Talk:Energy density

Dubious

I removed the following text from a {{citation needed}} template and replace it with a new {{dubious}} template that points to this discussion. The reason parameter of the template is far too long and includes characters that break the template. Plus, the reason had grown into a discussion (edits: edit 79.182.119.9, edit 140.239.58.226, among others)

Seems high, please check. Using a density of anthracite coal of 1.4g/cc and a specific energy of 32.5MJ/kg, you get 45.5MJ/L instead. - re: yes, correct it please. See wiki Coal_assay#Relative_density. Ideally for most materials we list the highest possible number, the record, then porosity is a separate issue, giving any low value you wish. However as coal above 91% C is classed anthracite, or even 88% C, the rest of the impurities, whether H,S or heavy minerals, affect the sp. gr up or down. Anthracite burns without much flame, not much H or CO or CS2 to pyrolyze out of it. So it depends on your definition of anthracite, if 100%C mineral graphite being excluded from it, then you may still find mined anthracite out there that's well above 1.8 sp.gr., and even mineral graphite may have internal porosity to get listed at <2.1 sp. gr., when ideally it's 2.23-2.26, the difference being attributed to porosity. Listing the highest, the record value and saying everything less is due to porosity or contamination may not be ideal. You can fix it to a more representative, average value. Lignite and bituminous coal by definition are vague compounds containing H, 0, N, etc, and porosity, and listing the "record" lignite or bituminous compounds, and saying the rest is due to porosity would not make sense, so for anthracite we should list the most representative average value from global coals classed as anthracite, as long as graphite is included and listed separately from anthracite. I think using a sp.gr. of 1.5 would be better than 1.4, (and better than 1.8-1.9 which is very high grade but very rare anthracite of relatively low porosity) all these cited values being still very far from 2.2 originally used.

((New Comment : 1.4g/cc is low. even decent bitumunous coal such as Newcastle or Richards Bay standard contract coals get to 27.5Mj/kg at SG's of 1.6g/cc. These coals have excellent volatile contents and hence burn very easily, so their Mj/L ratings should comfortably reach 40 and higher. The energy rating for Bitumunous Coal in the main article is misleading. The quality of coal used there is a low quality power station coal, typically referred to as Run of Mine (RoM) coal, which has not been treated in a wash plant or is the deliberate product of a wash plant set to generate two streams of coal : one for export and one for a power station. Typical Run of Mine coals contain significant amounts of ash (de facto rock) which means that RoM coal seldom has an SG of less than 1.8. Hence RoM coal at 22Mj/kg and an SG of 1.8 results in a Mj/L of close to 40. So the SG used in the main article used for bituminous coal is also dubious.)) — Preceding unsigned comment added by Historiese huise (talk • contribs) 11:42, 4 July 2015

Hydrogen

Can someone please verify the energy density of liqufied Hydrogen per Liter? It looks a bit asymetric to me, could be that's for gaseous H₂?

(changing IP) 2003:DE:4F05:3800:D428:F5DA:EEF:7AF2 (talk) 20:10, 12 August 2018 (UTC)

I don't think it's correct. Someone used the same value for the specific energy for three different forms of hydrogen (in the lower table). Liquid hydrogen certainly has a lower enthalpy than gaseous hydrogen, so it's heat of combustion is lower! I'll mark it. Eric Kvaalen (talk) 14:45, 29 March 2019 (UTC)

Consistent with including antimatter as an "ideal" energy source, metallic hydrogen could make an relevant inclusion on the table. This article https://www.nasa.gov/pdf/637123main_Silvera_Presentation.pdf indicates a specific energy of 216 MJ/kg for hydrogen, compared to 10 MJ/kg for hydrolox. But the bond dissociation energy of H_2 is 432 kJ / mol, so that's consistent.121.200.7.178 (talk) 05:10, 2 July 2020 (UTC)

Removing table

This article has become a mess. At one point it had a long table of energy contents, and in 2008 someone split it into two tables, the first for self-contained systems and the second for things like fuels which require oxygen. Then in 2011 some anonymous editor replaced the first table with two much shorter tables, the first giving various fuels (which do need oxidizer other than the first two rows) and the second (called "List of Energy Capacities of Common Storage Units") giving three kinds of batteries and a Subway sandwich! He put "The following is a list of the energy densities of commonly used energy storage materials" as an introduction to these two tables. Since then people have edited the first table, making it rather long. But there's no longer any justification for having both the first table and the later table with fuels. So I'm plannin' to transfer some of the information from the first table into the last table and then delete the first table. I will also try to put only lower heating values. At present some are higher heating values. Eric Kvaalen (talk) 14:45, 29 March 2019 (UTC)

I would just like to say that you are doing a fine job of improving this article. I am authorizing a 20% raise over what you are currently being paid. :) Keep up the good work! --Guy Macon (talk) 16:24, 29 March 2019 (UTC)

The table is indeed a mess. Too many sources/authors have yielded apples-to-oranges comparisons. Metallic iron >household waste > TNT, etc. True, in given contexts, but not clear information. Nuke it.

