Why are there different ways of measuring energy?
ourworldindata.org
ourworldindata.org
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.
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.
For the two power measurements, one is instantaneous power, the other is average power. Different situations call for different measurements.
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.
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.
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.
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.
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)
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.)
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.
(Which is an agreement with and amplification of your point.)
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?
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.
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.
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.
"Large semiconductor fabs use as much as 100 megawatt-hours of power each hour..."
https://www.mckinsey.com/~/media/mckinsey/dotcom/client_serv...
https://en.wikipedia.org/wiki/Sankey_diagram
Some nice examples:
https://www.researchgate.net/figure/World-energy-flow-in-201...
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.
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.