Talk:Energy density/Archive 1

Adsorbed Natural Gas
I placed remark about adsorbed natural gas in energy density table.But soon it have been deleted.Could I know what happened?There is lot of articles in Internet which prove that such technology really exist.It seems that ANG technology allows to store at least 2.5 times more gas than CNG under same pressure.

— Preceding unsigned comment added by 70.73.149.123 (talk) 16:44, 7 June 2009 (UTC)

What is energy density of soliton?
Does anybody know what is maximal energy density of long-living soliton such as electric, magnetic etc.? Could it be mesured in kilojoules,megajoules? —Preceding unsigned comment added by 70.73.149.123 (talk) 20:53, 21 January 2009 (UTC)

Split table into destructive and non-destructive release of energy?
Would it be useful to split this large and wonderful table of energy densities into "destructive" and "non-destructive" energy stores? There is a large difference between burning your energy storage medium (or direct matter -> energy converstion!) and storing energy in a battery/turbine. 152.91.9.9 (talk) 04:56, 7 May 2008 (UTC)

"**"
The ** thing a) looks stupid and b) is meaningless. There's no such thing as an "energy source". All of these are processes which can be used to store energy or as a source if you're supplied with the storage medium in its high energy state.

Distinctions which would be meaningful: Is it a reversible process (with how much loss)? Is the medium found in nature in its high energy state?

I think we should remove the ** and possibly add two new columns to indicate these boolean values.

Zkzkz (talk) 20:00, 14 March 2008 (UTC)

error?
the table lists "melting ice". should that be just "ICE"? MELTING ice absorbs energy. For that matter, should there just be a link to a table of phase-change energies of various materials? There's nothing THAT special about H2O in this respect. All phase changes can be viewed as energy storage. 216.107.193.67 (talk) 10:58, 23 February 2008 (UTC)

Some rambling request
I see that articles on various kinds of batteries claim they have a "high energy density". I want a single table that gives actual numbers. Is this the right place for such a table?

— Preceding unsigned comment added by 69.216.18.174 (talk) 08:06, 19 February 2007 (UTC)

Requests
Thanks to all contributers for an EXCELLENT article!!! If anyone can obtain the information, I would LOVE to know the energy density of the following:


 * gunpowder (and other explosives)
 * solid rocket fuel
 * clockwork spring
 * latex (or other elastic materials), which is used in modern catapults

If adding too many materials makes the list too long, perhaps it can be broken into groups (e.g. explosives, nuclear physics, elastic, momentum etc). --New Thought 12:02, 6 August 2006 (UTC)

Would like to see battery energy density covered here, with some common types listed, like lithium ion, alkaline, lead acid, NiCd, etc.
 * Added lithium ion. mastodon 22:22, 8 March 2006 (UTC)
 * Added clockwork spring (correct term is "power spring") jhallenworld
 * Thanks very much - much appreciated! New Thought 21:55, 26 October 2006 (UTC)

The flywheel entry should be removed. its not a constant - 66.92.33.119 20:00, 2 September 2006 (UTC)
 * I strongly disagree. I think most people will know its an approximation - and this is infinitely more useful than no information at all. --New Thought 06:52, 4 September 2006 (UTC)
 * I was going to suggest that we add the equation for energy in a flywheel, but it's there if you follow the link. --jhallenworld

Liquid hydrogen and compressed gaseous hydrogen at 700 bar should both have a higher energy per mass density than hydrogen at STP, because both do work as they expand. As an approximate calculation, 1 mole of ideal gas expanding isothermally from 700 bar to 1 bar at 300 K does 16340 J of work. Since hydrogren is 0.001 kg per mole, that gives an additional 16.3 MJ/kg for compressed hydrogren at 700 bar vs. hydrogren at STP. However, someone should find the exact numbers, because hydrogen isn't really an ideal gas, and the expansion isn't necessarily isothermal.

I would request the addition of molten salt energy storage (proposed for solar concentration techs). Also, is compressed air (300 bar) what is being proposed by companies such as General Compression for use with wind turbines? Overall, a great wiki article.

Merge
I say we merge. Thoughts? mastodon 22:22, 8 March 2006 (UTC)


 * I say don't -- energy density per unit mass is one thing, energy density per unit volume is quite another. Since energy density can mean either in common usage it needs its own page.  (A volume energy density has units of pressure, and many volume energy densities act almost exactly like pressure; one is the kinetic energy density of the molecules in an ideal gas (which acts exactly like pressure) and another is magnetic pressure. zowie

This page should go into Hydrogen versus Batteries (electric) as the energy storage medium for transportation of the future.
 * no - link to this page from that page - there's more to energy density than hydrogen v batteries. --New Thought 12:02, 6 August 2006 (UTC)


 * (Sorry, forgot to sign the last) I haven't seen any discussion in a long while on the merge issue, so I've removed the merge tag.

zowie 23:55, 16 April 2006 (UTC)

From PNA/Physics

 * Energy density - Needs cleanup for narrative viewpoint, and would probably be better folded into vacuum energy based on its current content. --Christopher Thomas 22:56, 6 Jun 2005 (UTC)

Why is the Nuclear Fission/Fusion energy density by volume marked n/a?
It seems to me that for a given amount of, say, U235, there should be a given volume associated with that mass, and hence, an energy density by volume.

Are the entries just set to n/a because no one has done this calculation, or because such a calculation can't legitimately be done? And if they can't be done, could someone please add an explanation to the page explaining why they're marked n/a?

Otherwise, I'd guess one could take the average relative density of U235 and use the mass numbers to compute an average energy density by volume. It sounds like it would be very high: uranium is pretty dense, so 1KG of it would be pretty small.

Thoughts?


 * I don't know why it's that way, but I like it. Many fission devices use forcible implosion, which drastically changes the volume of the fissionable material.  Most nuclear fusion in our vicinity takes place in a gaseous medium, which has no definite density -- be it the interior of the Sun, an exploding nuclear weapon, a tokamak, or a detonating inertial confinement fusion pellet.  zowie 19:35, 28 July 2006 (UTC)

Maybe we should include the amount of mass converted into energy just for clarification. Intranetusa (talk) 02:20, 25 January 2008 (UTC)

clarification of table (volume v weight)
I don't know why, but it took me a minute or two to figure out why the numbers in the columns weren't monotonically increasing. I added the "by weight" and "by volume" sections so that no one else has to think too much about it. I couldn't figure out how to make the text normal (no bold, no italics). can any one else make it look better?

— Preceding unsigned comment added by 75.108.162.241 (talk) 00:27, 27 September 2006 (UTC)

Btu/gal
Btu/gal (both US and UK) are non-SI units, non metric system. It's time we got rid of such things, mostly because at the conversion of units page there are 8 different listings for the definition of Btu, and 4 different defintions for the gallon (UK and US). That's ridiculous. The metric system was designed a very long time ago to get rid such idiotic confusions, and make most conversions in metric as easy as moving the decimal point around, including converting between volume/mass using the aqueous sp.gr≈1 g/cc of water, then multiplying with actual sp.gr. In any case, for Btu/US gallon, using 1 Btu=0.0010550 MJ, and 1 gal=3.785412 L, I calculated 1MJ/L=3588.07 Btu/gal, while the factor used in the table seems to be around 4308 (Btu/gal) / (MJ/L). Can anyone highlight the source of such a large discrepancy? Sillybilly 18:46, 26 November 2006 (UTC)
 * I ended up removing/replacing all Btu info, and left SI units of MJ columns only. Sillybilly (talk) 23:08, 28 December 2007 (UTC)

Serious discrepancies between similar data tables
I note that the data table here and the one in Fuel economy in automobiles contain some of the same information but with totally different values. I went through the table in that article and corrected the numbers that I was able to using the Bosch Automotive Handbook, which is a very authorative reference. The numbers in this table that should match are very different. This really does not reflect well on wikipedia in general.

I believe that we need to consider having this type of data contained in a separate article on properties of materials as it makes little sense to have separate tables in separate articles containing different values for the same physical properties. --Athol Mullen 22:53, 26 November 2006 (UTC)

You are right. If you find better updated references, please fix the data. But I'd like to temper the attitude a bit, as far as expecting science to be super accurate. Yes, there are super accurate measurements for the speed of light, or for the unit electric charge, because they are so important, but a lot of the stuff just doesn't get enough lab measurement investment, and sometimes super accurate results are not of interest, but measurement cost and labtime cost is balanced with need. In particular I had to calculate a lot of the values by hand using http://webbook.nist.gov/chemistry/name-ser.html, and by no means am I as authoritative as a published source doing calculations, and I can make mistakes. Futher below there is an outline of what I did. Still small discrepancies in fuel values for crude oil and coal are acceptable, because, for instance, there is a discrepancy between what is meant by "gasoline" because gasoline is a blend of hydrocarbons, and varies from source to source, from oil well to oil well, and varies over time even from the same oil well. For instance aromatic hydrocarbons which have a higher octane values than alkanes, but lower MJ/kg fuel values because benzene's overall formula is C6H6, with a C:H ratio closer to 1:1, while alkanes are CnH2n+2 (n=7 for heptane, n=8 for octane), roughtly C:H closer to 1:2, more hydrogen than carbon meaning more MJ/kg. So small discrepancy between values might be understandable, perhaps a range should be given, instead of a value to 2 decimal places. When you buy gasoline, it is the octane value that's guaranteed, not the fuel value. On the other hand, the values for methanol and ethanol should be exact, because these are pure chemicals, and there is no excuse for the same 22.61 MJ/kg for both methanol and ethanol. So now I took the values from the fuel economy page and entered them here. Of course there is the water distillation azeotrope and 100% pure ethanol issue, which fuel is actually getting used, but the error in the value listed on this page was still huge, listing methanol and ethanol with the same value. It never occured to me to check values in that table that were already there when I came to this page. Note that discrepancy in reported values is not unusual, see and  for values all over the place, though true, the error is less than what was originally on this page. I prefer going with the DOE reference on those pages. Still, here is a double check: At http://webbook.nist.gov/chemistry/name-ser.html we enter methanol, click search, click on condensed phase thermochemistry data, because we want to deal with the heat of formation of the liquid, not the gas, and find these values for ΔHf°, depending on reference:

