Limits of Range & Energy Densities
If all vehicles have a max range, which is the longest?
In theory we could calculate the maximum range for just about any fuel source, but it will only really apply to electric cars.
Why Does the Limit Only Apply to Electric Cars?
Batteries have a unique property not found in other power sources; the weight of the vehicle does not decrease as we consume energy. With other fuels, the weight will decrease as we consume energy (read: burning gas). That means the fuel we burn later is more productive since it no longer needs to move all the fuel we’ve burned off. There may still be a maximum range, but it won’t be the product of a simple ration; it’d be the result of some calculus and it’s not useful to calculate.
Why Not Derive the Range Limit of Conventional Fuels?
Remember that our gasoline becomes more effective the more we burn? We could pretend for the moment that is false and calculate the maximum range of gasoline if it were like a battery. Then you’ll see why it’s not worth figuring out how much further it’s maximum range would be if we accounted for the increased efficiency of the fuel as our vehicle moves.
How Much Energy is in Gasoline?
36 kWh per gallon. If you’re keeping track, you’ll note that single gallon of gasoline has enough energy to power a house for 2 days. Unfortunately, combustion engines are remarkably inefficient. Good engines will use 25% of the power of the burned gasoline and waste the rest.
A gallon of gasoline weighs 6.3 pounds. Now with the power of math, we can calculate the energy density per pound of gasoline.
1 ÷ (36.0 ((kWh) ÷ (Gallon)) ÷ 6.3 ((Pound) ÷ (Gallon)) × 25%) = 0.70 ((Pound) ÷ (kWh))
Our very inefficient gas engine manages to get 0.70 kWh per pound. If you recall from before, it takes us 20 pounds of lithium ion batteries to store 1 kWh. Our gasoline stores almost 30 times more power per pound in our engines. With perfect engines, we’d store 120 times more power in a pound of gas than in a pound of lithium ion batteries.
So…What Would be the Maximum Range of a Gas Car?
Given what we’ve calculated so far, this is easy. Our gas car has the same efficiency per kWh as the electric car, but our gasoline weighs much less than batteries(or has more energy per pound, however you want to look at it).
10,263 ((Pound) × (Mile)) ÷ (kWh) ÷ 0.7 ((Pound) ÷ (kWh))= 14,662 (Mile)
That range without refueling is plenty far enough for everyone, except perhaps mad max. Remember, our remaining fuel becomes more effective as we burn off the fuel we have – meaning this is an underestimate and probably a big underestimate. However, that value is so large that it isn’t worth figuring out how much bigger it could be.
What About Hydrogen?
Considering hydrogen only requires checking it’s energy density per pound, and that wasn’t hard to find. At about 15 kWh per pound, it has some kick.
10,263 ((Pound) × (Mile)) ÷ (kWh) ÷ 0.07 ((Pound) ÷ (kWh)) = 155,347 (Mile)
So what does this tell us?
If batteries could come anywhere close to the energy density of gasoline or hydrogen, they would be a great option for powering any vehicle; even commercial vehicles.
That would be expensive to develop, and likely take generations. That doesn’t mean it’s not worth doing. It is. It just means that it’s not a great solution right now.
What is a Better Solution Right Now?
In terms of giving an experience like gasoline (long range and quick fill-ups) we won’t do any better than hydrogen. And, as we already saw, it has plenty enough energy density for any of our needs.
Won’t Hydrogen Explode?
It has the potential to, as does gasoline and Samsung phones.
In terms of safely using hydrogen in vehicles, this is a solvable engineering problem. There are a myriad of factors to that include how it’s stored (gas, liquid, amount of pressure, etc.) and how it’s converted to energy (fuel cells, burned like gasoline for power right now) and how that energy is used (directly powering the wheels, or slowly used to recharge batteries that power the wheels).
What’s the Conclusion?
As we look toward what will power post-petroleum transportation, electricity is a great stepping stone to get consumers off of gasoline and minimize fossil fuel use while we convert our infrastructure. However, only hydrogen is a pollution free fuel with the energy density to move cars, trucks, and rockets.