Put 100 units of energy into a petrol car and you only get 20 units of motion out.
You made another mistake by drawing your energy box around the car, excluding the energy losses associated with producing the electricity in the first place. Power plant efficiency can be as low as 25% for peak power, then there are transmission line losses, the more distance, the higher the loss, and finally inverter losses between the battery and electric motor of about 10%. And then, of course, in cold weather battery output can drop as a much as a third, and there are losses in hot weather as well.
hi Hannah - nice analysis.
A small error (w large implications)
"But this is not true. With a switch to electric vehicles, we get rid of most of the ‘wasted’ energy from oil. "
You should write 'gasoline' here not 'oil'. Around the same amount of oil would have to be extracted and turned into many other products irrespective of whether all our cars run on gasoline or electricity. (ie only 40% of a barrel of oil is gasoline and the other 60% IS used and in high demand including the plastics, tires, etc in EVs, the asphalt in roads, etc).
Other than the oil for lubricants in engine etc, the wasted energy is from gasoline, not oil.
Thank you, Hannah, very interesting, I learned a few things.
However, I wonder how the EPA came up with 22% of regenerative braking. An F1 race car has the most sophisticated braking energy regeneration system on earth, and those cars brake a lot more and a lot harder than passenger cars, and still I do not believe that they come even close to 22%.
Do you have access to any background information supporting the EPA claim?
The question that springs to mind: does this analysis take into account the inefficiencies of generating and transmitting the electricity that we put into our cars? I'm assuming that, for now, most people are charging using utility generated power and not solar panels on their houses.
I always appreciate efforts to debunk energy misconceptions. But as often seems to be the case, I'm unclear on who actually says the things you're debunking here:
"When people compare how much gasoline we burn to how much low-carbon energy we generate, decarbonising transport seems almost impossible. They assume that we would need to produce the electricity equivalent of our global gasoline consumption."
Can you point us to some examples of the people who assume this? Are you thinking of academics, journalists, fossil fuel PR people, the general public, or someone else?
There is no doubt that electric cars are very efficient users of energy. Their main disadvantage is the high energy and mineral intensity of battery production and the need to create a high density fast charging network before they become practical for everyone. Hopefully batteries will improve over the next few decades and high density charging points will become ubiquitous. In the meantime a sensible transition is to mix full EVs with plugin and full hydrids. It may well be the case that green synthetic fuels arrive before the type of battery technology needed to go full EV for all motor vehicles.
Right. I did see that, but since the other losses were given as specific average numbers, I was hoping for a similar detail. OTOH, it's probably something I should be able to look up, but it is surprisingly difficult to find numbers, but this doesn't look very good: https://www.energy.gov/fecm/how-gas-turbine-power-plants-work. The range seems to be from 30% to 60%. If that's accurate, it would imply that the argument Hannah is making is kind of weak in the absence of rooftop solar providing the power.
Thanks for the article. I think EVs are a good option for municipal fleets, school busses, and public transit. However, EV cars for the daily commute or general transportation might not be good options.
In terms of overall energy use (i.e., extraction and transport of resources needed to build petrol or EV cars, highway development & maintenance, car-induced urban sprawl and increased travel time), wouldn't it be better to develop alternatives? For example:
a) convert petrol cars to EV/hybrid,
b) redirect resources to regional and local rail (and electric busses)
c) support the walkable/rollable, 15-minute community that is supported by municipal, regional, and national planning policy
I've used this exact same form of analysis myself ... but now reckon it's deeply flawed.
In thermodynamics they talk about the "quality" of different energy forms ... like heat and electricity and potential energy. Converting from a low quality energy to a high quality energy has an inevitable cost. So converting heat to electricity is intrinsically inefficient. But regarding it as a loss in a pejorative sense has to be carefully thought through.
Solar panels produces electricity without heat. Does that make them more efficient than a nuclear reactor that uses heat to drive a generator? You need about 4-10 gigiawatts of panels to get the same electrical energy as 1 gigawatt of nuclear (depending on where you are on the planet ... 10 for Germany). So in Germany, you need to mine about 70,000 x 10 tonnes of stuff to produce your panels. That's a lot of stuff. The thermodynamic efficiency has a considerable downside in terms of resource use (land and minerals).
Most of the worlds energy is used as heat ... so why get this from electricity via PV panels?