ΔfH°liquid -238.4	  kJ/mol  Ccr  Baroody and Carpenter, 1972	ALS

ΔfH°liquid -239.5 ± 0.2	kJ/mol Ccb  Chao and Rossini, 1965 see  Rossini, 1934; ALS

ΔfH°liquid -238.9 ± 3.6	kJ/mol Ccb  Green, 1960 Reanalyzed by  Cox and Pilcher, 1970, Original value = -238.5 ± 0.2  kJ/mol; ALS

ΔfH°liquid -250.6	  kJ/mol  Ccb	Parks, 1925  ALS

I'm assuming these references are all actual lab measurements instead of citing yet another citation, because that's really the only way to tell. No matter how authoritative a published reference is, if you can't measure those values in a lab, then it's worthless. The ultimate authority is always with Nature and experimental measurement. The Ccr and Ccb above mean rotating and static bomb calorimetry methods. In view of using different experimental methods, the values are pretty close. Note the dates of measurements - more recent ones probably have better instrumentation. While the 239.5±0.2 Chao-Rossini value is from 1965, it says see Rossini 1934, it might actually be a 1965 published reference based on a 1934 measurement. Also, note how different the 1925 data is. So when picking a number to calculate with, we still have to pick whose labwork we want to rely on, and these numbers are actually wonderful, have a scientific feel to them, because too perfect data with too many decimal places is sometimes absurd. I don't like authoritative sources that are too accurate, I'd rather have a wild array of different sources with very little authority disregarding each other and each telling me a different number, and then I go an compare. This is real life. Your task is to pick a number out of thin air given these 5 values! You still have to do some picking, and it's better than the situation with an authoritative single answer. Also note that the 1960 Green value has a lot more error, ±3.6, but such numbers are still much preferable to dry numbers such as Baroody-Carpenter and Parks, without ± ranges given. I don't mind if the error is high, but still, give me the error. Technically all of our wikipedia energy density data should have a ± sign next to it, throughout the table, that would be true science. I highly dislike reading Premium Gasoline 32.84 MJ/L, 43.50 MJ/kg on the fuel economy page. 32.84, 4 signifcant digits? You're dreaming! Premium gasoline is not such a pure and uniquely identified material, moreover even the same exact sample will be measured different by different labs, or even the same lab. 32.8, or 33±2 is probably a normal answer. Anyway, back to cherry picking a ΔHf° for methanol, I like the value 238.9 kj/mol. How about you? So now we look at the combustion equation

CH3OH+1/2 O2-->CO2+2 H2O

ΔHf° for O2 is 0, by definition, but looking up the ΔHf° for CO2 and water both in the gas state at standard conditions - note your car doesn't exhaust gases at STP. In fact I don't even know off first hand what temperature is used for the NIST webbook data, some 3 minute of effort of mine went wasted trying to find out, I'm assuming all their ΔHf° values are given at the same reference temperature throughout, whether it's 20°C, 25°C or 0°C. So back to CO2 gas and H2O gas at reference condition, after doing some cherry picking (with much more accurate numbers), I come up with -393.5 and -241.83 kJ/mol.

So armed with these values, the ΔHf° for the overall reaction is 2*(-241.83)+(-393.5)-(-238.9)=638.26 kJ/mol liquid methanol combusted to water vapor and carbon dioxide cooled back to standard temperature. From the methanol page in wikipedia we find that the molar mass is 32.04 g methanol per mole. So that gives 638.26 kJ/32.04 g methanol, or 19.92 kJ/g, or 19.92 MJ/kg. Bingo, that number matches the fuel efficiency page and the DOE article, yay!, and not the 22.61 value that was on this page, so those two places seem to be more authoritative than the others, more trustworthy, because they match each other, plus they match the calculation I did based on a 3rd source. So now I'll take the values for ethanol found in both these authoritative places that match each other, the fuel efficiency wikipedia page and the DOE article, and hope they will be true. Note the real authoritative way is to redo the calculation for ethanol, and even then, the real authoritative way is going to the lab and doing the measurement yourself, because otherwise you have to trust someone else's labwork, something you read somewhere, and how do you know they didn't just pick it out of thin air? Multiple sources enhance trust, but you never get full certainty. Who's got all day and all life to keep doublechecking and calculating everything? Only paranoid people keep checking and checking things over and over because of mistrust. You mistrust everything by default, as a matter of fact, but you don't go around being obsessed with mistrust. When you come across an error you point it out and correct it, but sometimes false info gets quoted all over the world for a long time til it's realized it's wrong. Still, "given enough eyeballs, all bugs are shallow" is what wikipedia is about. Eventually all bugs should be hammered out, if it wasn't for all the pranksters and more subtle deliberate wikipedia derogators, wikipedia should gravitate to something better and better. By the way, to finish up the calculations, from the methanol wiki page we get the density as 0.7918 g/cm3, and doing a quick google on methanol msds specific gravity, we find 0.7910, 0.795 and 0.8, so the wikipedia number is "nice". Note that density to 4 significant digits probably requires temperature control to 3 significant digits or better. Ever try that, controlling temperature well within 0.1 °C? It's not easy. So, going with 0.7918 g/cm3, or .7918 kg/l, the 19.92 MJ/kg value translates to 19.92 MJ/kg * 0.7918 kg/L = 15.77 MJ/kg. Note 4 decimal place is absurd, because who will ever combust methanol and cool the exhaust vapors to standard conditions exactly? But anyway, you get the method, and you can calculate more such values for yourself, and double check values if you want. Sillybilly 08:54, 28 November 2006 (UTC)

See the heat of combustion and heating value pages for other set of values. Heat of combustion was understood here by me as the energy content, which represents the ΔH, enthalpy change, and then a second column with energy extraction efficiencies is added to deal with the subtle issues. All heat engines have low Carnot-cycle efficiencies, most cars being on the order of 25%, power plants on the order of 35% efficient. Technically, instead of enthalpy the ΔG, Gibbs free energy should be used, because that limits the availability of how much work can be extracted, or more exactly, gives you how much work can be extracted even from reactions without enthalpy change, but a significant ΔS entropy change (a large enough entropy change can drive a "negative heat of reaction" value, such as in ice packs, and can drive engines based on only entropy change). So, should we list the ΔG free energy values instead of the ΔH values as customary for fuel heating values? ΔG=ΔH - TΔS, T in Kelvins, (ex. 25°C=273.15K+25=298.15K, plug it in) you can do the above calculations again. But from the methanol combustion reaction 1.5 moles generating 3 moles, and gases at that from a liquid, the entropy change is very positive and a significant driver without even looking up the values, and gives "extra" energy values. The page citing 22.034 MJ/kg for Methanol based on the ΔG Gibbs function instead of the 19.9 MJ/kg based on the ΔH heat of combustion bomb calorimeter value used by the DOE article citation. The difference is using two different meanings of stored energy - technically ΔG is what's correct, but ΔH is easier to measure. Technically there is some extra driving force present as entropy energy and that much more work(handed over as shaft power, battery electricity) could be extracted besides the heat energy driving force, because there is that extra nudge, extra form of thermodynamic energy present, in the form of entropy drive. But in view of the 30-50% efficiencies of even the best fuel cells, hairsplitting doesn't make sense, especially because the ΔG is very application dependent (i.e. is your upper Carnot cycle temperature in a natural gas combined cycle turbine 1200°C, or are you just dealing with just 150°C steam, the carnot efficiencies will vary tremendously, and but so will the ΔG values), so ΔG is very application dependent and highly sensitive to temperature, as noted in the equation ΔG=ΔH - TΔS, while ΔH is relatively constant for all temperatures, and therefore you can provide it as a single value with less confusion, even if it's technically not the "proper" energy storage value to cite. Still the ΔG° values should be the technically proper things to cite, because they represent the energy values that can be theoretically extracted from the system, whether it's more or less than the "heating value" ΔH part, based on how the entropy part happens to drive the system, whether it's positive and giving extra energy, or negative, consuming a large chunk of the heating value away, and in extreme cases, consuming it all. For instance, the reaction 2H2+O2--->2H2O has approx. the same ΔH value at any temperature, but an unfavorable negative entropy change, up to the point that at 2500°C the 3->2 molecule entropy reduction is so severe, that the reaction won't go forward at all, and no energy is extractable at all from hydrogen fuel, because ΔG is 0, or even negative, where water will thermolyse and self split up into H2 and O2 instead of H2 and O2 reacting together to give water. Thus hydrogen has a high heating value at any temperature, but less and less "free energy" extractable the higher the temperature. This fact is useful for high temperature electrolysis, but "unuseful" for high temperature fuel cells such as solid oxide fuel cells running at 1000°C, with low temperature Proton exchange membrane fuel cell running at 30°C giving better performance, at least as far as the ΔG part is concerned, or at least the "stored energy density" value is concerned. To reiterate again, the same hydrogen will look more energy rich, or have a higher energy density to a PEMFC than to an SOFC, simply because they operate at different temperatures, and if there were a fuel cell that ran at say 2499°C instead of 2500°C where it hits 0, the fuel value of hydrogen for it would be probaly less than 0.001 MJ/kg instead of the 120 listed in this table, calculable by ΔG. Above 2500°C the true fuel value, or ΔG would be 0. It's pointless to cite the standard free energy of formation at 25°C if your engine doesn't operate at 25°C. So that's another aspect of what "energy density" means at all. It's still important to have some kind of hierarchy and table listing these values, to get a good feel for things such as just how good a fuel gasoline is, how different batteries and liquid hydrogen are, and such things as fuel content of plastic, cow dung and household waste, even if the true fuel value, ΔG is such a vague concept without temperatures fixed to actual operating conditions. Sillybilly 09:24, 28 November 2006 (UTC)

an error imho
mass-energy equivalence 	89,876,000,000 	MJ/kg protons in the Large Hadron Collider 	6.7 ×10^14 MJ/kg

I know how the author thought this "protons in the Large Hadron Collider 6.7 ×10^14MJ/kg" but it's some missconception to say that energy of relativistic particle is the total relastivistic energy and the mass is only the rest mass (in stacionary state) so i thing there can't be written that energy densyty of something is grater than equal tu E=mc^2 eqantion, even hadron in hadron colider not, all energy has it's owen mass —The preceding unsigned comment was added by 147.32.122.137 (talk) 00:49, 9 December 2006 (UTC).


