Why are there different ways of measuring energy?

https://ourworldindata.org/energy-definitions

by _Microft • 4 years ago

62 29 4 years ago

dotancohen• 4 years ago

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

egberts1• 4 years 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• 4 years 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• 4 years 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• 4 years 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!

dredmorbius5• 4 years 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.

jyounker2• 4 years ago

The ongoing cost of mining sunlight is nearly zero.

blueflow5• 4 years 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• 4 years 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• 4 years 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

marcosdumay• 4 years ago

The power consumption is the integral of the current your device takes for each voltage of the AC cycle. Different devices do all kinds of different things during that cycle, so it's not simple to communicate it in a number.

Your grid power consumption is probably measured in terms of current alone. That means that the number on your power bill is different from the amount of energy your devices dissipate as heat. That measurement is converted into power using the RMS trick, but there is no guarantee that it will exactly match the actual power consumption of your house.

Your UPSs has different limitations for real power, current, and peak current. And your house wiring (or better, any wiring) has limitations for (windowed) average current (with many different limits for different window sizes). Wiring also has a limitation for voltage, but it's usually high enough to not matter on normal usage.

As a rule, with AC, there are so many degrees of freedom that any question becomes hard to answer.

otter-rock2• 4 years ago

There are actually three parts of the power triangle: real (W), reactive (VAR), and the hypotenuse apparent (VA) power. If voltage and current are exactly in-phase, VA=W and VAR=0. All of the power is doing work.

Being out-of-phase is like turning a crank with one hand while resisting with the other - wasted effort. Some of the VA becomes VAR instead of W.

The math thing is a simplification so you can take measurements with a multimeter, and do just a bit of arithmetic to get all three power values. It comes from the average power integral of trig functions with complex numbers.

Watt rating is what you'd expect. Voltage and current are working together to do work. The limit is probably thermal.

VA rating at max current is a short-circuit. If your load draws enough reactive power, the voltage and current get so far out-of-phase that a huge current sneaks through without much voltage. It could be many times as much current as the max current at max Watts.

larrik• 4 years ago

I thought for sure we'd get into "horsepower" vs "footpounds", but no...

FastMonkey• 4 years ago

This is an article by ourworldindata, who aggregate a bunch of (mostly economic) metrics from countries around the world. It is common for energy use to be reported in that way on a country level. This looks like an explainer for the users of their website on what the terminology means.

It makes perfect sense when you think about who the audience for this data is, economists, planners etc. In those roles, the primary concern is the actual quantity of heat and electricity that the population needs in their homes and workplaces, and you need to be able to back that out to how much raw fuel that requires, or how much transmission capacity you need. You need to know this summary info so you know where the focus needs to be. At moment for instance, they need to know how much gas they need in storage tanks in Europe for this winter, and it's information like this that helps them figure that out.

divbzero• 4 years ago

I suppose having non-technical terms makes sense considering the audience, but I would still want the fine print (i.e. this article) to explain how the non-technical terms map to technical concepts.

At the least, I would prefer renaming the non-technical terms to be less abstract:

– Primary energy → Gross energy or Raw energy

– Secondary energy → Transportable energy

– Final energy → Delivered energy

– Useful energy (no change)

dredmorbius5• 4 years ago

You're criticising this article based on something it's not.

This isn't about units of energy measurement. It's about energy reporting at different stages of human energy-sector activity.

You might as well criticise Disney World for not being the Louvre, or a McDonalds restaurant for not being a library. That's simply not their goal, function, or purpose.

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.

(I'm also aiming my criticism in part at those who've apparently up-voted the comment I'm responding to, who've compounded its author's error.)

blueflow5• 4 years ago

That's simply not their goal, function, or purpose.

For Disneyland and McDonalds its obvious because they dont use words and concepts that overlap and contradict established science.

You can't expect to re-use existing terminology and have the previous users be okay with ith.

_Microft• 4 years ago

These are existing terms [0], they did not make them up on the spot. Maybe it is the lack of familiarity with them that creates that odd feeling.

While we are at it, could you explain what that "energy potential" is that you are talking about? I am asking for clarification because while my field (physics) has definitions for "potential", "energy" and "potential energy", I am still unfamiliar with "energy potential". Could it be that you are using a layman term there?

[0] https://en.wikipedia.org/wiki/Primary_energy

blueflow5• 4 years ago

I live in a area where you do not study in English. To counter your rudeness, you must be from the US if you don't know the language barrier is a thing.

dredmorbius5• 4 years 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• 4 years 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_serv...

gumby• 4 years 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

Some nice examples:

https://www.iea.org/sankey/

https://www.researchgate.net/figure/World-energy-flow-in-201...

dredmorbius5• 4 years ago

The Sankey relationship is strongly hinted in this diagram:

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), 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/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• 4 years ago

Blub, probably GPT3, read a physics book.

Why are there different ways of measuring energy?

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