What does a kilowatt hour look like? • Hacker News Board

Re: What does a kilowatt hour look like?

#141

Post by whamlastxmas » Fri, Sep 23, 2016, 2:47 PM UTC

Reason077 wrote: post #40

spdustin wrote: post #29

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…

It's pretty safe so long as you use a battery controller with appropriate monitoring to prevent overcharging. Recycled 18650 cells that have worked fine in laptops for years are very unlikely to suddenly explode on you for no reason. I'd be more worried about the mystery Chinese ones you can get new on the web! Here's some Materials Science students at Oxford who built packs using recycled laptop cells. They used con…

>very unlikely to suddenly explode on you for no reason

It really depends on their condition. If you get some cells from a laptop and they've all fallen down to reading 1 volt, then yeah repeatedly charging them (especially at a high amperage) is going to be pretty dangerous.

Re: What does a kilowatt hour look like?

#142

Post by whamlastxmas » Fri, Sep 23, 2016, 2:50 PM UTC

adrianN wrote: post #105

revelation wrote: post #103

Earlier quoted context omitted.

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

But you don't ride at highway speeds ;)

Bike also doesn't weigh 2500 pounds

Re: What does a kilowatt hour look like?

#143

Post by whamlastxmas » Fri, Sep 23, 2016, 2:51 PM UTC

vamur wrote: post #102

Lithium-ion batteries require an expensive materials and overly complex manufacturing (Gigafactory). They are also dangerous as evidenced by the Samsung Note 7 debacle. Hopefully, there will be advances in making lead-acid and hydrogen fuel cells cheaper and safer. That would allow viable energy storage for solar PVs.

Dangerous depending on the chemistry. There are plenty of very low volatility lithium ion cells out there.

Re: What does a kilowatt hour look like?

#144

Post by [deleted] » Fri, Sep 23, 2016, 5:13 PM UTC

jrockway wrote: post #57

spdustin wrote: post #29

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…

You have to realize that 1kWh is a lot of energy. Imagine being hit (in a world without an atmosphere) by a 60 pound suitcase falling out of an airliner flying at 45,000 feet. Same amount of energy as that battery pack. (Alternatively: the most powerful air conditioner you can buy running full blast for 30 minutes. Incidentally, that battery pack has as much energy as 100mL of gasoline, which is why gasoline-powered…

[deleted]

Re: What does a kilowatt hour look like?

#145

Post by agumonkey » Fri, Sep 23, 2016, 9:47 PM UTC

205guy wrote: post #118

agumonkey wrote: post #39

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).

Efficiency is not the goal, it's more symbiosis. Humans benefit from "wasting" energy through exercise. Instead of lifting weight and riding bikes, why not try to leverage it.

Re: What does a kilowatt hour look like?

#146

Post by agumonkey » Sat, Sep 24, 2016, 7:14 PM UTC

dredmorbius wrote: post #114

mikeash wrote: post #76

Earlier quoted context omitted.

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...

I've seen similar things in Africa were people just attached bikes and drums together. Didn't have hot water though. For cold water + soap washing it's clearly a win.

Re: What does a kilowatt hour look like?

#147

Post by sesqu » Sun, Sep 25, 2016, 6:42 AM UTC

chriswarbo wrote: post #64

qoobaa wrote: post #18

Earlier quoted context omitted.

It's not pretty,but it's practical. Especially when it comes to electricity - watts and hours are quite easy to work with.

It doesn't make much difference whether you use Watts or Joules, since 1 Watt = 1 Joule per second, so both are just as convenient for electricity: 1 Watt = 1 Volt Amp, so 1 Joule = 1 Volt Amp Second = 1 Volt Coulomb (although amps seems to be more "normal" than coulombs). It's a bit redundant to multiply power by time, when that's just an energy, but going between Watts and Joules is trivial (by design), so it's not…

It's because power needs are reported as watts, and impactful devices are typically utilized for several hours. It's much easier to do your monthly utilization napkin math in multiples of kilowatt-hours than of 3.6 megajoules.

I'm personally not a fan of the kWh, because it keeps being mistaken for kW, but I recognize that lack of need for a conversion factor help a lot of people make sense of energy.