8 ms·

Why are there different ways of measuring energy?

62 points by _Microft 4y ago

deleted 4y ago
[deleted]
dotancohen 4y ago
The cookie popup on that site, at least on mobile, is one of the worse I've encountered.
egberts1 4y ago
It is quite simple, as it pertains to the matter phase as being of solid, gaseous, liquid, or supercritical (sometimes plasma) state. As with any attempt at delta measurement of energy, you need that starting reference point being used by your test instrument and that method of measurement is likely not to be the same one for different matter phases: Heisenburg uncertainty principle comes to mind here.
colechristensen 4y ago
>We can reduce losses from primary to secondary energy by transitioning away from fossil fuels because the losses for these sources are particularly high. This reduces the amount of heat lost from converting these raw fuels into a usable form, such as electricity. This is false, fossil fuel power plants have efficiencies between 30% and 60%, solar 15% to 25% (or much less if you consider the time that it's dark), wind 20% to 40% (or much less if you consider the time it's not windy). I suppose you can ignore these things because the sun and wind are free resources, but the basic fact is that transforming heat into electricity is considerably more efficient than photovoltaics or wind turbines.
- pfdietz 4y ago
  This comparison is absurd, for the reason you note and apparently dismiss. Efficiency comparisons are really only relevant when you're looking at the same input.
- sbierwagen 4y ago
  If you really wanted to do pointless stuff with numbers, you could say that fission has an abysmally low "efficiency" because not all of the mass of the atom is converted into energy, with the majority of it ending up as stable fission fragments or neutrinos that zip through the reactor walls. You start with a U-235 atom that has a rest mass of 218,871.5 MeV and only get 202.5 MeV of heat out of it? Pathetic!
- dredmorbius 4y ago
  Energy efficiency refers to how much useful output is delivered based on input. For thermal energy generation, net efficiencies tend to range from 20% to highs of about 40--50% via combined-cycle generation, perhaps with cogeneration of generation+thermal heating applications, the latter typically being district heating or industrial heating. There's also the concept of nameplate capacity vs. capacity factor. The former relates to the maximum possible output of a facility, the latter to the attainment of the nameplate capacity over a year. It's not clear to me which of these you're referring to. Moreover, the conversion efficiency of flows such as solar and wind is not directly comparable to the efficiency losses of termal generation for other reasons, namely that the environmental availablity of the uncaptured portion is still generally available for other environmental service. Burning a ton of coal and only extracting 30% of the total energy potential still means you've incurred an opportunity cost of 70% of that fuel stock's energy potential. I will note that there are a lot of shenanigans which are played with nameplate and capacity factors, by both boosters and opponents of renewable / carbon-neutral energy. That said, there's no need to add to the confusion. Confounding conversion efficiency, capacity factor, and deadweight opportunity costs and losses is a slippery business at best.
- jyounker 4y ago
  The ongoing cost of mining sunlight is nearly zero.
blueflow 4y ago
I found this article disappointing. Neither Joule, Watt(seconds) nor any kind of energy potential or entropy were mentioned. The "primary, secondary, final, useful" categorizing seems arbitrary to me an i have doubts about its usefulness. In the end of the day, energy potential is nothing intrinsic to matter, it depends on what you can and will do with it. In the diagram, the Oil, Wood and Coal chains are exclusively about burning that stuff. Oil and Coal are a climate problem just due to the fact that people dig/pump them out and put its carbon onto earths surface, burning it for heat is optional here. Think plastics. This article gives me a odd feeling.
- jolmg 4y ago
  Same. I was kind of hoping for an in-depth explanation on the difference between Watts and VA, which should be none, W = VA, but apparently for AC they're used for 2 different ways of measuring average power, one being the product of peak current and voltage divided by 2, and the other being the product of the root mean square voltage and the root mean square current. I still wonder why they both matter, rather than just sticking with one or the other. According to Wikipedia, > Some devices, including uninterruptible power supplies (UPSs), have ratings both for maximum volt-amperes and maximum watts. The VA rating is limited by the maximum permissible current, and the watt rating by the power-handling capacity of the device. Is there something besides the "maximum permissible current" that influences the "power-handling capacity" in a circuit? These sound the same.
  - InitialLastName 4y ago