 * This is the energy of protons stored in the collider. Energy is energy-- total relativistic energy counts if you're in a frame to see it. In this case, particles trapped in a collider add "invariant mass" to the collider equal to their rest mass PLUS their kinetic energy. In this case where the net linear momentum is zero, the relativistic energy/c^2 IS the rest mass of the system. The collider is heavier (if you could weigh it) by not only the weight of the protons, but their kinetic energy also. S  B Harris 03:38, 9 December 2006 (UTC)


 * The first writer is right. You cannot have more energy than E=mc^2. Breaking that equation would have quite...interesting consequences.--Darin-0 15:25, 30 January 2007 (UTC)

Storage density limits
Some years back I saw a theorem that related maximum achievable energy storage density to materials strength. (Not just restricted to mechanical-energy storage systems, as I recall.) Unfortunately I can't remember the details, and can't find the theorem now - any chance of somebody including this in the article? --Calair 23:31, 13 December 2006 (UTC)
 * As materials strength is a mechanical phenomenon, I believe you must have seen a mechanical-energy storage system discussion - such as discussion of the area under stress-strain curve, or discussion of a flywheel. Note that gravitational potential and electric potential energies are directly related to forcefields (usually force is kE, while energy is kE2/2), therefore maximum energy stored automatically means maximum force developed and sustained by load bearing elements, but even in a capacitor, usually the dielectric breakdown issues happen way before mechanical strength limits are reached. I don't see how chemical or nuclear energy storage densities would be related to mechanical strength - e.g. energy released in a fire(reaction) has nothing to do with how strong the fuel was, for instance a liquid or gas is not very strong mechanically (it falls apart) but it may burn a lot hotter than some chunk of solid coal or chunk of steel bar. There are many ways to store energy, and mechanical strength is the pivotal issue for mechanical storage, it can be an issue for electrical field potential storage as in capacitors but usually it's not, and it is a nonissue for chemical potential storage such as electric batteries and fuels, or nuclear storage. Sillybilly 18:36, 10 January 2007 (UTC)

Values and Estimates
I think the compressed air at 200 bar value may be off. I do not see a source on the page, and when checking the NIST webbook for nitrogen (to get a good estimate) I see 0.171 MJ/kg which differs substantially (http://webbook.nist.gov/cgi/fluid.cgi?Action=Load&ID=C7727379&Type=IsoTherm&PLow=200&PHigh=201&PInc=1&T=12&RefState=DEF&TUnit=C&PUnit=bar&DUnit=kg%2Fm3&HUnit=kJ%2Fkg&WUnit=m%2Fs&VisUnit=Pa*s&STUnit=N%2Fm). —Preceding unsigned comment added by Bavetta (talk • contribs) 23:56, 13 August 2008 (UTC)

Yes, I think there is something wrong here with quoting numbers that can be :-

accurate figures for some chemicals,
 * calculated from enthapies of formation etc (eg ethanol),

good approximations for imprecise mixtures,
 * usable in calculations with a reasonable accuracy,

and wild guesses
 * that cannot be used for proper calculations for example figures for flywheels.

The energy stored in a kilogram of gasoline/petrol is say 43 MJ/kg.

How much energy is stored in a stationary 1kg flywheel? And in one spinning at 10,000 RPM? And at 20,000 RPM. Maybe the article means the stored at the flywheels maximum RPM. Is it a large radius flywhel spinnin slowly, or a small radius flywheel spinning fast. Okay, the maximum energy stored might be independent of the flywheel size. Is it a hollow flywheel? What is it made from?

I believe the rotational speed of a flywheel is limited by the tensile strength of the material used and then the energy it will store is then further defined by the density of the material. I think either flywheel should be dropped from the list, or a very specific example should be quoted, eg solid carbon fibre disc of density 1750 kg/m3 and radius 10cm spinning at 50,000 RPM.

Other examples too like batteries will depend on how thick the container is and what it is made from, etc. If a reader is to have any confidence in the figures on Wikipedia, I think we need to separate usable scientific information eg chemical enthalpies, from rough guides that might indicate whether batteries of flywheels should be considered for a real world application, based on approximate values, or real values for very specific similar but different products.

If table entries can be coloured, I would favour a different colour scheme for measured scientific enthapies of combustion etc, eg ethanol, iso-octane, and finger in the air estimates, eg flywheel, battery.


 * I been thinking about colouring too, I totally agree with that idea, but I'm mainly offline these days and only get internet at the library, so I can't really sit down and spend a lot of time tinkering with it. I was especially going to take out the redundant "burned in air" comments I put in earlier, because throughout the table it's pretty much assumed, except for uranium, liq h2+o2, thermite, etc. Most practical energy carriers are chemical energy carriers and they imply combustion in atmospheric oxygen, as opposed to most batteries and rocket fuel where the oxidizer has to be carried along. Which is why metal air, or organic-air "batteries" (or other non-thermal-engine ways of getting at the energy) will be the future, IMHO. Sillybilly 21:39, 25 June 2007 (UTC)

Crysta1c1ear 17:55, 24 June 2007 (UTC)


 * I'd rather see "flywheel" shown with a dubious figure (which some kind soul may later change) than not have flywheels mentioned; my first visit to this article was to try to compare such zero-emission energy storage media with conventional fuels. I find references to be more informative than colour-coding.  However, a few days ago when I followed the flywheel efficiency reference to ccm.nl, I didn't find any figures of any kind.


 * To add "compressed air at 300 bar," I extrapolated MJ/kg from the 20 bar compressed air farther down (and rounded to one signifigant figure as I have no idea of the accuracy of the source figure) then borrowed the 12kWh for 300l at 300bar figure from Air car and used the conversion below the table in this article to get MJ/l. --Egmonster 22:55, 5 August 2007 (UTC)


 * I did the sums using compressed_air_storage and saw that these did not include the container and appeared to be valid for about 12°C, a typical temperature for an underground cavern. I then added figures for steel and fiber bottles (at 24°C). --Theosch (talk) 12:20, 9 May 2008 (UTC)

per mole
Is a unit like BTU/scf also considered energy density? scf is not a unit of volume, but a unit of quantity. — Omegatron 03:32, 5 June 2007 (UTC)

other popular candidates
NaBH4 <-> NaBO3 solution ... proposed by millenium for fuel cell chlorine to sodium chloride solution

can some knowledgeable soul run these?--Oldboltonian 21:36, 6 June 2007 (UTC)

LH2/GH2
Liquid hydrogen and gaseous hydrogen do *not* have the same energy content -- gaseous hydrogen (room temp) has significantly more, by virtue of being warmer. The heat capacity of hydrogen is non-trivial. At atmospheric pressure, the difference is about 4MJ/kg. Reference: NIST thermophysical properties of fluid systems,.

—Preceding unsigned comment added by Evand (talk • contribs) 03:15, 5 July 2007 (UTC)

hydrogen peroxide decomposition
hydrogen peroxide decomposition (as monopropellant) 	0.33 MJ/kg ?? -It looks strange that energy density of this redox chemical reaction is as low energy density of melting ice. I made an approximative computation using AM1 semiempirical quantum mechanical method in Arguslab 4.0 and I got about 2.43 MJ/kg, the computation could be wrong of about 10% but not 10times. But I better discuse it before changing.

— Preceding unsigned comment added by 147.32.122.200 (talk) 14:08, 12 July 2007 (UTC)

acording to http://www.du.edu/~jcalvert/phys/perox.htm the enthalpy of H2O2->H2O + O2 decomposition is 766cal/g*4.18~3.2MJ/Kg the value can also differ because of O2 expansion work and H2O heat of evaporization, but not much. So I changed this value.

also in main article about hydrogen peroxide http://en.wikipedia.org/wiki/Hydrogen_peroxide H of hydrogen peroxide is H=-98KJ/mol ~ 2.72MJ/Kg.

—Preceding unsigned comment added by ProkopHapala (talk • contribs) 04:20, 16 July 2007 (UTC)

Uranium -235
I was trying to track down a source for the energy content of 1kg of U-235. The only decent thing I could find was from the European Nuclear Society (http://www.euronuclear.org/info/encyclopedia/coalequivalent.htm). They say "During the complete fission of 1 kg U-235, 19 billion kilocalories are released".

