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Comment by belltaco | Hacker News Reader

Has anyone thought of large rafts of floating solar panels being towed behind a ship? Given the massive surface area of the ocean I wonder if a few football field sized floating solar panels can recharge the batteries during the day time.

Also, what about windmills on the ship itself?

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Large container ships are already larger than football fields. As in 61.5m wide and 400m long, though not a rectangle they are surprisingly boxy. You might get 4MW in ideal conditions and average a little over 1MW over the day, but those engines are putting out 58MW, these ships need a lot of power 24/7.

Remember for scale those 20,000 little boxes stacked up are the exact same thing you see semi trucks carrying.

It still might be worth doing, for a 2% reduction in fuel costs.

Kites are much cheaper and save you far more fuel.

I calculated it out once. The issue is container ships need MASSIVE amounts of energy to move.

As for windmills on the ship... well... sails are a thing we've used for generations :D No reason to convert mechanical energy into electric energy back into mechanical energy.

In terms of the scale of energy. The largest masts in the world are on the order of 100m. An 80m blade wind turbine is rated 8MW or so. A container ship produces 50MW or so.

It'd be feasible for slow steaming if you couldn't use sails for some reason.

I just don't see the point. That 8MW is after the energy loses of converting mechanical to electric energy.

That process is 20->40% efficient (meaning 12->32ish MW is ultimately lost to friction).

A mast is much more efficient simply because it's not doing the mechanical to electrical transition.

Perhaps it's worth it if you charged batteries while docked and used those batteries + mast mode while sailing? A hybrid if you will?

The potential upsides I can see are: ability to point or move through canals without tacking; time averaging; and geometry to work around the cargo better.

A kite seems like a better solution, but maybe a hybrid might be an option -- ie. get some power from wind and the rest from a battery. Then if you have to wait for a port or canal you're gaining range the whole time.

Could throw solar into the mix, but without high efficiency tilting panels it's hardly relevant.

Windmills on boats?

So like, sails? :)

Iirc there has also been wind-driven electrical generating devices on boats too.

Solar may be highly unlikely due to waves and salt salinization.

See windmill ships for more on the second question > https://en.m.wikipedia.org/wiki/Windmill_ship

A few football fields would cause a lot of water drag and also probably not even be enough power. A solar panel is about half a kW, and I’m guessing a big ship like that will take upwards of 80 to 100 MW normally, so you need like 160k to 200k panels.

> Also, what about windmills on the ship itself?

Great idea, powering a boat with wind. If only someone had thought of that sooner!

Less facetiously, it's usually better to use cylindrical rotating sails (which need power, but far less) or kites. Combined with solar could be an interesting prospect though.

Drag. If you really wanted to do only green shipping, you could have these pads sprinkled across the Atlantic/Pacific, and have boats pull up them to charge up so they can make it to the next pad and hop across the ocean.

> Also, what about windmills on the ship itself?

You mean, like sails?

Large surface area means a lot of friction. I didn't do the math, but my feeling is it's not going to be feasible.

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