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Comment by blueflow | Hacker News Reader

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.

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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.

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)

Not satisfied. Substances are fuel, not energy.

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.)

> 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.

Different ares of engineering and science use intersecting sets of terminology. This page is a very clear definition of how these terms are defined and what they mean in a particular context around energy production and utilization.

Above and beyond that, it's an explanatory page for the specific context and usage.

(Which is an agreement with and amplification of your point.)

And what kind of engineering or science is the article about?

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.

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

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.

You cover a lot of interesting topics. Some exposition:

Reporting power is easy with the power triangle. It's a mathematically exact concept.

Measuring power is a different story. Distortions of the assumed perfect sine wave create measurement errors. Meter bandwidth matters, but most have low bandwidth.

Grid meters at least use voltage phase, if not magnitude. Residential customers are billed only for real power, so the phase information is necessary to exclude the reactive power from the measurement.

One rating is for maximum output. The other describes a short-circuit that you can create with an overly reactive load.

The degrees of freedom complicate the implementation, but the bottom-line discussion abstracts away those details.

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.

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

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.

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

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