Battery production is measured in Wh per year because you care about capacity to store energy. 40GWh = 40,000,000 kWh / (80kWh per car) = 500,000 cars.

240 GWh = 3 million 80kWh cars.

Saying that the production capacity is 40GWh is like saying that a factory can produce a thousand cars. And then you are asking: Per week? Per year? In total?

It's always per year.

Isn't Wh/yr just W/8766? The units are still W but with a divider.

Same reason we give fuel efficiency in e.g. litres per km rather than square meters.

"20 MPG is about 0.1 square millimeters," according to https://what-if.xkcd.com/11/. "If you took all the gas you burned on a trip and stretched it out into a thin tube along your route, 0.1 square millimeters would be the cross-sectional area of that tube."

It's simple dimensional analysis (https://xkcd.com/687/).

So, X litres per km is X * 10^-3 m^3 per 10^ 3 meter. Which is X * 10^-6 square meter.

Cool. So my car has a fuel efficiency of 0.000007 square meter :D I love it.

It is, but that doesn't necessarily make it easier to use. If you have a factory producing batteries totaling x Wh/yr in capacity and every car needs a battery with capacity y Wh, then you can build x/y cars per year. The calculation is mathematically the same if the production is specified as z W (where z = x / 8766), but not as immediately obvious to understand.

Can I just quickly invent a “Watt-Hour Capacity(WhC)” and rephrase this as “40GWhC/yr”? (expecting “technically but please don’t”)

No, units don't work in this way here

You're not discharging the battery through a whole year

They are in fact equal as dimensioned quantities. Whether the comparison is useful or not, that doesn't make the rates unequal.

Not quite.

Watts are an instantaneous measurement, but the factory needs a higher output most of the time to cover downtime. Much like power plants you would say it’s capacity is X watts with an expected capacity factor of Y%.

You could say the output is expected to average X watts over a year, but to then use it for anything would mean converting that to Wh.

I mean, Watts are a unit. All of the things you are saying are important considerations when discussing the factory's pattern of output, but ultimately, as you point out, it is still valid to measure the average output in Watts, which is the point that is being made, that that's the dimension that quantity has; you can still write down an equation of dimensioned quantities even if real-world complications mean that the equation is not as meaningful as one would like!

If you’re describing the W output though you could be describing the average [charge in each battery (W*h) X the number of batteries / time period] . That’s the actual W output of the factory as actual energy.

Capacity created per time period is a different unit created as a discrete entity with each battery but having no instantaneous value.

That's not what a unit is. A unit is just a standard against with other quantities sharing the same dimension can be measured. Anything with dimensions of energy/time can be measured in Watts, not just instantaneous power in the usual sense. Whether comparing two such quantities is meaningful may, as you point out, be another matter, but they can still be expressed in Watts.

Watt is power, Watt hour is energy. 1 Watt hour is 3600 joules, which looks suspiciously like 1 joule = 1 Watt second.

Most batteries now advertise energy capacity in kWh or thousand Watt hour(s). 1 kWh would be 3,600,000 joules or 3.6 megajoules, which does honestly sound more badass.

In the past batteries would advertise capacity in Amp hours, but you have to know the voltage of the battery to convert Amp hours to energy.

The rate of production can’t be specified using energy, it needs to be the time derivative of it (unless the overall output of the factory from being opened to being closed is specified, which I don’t think is the case in the article). The unit needs to describe - power.

Whether you use Joules or horse power weeks is beside the point as they can easily be converted into each other.

Sure thing my dude. You also cannot express fuel consumption in miles per gallon. You must express it in square millimeters. https://what-if.xkcd.com/11/

We may occasionally write gallons per mile with a slash, but it is useful as a ratio, not an equation. It makes no sense to reduce a volume to a surface.

On the other hand, knowing if a factory puts out 240 gigawatt hours worth of battery capacity every year, or only over the entire lifetime of the factory, really is an important distinction to make.

My apologies. I did not read the first comment clearly enough, and the 2nd comment did not clarify the actual complaint.

> It makes no sense to reduce a volume to a surface.

It kinda does, it is the (average) cross section of the fuel flowing from tank to engine.

