Energy Storage

1. Collects
Energy is gathered from wind, solar, or fossil generators on the grid as electrical energy and sent to Malta’s energy storage system.

2. Converts
The electricity drives a heat pump, which converts electrical energy into thermal energy by creating a temperature difference.

3. Stores
The heat is then stored in molten salt, while the cold is stored in a chilled liquid.

4. Reconverts
The temperature difference is converted back to electrical energy with a heat engine.

5. Distributes
Electricity is sent back to the grid when it is needed.

Malta Inc

They have even built 2,000kWH portable systems. (Hopefully it didn't take up the entire shipping container)

I always thought a compost heating pile, coupled with the cool temperature of the ground, would produce enough of a thermal difference to drive a Sterling Engine. If it did, it would enable a lot of electricity on a homestead.

S Bengi,

For high temperature heat storage and heat transfer, molten salts are very hard to beat.  I am curious about the overall efficiency of this system as each step in the process loses a portion of the overall energy so I am intellectually interested in how much energy the system delivers compared to how much it receives.  Also, over time the hot side will cool over time and the cold side will warm.  But over short time spans (such as overnight heat storage, maybe even a couple of days depending on power needs and circumstances) this setup could have real potential.

Extremely cool idea though.  I did my masters research in the history of energy and I am starting to contemplate going for my PhD in the history of energy and by now I have an almost unhealthy fascination with all things energy.  I now see energy everywhere.  I see it in my coffee in the morning, sunshine streaming into my windows in the day, my Christmas tree—EVERYTHING!  I especially like new forms, sources, methods of generating and storing energy.

If I don’t stop now, I will ramble on incessantly so I will conclude by saying again, very cool and you have piqued my interest.

Eric

Ok , I am officially interested and I can’t stop yet.  Energy is notoriously difficult to store.  By its very nature, energy wants to disperse.  For energy storage, most people automatically think of batteries.  Even with the very best batteries, the electrons just don’t want to pack close to one another (which is why nature is basically electrically neutral over any appreciable timescale,  please correct me if I am wrong).  Thermal batteries want to cool to ambient temperatures even with the very best insulation, and the issue gets worse as the temperature differential grows.  Some power plants use compressed air and hydro electric plants can pump water to higher elevations, but both compressing air and pumping water are energy intensive operations that detract from overall efficiency.

Personally, I have thought of two systems that may work better.  First, electrolyzing water into hydrogen for storage later turned back into energy with a fuel cell might be overall efficient, but today is expensive and cumbersome.

Secondly, I have thought about a version of pumped hydro I call a mass battery.  In the mass battery, excess energy would raise up a heavy mass, say a huge block of cement, using a worm drive to elevate along a shaft.  After the mass is elevated, the worm drive would disengage would detach and a spur gear attached to a generator would generate electricity as the mass lowered back to ground.  The mass battery is my own idea, would only apply to stationary applications, is completely hypothetical/untested, but would not spontaneously lose energy just by sitting.

I still think the molten salts are fascinating and I would be very interested in others’ ideas of good energy storage.

Eric

I’ve gone overboard now.

Making matters worse is the fact that electricity is by far the most flexible form of energy ever discovered but perhaps the very hardest to store.  Almost anything can be powered by electricity (from motors to computers to spacecraft—ion drive).  This makes tempting the notion that all energy should be converted to electricity and back to some other form of energy.  Each energy conversion (say, heat to mechanical work in a car, or heat to steam to spinning a flywheel to electricity—4 steps—in a power plant) loses energy through inevitable inefficiency.  Far better to, say, convert sunlight to heat in a thermal mass only to be re-released back as heat.  The fewer the steps the better.

Eric

Pumped hydro and pumped mass require huge height/mass.
I like pumped air/compressed air. except for the heat lost.
my 2nd post pumps the air and pressurize it store that potential energy but it also stores the heat too and converts that to electricity.

The 1st one stores the heat in liquids vs air.
Like any other battery both system does have energy conversion loss. sadly we have to store solar.
Solar Panels are cheap compared to battery. So if a cheap battery can be made then the money saves can be used to double the amount of solar panels installed.

