3d ago

Power is not energy: why the difference matters

So, Alec over the Technology Connections channel made an hour long video explaining the difference with kW and kWh (obviously with other stuff around it).

I'm living in northern Europe in an old house, with pretty much only electric appliances for everything. We do have a wood stove and oven, but absolute majority of our energy consumption is electricity. Roughly 24 000 kWh per year.

And, while eveything he brings up makes absolute sense, it seems like a moot point. In here absolutely everyone knows this stuff and it's all just common knowledge. Today we went into sauna and just turned a knob to fire up the 6,5kW heaters inside the stove and doing that also triggered a contactor to disengage some of the floor heating so that the thing doesn't overload the circuit. And the old house we live in pulls 3-4kW from the grid during the winter just to keep inside nice and warm. And that's with heat pumps, we have a mini-split units both on the house and in the garage. And I also have 9kW pure electric construction heater around to provide excess heat in case the cheap minisiplit in garage freezes up and needs more heat to thaw the outside unit.

And kW and kWh are still commony used measurement if you don't use electricity. Diesel or propane heaters have labels on them on how many watts they can output right next to the fuel consumption per hour and so on. So I'm just wondering if this is really any new information for anyone.

I assume here's a lot of people from the US and other countries with gas grid (which we don't really have around here), is it really so that your Joe Average can't tell the difference between 1kWh of heat produced by gas compared to electricity? I get that pricing for different power sources may differ, but it's still watt-hours coming out of the grid. Optimizing their usage may obviously be worth the effort, but it's got nothing to do with power consumption.

So, please help me understand the situation a bit more in depth.

79 comments

People complaining about this video have clearly not watched much Technology Connections; I enjoyed it immensely. It's right in line with how Alec normally does his videos. We who are loyal to the Great Alec expect the pedantic content.

In here absolutely everyone knows this stuff and it’s all just common knowledge.
- Fair point, but basic physics has been a part of our education program for at least 60 years. Also for few years the 'exchange priced' or 'market valued' electricity has been somewhat popular and on the news, which adds up to the general understanding as if you know your stuff it means quite literal money as your bills are smaller. So, maybe 'absolutely everyone' is a bit of a stretch, but in general the majority of adult people understand the concept.
  And also a ton of common folk understand it at least a bit on a deeper level as basic physics is included to studies beyond elementary school regardless on what you study. Sure, not everyone understands (or cares) how 3 phase AC in here adds up to 400V or why you need to have 2,5mm² wires for 16A fuse, but it's still pretty common that people, specially in a separate house, understand how you can only pull 2300W out of a 10A circuit or 3600W from a 16A one (10 and 16A being the most common fuses in a household in here).

Also check out his other video on his Connextras channel where he basically suggests dismantling capitalism.
https://m.youtube.com/watch?v=Y2qSaD1v4cQ

So I’m just wondering if this is really any new information for anyone.
It's never wise to underestimate most people's ignorance.

If you think the average person understands watts, you live in a bubble, straight and simple. You have a very skewed notion of the average person.
- Yep that video is leagues beyond most peoples capabilities to understand. Thinking they already knew and understood it is crazy.
  
  Nah, the video is pretty straightforward, but it's presented in a way that most people would lose interest unless they're actually into the subject matter. I see three problems with the video:
  it's too long
  very few analogies
  mostly a talking head
  Power vs energy is fairly simple with a good explanation. Power is simply the speed at which energy gets used up. For example:
  if you make a big campfire, it'll use up your wood (energy) faster
  if you're playing games on your phone, your battery (energy) will die sooner
  if you sprint, you'll use up your energy faster than if you jog
  That's extremely intuitive. All a regular person needs to know is that simple concept, plus a way to measure it (the Kill-a-watt example). Boom, 5-10 min video.
  But the talking head made it way more complicated by starting with gas. That's just belabouring the point that you can increase or decrease power, which is already intuitive with batteries or things we can see (wood) or feel (tiredness).
  They could then segue into gas, once the power vs energy issue is established. A can of butane is like a battery, and the valve (e.g. screen brightness, game vs texting) controls how quickly it's used. We can compare gas and electricity directly because electricity can be turned directly into heat, just like gas can.
  And then you segue into heat pumps. Basically explain how your AC/fridge works (i.e. moves heat instead of creating "cold"). Make a demo where you move heat vs create heat and show how much energy is used. As in, heat a room from 72F or whatever to 90F, one using a heat pump and the other using a space heater. Show how temps compare on both sides of the heat pump vs space heater (other rooms shouldn't change w/ space heater). Then use that to show a real-world example of a house that swapped from furnace to heat pump to really drive the point home that moving heat is more efficient than creating it.
  
