
What does a kilowatt hour look like? - qoobaa
https://blog.kubakuzma.com/2016/09/22/how-does-a-kilowatt-hour-look-like.html
======
spdustin
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 cause
permanent damage to lung tissue if inhaled, and nasty, nasty chemical burns to
exposed skin. 18650 batteries are supposed to have several failsafes to
prevent thermal runaway, but counterfeit batteries can lack those failsafes.
Not to mention, in some laptop battery packs, the protection was pack-wide,
and not in individual cells. Not knowing the chemistry of the cells or the
state of the protection circuitry of the battery would make me very nervous.
Maybe someone else can provide more detail on how to test them safely.

~~~
jrockway
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 cars are so popular.)

When you put a lot of energy in a small space and release at all at once, it's
called a bomb. Li ion batteries are small bombs that can be used to power
electrical devices.

Some chemistries are safer than others, like A123 cells. The market did not
care about safety and they went bankrupt. Energy density is king.

~~~
ralfd
Wow, 100 ml of gasoline could propel a suitcase into the stratosphere? That
seems so counterintuitive.

~~~
chrismcb
Only if there is no atmosphere.

------
mpreda
1 Wh is about 0.9 kilocalories. So 1kWh is about 100g of butter. The energy
expenditure of a human in one day is about 2kWh. 1kWh is about the energy
needed to heat 10L of water from 0 deg celsius to 100 deg celsius.

~~~
javajosh
It actually takes some extra energy to move from ice to water, and also some
extra energy from water to steam, so your numbers only work out if you are
strictly inside the 0-100C range.

It's interesting to realize thought that we programmers are code producing
machines that run on roughly 2kWh per day. If we produce 100 lines of code in
a day, that's 20Wh per LOC. Not bad, actually.

~~~
jfoldager
Water can be 0-100 C, both temperatures included. No need for melting/turning
to steam. You could start with 10 L of 0 C ice, but he said water.

------
spodek
> David McCay - Sustainable Energy without the Hot Air

A fantastic book. A Caltech trained physicist at Cambridge does the
calculations to see if the UK could get all its energy needs sustainably.

Simple, easy to understand, and enlightening. It deserves the praise they talk
about.

And it's free to download.

~~~
titojankowski
Sustainable Energy Without the Hot Air Free from the author's website:
[http://www.withouthotair.com/download.html](http://www.withouthotair.com/download.html)

------
jononor
1kWh as gasoline is about 1/10 liter. Though one will not get anywhere near
that much high-quality electric energy with consumer/small-scale methods.

~~~
xyzzy123
1kWh as aluminium is about 66g (assuming 15kWh per kilo manufacturing input)
or about 4 drink cans.

~~~
mrfusion
Wow so I could gather up a bunch of cans and heat my house.

~~~
jrockway
The key to batteries is being able to use the stored energy. Bonus points if
you can add energy and get it back later.

~~~
xyzzy123
Thermite :p

~~~
marak830
I know it's frowned upon saying this, but damn if I didn't choke on my coffee
haha.

Yeah let's not use thermite to heat our houses people.

------
madengr
"So, what a kilowatt hour of high-grade electric energy can do for you? Many
useful things, i.e.:

deliver 4-5 kWh of low-grade heat (or cold) into your home (depending on COP
of a heat pump)"

Huh? I assume he means 0.4 - 0.5 kWh?

~~~
semi-extrinsic
Nope. Heat pumps have a COP > 1\. It's quite literally a pump moving heat from
a cold place to a warm place. If it takes 1 kWh to pump 3 kWh of heat from
outside your house to inside (in winter), you've heated your house by 4 kWh.
Note that the electric energy used to drive the pump is transformed into low
grade heat, which in this case is useful.

~~~
SilasX
Good point! It kinda threw me off too, since heat energy isn't usually
measured in kWh. But yeah, heat is a kind of higher-entropy form of energy
than electricity, so you can, in fact, turn one unit of the latter to more
than one unit of the former.

The "exchange rate" depends on the temperature; the maximum ("Carnot") heat
pump efficiency is T_high/(T_high - T_low), where T_high is the temperature of
the room being heated and T_low is the surrounding environment the heat is
being pumped from (all on the absolute scale).

When T_high = T_low, the max COP is infinity, which has the physical meaning
that "You don't need to spend any energy to keep a room the same temperature
as its environment; that happens automatically."

[https://en.wikipedia.org/wiki/Coefficient_of_performance#Der...](https://en.wikipedia.org/wiki/Coefficient_of_performance#Derivation)

------
dredmorbius
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](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](https://news.ycombinator.com/item?id=11500614)

[http://itila.blogspot.com/2016/04/index-for-
first-23-cancer-...](http://itila.blogspot.com/2016/04/index-for-
first-23-cancer-chapters.html)

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.

------
outworlder
> 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.

~~~
qoobaa
Interesting, is it Tesla? Which model is it?

~~~
freerobby
As a reference point, a Tesla 85D uses 290 watt-hours to go one EPA rated
mile. So 1 kWh takes you 3.448 miles.

