Sciencemadness Discussion Board

Reversible reactions for energy storage

hexahydrate - 30-3-2018 at 13:20

Hello, this is my first post on this board, although I've been a long time lurker here. I came across this site many months ago, when looking for information about solar energy storage systems, as that topic interests me and I discovered lots of fascinating chemistry stuff, albeit unrelated to my original search :). I spent many hours reading and even performed some simple experiments (chlorate cell, elephant toothpaste, various salts). There is so much cool chemistry things discussed here, that I doubt I will ever be able to understand and play with even 1% of it.


However, I decided to create a topic about things that originally sparked my interest in chemistry, that is storage of (mainly solar thermal) energy using reversible chemical reactions. I think little on this topic has been discussed here, so let's start :).

I read some papers (thanks sci-hub!) and basically, there are three main methods to store thermal energy:

1. sensible heat: basically heating a water tank. Cheap and easy, but not practical to store energy for a long time.

2. latent heat: using PCM (phase-change materials). Energy is stored by melting a material and released during solidification. For some materials, energy density provided by latent heat is greater than can be stored by heating water. Many materials (especially salts) exhibit phenomenon known as supercooling, that is material can be cooled well below its freezing point (i.e. to room temperature) and stay liquid and can be made to solidify (and release heat) on demand. This makes long term energy storage more practical. Among the most heavily researched PCMs are: sodium acetate, sodium sulphate, paraffins.

3. Thermochemical:
a.) sorption: mostly using salt hydration/dehydration process (most popular salts are: CaCl2, MgSO4, MgCl2). In theory this seems easy. Just use heat from solar thermal collector to dehydrate salt in the summer, then store it in air tight container until winter, then let it absorb moisture and release heat. However, most experiments run into problems with salts losing its structure, absorbing way less water than they theoretically could, heat transfer problems etc.

b.) Chemical reactions: i.e. CaO + H2O -> Ca(OH)2 + heat, although temperature required to dehydrate it back to CaO is above 400C IIRC, so not practical for typical flat solar collector. I've seen papers proposing some crazy ideas as well, like using process of concentration/dilution of H2SO4.

There is also lots of research on converting sunlight to fuels (artificial photosynthesis), but most of the methods seem too advanced to be replicated by the amateur.

All I have read on the topic so far, points to the conclusion that it's very hard to build a practical system. All of the above methods have several drawbacks (I can post links to some interesting papers if someone is interested).

I'm curious, if mad scientists have any novel ideas, what reactions could be used for energy storage ? Ideal reaction has to be:
1. Reversible in the temperature range below 200C
2. Use cheap, possibly non-toxic and non-corrosive reactants.
3. Easily triggered on-demand

RawWork - 30-3-2018 at 13:42

Good topic...
That is great for one reason, because your parents won't complain about you doing something in home. That is advantage I see over using normal more dangerous sources like fire or electric stoves...
But we must be aware that just making that something that will later be invisible, easier to hide, legal, less dangerous, we have to do something more dangerous to make it...
So it depends on what we have and what we want. And we have to use something we don't want (later) just to make something we want later. For example one way is if we have space open to sun or are we living underground or in prison or in institution where nobody will allow it. If we have personal space like roof, garden, balcony, whatever, that is exposed to sun, then use that to collect sunlight and focus it into small dot that will allow higher temperature, as you say up to 200.
I don't have exact idea because I am thinking about something else, but you get the idea. Remember that the more difficult is to make it, the more energy will give it. That is universal rule. For example the higher decomposition temperature of hydroxide or hydrate is...

Your whole idea is similar to charging a smartphone and using it outside. You are like asking how to use smartphone outside without charger, but you still use same energy of course. With a bit more losses, but it's unimportant. It has advantage.

[Edited on 30-3-2018 by RawWork]

hexahydrate - 30-3-2018 at 23:59

Quote: Originally posted by RawWork  
Good topic...
That is great for one reason, because your parents won't complain about you doing something in home.


