Power usage terms

General Discussion
#1

I thought I had the terms of power usage/consumption understood fairly well, but now I’m starting to confuse myself I think.

I did a quick google search on power consumption of the average home, and multiple answers said the average American house uses 30kwh per day. I know this number can wildly differ from home to home but let’s stick with it.

So my understanding of the kWh term. If you have a 1000 watt appliance, say a space heater, and you run it continuously for 1 hour, you have now consumed 1 kWh. If you continue to use that space heater for an entire 24 hour period then your total consumption for that day will be 24 kWh. Is this correct? I don’t see why not, assuming you have just a shed and that space heater is the only thing electrical you are running.

So here’s where I start to get confused. Is that electric space heater rated at 1000 watts per HOUR? Meaning it consumes 16.66 watts per second? Or is that space heater consuming 1000 watts the second it is plugged in?

I assume it’s consuming 1000 watts continuously from the moment it is plugged in.

Here’s where I tend to get confused though. Say you have a charging system that charges at 120 watts (12 volts 10 amps). Would that charging system then be said to charge at 120 watts per hour (0.12 kWh) ?

I think I’m just confusing myself more than I have to here.

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#2

Ha! Ha! JustinH, welcome to the confused.
But not the befuddled!
FYI electrical consumers at the best are rated at 95% conversion efficient, NOT the 100% too often quoted. And that’'s for resistances heating. Every other electrical power usage converts at a lower %.

The modern Befuddle’ers insist on converting and quoting ALL powers as kilowatts now.
Shaft powers. Stored chemical power potentials.
And this leads to even more calculation’s confusions.
I am mean, nasty, and 20th century old-school, and keep putting shaft powers into horsepower SO it will be known I am talking about mechanical power. Heat power in BTU’s (or if you insist, calories) so it will be known I am talking about HEAT power.

I look forward to the electrical kilowatt explanations from real working electricians answering you.
Very good questions you have raised.
Regards
Steve Unruh

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#3

Hey Steve! Yeah it definitely does not help when terms keep getting switched up all the time. From what I understand any electrical device is rated at its continuous power usage, and we are only charged in usage (kw) over a certain time (hours).

It definitely takes a little bit to get my mind around it. Because if an average home uses 30 kWh per day then maths would say that a 1250 watt generator should be enough to power a home (if it could be made to run continuously). Although we all know this is not the case since electrical usage has peaks and valleys. You might use 5kwh hours in the first 16 hours of the day and the other 25kwh the final 8 hours.

The ultimate solution I think would be to have a fool proof storage system, be it batteries, pumped storage, or whatever other means there may be.

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#4

One of the biggest ways to minmax, minimum cost and maximum results, your power usage is to try to use non electrical methods. Before my Grandpa died he was planning to add solar air and water heating. I still have the envelope he received from NASA, not sure why NASA unless it was a different company with the same acronym.
We hardly ever need to use lights in the house during the day because of our large windows. Also aids in cooling the house in the summer. Right now I’m just focused on keeping our fridges powered in the event of a power outage. We use a well pump and I can go manual if I have to. Would love to have a water tower to have the head pressure, pumped directly with solar panels during the day or battery when production is low.

I’m really just now getting into electrical stuff, but I want to say the rate given in KW or W or Amps will translate to those rates per hour if we can assume it’s a constant flow of the same energy. Ebike guys will say “well a 20ah battery will get you 20 miles” or car people tell you “this gets you 25 mpg highway” without elaborating fluctuations in demand will affect consumption.

I live in a mountainous area so vehicle distance ratings mean nothing to me. They might as well have been made up on a napkin in crayon.

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#5

thats a great way to reduce your energy needs. Some people I know are off the grid and they have things like a propane fridge and freezer, propane clothes dryer, and variously other ways to save on electrical demand.

It’s funny cause whenever sizing a generator for a home it’s always based on your daily usage. So if you average 30 kWh per day certain companies will tell you that you require a a 30kw generator. Technically that’s not actually true, or I don’t think so anyways. My thinking is if you average 30kwh per day, then a 30kw generator would meet your entirely daily demand in 1 hour. Really you would have to look at a power usage graph and find your peak usage and size your generator according to that.

