[HN Gopher] Why are there different ways of measuring energy?
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Why are there different ways of measuring energy?
Author : _Microft
Score : 42 points
Date : 2022-07-05 11:09 UTC (1 days ago)
(HTM) web link (ourworldindata.org)
(TXT) w3m dump (ourworldindata.org)
| dotancohen wrote:
| The cookie popup on that site, at least on mobile, is one of the
| worse I've encountered.
| [deleted]
| egberts1 wrote:
| 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.
| dredmorbius wrote:
| 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.
| colechristensen wrote:
| >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.
| dredmorbius wrote:
| 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.
| sbierwagen wrote:
| 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!
| pfdietz wrote:
| 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.
| blueflow wrote:
| 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 wrote:
| 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 wrote:
| 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 wrote:
| 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.
| dredmorbius wrote:
| 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.)
| blueflow wrote:
| > 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.
| jyounker wrote:
| 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.
| FastMonkey wrote:
| 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.
| larrik wrote:
| I thought for sure we'd get into "horsepower" vs "footpounds",
| but no...
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(page generated 2022-07-06 23:01 UTC)