Liquefied-air silos touted as enormo green 'leccy batteries A technology invented to use chilled air as a power source for engines has been put forward by Britain’s Institution of Mechanical Engineers as a possible solution for storing electricity generated by renewables, such as solar and wind power. One of the main criticisms levelled against renewable energy sources is their …
They are highly unlikely to achieve that 70% efficiency. It sounds like best case scenario under ideal conditions. But it doesn't matter. This is a solution looking for a problem. No matter how you slice it, renewable energy (aside from hydro-, and in some places geothermal) will never become load-bearing. It is simply too inefficient and expensive to maintain.
We're inevitably going to move to nuclear, even if some people will need to be dragged kicking and screaming. The only question is when - before we lose any remaining competitive advantage to China (and other emerging nations) or after. Right now China is building 25 nuclear reactors and has another 30-40 in the planning stages. For comparison, UK has a total of 18 nuclear reactors used for power generation. As labor cost gap narrows due to globalization, whoever can supply its industry with cheapest energy owns the future. Right now, it doesn't look like it's us.
A world-wide grid would minimise the need for storage of any kind, and maximise the benefit from baseload generation. Unfortunately, it's a long way off the roadmap for governments and utilities, since it would require strategic thinking, and getting along with the neighbours.
"Not if it was a high-voltage DC network. HVDC is suitable for long distance transmission, but not short distance."
Ummmmm, HVDC for long distance transmissions??? There is a reason Westinghouse/Tesla WON the AC v. DC battle you know! And one of those reasons is the inability to transport DC over any significant distances. 3 Phase AC links have much lower transport losses (Or why would EVERY single long distance link already in use be AC?)
Solar and wind will NEVER be a baseload power-supply. The ability to store energy does not a baseload make. A long enough "dry spell" (Several low wind, clouded days in succession and you still lose all power generation.) The idea behind a baseload is that it should be reliable. It should just work.
On top of that, I find the modern wind generator to be but ugly. Solar panels are not much better to look at. And to those about to scream about me wanting a nuclear plant in my back-yard. YES I would have no trouble having a single nuclear plant nearby. I find a well designed one easier on the eye than the eye-sores called wind-generators popping up everywhere.
"Ummmmm, HVDC for long distance transmissions??? There is a reason Westinghouse/Tesla WON the AC v. DC battle you know! And one of those reasons is the inability to transport DC over any significant distances. 3 Phase AC links have much lower transport losses (Or why would EVERY single long distance link already in use be AC?)"
A compelling and well written argument. Except most long distance links are DC. Especially where they go under the sea. Check it out on Wikipedia. :-)
(Nice username though.)
The reason why all long-distance links are HVDC is very simple:
Every single generating set in a linked AC system has to be exactly* in sync, as otherwise they end up consuming power instead of generating it.*
It would be incredibly complicated and extremely unreliable to try to keep all of mainland Europe in sync with each other, or even just keeping France in sync with the UK.
On top of that, once there's more than one link with enough geographic distance between them it becomes impossible due to speed-of-light delays.
So we use HVDC for these long-distance links between different Grids - that way we don't have to keep our generators running at exactly* the same speed and phase as the French.
Originally these really were big DC motors driving big AC generators (and vice-versa)!
- High-power silicon is now good enough for solid-state versions, which are much better as they can sync instantly and as well as being more efficient.
Icon for what happens if you don't sync the generators.
* Rather simplified.
@ imanidiot:
"Ummmmm, HVDC for long distance transmissions??? There is a reason Westinghouse/Tesla WON the AC v. DC battle you know! And one of those reasons is the inability to transport DC over any significant distances. 3 Phase AC links have much lower transport losses (Or why would EVERY single long distance link already in use be AC?)"
While it was certainly true in Teslas time that DC was unsuitable for long distance transmission, and AC was better, it's just not true now.
A simple search for power transmission will give you lots of information, and if you're interested in specific examples, you can search for "Pacific DC Intertie" which should get you info on one example which is over 800 miles long.
Using DC now with modern technology is better than AC which introduces all sorts of issues when tying disparate grids together.
The reason why AC won over DC in Edison's day was more to do with generation than transmission, plus issues with stepping up the voltage. You can transfer HV DC a lot more efficiently than HV AC. This is why most power lines from off shore wind farms are DC.
With modern power electronics it is far more efficient to convert fro AC to DC and back again. Similarly renewables such as wind farms are moving to DC generators so removing another inefficiency in the chain. World wide energy transmission is more an element of cost and politics than technical issues.
You are welcome to your opinion as to the beauty of wind, personally I find them quite elegant. Certainly I would prefer living next to a wind farm than the local coal powered station I do now.
"You are welcome to your opinion as to the beauty of wind, personally I find them quite elegant. "
It's the <26% duty cycle (for onshore wind) and the fact *something* (probably connected to a fossil fuel supply) that will have to take up the slack I find rather ugly.
Although I've heard their low frequency/high amplitude noise output is pretty irritating as well.
> Although I've heard their low frequency/high amplitude noise output is pretty irritating as well.
You've heard wrong.
You have to literally be standing right next to a modern windmill to hear anything at all. The older ones were pretty whiney, but the modern equivalents are practically silent.
That would have been a good argument 25 years ago, and it's one I've previously made myself ... but since then I've taken the trouble to familiarise myself with the more recent advances in voltage transformation and electrical transmission technology.
Long story short, AC is a good tech for driving synchronous motors, and ramping up power generated from low-voltage alternators to high voltage for long distance transmission, but when you take those two things out of the equation it is itself actually rather wasteful. Hence why very nearly all electrical devices that aren't synch motors or simple heating/lighting filaments internally run on DC.
Back in the day - especially Edison & Tesla's day - converting between LVDC and HVDC was a difficult and wasteful, if not flat-out impossible task, whereas doing so for AC required a lump of magnetised iron with a bunch of wires wrapped around it (and then, if you needed DC back out the other end, a liquid-mercury-and-spark rectifier and some kind of primitive capacitor). Nowadays, we have high power MOSFETs, IGBTs and the like which allow us to convert DC voltages much more easily and efficiently than hooking up a motor and a dynamo on the same shaft, or shedding most of a high supply voltage as heat through a high-ohm resistor.
This page may also be of some interest to you
http://en.wikipedia.org/wiki/High-voltage_direct_current
Oh, and also... coal generators break down just the same as anything else. As can the supply. By your standards, that precludes them from being a baseload generator as well.
There are very few seconds out of the year where the air over the whole UK is so still as to preclude wind generation, and very few hours per year between sunup and sundown where the sky is so dark you can't get at least SOME power out of a PV array. Even when it was chucking down with rain under gloomy skies recently the few-kW experimental installation at my workplace was still making 700w. Sure, that's not a great deal even vs its modest maximum, but it's something.
And who says we wouldn't retain a few traditional type power plants, able to be brought into service with a few hours' notice if the energy store was running down and we needed a backup?
"There are very few seconds out of the year where the air over the whole UK is so still as to preclude wind generation, "
If only that were true. In some quarters the capacity factor of onshore wind has been as low as 14% for three whole months. Given that there were some windy days, that's a whole bundle of seconds (amounting to weeks)when there was no useable wind power. And when you get a winter high pressure zone you'll find that there may be no useable wind across all of northern Europe, whilst electricity demand goes through the roof.
Regarding the PV output, I see yet more touching optimism on your part, but as a rule at these latitudes you'll get only 25% of summer output in January, and on any day stuff all output outside 8:30 and 17:00 local. So two thirds of the time PV isn't available because the sun is below the horizon or has poor azimuth, and for one third of the year the output is crap even when the sun is up. If you want to use solar it makes sense to move to Spain.
I'm afraid you're waving your ignorance around in a big way there. Fom a purely technical level, DC kicks AC's arse. Anything with AC behaves like a radio transmitter, and that saps power which you would rather be selling to your customers. DC simply doesn't. If you want to talk theory, there are reactive losses for AC (extra impedance due to capacitance and inductance) which just don't apply in DC-land.