Haha, RawWork, I don't live with my parents. I have my own house with a big garden, so I can decide myself, what I do there :). My house has central heating system powered by natural gas, that works very fine, but I'm interested in renewable energy and I love DIY projects, so I plan to build this type of solar collector and use it to do some experiments with various methods of storing thermal energy. Maybe it will be just an experiment with no useable outcome, but ideally I would like to build this year a small scale, proof-of-concept device, able to heat my house for just a few days in the winter (so less than 100 kwh storage capacity). Just for fun, my own satisfaction and to learn something new :).

Quote: Originally posted by RawWork  

For example one way is if we have space open to sun or are we living underground or in prison or in institution where nobody will allow it.


I have lots of space around my house and south facing roof, so that's not a problem.

Quote: Originally posted by RawWork  

Your whole idea is similar to charging a smartphone and using it outside. You are like asking how to use smartphone outside without charger, but you still use same energy of course. With a bit more losses, but it's unimportant. It has advantage.

[Edited on 30-3-2018 by RawWork]


To give you some idea, what I'm talking about, here is the article about the system built by the researchers in the UK, using calcium chloride as a storage media, supported on vermiculite (to increase water vapor permeability).



Sulaiman - 31-3-2018 at 02:51

100 kW.h = 100,000 x 3,600 = 360 MJ energy storage.

The first thing to appreciate is that the stored energy is equivalent to 86 kg TNT !
Therefore, any storage system must be incapable of rapid/uncontrolled energy delivery to avoid explosion/fire etc.

The easiest way to store summer energy for winter is to
sell power to the grid in summer as it is produced,
and buy it back in winter when you need it.

I have built my own photo-voltaic collectors and even that puny quantity of energy requires non-trivial storage.

Fulmen - 31-3-2018 at 03:08

The idea of storing seasonal energy chemically isn't really viable, you would have to store an insane amount of energy or this to be of any use. If you have a decent water source and some drop available you could look at hydroelectric storage.

JJay - 31-3-2018 at 05:21

Lead to lead sulfate and back is a popular one.

Bert - 31-3-2018 at 07:27

You just want space heating, not to generate electricity or heat water for your bathroom/kitchen?

How far North/South of equator are you?

Can you quantify your average winter time energy needs for space heating? Typical heating degree/days?

You have a substantial and largely unobstructed southern exposure? How many square meters facing South are you willing to invest in collector space? Would you be willing to install more collector area if the collector looked like (and could be used as) an attached solarium/greenhouse rather than an assembly of big black panels.

How many cubic meters would you be willing to devote to a thermal storage cell? Are you willing to dig a largish hole on the South side of your home?

[Edited on 31-3-2018 by Bert]

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sodium_stearate - 31-3-2018 at 09:00

How about using a woodburning stove to get some
heat? Wood has lots of stored energy which gets released
when it's burned.

Leave the energy storage portion to nature.

Then you get to release the energy when you burn the
wood.

Swinfi2 - 31-3-2018 at 18:52

For the chemistry of it, redox flow battery?

Definitely probably way more expensive than a commercial option though.

Vanadium is the most common type but there are lots of options in the literature, lithium/tempo had a decent energy density iirc, things like riboflavin and benzoquinone were done successfully in research too but iirc they weren't as good. Lots of metal complexes too, they had the most potential but stability issues.

I want to do one of these eventually. Also while were on the subject what do you guys think would be the difficulty of making an arduino/raspberryPI potentistat?

RawWork - 1-4-2018 at 03:26

It doesn't have to be all chemistry if all you want is energy using something reversible, there are reversible electrical, magnetic, mechanical reactions. Just use computer fan which is actually dc motor. If you can apply strong enough water flow accross it, it will give you dc voltage and current, exactly same as it uses normally. Of course some modification may be needed, at least to isolate electric parts inside from water and anything outside.

Sulaiman - 1-4-2018 at 11:44

Hydroelectric, at 100% efficiency;
using E = m.g.h,
E = 360 MJ, g = 9.81, let h = 10m ... m = 3,670 metric tonnes of water.

