Yet another Hacker News

Electric Ship Batteries Promise Compact, Cooler Power

29 points rbanffy 2 hours ago 17 comments

dmtroyer 1 hour ago | parent

I assumed they would use sea water for cooling but that doesn't seem to be the case? Maybe the battery coolant is cooled using some sort of sea water heat exchanger?

zdragnar 1 hour ago | parent

A closed loop is probably easier to maintain compared to pumping caustic saltwater and all the things in it near batteries.

Xylakant 1 hour ago | parent

You really don't want to cool anything with sea water directly. It's corrosive due to the salt and contains all kinds of fun things from flotsam to critters, some of which might make a home in your cooling loop. in this case, additionally, sea water is conductive and that's not acceptable in a battery.

However, feeding the coolant through some sort of heat exchange with the sea water is very likely something they do.

baud147258 57 minutes ago | parent

> However, feeding the coolant through some sort of heat exchange with the sea water is very likely something they do.

Aren't ship engines usually cooled with sea water already (through a heat exchanger, not directly)? So it's not really something new

Xylakant 45 minutes ago | parent

Yes, that's the absolute norm (you often also want to cool the exhaust pipe itself and there you often see coolant water pumped straight into the exhaust). That's the obvious thing to do: You do have a huge reservoir of readily available coolant, tapping it is the sensible thing to do :) That's why I fully expect them to run their coolant through some heat exchange with sea water.

msandford 52 minutes ago | parent

Also saltwater is conductive so if you submerged your batteries in it, you'd have an immediate short circuit. It's definitely through a heat exchanger.

pjc50 1 hour ago | parent

The immersion fluid has to be non conductive and non corrosive. Hence the choice of oil (flammable) or weird fluorocarbons.

bob1029 50 minutes ago | parent

Batteries for ships seems really silly but at the same time its the perfect regime for a ridiculous quantity potentially hazardous items. Nuclear obviously works well here too. You have an unlimited amount of water with which to fight any fires or cool off equipment and you could theoretically engineer a way to dump the entire assembly into the ocean in an emergency.

Hydrodynamics are brutal, but the square-cube law works in your favor. The ocean doesn't care about what's inside your ship. Just the surface of it. The mass is mostly irrelevant. This is why cargo vessels are so large. The bigger the boat the bigger the energy density benefit.

The only real problem is the cost. To compete with a supermax you would need something like two billion dollars worth of batteries to survive a transpacific voyage.

dieselgate 41 minutes ago | parent

I hear you and while this is out of scope for the article a lot of sailing yachts are being converted to electric motors.

bluGill 20 minutes ago | parent

for sailing yachts that makes sense. They would use wind for most movement. While in harbor though they want the finer control that being under power allows - they don't need high speed/high power then though. They also don't spend a lot of time in this situation.

ZeroGravitas 15 minutes ago | parent

Electric tugs are now a thing to do similar for big ships.

A step before that is to have shore power to run things when in port.

In general stopping pollution near populated areas and busy ports is a bigger win and so a good place to start.

lukan 19 minutes ago | parent

I think sailing uses mainly some other kind of energy source.

bluGill 47 minutes ago | parent

Question is can they get enough power to be useful. Marine diesel engines are very fuel efficient, fuel oil is very energy dense, and they need to run for a long time. Electric cars work in part because people expect to refuel few couple hours anyway. Enough batteries to cross the ocean is going to be vastly worse.

The only useful picture in the article is a "solar powered board", which doesn't give a good scale but appears to be barely enough solar power for the rich owner to enjoy their luxuries and will barely move all day while forced to anchor all day. I'm sure it can go really fast on battery power, but not for long. Sails would be a better primary movement source with battery for in harbor navigation or when the wind stops backup only.

Xylakant 43 minutes ago | parent

A lot of ships don't go across oceans and can benefit from batteries. Think ferries, feeder ships, river transport. Those all dock in relatively predictable intervals.

mmooss 13 minutes ago | parent

As a crazy thought: On predictable routes in shallow enough water, implement an underwater power source similar in function (if not physically similar) to overhead electric bus/trolley power lines? The boats would move along their routes with a cable running down to to a connector that slides along the power source.

I'm imagining channels in a busy waterway or a regular ferry route. Of course it needs economy of scale, but at that point everyone saves on batteries, etc. Unless there are submarines, I don't know what would pass under the boat and cut the connection.

Maybe watercraft usage or routes aren't predictable enough? Maybe the sliding connector is too expensive underwater, especially in sea water.

bluGill 8 minutes ago | parent

sea water is too corrosive and too conductive. You could make a single overhead cable and use sea water as your return work. However it wouldn't be practical since ships multiple stories tall need to pass under the wire (and draw a lot of power), while also tiny fishing boards that couldn't even get a pole that high.