  Explaining to people learning to cook that oil is liquid pan that carries heat is just too mind blowing. The simple shit is wayyyyyyyyyyyyyyyyyyyyyyyyyyyyy beyond the average smartwatch wearing doof
- We live in a world where people demanded (and succeeded) in having the Meteorological Service of Canada to report windchill as "feels like C" instead of, ya know, a measure of actual heat loss in Watts / M^2 / s
  
  You say that like it’s a bad thing? I prefer not to dust off my slide rule everytime I want to know how cold it is out.

Saved you a click: power = rate of energy use (energy/time)
- He says it so many times in so many ways that he actually starts to make it seem more complex than it is. You start wondering if you’re missing something, because you got it in 6 seconds but 12 minutes later he’s still talking about it.

kW/kWh aren't commonly used outside of electrical applications in the US, so people are less readily able to quantify and compare in other contexts. Looking at a variety of natural gas companies' bills, you'll get volume multiplied by a therm factor instead of simply using kWh; horsepower for not just cars but even electrical motors and pumps.
I think the average person will have looked at their electricity bill and put the basics together about watts and watt hours. As for comparison with natural gas, I think he didn't touch on the real metric people then turn to- cost. Depending on the state it can be much cheaper to use gas vs electricity.
- Yeah, electric motors are what I notice the most. Be it on washers/dryers, garbage disposals (which range from 1/3, 1/2, 3/4, 1HP) and more.

I think you are greatly overestimating the basic functional knowledge of the general public...

In here absolutely everyone knows this stuff and it's all just common knowledge.
Absolutely not. Not even close.

After watching the video it was a bit over explained. I think he got his point across in the first 10 minutes, though I am an engineer by trade.
I appreciate his rigour in explaining and it is a good refresher on the power/energy calculations.

Follow-up video idea: speed ≠ distance
- The one that I think more people misunderstand is temperature Vs heat Vs something feeling hot/cold. One is a property, one is energy, and the other is the transfer of energy.
  
  You know a nation of people who may not be able to articulate their understanding, but definitely have a high intuitive understanding of that?
  We Finns.
  100C sauna and no problem sitting on wood, but happen to touch something metal and oooh-weee.
  Also same thing happens the others way around when it's - 20c outside. I don't think there's many people in Finland who don't have a core memory of what cold metal tastes like in winter, because of the resulting trauma. And it doesn't even need to be metal to stick.
  Nicely explained.
- Yeah, what the hell is this video subject. I honestly thought this stuff was common sense.
  
  Should be but search for "kwh per hour" and there's plenty of people who seem confused by it all.

New Technology connections video drops:
I'm going to go buy a kill-a-watt.
- Do it, it teaches you things.
  Most of your power isn't going where you think.
  
  Oh I love this stuff.
  My dishwasher pulls over 1000W, but overall actual usage pales in comparison to my server cluster, which utilizes a multiple 35W mini PCs.
  I started measuring a bunch of things in February (using zigbee-compatible smart plugs to HA), so here is a graph of the above for the entire month of March:
  It was eye opening, to say the least.
- I moved into a tiny home and got one for measuring the current draw of my kitchen appliances and keeping track of the cost of my electric space heater ($40/month so far, yeesh)
- I'm over here heating water in a kettle because of Technology Connections (and also pre-heating my dishwasher)
  
  Its the midwest pragmatism that sells it.
  I just do what he says because it sounds so practical.

is it really so that your Joe Average can’t tell the difference between 1kWh of heat produced by gas compared to electricity?
Most people don't even know what a watt or watt/hour is. And have no idea how energy from gas relates to energy from electricity.
- watt/hour
  Oh yeah I've seen that used before, makes me cringe every time.
  Anyway, do must people not go to high school? Or is stuff like that not part of the physics curriculum in some places?
  