There's a better reason why Westinghouse won the AC v. DC battle - and it's that if you don't have semiconductors, getting high-voltage DC back down to low-voltage DC is a seriously complicated procedure, and if you can't go high-voltage then you need much thicker cables. With AC though it's dead easy to use transformers to step voltages up and down, so back in the Westinghouse/Tesla days, it was AC all the way. But now we have these things called "transistors" and "diodes" which you may have heard of. In fact transformers are still more efficient than semiconductors, so local grids still use AC - but start pushing power over any real distance and AC gets proper f*cked from the extra losses in umpty-tum hundred miles of cable.
So since the 50s MOST long-distance links were HVDC, and since the 70s EVERY single long distance link was HVDC. Do yourself a favour and google "HVDC".
(PS. Yes, I did actually have a job at a place which designed and built HVDC equipment for national grids, once upon a time.)
FWIW I happen to agree with you on alternative sources and nuclear, although the fact that you can't rely on alternative sources isn't a complete disaster. If you've got a few days of storage lined up, you've got plenty of time to start ramping up those power stations which have been offline for the last month or two. All you need is to ensure that all the offline power stations can meet the nation demand if necessary. So it won't let you get away with fewer power stations, but it *will* let you cut their fuel bill pretty dramatically.
HVDC has much lower losses during transport than HVAC, which is why it's commonly used on long (400km+) runs and subsea cables. See http://en.wikipedia.org/wiki/High-voltage_direct_current
The issue at the start of the 20th century was that AC is easy to step up/down via transformers. This was particularly important in Tesla/Edison's day but addressable these days using large inverter systems. Edison was always interested in local generation in order to sell heat as well as electricity, but the lousy economies of having to build/run a small generating station every 2-3 miles is what finally killed off DC. Larger plants are far more efficient and hydro/geothermal resources are seldom close enough to where the demand is for Edison-style DC to work.
Railway traction supply systems commonly use DC or 15Hz AC for the same reason (reduction of trasmission losses). The tradeoff for low frequency AC is bigger transformers, but that's not an issue in most cases.
AC is still a win for local distribution or for lines where power needs to be transported in both directions (but modern electronics is making bidirectional DC links more feasible)
Aircraft use 400Hz to reduce transformer iron. it works for them, but such frequencies for long distance power distribution would have devastatingly poor efficiency.
Tesla beat Edison not because he used AC but because the use of AC meant that he could use higher voltage and therefore lower current. Until a few decades ago conversion to and from HVDC was difficult and expensive. Now, comparatively, it is neither. When Tesla was at the peak of his abilities there were no controllable high voltage valves, even when they did become available they were bulky, expensive, and fragile. ASEA started development in the 1930s but real systems weren't up and running (as far as I know) until the 1950s.
See https://en.wikipedia.org/wiki/High-voltage_direct_current for an overview. This shows a lot of DC interconnects in Europe and points out that the longest in the world is in China, just over 2000km.
I suppose at this point I should reveal that I work for ABB which makes these things (althoughin a related division). Of course I speak for myself not ABB, etc.
Speaking from first hand experience (ie, I have both a nuclear power plant AND a crap ton of windmills in my "back yard"), I have to agree that the nuclear plant is far less impactful on the aesthetic of the area. Windmills, when installed, have to be everywhere; every ridge of all of the surrounding hills/mountains (highly variable term based on the altitudes that you are used to) has to be covered in the windmills. If you happen to like the hills/mountains or the overall horizon, then, with windmills, you are out of luck.
Having lived next to two different nuclear plants, I can say; they need not be any more aesthetically unpleasant than any quirky architect's grand design.
"A world-wide grid would minimise the need for storage of any kind"
Do you have the first clue how much power is lost transmitting it across a state, let alone between countries?
"Unfortunately, it's a long way off the roadmap for governments and utilities, since it would require strategic thinking, and getting along with the neighbours."
Its a long way off the road map because it would require re-writing the laws of physics to make it work, not because governments don't want to talk!
Perhaps you could explain why we have high power DC interconnects between France and England, Norway and Denmark, etc. if the laws of physics make it unworkable. Yes transmission losses in low voltage high current AC lines are high which is why the electricity transmission industry has been building ever higher voltage transmission lines. Now that we have effective high voltage semiconductor switches we can use DC instead which dramatically reduces the losses and also enables networks of differing phase, frequency and impedance to be connected together.
Interconnecting national grids allows, for instance, solar power to be sold to areas where it is dark. And yes I am aware that all this needs a large investment and a higher degree of political stability than obtains in some areas but it requires no new technology, it can be implemented now. The technology involved is scalable and much of it can be built incrementally.
Well, maybe initially in 2 sections, Eurasia/Africa and America . The likely geographical routes between these 2 largest landmasses appear uneconomic for DC interconnect trading, due to very low population densities and massive distances in the Greenland/Baffin Island and Alaskan/ Eastern Siberia regions, though development of untapped hydro and wind potential in these regions might change even that. The rest is happening through local interconnects anyway regardless of preferred generation methods, and so long as there are localised economic benefits from export/import DC links between AC control regions no-one is going to stop this from happening. DC links already exist between the 3 US AC control regions, also across the Channel and North Sea, more are planned between UK, Iceland, Norway and Ireland etc.
There remain limits to the economic size of synchronised AC control regions - the US has three of these, with DC trading between them. Having larger synchronised AC regions reduces DC conversion losses, having smaller ones reduces the risk of geographically widespread cascade blackouts.
I'm not convinced extending and interconnecting grids will entirely eliminate the need for localised storage though, due to the limited capacity of the most cost effective interconnect capacity and routes, and losses due to long distance interconnections. Greater interconnection, however, is likely greatly to reduce the need for storage.
Very isolated islands will continue to have completely local grids and relatively expensive electricity due to the very high cost of undersea DC links.
"A storage mechanism to store excess generation until its needed is equally useful for nuclear."
Nuclear plants are by their nature "baseload" plants because they output continuous steady power. Unlike gas or renewable generators they're actually difficult to shut down.
>"Nuclear plants are by their nature "baseload" plants because they output continuous steady power."
Doesn't this mean an energy storage mechanism would be very useful for them too? Otherwise in a fully-nuclear energy economy you would have to dimension the nuclear capacity according to the peak consumption, and then would have overproduction most of the time.
Opponents of nuclear like to point out (at least over here) that because of the inflexibility of nuclear power plants, they cannot rid us of fossil energy plants and their CO2 emissions, because those are needed for responding to the varying load. An efficient energy storage system would counter this argument.
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because they output continuous steady power. Unlike gas or renewable generators they're actually difficult to shut down.» Well, «Charles 9», you obviously don't live here in Sweden, where nuclear power plants often seem to break down and/or be forced to run with reduced output just during the winter months, when need for power is at its peak. This variablity in output is particularly profitable for our power companies, as electricity from other sources, e g, their hydropower plants can be sold at drastically raised prices....
Henri
"Nuclear plants are by their nature "baseload" plants because they output continuous steady power. "
That is truly a great feature, if we were using the energy evenly spread over a 24 hour period. Unfortunately, 70% of our energy is used over a 12 hour period. The other 12 hours, nukes "pump" excess electricity into the ground. That combined with an average of 60% loss in transportation (official EDF figures) ...
Haven't you read the word "baseload" in the bit you copied. Do you not understand what baseload is. It means the base or minimum level at which power is forecast to be required 24/7.
It's obvious that we use more power in winter for heating than in summer and more during the day than during the night. Power stations can be adjusted to cope with these forecasts very easily. So no baseload electricity is pumped into the ground.
What might get pumped into the ground is the output from wind turbines spinning madly in a gale in the middle of the night.
"nukes "pump" excess electricity into the ground. That combined with an average of 60% loss in transportation (official EDF figures) ..."
Go on then, produce evidence that supports 60% transmission losses for nuclear power. I say that's crap, and that you should think more carefully before posting such nonsense.
UK electricity generated amounts to 29.5 MTOE (DECC aggregate everything to MTOE), and distribution losses and use amount to 4.5 MTOE, so that's 16% losses on average, mostly on the LV side which affects all sources equally.
Sure. But this storage mechanism could be used to adjust output according to demand, in situations where the "base-load" plants cannot match te inevitable fluctuations in demand. And since we're getting (some) wind/etc renewable power generation whether you like it or not, this kind of tech will at least help iron out their intrinsic variability.