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#6

It’s actually interesting not just with electricity and kWh. Even a vehicle, say a pickup truck with 300 hp for an easy number. 300 hp is just the maximum rated power, if somehow you could graph your horsepower usage during a trip, towing and empty, and see how much of that 300 hp you actually use on average.

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#7

You are smart with your questions wording, JustinH.
Power. Is the ability to make work happen. Both of these get a time-in-use, or a time-of-achievements factor in their calculations.

Energy now that gets really modern squishy.
Current moderns want to use joules for this.
Joules as a fits-all.
It does not.
(Jewels: the long past courting holes on my pocket I had to discover was NOT the way to my sweetie’s good graces. Flowers. Doing the dishes. Cleaning bathroom porcelains. Clothes washing. I tried that last as my impressing, I really did. Too many mistakes got me fired. We were married by then, so’s not so much a setback.)

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#8

You’re right about joules not seeming to work for everything Steve. If you go online there’s apparently a conversion for joules to kWh. This doesn’t make any sense to me, since joules is just potential energy, the correct way I would assume would be to convert joules per second to kilowatts per hour. I don’t see how a conversion like that even exists.

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#9

Ha! Ha! Yes. Yes.
“And he the bulging muscles entertainer can power lift 857 pounds. Slam that hammer to ring that bell . . .” one . . . time.
“And the Vegas world champion arm wrestler daily works as a truck loader. He can solo, by hand, empty a whole 40 foot truck trailer in 1 hour, 20 minutes”

Now maths out these non-comparables’ as comparable.
Or easy way, recognize, and say: one can get useful measurable work done. The other sells Ooooh-hurrah viewer time. And in the socialists, influencers, politicians world-views that is only power measurement that counts.
S.U.

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#10

The work done, or the energy used to do it, is measured in Joules or Ws . 1 Joule is the work done when a force of 1Newton is applied to 1 metre and is equal to the work done with a force of 1Wat, which takes 1 second. 1 kWh is therefore equal to 3600kJ, which would mean that with this energy you could lift a weight of 100 kg 3600m high, or load 100 tonnes of stones into a wagon over a 3.6 m high barrier, but interestingly this energy is contained in only 1 deciliter of oil or grease, so if you wanted to lose 1 kg you would have to load 10 wagons of stones.
:grinning:

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#11

I think the 30kwh is concurrent as in adding up from the whole day, not necessarily 30kh per hour but it’s a median measurement. I need to have my mother send the latest power bill for our consumption. We use a propane stove range and electric central heat&air, electric hot water. Pretty good about leaving lights off and swapped to the lower wattage bulbs.

#12

I use the only formula that really works and has pin point accuracy every time you use it. The formula is this. [WHAT]+(YOU)+[GET] = [WHAT]+(YOU)+[GET] @ THAT MOMENT IN TIME AND SPACE.
It has proven to be never wrong.
The KISS WYG Formula is good for everything in this world we live in. Lol
Bob

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#13

Oh okay, so what then is the difference between the joule measurement and the joule per second measurement?

#14

Justin, if you load a wagon with stones in one hour, you will have to develop a power of 1 kW, but if you work for 10 hours, you will use a power of 100 W, so, Joule per second, it expresses power to you.

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#15

Am I just thinking too simply: isn’t a watt = volts x amp? And a kilowatt-hour just the usage of the average of how many thousand of volts and amps per hour?
kent

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#16

Oh okay so let me see if I have it now. Joules is work completed. So many joules equals so much work. Joules per second is rate of work, am I correct?

So in your example, loading 1000kg of rocks is so many joules, and that number will not change no matter how fast you load them because the end result is always going to be 1000kg of rocks being loaded. How fast you load those 1000kg is going to determine your joules per second. Joules per second/minute/hour is the rate at which that work or any amount of work is completed correct?

