (partially) dehydrate the salt that is used.
You list it as energy storage, but I think it makes even more sense as a generator itself. You can use the sun to dry it out directly at a much higher efficiency than a solar panel, and then also store it till needed for release. I think it really is both in one.
@@chris993361 You could charge something like this very well with solar heat. Industrial waste heat is another interesting option.
You have to consider it in terms of comparison. It's not simply about if it can do a job, but if it has characteristics that are better than other alternatives and if it is reasonable to use in scenarios where it provides the most benefit.
Yes, you can put it out in the sun, but you can also put a solar panel out in the sun and collect the same amount of energy. In this specific scenario the question then becomes, which of those two options provides the greatest return, or the efficiency of taking a set amount of solar energy, storing it in some medium, then converting the stored energy into useful energy, in this case heat.
@@blackoak4978 My point was that you would collect more of the sun's energy, not the same amount of energy as with a solar panel. I don't know what the efficiency of drying out the salt is with the Sun but it's got to be higher than the abysmal efficiency of a solar panel.
@@chris993361A solar heat collector is more efficient drying salt directly compared to using a PV panel and electric heating. But if yoh already have PV panels, and once in a while have to disable them when there's no demand, then electrically drying salt still makes sense, since it's better than turning the panels off entirely.
This more broadly applies to other heat storage too: heating a water heater with solar heat is more efficient than an electric water heater powered by PV, but if you already have PV panels, and at times no purpose for their energy, an electric water heater can be a good idea to install.
Your error bars are nearly bigger than your signal. You also didn't include the power to run the fan, but given your measurement accuracy it would be below the noise floor and is probably not a major factor anyway. You're also comparing apples to oranges. The lithium-ion batteries are measuring useful electrical energy, whereas you're just measuring energy in the form of heat which is much simpler. You have no way to convert it efficiently to electricity. It's useful only for heat storage, and for that there are just much better and simpler alternatives. Nobody would recommend using a lithium-ion battery as a heat storage device. Bizarre comparison.
@@human_shaped No one would use li-ion batteries to store heat, because they're much too expensive and there are far cheaper effective alternatives. That's pretty much also what I said in the video. Now of course, you can argue that's too obvious to even include them, but I decided to put them in there anyway, for the following reasons:
1) they are a useful benchmark for energy density since a lot of people (at least in my audience) are familiar with their size which helps visualise the kind of energy density we're talking about.
2) although arguably stupid for storing heat, li-ion batteries are pretty much the only available method of storing heat that doesn't lose energy over time. If you wanted to store heat for a long time, sensible heat or pcm storage won't work. The only option that is practically available would be batteries.
The fan was running at like 25% speed, it consumed less than a watt of power, I decided to not bother with that haha. It would have been good to mention that in the video.