"A storage mechanism to store excess generation until its needed is equally useful for nuclear."
No it isn't. A nuclear power station can provide a steady level of output and can be ramped up or down to adjust for changes in demand. A means to store excess power is therefore of only marginal use for nuclear because mostly it wont be generating excess. As the storage and retrieval process of power has inefficiencies, it is intrinsically worse than just getting the right amount of power output in the first place. Wind power cannot produce a steady level of output and only ever produces the right amount of power needed as one moment of intersection on the graph as it slides lower or higher that what is actually desired. Therefore a means to store excess generation of power is highly useful for Wind Power. Ergo, the mechanism is not equally useful for nuclear as it is for wind power (and other renewables to a greater or lesser extent). For nuclear, it is of marginal value (I don't say no value).
@Robbie The reason why all long-distance links are HVDC is very simple: Every single generating set in a linked AC system has to be exactly* in sync, as otherwise they end up consuming power instead of generating it.*
Utter nonsense I'm afraid. An electricity grid is self-synchronizing in the same way that two people pedalling a tandem are self-synchronizing. If something synchronous (generator or motor) gets even very slightly ahead, it will start supplying energy to the grid until it is back in synch. If it gets behind, it will start draining energy until it has once again attained the same speed as everything else. If the total power drain exceeds the amount of power going in, the frequency and voltage of the whole grid will droop, until regulators at individual power plants notice this and open valves to increase the flow of steam to the turbines. The regulation is totally decentralised. There's no single control centre, no master grid-regulation station that could be attacked by terrorists.
The only time there might be trouble is if a (synchronous AC) generating plant gets disconnected from the grid and has to be reconnected. This requires careful monitoring of both the frequency and phase of the plant to make sure that they both match the grid before the connection switch is thrown. Otherwise, there would be a massive surge that would blow "fuses" and probably break many other things.
As for HVDC, as other people have observed, technology has advanced since Tesla and Westinghouse's day. Transmission losses are reduced with HVDC, and HVDC to grid-AC conversion is no longer impossible or uneconomic. Long-distance HVDC has another large bonus. It is immune to the effects of solar storms (which increase as the length of the line increases). If a huge CME induces a DC current in a DC line, it either adds to or subtracts from the power being transmitted, but it doesn't appear as any sort of abnormality to the plant at the ends. When the same happens to a conventional AC line, the DC current cannot be transformed by the transformers, and instead becomes waste heat inside the transformers. If someone doesn't break the circuit fairly rapidly, the transformers catch fire. In other words, either we suffer a short-term blackout or a long-term blackout (possibly an end-of-civilisation blackout were all the safeties to fail). Had a Carrington event occurred in, say, the 1960s, this would have been a real possibility. Today, we know to watch our sun closely, and to cut the power to save the grid if it throws another big belch at us).
Errr - hate to point out the flaw in your argument. If we went 100% (or even close it it) nuclear there would be a huge need to store that excess power because it would have to be set up to meet peak power demands - which afaik are much much higher than the average.
Ergo Nuclear would benefit almost as much as Renewables from this technology.
"As labor cost gap narrows due to globalization, whoever can supply its industry with cheapest energy owns the future. Right now, it doesn't look like it's us."
This kind of them/us attitude has always bugged me. It's not a competition: no matter where people happen to live they have feelings and families same as everyone else. Fortunately the globalisation you mention will help make borders less relevant.
@stucs201
Storage mechanism is absolutely necessary for baseload renewable energy and unnecessary for nuclear. They are far from equally useful. Logically, your statement is false.
@Martin Budden
I'm sorry if the realist approach makes you uncomfortable, but us/them division is a natural product of evolving in competing tribes. It has aided the survival. While you may snobbishly consider yourself enlightened enough to dispense with such archaic nonsense, most people in the world aren't. Ignore their views at your own peril.
I agree, this reminds me of the TATA compressed air car. They were claiming ridiculous efficiencies when in fact the full cycle efficiency was in the single digits. Compressed air is a horrible energy storage medium. Pure gas is a little better, but in the end the thermal dynamic losses of the compression/decompression cycle render it useless for energy storage.
"but in the end the thermal dynamic losses of the compression/decompression cycle render it useless for energy storage."
I think they're talking about storing the bulk of the energy in a phase change in the fluid, rather than just compressing it. I can't understand why not choose a working fluid which doesn't need to be cooled so much first and keep it in a closed cycle, like propane in an empty gas field for example.
"Pure gas is a little better, but in the end the thermal dynamic losses of the compression/decompression cycle render it useless for energy storage."
You might like to read the article a little more carefully.
What is being proposed is liquifaction *not* compression.
"I agree, this reminds me of the TATA compressed air car. T"
Compressed air systems store energy by using work = change in volume x change in pressure.
Normally one is held constant (typically the fixed volume of the tank) and the change in pressure drives the pistons/turbines/whatever.
Compressing air makes it *hotter* which for a compressed air engine is *better*. As the air is used to drive an engine it gets *colder* possibly to the point it goes to liquid which is a *bad* thing in CA engines.
This system stores energy in a *phase* not a pressure change. Phase changes can store *huge* amounts of energy without ever rising stress in the tank (bigger power needs *much* higher peak pressure tanks while bigger liquid air tanks are relatively simple and its the dead weight they are carrying). Where the amount of pressure you get from your compressed air tank *falls* as the tank empties (and the heat you need to dump into *rises* the volume change of liquid air -> gaseous air remains *constant* (providing the warming temperature remains constant. The volume change from LOX to LO2 is roughly 1:700, contrast with a diesel engine of something like 1:50.
Phase change is the basis of *all* steam power plants. The amount of energy stored in the temperature rise of water (like the temperature fall of air) is *trivial* compared to the energy gained (or lost) in a phase change.
So it might sound like a compressed air engine to you except it isn't.
"renewable energy (aside from hydro-, and in some places geothermal) will never become load-bearing"
I'm not saying that renewables will ever rival nooclia, but this is a bit of a sweeping statement. The tech will no doubt advance. Who knows what the future will bring?
Anyway, I'm all for trying these clean energies. I'd rather see money 'wasted' on these than the trillions currently pumped into the military.
"The tech will no doubt advance."
Enough to alter day/night cycle, eh?
"I'd rather see money 'wasted' on these than the trillions currently pumped into the military."
Money pumped into military was instrumental in creating the Internet via which you made this post (military waste is a separate matter). Money pumped into renewables has (paradoxically) increased the price per kWh you pay to run your computer and allowed concrete companies, Chinese factories, and Al Gore to make some windfall profit. I'll take the military spending.
"No matter how you slice it, renewable energy (aside from hydro-, and in some places geothermal) will never become load-bearing. It is simply too inefficient and expensive to maintain...We're inevitably going to move to nuclear,"
Ready to throw your sabots into the wind turbines, I see!
Clearly, your mind is already made up, and no amount of innovation is going to change it.
You state as certainty what is clearly massively uncertain. Viable energy storage or new developments and increased efficiency could be around the corner, so I feel it's foolish to fix your thinking in such a way. Sure: You might be 100% right; but you don't leave much room for changing your mind if the situation changes.
The situation you're describing is the day/night cycle. Currently, solar energy is 4x as expensive to produce (including capital & fuel costs) as coal/gas/nuclear. The efficiency of most solar panels is ~15%. It would take four-fold increase in in efficiency just to get even with our current cost of generation for all other methods. But wait, we didn't account for the fact that the energy needs to be stored for the nighttime use. Even assuming this liquified air system's unrealistic 70% efficiencies, it would require solar cells to have 86% efficiency. That's very fortunate as it happens to be the Shockley–Queisser theoretical limit for solar cells with infinite layers. We've gained about 0.5%/year in solar cell efficiency since 1980. At these rates, we should be hitting the theoretical limit, oh say, in 2130. So, there you have it, in a best case scenario, you need 2100s solar cell technology to match 1800s coal technology and 1950s nuclear technology electricity generation cost. Do you agree with me that solar is useless?