S Bengi,

Yep, I agree.  Basically any energy storage has its own energy cost and the fewer energy transformations, the more efficient.  I looked long and hard at pv solar for my house and never considered batteries because of the expense.  In Illinois, we can grid tie and essentially use the grid as the battery.  At least that was the case when I last looked at it.

Energy is a tricky subject and there are some good, practical reasons renewables have not really taken over the market yet.  Not saying renewables are a bad idea in any way, just that there still exist real difficulties in replacing coal (and for the record, I do want to get rid of coal).

Thanks for the intellectually stimulating thread.  I hope it continues.

Eric

There are two ways of dealing with energy storage. One is to avoid it. Living Energy Farms (I haven't been there, just from reading) uses solar when it produces enough to run the equipment. This is tough for planning for sure. If you must store it, you have to decide what density (Wh/kg) you need. High density storage tends to be volatile. Low density storage is of course heavy. I am fascinated with NiFe batteries for long term storage, but they take up the best part of a room, and have to be on ground level (or in some monstrous structure). Your generating source is likely to be somewhere other than in the basement, so there is loss and cost in the transmission. That being said they are a mature technology. For obvious reasons they suck for transportation.

Lead acid is somewhere in the middle, but they need to be maintained. When I was in Cambodia, I saw a bunch of SLA implementations that lasted only a year or two because they were not maintained. That is a giant waste.

Lithium is finicky but the density is awesome! I'm working on a conversion, but it takes a lot of time and unless you are in the industry, learning a lot of information to keep from exploding stuff in the garage. This is probably a couple years' project for me.

All the other storage (mass, thermal, pressure) have very very poor density compared with batteries, and not just from the losses essentially running a generator from storage to electric output. I do like pump storage, there is a large artificial lake in Massachusetts I remember visiting as a child that was recharged in the middle of the night and run as hydro at peak hours. It was coupled with a nuclear plant to use the waste energy.  

Eric Hanson wrote:Secondly, I have thought about a version of pumped hydro I call a mass battery.  In the mass battery, excess energy would raise up a heavy mass, say a huge block of cement, using a worm drive to elevate along a shaft.  After the mass is elevated, the worm drive would disengage would detach and a spur heat attached to a generator would generate electricity as the mass lowered back to ground.  The mass battery is my own idea, would only apply to stationary applications, is completely hypothetical/untested, but would not spontaneously lose energy just by sitting.

Nope, not at all. I think it is being done in Denmark.

What they are doing is, using automated cranes to hoist concrete blocks to massive heights when the cost of electricity is low (middle of the night), then when peak demand hits, and power is bought from power companies at premium rates, the same crane takes the blocks and lowers them, the weight powering electrical generators that send power to the grid.

One problem was the high cost of concrete, but my suggestion is to use old quarries where depths can reach 1000 feet or more and the weights are simply the granite or marble blocks taken from the quarry.

For off-grid cabins the same thing could be done on a smaller scale.

Don't forget LiFePo4 batteties.
You can extract 80% of the stored energy during each cycle vs just 40% for lead batteries.
Given the 2x battery capacity per cycle. It really cost about the same.
They are safe, and will give you 3000 cycles before they lose 20% of their capacity at 80% DoD
So we now have 6x life aka 18yrs vs just 3yrs for lead.

TJ,

Lithium batteries have awesome storage potential--for batteries.  There are hypothetical Magnesium and Aluminum batteries that get approaching double and triple the storage capacity (per unit volume) respectively because they have 2 and 3 electrons to give up to Lithium's 1.

On the other hand, chemical storage far surpasses batteries.  A gallon of gasoline has far more potential energy than the best Lithium-ion battery of comparable volume.  If only we could store extra energy by directly making gasoline (or some other fuel) and then run that fuel through a fuel cell, the energy storage capacity would be tremendous.  This is the basis for some hydrogen fuel cell setups.  Sadly, fuel cells have not gone anywhere for almost 20 years.  Around the year 2000, there was some promising developments with positron exchange membrane fuel cells (PEM Fuel Cell), direct methanol fuel cells and a few other types of fuel cells, but sadly these technologies have stagnated for 2 decades as far as I can tell.

I would love for someone to prove me wrong on this last part, but there it is for the mean time.