Sure, but to be useful you need flow rate, at which point you're basically back to calculating volume. Gas is purchased in volume, and stored in volume. Why not keep the measurement of use as volume per time or distance?

I wish people like you who make these intelligent,factual, and short comments could have a reputation value on HN. This value could give you some automatic upvotes or a more prominent location displayed.

Meh, I'm not always right, and often wander int territory of conjecture (though I like to think I try to be clear about which is which).

I'd rather keep the freedom to post as I please rather than limit my expression just to chase clout.

It's not for you, it's so that factual information is promoted

OP is right. GWh is the measure of a battery’s capacity. How often will that total battery capacity exit the manufacturing facility?

Annually

Thanks. Guess I missed that part in the article.

Well it’s not there, which is exactly my point ;)

It is usually accepted per year when not specified. For example when you talk about GDP, it is yearly. Salary? Yearly usually yearly unless specified. Factory production? Yearly.

And no, you cannot use watts, unless you invent a new unit, watts of capacity?

The units used are correct.

>>Salary? Yearly usually yearly unless specified.

That's a very uniquely English thing. Where I'm from(Poland) you always list the salary per month and that's how people talk about it. I've never seen anyone refer to a salary on an annual basis.

> Where I'm from(Poland) you always list the salary per month and that's how people talk about it.

Depends on the type of contract. I'm also from Poland and unit I use most often is the daily rate because it's the only reliable way for a contractor to calculate earnings.

Job listings indeed still use monthly, but their understanding of a month is usually "20 workdays", which is obviously off by at least 10%.

Well, if you are a contractor you don't have a salary, strictly speaking.

Over 80% senior job listings are formally contracts around here. It's a popular method of tax optimisation.

You can thank our people’s republic past for that. In the whole bloc and the USSR, monthly has been the standard. It just carried over.

(Troubled post-socialism past and, to some extent, present, in which the vast majority is living paycheck to paycheck with little to no ability to save up, is sure contributing to this mode of thinking.)

Rest assured that in many other EU countries that were never a "people's republic" salary is usually talked about on a "per month" basis.

It's US thing, not English. English would be weekly :-).

I live in UK currently and everyone says their salary per annum :-)

nobody I know (here in England) would say their salary is their weekly earnings. Salary is always per year

When I did a summer holiday job during my A-levels, people talked about hourly rates and got paid weekly; when I was at Aberystwyth at the end of my degree, I remember some local employment scheme that listed pay per week; I think the job contracts after I graduated and before I moved country were usually listing annual pay, but I can't remember. Now I'm in Berlin, discussion is mixed between monthly and annually.

yeah for temporary/part time work you'll often have hourly rates with weekly pay, but that wouldn't normally be called a salary

Sounds like it’s English thing, that monthly- and yearly-income shares the word ;)

It's energy over time, that makes power. 240 GWh / 1 Year = 27,379,093 W.

No it's not energy over time. GWh of capacity is not energy.

It has dimensions of energy, which is what's being discussed. Things do not need to be measuring the same thing to have the same dimensions.

It’s not really watts as there is no real power output. It’s an accident that the units are homogeneous but the output is in Wh/y, where Wh is a convenient way of describing the capacity of a battery (under standardized conditions) and not real energy outputted.

That’s like saying that battery capacity isn’t really kWh because there’s no real energy storage when they are empty. The unit for energy capacity output is still Watt (or horse power seconds per year or any other unit).

Besides that, those battery cells are charged as part of the production process (though not completely), so I could argue that actual energy is leaving the factory.

kWh as capacity of a battery is similar to ml as capacity of a bottle.

Thanks for adding the "/y" which is what was missing for me.

Could you elaborate please? Why is there no real power output?

When you purchase a battery are you interested in the energy that they contain or in their capacity to store and output energy repetitively?

Interesting. I think I would still be interested in the total energy held by the battery, plus the amount it is expected to degrade year on year.

I'm still not sure why you say Wh/y would be a more appropriate unit, given that it would change as the battery degrades.

Watt hour is a unit of energy. Energy is the capacity to do work. When the batter leaves the factory, it is empty. It has no energy, but it can hold energy if you give it some.