19 billion kcal = 7.9496 × (10^13) joules = 79.49 million MJ

I a little afraid of changing it though. If someone wanted to verify this and change the article I think it might be worth it. Thanks.

— Preceding unsigned comment added by 75.70.78.238 (talk) 21:14, 24 July 2007 (UTC)

Lithium Ion (and reference 2)
The figure in the table is 0.23 to 0.28 MJ/kg. However http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2763 is an example of a commercially available cell which is 0.72MJ/kg. The figures appear to be based on reference 2, which I'm rather surprised to find is only a few months old - meanwhile Dell for instance has been using laptop batteries with a better power density double what is quoted there for several years. I'd suggest that given it's totally inaccurate information, it is a very poor reference. I'll leave this in for discussion for a while, then if I remember dive in and modify the article (reluctant to do that straight away, as I don't have a good reference, just know that the one used at present is wrong). —Preceding unsigned comment added by 192.102.214.6 (talk) 12:43, 3 March 2008 (UTC)


 * Agreed. I'll make the edit, using your link as a source.  I'd prefer a better source than a commercial link, but this is a high traffic article and this incorrect data needs to be changed asap. Roidroid (talk) 04:04, 18 June 2008 (UTC)

What is the difference between an energy carrier and an energy source?
Surely there is no difference since energy can never be created, only transformed from one form to another (including mass).

161.51.43.37 (talk) 03:08, 11 March 2008 (UTC) David McCarthy.

On Scientific Relavence and on Hydrogen
In requards th the comments at the top addressing the scientific relevance of this article, I have to point out that there are a lot of readers out there that are trying to get their heads around the energy problems of today, and as such this table really helps to give perspective to the many alternative energies being proposed. This may not be an important topic 50 years from now but for now we need it on wikipedia. However it might be appropriate to separate the table from the definition of Energy Density into its own article, perhaps labeled as Incomplete List of Energy Densities. On Hydrogen: If its being used to power a vehicle, its unlikely that the energy of its expansion will be captured so stop whining. I do agree that the table needs to be more specific. I came here to get an idea of how a car running on expanding liquid nitrogen compares with petrochemical engines, so for me the table needs to be clear that its talking about the "energy density of liquid hydrogen for combusting with oxygen", and for "liquid nitrogen to expand at STP" (if that is what the numbers actually represent). 76.212.147.34 (talk) 11:09, 23 August 2008 (UTC) Sandy

brilliant article
this is indeed a brilliant article, but could I put in a plea for a subset to be viewable of all the stores and carriers likely to be of use in practical energy scenarios - power generation and storage and transport? All the other interesting ones like explosives and orbiters make it hard to compare the likely practical ones. Also there could usefully be a link to a purely electrical battery list.Engineman (talk) 04:07, 5 September 2008 (UTC)

Table sort broken
I tried to determine what was wrong with numeric-mode sorting in the table. There may be more than one cause (the table uses several obscure markups), but I believe I found at least one, and that is that wikipedia tables do not support formats like 4.32×104. Help:Sorting claims it does, but I suspect it is out of date, and so I made these two posts there. See Help talk:Sorting and Help talk:Sorting, and then meta:Help:Sorting. Note that it appears that smn support is also removed (I have no idea when it was ever working of course). -84user (talk) 04:04, 5 October 2008 (UTC)
 * Update. First, I split the large table into two: a table with values for complete systems including needed oxidisers; and a table with "fuel" systems that use external oxidisers (usually oxygen from the air). Then I made adjustments to get the tables to sort better. I removed all smn templates as they do not work, and I suspect they also break sorting now. I also removed a few display styles and reworded some figures and moved one reference. They sort better now, but still not perfectly. -84user (talk) 20:29, 2 November 2008 (UTC)

Thermal Energy Storage
The Energy Density of any substance used as Thermal Energy Storage is the sum of its latent and sensible energy densities over the temperature range used in the application. In that there are now real examples, and practical temperature ranges for those applications, It is important to compare the densities of Thermal energy Storage against batteries and other alternatives. I used 300 degrees C as a range, 300kj/kg for fusion, and 3kj/kg/c for sensible heat. These figures are in the rough range for a variety of PCMs used in High heat applications, although I could not find the particulars for Saltpeter as used in Barstow Solar II. The Energy Density is 1.2, but I rounded to ~1 because it is intended only to estimate the value for numerous possible examples in this space. Clarifications are encouraged. Best... Benjamin Gatti (talk) 18:13, 2 November 2008 (UTC)

Values for compressed air?
Could someone define where the MJ/L values for compressed air come from? Which volume do we take into account (decompressed at 0°C/24°C, compressed with/without bottle) and why does the bottle type matter? And even if the values are correct, they're certainly not that precise. Unless the article cites some sources, the values should be changed to one row like "compressed air at 300 bar with container - 0.05-0.50" Tokenzero (talk) 12:44, 8 November 2008 (UTC)

Fuel Cell
A regenerative fuel cell is the only fuel cell that can be given a meaningful energy density. This is one that contains its own internal hydrogen store. Normal fuel cells are more like motors. Their energy density is meaningless as they burn fuel (usually Hydrogen but can be anything).

Mike Young (talk) 22:51, 25 November 2008 (UTC)

Helium binding energy
Is the binding energy of Helium-4 nucleus correct (per litre)? How can it contain more energy than mass-energy equivalence? --CharlesC (talk) 11:00, 9 December 2008 (UTC)

EEStor release
I'm sure some have seen the recent granting of EEStor's patent. The patent papers claim 52 kWh from a "battery" (actually very accurate terminology in this case) massing 281 pounds. If I'm doing the conversions correctly that's 0.7 MJ/kg, a little bit lower than the number quoted here.

The weight is higher than I would have suspected at first guess, but it's about the same as a common 4-cylinder engine. Eliminating the transmission and fuel and replacing that with a motor might suggest overall curb weights will be slightly lower than ICE. Very interesting.

Maury Markowitz (talk) 15:28, 22 December 2008 (UTC)

this can't be right ?!? "individual abstaining from alcohol"
"Carbohydrates, fats, and proteins are the only sources of energy for an individual abstaining from alcohol, and they make up ninety percent of the dry weight of food."

I have a hard time making sense of this, vandalism ? aren't alcohol carbohydrates ? 69.172.116.133 (talk) 19:34, 9 February 2010 (UTC)

Query on Energy Densities for Natural Gas
I'm querying the data in the Energy Densities Table. Please review the data below for Natural Gas, with the examples of liquid Hydrogen, gaseous Hydrogen and Biodiesel added for contrast.

Are we saying that 1L of uncompressed Natural Gas has 10 MJ of energy, hence 1m^3 = 10,000MJ? I refer to the following URL to support my query. http://www.natural-gas.com.au/about/references.html

Therefore, I suppose the valve for Natural Gas should be 0.0387 MJ/L? —Preceding unsigned comment added by McGuinn (talk • contribs) 22:28, 12 March 2009 (UTC)

I agree. Whoever entered 10 MJ/L for natural gas "burned in air" was clearly using the figure for compressed natural gas. I'll split this into two entries. --Vaughan Pratt (talk) 20:01, 5 June 2009 (UTC)

Please note that some of these values are the higher heating values. This is confusing as mostly the Lower Heating Value is used in industry!!!! There are interused in this table. For instance, for H2, the HHV is given, whereas for methanol, the LHV is given.

Compressed air?
Didn't this table used to include a couple of entries for compressed air? I personally think that it was helpful to have them for relative comparison. —Preceding unsigned comment added by 98.175.228.222 (talk) 22:43, 30 March 2009 (UTC)

Highest chemical energy density
Which chemical reaction has the highest energy per mass of the reactors? (just don't tell me the H2 and O2 is 143MJ/Kg, put the O2 in the calculation and it would be about 16MJ/Kg!) —Preceding unsigned comment added by 217.219.151.190 (talk) 16:39, 9 August 2009 (UTC)


 * This question doesn't make good sense, because your answer would be something very nonpractical. The highest chemical energy per unit mass would be most probably from something like elemental fluorine liquid(corrosive/supertoxic) and beryllium powder(supertoxic/rare-expensive). Both are impossible to deal with from a practical standpoint, and require extremely heavy safety/containment devices (though teflon is not that heavy) and corrosion resistant reaction chamber components not presently known to us, unless a lithium ion type battery setup is found, then teflon/graphite could work. But beryllium's rarity, toxicity and tendency to form covalent compounds nix it compared to say lithium in the same battery type application, which only leaves high temperature thermal harvesting/corrosion issues with beryllium and fluoride. Something currently totally nonpractical. Also, the cost of generating elemental fluorine is extreme compared to free(not really free, from an energy standpoint, but abundant and freely produced by photosynthetic lifeforms) elemental oxygen in the atmosphere. Also, the public dealing with elemental fluorine would pose a risk almost comparable to it dealing with nuclear materials, which are an order of magnitude more efficient/practical, if it were not for the malice type public safety issues they pose. So the only practical and publicly safe oxidizer in chemical energy storage is oxygen.


