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Author: Subject: Reversible reactions for energy storage
RawWork
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[*] posted on 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. :(
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happyfooddance
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[*] posted on 2-4-2018 at 11:39


Aww, cheer up, mate! ;)
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hexahydrate
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[*] posted on 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.

Attachment: solar_energy_storage.pdf (1.5MB)
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Attachment: trausel-2014-review.pdf (363kB)
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NEMO-Chemistry
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[*] posted on 2-4-2018 at 12:08


Leave the guy alone! he makes me look smart :D
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hexahydrate
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[*] posted on 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
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[*] posted on 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.




[Edited on 04-20-1969 by clearly_not_atara]
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hexahydrate
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[*] posted on 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.
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happyfooddance
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[*] posted on 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.
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clearly_not_atara
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[*] posted on 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.




[Edited on 04-20-1969 by clearly_not_atara]
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RawWork
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[*] posted on 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.
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[*] posted on 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]
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[*] posted on 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]
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clearly_not_atara
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[*] posted on 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.




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 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.
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[*] posted on 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.




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[*] posted on 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.
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[*] posted on 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.
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[*] posted on 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:
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