So that being said it is theoretically possible to power a home that consumes 30kwh per day of electricity with a 1250w generator running continuously. Because it’s the same thing your end result will end up being 30kwh. Yes I do realize the way we consume power in our day to day lives that this would not actually work but for theory’s sake it would work, it helps me understand in my backwards and twisted mind lol

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#17

Cody definitely is concurrent, I was just pointing out how if you were to call up a company and ask for a generator sized to your home they would simply ask for your daily average consumption and tell you that’s the size of generator you need. I think they just try to upsell you a unit that they know is way bigger than your peak requirement, pretty slimy lol

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#18

I know for sure that my AC system would be a majority of power consumption personally. Two big Trane units. If I’m running the house on inverters I won’t even bother turning those on.

#19

kW is how much power is being generated/consumed at that moment.

kWh is the energy generated/consumed over time.

I stay away from joules and newtons.

Best analogy I’ve heard is odometer vs speedometer. kW is the speedometer, how fast you’re traveling right now. kWh is the odometer, how far you’ve traveled. You could go the same distance at half the speed with twice the time.

Generator sizing has to account for the maximum draw not the average. If you try to draw more than it can provide you either overload the generator and trip or sag the voltage so low you can’t run the load. If starting motors with a generator it has to be sized even larger. My Honda 2000W generator would not even run a small air compressor.

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#20

Bingo!! DanielG,
I’ve linked back to this topics originator’s Justin Haddens first post.
I think JustinH what you really wanted to know was just how big of home power station you’d have to set up. And how much it would then cost you to fuel it.

So your actual grid power meter or power bill is not going to give you this.
DainelG’s example that his Honda 2000 watt inverter-generator unit will not start and run a small air compressor.
I bough the wife a Honda 2000.
I already had an oilless diagram type portable Sear air compressor I’d used for family/friends go-too auto repairs. Air tools I wanted to speed buzz at least at 150 PSI. 115vac. On common shop/household 20 amp circuits.
That crazy little Honda would try, try to start the compressor for a minute or two until it would kick out. O.K. sez I. I need a bigger generator. Next I got a 20% larger unit in a Yamaha 2700 inverter-generator unit. It would not even try to start the air compressor motor. Kick out immediately. By wattage rating it should have. By listed horsepower ratings it should have marginally.
Back-up, fall-back, planB&C me I can first start the Yamaha. Get it warmed up stabilized. THEN parallel connect up and start the Honda and it will frequency sync with the Yamaha. They together will run my portable air compressor.
Sure. Sure. I could have just bought a Honda 9000 Inverter-Generator first. Did not have the money and my she-bank would not approve a honey we need this $ grant.

So horsepower, KW, kWh depends on who’s asking. And for what purpose.
Sure sound just like another lawyering, mealy mouth Clintonese, doesn’t it. “It depends on what the meaning of the word ‘is’, is.”
No. No.
It is because of electromotive dynamics.
Start with a supply Grid with a huge depth of surge capacity. Your house full out individually is a percent, of a percent, of a percent, of a percent, of that systems capability.
DIY home power you’ll never, ever match that depth of capability. So do not use their numbers.
Then the add together all of your appliances ratings will still will not give you the information that you need.
For three basic reasons. You do not operate them all at the same time. And every single one of them will change the real power they will need from cold not operating. To warmed up stabilized operating. To loaded operating. To power starved operating.
Opps. A fourth reason - those plug in heaters actually do cycle off and on. Refrigerators, freezers, AC units, and others the same. They cycle with needs demands.

So as jack-legged as it sounds for us individuals it makes sense to just do something. Anything. And work up (or down) from there.
Down? You say. Yes. Just be the guy with the old gifted, scrounged, bought for a song, great name brand big’un that gobbles power and fuel.
400-600 amp welders. Three phase. You got for free haul-a-way. Worse. You spent money to get it.
20 and 30 kW big trailer industrial 6 cylinder, water cooled propane/natural gas generators.
10 and 15 kW Detroit Diesel, or Perkins diesel industrial generators.
Now fuel these even on woodgas. Repair those expensive diesels.

Starting small. Knowing this is too small will focused you on real power uses. Circuits separating out for usages. Prioritizing usages. Get your household to really understanding loads managements. Loads shedding. Loads scheduling.
Only then add, and build up. A step at a time.
Live-in RV folk learn this. Live-on boat folk learn, and live this.

Ha! You want to turn my house into a self-sufficient habitat, floating in a sea of personal freedom. Think this way. And then step by step work towards that.
Regards
Steve Unruh

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