Allowing for conversion efficiencies etc. you'd probably need 10,000 metric tonne (cubic metres) reservoir 10m above ground,
and a similar reservoir at ground level :D

RawWork - 1-4-2018 at 16:01

Quote: Originally posted by Sulaiman  
probably need 10,000 metric tonne (cubic metres) reservoir 10m above ground,
and a similar reservoir at ground level :D


What about doing recalculations? :o
You only calculated energy. Probably only kinetic or potential.
If you didn't know energy has time dimension, which your doesn't.

Except if we plan to use all energy at once, and get temperature of few thousands degrees celsius.
:cool:

[Edited on 2-4-2018 by RawWork]

Sulaiman - 2-4-2018 at 02:04

No, power (Watts) is energy (joules) per unit time (second).

In the initial calculation 100 kW.h was requested ... a measure of energy.

RawWork - 2-4-2018 at 02:58

Wrong. Energy is power per time like W=P/t or W=P*t, forgot exactly. My electric energy bill is for one month, it can't be timeless. Try sleeping more to regain elementary school knowledge. Trust me, it helps.

I still remember that formula for electric energy. W=P*t. Or W/t. Forgot exactly. Since P=U*I, it is also W=U*I*t. Something like that.

[Edited on 2-4-2018 by RawWork]

Sulaiman - 2-4-2018 at 03:20

Quote: Originally posted by RawWork  
Wrong. Energy is power per time like W=P/t or W=P*t, forgot exactly. My electric energy bill is for one month, it can't be timeless. Try sleeping more to regain elementary school knowledge. Trust me, it helps.

I still remember that formula for electric energy. W=P*t. Or W/t. Forgot exactly. Since P=U*I, it is also W=U*I*t. Something like that.

[Edited on 2-4-2018 by RawWork]


You obviously did not pay attention to your schoolwork so I'm in no mood to teach you.
Please learn the difference between energy and power.

While you are at it, you probably should look at heat vs. temperature too,
because if you are confusing one, you may be confusing the other also.

P.S. sorry for feeding the Troll, it seems that some people are incapable of learning.

[Edited on 2-4-2018 by Sulaiman]

RawWork - 2-4-2018 at 04:14

Please, please consider relearning elementary school knowledge, at least from physics. It doesn't take long to learn.
Let's take example with electricity, power is P[W]=U[V]*I[A]. Energy is W[Ws]=P[W]*t[s]. Which can be converted to [Wh] or [kWh]. We all see who is troll here, and who is too lazy to learn even only this.

What works for electric energy should work for any other energy too. I know you think about energy like kJ/mol which can be converted to kWh/mol, and many other examples. But it's not practical. Energy is used OVER TIME! :cool:

Your advice is too dangerous. You should be banned. If op tried to use all energy all at once, he would not only get burns, but immediately die. :mad:

Oh, let's make a conclusion that we know the difference between W (in some countries probably E) and P: power is timeless dimension, both practically and theoretically. While energy can be timeless only theoretically as in kJ/mol, but not practically.

Oh, and if you didn't know, the only thing that prevents or slows me down from succeeding, for example from making my first youtube video is time. Time is something that should be considered in everything. If we satisfy our time demands, we can hope to satisfy our other demands like energy, mass, power, quantity, temperature...

[Edited on 2-4-2018 by RawWork]

Fulmen - 2-4-2018 at 08:46

Quote: Originally posted by RawWork  
Energy is power per time like W=P/t or W=P*t, forgot exactly.

Wait, what? You can't remember if you should multiply or divide, yet you try to school others on the topic? Really?

Sulaiman is correct, you're wrong. If you're wondering why, start here:
https://en.wikipedia.org/wiki/Energy
https://en.wikipedia.org/wiki/Power_(physics)

RawWork - 2-4-2018 at 09:11

Calm down, I mean practically. Such energy can be stored like that "just energy". But it can't be used without time. It's used over time, like per second or per day. Op planned to use it per winter. Or per 3 months. And I already read whole wikipedia few months ago, thanks. OK?

happyfooddance - 2-4-2018 at 09:21

Quote: Originally posted by RawWork  
Calm down, I mean practically. Such energy can be stored like that "just energy". But it can't be used without time. It's used over time, like per second or per day. Op planned to use it per winter. Or per 3 months. And I already read whole wikipedia few months ago, thanks. OK?


Maybe read it again.