    The key concept you're missing is Power Factor[0]. With reactive (inductive or capacitive) loads, the current and voltage will be out of phase with one another, leading the peak current to occur at a time other than the peak voltage. This reduces the power delivered to the load to less than |V|*|A|; in a situation where you hold power demand and voltage steady, you would need to deliver more peak current. For the two power measurements, one is instantaneous power, the other is average power. Different situations call for different measurements. [0]https://en.wikipedia.org/wiki/Power_factor https://en.wikipedia.org/wiki/Power_factor
  - 4y ago
dredmorbius 4y ago
For those who seem to be missing the point, this article is about how energy is reported and discussed within the context of national and global energy utilisation. It is not about units of energy measurement. Such articles exist, but their goal differs from the one here. For those who report on energy utilisation, and those trying to understand those reports, the distinctions made here are highly useful and informative. The article should be assessed on that basis. Primary energy addresses the total available stocks, flows, and withdrawals from the environment. Those are values determined and dictated by nature. These are submect to aquisition costs --- drilling, mining, fracking, dam-construction (and environment disruption & risk), deployment of solar collectors and wind turbines. Secondary energy is largely what is actually transacted through wholesale commerce: generation and fuel deliveries. If you're interested in commercial-level transactions and international trade, these are the values of principle interest. In the case of electrical generation, conversion losses are largely dictated again by physics (e.g., Carnot's law), and while incremental improvements may be possible they're often quite difficult, and ultimately limited. Final and useful energy are the retail-level delivery to end-uses, and the actual intended delivered benefit of that energy. Here again physics enters into the discussion --- light bulbs, computers, combustion engines, air conditioners, and electric motors have their limits to conversion of electricity or fuel to light, computations, movement, and thermal management. They're also governed by other factors (insulation, daylighting, focused- rather than generalised-delivery, land use). Discussions are why we'll see discussion in units of MWt vs. MWe --- megawatts of thermal vs. electrical energy. Which might satisfy some of the units-fans out there. Otherwise, as the piece says, if you want to understand the energy picture as a whole, you need to understand the parts, their relations to one another, and their own specific behaviours, characteristics, and limitations.
avalys 4y ago
I ran into this report from Mckinsey a few weeks ago, and stopped reading after the opening sentence. "Large semiconductor fabs use as much as 100 megawatt-hours of power each hour..." https://www.mckinsey.com/~/media/mckinsey/dotcom/client_service/operations/pdfs/bringing_fabenergyefficiency.ashx https://www.mckinsey.com/~/media/mckinsey/dotcom/client_serv...
- deleted 4y ago
  [deleted]
gumby 4y ago
This is really about the flows in a Sankey energy diagram, yet they didn't use one. It makes more sense if you know this, though in that case you don't need the article. https://en.wikipedia.org/wiki/Sankey_diagram https://en.wikipedia.org/wiki/Sankey_diagram Some nice examples: https://www.iea.org/sankey/ https://www.iea.org/sankey/ https://www.researchgate.net/figure/World-energy-flow-in-2011-PJ-LLNL-2016_fig1_317688860 https://www.researchgate.net/figure/World-energy-flow-in-201...
- dredmorbius 4y ago
  The Sankey relationship is strongly hinted in this diagram: https://ourworldindata.org/uploads/2022/04/Four-ways-of-measuring-energy-1536x886.png https://ourworldindata.org/uploads/2022/04/Four-ways-of-meas... Even in a traditional energy-flow Sankey diagram (see the LLNL examples: https://flowcharts.llnl.gov/commodities/energy https://flowcharts.llnl.gov/commodities/energy), the four concepts aren't always clearly expressed. LLNL also includes numerous assumptions and framings which aren't necessarily clear. The "wasted energy" component, which in my experience people always focus on strongly, for example, is based on an assumed efficiency of processes, it is not directly measured. Another aspect I'd not realised until the past year or so is that the values associated with renewables (hydro, geothermal, wind, solar) is based on the inputs of equivalent fossil-fuel thermal generation. You'd only get that by reading the tiny and faint legend at the bottom of the chart, e.g.: https://flowcharts.llnl.gov/sites/flowcharts/files/2022-04/Energy_2021_United-States.png https://flowcharts.llnl.gov/sites/flowcharts/files/2022-04/E... LLNL don't seem to have a methodology published anywhere that I've been able to find. The fact that Our World in Data does is both remarkable, refreshing, and quite helpful.
foxes 4y ago
Blub, probably GPT3, read a physics book.