  A W/h either is a big problem or will be soon.
  
  Even if it was covered in high school, I think because most people never use it again in daily life it's easy to forget.
  
  In my highschool physics was optional. You had multiple options for science credits and could get through without taking it.

lot of people from the US with gas grid (which we don’t really have around here), is it really so that your Joe Average can’t tell the difference between 1kWh of heat produced by gas compared to electricity
Right, because for most people gas is metered and sold by the CCF, and not converted into kW at any point in the chain.
So I know i used 30ccf last month, but there's zero indication what that is in kW, because we usually don't convert between the meter (which is volumetric) and the billing, which could be anything but why bother?
- Reticulated gas is charged by the kWh here in New Zealand. The meter may well be calibrated in m³ (I don't have gas at home, so I don't know for sure) but all pricing is energy, not volume.
  For bonus points, if instead you buy your gas in cylinders - a pair of 45kg (~100lb) cylinders is a common installation for houses without piped gas - those are sold simply by the unit. The best conversion for that I can find is one energy retailer describing one 45kg cylinder as 2200MJ (611kWh).
  I expect this is one of those things that is overall horribly inconsistent depending on where you live.
- Also from Europe, gas is measured/billed in kWh here as well.
  
  Not everywhere, in Lithuania they charge per m³.

There's no way even 1% of people understand this in the world. Maybe 1% know of those measurements "existence" asking them what they are would get an "uhh"
- In the world? Me and millions of other people got this info in middle school physics. Sure, maybe we mostly forgot the details by now. But it's not arcane or ancient knowledge lost to time. It's in your electricity bill every month. A quick visit to Wikipedia and I got the gist of it back. Every single physicist, engineer, and electrician got this explained again to them.
  
  "a quick visit to wikipedia" is a good example confirming what I said, majority of people are not willing to do that to learn any subject. 0.483% of humans are engineers, of that I'd say there are a small chunk that are near worthless and probably don't even know these basics.
  
  It’s in your electricity bill every month.
  You get a comparison of electric vs natural gas flow in your energy bill? Wow!!
  I think most people understand W vs kWh, at least on some level. They know things use different amounts of energy depending on what it's doing (i.e. a microwave sitting idle vs actually warming things), but they may not be comfortable estimating kWh from watts.
  But that's only the first part of what OP talked about. The meat of the discussion was about energy stored in something like natural gas vs electrical energy. How exactly am I supposed to compare a gas furnace and electric AC vs an electric heat pump? Not only would I need to somehow convert therms (or whatever local unit you use for gas energy) to kWh, but I also need to understand efficiency of heat transfer for heat pumps, which will vary quite a bit based on the weather (much less effective in cold weather).
  That's complicated, and many HVAC professionals here don't like heat pumps for whatever reason so they tend to think in terms of resistive heating vs gas heating, which is absolutely wrong. I want a good idea of cost difference between gas furnace + electric AC vs a heat pump, but that's not something I have easy access to.

He’s making a point about instantaneous versus overall energy use, which it sounds like you already understand. “Power” and “energy” are already kind of loose terms, which could make that conversation confusing IMO.
But for anyone confused by this:
For the typical energy consumer, Watts (W, kW) are relevant when considering circuit capacity. Otherwise, Watt-hours (Wh, kWh) is likely the metric you’re looking for when considering energy use.
Concretely, your coffee maker might pull 1.2 kW while in use, more than most appliances in your house, yet it probably represents a minuscule portion of your electric bill, perhaps less than 1 kWh, since it only needs to boil a small amount of water with each use.
- How are energy and power "loose terms"? Energy might be difficult to fully explain rigorously, but it's one of the fundamental elements of our universe. And power is just energy over time
  
  How are energy and power "loose terms"? Energy might be difficult to fully explain rigorously, but it's one of the fundamental elements of our universe. And power is just energy over time
  Well, you yourself just provided the example, since your definition of energy and power are the inverse of the definitions used in the video.
  It’s the fact that people use them differently or interchangeably that makes them “loose” IMHO.

haven't seen it so far, but technology connections will always get an upvote.
also consider subscribing to his channel, his videos are amazing.