Eric

Travis,

Thanks for the input on the "mass battery."  I had no idea that this concept was in fact being put to use.  The strengths that it has is that it does not spontaneously lose energy unless it falls over.  You are probably right about the price of cement and really, any heavy object would do.  Gravel from a huge, deep open pit mine would work just fine.

I did all this research in energy and there I go and find things I did not know before--Thanks Much,

Eric

S Bengi wrote:

1. Collects
Energy is gathered from wind, solar, or fossil generators on the grid as electrical energy and sent to Malta’s energy storage system.

2. Converts
The electricity drives a heat pump, which converts electrical energy into thermal energy by creating a temperature difference.

3. Stores
The heat is then stored in molten salt, while the cold is stored in a chilled liquid.

4. Reconverts
The temperature difference is converted back to electrical energy with a heat engine.

5. Distributes
Electricity is sent back to the grid when it is needed.

Malta Inc

It seems to me there's a line connecting #2 and #4 (generation directly to grid) which is missing. As Eric says, losses at each conversion...

There's heat to be captured everywhere! Compost is one that's free, but think of all the situations where COOLING is also being PAID FOR! Server farms come to mind... All sorts of buildings, offices, hospitals, apartment blocks.
Heat pumps and storage could offer both short term (peak pricing) and long term (seasonal) benefits.

This is kind of a neat idea.

I disagree with them that they have a patent on "a proprietary set of gears that makes continuous rotation possible." I have a book, published in 1896 that show that same train of gears. I know what is old is new again, but please, don' say it is patented.

In any case I think it would be possible to scale this to home use.

TJ,

I am afraid I misread your earlier post regarding using pumped hydro from waste energy from nuclear plants.  This is another area I find fascinating for its complexity and diversity of often conflicting opinions.  

Commercial nuclear power plants are basically designed to run at a specific power output level and while they can change their output, they often can’t respond to rapidly changing power needs.  When they do change power, they do so slowly.  Several tons of uranium still put out a lot of heat even if the reactor gets SCRAMed (Military nuclear plants are a different matter).  Also, when the nuclear reactions are increased, they have to heat a LOT of water which soaks up that energy.  It’s not that a nuke can’t change power settings, but they run best at a constant power output.

So how do they meet an increasingly erratic power demand?  Some reactors run at a more or less constant power output and make up the difference with natural gas fueled gas turbines that adjust to load quickly.  As you pointed out, others run slightly above average load and store the excess either in pumped hydro storage or compressed air in geological storage.  Neither solution is perfect.

Strangely dovetailing with the OP’s comments about molten salts is the molten salt nuclear reactor that used molten salts as both coolant and fuel.  These are experimental reactors that operated in the 50’s and 70’s with a movement to restart them today.  Some hate the idea and some love it, but either way, an important factor in its safety system is that salts are used to capture and store the heat and have an enormous capacity to store that heat without creating associated pressure and the accompanying risk of a steam explosion like at Chernobyl (but not Fukushima—just to be clear, that explosion was NOT a nuclear explosion, it was a hydrogen gas explosion that would also be extremely unlikely as a molten salt reactor uses no cooling water that serves as a source of hydrogen).

Sorry if I rambled again, but I find energy in all its forms a fascinating concept.  I am trying to be neither pro, nor opposed to any energy form in any of my commentary.  I am just trying to describe the relationship we have with it.  I can also barely resist the opportunity to discuss the qualities of molten salts.

Thanks for your patience,

Eric

Kenneth you are correct, the picture omitted the direct connection from 2 to 4.
But like you assumed it is there only the 'extra' energy is stored over for night time.  

Eric Hanson wrote:TJ,

I am afraid I misread your earlier post regarding using pumped hydro from waste energy from nuclear plants.  This is another area I find fascinating for its complexity and diversity of often conflicting opinions.  

Commercial nuclear power plants are basically designed to run at a specific power output level and while they can change their output, they often can’t respond to rapidly changing power needs.  When they do change power, they do so slowly.  Several tons of uranium still put out a lot of heat even if the reactor gets SCRAMed (Military nuclear plants are a different matter).  Also, when the nuclear reactions are increased, they have to heat a LOT of water which soaks up that energy.  It’s not that a nuke can’t change power settings, but they run best at a constant power output.

