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What does a kilowatt hour look like?

blog.kubakuzma.com

111–120 of 147 posts

Re: What does a kilowatt hour look like?

#111
It would have been nice if the article's author had provided a short technical explanation of kilowatt-hour. A kilowatt-hour is a unit of energy, and energy is the time integral of power. It follows that energy in kilowatt-hours is the time integral of power expressed in kilowatts, i.e. one watt for a thousand hours, a thousand watts for one hour, and so forth.

I think that's pretty accessible and could only add to the article's value by answering the question, "What does 'kilowatt-hour' mean?"

Re: What does a kilowatt hour look like?

#112

> So, what a kilowatt hour of high-grade electric energy can do for you? According to my car, it lets me drive 4.2 miles at highway speeds.

A kWh gets me easily >30km on my bike (250W for 1h if you assume average 25% efficiency)

Drivetrains on bikes can be > 98% efficient, so I assume you mean the human power output efficiency. But 250W applied directly to the crank via an electric motor should get you a good 40km/h for 4 hours! :)

Re: What does a kilowatt hour look like?

#113
post #62

Earlier quoted context omitted.

COP: Coefficient of Performance. PV: Photovoltaic. EV: Electric Vehicle. TMDA: Too Many Damn Acronyms (It's a joke I heard at a company that had acronyms for everything).

Well, a TLA is a TLA, but an FLA is not an FLA (it is also a TLA)...

ETLA is a FLA.

DETLA is also a FLA.

Re: What does a kilowatt hour look like?

#114
post #76

Earlier quoted context omitted.

200w seems for pro cyclists. 100w for above average sports fan. Today lots of computing devices fall under 10w power usage. Hence my daydream. For light or electric appliances that's another story.

Powering a decent computer with an exercise bike should be fairly easy. A washing machine, less so.

The GiraDora is a pedel-powered washing machine: http://inhabitat.com/human-powered-giradora-washer-needs-no-...

There are other concepts which are more bike-like: http://webseriesnetwork.com/photo/pedal-power-washing-machin...

Re: What does a kilowatt hour look like?

#115
The book recommended here, David MacKay's Without the Hot Air really is remarkable, and I highly recommend it to anyone with an interest in energy, renewables, or nuclear (which MacKay somewhat grudgingly endorses), and the energy-intensity of modern industrial life.

http://www.withouthotair.com

MacKay himself, a CalTech-trained physicist, worked at Cambridge. He died about five months ago, noted only modestly at HN: https://news.ycombinator.com/item?id=11500614

http://itila.blogspot.com/2016/04/index-for-first-23-cancer-...

Of the book, I find a few things particularly illuminating. For starters, it is rather UK-centric, though the concepts are of course generally applicable. Beyond that:

1. It goes through the major uses of energy in modern life. Getting a feel for the comparative magnitudes is quite useful.

2. It compares the various options for renewable energy. It turns out that there's a lot less energy in renewables than would be convenient. Wind and Solar are much of the easy stuff.

3. It mapps out both energy consumption and use by area. Realising how many watts per square meter are used and are available is useful.

4. He really presses the point that solving the energy conundrum requires large changes. Unplugging charging devices won't cut it. Hitting major consumption, especially transport, heating, lighting, and refrigeration, help a lot.

If you're interested in pursuing the issues further, I strongly recommend Vaclav Smil, whose books I've been going through. For a historical view, Smil's Energy in History, and the more recent two-volume book, Sources of Power, by Manfred Weissenbacher, explore how human history has been shaped by access to energy, from gatherer-hunter days, agriculture, coal, oil, and whatever comes next.

Fascinating and terrifying at the same time.

Re: What does a kilowatt hour look like?

#116

> So, what a kilowatt hour of high-grade electric energy can do for you? According to my car, it lets me drive 4.2 miles at highway speeds.

In a Nissan Leaf, you can get around 5 miles per KWh average. You can plug in the 1.1 kWh charger and realize you will get 5 miles per hour. If you use a bigger 6.6 kWh charger, it's 30 miles per hour.