 * Actually I thought about this today, and it's beryllium + oxygen not beryllium + fluoride that's top energy density mixture. At http://webbook.nist.gov/chemistry/name-ser.html BeO's deltaHf_solid is -609.4 kj/mol, and molecular weight is 25.0116 g/mol, from which we get 24.4 kJ/g (or MJ/kg). BeF2's deltaHf_solid is -1026.75 kj/mol, but the molecular weight is higher, 47.008988 g/mol, giving a 21.8 MJ/kg. In fact even LiF is more energy dense on a mass basis than beryllium fluoride. Here is a list below. [[Image:topfueloxidizerchemicalenergydensities.png|center|600px| Top elemental fuel + oxidizer energy densities]] The above list only contains elemental reaction, but you get a good feel for what matters. There are various hydrides, such as LiH, BeH, BeH2, B2H6, BH3, BH, BH2, etc, whose condensed phase deltaHf data I did not find, only the gas phase, and it shows a positive formation energy density, meaning it takes energy to make it from components, so the fuel contains additional energy beyond what's just an average you'd get from the elements. Bringing the fuel into high energy metastable states is one way to "theoretically" increase the energy density. In fact starting from vaporized beryllium and yielding solid oxide gives more energy than starting from solid beryllium, and staring from beryllium that's heated to 10000 °C gives even more. Also on the oxidizer side, there is also OF2, oxygen difluoride, whose gas dHf is 24.52kJ/mol, is positive, therefore it takes energy to make it, which is released during combustion. A way to improve the above list could be to include all the binary compounds such as LiH+OF2 combinations. Sillybilly (talk) 22:43, 10 August 2009 (UTC)


 * If the question is per mass of reactor? If you allow for a reactor to be a couple billion cubic kilometers, the walls of it compared to the volume will be insignificant, and then the container size is irrelevant in the question. So basically you have to specify maximum engine size and storage size accurately, and then the containment cost between various fuels(such as fluorine, hydrogen, oxygen) can be compared.


 * The highest practical chemical energy density fuels using atmospheric oxygen are in common use already: methane, propane, butane, gasoline, diesel, and coal. Boron, borohydrides or hydrogen are lighter, more energy dense per unit mass when combined with atmospheric oxygen, but represent either storage(hydrogen), reactivity(solid boron), or manufacturing net energy gain cost / waste stream recycling issues (boron, hydrogen, borohydrides) when compared to hydrocarbons.


 * I forgot to mention lithium/air(oxygen), which is quite energy dense, without emissions, relatively safe, relatively abundant/cheap(compared to beryllium), and with relatively easy recycling/recharging (at least compared to boron chemistry). Lithium's mobility through ionic matrices gives way to tapping battery type applications that can be 90%+ efficient with less than 10% waste. Batteries bypass the Carnot-cycle thermodynamic efficiency limits of heat engines (usually running at 20-40%, 60-80% untouchable energy wasted out the exhaust/chimney). It's kind of funny that for a battery, the lithium has to diffuse through an ionic matrix to yield dilithium oxide. Startrek used to run on a dilithium matrix, however chemical energy densities are nowhere near enough to make a starship like that accelerate to warp speed in under a year, let alone under a second. In the movie they probably mean nuclear fusion energy harvesting, where lithium is a fuel. Sillybilly (talk) 03:28, 11 August 2009 (UTC)


 * Lowest mass reactors per unit of energy output devices tend to be inefficient and waste energy compared to the highest efficiency devices. Highest efficiency reactors are necessarily large, and used in places such as stationary combined cycle power plants. In fact the more efficiency one tries to obtain, the more devices and weight has to be added - more stages/smoother gradual temperature changes, larger recouperator heat exchangers, etc.


 * Weed whacker type 2 cycle engines have a high output/mass, but inefficient, and even more power/unit mass are rocket engines, but even less efficient, and waste even more fuel compared to a smooth, 4 cycle diesel engine, or compared to a combined cycle power plant. So usually in a reactor the size and the efficiency are balanced, depending on capital cost(meaning interest rate) and mobility requirements.


 * The present technologies are pretty much saturated and optimized, it's hard to foresee any fuel better than what we already have. Coal, oil and natural gas combined with atmospheric oxygen ARE the most practical chemical energy density carriers. The only issue is how to use solar energy to create the fuels, which, given the extremely low price of mined oil even today, is not done yet on a significant scale, at least not until we run out of the minable reserves or create a catastrophic global climate change that we cannot predict (it may or may not be as bad as predicted. Plants grow much better in high CO2, and in fact the future might be CO2 injected greenhouses or lakes and CO2 will carry a useful price). Biofuels and biomass can stick with hydrocarbons, and guarantee recycle of atmospheric CO2. In any case, even with biomass the future is still diesel, gasoline, or propane, unless unexpected ergonomics or efficiencies in production of say ethanol or something exotic like dimethylfuran is found, which is unlikely. Those other oxygen containing carbon-hydrogen materials derived from biomass can always be upgraded to one of those three pure nonoxygen carrying hydrocarbons in a conventional refinery with Fischer Tropsch type conversions, unless the net energy gain calculations ultimately dictate using them as is. There is always a balance between practicality, ergonomics and capital investment costs. The most energy efficient way of capturing solar energy is via multilayer solar panels that have a record of near 40%, practical limit of 8-30%, compared to the less than 0.1% that life captures. However life is cheap, and takes care of the maintenance on its own, while solar panels are expensive to build and maintain. However, with automation/robots, those solar panels will eventually be less expensive and ultimately more energy efficient. The problem/question with advanced robotization is artificial intelligence eventually surpassing human intelligence and creating something smarter than us, and posing a danger to us. With nonlife based solar energy production, boron/borohydride/boric acid recycle streams might become the chemical energy carriers, but with biomass, hydrocarbons/co2 recycle streams are the practical choice.
 * One important aspect of any engine operation is reaction rate and flow. Solid phase reactions are very slow, and carbon, though not very energy dense from the above table, it serves as both a very useful hydrogen carrier/volumetric compactor through chemical bonds in hydrocarbons, and as an easily flowing/exhaustible reaction product. The phase is quite important in an energy harvesting scenario, and having to dissolve/dilute materials simpy to get them into a fluid state for any kind of reaction rate reduces energy density. But that's what life does, every life form we know is one big bag of water, running on water dissolved hydrocarbons(fats/sugars), and easily exhaustable/inhalable CO2+H2O. Exhausting boron oxides or litium oxides in a concentrated form is an issue. Only carbon and hydrogen oxides are liquid/volatile at ordinary temperatures. With fluorides, besides carbon and hydrogen, there is boron trifluoride and silicon tetrafluoride that are also gaseous, that could be quickly exhausted from a reaction chamber, if we had the proper technology to easily tackle and recycle these materials back to well contained boron hydrides and silicon hydrides and elemental fluorine. Hydrocarbons/oxygen just seem so much easier and doable.Sillybilly (talk) 03:52, 11 August 2009 (UTC)


 * A recent/near future engine development is the microturbine, some operating at 100,000 rpm, with both high energy efficiency and high power per unit mass. Cost is currently very high because of extreme mechanical tolerance and rotational balance requirements, whose cost however is dropping through the floor as automated CNC equipment becomes ubiquitous, and within the next few decades we might see a complete replacement of cylinder/piston/oil lubed engines by microturbine/air bearing engines. Sillybilly (talk) 18:14, 9 August 2009 (UTC)

Value for natural uranium in breeders
The cited 24 000 000 MJ/kg for natural uranium is the approximate value after conversion to electricity. The thermal energy density is 86 000 000 MJ/kg - mentioned in the Cohen paper. —Preceding unsigned comment added by Tweenk (talk • contribs) 21:06, 13 December 2009 (UTC)

Total energy density of fusion
What would the energy density of fusion be if you added up all the fusions from hydrogen to iron? Eg how much energy would be release if you fused 1kg of hydrogen into bigger elements all the way to iron and how much of that kg would have been converted from mass into radiant energy? Would this be an approximation of the energy density of a large star formed from a hydrogen cloud? —Preceding unsigned comment added by 168.103.182.177 (talk) 05:33, 15 January 2010 (UTC)

LOX + liquid hyrogen?
Is there some reason oxygen + hydrogen isn't on the list? According to the Rocket propellant page it is used in the Space Shuttle orbiter, the Centaur upper stage of the Atlas V, Saturn V upper stages, the newer Delta IV rocket, the H-IIA rocket, and most stages of the European Ariane rockets. 192.171.3.126 (talk) 15:41, 1 June 2010 (UTC)

Natural Uranium in Fast Breeder Reactor Efficiency
I am removing the practical recovery efficiency rating for the Natural Uranium in Fast Breeder Reactor, seeing how it only deals with thermal efficiency, not total power conversion efficiency.173.66.0.205 (talk) 06:56, 30 June 2010 (UTC)


 * Thermal output is more appropriate, since reactor process heat can be used directly, and since the efficiency of electricity generation depends on the thermodynamic cycle used and other "balance of plant" issues that are (largely) unrelated to the design of the reactor. beefman (talk) 21:16, 16 January 2011 (UTC)

zero point energy
Is it me or does this section appear to be unrelated to the rest of the article, and not really about anything? mavhc (talk) 15:51, 8 November 2010 (UTC)

SVG of energy densities error?
I assume that the SVG plot's data point for Natural Gas should be labled 'Methane 700bar' or similar? I believe the biggest component of natural gas is methane. Comments/corroboration welcome. Otherwise, excellent graphic. Tommyflockton (talk) 11:19, 8 February 2011 (UTC)

superheated water
Why is superheated water not on the list? — Preceding unsigned comment added by 60.228.216.171 (talk) 16:34, 5 July 2011 (UTC)

Someone removed a lot of useful energy densities
I refer to this page frequently because it used to be a wonderful resource. However, now I see that most of the nuclear sources are gone except uranium. There is no mention of fusion in the table at all. The article reads "The highest density sources of energy outside of antimatter are fusion and fission." but doesn't give any numbers.