Now as to wind. It should be noted that it's also subject to day/night cycles, but the variance of peak times in different locations make it a little more palatable. However, off-peak energy storage is not really the problem here anyway. Offshore wind generation is similar in cost to solar, but with the exception that wind turbines are already operating close to peak realistic efficiency (unless you have a way of eliminating friction as a force). It means that it will never become competitive with other energy sources.
Onshore wind is slightly better. In fact, according to Parsons Brinckerhoff study it's directly comparable to nuclear (8-11 vs 8-10.5p/kWh). That's with one small caveat. It didn't account for all the subsidies and tax breaks given to wind power. If it had, you would be looking at 1.5-2x the cost of coal/gas/nuclear. Note that economy of scale doesn't apply to wind. The windiest spots that are cheapest to develop get snatched up first. It means that wind power would actually get more expensive, not less, as it's scaled up. And that's before we take into account having to store excess peak power due to wind variability. It doesn't matter whether their efficiency is 25% or 70%. Wind will never become economical. And that's in the UK, which is one of the best countries to utilize wind in. What's everyone else supposed to do?
In conclusion, we both made up our minds. I did so based on current and projected figures and you based on a pipe dream that may happen around the corner. That's all fine and dandy, as long as the ruling class doesn't socialize the cost of that pipe dream. I, for one, don't see why I have to pay higher fees for energy, so that you can have a warm and fuzzy feeling generated by the marketing campaigns of environmental lobby.
"It would take four-fold increase in in efficiency just to get even with our current cost of generation for all other methods. "
And so what, its completely irrelevant. If you get a 4 fold increase in efficiency but it costs 8 time as much to make and run, then you are worse off. You need to reduce the unit cost to make the stuff economically viable, no more no less. So half as efficient at 1% of the cost and you would be more than good to go for example.
Low interest rates will also help, as then the up-front capital costs become easier to absorb, otherwise after about 25 years net present cost of fuel for a coal station is effectively zero, just like solar.
Oh, wind turbines are limited by the Betz Law, not by any considerations of friction, and again the price of energy has sfa. to do with the efficiency of the machine, ih has to do with how much it costs to buy, how much it costs to run, how long the machine will last, and how expensive it is to borrow money. (and how much it costs to get rid of the stuff afterwards, but I believe it is normal to ignore this when you look at nuclear :P, or just build an extra reactor or two to cover the disposal costs if you live in Britain! ).
@dkjd
You're absolutely right that efficiency is not the sole factor, but I've never claimed it to be. It's simply the one that's ostensibly easiest to modify and the one that people look up to future technology(tm) to solve. It would've been nice if you provided some data to support the assertion that price decreases in materials would make it all better. But the truth is, there isn't any. I don't have any data on wind, but its hard to imagine construction costs of turbines going down significantly. Solar, on the other hand, has been approaching an asymptote in terms of price per W. See this: http://blogs.scientificamerican.com/media/inline/blog/Image/naam-solar-moore_s-law-1.jpg
Betz law limit is ~60%. However, most turbines get only 30% efficiency for energy extraction (assuming constant wind). Most of that loss is due to friction. You can't do anything with Betz law, but friction can potentially be addressed (though not at all effectively).
Nuclear companies are required to amortize the cost of decommission of their stations and set up special funds for that purpose into which they pay from operating proceeds. All nuclear electricity cost estimates already account for decommission. Nice straw man though.
To be competitive, soalr doesn't need to be four times more efficient than it is now, the ration of efficiency to cost needs to be four times as great. It is much more likely that this will be obtained by a combination of small increases in efficiency, and large reduction in the cost of manufacturing the materials and economies of scale cut in, and the technologies continue to mature. In reality, this is what we are already seeing.
So yes, solar is currently more expensive than other forms of generation, but if you were to draw a graph of cost per kWh over time for each type of power generation, you would see that the cost of solar is creeping down, whilst gas and coal are increasing as the fuels become more expensive to extract. There will come a point where those lines cross, and solar will be the economic choice.
"..if you were to draw a graph of cost per kWh over time for each type of power generation, you would see that the cost of solar is creeping down, whilst gas and coal are increasing as the fuels become more expensive to extract. There will come a point where those lines cross, and solar will be the economic choice..."
I don't know what kind of world you inhabit, but in ours the cost of gas is plummeting. Here are the US FPO figures (dollars per therm) for the last few years:
2009 $1.2835
2010 $0.8420
2011 $0.8126
2012 $0.6919
That's a 46% drop. Coal is also about as cheap as a fuel can get. With modern technology the fuels are getting CHEAPER to extract, as Julian Simon's cornucopia theory predicts.
Being 100% wrong in this assertion rather ruins your argument, doesn't it?
"cost of gas is plummeting"
That's not the total cost of Gas. The total cost is the cost of purchasing gas plus all the externalities: pollution, floods, freaky weather, higher insurance bills due to more storms and more freaky weather and uninsured losses as well, and more expensive food. Just because the fracking gas industry hasn't been sent the proper bill yet, don't misquote their costs of production.
Appropriate handle, Mr Dodgy Geezer.
It doesn't really make a lot of sense to compare the efficiency of a thermal plant to solar.
If you are saying solar is useless because it's total free energy in / electrical out is less than the Carnot efficiency of burning coal then you should also include the solar energy to make the coal in the first place.
On the other hand saying it's useless because it's expensive and unreliable is perfectly true
I don't see how the efficiency of solar panels really matters in the argument. If you take the fact that you can install a 3.8 kw peak system in a favourable position and this will produce about 3500 kw hours per year for about £7500. Take that cost and add £1500 maintenance and then the cost per kw over 25 years is going to be about 10p per kwh, so consumer grid parity has been reached, and this does not take into consideration the continued inflation of fuel and electricity prices.
You fail to point out that nuclear received massive subsidies, and we still haven't got a viable plan of what to do with the waste.
@Pat M
If you can make the solar cells significantly cheaper, efficiency matters less, you just cover a larger area, but its extremely unlikely there will be significantly cheaper solar cells without a major tech breakthrough (see graph in my previous post). Until then, efficiency is the metric for solar that's most likely to budge and, considering how it fares and the likely projection, investing in solar is pointless (aside from research).
As to your math, it's wrong. You're comparing solar cost in point of delivery with one in point of production. 60% of energy is wasted in transport and other inefficiencies. Corporate administration and profits for investors require an overhead. Hence you get 3-4x the cost of nuclear/gas/coal. Solar does make sense for individual use by some people. It's just completely useless as a national policy or for any significant amount of energy in the grid.
"60% of energy is wasted in transport and other inefficiencies"
Citation needed.
Losses between power station electrical output and end user are typically less than 10%, most of which is in the parts of the distribution network close to the customer, so there is little advantage from this point of view in moving from centralised GW-scale generation to distributed MW-scale generation (though such an approach may have other benefits). Ref: Mackay and others.
I happily agree that in a typical thermal power station there are lots of inevitable losses which massively outweigh the "transport" losses.
"Right now China is building 25 nuclear reactors and has another 30-40 in the planning stages. For comparison, UK has a total of 18 nuclear reactors used for power generation."
Right now, China has a population of 1.3bn, is a huge country with a rapidly expanding* economy. For comparison, the UK has a population of 63 million, is a tiny island and has an economy which is in the shitter.
Also, for comparision, China has an area of 9.6M million square kilometres compared to the UK's 250,000 and a population of 1.3 billion compared to our 60 million. I don't thinka a comparison of the number of nuclear reactors each country has has anything to say about competetiveness.
...would be simpler, cheaper and likely more efficient. Oh, and that trick has been done before in some rather special circumstances. The difference here is that we are talking about trying it everywhere we intend to generate power on an intermittent basis. Water running downhill could and would even out the output. Now, who wants to volunteer their scenery for obstruction by not just windmillls, but water towers as well? Well out to sea is no problem, save that you still have to get the generated current to market with so little waste as to keep it profitable. If I were forced to bet on something like this, I would argue the merits of flow batteires.
http://www.vrb.unsw.edu.au/
Pumped storage hydro-electricity has an efficiency of about 70%. You run electric pumps (off peak) using your excess baseline power and pump water into an elevated reservoir. During peak time the water runs back down through the same pumps which become generators through the magic of, well, through no magic at all.
There are two of these in Scotland. The Soviets built one in Lithuania back in the olden days.
