# Efficiency and capacity comparison between power grid and container ships

Both power grid and container ships can be considers as energy transmission channel.

And I’m wondering which one of them is doing better in long distance setting.

In a simplified example, a high voltage power grid might be able to transmit with maximum $$x$$ power. And a container ship with $$y$$ volume can be fixed to ship petroleum which has energy density $$z$$.

Of course there might not a a general better solution, but for long distance and high capacity setting (able to move huge among of energy in a fixed time period) which one is better?

In a simplified example, a high voltage power grid might be able to transmit with maximum 𝑥 power.

Transmission grids are fantastically efficient. The entire US grid put together loses about 6 to 7% of the energy fed into it. The vast majority of that happens at a few well known locations, and generally close to the end user.

Power in an electrical current is a function of two measures, the number of electrons moving, and the individual energy of those electrons. The former we measure as Amps, the later as Volts. Volts x Amps = power in Watts.

Now here's the magic... the wire carrying the power generally does not care about the energy of the electrons, only the number of them. In the case of home wiring, its generally rated for 15 A. Now if you run that wire at 110 V, you can pull 15 x 120 = 1800 W. Ever notice the rating on the side of a hair drier? But if you're in the UK, and you run it at 230 V, you get 3450 W. From the same wire.

Now the amount of energy lost in a wire is also a function of current. You can think of it as there being a fixed chance that any one electron will get lost on the way, and release its energy as heat in the wire. That's why wires have a limit in the first place, because the losses heat the wire and if they get too high you have the chance of starting a fire.

So what does all this mean? Well since power is a function of current and voltage, but the wire is really limited by current, you can carry more current by increasing the voltage. So when you want to haul a bunch of power from your power plant, you boost up its voltage to 230,000 or something, and can put that into a surprisingly small wire, about the size of your arm. Better yet, the chance that one of those electrons will be lost is a function of the voltage, so the total losses goes down.

Now why don't we go to a billion V or something? Because higher voltages are generally more difficult to keep in the wire - they tend to try to get out when you push them that hard. And they're more dangerous to punny humans. And you don't want 230 kV running into your house.

So we use transformers to step the voltage down, in steps, from 230 kV to 120 V. And a lot of the losses in the grid, as a whole, occur on those conversions. That's why the transformers in your neighbourhood sometimes blow, but it's pretty rare for that to happen up the chain.

So I would say that in terms of moving power from one place to the other, the modern power grid is pretty great.

Now, a boat. I guess the problem here is deciding what the measure of power being delivered is?

• Plus the wire just keeps delivering power without stopping, while the boat has to unload and go back, a round trip that takes weeks (Mideast to pretty much anywhere). Nov 30, 2021 at 14:58
• Something like coal or Petroleum? a huge container ship carrying a full load of such material. As in the data industry, when transmitting a huge amount of data, using a truck to load all the hard drives is much efficient than any optical fiber. I'm wondering if energy transmitting also have such behavior Nov 30, 2021 at 14:58
• @JonCuster delivering without stopping is good quality, but not necessarily amortized efficient. E.g. municipal water vs delivered tank of water when filling a swimming pool. Nov 30, 2021 at 15:52