Also, I don't think anyone needs reminding that work takes time in this world. Saying that Sulaiman is dangerous and should be banned is the stupidest thing you've said, and you've said some stupid things in this thread.

RawWork - 2-4-2018 at 09:45

Well, maybe he is not dangerous, maybe he is just some small weak guy or girl. But "3,670 metric tonnes of water" is. It's huge difference between them being used at once and over 3 months, how long winter is. Time is not a small thing that should be only reminded occassionally. But things that has to be used in calculations. In the end it's wrong that we'll "need 10,000 metric tonne (cubic metres) reservoir 10m above ground, and a similar reservoir at ground level ".

It's better to be banned than to end up in prison. Few years ago two construction workers killed 3rd one, because they miscalculated something. Now both are sentenced to over a year in prison. That isn't the place where you and Sulaiman want to end up, is it? Just because of miscalculation and ignorance that you "don't think anyone needs reminding".

:mad:

Fulmen - 2-4-2018 at 09:57

Stop digging, you've already hit rock bottom.

happyfooddance - 2-4-2018 at 10:21

Quote: Originally posted by RawWork  
Well, maybe he is not dangerous, maybe he is just some small weak guy or girl. But "3,670 metric tonnes of water" is. It's huge difference between them being used at once and over 3 months, how long winter is.


The only person in this thread that has even mentioned the ridiculous idea of releasing 100kw hours instantaneously is YOU. Sorry, but for people with practical knowledge and experience with these things (which Sulaiman clearly has and you clearly don't), such warnings don't need mentioning.

RawWork - 2-4-2018 at 10:32

OK then, you build your extremely large 10 m reservoir above ground and similar size below...
I'm gonna build my much smaller one, that can be put in pocket. I think it'll satisfy my demands.

And he didn't say "No, power (Watts) is energy (joules) per unit time (second)."?
If you agree with this theory then you must have access to some science fiction version of wikipedia?

:P

[Edited on 2-4-2018 by RawWork]

OldNubbins - 2-4-2018 at 10:42

It makes me sad to see so much willful ignorance in this world despite a wealth of knowledge freely available to almost anyone.

Overcoming natural selection will be humanity's downfall. Kind of ironic...

happyfooddance - 2-4-2018 at 10:51

Quote: Originally posted by RawWork  

And he didn't say "No, power (Watts) is energy (joules) per unit time (second)."?
If you agree with this theory then you must have access to some science fiction version of wikipedia?

:P

[Edited on 2-4-2018 by RawWork]


Actually, that is pretty much exactly what wikipedia shows me. Also, I think you meant "didn't he say" because you put a question mark, and because "he didn't say" is an easily disproven falsehood.

Are you looking at the english wikipedia? Maybe you are not understanding it.

RawWork - 2-4-2018 at 11:21

I give up. You win. I looked into various wikipedia articles and it's very confusing. I just can't think anymore. Some say I am right some say you're right, some say it's timeless, some say it's time. There are just too many units that I can't think all in one day. Will try to solve that mistery one day hopefully. :(

happyfooddance - 2-4-2018 at 11:39

Aww, cheer up, mate! ;)

hexahydrate - 2-4-2018 at 12:05

It makes me sad to see the discussion is going "off-road". I hoped to discuss ideas how to store heat chemically. Let's not argue what is energy and power, nor discuss building water reservoirs. To move discussion in good direction, I'm attaching two papers, regarding salt hydrates. They seem to be the most often studied materials, because dehydration usually take place in place in temperatures below 200C, sometimes below 100C, however energy density is modest, at 2.8 GJ/m3 for MgSO4 cited in papers (and even less for other salts), typical seasonal storage system would still require a few m3 of salts.

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NEMO-Chemistry - 2-4-2018 at 12:08

Leave the guy alone! he makes me look smart :D

hexahydrate - 2-4-2018 at 12:13

Among papers concentrated aroung salt hydrates, I found unusual idea of using thermoreversible reactions between organic acids and amines (first part of the paper talks about using CO2 hydrates for cooling purposes).

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clearly_not_atara - 2-4-2018 at 12:23

The best small-scale storage method is a battery, and good batteries are quite hard to make so you're probably better off buying one.

