#4: Transportation for a Sustainable Future
“Get an electric car” is common advice for people who want to reduce their carbon footprint. If the whole country does this, let’s see how far that gets us.
From where we left off last time, transportation still consumes 27.3% of our energy usage and is almost entirely powered by fossil fuels.
Remember, the goal is to electrify energy consumption so that we can supply the energy via renewables. Unfortunately, there are a few different modalities of transportation. Some are easier to electrify than others.
The EPA tracks the share of emissions from a few different types of transportation:
Light Duty Vehicles
Medium and Heavy Duty Trucks
Ships and Boats
This chart shows emissions produced from each type of transportation.
Cars, Buses & Motorcycles
Cars, buses, and motorcycles account for 65% of transportation carbon emissions.
The easiest sources to electrify are light-duty vehicles and “other”, which can be read as passenger cars, buses and motorcycles. Only about 1% of these on the road today are electric. Let’s assume we’ll get to 100%. That converts 64% of our transportation needs to electric sources.
100% of cars, motorcycles, and buses are electrified, bringing our cumulative total to 65% of transportation moved off fossil fuels.
Medium and Heavy Duty Trucks
Trucks account for 23% of transportation carbon emissions.
These are a bit tricker to electrify because unlike regular passenger cars, these cars consume way more energy, and are expected to travel much longer distances. A typical semi truck can travel 2100 miles on a single tank which stores 300 gallons of diesel. Let’s do some quick math on how big of a battery would be needed to support that.
1 gallon of diesel has 40.7 kWh of energy
This means a semi uses about 5.8 kWh per mile.
The new Telsa semi is boasting less than 2 kWh per mile (let’s assume 1.5 kWh). This means electric semi’s are 3.86 times more efficient.
300 gallons = 12210 kWh
If we assume electric semi’s will be 3.8 times more efficient than standard semi’s, then we will need a battery that can store 3200 kWh. The 2020 Tesla’s largest battery size can currently only store 82 kWh, so this hypothetical 3200 kWh battery would need to be about 40 times bigger.
It’s probably really expensive to build a battery that big, I don’t know. But the biggest challenge here is the weight of that battery. It turns out that batteries aren’t very energy dense.
Diesel gas = 0.0623 kg / kWh
Battery = 4.5 kg / kWh
Diesel gasoline is about 70 times more energy dense than the batteries we currently have today. A battery that can hold 3200 kWh will weigh a whopping 15000 pounds.
Either electric car’s will need to get much much more efficient or batteries will need to be much more energy dense to match the performance of existing diesel based semi’s.
With these limitations, let’s assume only a quarter of semi’s are electrified.
That’s a quarter of 23% which comes out to an additional 6% of transportation electrified, bringing our cumulative total to 71%.
Aircraft, Trains, and Ships
These three modes account for 13% of transportation carbon emissions.
Everything I mentioned above that made electric semi’s inconvenient, make electric air / rail travel impossible. There’s not a lot of point pulling the numbers, but let’s take a look just for fun.
Airplane fuel has an energy density of about 37 kWh / gallon, and weighs about 3.1 kg / gallon. That comes out to about 0.083 kg / kWh, (a bit heavier than diesel). The Boeing 747 can carry up to 200,000 kg of fuel, coming out to about 2500000 kWh of energy. It’s unimaginable we can make a battery that large that can fit in an airplane.
The same applies to trains & ships.
0% of airplanes, trains and ships are electrified, we’re still at 71%.
Where does all this electricity come from?
The caveat here, is that 65% of generated electricity is lost, so if we electrify transportation, we will actually have to produce more energy to maintain the same net transfer of energy (energy that actually makes it from the producer to the consumer), since so much of it is lost.
However, what offsets this is the fact that electric cars are more efficient than gasoline cars. A 2020 Tesla can travel 4.2 miles / kWh while the 2020 Toyota Prius can travel 1.5 miles / kWh, which makes it almost 3 times more energy efficient, so we can actually travel further with the 35% of electricity that’s usable.
This also brings up an important point: It does no good to switch from gas cars to electric cars unless the electricity is provided by a renewable source. Otherwise, we are just trading emissions from one place (your car) to another place (electric plants). In the scenario I just described, we actually aren’t reducing emissions at all.
Batteries are far less energy dense than petroleum.
Cars, buses, and motorcycles can be completely electrified with batteries because of their short range.
Medium and heavy duty trucks are much harder to electrify due to the weight of the batteries necessary.
Airplanes, trains and ships are simply not possible to electricity with the technology we have today.
Now that we have electrified a good chunk of transportation, let’s create some more renewable electricity supply with solar panels.
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