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> I'd like to see the the energy density of petrol for comparison.

Petrol's higher energy density doesn't matter as much as people think.

Electric vehicles are around four times as efficient as petrol. In a petrol car, only 20% of the energy is converted to motion. In electric cars, this is around 80% (with some variation dependent on regenerative braking). I wrote about this extensively in a previous article: https://www.sustainabilitybynumbers.com/p/electrification-en...

Ok, how about "effective energy density"?

Batteries aren’t just used in cars man.

Really hard to beat propane or diesel for heat in the wilderness right now.

“Heat in the wilderness” must be so small in terms of global emissions footprint to be almost irrelevant, no? The wilderness implies ultra low density sort of by definition.

We don't have billions of people living in the wilderness. And technology has reached a price level where off-grid solar is actually an affordable and superior alternative to propane and diesel for household use in rural Africa.

Heat pump heat, in the wilderness or otherwise, is about 4x as efficient as resistance or fire.

This is somewhat silly, since a gas-fired heat pump can be very efficient, but gas-fired heat pumps are quite rare.

(California has a pricing/policy problem here, IMO. Electricity is absurdly expensive, gas is somewhat reasonable, and the result is that electric heating is not nearly as economical as it should be.)

Gas-fired heat pumps are neither economical nor efficient for single-apartment or single-house systems. Internal combustion engines with shaft power output of 1-2 kW are inefficient, loud and maintenance intensive.

They can start to make sense from around 50 kW heating/cooling capacity and upwards, so the smallest units are suitable for 8-15 apartments depending on size.

Yeah but the article is just about batteries and someone asked to see a graph about energy density.

Plus they asked about airplanes and somehow you made it about cars.

The person you are responded to did not make it about cars. They were responding to someone talking about cars

That is not even comparing apples to oranges, that is comparing apples to steel. You are correct in that energy density does not matter very much for weight-insensitive generation such as grid-scale generation, but energy density matters for weight-constrained applications such as airplanes and rockets as the poster mentioned.

However, assuming that the renewable generation cost curve continues to improve exponentially then the most likely outcome for a carbon-neutral or carbon-negative future will be using electricity to manufacture high density combustible fuels out of atmospheric carbon, effectively using it as a high density "battery" for use cases that demand high energy density.

To the extent that your analysis is relevant to the concerns of the poster, all it means is that batterys are actually ~4x better than the raw energy density would indicate. As to the specifics, Wikipedia claims petrol is ~12,888 W*h/kg or ~24x the battery energy density in the article, so ~6x better with respect to car motion. Note that the current curve has only gone from ~100 W*h/kg to ~500 W*h/kg, so we would need to see density growth comparable to the last 30 years to happen again.

What are the theoretical limits of electrical energy density?

Excellent question! A sufficiently advanced battery can theoretically beat gasoline.

Any given energy storage technology can store a maximum amount of energy in a fixed volume or mass. Behold one of my favorite plots: [1]

From lowest to highest energy density:

- springs, which use mechanical elastic potential energy, are kinda horrible

- capacitors, which use electric permittivity, aren't great

- next are both batteries and combusted fuels, which both use chemical reactions.

- nuclear gets us another few orders of magnitude

- finally, antimatter (E=mc^2) is a ways beyond that

Both batteries and fuels rely on the energy difference between unreacted molecules, so their theoretical energy density is the same. Well, actually, fuels are burnt to create heat which is converted to energy, and this heat->energy conversion is fundamentally thermodynamically inefficient (only ~tens of percent), whereas batteries are the same sorts of reaction but much more controlled. A sufficiently clever battery, which moves atoms around to react in the right places at the right time, is thus more efficient and thus energy-dense than fuel. However, moving atoms around like this to make a more efficient battery is much more advanced nanotech than what we currently have. But it's theoretically possible.

This is what biology does: us humans are powered by chemical storage (sugar/fat/glucose), which is used more efficiently than current batteries but without combustion. (lithium-ion is ~0.8 MJ/kg, glucose is ~16 MJ/kg, gasoline ~46 MJ/kg)

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

That is indeed a fun chart.

One thing I wanted to add is that fat (lipids) are much more energy dense than glucose. ~38 Mj/kg, though I am not sure what fraction of that the body recovers. Which makes sense, you want to maintain your long-term storage in a denser format.

Fuel(gasoline, carbohydrates, fats, etc. but not rocket one) does use oxygen from the atmosphere.Batteries are self contained (like rocket fuel).

So the density of chemical reactions is by definition higher.

Side note: energy density should apply to volume, not weight, but we'll - it is too common now.

What makes one chemical more able to store a greater energy per unit mass than another? Wouldn't the theoretical limit be a volume of pure electrons compressed in the densest unit volume possible? Say, stored in a magnetic field?

Compressing neon gas won't do much, aside storing energy as compressed fluid.

My point was the traditional fuels (incl. the edible ones) use more material/weight than their own. So it is very likely they'll be more efficient. The batteries require a reversible action by just applying current - this is quite the climb compared to most chemical reactions.

We have not done much since the li-ion inception, using FePO4 instead of cobalt is more sensible from an economic point of view but the energy density is even lower.

"Doesn't matter as much as people think"

Doesn't matter for WHAT? You start out talking about energy density, and then cite some numbers regarding efficiency. What does one have to do with the other? You've done nothing to support your opening claim here.

"Energy" value of gasoline and "energy" value of a battery pack are measuring two very different things even though they are both units of energy. When you burn gas in an engine, the engine has a theoretical upper limit on its efficiency which is FAR below 100%, and electric vehicle does not. So saying that gasoline has an energy content of 115,000 BTU/gal doesn't mean much since you'll be lucky to see 30% of that be turned into useful work.

Well, acording to wikipedia gasoline has an energy density of 46.4 MJ/Kg and LiPo batteries have an energy density of 0.36–0.875 MJ/Kg. So if your electric drivetrain has a 100% efficiency and your gas drivetrain has a 30% efficiency then the gasoline car would be able to do 16 times more work per unit of fuel.

And yet, electric cars you can by today don’t have 1/16th the range of a gasoline car. So energy density is not enough.

Not enough for what? The energy densities of both LiPo batteries and gasoline are enough to make a passenger vehicle with an acceptable range. For gasoline it is more than enough and for LiPo it’s barely enough.

Sorry, got cut off. So energy density on it's own is not enough to tell you whether is viable for making a car based on it.

> then the gasoline car would be able to do 16 times more work per unit of fuel

OK, so we've got ~300 mile range electric cars.

Where are the 5,000 mile range gasoline cars?

A Tesla Model 3 has 1060 pounds of batteries. If you replace those with a 177 gallon gas tank (at 6 lbs/gal) you should be able to go 4,780 miles at 27 MPG. It’s just that nobody wants to give up that much volume (visualize a 6x6x5 cube of gallon milk jugs).

I’m not accounting for a gas engine having more heavy parts, that mostly matters in city driving.

27 MPG is abysmal. The 2024 Prius gets over 50 MPG so it could be closer to a 10,000 mile range.

I was surprised a Prius does that well beyond the range of its battery. I took a number from https://en.wikipedia.org/wiki/Fuel_economy_in_automobiles after a quick search, though it’s about 20% worse than my aging Hyundai.

Yea it doesn't really follow. I think the idea is that the energy density being 50 times lower doesn't matter because the battery is efficient enough that you can make an EV with a 300 mile range which is good enough for most people. Of course if anyone wanted one, you could build a gas car with a 5,000 mile range if it had a gas tank as massive as an EV battery.

> In a petrol car, only 20% of the energy is converted to motion. In electric cars, this is around 80%

How does it settle out when you take into account the significantly higher weight of EVs?

By "significantly heavier" it is often a difference of a few hundred pounds on a few thousand pound vehicle. A 2L engine is about 400lbs, an automatic transmission is another 220lbs, 20 gallons of gas is 120 lbs, add another 100ish pounds for a much larger cooling system. So sure, the battery is like 1,000lbs but you traded 840 pounds for 200 pounds of EV motors (assuming two of them!) so in reality you're up like 360lbs.

Combined with regenerative braking, it doesn't make that big of difference in total energy usage. A massive chunk of the energy used in an EV is aero drag which makes little difference about weight. Weight makes a bigger impact with stop and go traffic on non-regen cars as slowing down that extra mass turns more energy into heat. An object in motion wants to stay in motion and all, once you're up to speed you're using about the same energy. This is why a lot of the EV trucks have close to the same range if the bed is full or not assuming it has the cover on the bed, but towing even a small trailer becomes a massive range hit.

I get on average 3.5mi/kWh in my EV, ~1MJ/mi. A gallon of gas is like 120 MJ, an average hybrid will get like 40mpg, so 3 MJ/mi being burned. You'd need to get like 120mpg to match my average efficiency of energy usage, and my EV isn't even that incredibly efficient of an EV.

>Petrol's higher energy density doesn't matter as much as people think.

When vehicles uphill, ramp, and fight with the increasing wind resistance due speed, it is needed a high torque for to motion.

The petrol's energy density is translated in high torque, that the gearbox latter transforms progressively.

In electric vehicles, generating high torque and cooling the overheated coils for to obtain such high torque drains the battery quickly, the range drops quickly.

And for to increase the range, more weight is added (more batteries), that requires higher torque for motion, that requires more energy again, and so on.

This is why the energy density it is important, in batteries are the watts hour per kilogram. As also it is important the number of cycles before such batteries start to drop energy density until to fail (to note the weight keeps being the same along all of this degradation).

With the current technology, due the magnetic fields strength generated in the coils, and the energy density of the batteries, EVs just can not compete with petrol vehicles. It is about torque, among other things.

What is needed? batteries with bigger energy density ( higher Wh/Kg with higher number of recharge cycles), and/or higher efficiency generating magnetic fields of high strength (ambient superconductivity, also stronger magnets would help some coil's topologies).

This is completely wrong: an ICE has 20-25% of the energy of petrol to use to do all those things. The rest is lost as heat.

Regardless of theorical efficiency or not of the energy, in practice the ICE gets the torque needed by the vehicle for driving on all types of slopes (and speed, by transforming part of that high torque with the gearbox).

This is why electric and combustion vehicles have such different ranges at even the same weight. Nowadays.

Such high torque is needed at the same moment the vehicle doesn't circulate on a flat terrain, or when have to reach highway speeds.

For to get at least the same ranges, the electric vehicle must reduce the energy consumption for the generation of the required torque (and speed), or needs to increase the energy density of the battery in companion of increasing the recharge cycles.

will be possible to achieve this? of course.

(The losses cooling or heating the battery and avoid the self-discharge should get the same advances, as it's counted as stored energy but it's not used for motion)

The mention of air travel was strange. I wasn't aware of anyone who thought long range flight would ever be electrified. At least not without some fundamental breakthrough.

S-curves are hard to predict. Basically every time someone attempts to do it, they are way off. This [0] is a neat paper that addresses the question. We've blown past every single prediction.

[0] https://www.inet.ox.ac.uk/files/energy_transition_paper-INET...

There are some very early stage tests, there is some kind of island hopper electric airplane that flys regular service, and it's only like 5 or 10 miles across water.

Batteries will get more energy dense, the range will increase a bit. But yeah, it's hard to see it getting to a few 100 miles.

Hello, do you have a link or name?

Here's the link, but the range isn't as bad as they said.

https://www.prnewswire.com/news-releases/eviation-announces-...

https://en.wikipedia.org/wiki/Eviation_Alice

https://en.wikipedia.org/wiki/Cape_Air

There's also an electric "flying water taxi" https://sfstandard.com/2024/01/18/san-francisco-navier-elect...

Testing and development by an actual operational airline, but running into regulation and certification issues. Could be a while even for this relatively narrow use case of seaplane flights of under an hour duration. Interesting update. https://harbourair.com/earth-day-eplane-update/

In terms of battery density, the fact that they have an operational, flyable aircraft, just stuffing batteries and an electric motor into a 60 year old air frame... pretty good and only going to get better!

I read a book in the 1980s about how you could fit S-curves to predict everything.

When I've actually tried it with tools like

https://docs.scipy.org/doc/scipy/reference/generated/scipy.o...

it's frequently been terribly, terribly wrong.

Can we use excess solar energy to create synthetic fuel (hydrogen?) to power jets?

I know almost nothing about this space. I would appreciate a comment on why this is feasible or not...

There are people researching it, I believe Airbus is about to test flying with hydrogen. It's the usual thing though for "green hydrogen", there's not much green hydrogen, there are some testbeds but just like for cars it seems to be mostly extracted from natural gas. You can extract it with any energy source like solar power. There's still the challenge that hydrogen fuel is not very compact, so it's hard to carry enough energy (in a car or plane) for much use, you end up with very very high pressure tanks. I think hydrogen will make sense eventually for trucks, tractors maybe. The question is will the massive investments in improving batteries make hydrogen vehicles obsolete or not.

There are also research programs about making fuel from other sources, like https://www.sciencedirect.com/science/article/pii/S016523702...

Answering my own question: Looks like there's something called solar fuel https://en.wikipedia.org/wiki/Solar_fuel

If advances in solar continue, yes. Currently, the IRA provides very lucrative investment and tax credits for green hydrogen projects (solar and wind powered electrolyzers). Power producers like AES are already building multi-billion dollar projects, and there are a lot more in the pipeline. One day the tax credits may not be needed for this to be economically feasible.

Companies like terraform industries are doing something similar, but creating natural gas. With enough cheap solar, all hydrocarbons are pretty much on the table as well.

It'll be a decade or more until this is scaled up and not dependent on subsidies.

Why do you mention long range flight? I don't see anything in the article saying batteries will take 100% of the airplane market.

It does say batteries will start to take market share in 2030. That's almost certainly true. It's a high priority for the Norwegian company to electrify the short distance airplane network in the next coming years. There are already battery electric planes coming out. And battery chemistries suitable for short range planes are starting early production.

I suspect battery electric plane will get a surprisingly good range once we start to get highly optimized battery chemistries and optimized airplane designs for that market. The hardest part is to get the first few products to mass market.

They might creep into the medium range market by 2050.

But long range? It might never happen. Unless we get something like aluminum-air batteries that can exploit oxygen in the air somehow. But it doesn't matter. Long range flights are not the majority of flights. It's a small enough market that e-fuels could cover it.

Since flying battery electric will be so much cheaper it's also possible people will have to switch planes multiple times on a journey. Maybe there will be some innovations/optimizations that make that faster and easier.

Long haul might not be the majority of flights by number, but they account for ~40% of the emissions from commercial aviation (well more accurately, wide-bodies do.) Regional flights that are prime targets to go fully electric only account for around 6% of emissions.

But you're right that starting somewhere is better than not doing that.

2. If batteries are growing exponentially right now then we are in the beginning of the S curve.

#1: certainly decades. Probably several, not few, decades. Unless a BIG breakthrough happens.

Lithium Battery 0.5 kWh/kg

Diesel 12.7 kWh/kg

Diesel is more like 3.175 (25%) due to the inefficiencies of small heat engines. You're throwing away like 3/4 of the energy as waste heat. Electric motors are >95% efficient and lithium batteries are in the high-90s percent efficient.

Electricity is already low-entropy, whereas energy from burning petrol is high entropy and thus contains less useful work.

Also, a kilo of diesel can emit that energy once. A kilo of battery can emit that energy hundreds or even thousands of times

it's not waste half the year

True if you are cogenerating, but few people do that. Only a miniscule fraction of waste heat from a car engine is required to heat a car.

Tangent but: I've always wondered why home cogeneration never took off. Too bad we don't have gas water heaters and gas furnaces that generate electricity and dump the excess onto the grid and heat with the waste heat.

Even a low-efficiency thermoelectric generator would recover some useful energy that is otherwise kind of wasted.

It's still waste, because if you're in a fixed location (which you'd have to be in order to benefit from much of the heat) you'd be better off running a heat pump.

Diesel has efficiency of 40% not 25%.

Taking the numbers from: https://www.sciencedirect.com/science/article/pii/S030626192...

- Diesel has a peak efficiency of 40% but an average efficiency of 20-25% (depending on the type of driving)

- Gasoline has a peak of 35% and an average of 16%–20%

- Battery has a peak of 85% and an average of 80%

Who cares, we need to stop burning fossil fuels, relative energy density in the abstract does not matter in the context of climate change

Comparing energy density between batteries and oil is not "transparency and realistic expectations"

Once the oil is used it's gone. Batteries can be recharged

That's not really their point, it's do we have any reasonable hope of applications that require the energy density of fossil fuels (flight) to be powered by electricity.

Flight will never be powered by electricity, so you can stop checking. Using synthetic liquid fuels for flight is the only currently-foreseeable path to carbon-neutral, long-haul passenger flight.

Flight will never be powered by electricity, so you can stop checking.

Fuel cells could well enable 30X better power densities. That would count to me as flight powered by electricity. There's also beamed power. Perhaps this wouldn't be practical, but it's a thought experiment that shows there's nothing impossible from first principles for electrical powered flight.

Long haul yes, but it's a little known story that regional airlines are on the edge of disaster because: (1) they can't find pilots, (2) manufacturers have stopped making the 50-seat jets that are the mainstay of that business. Airports like ITH are already at the top of the "regional development problems" in third-tier cities and it is not so clear they're going to be able to have service in 20 years the way things are going.

Given that the status quo is "go out of business when old planes can't be maintained anymore" the possibility of some radical change like electrification or a change in the scope rules is increasingly likely.

Perhaps I am missing your broader point, but the fact that ITH exists and only has scheduled service to New York is a bit ridiculous. That should be a high-speed rail route that takes you from city center to center, if America intends to become a developed nation.

God it's gotten worse. Last time I looked they had flights to PHL and DTW.

As it is now there is fierce competition for bus service from Ithaca to NYC (budget to various grades of premium) and I find it almost unimaginable that I'd fly to NYC to get to NYC because flying to JFK or atrocious EWR (never once made a transfer at EWR that didn't involve re-entering the secure zone) wouldn't save time to get to Midtown.

If you try to take the bus in the other direction you find you can't get from here to there. A friend of mine who used to ride the bus through Canada to get to the Detroit suburbs now takes the bus up to Syracuse, then takes Amtrak and gets out at 4am. On the way back one time there was no room on the bus although he paid for a ticket ahead of time.

The real significance of the regional airport is that it connects to a hub that goes everywhere. As it is if I have to fly somewhere I'll probably have to go up to SYR where at least I can fly on Jetblue and know I'm flying on an Airbus.

ITH used to get

https://en.wikipedia.org/wiki/De_Havilland_Canada_Dash_8

which I really enjoyed flying in, but they got replaced with 50-seat regional jets because regional jets are less likely to break down at a small airport requiring a crew to travel two hours to repair them.

As it is, academics at Cornell and Ithaca College will struggle to bring in speakers and it's just one more bit of "stave the countryside" that will drive knowledge workers to go to blue cities where their votes don't count -- it's how you hand the next election to a Demagogue.

You're right I was not thinking of the probable more common use case that a trip originating at ITH is only connecting at JFK and eventually arriving elsewhere. For that traveler a train to Manhattan doesn't work as well.

If it was all integrated it could be great. I have always been puzzled about how few Americans will use public transit to the airport. When I go to a conference in San Francisco I run into European conference goers on the BART but if I am with American coworkers they always insist on taking the SuperShuttle. Similarly I’ve usually taken the subway to JFK even when it meant riding on an insipod shuttle bus

...which 50 seat jets are you talking about? At that size I would expect turboprops to be preferred, and turboprops of that size are definitely still being built..

https://en.wikipedia.org/wiki/Bombardier_CRJ700_series

https://en.wikipedia.org/wiki/Embraer_ERJ_family

both of which stopped manufacturing circa 2020. We used to get the DASH-8 which I liked to fly more but they stopped using it because it breaks down more often which is no problem if it happens at PHL but takes hours to get a crew to fix if it breaks down at ITH.

Computers will never need more than 640k of memory, so you can stop checking.

You don't know what the future holds and neither do I.