So how do they meet an increasingly erratic power demand?  Some reactors run at a more or less constant power output and make up the difference with natural gas fueled gas turbines that adjust to load quickly.  As you pointed out, others run slightly above average load and store the excess either in pumped hydro storage or compressed air in geological storage.  Neither solution is perfect.

Strangely dovetailing with the OP’s comments about molten salts is the molten salt nuclear reactor that used molten salts as both coolant and fuel.  These are experimental reactors that operated in the 50’s and 70’s with a movement to restart them today.  Some hate the idea and some love it, but either way, an important factor in its safety system is that salts are used to capture and store the heat and have an enormous capacity to store that heat without creating associated pressure and the accompanying risk of a steam explosion like at Chernobyl (but not Fukushima—just to be clear, that explosion was NOT a nuclear explosion, it was a hydrogen gas explosion that would also be extremely unlikely as a molten salt reactor uses no cooling water that serves as a source of hydrogen).

Sorry if I rambled again, but I find energy in all its forms a fascinating concept.  I am trying to be neither pro, nor opposed to any energy form in any of my commentary.  I am just trying to describe the relationship we have with it.  I can also barely resist the opportunity to discuss the qualities of molten salts.

Thanks for your patience,

Eric

This is how many power generating stations, generally anything with a steam turbine whether it is coal, nuclear, natural gas, or biomass that is the heat source, they just cannot be shut down. This is why have diversified power generation is critical for the grid. For instance at peak times, hydro dams can be put on or off line in an instant via remote controlled penstock valves. Sadly in Maine they are ripping them out as fast as they can.

The best battery bank in the world is the tide though. Here in Maine where we share the highest tides in the world with Canada, if we could harness that power, a tremendous amount of power could be generated. They tried back in the 1940's. but then stopped the project. Too bad...

Travis,

As it turns out, the single most efficient method of generating electricity is a large spinning flywheel, and currently the most efficient way to spin that flywheel (assuming you don’t have falling water) is with steam.  Obviously, to make steam you need heat, be it coal, nuclear, concentrated solar, etc.  

Presently there is some interesting work on supercritical carbon dioxide, that would be CO2 pressurized up to its critical point where it can’t decide if its a liquid or a gas so it tries to be both.  It is about 2/3 the density of water so it is dense stuff, but it expands to fill a container like a gas.  Supercritical CO2 (SCO2) density is extremely sensitive to small changes in temperature and therefore makes a rocking working fluid to spin a turbine.  If the details can be worked out, then SCO2 can really push the limits of efficiency in a power plant.

But then again we are talking about spinning flywheels again.  In theory, an SCO2 system should respond to load better than steam, but we still need something to respond to the need for instantaneous changes in power load.  

I actually do like the OP’s solution being molten salts for overnight storage.  Concentrated solar does something similar.  Let us know if you have any further thoughts on this intriguing discussion.

Eric

Just thought I’d link to my thread rgdg the new method of storing energy from solar in a molecule that can store the energy for years and release it only when the molecule is exposed to a catalyst: https://permies.com/t/97272/Molecular-Solar-Thermal-Energy-Storage

James,

Fascinating idea!  230F is not terribly high and a lot of that energy would simply be used to heat the water (which is perfectly fine if you want hot water).  If you want electricity, combined with supercritical carbon dioxide, this has some real potential.  

Thanks for adding this information.

Eric

A note about supercritical carbon dioxide (SCO2)

I have mentioned SCO2 for energy production a couple of times and I thought I should clarify a couple of points of misunderstanding.  In SCO2 systems, the CO2 is in a closed loop,  CO2 would not be released to the environment like steam from a power plant.  The SCO2 is merely a working fluid (but an awesome one) that would turn a turbine better than steam in a traditional open cycle.  I want to be clear I am not endorsing pumping CO2 into the air in any uncontrollable fashion.

I just thought I would clarify this for anyone not familiar with SCO2.

Eric

Let me as a simple question.  What is the goal of such a system?  Storage time, lack of loss etc??

