Over at Hackernews is a link to a WindPower Engineering article from September on Electricity stored as a temperature difference.
This is basically a write up of the Isentropic energy storage system which uses a gravel storage medium and argon gas as a thermal transfer medium:
James Macnaghten and Mark Wagner, co-founded Isentropic, Ltd., a company that is currently developing a new storage technology called pumped-heat electricity storage (PHES), which stores electricity as heat and cold. PHES, Isentropic claims, is cheaper than pumped hydro, is deployable anywhere in the world, and is comparable—and in some cases superior—to pumped hydro with a round-trip storage efficiency of 72 to 80%.
...
An independent study by Parsons Brinckerhoff reports that PHES costs 30% less than pumped hydropower with a per hour storage cost of $103/kWh. Currently the technology is scaled to support up to a 2,000-home town. For this scale, the building housing the system is estimated to be 20 to 40m tall.
Note: as highlighted in the HN threads the storage cost quoted above appears to be capital cost of building the store, not the operating cost.
The Isentropic homepage has an informative Youtube video describing the PHES process, and an Isentropic process is formally defined as one where "the entropy of the system remains constant throughout".
Original HackerNews link. Although relatively old this is an interesting storage technology I haven't seen covered previously on SN.
(Score: 4, Interesting) by anubi on Sunday November 23 2014, @05:32AM
Consider 1 bar ( barometric pressure ) is right at 15 psi. 12 bar is around 180 psi. Consider your air compressor... around 120 psi or so? Get much heat off of it? Consider releasing the pressure by venting the compressed air... does it get really cold?
How much power does the air compressor draw?
Observe, and get a gut feeling on this to get some idea what to expect.
I am a little dubious on this. I would love to see a small working model before I plunked over any investment.
Now, I have personally been doing something like this, but my working fluid is propane. Its cheap, and has a convenient "liquid line" of state, that is at which pressure/temperature it is a liquid and which pressure/temperature it is a gas. ( Mollier charts give a good overview of this ). [ihrdc.com]
I cannot store much energy as a temperature differential, as the Carnot efficiencies at lower temperatures will kill me. I would be lucky to get back 1% of what I put in considering all the losses. So, my attack vector was to store thermal energy as phase changes of water. That is I use the heat absorption of vaporizing propane end to make a big block of ice.
I can melt and re-freeze water an infinite number of times without wearing it out. And its a pretty cheap energy storage medium.
I never try to reconvert the thermal back to electricity.
Rather in hot days, I make the ice at night when its easier to get rid of heat, and use it in the day, especially if Edison is having a bad day and needs to lighten load.
My intention is to later move to a remote area where it may get cold. In that case I use the ice bank in reverse... I melt it during the day using solar thermal collectors, then at night I freeze it again, as its colder outside than 0 deg C, and I have less problem getting heat out of freezing water than out of -5 deg C air.
Yes, most of it is made from parts scrounged from junk.
Even as I am typing this, one of the projects I am working on is a 8X32 "propeller" chip interfaced to an Arduino which will supervise one of those Fisher and Paykel motors so I can run the whole refrigeration system at the maximal power point from the electrical power coming from photovoltaic panels. The propeller was chosen for its low power as well as task fidelity, as I want it to generate Don Lancaster's magic three phase sinewaves, and I can vary the processor clock to track. ( This is when I really appreciate the I2C protocols, as they are not time critical. ). There is a lot of computational work to do, as not only do I need to set the exact timing for motor drive, I also need to continuously optimize the voltages/currents by playing games with the DC/DC boost converters.
This is not rocket science. It's refrigeration. [ecorenovator.org]
And, no, this is not last week's project. I have been tinkering with this thing for about ten years now...and am just now beginning to understand where to take it. I feel I could easily spend the rest of my life building it. Definitely a labor of love or a love of labor - I do not know which. But its how I get my jollies off, as TV and sports bore the living daylights out of me. Can't do it for work as the boss would want it done now - and I can tell you something like what I am doing takes time, lots of time, and then some.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
(Score: 3, Informative) by tonyPick on Sunday November 23 2014, @02:22PM
I would love to see a small working model before I plunked over any investment.
Looks like there's a project in conjunction with the UK government:
http://www.eti.co.uk/project/distribution-scale-energy-storage/ [eti.co.uk]
Using this technology, the project will develop and demonstrate a cost-effective 1.5MW/6MWh energy storage device that will operate on a Western Power Distribution network site.
Which it will be interesting to keep an eye on - they have about £15M (or ~23.5M USD) to play with, so this should be kicking along.
According to a 2012 article http://www.v2g.co.uk/2012/06/isentropic-and-western-power-to-test-pumped-heat-electricity-storage/ [v2g.co.uk]
...
I called Isentropic and spoke with their Chief Technology Officer Jonathan Howes earlier today. Unfortunately in all the circumstances, Jonathan told me that whilst a scaled validation system will be up and running in the not too distant future, a utility scale machine capable of delivering 1.5 MW of power and 6 MWh of storage in the field at an overall efficiency of 75% is still several years from fruition.
And there's an Economist article from 2014 at
http://www.economist.com/news/technology-quarterly/21603184-reversible-heat-pump-promises-cheap-way-store-renewable-energy [economist.com]
which says they have:
developed several prototypes of what the trio call pumped-heat electricity storage (PHES).
Which, taken together, implies there's been some demonstration stages before scaling up to the 1.5MW/6MWh plant, but I can't find any more updates (or any hard numbers) over that...
(Score: 1) by anubi on Monday November 24 2014, @02:44AM
Thanks for the reply... I wish I could give you a good mod for it.