I don't want to just revert the table back to the way it was but the old version was much more useful. — Preceding unsigned comment added by 71.217.11.36 (talk) 00:04, 17 July 2011 (UTC)

Merge with List of energy densities
I didn't see a section here for this, so I'm making one.

Yes, by all means they should be merged. If anyone agrees/desires, I volunteer to do the work. beefman (talk) 21:19, 16 January 2011 (UTC)


 * I agree with merging list of energy densities into energy density.
 * I suggest also merging orders of magnitude (specific energy density) into this article. Or would merging it into specific energy be better? --DavidCary (talk) 12:02, 15 August 2011 (UTC)


 * I also agree with merging list of energy densities into energy density.
 * But I'm opposed to any action to remove orders of magnitude (specific energy density). Specific energy density is fundamental in understanding fuel and energy storage.  The ~30 articles in Category:Orders_of_magnitude, taken together, give a broad overview of the universe.  Removing orders of magnitude (specific energy density) would leave a hole in that overview.  Mynameisnoted (talk) 23:30, 1 November 2011 (UTC)

Lead Acid / Car Battery in List of Energy Densities
How come the lead acid car battery is different than the lead-acid battery in the table. These should be the same for the purposes of this article. 70.113.25.151 (talk) 07:04, 29 July 2011 (UTC)

Energy density of coal is clearly incorrect
Folks, according to the EIA, ( and [www.eia.gov/totalenergy/data/annual/pdf/sec8_3.pdf]), coal got converted to electricity at (19.19 quadrillion BTU) / (970 million short tons) = 23 megajoules / kilogram in 2012. If 24 MJ/kg is the maximum extractable energy density, we are operating our plants at 95% efficiency? I think not. Jcmcclurg (talk) 22:01, 3 May 2012 (UTC)

Discrepancy of Hydrogen / Gasoline energy density comparison?
The intro paragraph says that Hydrogen has a much lower energy density than gasoline, even in liquid form, but the tables list Hydrogen as having a much higher energy density in liquid form. Can someone reconcile these two contradictory statements? Tossrock (talk) —Preceding undated comment added 02:46, 16 August 2011 (UTC).

Yes. The "energy densities" tables, in addition to energy density, *also* list specific energy.

According to the tables in this article, liquid hydrogen (10.1 MJ/L) has a much lower energy density than gasoline (34 MJ/L). In other words, a fuel tank with a volume of 1 liter can hold more energy if a person fills it with gasoline than if that person fills it with liquid hydrogen.

However, the tables also say liquid hydrogen (143 MJ/kg) has a much higher specific energy than gasoline (46.4 MJ/kg). In other words, when a hiker, airplane, elevator, rocket, etc. has only a limited amount of mass it can pick up, such a vehicle can can carry more energy if a person loads it with a kilogram of liquid hydrogen than if that person loads it with a kilogram of gasoline.

The intro paragraph currently says "hydrogen has a higher specific energy than gasoline does, but, even in liquid form, a much lower energy density.", which is entirely consistent with those tables.

Alas, it is very easy for a person to confuse "specific energy" with "energy density". How can we make this article less confusing? --DavidCary (talk) 18:24, 25 August 2011 (UTC)


 * The word "specific" in science usually means "mass-specific" which means you divide by mass. See the science section of specific.


 * However, there are many other specific quantities in which other denominators than mass are used, and many of them tend to correct for quantity. For instance in specific-gravity you divide by the density of water. Sometimes quantities are volume-specific (where you divide by volume).


 * Energy density is sometimes given in volume-specific terms (per liter) but also in mass-specific terms (some of the columns in THIS article are "per kg," which is the mass-specific measure of energy density). This article probably errs in initially defining energy density in volume-specific terms, rather than mass-specific terms. In fact, both are used.


 * Obviously liquid hydrogen with its very low liquid density (just 0.071 g/mL or 7% the density of water) has a very LOW volume-specific energy density, but still has a very high mass-specific energy density. The latter is sometimes called "specific energy" for short, as when "specific" is used in science without giving the unit, it usually (though not invariably) means "mass-specific".


 * I would simply re-write this article to say that "energy density" can be given in "per mass" or "per volume" terms. The former is often used for solids (like food) but the latter meaning is often used for liquids (like fuels). The "per mass" term is usually the same as specific energy, but mass-specific is preferred to as to be precise. The "per volume" term is often called "energy density", but is not synonymous with it. Energy/volume is only one measure of energy density. Energy/mass (as in the calories per gram in Grainola bar) is another. S  B Harris 22:06, 25 August 2011 (UTC)


 * If I understand correctly, Sbharris is suggesting that, in this Wikipedia article, we use the term "energy density" as a kind of generic term that covers both mass-specific energy density (J/kg) (aka specific energy, aka "gravimetric energy density") and volume-specific energy density (J/L) (aka "volumetric energy density"). That sounds reasonable to me.
 * The only reason I hesitate to do that is because most sources I've seen seem to use the term "energy density" exclusively to mean energy per volume, which supports the definition in the current version of our "energy density" article.
 * Using the title "energy density" to mean something other than what our sources say it means seems to contradict our Article titles policy. We are forced to use titles like dephlogisticated air until we find sources that support the use of reasonable names.
 * Does anyone have any good wp:sources that use the term "energy density" as something other than energy per volume -- either as energy per mass or a generic term that covers both ?
 * --DavidCary (talk) 18:47, 29 August 2011 (UTC)
 * There are plenty of references in the food energy article. ALL of them are energy density per GRAM of food. S  B Harris 04:14, 10 December 2011 (UTC)

Also add the energy density of nuclear fussion. — Preceding unsigned comment added by 70.176.87.72 (talk) 01:04, 10 December 2011 (UTC)

Antimatter energy density
http://www.niac.usra.edu/files/library/meetings/fellows/mar04/Edwards_Kenneth.pdf states "Specific Energy Antimatter = 180Mj / μg". While http://athena-positrons.web.cern.ch/ATHENA-positrons/wwwathena/FAQ.html states that "1 kg of antimatter with matter would generate an enormous amount of energy (9 · 10^16 J)"... that language may imply the energy is 90E15 "with" both the mass of matter and antimatter... I have been told by an astrophysicist "1 g of antimatter is about a gigawatt-day of energy". Someone please check my numbers... 1e9 J/s * 86400s = 86.4 Terajoules per gram (or approximately 90,000 Terajoules/kg).

I was thinking that it may not be a coincidence that the two values are a factor of 2 off, as the amount of mass required is exactly double if we include the required matter to accompany the antimatter for annihilation... but that would half the energy value not double it, so the 180*10^15 J/g seems like it may be the more real value. The matter-antimatter collider experiments probably produce very accurate numbers for this and I'm hoping to find a more accurate reference in one of the Fermilab Tevatron publications, but I'm not having much luck yet. I'm switching the page value back to 180000 TJ/kg until then. Luminaux (talk) 05:25, 2 September 2011 (UTC)

This is a simple application of E=mc^2. If you want 500g of antimatter + 500g of matter (1kg total) then E=(1kg)(299 792 458m/s)^2=8.98755179e16 J (or J/kg). If you want a whole kg of antimatter (assuming the matter is provided by something else, much like oxygen begin supplied to a fire) then the answer is twice the previous calculation (1.797510358e^17 J/(kg of antimatter)) because you are annihilating two full kg of mass but only counting 1 of antimatter. I'm going to leave the 180 PJ/kg but change the page to be clear that this table is NOT including the mass of matter (I checked and the hydrogen doesn't include the oxygen as a quick test. It maybe good to double check that the others do not consider the mass of the other reactants) Hologram0110 (talk) 17:16, 3 December 2011 (UTC)

Note about Storm & Smith
Recently a reference to the Storm & Smith studies was injected into the discussion of uranium availability. These shoddy analyses amount to little more than hoaxes, since the stipulate that the Rössing uranium mine cannot exist, as it would consume more energy than is produced in the entire country of Namibia. More details here. --Tweenk (talk) 15:31, 11 February 2012 (UTC)

Cleaning up the tables?
Why are the tables titled 'Energy densities ignoring external components' and 'Common energy densities' separate? I think they should be combined. They are listing the same information. I also don't like the efficiency information. Are you converting the potential energy into heat? into mechanical work? into electrical work? chemical work? It could be combined with the 'direct uses' column into a notes column. Hologram0110 (talk) 17:28, 3 December 2011 (UTC)


 * The purpose of that table is to be a sort of "introduction to energy density" for the layman. It's a list that compares the energy density of most of the materials that regular people have used or heard of, and specifically excludes the more experimental or obscure materials. InternetMeme (talk) 09:53, 8 November 2012 (UTC)

Human Food Energy
The inclusion of the energy density of a 6-inch Subway Club Sandwich inspired me to some calculations which I present only for perspective and insight. I take no issue with the article by this post. The 1.3 MJ of energy listed for the sandwich is 1.3MJ x 277.8 watt-hours/MJ = 361 watt-hours. The lithium-ion (rechargeable) battery in my son's electric bicycle holds 36-volts x 10 ampere-hours = 360 watt-hours of energy. They are equal in energy content. Similarly, the 2,000 Calorie (food calories or kilo-calories) diet of a rather sedentary human provides 2,000 x 1.163 = 2,326 watt-hours of energy, equivalent to operating a 100-watt incandescent light bulb for 23.26 hours, or a 97-watt incandescent bulb 24 hours. Jkaness (talk) 14:33, 12 October 2012 (UTC)

Question for the scientific community. The equation "1 Calorie = 1,000 calories" is true but confusing. Surely there is a deserving person for whom one of these "calorie" energy definitions could be re-named!Jkaness (talk) 17:04, 12 October 2012 (UTC)

Why so many thing was removed from table ?
Hello, I think this table is was especially infromative to compare specific energy stored by different means, non only in fules, but also in any other means ( radioisotopes, capacitors, strings, explosives and many other ) I understant that for clarity and easiness for the reader, many things was removed from the main table. However, I don't think that it is good to trade information contend for clarity. I think it is possible also to provide extended version of this table with as many items as possible, just as a reference table. In order to keep this page clean and reasonably short, I recommand to make this as a sparate page.