Energy efficiency isn't an end in itself, it's just one of many metrics that we need to think about to decarbonise intelligently. It's a little bit like water. If you have it in abundance, does it matter if you waste it? As long as it is zero carbon, the answer is "no". Storing it for a rainy day has costs ... storage isn't free from a resources perspective.
Sadly this is not a like for like comparison.
Equating the miles travelled per unit of raw energy requires the following factors to be considered
Conversion from raw energy to electricity: Coal (32%) or Gas (37%) power – but these provide 45% of supply mix (so .35*2% CO2 efficient) - 0.7 unit of electricity per unit of Fossil Fuel burnt
Electricity delivery over the power grid: Transmission efficiency – 92% efficient
Power delivery: Electric motor – 70-80% - 75% efficient
Rolling resistance: EVs are 750 heavier than an average 3000 lb car and require an additional 25% for rolling resistance compared to between 4-11% for a lightweight car (85% efficient)
So on average – 35% (*2) * .92 * .75 * .85 = 41% overall fossil fuel efficiency (to be compared with the petrol car at 20% overall fossil fuel efficiency)
That is an electric car currently has an equivalent 'mpg-fossil fuel' around 50% of a petrol car - this will improve as a greater % of electricity on the grid is from renewables.
The estimate is that the energy requirement to produce a petrol car is 474 gallons of petrol, an electric car required 25% more (118 gallons). Assuming a 10 year vehicle life and 50 mpg the energy equivalence point is 1180 miles per year - so the electric car only starts to reduce CO2 emissions after 1180 miles each year. Regenerative braking applies to both EVs and Petrol vehicles.
These calculations are based on UK data - here 10% of cars have an annual mileage below the 'break even' point, that is making these EVs would be a net addition to CO2 emissions
This is useful and the point about the need to et renewable energy up and running as uickly as possible is important. But the world's electricity supply system will still have to be a lot larger than it is now (2 times as big? 3 times?) IF we use energy, whatever its source in the profligate way it is used now and if those billions in the lobal South who need an electricity supply are to get one. This means reducing our access to motor cars and a lot of other forms of waste - in commodities, in heating and cooling buildings and so on.
One way in which all cars are inefficient is that they use over a tonne of metal, glass and plastic to move (most often) about 70kg of person. In this respect and electric car is less efficient than the equivalent ICE one, as it is usually about 50% heavier, so the energy saving will be less than the 80% calculated here. An electric bicycle uses 20 times less energy than a small electric car. The energy saving in going from an ICE car to an electric bicycle is about 97%.
I wonder whether EVs are really effective in diminishing carbon emissions. A lot of the numbers being put forward seem to be theoretical. Take e.g. the EPA claim of 34% energy recovery from braking in urban traffic. That sounds good but defies physics.
Another point I do not see at all being argued is the fact, that EVs start saving CO2 only from 65.000 - 70.000 km on (disclosed e.g. by VW) because manufacturing an EV is so much more costly in CO2 emissions. Considering that the average mileage is 13.000 km per year (e.g. in Germany), an EV you put on the road today will effectively start saving CO2 in 5 five years at best. By then it may need a new battery and the hoped-for gain will never materialise.
There must be lower hanging fruit in curbing carbon emissions.
Great data driven post!
I’d be curious to know how hybrid cars compare, once their battery is depleted. In other words, does regenerative braking improve the efficiency of a petrol car?
I’d look forward to a post that compares power plant efficiencies, from old lignite plants to new gas plants. That way we could have an overall picture, as you point out.
Excellent article. There are many other factors to be integrated into this thinking. Three that come to mind immediately:
1. The market price for energy as consumed by the user differs between electricity and petroleum based fuels. Shouldn't the analysislook at both the relative number of ergs consumed and the cost per erg for e vs p (electric versus petroleum based) transport?
2. The pricing distortions produced by government regulation. For example, the electricity market is in part highly regulated and in part sort of unregulated. Government regulation of petroleum processes is different. This breaks down into differences in the cost of energy production infrastructure and the operation (and efficiencies/inefficiencies) of the production, storage-logistics and distribution of the energy products. (I am not opposed to government regulation but I'm thinking about the asymmetries applied to electricity's and petroleum-based fuels. How do we make them more even? Or should we?)
Its too bad EVs are so crazy expensive, those efficiencies have quite a pricetag.
That’s great, but America needs to focus on building non-car infrastructure. Bike lanes, rail, and transit-oriented housing development are way better for the planet than EVs could ever be.