Does that mean mankind has to grow its energy usage 24 times to match the energy absorbed by the Earth?
I'm not even sure if driving a car from one city to another really uses energy.
For example, let's look at it this way: The energy from the sun is heating earth. When we use some of it to drive a solar-powered electric car from one city to another, does that lower the temperature of planet earth? I would think it does not. So why did we get the energy to drive the car for free? I would think that the surprising answer is: Moving something from A to B does not use energy at all. But I'm not sure.
There’s this little detail of efficiency. Much less than 100% of energy used for acceleration and overcoming friction is actually spent on those. Most ends up heating up random stuff like engines, brakes, roads and tires.
I’m confused why do you think anything could be moved from A to B for free? You have to charge the car, or fuel it up, after all?
The energy coming from the sun has low entropy and that makes it easy to capture and convert into electricity/plants etc. When you use some of that energy to move a car, you're converting the useful low entropy of the electricity/fuel into high entropy "waste" heat that can no longer be easily captured and used.
Toy ODE model:
dx/dt = -k x + a + b.
Here, x is temperature, a is solar heat input, and b is heat input from human sources. I'm dropping some coefficients that would make the units strictly work. We have a >>> b. The coefficient k says how easily the Earth radiates heat. Adding greenhouse gasses makes k closer to zero.
At equilibrium, dx/dt = 0. Solving,
x = (a + b) / k ~= a / k
Again, b is tiny relative to a. So almost the only thing that matters is k.
We actually spend quite a bit of energy doing the work of moving heat from colder to hotter areas because humans don't like to be too hot.
Say there is a completely static, black planet. All sunlight that hits it is turned into heat which is dissipated into the universe. Nothing moves on that planet.
The static black inhabitants of the planet are very thankful for the sun that it makes their planet nicely warm and cozy.
Now one day, one of them is allowed to travel to planet earth and read Hacker News. He reads this very thread.
Are you telling him that they are wasting half of the benefits they could get from the sun? They could have a nice warm planet AND drive around in electric cars all day? For free? Everything else would stay the same?
If so, doesn't that make driving a car "free" in that it not even increased the amount of entropy? Since the sunlight would have turned into high entropy heat anyhow?
> Are you telling him that they are wasting half of the benefits they could get from the sun? They could have a nice warm planet AND drive around in electric cars all day? For free? Everything else would stay the same?
Strictly speaking, yeah, they're not using all the energy they could. "Wasting" seems like a weird way to say it though, because it feels like that implies they want to be doing something with it.
> If so, doesn't that make driving a car "free" in that it not even increased the amount of entropy? Since the sunlight would have turned into high entropy heat anyhow?
On a long enough timescale nothing matters from the point of view of entropy. Net entropy will always increase. This is a pretty useless observation if you're trying to make a value judgement on the much smaller timescale of a civilization or the much smaller physical system of a planet, where having easily harnessable energy is important.
Fuel being petrol or electric is only a small part of it
A kilogram bar of solid gold is worth about $70K.
Take every atom of that gold and sprinkle them separately into the ocean. You haven’t used any gold: it’s all still there. The difference in value of the bar and the seawater containing the exact same gold is in the arrangement and availability of the gold, not its mere existence.
Same with energy stored in a battery vs stored in slightly warmer atmosphere.
I was comparing a car in city A with a car moved to city B. Both in warm atmosphere. You can heat the atmosphere AND move the car, without creating more entropy than by just heating the atmosphere. So it looks like moving the car does not create entropy / does not use energy.
With the gold, you cannot buy an apartment with it if you sprinkle it in the ocean. You have to decide: Buy an apartment OR sprinkle it in the ocean. You can't get the apartment AND an ocean with gold sprinkles. So you can't get the apartment for free.
it'd be more like 24 x 365 (and a bit) to match the per hour input to per year usage.