Now, if you put in some windmills to run a separate set of pumps, you could have renewable energy rather than baseline energy doing the filling. The reservoir becomes your energy storage "battery" and voila! -renewable energy is practical and efficient and you've only had to dam and flood all the glens in the highlands to keep the lights on in London. Who could possibly object to that?
The problem with pumped storage is one of scale. Atm, in the UK the pumped storage is used to deal with short term outages in base load supply, and to provide 'instant' extra capacity at peak times. It's not sufficient to act as a battery for renewables. This means we'd have to find sites that have sufficient area to be able to provide longer term (a period of one or two weeks perhaps) storage. In the UK they are few and far between and would be costly to construct, not to mention the planning issues if the best sites happen to be in the national parks.
Nope, it won't fly I'm afraid. How about flooding old mine workings with water and then heating the water using 'renewables' for later recovery to provide heating for homes and businesses, similar to ground source heat pump?
The problem with pumping water up hill is energy density - you need to move a lot of water a long way to store a lot of energy, and if you want to buffer *power* then you need to be doing it pretty fast too. Dinorwig uses two largeish lakes and an entire mountain to house the infrastructure, and it's still only just tickling the demand peaks in a relatively small, relatively energy-efficient country. Not really an option for places like the US, especially somewhere like Kansas where mountains are a bit scarce.
Like you say, flow batteries seem a better bet. More complicated, sure, but you're not dependant on having a spare mountain that you can hollow out.
Compressed air has horrible efficiency because of the dynamic range of pressure.
Using liquified air reduces the problem with varying pressure, but the thermodynamic efficiency is still very low.
If you compress the air to liquify it, you need to get rid of lots of low-grade heat. It's hard to extract the energy from that heat without making the compressor work harder.
You have the problem in reverse when you let the liquid boil -- you have to keep putting in heat. You might try to recover energy from the temperature difference, but you need either a very large plant or lots of time.
Besides the giant heat exchangers, you also need massive pressure tanks for this scheme. A failure will result in a cryogenic liquid spill. The cleanup will be easy, but most equipment it touches will need to be scrapped and the humans buried. Not everything that goes wrong can be fixed with a wrench.
"If you compress the air to liquify it, you need to get rid of lots of low-grade heat...."
They will use "gravel" (like a reverse storage heater), that has been previously cooled by the discharging gas overnight, to help the chilling process.
"You have the problem in reverse when you let the liquid boil -- you have to keep putting in heat."
That's why the suggestion is to stick it next to a standard generating station, which by the very nature of the way they work, generates a shit load of excessive heat.
FFS people, it's not "Everything has to be made by windmills or everything has to be using combustion, the two can, as hard as it may seem, be used together"
And by the reuse / storage of excess energy is nothing new, Hydroelectric plants have been using it for ages, flow downstream during day, pump back up overnight.
"That's why the suggestion is to stick it next to a standard generating station, which by the very nature of the way they work, generates a shit load of excessive heat."
Lovely idea, but CCGT's don't generate that much useable waste heat, because the "combined cycle" of the name is all about reusing high grade waste heat. That leaves the older thermal (largely coal) plant that does waste a lot of heat, some of which will close before 2015 under EU diktats, and the remaining plant (Drax, Ratcliffe, Longannet etc will all probably close within a decade to fifteen years max.
Fifteen years might sound good, but the government's carbon floor will probably make these remaing plants uneconomic, added to which large scale liquified air storage couldn't be built out in less than about a decade due to the scale and complexity.
There was a recent press release from Siemens trumpeting that their latest CCGT had broken the 60% barrier, so state-of-the-art is a little under 40% of waste heat going up the chimney. Isn't that plenty? And just as "wate coolness" could be stored in gravel, so could waste warmth.
I agree the overall thermodynamic efficiency of liquid air energy storage won't ever be high, but it looks to me as if a lot of the "wastage" can be made up out of low-grade heat that's going to be wasted anyway.
If the liquid air storage plant were sited alongside some large factory that both emitted much waste heat AND needed air-conditioning, things might get better still (scrap the electrical air-conditioning, and just pipe the cold air into the factory).
Still wonder why things have gone quiet on the big Vanadium redox flow-battery storage front. That looked like a pretty efficient way to store electricity, albeit one that needed Vanadium by the kilotonne.
"their latest CCGT had broken the 60% barrier, so state-of-the-art is a little under 40% of waste heat going up the chimney. Isn't that plenty?"
It might help, but the energy density of low grade heat gas is obviously low, and heat transfer is slow. So although you can use low grade heat to regasify liquids, it is generally slow and inefficient for demand shifting and peak lopping plant.
You certainly can do it - this is already being done in part at the Grain CCGT in Kent, where a CCGT has been built next to the Grain LNG plant and that helps by raising the CCGT (equivalent) efficiency to 72%, on the basis of avoided heating gas used by the LNG regasifiers. That might sound good, but when you look at the energy still wasted in LNG liquification/regasification you'll find that about 35% of the original energy content of the gas is required for the process, so the gas cycle for LNG is actually less thermally efficient than an old school coal fired power station, before the 30-40% losses in CCGT generation.
But the key issue is timing. In the Grain example, it takes around 12 hours to unload a 140,000 m3 vessel (probably a representative volume for a liquified air energy storage plant). The whole point of the mooted liquified air is time-shift, and that means that you need to be able to regasify the air quickly and on demand, and taking 12 hours using low grade heat isn't quick.
"Lovely idea, but CCGT's don't generate that much useable waste heat, because the "combined cycle" of the name is all about reusing high grade waste heat. That leaves the older thermal (largely coal) plant that does waste a lot of heat, some of which will close before 2015 under EU diktats, and the remaining plant (Drax, Ratcliffe, Longannet etc will all probably close within a decade to fifteen years max."
Or park it next to a nuke plant. They're only 35% thermally efficient at best.
'Tis better than dumping all that excess heat into rivers (As EDF currently do)
Couldn't they put the waste heat from compression into gravel beds, then use it to boil the air when they want the energy back?
I'd imaging some heat exchanger system would be needed, pouring liquid air onto hot gravel would be a bitch to seal off to get any pressure out.
The full cycle efficiency is apparently "up to" about 30%
The "70%" claim was if you use the heat output of another plant to boil the liquified air more rapidly - in other words, if you dump yet more energy into the system you'll convert some of the extra into electricity - obvious to anyone with a passing knowledge of heat engines.
They don't appear to be counting that extra energy as being energy.
Alternatively, you could use that heat to do some other useful work, or not waste it in the first place - as most UK industrial plant already does whenever practical.
For example, heating the office areas a'la CHP.
On top of that, the waste heat that remains is not controllable! If a slab of steel needs cooling, it needs cooling now, at specific rate, not later when the Grid needs some of the energy stored in your LN2 tank.
This is snake oil, which is why I'm shocked that the IMechE even mentioned it, and I'm rather glad I'm no longer a member
"Alternatively, you could use that heat to do some other useful work, or not waste it in the first place - as most UK industrial plant already does whenever practical. For example, heating the office areas a'la CHP."
A sound objective (ignoring the thermodynamic impracticalities others have already noted), but remember this is about storing energy when it is available, not wanted. So the chances that any waste heat could be usefully deployed are small (and otherwise we could use the renewable output at the time it was generated without storing it).
First we need a source of heat. In this example I will use a large (10MW) data centre providing air at 25°C (http://en.wikipedia.org/wiki/Data_centre#Environmental_control). The article says the liquid air is at -190°C. If we use the most efficient possible theoretical engine the maximum efficiency is 1-(Tcold/Thot) with temperatures in Kelvin 1-(273-190)/(273+25) = 0.72. Have we found that 70% efficiency figure? I hope not because this is the efficiency of turning 10MW of waste heat into mechanical energy. So we are looking at 7.2MW of mechanical energy and 2.8MW dumped into the source of cold. If we assume mechanical to electrical efficiency of 80%, we are getting 5.8MW of electricity.
