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Comment by ars | Hacker News Reader

"It’s long been known that an average person on a bicycle is a more efficient translator of energy per gram per kilometre than any other machine or animal"

Yah, that's not actually true. A human is around 25% efficient (counting only the actual energy in the food), while electric cars are around 60%.

And if you count the energy needed to grow the food, even gas cars are more efficient than humans. And that's even if you only count the payload and not the weight of the vehicle.

And flying birds easily are more efficient than humans on a bike because they can use wind to help them.

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It's giving you the metric right there. Energy consumed per gram of weight moved per kilometre traveled. Not percentage of energy used for locomotion versus lost as heat (note that maintaining internal homeostasis in a human is not exactly "losing" energy to heat, but certainly some excess is generated when you're exercising as opposed to just sitting around).

You're definitely still right about creatures that can simply catch sea and air currents, though.

Yes, I saw that metric, and my point stands. Cars are more efficient than humans, even humans on bikes.

> note that maintaining internal homeostasis in a human is not exactly "losing" energy to heat

If you bike a lot you will eat more. People tend to forget that and assuming the biking is "free" energy. I guess if it's just a causal activity then it is, but if you do it to commute you will end up eating more.

Is your number for electric cars including the losses of creating that electricity (coal is perhaps 30-40% efficient, solar around 15-20%). Otherwise, we're comparing apples with oranges. Or perhaps, since all energy (perhaps lets put nuclear aside for now) comes from the sun, we can compare system efficiency between solar energy input and energy/g/km output.

Humans on bikes can also use the wind to help them; birds fly in formations that greatly increase system efficiency (much like pelotons)

If you count the losses of solar power you should also count the losses of photosynthesis (and the energy used for farming, and the energy lost by the animals that you eat).

Given that the energy used for both humans and electric cars is about 50% from dinosaurs, an internal combustion engine car has better efficiency on dinosaur to joule conversion than an electric car. So a human is basically not competitive with any form of transportation.

> And if you count the energy needed to grow the food, even gas cars are more efficient than humans. And that's even if you only count the payload and not the weight of the vehicle.

It's a lot more complicated than that. A certain baseline is eaten anyway for nutrition, and some foods have too many calories per unit of other nutrients for sedantry life. Maize for example can provide a decent chunk of your protein (with some pulses to round out the amino acids) and some other nutrients, but you need to be active for an hour or two per day to not get sick from the quantity of carbohydrates that entails. There's also a minimum activity level that is best for health that many people do not reach (so the calories between current activity and that threshold have a negative cost).

If we take wheat or oats as a fuel, the CO2e footprint is roughly the same ballpark as the mass of food (or less if they are grown in certain niche ways which are high labour or use green ammonia for fertilizer reagent and electric tractors).

100g of either will get you 15-20km at a calm pace. This is ballpark 5-15g/km or roughly on par with electric trains.

You need to fill an EV with people every trip to match the upper bound here (including embodied carbon). Including infrastructure makes the bike a winner. Electric busses might still place if full. ICEs are out of the running.

If your fuel is exclusively beef protein though then better to use the deisel truck or just go set fire to a forest or something.

The optimal is a solar charged recumbent pedelec because it uses sunlight so much more efficiently than plants do. Something with just enough motor to keep you going at 25km/h on a mild 2% incline with the same power from the rider as walking, just enough battery to last one trip (about what a laptop holds, or double that to decrease discharge % and increase durability) and just enough solar to charge while parked. You can increase speed/distance to around 40 km/h at roughly constant emissions by adding a fairing.

After that is a ferry full of people.

Then a train/regular bike.

If you need to go extremely fast/far only trains work for large quantities of people, and the ones for whom coverage is prohibitive are best with cars.

Well, humans can use Windpower as well (e-bikes)

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