It's like if you produced gallon-sized plastic water jugs. Let's say you made 1000 a day. Would it be accurate to say you produced 1000 gallons of water a day? No, you produced 1000 empty jugs.

Batteries are charged when they leave the factory. Besides that 1000 gal/d of storage capacity in your example is a valid unit for specifying factory output, is it not?

Yes, "1000 gal/d of storage capacity" is valid. "1000 gal/d" is not. Even if you used 1000 gal/d colloquially, you would have been talking about the capacity of the bottles.

The misconception you're having here is that "GWh of storage" is the volume of the bottle. You're interpreting it as "GWh", which in the bottle example would be like saying "They produce 1000 gallons of water / d".

Both?

Rough rules of thumb for battery production that I heard in 2021:

10x increase in world production capacity every five years.

Currently at about 200-300GWh/year. Expect 2-3TWh/year by 2026, and 20-30TWh/year by 2031.

Volkswagen had better pick up the pace quite a bit.

Yes but this assumes infinite availability of the resources required for battery production. Given they are in Africa and Asia, this is gonna be way more difficult in the rising new world order with the shrinking influence of the US and EU as the Pax Americana is dying a slow death.

BRICS nations and friends will make the near future very uncomfortable for Westerners used to affluence.

Out of the world's five largest lithium producing countries, the largest one by far is Australia, only China is in Asia, and half the world's reserves are in South America anyway.

The US will simply do whatever it always did and, should the need arise, simply putsch away whoever governs these reserves.

[1] https://en.wikipedia.org/wiki/List_of_countries_by_lithium_p...

[2] https://en.wikipedia.org/wiki/Lithium_Triangle

Or companies will find alternatives.

Or someone will start digging for raw materials in a place that isn't hostile.

30TWh/year in 2031 is not infinite, and is in fact quite finite...

Also, essential minerals are alllllll over, only some (cobalt nickel) are concentrated in a few areas and those are actively being minimized and eliminated from future chemistries.

Isn't saltwater lithium extraction close to being a thing, as well as recycling?

Yeah, every non "western" country is just longing for suicide russia style.

This is one of the reasons I'm not sure why car companies are getting directly in to batteries. Plus they are locking themselves into a technology which may well be superseded.

It seems to me equivalent to pc manufacturers making their own chips.

With the coming shortages of production and massive demand, guaranteeing supply is table stakes for the game of game manufacturing.

There is no alternative around the corners IMHO car companies are not thinking big enough with their investments.

Table stakes for *car manufacturing

hi. interesting stats. Could you please give some references for this? thanks.

I appear to have lost my bookmark, it was about 30 minutes in to an episode of the podcast The Energy Gang, or their sister podcast, during an interview with a CEO that has raised nearly a billion dollars over the years for battery related businesses.

This is vague enough that perhaps you shouldn't take my word, but I unfortunately don't have the 15 minutes this weekend to track it down... if I find it again I will try to email you.

I find the watt thing cool too, and I'm glad you pointed it out

> Why can't journalists use units correctly?

I’m pretty sure the answer is - they took physics in high school, they’ve been (on average) at least ten years out of high school, and it never came up, even once.

Do people outside of stem fields have this issue with us? It is really strange to think that most people don't remember any calculus or statistics, or chemistry or physics. While my social intelligence is certainly lacking, I do at least feel like I understand what my friends in non-stem careers are talking about, and the opposite is definitely not true.

STEM knowledge is non intuitive and highly perishable.

Plus, they never liked studying it. It's amazing how much you can cram in short term memory that gets erases within day or weeks.

Outside of the relatively narrow niche of web related tech, is any other STEM perishable? Physics, chemistry and calculus haven't changed that much right?

My bad, I meant it more in the sense that your memory of it decays quickly :-)

> Why can't journalists use units correctly?

> Side remark: it's actually kind of cool that you can literally specify the battery output of these factories in Watts.

The unit is Watt hour storage capacity.

I think he means the capacity will be 40 GWh / year = 4.56MW.

Sorry I’m not sure I understand. Watt hour is a unit of energy. Energy can be stored. They’re making batteries that store energy. A Watt is a unit of power. They’re not making power. So after a year of making batteries, they will have produced exactly 0 Watts. I guess in that sense you can measure their (power) output in Watts: they produce 0 Watts.