This is something that I would love to see a small model of... as I see nothing that nonlinear in it that it wouldn't scale nicely. Kinda like a water cooler and big industrial refrigeration system use the same basic physics.
They may be onto something by using argon, however its molar heat capacity is very similar to nitrogen which is about 78% of air. They did not look like they were anywhere near using phase change properties of the gas.
Argon is pretty plentiful, we get it by distilling air. From what I see, about 1% of air is argon. Welders love the stuff, as a blanket of it around their welding work keeps oxygen pushed out of the way until they finish their weld. I have often wondered why nitrogen or carbon dioxide would not work, but the welders I know love argon for this. I would have thought CO2 would be perfect, as you get a helluva lot of it in a tank, and it comes as a liquid in the tank, like propane does. ( Matter of fact, CO2 also makes a good refrigerant - but it does run at significantly higher pressures. ).
Again, this is their research. Every scientific breakthrough I have ever heard of started with some phrase similar to " Hmmph! What in the hell just happened?!!?". And someone got a wild hair up their arse to find out. They may have seen something that has been ignored for years.
I have had my share of people try to interest me in tensor coils and magnet motors with claims of energy from the vacuum. They all sucked ( pun intended ).
My fear of governments though is that I have seen them all too often spend lots of money for political reasons. That's one of the benefits of having a charter to disburse public funds by coercing the public taxpayer to remit those funds. Even if a government doesn't have the funds, it doesn't stop them from issuing bonds to cover their spending; or they will spend money that was to go for important things, such as police, fire, schools, and public infrastructure, then claim a fiscal crisis that only another tax increase will solve.
Incidentally, anyone have any more info on Rossi's E-Cat? The marketing folks keep egging us on that it works, and even high-falutin' degreeware people say it does, however, I simply can't trust doctorate degrees and university spokesmen any more than I can trust "trustworthy computing" said by a major software vendor. I have seen way too many "magic shows" involving trick science. ( Yes, I have a friend who practices magic and he lets me in on how these deceptions work... I see the very same stuff being done to investor audiences. ).
That is why I feel I must personally check it out. However, the problem is even if I get invited to assist in checkout, I often run into the inventor refusing to reveal key data I need to verify whether or not the device is functioning as claimed, and I soon find myself surrounded by highly degreed shills eager to recover the costs of their degrees.
I can not trust what a marketer says; I need my own physics, which I have never known to lie to me, to verify the claims of the sponsor. They have their legal forms drawn up full of legal trickery to make payments binding, and I have my measuring equipment to verify their thing actually does what they say it does. And to make matters worse, I default to "skeptic" until I am convinced otherwise. Sometimes all it would take to convince me is nothing more than heating up a well-insulated bucket of water. Playing games with power factors, duty cycles, and other phenomena which thwarts conventional measurement instruments does not impress me. I have had the best of measurement instruments lie to me when I feed them something they were not designed for.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
(Score: 2) by Immerman on Monday November 24 2014, @05:50AM
I think the issue with welding is reactivity - at the temperatures involved you're likely going to be breaking the molecular bonds in the gas, resulting in a bunch of free nitrogen (or carbon and oxygen) which will then react with your metal. Argon though is a noble gas - it's extremely difficult to get it to react with anything, even intentionally.
For thermal systems the only thing that jumps to mind is that argon is monatomic - it's normal molecular structure is just a single unbound atom, which makes it behave almost exactly like an ideal gas, with thermal energy being stored only in the atom motion, and not also as vibration of the molecular bonds.
(Score: 1) by anubi on Monday November 24 2014, @07:41AM
Thanks for bringing up the monoatomic angle.
Thanks for the observations about the gases breaking down during the heat and metallic chemical reactions during welding. I considered N2 and CO2 relatively inert, but then I was not evaluating them in the presence of welding metals.
I do not know how much being monoatomic would affect the thermodynamic aspects, as all the gases I have worked with by and large came pretty close to ideal gas. I know there are correction factors to throw in if one wants to get within a couple of percent. I never have compressed anything but air just for compression, as most of the time I have compressed a gas, I was trying to get it to reject heat and change to a liquid, so none of my pressure changes were very extreme.
I have known I could make a stream of compressed air cool a chamber, but the amount of energy I had to burn in the compressor made this impractical for most things.
I know there is a lot of heat storage and transfer possible with phase changes - and I was not seeing that in this device.
Its not the electricity to heat conversion that I find tricky, rather its the other way around... I have found it hard as all getout to extract usable shaft work from differential temperatures. I can do it, but I run up against the Carnot limit pretty damn fast, and as of yet, I have found no way of getting around it.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
(Score: 2) by Immerman on Monday November 24 2014, @08:11PM
As I recall gasses mostly start departing dramatically from the ideal behavior near near the extremes - very low temperatures, high pressures, anywhere the molecules start getting jammed closer together or the chemical bonds start getting excited. Couldn't swear one way or the other about the cold-vacuum extreme. As for his system, at 12bar I'm not sure if he's pushing those extremes or not - but any deflection from the ideal gas law is a loss to entropy, and if he's trying to run an isentropic process even only moderate losses might be worth eliminating up front.
Something about the system bothers me as well, though I can't put my finger on it. Keep in mind though that this system has both a heat and pressure differential to work with - in fact it has to keep them perfectly balanced to avoid altering the entropy levels. When charging he's converting mild low-pressure air to hot, high-pressure air, while simultaneously converting mild high-pressure air to cold, low-pressure air. And vice-versa when discharging. Almost like he's managed to replace the "vertical" entropy-altering legs of the Carnot-cycle with a mechanical interlink, allowing the process to be made reversible.