For large-scale, there's an arms race between the compressed air people and the molten salt people, but neither is accessible to you. Molten salts only make sense at the largest scales because storage is proportional to volume and loss is proportional to surface area, so because A^3 ~ V^2 you have better storage efficiency the larger you get and small systems are very inefficient. For compressed air you have to design a high-pressure tank which might require a welding license, or fabricating composite materials (not easy!) or go underwater.

Underwater compressed air is something I toyed around with building myself on one occasion, because no advanced materials are required, however it requires using a _very_ big underwater "bag" of air because the gauge pressure is much lower. If you're using a bag 20 meters underwater the pressure is 303 kPa and the energy density is 333 joules per liter so 100 kWh = 360 MJ -> 1080 cubic meters of storage or about 10000 30-gallon garbage bags anchored to the lakebed. At a cost of 15 cents per bag that will run you $1500 on bags alone, but the hoses are the real issue with this setup.

After investigating this for a while I decided it was clearly much more practical at small scales to buy a battery, although I did consider making my own larger tanks from bulk plastic, anchoring them with sandbags, using an open-at-the-bottom design to save on materials, etc. I have diagrams of the apparatus somewhere with calculations and stuff.

One more entertaining idea IMO is electrocatalytic reduction of CO2 -> methanol. It's possible you could order a fancy catalyst and make lots of easily-burned fuel by this method. However, capturing large amounts of CO2 requires a fancy apparatus. Storage efficiency is terrible, but regeneration is by combustion, which beats the convenience of any other method by parsecs.

hexahydrate - 2-4-2018 at 12:40

Very interesting ideas clearly_not_atara. I know about molten salt storage and I agree with you, that it only makes sense in huge systems. Batteries are also interesting thing for me and I would like to try to build small Edison (NiFe) rechargeable battery at some point. 19th century technology should be acheivable by an amateur in 21st century :). I'm surprised I didn't find much battery chemistry discussed on sciencemadness.

happyfooddance - 2-4-2018 at 14:19

Quote: Originally posted by hexahydrate  
I'm surprised I didn't find much battery chemistry discussed on sciencemadness.


That surprises me, too. There are almost 40 pages of threads in the technochemistry sub-forum, and probably 1 in ten of those threads is about chemistry that relates directly to batteries. This, however, is a novel thread, and I am all ears.

clearly_not_atara - 2-4-2018 at 15:14

I guess you might be able to make a potassium-ion battery? They're supposed to be easier to manufacture than the lithium and sodium counterparts, and very stable (cycle life >10000):

https://www.sciencedirect.com/science/article/pii/S037877530...

Several related papers by Eftekhari describe further work with the system. The simplicity and durability of K-ion are its chief advantages over Li and Na chemistries; these also seem to recommend it for hobbyist work. Potassium graphite is the anode and Prussian Blue is the cathode.

RawWork - 3-4-2018 at 07:58

Replying to Fulmen, happyfooddance, Sulaiman and probably OldNubbins. Sorry for damaging/polluting the op's topic/thread.

I looked into various wikipedia articles and realized something. You were saying that power is time dimension and energy is not, while i was saying vice versa. Meaning for example you were saying that W is time variable unit or practically said "varies with time", and Wh is not time variable unit or practically said "doesn't vary with time". Well, it's confusing.

Let's first try to understand what does "varies with time" mean. It means that if some value exists already in one second, it will be different in 2 seconds (aka +1 second more than starting time). So let's see:

I have light bulb with label "60 W". That's it's power, correct? It's always. It doesn't vary with time. Correct me if I am wrong.

One thing that kind of confuses me with above statement is P=U*I. While I=Q/t. While it's obvious from this that I is Q per second. So I is time unit??? Confused! Perhaps Q has time unit in itself so overally I is not time depending. Because for example s/s = 1 or nothing.

I have electric bill that depends on how long I use this 60 W light bulb. In that bill energy is needed to be paid. It's in kWh per month. It's depending on power of light bulb and time. So for 2 days use I will get double the price of one day use.