62 points by _Microft 4y ago

deleted 4y ago

[deleted]

dotancohen 4y ago

The cookie popup on that site, at least on mobile, is one of the worse I've encountered.

egberts1 4y ago

It is quite simple, as it pertains to the matter phase as being of solid, gaseous, liquid, or supercritical (sometimes plasma) state. As with any attempt at delta measurement of energy, you need that starting reference point being used by your test instrument and that method of measurement is likely not to be the same one for different matter phases: Heisenburg uncertainty principle comes to mind here.

colechristensen 4y ago

>We can reduce losses from primary to secondary energy by transitioning away from fossil fuels because the losses for these sources are particularly high. This reduces the amount of heat lost from converting these raw fuels into a usable form, such as electricity. This is false, fossil fuel power plants have efficiencies between 30% and 60%, solar 15% to 25% (or much less if you consider the time that it's dark), wind 20% to 40% (or much less if you consider the time it's not windy). I suppose you can ignore these things because the sun and wind are free resources, but the basic fact is that transforming heat into electricity is considerably more efficient than photovoltaics or wind turbines.

pfdietz 4y ago
This comparison is absurd, for the reason you note and apparently dismiss. Efficiency comparisons are really only relevant when you're looking at the same input.
sbierwagen 4y ago
If you really wanted to do pointless stuff with numbers, you could say that fission has an abysmally low "efficiency" because not all of the mass of the atom is converted into energy, with the majority of it ending up as stable fission fragments or neutrinos that zip through the reactor walls. You start with a U-235 atom that has a rest mass of 218,871.5 MeV and only get 202.5 MeV of heat out of it? Pathetic!
dredmorbius 4y ago
Energy efficiency refers to how much useful output is delivered based on input. For thermal energy generation, net efficiencies tend to range from 20% to highs of about 40--50% via combined-cycle generation, perhaps with cogeneration of generation+thermal heating applications, the latter typically being district heating or industrial heating. There's also the concept of nameplate capacity vs. capacity factor. The former relates to the maximum possible output of a facility, the latter to the attainment of the nameplate capacity over a year. It's not clear to me which of these you're referring to. Moreover, the conversion efficiency of flows such as solar and wind is not directly comparable to the efficiency losses of termal generation for other reasons, namely that the environmental availablity of the uncaptured portion is still generally available for other environmental service. Burning a ton of coal and only extracting 30% of the total energy potential still means you've incurred an opportunity cost of 70% of that fuel stock's energy potential. I will note that there are a lot of shenanigans which are played with nameplate and capacity factors, by both boosters and opponents of renewable / carbon-neutral energy. That said, there's no need to add to the confusion. Confounding conversion efficiency, capacity factor, and deadweight opportunity costs and losses is a slippery business at best.
jyounker 4y ago
The ongoing cost of mining sunlight is nearly zero.

blueflow 4y ago

I found this article disappointing. Neither Joule, Watt(seconds) nor any kind of energy potential or entropy were mentioned. The "primary, secondary, final, useful" categorizing seems arbitrary to me an i have doubts about its usefulness. In the end of the day, energy potential is nothing intrinsic to matter, it depends on what you can and will do with it. In the diagram, the Oil, Wood and Coal chains are exclusively about burning that stuff. Oil and Coal are a climate problem just due to the fact that people dig/pump them out and put its carbon onto earths surface, burning it for heat is optional here. Think plastics. This article gives me a odd feeling.

jolmg 4y ago
Same. I was kind of hoping for an in-depth explanation on the difference between Watts and VA, which should be none, W = VA, but apparently for AC they're used for 2 different ways of measuring average power, one being the product of peak current and voltage divided by 2, and the other being the product of the root mean square voltage and the root mean square current. I still wonder why they both matter, rather than just sticking with one or the other. According to Wikipedia, > Some devices, including uninterruptible power supplies (UPSs), have ratings both for maximum volt-amperes and maximum watts. The VA rating is limited by the maximum permissible current, and the watt rating by the power-handling capacity of the device. Is there something besides the "maximum permissible current" that influences the "power-handling capacity" in a circuit? These sound the same.
- InitialLastName 4y ago
  The key concept you're missing is Power Factor[0]. With reactive (inductive or capacitive) loads, the current and voltage will be out of phase with one another, leading the peak current to occur at a time other than the peak voltage. This reduces the power delivered to the load to less than |V|*|A|; in a situation where you hold power demand and voltage steady, you would need to deliver more peak current. For the two power measurements, one is instantaneous power, the other is average power. Different situations call for different measurements. [0]https://en.wikipedia.org/wiki/Power_factor https://en.wikipedia.org/wiki/Power_factor
- 4y ago