Riventree (talk) 17:37, 5 April 2019 (UTC)

@Riventree: No, we should certainly not nuke the table! What I was complainin' about was the presence of two tables for no good reason. But I got rid of the first one, mergin' some of the information into the second one. You have added a "self-contradictory" template, with the comment, "Too many disparate sources yield apples-to-oranges values. We should explain why TNT is below household waste and metallic zinc". Well, the entries are ordered more or less by energy density. If you want to improve the ordering, fine. I think we should remove that template. I don't see anything self-contradictory. Eric Kvaalen (talk) 12:51, 23 April 2019 (UTC)

@Eric Kvaalen: Intuitively, the spectrum ( Metallic iron > household waste > TNT) is self contradictory. The table has an intrinsic dismissal:

"Disregard the mechanism which provides this number"

This is the principle I rail against. I feel it's silly to suggest, and it makes the comparisons in that column useless to "normal" readers. Taken to logical extension, it would indicate that ALL fuels have an identical energy density in mass via E=mc2.

Thus, I say nuke the table or split the values out into comparable, relevant mechanistic bases so the data are internally comparable:

• "energy obtained by burning in still air at 1 atmosphere", which is what MOST of the fuel values (coal, heating oil, etc) mean,
• "energy obtained in an internal combustion engine designed for this fuel" for gasoline and diesel and other such values
• "energy obtained by reacting this compound with appropriate eletrolytes in a battery" for lithium, silver peroxide, etc.
• "energy obtained by burning this fuel in a hypothetical 100% efficient fission/fusion reactor", for plutonium, hydrogen, etc...

Doesn't that make sense? Anyone?

Riventree (talk) 17:52, 25 April 2019 (UTC)

@Riventree: I disagree. I like having everything in one table. You can certainly add comments in the last column if you want to make things clearer, but I think most people understand that, for example, when you use plutonium in a nuclear reactor you don't burn it with air. By the way, I don't even find silver peroxide in the table. And what is so self-contradictory about Metallic iron > household waste > TNT? Eric Kvaalen (talk) 19:45, 25 April 2019 (UTC)

Continued with simpler mental gymnastics and less indentation

• This article about energy density contains a table with a NUMERIC column labelled "MJ/kg"
• Using a numeric value implies certain things: mathematical operations (such as >, ≤, ×) should apply.
• @Eric Kvaalen: poses a Q: "what is so self-contradictory about Metallic iron > household waste > TNT?"
• A: There is no "real world" way that dry celery stalks have more energy per kilo than TNT. That should be manifest to even the most committed semanticist.

I assert: For all fuels composed of "normal matter" (not antimatter, neutronium, bose einstein condensates, etc) the correct value for their energy density is precisely 9×10¹⁰ MJ/kg. See here for the proof of this statement. This represents a perfect conversion of any matter to its equivalent amount of energy by some hypothetical matter decomposition tool. This value must be in excess of all other possible values produced by other ways of extracting energy from the fuel, therefor it is The Right Value.

Therefor, my modest proposal would be: We should correct all the entries and enter just this single value. This would be equally useful and free of any possibility of entering the data incorrectly.

I think this right-but-ridiculous proposal illustrates what's wrong with a single table: The values in the various rows are incomparable. A table implies a relatedness for its rows that is not true here.

Therefor, I think a single, unified table is very misleading construct. (consider just your example, household waste > TNT) Misleading data is anathema to WP:ENC, therefor this table should not exist in its current form.

Riventree (talk) 20:58, 25 April 2019 (UTC)

Alternatively, exclude all values that are not given as the "lower heating value" that the text above the table claims. :) See Heat_of_combustion for the definition. Since antimatter would not combust in our universe, we can delete that row. Riventree (talk) 21:04, 25 April 2019 (UTC)

@Riventree: I still disagree. I still think it's interesting to be able to compare these values, knowing full well that the definition of the energy content depends on what we're talkin' about, whether it's annihilation of antimatter, fusion, combustion, explosion, or battery power. And I still say there's no contradiction. As for household waste and TNT, first of all it means average household waste (like what goes to the dump or the incinerator), not every single kind of household waste (like dry celery stalks — though in fact dry celery stalks probably do have a lot of energy, being mostly cellulose, no?). The value for TNT by the way comes from the definition of TNT equivalent, which is 1 kcal/g or 4.184 MJ/kg. It's interesting that TNT has less energy (when it explodes) than household waste (when burned).