I think the confusion is that the unit of their product is not GWh. It’s (GWh of capacity) which is not the simple product of Watt and hour)

How much battery capacity are they producing per day? Impossible to tell from the article. I’m relatively sure that the period of time the specified capacity is produced in is one year.

You can divide the hours in GWh by the year time span and the time units cross out. The unit is Watt, but the physical quantity it’s describing is arguably not power but energy capacity production rate or something similar.

There’s no 1:1 mapping between units and physical quantities, just think about specific impulse in rocket engines being quantified in seconds.

The unit is not GWh. It's "GWh of storage." It's ironic that this thread started with you lamenting that units are used incorrectly.

The unit is GWh, the physical quantity it describes is “energy storage capacity”. Those two are not the same.

Take this example:

Unit: second, physical quantity: could be things like “time”, “specific impulse”, “distance” (light-second), etc. Many physical quantities can be measured in seconds.

Is it really true that you can measure distance in seconds? I think light-seconds are different units from seconds hence why they measure distances, similar to how Watt-hours and Watts are not the same unit. If a second was a measure of distance then speed would be unit-less (second / second) as opposed to the speed of light which is light-second / second ≈ 3e8 m/s.

You are right, light seconds don't fit in well. My point still stands, you can't really know what physical quantity is measured just from looking at the unit alone, that's now what units are made for.

You can still divide GWh of capacity by a year and get GW of capacity, ie the instantaneous production rate of capacity.

No you cannot. Watt hour is a unit for energy derived by applying power over time. That’s why when you divide by a period of time you’re left with power. The unit “GWh of storage” is a complex unit that’s not easily broken up. When you divide by time you get a new unit, “GWh of storage per unit time”

You are conflating two different concepts here. One is "unit" which is a measure of a physical quantity (ie "GWh"). The second is the physical quantity itself ("battery storage capacity"). The relationship between the two is that a unit can be used to quantitatively describe a physical quantity ("5 GWh of battery storage capacity"). Physical quantities like "battery storage capacity" can usually be quantified in different units which can be converted to each other ("5000kWh = 5GWh = 1.8 * 10^13 J"). The unit itself ("GWh") doesn't describe precisely what physical quantity is being measured. It could be mechanical energy stored in a flywheel, the total heat output of a chemical reaction, battery storage capacity, etc.

You’re fundamentally misunderstanding the units. I don’t know what else to say. “Watt hour of storage” is not the same as a Watt hour. You can’t divide by time to get power. That should be obvious.

"Watt hour of storage" is not a unit, it's the physical quantity "storage" quantified by the unit "Watt hour", ie the combination of the two.

That’s what you’re not understanding. “GWh of storage” is a unit. It’s not an SI unit, but it is a unit, i.e. a thing you can use to measure something. The production of this factory is being measured in this storage unit. Watt is also a unit, a unit to measure power. There is no way to convert a unit of power to this unit of storage.

Do you have a reference for the definition of this energy storage unit? I have never heard of it before and my attempts at searching the web seem to contradict you.

Wikipedia writes: “Storage capacity is the amount of energy extracted from an energy storage device or system; usually measured in joules or kilowatt-hours and their multiples”

https://world-nuclear.org/information-library/current-and-fu... writes: “Storage systems for electricity include battery, flywheel, compressed air, and pumped hydro storage. Any systems are limited in the total amount of energy they can store. Their energy capacity is expressed in megawatt-hours (MWh), and the power, or maximum output at a given time, is expressed in megawatts of electric power (MW or MWe).”

Both of which to my layman reading opposes your claim.

You decided all on your own that GWh of storage cannot be divided by a time unit to create another 'new' unit, GW of storage. Repeat: _You_ decided that. I can explain it simply: One GW of storage is equivalent to producing one gigajoule of storage per second.

We really need to rename these things to be based on Joules instead. A lot more intuitive.

This battery stores X Joules. 1 J = 360 kWh

This battery releases Y Joules per second. 1 J / s = 1 Watt

> Why can't journalists use units correctly?

If they could, they would have better paying jobs.

I don't mean to say journalists are stupid. They're generally not at all. But their required talents are verbal and social.