Now lets see how fast we are vapourising liquid air (numbers from wakipedia):
Latent heat of vapourisation: Nitrogen 5.56 kJ/mol Oxygen 6.82 kJ/mol
Molecular Weight: Nitrogen 28g/mol Oxygen 32g/mol
Specific heat of vapourisation: Nitrogen 198J/Kg Oxygen 213J/Kg
Composition of air without water and CO2: Nitrogen 78.8%, Oxygen 21.2%
Composition by weight: Nitrogen 76.6%, Oxygen 23.4%
Specific heat of vapourisation for air: 202J/Kg.
Density of air: 870 kg/m³
Volumetric heat: 176 kJ/m³
This means that the 2.8MW dumped into the liquid air vapourises 16 cubic meters per second. (An olympic swimming pool every 2½ minutes). Lets pretend liquid air is £0.1/kg in bulk (I found bulk liquid nitrogen for $0.06/litre). That makes £0.86 / kWH. If only all green energy schemes were as practical.
The point of this is it's for energy storage, not generation. Comparing it to nuclear is the wrong way to look at it, you should be comparing it to pumped storage, flywheels, hydrogen or batteries. Yes the efficiency is low but presumably the reason you're storing the energy in the first place is because it's excess energy - ie otherwise it would be lost. So long as it's more efficient (overall, ie including build and maintenance) than 0% you're going to come out ahead.
Ultimately I think nuclear is the way to go, particularly in the UK, but not having all your eggs in one basket is a good thing, so we need to invest in wind too and this is going to help that along.
Energy stored at Dinorwig: 3.2x10¹³J
Volume of Marchlyn Mawr: 6700000m³
Maximum power output: 1.8GW.
Efficiency: 75%
Imagine a liquid air storage facility built according to the description:
When it is windy, air gets pulled in through some gravel. The surface of the gravel is ambient temperature. As you get lower, the temperature falls. At some depth (the boundary) the temperature is -190°C. Below the boundary, the temperature remains at -190°C to the bottom of the gravel pit. This gives you a source of gaseous air almost at boiling point, but taking this air lowers the level of the boundary. When the boundary reaches the bottom of the gravel pit, you have reached the limit of its capacity. When it is not windy, you take air that was boiled in a turbine and push it into the bottom of the gravel pit. This raises the boundary layer and restores the system back to its initial state.
When it is windy, you use a heat pump to pump energy out of your cold air to liquefy it. The heat you pump out of the cold air goes into the atmosphere. The atmosphere is the place where the energy is actually stored, but because it is so big you will not be able to measure the increase in temperature. When it is not windy, you use heat from the atmosphere (or preferably waste heat from a power station of data centre) to boil the liquid air and drive a turbine which spins a generator.
Lets start by matching the maximum power output of Dinorwig: 1.6GW electrical. If the losses at Dinorwig are split equally between the pumps and the generators, that makes the generators 87% efficient, so to get 1.6GW electrical, we need 1.84GW mechanical. The maximum possible efficiency of converting heat to mechanical energy is: 1-(Tcold/Thot). Using -190°C and +25°C gives an efficiency of 72% so we need 2.55GW thermal from the atmosphere. There aren't any data centres that big. For that much heat, you need all the waste heat from a big nuclear reactor. If you do not have one handy, Thot will be less than 25°C, the efficiency falls and you need even more thermal energy from the atmosphere (and more liquid air) to get 1.84GW mechanical out of your turbine.
We just got 2.55GW of waste heat for free from our nuclear power station, but only put out 1.84GW mechanical from the turbine. The rest: 0.71GW boils liquid air. If you run out of liquid air, Tcold gets bigger, the efficiency falls and you need more nuclear power stations to get enough waste heat. Last time we calculated boiling liquid air requires 202J/kg, so we need 3500000 kg/second of liquid air. That is 4000m³ per second. Dinorwig can run full power for over 4.9 hours. The vacuum flask needed to store this liquid air is over ten times the volume of Marchlyn Mawr (the upper reservoir for Dinorwig).
The boiled air from our turbine is still cold, and we have to store that cold in a gravel pit ready for the recharge cycle. The cold air gets heated at constant pressure from -190°C to ambient (say 10°C) by the gravel. Wakapedia tells us the constant pressure specific heat capacity of air is 29.07J/mol/K (a mol of air is about 28.8g). I could not find the specific heat capacity of gravel, but it should be similar to that of glass: 840J/kg/K. The 3500000 kg/second of boiling air will cool 4060000 kg/second of glass. The density of glass is about 3700kg/m³, but we need space for the air to get through, so call it 2.7kg/m³. That is a mild 1500m³/second. To last as long as Dinorwig we need a thermally insulated gravel pit four times the volume of Marchlyn Mawr.
But we have not finished yet. We still have to do the recharge cycle. We need to take cold gaseous air and use electricity to pump heat out of it so it liquefies. Pumping heat from a cold place (-190°C) to a hot place (atmosphere say 10°C) requires at least (Thot-Tcold)/Tcold times as much mechanical energy as the thermal energy you want to pump. We only need 3x10¹³J of mechanical energy (yes less than the 3.2x10¹³J we are storing. We get the difference from the waste heat from our nuclear reactor). Assuming the electric motors are 87% efficient we need 3.45x10¹³J of electrical energy to refill the vacuum flask with liquid air.
To match the capacity of Dinorwig, a liquid air energy storage facility would need a volume 14 times the size of Dinorwig's upper reservoir and the waste heat from a large nuclear power station. The best possible efficiency is 92.5% (assuming the best theoretically possible heat pumps) compared to Dinorwig's 75% (with real world turbines). Although Dinorwig is big, it is only there to handle fluctuations in demand. Its peak power is nothing like the base load. Most winters, the wind is calm over the whole of Europe for 5 days - not 5 hours. If your energy plan is mostly windmills then you have to convince people that Scotland or Wales is mostly pumped storage - or you could cover England with vacuum flasks and gravel pits.
And the inventor has already powered a car using this technology, for all the naysayers on here why not invent your own free energy source?
http://www.airproducts.com/industries/Energy/Power/Power-Technologies/product-list/liquid-air-energy-storage-laes-power-technologies.aspx?itemId=7D677622F27440B18EC9F6D33CC19C5E
http://www.smartplanet.com/blog/bulletin/the-latest-renewable-energy-liquid-air/1505
Well done, you've managed to find sister articles reporting on (or the sources for) the exact same news. What was the point?
Also, air powered cars ... hahahaha.
OK, go find me one, show me exactly how much energy is required to fill it up, and I'll happily drive it for a day and see how far I get on the tank. And how fast it goes.
So far any demonstrated air car has been terribly inefficient, and despite being based on a small lightweight frame (usually a recycled GWiz or Aixam "glider"), has had performance and range that a typical cheap battery-electric would consider embarrassing.
It has the potential to be far simpler, cheaper, more reliable and above all far cleaner than battery storage, if the engineering is absolutely top-notch, but right now it's streets behind. The only reason it's been considered by the national grid is that they're desperate, and buying the necessary battery storage for such a task would be insanely expensive if not impossible.
Firstly, calling this an "energy storage" is a misnomer. The energy is not stored but discarded to the environment in the form of waste heat (as liquefaction is exothermic). New energy is then needed to extract work from the stored liquid gas.
In itself it does not mean it's a bad idea because if there is a source of heat which can be used to regasify the liquid and which otherwise would be completely wasted anyway, then why not use this method? However, I think that means that the real efficiency of the system would be even lower than thought. But, again, if it can be used economically - why not?
But, I would argue that this, as any other method of smoothing power generation levels, would still work best if there will be NO wind power in the grid and the liquifaction would use the off-peak baseload and not the unpredictable and fluctuating renewables.
Any operator of this liquefaction/regas plant will want predictable and manageable stock production rates, they would want to know how much stock they can release back into generation without depleting the storage and upsetting their heat providers (who would presumably be some kind of industrial facilities who in turn will want to know when their extra heat-sink will be available and how stable it will be in order to plan their own production).
If such plant is going to be connected to a specific wind farm, the unpredictability will make things inefficient. Which defeats the whole purpose of the exercise. In other words, as a Russian saying goes, you can't make a candy out of cr*p.
P.S. Congratulations, BBC, on achieving a new scientific low - gravel that "stores coolness"!
Find a bay, stick a dam across one end of it, pump water out, let water flow back in.