This is why I started page Energy density Extended Reference Table   — Preceding unsigned comment added by ProkopHapala (talk • contribs) 09:50, 14 December 2012 (UTC)

Energy content of carbohydrates (including sugars)
The table gives a figure of 17 megajoules per kilogram, but most sources seem to agree that a kilogram of normal household sugar contains around 4000 calories, which would correspond to around 17 kilojoules, not 17 megajoules. Right?--Distinguisher (talk) 09:59, 18 January 2013 (UTC)


 * The Calories the sources are talking about are nutritional Calories (capital 'C'), which are actually kilocalories, so the data holds (Also note the inter-usage of grams and kilograms).Octaazacubane (talk) 04:04, 4 March 2013 (UTC)

add this
add energy density of anti-matter and energy density of Quantum vacuum — Preceding unsigned comment added by 108.49.217.56 (talk) 01:02, 20 February 2013 (UTC)

Removed energy density of quantum vacuum, it's complete speculation and uncited. If you want to talk about this stuff, keep it to the page(s) that cover it; Energy Density is meant to be a reference page about current physics, not a discussion page about new physics.TheNeutroniumAlchemist (talk) 04:06, 25 February 2013 (UTC)

Quibble
I get the gist of this sentence at the end of the intro:

"A pressure gradient has a potential to perform work on the surroundings by converting enthalpy until equilibrium is reached."

but I think the language is sloppy, since enthalpy doesn't change with the PV work described. It's the internal energy that's converted to work. I would change it only because differentiating enthalpy and energy is hard enough for new learners without compounding it with ambiguous statements.

173.25.54.191 (talk) 02:31, 7 August 2013 (UTC)

UNCLEAR: most in "ignoring external components" section
It needs to be mentioned, if only in passing, that these figures are for COMBUSTION, in air (I assume) — Preceding unsigned comment added by 97.115.157.98 (talk) 22:09, 20 August 2013 (UTC)
 * ✅. —  Reatlas  (talk)  09:36, 21 August 2013 (UTC)

Possible source for table "Energy densities of common energy storage materials"
Right now the Energy densities of common energy storage materials table is unsourced, except for a circular reference to the Wikipedia page for Uranium-235.

This is quite unacceptable - we need a source for this data ASAP. What does everyone think about this document as the basis of the data used in the table on this page? The data table on page 2 is an aggregate of the studies quoted on pages 4-9 within that PDF.

Unless there is any dissent, I think this source should replace the current data. Stuart mcmillen (talk) 10:51, 10 October 2013 (UTC)

Introduction to energy density section.
Hi guys,

Various people have added some very interesting items to the table. I love the information, but I think certain items are not common enough to warrant inclusion in a table for laypeople. I've moved them here for future inclusion into an appropriate table:

Hi, interesting thing: it's possible to keep greater energy density than matter-antimatter using just charges. A sphere made of only protons or electrons will contain an amount of potential energy that increases like it's charge squared, approximately, and will soon reach much greater energies than its mass converted to pure energy. It's very unstable I know, but antimatter too isn't something you can carry around that easily, besides you have to produce it just like this hypothetical object. Funny thing that what makes up everything around us (charged particles) is so dangerous in other forms. 2.230.238.141 (talk) 22:46, 7 November 2013 (UTC)

Does anyone know what the energy density of Dimethyl ether is? Is it relevant on this chart? It is being proposed as more green diesel alternative. — Preceding unsigned comment added by MBizon (talk • contribs) 09:08, 17 December 2013 (UTC)


 * This paper gives values in imperial units, which translate to 28.2 MJ per kg and 18.6 MJ per L,


 * http://www.afdc.energy.gov/pdfs/dee.pdf


 * (Yes the paper is about diethyl ether, but the data table includes dimethyl).


 * I think it'd be relevant here, it's reasonably notable.


 * Tom (talk) 09:52, 15 May 2014 (UTC)

Flywheel energy storage is quoted as having a specific energy of 0.36 - 0.5 MJ/kg. Although it is mechanical and can only store energy as rotation, I think it's relevant enough to be included in the table. --77.0.50.85 (talk) 21:52, 4 March 2014 (UTC)

kWh notation
Comment is invited at Wikipedia_talk:Manual_of_Style/Dates_and_numbers on the question of whether kWh (with no space and no dot) is an acceptable unit symbol for use in articles, as opposed to restricting the choices to kW&middot;h or kWh (i.e. with either a space or a dot). EEng (talk) 22:45, 30 July 2014 (UTC)

Quibble
1. The "Planck density" entry was wrong so I removed it. 2. The "antimatter off by factor of 2" comment above is correct, except that the list is ambiguous about whether it counts just the mass of the fuel or fuel + reagent. 3. Where did we get the antimatter "MJ/L" line? Unlike the "MJ/kg" line, that should completely depend on what kind of antimatter you have and how densely you are storing it. Having a official "kg/L" for all antimatter is as nonsensical as having one for all matter. — Preceding unsigned comment added by RoadMap (talk • contribs) 21:26, 8 October 2014 (UTC)

Possible source for table "Energy densities of common energy storage materials"
Right now there are many unsourced items in this table. This is quite unacceptable - we need a source for this data ASAP.

What does everyone think about this document as the basis of the fossil fuel data used in the table on this page? i.e. coal, oil, petrol, diesel, kerosene, hydrogen, etc.

The data table on page 2 is an aggregate of the studies quoted on pages 4-9 within that PDF. Unless there is any dissent, I think this source should replace the current data. Stuart mcmillen (talk) 21:57, 25 November 2014 (UTC)


 * What ever happened with this? Most of the stuff in the tables are still totally unsourced.  I've begun to challenge a number of those uncited claims.  N2e (talk) 04:12, 6 July 2015 (UTC)
 * link 2 paragraphs above, dead link. Here's two links that may be of use: http://www.engineeringtoolbox.com/energy-content-d_868.html

http://www.world-nuclear.org/info/Facts-and-Figures/Heat-values-of-various-fuels/ go for it. GangofOne (talk) 06:03, 7 July 2015 (UTC)

Energy Density of Antimatter
The original author entered 10 to the 104th power, obviously wrong. I pointed this out with a comment in the page that was erased 5 minutes later. So I guessed it was a typo and the author meant to say 14th power so that is what I changed it to. But is it really 14th power??? I wanted someone to see my comment and think about it and put in the right number. Also not every reader is going to take the time like I did and edit the text. Some people might want to just put in a comment at the top of the edit screen that will hopefully be seen by a human maintainer and acted upon. — Preceding unsigned comment added by 172.8.156.52 (talk) 20:38, 13 February 2015 (UTC)
 * The problem is that's *not* the way to do that. If you think there's a problem add a template:dubious or template:citation needed, perhaps with a reason, and/or an edit summary.  Or if it's too complicated for a one line explanation, start a discussion on the talk page.  In any event, the energy density on a volume basis for antimatter seems suspect.  It has seven significant digits, and the density of antimatter can vary considerable.  Not to mention that the energy density on a mass basis only has two significant figures.  So unless there's a very specific (and precise) condition under which the antimatter's density is measured, this has to be wrong.  Much like the two lines for hydrogen gas just below the antimatter entry.  Rwessel (talk) 08:42, 14 February 2015 (UTC)
 * Made a fix. GangofOne (talk) 21:51, 5 July 2015 (UTC)
 * In further thinking about my revert, I think your error was only assuming the energy equivalence of a 1KG mass. The reaction would proceed by reacting two 1KG masses, just like we assume the Oxygen required for burning gasoline.  In any event, the density per liter is still problematic.  Rwessel (talk) 23:08, 5 July 2015 (UTC)
 * I purposefully left off the "reactant", ordinary matter, since such is left off the rest of the table, as stated: "These figures do not take into account the mass and volume of the required components as they are assumed to be freely available and present in the atmosphere." I hoped to make it clear about the density in the comment under Energy Density, as said above in Talk:, it all depends on what your antimatter is, so I choose a simple example, antiwater. But why quibble over a factor of 2, E=mc^2 blows every other reaction out of the running... Actually, to my mind the decision to exclude other reactants from the calculations is the wrong choice. It is more informative to put it in. Especially when there is the question of space flight, so popular these days.GangofOne (talk) 03:56, 6 July 2015 (UTC)
 * Another unclearity is the ASSUMPTION of the unmentioned reaction. For example, gasoline + O2 -> CO2 has a certain energy release, but there are other possible reactions, gasoline + florine, or even more exotic, gasoline + antigasoline ...GangofOne (talk) 03:56, 6 July 2015 (UTC)
 * I'm not going to argue that this isn't a bit of a mess, it clearly is. But if I'm comparing a battery to gasoline as a power source for some device, I'm almost always going to ignore the mass of oxygen needed for the gasoline, since I usually will be getting it from the atmosphere.  Obviously an application like space travel, where I have to supply the oxidizer, is different, but it's hard to say that more than a handful of the listed items would actually apply to space travel.  As to the assumed reaction, I agree, that could be better stated, although I think that no one is going to be expecting us to be talking about isooctane/fluorine reactions when we mention gasoline!  Given the relative scarcity of antimatter, I don't see that the need of a kilogram of ordinary matter to react with it is really that different than assuming the (approximately) free availability of oxygen containing air for gasoline.  I think, at this point, that the volumetric energy density for antimatter should simply be removed, as it's just not relevant - any form of antimatter has the same potential, and unless we start specifying state (as in the immediately following hydrogen lines), we really haven't selected anything we can hang a (mass/volume) density on.  Rwessel (talk) 05:26, 6 July 2015 (UTC)
 * Right, it's a mess. I just saying it could be clearer; remove the antimatter from the chart, it's a separate concept. There is a dicotomy about uses for this chart. Engineering wise, we have real fuels in real vehicles on earth, and can make useful comparisons. Then another table will a more fundamental approach, take all the reacants into account, mass and volume; this would also be practical if one is a rocket engineer... Or somehing.GangofOne (talk) 05:37, 6 July 2015 (UTC)
 * Just to clarify, I was suggesting removing only the MJ/liter number for antimatter, not both. Rwessel (talk) 06:00, 6 July 2015 (UTC)
 * OK Done. GangofOne (talk) 06:09, 7 July 2015 (UTC)
 * As far as antimatter goes, say electron + positron -> gamma ray. As far as I know electron have no size, no diameter that has ever found to be greater than some rediculously small margin of experimental error, so you might say the e + p have no volume, thus infinite energy density, and you wouldn't be "wrong" but it wouldn't be very useful. GangofOne (talk) 04:01, 6 July 2015 (UTC)