By the way, I don't know whether it was by accident but you deleted what I wrote yesterday. You're not supposed to do that on a Talk page.

Eric Kvaalen (talk) 07:36, 26 April 2019 (UTC)

Ack! Sorry! I hadn't intended to do that. I'll put it back (above)

As far as the table goes, I've said my bit about how misleading it is. Do as you think best. Riventree (talk) 09:33, 26 April 2019 (UTC)

I agree this table unfortunately is now kind of a mess.

Another table has been added since specifically for batteries with dedicated columns (dimensions, weight, etc.).

Note#1: Watts/h are missing from this second table while present in the first and main one. Watts are used by engineers instead of Joules (e.g. in feasibility studies).

Note#2: Indeed it could make sense to have a rough idea of batteries dimension, weight, etc. as long as it is not commercially oriented (also keep in mind that the battery cylindrical or prismatic formats influence their energy density, shall we then split values ?).

Thing is that some battery rows / values still are in the main table.

So why 2 tables and not several (cf. above discussions) .

My point is that I would agree to add a column to the main table stating what already is stated in one of the paragraph of the Wikipedia page, i.e. the type of reaction, e.g. Nuclear, Chemical, Electrochemical, and would even add some more like elastic (cf. talk above) or potential (cf. dam row) if this makes sense. And I would let somebody add a small chapter to decrypt/explain all these as said above by @Riventree: "burning in still air at 1 atmosphere", "internal combustion", "reacting with appropriate electrolytes", "nuclear fission", "nuclear fission", etc.

I would also like someone to add some deep explanation about why is it that waste burning and TNT explosion energy density cannot be compared (and keep them all still in the same table for comparison reason).

Finally, values for Lithium-Ion are based on dead links references and even the news ones from Panasonic are 2007 old (12 years old at the time of writing).

Didn't labs and industries achieved progresses in these fields and reached better values that we could update since ?

Could we also have a rough idea of what is inside labs in term of future batteries energy density ?

Golem Le Brut (talk) 12:41, 30 August 2019 (UTC)

Indeed, IMO, the post-"condensation" version of this table is almost completely value-free to the majority of wikipedia readers. The attempt to merge the previous multi-table data into a single table seems misguided. (AGF, otherwise EK's efforts would seem malicious)

Riventree (talk) 05:11, 31 August 2019 (UTC)

I like the table, particularly for comparing energy density of batteries. Most of the items in the table would benefit from citations. Oddly, among the very few 'citation needed' tags was one on the heat of fusion of ice, a standard value tabulated in so many sources [e.g., The Handbook of Chemistry and Physics, The Standard Handbook for Mechanical Engineers, The Steam Tables, or any basic textbook on Heat Transfer or Introductory Chemistry, etc.] that no citation is needed. If no one objects, I will remove 'citation needed' and use 3 significant digits [0.334 MJ/kg instead of 0.33355] Topper'sDad (talk) 03:51, 2 December 2021 (UTC)

Table Cleanup

There are still numerous issues with these tables. Inconsistent units have confused at least one reader who got the impression that rubber bands are denser than gasoline. I am going to make some edits to make the tables more readable, consistent and meaningful. I noticed the nuclear table doesn't have density values at all for most substances. I will fill it in with values derived from binding energy and physical density for the liquid or solid state of the substance. I am aware these may not be the conditions that a nuclear reaction occurs in, but I think it is still a valid way of measuring energy density. We can include appropriate caveats and still have values in the table. I think we should adopt scientific notation so that values of different orders of magnitude can be more easily compared. Circuitboardsushi (talk) 13:59, 8 December 2023 (UTC)

The more I read this article the worse it is. Citation 1 is unnecessary. It is just a working definition that we need to have in order to give values. The reference is a generic guide for SI units which isn't really helpful for affirming the cited statement. We can assume SI units without invoking NIST.

I still don't understand what is meant by "inaccessible energy". It says, "such as rest mass", which should be obvious. There is no indication of any other forms of inaccessible energy, I would assume it might include things like thermodynamic losses depending on context, but it doesn't say.

Then we go on to over explain the rest mass thing, invoking "cosmological and general relativistic contexts." The article doesn't give any examples of these. For the actual examples, rest mass is only relevant to nuclear reactions. It might make sense to include it as part of an explanation of nuclear binding energy. In the introductory paragraphs it doesn't seem necessary to mention it. Circuitboardsushi (talk) 15:25, 8 December 2023 (UTC)

LEU

Note that fission power in non-breeder reactors produces a fair amount of power from generated Pu239. Gah4 (talk) 10:25, 28 August 2022 (UTC)