With a bit of imagination entire estuaries could be used. Indeed the bulk of the proposed Severn barrage could be pumped storage rather than a simple tidal flow generator.
There's enormous amounts of space this kind of storage could be put in in the UK.
Incidentally nuclear needs storage as well, so that fluctuating loads can be accommodated. Not just wind.
Ah ok, so as long as the estuary was a marine desert with little marine life and only a few migratory birds to worry about, and the tidal system wasn't entirely stopped but merely attenuated, this would be ok?
Because that's what was proposed for the Severn barrage.
We simply need to build more mountains.
Most of the nice mountains aren't where anybody wants to live (Wales or Scotland) while the majority of the population live in SE England without so much as a decent hill.
If we were to simply move Snowdonia to the Thames estuary we would provide lots of pumped storage, recreational activities and get rid of Essex in one simple operation - I commend this proposal to the house.
Whilst any effort to get rid of Essex is to be applauded, moving mountains is a more challenging endeavour than building a few dams.
The Thames would make a good pumped storage facility as well and to some extent has already been dammed. Would need a full flush to remove the turds every so often mind.
Maybe we are.
Now, given that the output of a network of nuclear stations is largely inflexible and thus constant (for reasons of physics and metallurgy and economics) but demand varies significantly, how is that mismatch (which is currently tens of GW between peak and offpeak on a daily basis in the UK, [1]) going to be managed?
Pumped storage in the UK has gone about as far as it can, a few GW for a few hours before the reservoirs empty.
A bidirectional HVDC link from here to Norway (transmission losses: near negligible) might add a few more GW for rather longer. The undersea stuff is tried and tested, there's already a gas pipeline.
Mackay (you know who he is, right?) has speculated that a fleet of a few tens of thousands of electric vehicles across the UK, each contributing a few kW at peak time and recharging at off peak, would be a useful addition.
No one technology is going to fix this. The gas liquefaction idea sounds like it ought to be worth looking at some big industrial customers (to do local peak lopping) even if it isn't a panacea.
Mackay and others will confirm that transmission losses between power station generator output and consumer are maybe 10% or less, most of which is in the lower voltage (close to customer) side of things. That's in part because the 400kV side of things, and the associated transformers, are actually quite efficient. But over long distances and especially underwater, HVDC is better, especially with modern power electronics.
[1] http://www.gridwatch.templar.co.uk/
Stuff like Magnesium Oxide
http://en.wikipedia.org/wiki/Magnesium_oxide
can be heated to 3100K. That is about 27 times more heat than boiling water. So, heat the MgO by excess electricity (using Wolfram filaments)
http://en.wikipedia.org/wiki/Tungsten
During the night or when all the ladies turn on their cooking ovens, pipe helium (or another noble gas) through the MgO (using Tungsten tubing) and drive gas turbines. Cool down the helium using water so that it can be recycled for the process.
The Carnot Efficiency could be up to 1 - 350K/3100K = ca 90%.
Energy capacity is 873,6 J/(kg·K), which means 1kg would store about 2700K*873j/kg*K = 2,3MJ/kg. That means storage density would be 1/15th of Diesel/Petrol. Which is impressive compared to hydro.
Of course the MgO must be properly isolated or it will quickly lose the heat.
Can someone tell me why we would go for cooling, compressing and liquefying air using the excess renewable load (presumably some point in the far future where we actually have more renewable generation than we do baseline consumption), to be dealt with and stored at some massive central facility ...
... rather than just using the same energy to produce hydrogen (and increased atmospheric O2) from water?
Sure you don't want a huge store of THAT as a potential target, but... lots of smaller facilities, maybe?
Then run it back through a fuel cell to produce water and electricity as required.
A certain amount - or just whatever exceeded the facility's storage limits - could then be shipped out and sold to run private cars and other things that can be hydrogen-fuelled.
If set up to use sea water, it could even function as a desalination and mineral-production plant.
Another idea: use the excess power to convert atmospheric CO2 back to oxygen and elemental carbon, perhaps locked in some kind of synthetic sugar or starch type compound by the addition of water (and nitrogen to make synthetic proteins?). Sort of like mechanical trees, biting into our carbon footprint even if it's not by dint of further reducing the amount of fossil fuels being burnt.
OK, you don't get to re-use that generated energy later, but if we get to a point where we have enough renewables to seriously NEED a storage facility, maybe the focus will already be switching from "reducing the amount of CO2 we're generating" to "mopping up the CO2 we've already shoved into the air".
...in Germany there are already times of excess renewable energy generation, due to massive subsidies for solar panels and windmills. Think of a summer day or a quite windy day. Hydro storage facilities are PAID to consume electricity on these days, as energy companies must accept almost all renewable electricity produced. Later (during the night; usage peaks etc) they can sell electricity for top euros.
Regarding H2 and biomass fuels, it is always about Economics. There are almost infinite ways of storing energy; finding economic ways of doing it are the challenge. H2 electrolysis is one of the economically worst ways of storing energy, as electrolysis is an electrochemical process which consumes expensive materials. Fuel cells aren't cheap either. All commercial H2 is currently made out of CH4 steam-cracking. Which of course generates lots of CO2.
Politicos are scammers and that is why they don't demand hydro storage capacity buildout or batteries with each solar panel and each windmill. Also, most of them are lawyers. Any more explanations required ?
"Can someone tell me why ... rather than just using the same energy to produce hydrogen (and increased atmospheric O2) from water?"
Yes. The reason we're not going for hydrogen is for two mains reasons.
1. There isn't the infrastructure to use it properly - to store, transport, dispense and combust. If you could overcome that (which you can, but at significant cost), then you come back to the second reason we don't do it:
2. The efficiency of an industrial scale electrolyser is not too bad (say 70%), but that's saying that you lose a third of your input up front, before your compression and decompression losses, and subsquent combustion effeciency. To store any worthwhile volume of hydrogen for power generation or transport purposes you'd be looking at liquid storage, so the electrolyser becomes an extra layer of inefficiency that a pure liquified air system doesn't have.
"A nuclear power station can provide a steady level of output and can be ramped up or down to adjust for changes in demand"
Citation needed.
Show me some evidence that it is anything more than a theoretical possibility and I will be astounded (occasionally it happens).
There is no way they can follow the daily cycle, though the seasonal cycle might be a bit easier.
"Citation needed."
Stitch this:
http://www.oecd-nea.org/nea-news/2011/29-2/nea-news-29-2-load-following-e.pdf
But you could have found it if you'd looked. I know this goes on 'cos I work for one of the companies concerned, but I found the linked resource on a fabulous but little known site called "Google" that you might want to check out.
I'm not surprised you work for one of the companies involved. Actually I had seen (and forgotten) that paper before. I prefer my papers peer reviewed but on this subject that's hard to find. Obviously it's good to see a proof of concept, though obviously there's a world of difference between occasional downrating, and long term daily cycling over decades. Apart from anything else, routine repairs to the metalwork and plumbing on the hot end of a nuclear station aren't quite as simple as they are on the fossil fired equivalent.
Anyway, now take a look at how the French nuclear capacity actually routinely operates [1], rather than a few short experiments. See demand vary. See nuclear output flat. Now there may be good reasons for that, but if it's really so trivial to load-follow on a nuke, then why not do it routinely?
So, as you said, "stitch that".
[1] http://www.rte-france.com/en/sustainable-development/managing-our-use-of-electricity/eco2mix-real-time-demand-production-and-co2-content-of-the-french-electricity#mixEnergetique
Looking at the 2nd graph I note the biggest shift in production comes from "Hydraulique" which I presume would include the rhone barrage as well as the rest of the French Hydroelectric schemes.
Occam's razor suggests use the *simplest* to control system rather than the most complex.
IOW, tuning nuclear plants aren't as necessary when you have alternate plants that are easier to tune, like hydroelectric plants that are very easy to adjust (via their sluice gates).
Another way would be to use a small number of natural gas turbines (many of which are already set up for surge capacity). Sure it's a fossil fuel but only as a secondary source, which reduces its consumption and side effects.
This comments section has made me sad :(
"A storage mechanism to store excess generation until its needed is equally useful for nuclear."