I see no reliable source for the antimatter line in the table. Seems it could simply be removed until such time as someone locates a good source. N2e (talk) 11:15, 6 July 2015 (UTC)
 * antimatter + matter -> (massless) radiation as per E=mc^2, I'm sure our Antimatter page says that, although I haven't checked yet.GangofOne (talk) 06:09, 7 July 2015 (UTC)
 * It does, but, of course, that's not a valid source (although the sources for that might well be). Rwessel (talk) 07:21, 7 July 2015 (UTC)

Liquid methane
Liquid methane is becoming somewhat popular and common in new bipropellant liquid rocket engine development, with new engines being worked by the Russians, Chinese, and American (e.g., Project Morpheus) government space programs, as well as two large engines (Raptor (rocket engine) and BE-4) being privately developed by two well-funded US private companies.

Therefore, it would be helpful to have some energy density numbers for "Methane, liquid" in the table in the article section Energy densities ignoring external components, where there is already "Hydrogen", "Hydrogen, liquid", and "Methane" (gaseous) entries in that table. Does anyone have a good source for these data? Cheers. N2e (talk) 03:14, 11 January 2016 (UTC)


 * LNG is already listed, liquid methane would seem to be at least partially redundant. Rwessel (talk) 05:55, 12 January 2016 (UTC)

antimatter is off by a factor of 2?
Hey, 1 kg of antimatter reacted with 1 kg of normal matter makes 180,000 TJ according to Einstein's famous equation. But doesn't that mean the energy density should be 180,000/2 = 90,000 TJ/kg?

Come to think of it, if we're using this paradigm, then all the fossil fuels (and hydrogen too) are wrong. We would need to factor in the mass of the O2 used in combustion, which would make all of values smaller. Since the article explicitly says it doesn't condsider things like oxidizers, maybe it is consistent after all?DrZygote214 (talk) 05:10, 8 October 2014 (UTC)


 * Usually the oxidizer is assumed to be free (though not true for rockets that carry their own oxidizer). When antimatter is used as a fuel the natural presumption would be that matter is free.   Vaughan Pratt (talk) 22:45, 19 July 2016 (UTC)

Self conflict
A number of these numbers conflict with other parts of Wikipedia. For Instance Jet_fuel states 42MJ/KG vs the 46 here - AA 38.96.210.190 (talk) 04:18, 22 August 2016 (UTC)

Lithium-ion underrepresented in selected energy densities plot
According to this paper: http://www.rsc.org/suppdata/ee/c0/c0ee00777c/c0ee00777c.pdf. C6/LiCoO2 (very popular battery) has an energy density of 1901 Wh/L which is 6.84 MJ/L, greater than that of compressed hydrogen. Both the table and figure list the upper limit at 2.63. Which might be more practical, but is FAR from the theoretical capabilities of these devices (gravimetric energy density should also be adjusted to 568 Wh/kg or 2.04 MJ/kg). — Preceding unsigned comment added by Viewsk8 (talk • contribs) 19:06, 1 December 2016 (UTC)

Fusion needed
While I realize the only nearest operational fusion reactor to date is 93 million miles away, it would still be nice to have an entry for it. How many joules are released by the fusion of a kg of H to form He in the Sun? (It's too hot to call it H2.) You'd think it would be stated clearly somewhere, but the proton-proton chain reaction article is rather waffly and doesn't seem to offer a definitive answer I'm comfortable putting in the table. Vaughan Pratt (talk) 01:58, 6 January 2017 (UTC)

Including Watt-time [Wh] column, as it's the Universal unit of Energy
I created [Wh/L] column for better understanding instead of seeing density values in MJ/L, but if someone is familiar with the density of the materials, please include the [Wh/Kg] column too, which will be very practical and understandable and useful for everyone. Frozenprakash (talk) 19:27, 3 January 2017 (UTC)


 * One editor's "understandable" is another's "incomprehensible" (though in this case there's only a factor of 3.6 = 3600/1000 involved). That's why we have SI units. (Although the liter is outside the SI it is arguably "more accepted" than the hour.  Moving decimal points around is easier than dealing with factors of 3.6.) Vaughan Pratt (talk) 19:01, 6 January 2017 (UTC)

Watt-time as Universal unit of Energy
We do not use Joule in real life scenario, for detailed explanation, let me explain,

Different units of Energy,

Joule = Watt Second = 1 Watt consumed per second

Watt hour = 3600 Watt Second = 3600 Joule

KiloWatt hour = 1000 Wh = 3.6 Mega Joule

So, these above units are universally used while denoting energy storage, below are the examples,

Average battery storage capacity of different types [approximate values, for your understanding],

AAA [NiMH] = 1 Wh

AA [NiMH] = 2.5 Wh

AA [Li-ion] = 3 Wh

C [NiMH] = 5 Wh

D [NiMH] = 10 Wh

18650 [Li-ion] = 8 to 13 Wh

26650 [Li-ion] = 15 to 20 Wh

mAh and Ah are completely wrong units and marketing bluff, which doesn't give the energy capacity, as it's skips voltage,

so for same mAh or Ah, the energy [in Wh or kWh] is completely different with different voltages.

I hope now you know why we use kWh [Universal Electrical Unit] in home energy meter.

And Finally, Joule or Watt second [Ws], kilo Joule or kiloWatt Second [kWs] are used to rate the capacitor Energy,

For example, Maxwell 3.V Supercapacitor has around 3.85 Wh [13,860 Ws or 13.86 kWs],

but as the primary use of capacitor is to blast the power in couple of seconds or to charge in couple of seconds, thus Ws or kWs is commonly used to rate them [and humanely understandable too].

Even camera flashes were rated in Watt second per flash.

In general,

Power density are rated in [Watt / Kg] and

Energy density are rated in [Watt hour / Kg]

Now i hope you got bit of an understanding about the Watt and time used to define the energy !

Frozenprakash (talk) 12:33, 10 January 2017 (UTC)

Energy density of nuclear fuel
The figure of 80 million MJ/kg for nuclear fuel is a theoretical calculation based on fission rate. The actual energy obtained from a modern nuclear power plant is about 60GWday/tU (ton of uranium) or 5.2 million MJ/kg, only 1/16 of the number in the table, with the remaining 15/16 cooling its heels in the plant's spent fuel rod cooling pools and storage casks. What would be a reliable source for the 60GWday/tU figure? Would people accept http://www.plux.co.uk/energy-density-of-uranium/ as reliable? Vaughan Pratt (talk) 18:54, 27 January 2017 (UTC)

Diesel vs. Gasoline incorrect?
In the table for different energy densities, diesel i listed as having 3.4 % higher energy/weight and 4.7 % higher energy/volume compared to gasoline. However on the wiki page for diesel "https://en.wikipedia.org/wiki/Diesel_fuel" diesel is said to have less energy/weight (only 0.2 % less) but significantly higher energy/volume (11 % higher) compared to gasoline.

Quote from diesel wiki-page:
 * As of 2010, the density of petroleum diesel is about 0.832 kg/L (6.943 lb/US gal), about 11.6% more than ethanol-free petrol (gasoline), which has a density of about 0.745 kg/L (6.217 lb/US gal). About 86.1% of the fuel mass is carbon, and when burned, it offers a net heating value of 43.1 MJ/kg as opposed to 43.2 MJ/kg for gasoline. However, due to the higher density, diesel offers a higher volumetric energy density at 35.86 MJ/L (128,700 BTU/US gal) vs. 32.18 MJ/L (115,500 BTU/US gal) for gasoline, some 11% higher, which should be considered when comparing the fuel efficiency by volume.

I am not on expert on the differences between these fuels, but it is clear that there is a discrepancy between these two wiki pages (incorrect values?, different measurement techniques? or something else?) EV1TE (talk) 15:08, 5 February 2017 (UTC)

Energy in a match head
What is the energy density of the red material used in a standard household wooden safety match? Or just the energy since I can easily weight a match head. Vaughan Pratt (talk) 05:49, 17 March 2017 (UTC)

Inertial Energy Storage
Is there any reason why inertial energy storage (fly wheels) is not included?--Damorbel (talk) 06:44, 24 July 2017 (UTC)

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