A heat pump adds great complexity especially given the temperature differentials you want to reach.  So why is it in the system?  Do you have a huge untapped source of low grade heat you are trying to gather energy from?  That would be the only reason I can see for adding heat pumps to the effort.  A resistance heater is one of the only systems that is basically 100% efficient at the input terminals.  Everything it produces basically comes out as heat.  So you are taking something that unless it is being used to collect added energy from somewhere that is less than 100% to replace a system that is 100% efficient.  You get minor gains in efficiency on the output end by having a cold source too.  But will it even balance out?  Molten salts have the advantage of high energy density.  But one other question I like to add is,  Is there something you can melt to get phase change that you can make something with.  For example the big solar thermal mirror farms that store the heat in molten salt.  What if they melted glass instead.  You are still doing phase change.  You still have a large mass you can progressively cool to generate power but it might generate a product as well.

There are literally hundreds of answers being tried.

You mentioned not liking compressed air storage because of heat loss.  There is a US company that was working on storing the heat separately from the air for just this reason.  They were storing the heat in reversible chemical reactions and as molten salts both.  And then storing that air at huge pressures.  Another answer is in ground storage.  This one to begin with the heat loss is huge.  But as you keep dumping heat in an underground geologic structure the ground gets warmer and it turns out that hundreds of feet of rock are actually a fairly good insulator once you get the heat gradient built in.  These are usually lower pressure systems but high volume.  A third air system is a large heavy movable piston in a vertical shaft.  It combines movable mass with compressed air There again things get hot but the heat loss is minimized thru the fact it is buried in the ground and once it has been hot for a while the heat loss slows as the ground gets hot around it.

There are lots of mass systems.  Be it water pumped to the top of the hill or the guy building what amounts to a ski lift for gravel or hundreds of other ideas.  The big advantage of most of these systems is low loss in the actual storage condition.

Personally I still think a combination of steam electrolyzers, fuel cells, hydride storage tanks and batteries looks like the best system if longer storage is needed.  Batteries to level peak load and allow for throttle up and down of fuel cells.  I happen to like this because of the ability to utilize waste heat streams.  Anything that will preheat the water going into the steam electolyzer contributes heat energy on that end.  And certain types of fuel cell are endothermic when run at low power conditions providing a cool side too.  Since idling the fuel cells allows for faster start up there is reason to do so.  It only really works for stationary applications because the iron titanium hydride tanks are heavy and large.  The big advantage here is the energy can be stored for years with almost no loss.

And in batteries one other one should be on the list and that is nickle iron batteries.  Their efficiency sucks compared to lead acid or lithium.  But they run for decades with only water replacement and they can be 100% discharged without harm.  So if you can find a way to tap their waste heat they might be a very good answer.



SCO2 systems I need to read more.  I remember briefly looking at them a decade ago but have no idea what has happened in the mean time.

How about using photosynthesis to convert sunlight, water and carbon dioxide to biomass eg a tree. The wood makes a great storage medium and can be burned when the energy is needed. Also carbon neutral if you're worried about that sort of thing.

Here’s a blog about “micro grid” in Thailand with use of Redflow batteries:
https://www.victronenergy.com/blog/2019/07/04/thailand-micro-grid-fills-redflow-zbm2-with-victron-energy/

Eric Hanson wrote:S Bengi,

For high temperature heat storage and heat transfer, molten salts are very hard to beat.  I am curious about the overall efficiency of this system as each step in the process loses a portion of the overall energy so I am intellectually interested in how much energy the system delivers compared to how much it receives.  Also, over time the hot side will cool over time and the cold side will warm.  But over short time spans (such as overnight heat storage, maybe even a couple of days depending on power needs and circumstances) this setup could have real potential.

Extremely cool idea though.  I did my masters research in the history of energy and I am starting to contemplate going for my PhD in the history of energy and by now I have an almost unhealthy fascination with all things energy.  I now see energy everywhere.  I see it in my coffee in the morning, sunshine streaming into my windows in the day, my Christmas tree—EVERYTHING!  I especially like new forms, sources, methods of generating and storing energy.

If I don’t stop now, I will ramble on incessantly so I will conclude by saying again, very cool and you have piqued my interest.

Eric

Tesla, im sure you know had much the same observation. You better quit now or you will be washing your hands 33 times in a row every 9th time and feeding pigeons because they are your only friends!

there are commercial facilities here in ontario which buy power at night when it is cheaper and spin large cylinders of concrete on a bearing

there are expensive machines (100000 to 2000000) which use supercritical co2 to extract oils... if you could combine the two you may make it more profitable/worth it