You see, I am right in everything, except that some confusion appears in that group of text "One thing...". I doubt that you have an explanation to defend yourself or each other.

RawWork - 3-4-2018 at 08:13

Actually, wait a little. Another think came into my mind.

Looks like confusion is in the words. Here's confusing word: "time dimension" (is composed of time units among other things) and "varies with time" (some units are divided by time unit).

For example it's correct that power is used over time. Like I can use 60 W light bulb over 2 days. This is W/s or W/h or W/day, whatever. But this doesn't make sense. It would mean that after 2 seconds power becomes half. Instead it means that to use that same power for 2 seconds it's same as using twice less than that for 2 seconds. Power is constant, it's not changed over time. Got it now?

But energy is composed of W*s or kW*h, whatever. You can see that it increases with time. Depending from which side you watch. It means that much energy is collected or used.

This is still somehow confusing for all. But that's how it is, we can't change that. That's why I hate complications. Simple theory is needed for success.

[Edited on 3-4-2018 by RawWork]

RawWork - 3-4-2018 at 08:17

Oh, one more thing. Please note that time dimension units can't be used over time. It's like trying to use them doubly over time. Like +2-2=0. Or like s/s=1 or nothing. They cancel each other. For example kWh / h = kW. Energy becomes power. Now everything makes sense. I am satisfied.

Let me try to make conclusion below:
Units composed of time can't change over time, because they're already units which "change over time". And vice versa:
Units not composed of time can change over time, but it doesn't change that parameter, but more of that parameter is needed...which means it can't even be compare to above sentence.
Actually they can't. They can only be used aka "diluted" over time. But they are not changed. That makes sense!!!

Sorry for confusing talk, I do not speak english so often. But even If I spoken I would not know better how to explain. :(

[Edited on 3-4-2018 by RawWork]

clearly_not_atara - 3-4-2018 at 11:07

RawWork:

First, any physical quantity, including power and energy, can "vary with time". This is a different consideration than the dimensionality which is expressed by the statement that power = energy / time. For example, if I stretch a rubber band, the length varies with time, although length does not have dimensions of time. The idea that something varies with time is expressed using a function of time; it has nothing to do with the dimensionality.

Second, power is the rate of energy consumption over time. What Sulaiman and the others told you is correct.

Third, physics should not be understood as a collection of miscellaneous facts but as a structured theory that requires the understanding of certain concepts to make sense of others. You are not understanding the Wikipedia articles because you lack the necessary background in the subject. It might be a better idea to read this article:

http://simple.wikipedia.org/wiki/Power_(physics)

I strongly suggest you stop trying to "argue" this point and study physics from the beginning if you want to make sense of it.

RawWork - 3-4-2018 at 11:17

I doubt that power can vary with time. Maybe power usage (wasting) can, but power rating can't. 60 W light bulb doesn't vary with time, it's always 60 W, a constant.

JJay - 3-4-2018 at 11:20

Quote: Originally posted by RawWork  

Let me try to make conclusion below:
Units composed of time can't change over time, because they're already units which "change over time".


There is an entire field of study referred to as "differential equations" that covers this sort of thing. I've surely gotten into my share of stupid arguments, but you need to understand the basics before you do any further philosophizing on this topic.

RawWork - 3-4-2018 at 11:24

Oh, remember that topic. That's where I actually failed at school from "impulse and digital electronics". It's too complicated. Will never understand it probably.

happyfooddance - 3-4-2018 at 11:26

Quote: Originally posted by RawWork  
I doubt that power can vary with time. Maybe power usage (wasting) can, but power rating can't. 60 W light bulb doesn't vary with time, it's always 60 W, a constant.


No... A 60 watt lightbulb is almost never exactly 60 watts, it varies all the time.

Power can be adjusted (think of a dimmer switch). This CHANGE can be expressed as "watts per second, per second".
Or w*s*s.

This is a simple equation used to express constant change.

Gravity is expressed the same way, it is a change in velocity, expressed as 9.8 m per second, squared.

RawWork - 3-4-2018 at 11:59

Whatever, I am incapacitated to discuss this anymore. I will try to prove it to your eyes one day. Talking is boring and not helpful. :mad: