Stupid Physics Question

[timbop]

Here's another thought experiment: if you had a tank/giant balloon in the ICE car that captured all of the exhaust gases and stored them in/on the car, would the car weigh more (have more mass), less, or the same after burning all the gas?

A: More, because the engine takes oxygen from the atmosphere and combines it with the gas during the process of combustion. One gallon of gasoline weighs around six pounds, but burning it produces 19.5 pounds of CO2.
https://www.epa.gov/greenvehicles/greenhouse-gas-emissions-typical-passenger-vehicle

This is one of the reasons why gas appears to be so much more "energy dense" than an EV battery: a large portion of the mass needed for the chemical reaction comes from the air and is not "counted".

Finally: energy density is NOT the same as energy efficiency, which is why EV's can go 80 to 120 miles on the same amount of energy that is released burning a gallon of gas.

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[P. T. Magoo]

Depends if you get out to take a leak during the trip.

 

[MW1515]

Actually the friend is right on both points……. For vehicles where energy density is important.

Airplanes and boats come to mind.

It would take around 12,000 lbs in batteries to replace the 100 gallons of fuel in my 23’ boat. That’s not going to work in a boat with a dry weight around 3600 lbs.

And flying NY to LA in an electric airplane carrying 300 passengers? Not with battery power.

Go figure we have a bunch of battery fanboys on a BEV forum. But sometimes it’s ok if your friend wins a single point in an argument.

Good point, however batteries have a LONG way to go when it comes to R&D and innovation and so one day much more efficient solar panels combined with much more energy dense batteries may be able to power passenger planes. Solar powered planes already exist (but weight has to be kept very low). Also, you have to completely take away environmental impact in order for the friend to be right on the second point. Gasoline is a wonderful fuel but with a very high environmental impact that cannot be avoided.

 

[ctenidae]

my bet is on biodiesel for trains, trucks, boats, planes (kerosene being one step from diesel). Algae-oil is promising, but a good 10 years out since most Algae research dollars are going into food and medicines

I vividly recall (think I have the business plan around here somewhere) wanting to do a start up algal oil project, 15 years ago. It is truly the wave of the future, and always will be.

I think trains will get electrified, eventually. Cross country track is an awesome pre-existing right of way for running power lines that can be both transmission and catenary lines. This could bring wind/solar power from places that produce it (like Nebraska) to places that need it (like the East Coast). Trains can also carry the cranes and parts needed to build offshore-scale turbines, which can be built in the railroad right of ways. Bonus is the railroads can basically do whatever the hell they want with their rights of way (thanks, Robber Barons), only snag is FERC rules on interstate transmission and getting the individual states to shut up about it. Would help to get Texas integrated with the rest of the country, would provide a great project for improving grid stability, and would make cross country shipping dirt cheap using free electricity.

 

[ctenidae]

The REAL question is 'so what?'
We all know the days of gasoline powered autos for transportation are numbered. We also know that we will likely have to change our expectations to adjust to available technology.

This

 

[Mach1E]

Good point, however batteries have a LONG way to go when it comes to R&D and innovation and so one day much more efficient solar panels combined with much more energy dense batteries may be able to power passenger planes. Solar powered planes already exist (but weight has to be kept very low). Also, you have to completely take away environmental impact in order for the friend to be right on the second point. Gasoline is a wonderful fuel but with a very high environmental impact that cannot be avoided.

You’re still fighting physics with your future hopeful technology.

Just like batteries have physical limits (they can only store so much power), solar panels have physical limits too (there a fixed amount of solar energy to capture on a given surface area).

Modern solar panels are already extremely efficient. Even if you made them 100% efficient (impossible) they don’t generate enough power to power a car or a plane with any meaningful payload.

A slow blimp maybe.

Now the last point about environmental impact just isn’t true. The impact can be (and has been) significantly reduced.

But battery production doesn’t necessarily fair much better from an environmental impact

And the end of the day, no matter which tech we pick, there will be an impact. We just have to be responsible enough to reduce when possible and not do more damage than can be repaired.

 

[Mach1E]

The energy 'density' of gasoline is indeed staggering.

It is nonsensical to compare to electrons.... which are neither 'created' or added, or 'destroyed' or depleted. They are just moved around in batteries. So your more accurate comparison is dependent on battery chemistry ( flooded lead-acid, AGM, Lion, LFP) when you talk about energy density.

The more direct comparison of ICE/BEV would probably be to include not only the weight of fuel (or batteries) tank, but the entire drivetrain as there is a significant difference in the total weight of motors, cooling systems, exhaust, etc.....

At the end of the day though, the same weight ICE vehicle will have a longer range than a comparable BEV because of the energy density of gasoline.

The REAL question is 'so what?'
We all know the days of gasoline powered autos for transportation are numbered. We also know that we will likely have to change our expectations to adjust to available technology.

The point about “so what” is the most important one.

At the end of the day the “why does this matter” is the most important question.

Reminds me of the old Hp/liter arguments on car forums. And unless you live somewhere with a displacement limit (Japan) or race in a class with a similar limit, it’s just a meaningless fun fact.

People used to brag the Ford 5.0 had more hp/liter than the Chevy 6.2. ButI’m the 5.0 weighed more, cost more, and took up more space. In the “so what” category, I’d argue the weight, size and cost matter more than the cylinder displacement.

 

[DomiinUS]

Did you know the earth was flat? The internet says so: 50 Reasons Why You Should Believe The Earth Is Flat (theodysseyonline.com) Regardless of what people post on-line, reality is reality. There is only a change in mass in a nuclear reaction. Your batteries are a closed system - for every electron that flows out of the anode, an electron flows back into the cathode. Nothing inside the battery transfers in or out. There is no change in mass.

Well, whatever you think about physics - E = m c^2 is VALID also in this case (actually in all cases, but only in nuclear - fusion and fission - reactions relevant)
And, as I pointed out before, the difference in weight is negligible, but it is there (and even without doing the numbers, I am sure it is below milligram for the 91 kWh or whatever number of kWh you want to take....)
It will be for sure impossible to measure this difference in weight though

Whoever wants to disagree with me about this: fine for me
Whoever wants to stick to facts: better

Short explanation: the number of electrons is for sure the same, but the weight of the sum of anode and cathode material depends on the state of charge. If you want, I am sure there is a good article online about weight differences for charged and discharged batteries...

 

[MW1515]

You’re still fighting physics with your future hopeful technology.

Just like batteries have physical limits (they can only store so much power), solar panels have physical limits too (there a fixed amount of solar energy to capture on a given surface area).

Modern solar panels are already extremely efficient. Even if you made them 100% efficient (impossible) they don’t generate enough power to power a car or a plane with any meaningful payload.

A slow blimp maybe.

Now the last point about environmental impact just isn’t true. The impact can be (and has been) significantly reduced.

But battery production doesn’t necessarily fair much better from an environmental impact

And the end of the day, no matter which tech we pick, there will be an impact. We just have to be responsible enough to reduce when possible and not do more damage than can be repaired.

Agree to disagree. The most efficient solar panel ever produced in a lab was under 40% efficient. Most panels commercially produced are between 20 and 30%. Solar panels have a long way to go. A combination of solar plus much higher energy density batteries could definitely power a plane in the future.
Oil takes millions of years and the right conditions underground to be created and burning it (at about 30% or 40% efficiency at best) releases that carbon into the atmosphere. I agree that what goes into batteries and where our electricity come from right now have a long way to go in terms of environmental impact, but, for example, there is research being done on using sodium ion batteries in EVs now, so battery development is still very much in it's infancy in terms of density, safety, and environmental impact.
https://electrek.co/2022/07/14/sodium-ion-battery-breakthrough/

 

[Blue highway]

Right. I was going in that direction BUT a friend of mine keeps insisting that gasoline is the most efficient way to store energy (short of leveraging nuclear bonds). He references the energy density per kilogram. So, I’m trying to rationalize the amount of energy required to move a certain distance (I’m going to simplify the problem by saying both vehicles are using the same amount of energy and moving equal distances - yes, I know those are incorrect assumptions, but order of magnitude, they will work for this problem).

where to start... the reason jets run on kerosene vs gasoline is because the energy density per Kg is higher for kerosene than gasoline... so gasoline is not the most efficient way to store energy even among commonly burnt fuels.

 

[Mach1E]

Agree to disagree. The most efficient solar panel ever produced in a lab was under 40% efficient. Most panels commercially produced are between 20 and 30%. Solar panels have a long way to go. A combination of solar plus much higher energy density batteries could definitely power a plane in the future.
Oil takes millions of years and the right conditions underground to be created and burning it (at about 30% or 40% efficiency at best) releases that carbon into the atmosphere. I agree that what goes into batteries and where our electricity come from right now have a long way to go in terms of environmental impact, but, for example, there is research being done on using sodium ion batteries in EVs now, so battery development is still very much in it's infancy in terms of density, safety, and environmental impact.
https://electrek.co/2022/07/14/sodium-ion-battery-breakthrough/

That’s the thing, 30-40% efficient is extremely efficient. But again, it’s a physics problem, not really a tech one.

Even if they doubled solar panel efficiency and cut battery weight in half, we are still nowhere even remotely close to flying 300 people across the country that way.

You could even have a magic weightless battery and those 80% efficient solar panels, and it’s still not happening.

Solar sails in space? Sure. But again, on earth you’re fighting physics not tech.

My gut still says “better batteries” aren’t the solution. Sure, they’re better, but they aren’t the end game. And neither is solar.

 

[DevSecOps]

Agree to disagree. The most efficient solar panel ever produced in a lab was under 40% efficient. Most panels commercially produced are between 20 and 30%. Solar panels have a long way to go. A combination of solar plus much higher energy density batteries could definitely power a plane in the future.
Oil takes millions of years and the right conditions underground to be created and burning it (at about 30% or 40% efficiency at best) releases that carbon into the atmosphere. I agree that what goes into batteries and where our electricity come from right now have a long way to go in terms of environmental impact, but, for example, there is research being done on using sodium ion batteries in EVs now, so battery development is still very much in it's infancy in terms of density, safety, and environmental impact.
https://electrek.co/2022/07/14/sodium-ion-battery-breakthrough/

There's also research being done on e-fuel by Porsche and a Canadian company that makes fuel from air both of which would take all existing ICE vehicles and make them burn carbon neutral fuels. Additionally, there's also things like the zero emission turbine engines which are being worked on. Unfortunately, people are stuck on electricity, batteries and solar as the great savior. It's sad that so many people have electrical tunnel vision. People need to wake up to all alternatives.

Solar is becoming the "nuclear waste" of our time (recent article). Solving atmospheric problems with more toxic ground problems isn't a win in my books.

 

[Mach1E]

where to start... the reason jets run on kerosene vs gasoline is because the energy density per Kg is higher for kerosene than gasoline... so gasoline is not the most efficient way to store energy even among commonly burnt fuels.

You can’t win an argument about apples and oranges by talking about pears.

It’s gasoline vs batteries, not kerosene. And yeah, batteries weigh more. It’s an unwinnable argument despite pages of people here trying to win.

80 lbs of gasoline vs 1200 lbs of batteries. It’s not even remotely close.

Even if you add in and compare the entire drivetrain (which you should), engine, transmission etc, it’s still not close.

 

[bp99]

Finally: energy density is NOT the same as energy efficiency, which is why EV's can go 80 to 120 miles on the same amount of energy that is released burning a gallon of gas.

But the density does relate to range. Some use cases are much better served by density. Typical daily driving is well served with batteries. If you want to go off the grid in the outdoors for an extended time, it's much easier to carry extra cans of gas than it is to bring more batteries.

Daily commuting is a much more common use case, so batteries can fulfill the bulk of the market going forward. But that does not mean that the use cases where gas wins are going away. There are pros and cons to everything. Gas is more universally applicable due to its density and portability. Yet that does not make it the best choice over all. It all comes down to the right tool for the job.

 

[Mach1E]

But the density does relate to range. Some use cases are much better served by density. Typical daily driving is well served with batteries. If you want to go off the grid in the outdoors for an extended time, it's much easier to carry extra cans of gas than it is to bring more batteries.

Daily commuting is a much more common use case, so batteries can fulfill the bulk of the market going forward. But that does not mean that the use cases where gas wins are going away. There are pros and cons to everything. Gas is more universally applicable due to its density and portability. Yet that does not make it the best choice over all. It all comes down to the right tool for the job.

That’s a good point about range.

Maybe a better ratio to consider than energy density would be drivetrain weight/range.

less weight and more range are better..

Or a simpler, more even version would be energy density x efficiency.

If you have double the energy density but half the efficiency……. You’re equal.

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