Talk:Energy conversion efficiency

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Antimatter Annihilation[edit]

Do we really need this? This is more of a trivial detail. —Preceding unsigned comment added by (talk) 15:40, 1 August 2010 (UTC)

Reciprocating Steam Engines[edit]

Since reciprocating steam engines were largely responsible for the industrial revolution and energy conversion efficiency studies it would be worthwhile to provide accurate values.

Examples - from which to which energy form?[edit]

In the examples section, it would be nice to add columns from and to in order to understand exactly, where the energy is lost, e.g. from visible light to electric energy (Solar panel) or from electric energy to mechanical energy (Motor). This might also clear up the misunderstanding about the heat pump which has an efficiency (CoP) of up to a few hundred percent, one may say. I might insert that the next days, if nobody objects. Zeptomoon (talk) 16:09, 19 November 2009 (UTC)

Examples - efficieny[edit]

Please do not change electric heater efficiency to something below 100% All electrical devices convert electric power into heat with absolutely 100% efficiency —Preceding unsigned comment added by (talk) 16:08, 21 February 2011 (UTC)

Solar cell efficiency[edit]

The source PDF for solar cell efficiency mentions 85% in the context "can absorb up to 85% of above-band gap sunlight". There are two additional sources of loss here - lower frequencies of light are lost as heat, and higher frequencies of light are absorbed but only the band-gap potential of the light is converted - the extra energy of the higher frequency photon is also lost as heat. This number should be changed to the highest efficiency that a solar cell has actually achieved from normal sunlight, or it should note that such efficiency requires a monochromatic source. (talk) 02:29, 9 April 2011 (UTC)

Combustion engine efficiency[edit]

The table gives a combustion engine efficiency of 10-50%, based on a broken link. However, the Internal combustion engine article says it's about 18-20% efficient, with a theoretical limit of 37% and one of the sources states that experimental models reach only 28% efficiency. So what is the 10-50% efficiency based on?
Note that the abovementioned source is about cars, but the efficiency is for fuel-to-crankshaft, so that should not matter. Or are car enignes inherently less efficient? However, this is about actual efficiency. If the engine works constantly at the ideal speed, that should improve, but still not come close to 37%, I assume. DirkvdM (talk) 12:54, 21 January 2012 (UTC)

Efficiency of light sources[edit]

The values for different light sources in the table are either wrong or extremely misleading. For example: The energy conversion efficiency of any incandescent lamp should be near 100 per cent. Most of it is in the infrared region and thus no benefit to human vision; however, in terms of radiated energy from the filament light bulbs are extremely efficient. The lighting efficiency has nothing to do with energy conversion, but with the physiology of human vision. The details are described in Luminous efficacy. Mixing both up is extremely misleading and very bad style.

Please correct these values so that they give the true energy conversion efficiency (i.e. without mixing up with photometric terms!). For incans, as said above, it should be >90% (the rest is used to heat up bulb and socket, and eventuelly given off as far IR and convective heat), for LEDs and CFLs I would guess something between 20% and 50% (the rest is waste heat inside the electronic components or absorbed by the phosphor and never been radiated off as light/IR/UV). Does anyone more accurate values for this? If not, I suggest to remove the data for light sources, since they are entirely useless in this form.--SiriusB (talk) 12:11, 12 May 2012 (UTC)

Addition: Someone has cited the article Luminous efficacy but given wrong values. However, neither luminous efficacy nor luminous efficiency is a measure for energy conversion. The former is not even a dimensionless number, while the latter is arbitrarily related to the maximum value of 683 lumens per watt. There is no comparison of output energy with input energy. In the given form it makes about as much sense as specifying the energy conversion efficiency of a PhD student in terms of papers published per calories consumed. In other words, the example of light sources is misleading here.--SiriusB (talk) 19:04, 12 May 2012 (UTC)
Actually, the conversion efficiency of an incandescent bulb is very low, although it is higher than the efficacy. (See below.) While true that the filament emits a huge amount of IR (increasing in intensity down past the far IR), nearly all of it is absorbed by the glass, except the very near IR. Glass is quite opaque to wavelengths lower than ~ 1000 to 1500 nm. Thus, most of the light energy is absorbed by the glass and lost via convection to the surrounding air. A great amount of energy is lost simply overcoming the resistance of the wiring, which is demonstrated by a simple experiment where twelve 100 watt bulbs are connected in series, powering each with only 10 volts, but when the wiring is placed in liquid nitrogen making it superconductive, all glow with their full brightness. The incandescence from carbon-arc lamp (open flame, with no glass shielding) produces a truer blackbody curve. Still, I agree that this needs fixing, and plan to help as soon as I can. Zaereth (talk) 08:03, 9 September 2015 (UTC)

The table is very uninformative[edit]

The table should be split in categories for each type of conversion. For example:

  • electrical to motor
  • motor to electrical
  • electrical to heat
  • luminous to electrical


"Muscle is 8 to 21% more efficient at natural process energy conversion than photosynthesis" is a very bad kind of sentence and it is what that table is sending as a message (talk)

and what about nuclear energy plants? — Preceding unsigned comment added by (talk) 06:29, 1 September 2015 (UTC)

The table does that already. For example, electrical generation is broken into different methods of generation, including combustion engines. (Albeit, not nuclear, but feel free to add if you have sources.) Motors are divided into the two types, combustion engines and electrical, so it already does what you are asking. Photosynthesis is the conversion of solar energy into chemical energy, and muscles convert that chemical energy into kinetic energy. The graph shows that it's easier to burn sugar than it was to make it. Zaereth (talk) 18:29, 1 September 2015 (UTC)
I added another column to the table, helping to show what kind of conversion was taking place. I might add, however, that some of these numbers seem to be for efficacy rather than efficiency. An incandescent bulb around 100 watt, for example, has a typical efficacy of about 3 to 5%. That's input energy per usable light. (Not to be confused with luminous efficacy, which augments that by the eye's sensitivity to certain wavelengths.) However, the other number of about 5 to 10% is just about right for efficiency, which is total input per total output, including invisible radiation. (Efficiency gets higher with wattage too.) I'll try to gather my sources on the various lights when time permits. Zaereth (talk) 00:28, 9 September 2015 (UTC)
I had a chance to finally read through the article, and I see now where a lot of the confusion is coming from. The article states that conversion efficiency is the conversion into usable energy, and this is more the definition for efficacy. Instead, conversion efficiency is the proportion of energy converted from one type to another, regardless of whether it's usable or not. Energy is lost during the conversion by changing some into various forms of other energy, for example heat is lost in a gas turbine, and therefore is not turned into electrical energy. The conversion of one form of energy into another is called work. Some of lost energy may be recoverable, but never all. (ie: gas turbine plus steam turbine.)
Flashtube outputs, all operated at the same energy, to help clarify what I mean.
When talking efficacy, on the other hand, then what we really mean is how effective the converted energy is. For example, a flashtube has about the highest conversion efficiency of any light source, up to 50% for xenon and 40% for krypton. However, when xenon is used for pumping an Nd:YAG laser, the efficacy is extremely low, because none of xenon's spectral lines are equal to Nd:YAG's absorption lines. Krypton is different, because most of its energy is placed into a few spectral lines that almost perfectly match Nd:YAG, so the efficacy, or effectiveness, of the energy conversion is greater, even though the conversion efficiency is lower. Zaereth (talk) 21:22, 10 September 2015 (UTC)

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