Better yet, you can fiddle with the dash controls and get a power meter: acceleration takes 30-60 kW, but regeneration can make up to 30kw.

Like the OP says, this kind of thinking really changes your perspective.

Re: What does a kilowatt hour look like?

#117
post #107

Then you compare with the amount of energy in a liter of petrol (~10kW/h). And you realise how we're living literally awash in crazy amounts of energy, equivalent to having all hundreds of slaves working for us 24h a day.

It's even more terrifying considering the fact that it took millions of years of to accumulate such amounts of energy in fossil fuels (it's literally sun energy laying underground). Sooner or later, we'll run out of it…

BTW, it's not 10 kW/h, but 10 kWh in a litre of petrol.

Re: What does a kilowatt hour look like?

#118

I've been very curious for a very long time about people doing indoor bike workouts while storing the pedaling energy in batteries. Any of you do such things ?

One the one hand, this would be good for people who overeat (more calories than they usually expend). On the other hand, in absolute terms, it is just turning agriculture into a source of power very inefficiently (a methane digester would be much better).

Re: What does a kilowatt hour look like?

#119

Earlier quoted context omitted.

I think your concerns are somewhat alarmist and tend to be a bit scaremongering. You may want to read an actual study about just how much HF is present in the fumes of burning cells. In this one, near the end they burned a whole laptop pack and analysed the gases that were emitted: http://www.brandforsk.se/MediaBinaryLoader.axd?MediaArchive_... The relevant datapoint is on page 61: "As seen the yields of HF is much l…

I had to come back because the paper doesn't specify the chemistry of the laptop battery; you can't use this as evidence to support anything other than caution around Li-ion batteries and cells. And, more alarmingly, the part you omitted or glossed over: their plausible explanation for the lower HF detection (which, again, would depend wholly on the chemistry of the cells): > the laptop cells exploded with liquid spl…

And, more alarmingly, the part you omitted or glossed over: their plausible explanation for the lower HF detection (which, again, would depend wholly on the chemistry of the cells):

> the laptop cells exploded with liquid splashed on the walls in the equipment

The less electrolyte that gets burnt, the less HF generated, which I hope you agree is a good thing.

and more recently, the Samsung Galaxy Note 7.

How many actually burned? It's a very tiny fraction. Manufacturers recall precisely to avoid the sort of hysteria that statements like yours generate, and it's not any indication of impending doom. The aviation industry is particularly risk-averse, so it's not surprising. But I don't think the risk is very high compared to a lot of other things in our lives, especially when you consider all the lion cells out there of questionable quality in use and yet behaving themselves. China has taken the lead in making 18650s and other lion cells almost as easily available as alkalines, but reports of fires do not appear to have increased anywhere near in a direct proportion to that. (Reports of cells failing to meet capacity specs, on the other hand...)

By all means handle with care (as you should with any energy source), but lion cells are not lethal weapons that will instantly kill you at the slightest provocation.

Re: What does a kilowatt hour look like?

#120
post #46

Given how popular (and damn near impossible to discern) unsafe and unprotected lithium-ion batteries are, the idea of making a homegrown power wall terrifies me in ways I can't even begin to contemplate. An 18650 battery, if combusted, can produce hydrofluoric acid with just water vapor in the air (or the water in your lungs) if they use lithium hexafluorophosphate as the electrolyte. Hydrofluoric acid can and will c…

Building a pack from random cells like this is pretty much a cardinal sin with Li-Ion pack design. Cell resistance and state of health are carefully matched during pack manufacture to ensure cells charge and discharge evenly. Li-ion cells are pretty sensitive, so on top of that, large packs have battery management systems (BMS) to balance cell voltages and monitor for faults and damaged cells. Attempting to charge a…

Charging the "pack" shown is impossible. There are no wires connecting any of the batteries.

He made a case that can hold a bunch of cells. Not a battery pack.

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