13 Upvotes / 3 Downvotes
Is critical thinking getting old fashioned? A couple of other people later on have got it right.
Nuclear can easily produce most electricity for a country (see France at around 85-90% Nuclear), Let's say we have to just dump 50% of it 50% of the time (which doesn't happen, it can be used in Industry when it's cheaper). That still gives us 75% efficiency WITHOUT energy storage. This energy is on a par with coal with carbon capture price wise.
Let's go back to renewables. It's very rare that you're producing what you need, you're almost always generating too much or too little. If you're using energy storage 90% of the time and that storage is 50% efficient (very high), you're 55% efficient WITH energy storage and a complete joke without it. Renewables are way more expensive than nuclear without this energy storage, let alone with it, that's why your energy bills are going up.
So the above should make it perfectly clear. Energy storage is of negligible importance to Nuclear and absolutely critical for using renewables as a base load.
There's a horrifying lack of awareness as to the limitations of renewable power. The first 20% is the easy stuff, when you start going beyond that you start hitting real problems.
Quick question: where are you going to dump those tens of GW of surplus nuclear energy?
In recent years the French have had unplanned shutdowns of nuclear generation during exceptionally warm weather, because the power station cooling couldn't cope. Now you want to add more heat into rivers and lakes? The sea might cope (according to Liewis anyway).
"Quick question: where are you going to dump those tens of GW of surplus nuclear energy?
In recent years the French have had unplanned shutdowns of nuclear generation during exceptionally warm weather, because the power station cooling couldn't cope. Now you want to add more heat into rivers and lakes? The sea might cope (according to Liewis anyway)."
That's not exactly true. Shutdowns weren't because the plants couldn't cope, it was because their coolant water was coming out into rivers was getting too high for environmental concerns due to very hot weather. Nothing to do with plant operation. Warm water has a lower oxygen solubility.
Where to dump the power? Anywhere you like, it's on an electrical grid. There are plenty of industries like aluminium production (done through electrolysis requiring massive power use) that can use predictable cheap power that this would produce.
"Where to dump the power? Anywhere you like, it's on an electrical grid. "
And the electrical grid can suddenly and at no cost find homes for GW of use in places which didn't previously use much electricity at all?
And do you know how much electricity an aluminium smelter actually uses ie how many of them you'd need to dump 10GW of surplus electricity? [There used to be a smelter and a Magnox (?) at Wylfa on Anglesey, where the Chinese and most others have pulled out of the replacement nuclear station bid].
And what are the smelters (or whatever) supposed to do when the grid isn't paying them to use electricity? Where is the market for their aluminium, or their supply of the raw materials?
Go on, find me a realistic 10GW worth of industrial electricity usage (that's roughly what the UK would need) that can sensibly absorb surplus energy on demand and still make a viable business including the times when the subsidised electricity isn't available.
It'd make more far more sense in a joined-up nuclear-centric energy picture to pay people to drive battery-electric vehicles (not just cars but round-town delivery fleets etc) and use their batteries as a distributed energy dump overnight and energy source at peak times. Wouldn't it?
"It'd make more far more sense in a joined-up nuclear-centric energy picture to pay people to drive battery-electric vehicles (not just cars but round-town delivery fleets etc) and use their batteries as a distributed energy dump overnight and energy source at peak times. Wouldn't it?"
No. Because the transport needs to have fairly well charged batteries prior to use, or has depleted batteries after use and those periods tend to be very close to peak power demand. You'd not be very happy if you walked out to your still-frozen G-Wiz on a winter's workday morning, and found that National Grid had helped themselves to all the charge, would you?
Obviously if you don't use the vehicle much relative to its battery capacity then you might have some headroom, but how much do you want to pay extra to carry around batteries for National Grid?
Perfectly true, which is why I'm not limiting the concept to cars, but also including light commercial vehicles (today's equivalent of the LDV Electric Maxus, RIP, thank you Lord "Two Resignations" Mandelson). Many of those could happily carry around plenty of spare capacity for the Grid if there was a big enough incentive to use them this way.
Even smaller vehicles that are only used on the school/supermarket run (which is a vast number of vehicles already) could make a worthwhile contribution, more predictably more usefully and more reliably than solar PV.
Makes far more sense than subsidies for PV on a household scale,or even the stupid subsidies for "high efficiency light bulbs", surely?
What's a G-Wiz (I'm from outside the M25, I've never seen one for real).
"The company that took the proposal to IMechE, Highview Power Storage, says scale is the key. A large cryo-generator could be co-located with a large-scale conventional industrial plant or power station, to harvest waste head otherwise released to the atmosphere. This heat could be used to speed up the warming of the stored air, boosting the power output. Also, when the cooling process has been completed, excess low-temperature air could be passed through gravel-filled tanks, to help prime the cooling process on the next cycle. This, the company says, could yield efficiency of as much as 70 percent (if its calculations are accurate)."
This is quite obviously bollocks, designed to attract funding / interest - the first part of this supposed 'efficiency' increase is nothing of the sort - they are simply proposing to put more energy into the system in the form of captured heat from a power plant. And I VERY much doubt that the second part - pre-cooling gravel could bring anywhere near the efficiency improvement proposed.
Even accepting the above; 70% MY ARSE!!!
Heat is a better choice than cold.
When you compress air, you heat it. That heat is lost, typically, and is the huge reason for the 75% losses.
Build a huge underground water cistern and simply heat the water.
Water has the highest specific heat of any ordinary substance, and that heat can be recovered quite efficiently with a Stirling-cycle engine.
No need to get the water to boil, in fact, you'd avoid that.
Compressed air as a storage medium has a long history. Usually it is found that you need to ADD energy to the compressed air as it expands to get it warm enough to use, a simple heat exchange with the environment is usually insufficient. And in the case of liquid air storage you have the phase-change energy to add back in before you get any gas evolved at all.
It's a nice simple idea for electrical storage but its a lot of cold air. (apols pun)
If we implement packaged flywheel storage accross the grid and local distribution system, we can store all the electricity we need, its extreemly efficient up to 90% and a proven technology in use today.
http://en.wikipedia.org/wiki/Flywheel_energy_storage
...it uses lots of volume. About 2 m^3 for the equivalent of about 1 litre of petrol.Requires expensive carbon-fibre flywheels and all sorts of precision stuff. I do think they are far from the economy and scale of pumped storage.
Just tell people that each Windpark Needs A Pumped Storage Reservoir. And build them. Relocate people for the reservoir to make them pay for their green dreams.
So, fashionable wind turbines and stuff produce quite a lot of energy at night when no one needs it? My solution is to install in all new houses boxes strapped to the wall full of bricks, and a heating element. At night, make electricity really cheap, cos its gonna be wasted anyway. This cheap leccy heats the bricks, which then store the heat from the element. People can also have a big immersion heater for water, again only using this really cheap night time electricity. This heat is then released through the day both into the air in houses, and through taps for hot water. People will then use less leccy, oil and gas to heat their houses. So, this wasted leccy is 'stored' in 'heaters' in peoples houses. I'd say the '7' hours or so of low demand would provide a lot of 'economy'. A winning idea?
Apparently the French make substantial use of off peak heating, just like we used to in the UK.
They have to, because their nuclear power stations (just like everybody else's) have to run pretty much at constant output, as they can't realistically do load following. So lots of electric power needs dumping into something overnight.
The renewables are powering during the day. Very few bright sunshine days at night and few windy nights. But your electric stove could indeed be heated up during the day and then used for the next 24 hours.
Problem are all those pesky lightbulbs, stoves, electric motors, trains (a MAJOR user) which want to run at arbitrary time. Only the French use electric heating massively, because they have - duh - nuclear power.
THE WHOLE POINT about electricity is that you can flick a switch and then instantly power lights, machines and trains. Or make toast. Or iron a shirt. Or fry an egg. Do you only want toast on sunny and/or windy days ? Crumbled shirts on cloudy, calm days ??
This technique is feasible, provided. I have to apply a salt-shaker to the claimed total efficiency of 70%, there's several other ways the concept itself could be implemented *much* more logically, and under lab conditions a thing like this works like a charm. Large scale *could* work, since liquid air is actually quite easily transported, so centralised production makes sense.
/goes back tinkering in his old shed.
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