~~~
chrisseaton
> one EPA rated mile

Are EPA miles not the same as normal miles?

~~~
detaro
What's a "normal mile" regarding energy consumption?

There is a series of standardized driving profiles that is averaged to get a
comparable, somewhat realistic value.

------
mncharity
What does a Newton-meter of torque feel like?

Reopening a plastic soda bottle.

From a web interactive I wrote:
[http://www.clarifyscience.info/part/ZoomB?v=A&p=CK6Ji&m=torq...](http://www.clarifyscience.info/part/ZoomB?v=A&p=CK6Ji&m=torque)
(2014)

~~~
Koshkin
> _Newton-meter_

I do not know why (and I do not have a strong opinion on this), but somehow
this (relatively recent) tradition of naming units after people feels weird to
me. I know we are already used to these units, but imagine the unit of mass
was called Einstein instead of kilogram.

~~~
nitrogen
How recent is the trend? Most of the units I know are named for people: Joule,
Watt, Volt, Ampere, Newton, Angstrom, Ohm, ...

~~~
Koshkin
I am sure Newton didn't name the unit of force after himself, so I would
roughly place the invention of such possibility around early/mid nineteenth
century, that is, about 200 years ago, which is when the research in such
areas as electricity and magnetism, thermodynamics etc. was in full swing.

------
grondilu
Not related, but I hate this unit. Can't we just talk about Joules?

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

~~~
chriswarbo
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 too
bad.

However, I can't think of a reason why hours would be easier to work with than
seconds (as kiloseconds, if you want the same order of magnitude), especially
regarding electricity?

~~~
sesqu
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.

------
wazoox
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.

~~~
qoobaa
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.

------
lutusp
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?"

------
robbrown451
Less acronyms please. (COP, PV, and even EV)

~~~
Jugurtha
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).

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

~~~
Jugurtha
It depends. Facing each other, when one says "to the right", does he mean to
his right or to the interlocutor's right?

Furthermore, Are RFCs TLA? It appears that IANA, an FLA itself, standardized
the use of TLAs in an RFC.

[https://tools.ietf.org/html/rfc5513](https://tools.ietf.org/html/rfc5513)

------
throwaway7767
Riding an electric bike has made me very aware of how much work can be
performed with a given amount of power. Watt-hours aren't abstract anymore.
1kWh can get me and my stuff 120km easily if I pedal, probably closer to 80km
if I used battery power only. Also instantaneous power, 200W is enough to move
my bicycle, me and my stuff at a low cycling speed (15-20km/h) on the flat.

It really puts things in perspective when I look at a 1KW space heater. That's
a lot of power!

------
ge96
I like his battery haha, colorful. Also nuts to test all those cells. Make
sure they're all roughly the same performance. wonder how hard it would be to
find a bad cell.

~~~
TD-Linux
Probably the most obvious indication would be temperature. Assuming they are
in parallel, it'd be quite wise to measure their discharge curves to only
select similar cells - that would also highlight any bad ones.

~~~
ge96
Hmm. It did appear that the cells were all oriented in the same direction.

What a great idea I think although I wonder if it's a pain, cutting through
that hard, protective plastic that these cells are in for laptop batteries.
Unless you buy just the cells themselves.

------
basicplus2
"deliver 4-5 kWh of low-grade heat (or cold) into your home (depending on COP
of a heat pump)"

If you don't use a reverse cycle system you can more like 8 kwh of heat or
cold

------
jqkeller
I was just commenting today how approachable this book makes understanding the
requirements to transition to renewable energy. I would warn though that the
little bit of economics and the discussions about battery storage and solar PV
at the end are very dated. The exponential drop in pv prices wasn't
anticipated by the author. I think if modern prices were used the 5 models at
the end would look very different.

------
walrus01
If you like this, watch the videos from this guy:

[https://www.youtube.com/user/jehugarcia](https://www.youtube.com/user/jehugarcia)

he methodically tests old 18650 laptop cells, sorts them, builds battery packs
and so on. He's converted a classic VW bus to electric power using his home-
made battery packs and packs salvaged from wrecked teslas.

~~~
sporkologist
> wrecked teslas

Wait what? where is this supply at

~~~
maxehnert
Copart is a good site for buying wrecked cars in various conditions. Otherwise
try calling your local junk yards.

[http://www.copart.com/us/search?q=tesla](http://www.copart.com/us/search?q=tesla)

------
vamur
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.

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

------
lightedman
A single 12V 100Ah VRLA Deep-Cycle battery might be a better idea that's more
familiar to a much larger chunk of the population, and you have the added
bonus of having enough capacity to make up for the typical
conversion/transmission losses in most scenarios, thus delivering a true
kilowatt-hour!

------
jasoncchild
Batteries have different discharge curves, influenced by many factors such as
chemistry, age, etc. Often "packs" of cells are balanced in an attempt to
minimize variance. Something tells me your 10kW "wall" may not perform as you
expect it to (providing you are actually loading it for real use).

~~~
qoobaa
I know it's not as simple as "connecting 10k batteries together". It's an
interesting topic anyways, there are a few guys already doing it with
promising results (check HBPowerwall on youtube for instance).

BTW: I haven't even connected these cells together yet - even that is not as
simple as it may look like.

------
cowardlydragon
If we don't have to move the battery around, why not use cheaper but less
compact techs for storage?

------
agumonkey
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 ?

~~~
205guy
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).

~~~
agumonkey
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.

------
perilunar
1 kWh = 3600 kJ = 95g of lard (or body fat!) = 85g (115 mL) of petrol/gasoline
= 1.5 Big Macs = 40% of an average male's daily energy intake = ...

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ninja-wannabe-7
1/33.7 of an exceptionally privileged imperial gallon of petrol, according to
US regulators.

------
soperj
What.

~~~
qoobaa
Thanks, I fixed the title. I'm not an English native, so I make a lot of
errors like this :-).

~~~
soperj
No problem.