dredmorbius 4y ago

For those who seem to be missing the point, this article is about how energy is reported and discussed within the context of national and global energy utilisation. It is not about units of energy measurement. Such articles exist, but their goal differs from the one here. For those who report on energy utilisation, and those trying to understand those reports, the distinctions made here are highly useful and informative. The article should be assessed on that basis. Primary energy addresses the total available stocks, flows, and withdrawals from the environment. Those are values determined and dictated by nature. These are submect to aquisition costs --- drilling, mining, fracking, dam-construction (and environment disruption & risk), deployment of solar collectors and wind turbines. Secondary energy is largely what is actually transacted through wholesale commerce: generation and fuel deliveries. If you're interested in commercial-level transactions and international trade, these are the values of principle interest. In the case of electrical generation, conversion losses are largely dictated again by physics (e.g., Carnot's law), and while incremental improvements may be possible they're often quite difficult, and ultimately limited. Final and useful energy are the retail-level delivery to end-uses, and the actual intended delivered benefit of that energy. Here again physics enters into the discussion --- light bulbs, computers, combustion engines, air conditioners, and electric motors have their limits to conversion of electricity or fuel to light, computations, movement, and thermal management. They're also governed by other factors (insulation, daylighting, focused- rather than generalised-delivery, land use). Discussions are why we'll see discussion in units of MWt vs. MWe --- megawatts of thermal vs. electrical energy. Which might satisfy some of the units-fans out there. Otherwise, as the piece says, if you want to understand the energy picture as a whole, you need to understand the parts, their relations to one another, and their own specific behaviours, characteristics, and limitations.

avalys 4y ago

I ran into this report from Mckinsey a few weeks ago, and stopped reading after the opening sentence. "Large semiconductor fabs use as much as 100 megawatt-hours of power each hour..." https://www.mckinsey.com/~/media/mckinsey/dotcom/client_service/operations/pdfs/bringing_fabenergyefficiency.ashx https://www.mckinsey.com/~/media/mckinsey/dotcom/client_serv...

deleted 4y ago
[deleted]

gumby 4y ago

This is really about the flows in a Sankey energy diagram, yet they didn't use one. It makes more sense if you know this, though in that case you don't need the article. https://en.wikipedia.org/wiki/Sankey_diagram https://en.wikipedia.org/wiki/Sankey_diagram Some nice examples: https://www.iea.org/sankey/ https://www.iea.org/sankey/ https://www.researchgate.net/figure/World-energy-flow-in-2011-PJ-LLNL-2016_fig1_317688860 https://www.researchgate.net/figure/World-energy-flow-in-201...

dredmorbius 4y ago
The Sankey relationship is strongly hinted in this diagram: https://ourworldindata.org/uploads/2022/04/Four-ways-of-measuring-energy-1536x886.png https://ourworldindata.org/uploads/2022/04/Four-ways-of-meas... Even in a traditional energy-flow Sankey diagram (see the LLNL examples: https://flowcharts.llnl.gov/commodities/energy https://flowcharts.llnl.gov/commodities/energy), the four concepts aren't always clearly expressed. LLNL also includes numerous assumptions and framings which aren't necessarily clear. The "wasted energy" component, which in my experience people always focus on strongly, for example, is based on an assumed efficiency of processes, it is not directly measured. Another aspect I'd not realised until the past year or so is that the values associated with renewables (hydro, geothermal, wind, solar) is based on the inputs of equivalent fossil-fuel thermal generation. You'd only get that by reading the tiny and faint legend at the bottom of the chart, e.g.: https://flowcharts.llnl.gov/sites/flowcharts/files/2022-04/Energy_2021_United-States.png https://flowcharts.llnl.gov/sites/flowcharts/files/2022-04/E... LLNL don't seem to have a methodology published anywhere that I've been able to find. The fact that Our World in Data does is both remarkable, refreshing, and quite helpful.

foxes 4y ago

Blub, probably GPT3, read a physics book.