Power is water throughput in a pipe, energy is water filling a bucket. Simplest way I've found to explain it in my 15 years in the energy space.
- Power is a measurement of the velocity and volume of water flowing through a pipe at a given instant*
  I'm so sorry, I am officially 'that guy', taking a simple analogy and making it annoying...
  
  I think it's simple enough without even using analogies to explain. The unit Watt is Joules per second. Multiply by units of time and you get the total units of energy in Joules. Watt and Watt Hour are just that with without the additional units showing or being simplified.
  
  Lol you're completely right of course but when you start adding all this it is less relatable to someone who is not familiar with it already

is it really so that your Joe Average can’t tell the difference between 1kWh of heat produced by gas compared to electricity?
Yup.
I totally understand electricity because it's pretty intuitive. Everything is advertised in watts, my bill comes as kilowatt hours, so it's pretty easy to calculate how much energy something uses by plugging in a kill-a-watt and measuring it.
My gas is billed in therms. I don't really know what that is, nor do I know what the flow rate is for my furnace or gas stove, so I have no concept for how much energy I'm using. I don't have an electric one to compare with, so I that's not an option either. So how exactly would I get to the point where I would be able to compare the two without a lot of annoying testing? Even then it would be extremely imprecise.
And no, it's not "watt hours coming out of the grid," except in the pedantic sense that they can be converted. They come from very different sources, so it's like comparing an EV to a horse, and while you could, it's completely nonsensical.
But yes, at some base level your average American knows there's a connection between the two (after all, I can choose between electric heat/heat pump and a gas furnace), but they'd rely on an expert to estimate the monthly price difference between options, since that's ultimately what we care about. The problem is mentioned near the end of the video, HVAC experts don't seem that familiar w/ heat pumps, so you may not get a decent estimate, depending on who your technician is. And that adds to the misinformation.

I sometimes make a conscious effort to understand electricity. For a few days, I then think I understand what's going on and then promptly I forget.
(Yes, I shall watch this video.)

Full disclosure, I didn't watch the video yet, but it's likely a difference of environmental impact.
He's described in previous videos how burning gas at home is less efficient from the standpoint of a carbon footprint. I imagine this video is to help explain everything in a way that helps you come to that conclusion yourself. Teach a man to fish instead of just giving a fish and what not. So you can apply the knowledge to other things in your life

I started to watch this video and gave up mid way. It spends like 15 minutes on gas stoves. Maybe I’ll revisit it.
Btw, I really liked his other video on microwaves.

I haven't watched it but its really simple. If you receive 1kW within 1hr and you compare that amount of power to 1kW over one second things are much different. The first is like a nice heater in a cold winter night...nice steady energy, a little bit of power. The second is like hell hole, tons of energy but still only a little bit of power. Power is the ability to do work or simply move things. Energy is the total amount of moving things regardless of the actual power used. So if you toasted a toast, that was a lot of power delivered quickly, but you could also do all that work slowly over centuries and eventually end up with the same molecular arrangement using the same amount of energy.
- “1kW within 1hr” isn’t power. That’s energy.
  “nice steady energy”? You mean nice steady power, right?
  “The second is like hell hole, tons of energy but still only a little bit of power.” No. They are both precisely the same energy.
  “So if you toasted a toast, that was a lot of power delivered quickly.” No. That is a lot of energy delivered quickly.
  I typically wouldn’t be pedantic about this, except that this is precisely the point the video is making. These two unit types are often confused.
  
  “1kW within 1hr” isn’t power. That’s energy.
  The watt is always power, not energy. I'm assuming OP here got some prepositions mixed up and meant 1 kW delivered for 1 hr. That amounts to an energy of 1 kWh.
  The second is like hell hole, tons of energy but still only a little bit of power.” No. They are both precisely the same energy.
  No, they are the same power. The energy in the case where 1 kW of power is delivered for 1 hour is 1 kWh. The energy in the case of 1 kW delivered for 1 s is about 0.28 Wh.
  If instead 1 kWh was transferred over the course of 1 hour, that is an average power of 1 kW (but does not have to be uniform, without more information we can't know the power profile). If 1 kWh is transferred over the course of 1 s, that is an average power of 3.6 MW which is the example I think OP was getting at (ref. hell hole comment).

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