Watching the RO-RO ships travel around the world, something struck me.
I've written a couple times (here and elsewhere) about how while it's not economically practical (with current tech) to make large electric-powered cargo ships that travel nonstop (don't care to redo the calculations yet again, but feel free to do them yourselves), it is economically practical to use them with floating "gigachargers" (deep sea wind, floating solar, inside a breakwater - ideally with the breakwater being a wave-power generator). These would transfer - for ships the size of a Maersk Triple-E - about a gigawatt hour per 80% charge, about every day or so.
Something occurred to me, though - and the situation could actually be a lot more than merely "economically practical" - rather, a major economic advantage.
Speed is a key part of the economics of shipping. For one, the faster you deliver your cargo, the more trips you can take. For another, the faster you deliver cargo, the more you get paid for that delivery (the reason why people do air shipping even though it's insanely expensive compared to shipping at sea). Double the speed and you might quadruple your revenue, for a given capital investment.
So why don't ships just go faster? Energy consumption, of course (operations, not capital, costs). The faster you travel, the more energy your ship has to burn to do so. Ships today don't want to have to pay more for fuel, so their cruising speeds are limited (the Glovis fleet usually cruises at about 20mph/30kph, for example).
Now, this might seem even worse for electric shipping. After all, big batteries are expensive, and the more power you burn, the larger the battery you need to have in order to charge at a given interval. But what happens if we reduce that interval significantly?
The rate at which you can charge a battery pack is irrespective of the size of the battery pack; for a given cell and cooling design, a 1kWh pack takes the same amount of time to charge as a 1GWh pack. A ship can do the same 30 minute 0-80% that a car or truck can, so long as the charger are sized to do so (just through a *much* fatter, crane-hoisted cable!). You certainly have more overhead - sailing a ship into a breakwater, docking alongside a charger tower, and connecting a liquid-cooled cable wider than your thigh, is not a 1-minute job like parking your car at a Supercharger and plugging in. But assuming that overhead can be kept "reasonable", there's nothing to stop you from charging far more often than once per day.
(Note that electric propulsion makes things like azimuth-mount thrusters ("azipods"), which allow ships to sail sideways and tightly control their position, more practical)
Let's say that instead of sailing for 23 hours and docking / charging for 1 hour, you sail for 5 hours then dock/charge for 1 hour. Now you're charging 4 times as much energy per day, for 87% as much sailing time. Burning four times the power lets you roughly double your travel speed - ~40mph/60kph. Meaning you can depreciate your capital costs across far more trips, and get paid more per trip for the faster delivery speed.
The only downside is that you burn twice as much power per trip. From an environmental standpoint, it's really a nothing issue: it's the power of the wind and/or sun, and most of the world's oceans are "deserts" - vast expanses with relatively little life, due to the lack of the sort of nutrient upwellings that you get near the coasts:
In the above map, dark red zones have 1000 times more photosynthesis as dark blue zones, 150 times more than cyan zones, and 50 times more than green zones. It's mineral-limited, not sun-limited; if you block some sun in one location, it just leaves the minerals for the next bit over. On the other hand, sea life tends to flourish around manmade floating structures, akin to how it does around reefs.
Historically, ships have been getting a great rate on fuel costs, as they've been burning high-sulfur bunker fuel. Those days come to an end at the end of this year - the standards on bunker fuel have been raised to the point that it's now basically diesel, and in direct competition with diesel to boot. Ships can still use low grade fuel, but only if they put in (expensive) scrubbing systems on their ships that may cost more than just switching fuels. You're looking at at least "$2/gal" equivalent (prices are usually measured in $/MT), and more if oil prices rise from their (currently low) pricing regime, or further emissions restrictions (or carbon taxes) increase costs further. Let's say a long-term average of $2,50/gal - and that may well prove incredibly optimistic in the long run.
Ship engines are efficient - about 50%. Now, EV motors would also be unusually efficient in such situations, as they'd be large motors tuned for cruising speeds, and the charging process would also benefit from operation at scale. Let's say 87% round-trip efficiency. The fuel-powered ship gets propulsive energy for 27MJ/$. So if we're doubling the propulsive energy requirements, in order to match the price, electricity (at industrial rates, not home rates) needs to be generated at 54MJ/$ - aka, $0,067/kWh. Remember that it doesn't actually need to match bunker fuel costs, as you're shipping at nearly double the rate, drastically slashing your depreciation per trip while drastically increasing your income per trip.
That said, it would be awesome if electricity costs could beat fuel costs even when moving at double the speed. Is $0,067/kWh achievable? Well... "probably"?
Floating solar, at present, looks like the most realistic option for the bulk generation, with deep sea wind only as a supplement (turbine towers could double as platforms for storing charging hardware and/or docking ports)
- Floating solar plants have so far mainly been built in freshwater, but if you have an effective breakwater, then it just comes down to an issue of material compatibility. Prices are similar to that of land-based PV - for example, Three Gorges Group is making a 150MW floating solar plant for a construction cost of $151M, or $1/W. That's just a few cents per kWh generated. The fixtures are more expensive, but installation is simpler and cheaper, on cheap/free "land". Since floating solar is a newer technology, it also has more room for price improvement.
- Deep sea wind is not yet there in pricing; it's currently significantly more expensive than land-based and shallow-water wind. That said, it's also highly immature, and has a lot of room for improvement (and all oceanic wind has the advantage of being basically unlimited in tower height, with hardware shipped cheaply to its destination). Additionally, one of the major costs of deep-sea wind is transmission back to the shore, which is not applicable here.
- Wave power is currently expensive, but regardless, not much is needed - only enough to make a breakwater.
Can chargers (and battery banks) be built at scale, using adjacent-generated solar at current solar pricing, and sell power for $0,067/kWh? That's harder to say - but this is exactly Tesla's plan for megachargers for Semi - and their announced pricing is $0,07/kWh (combining the low cost of solar generation with the battery banks it needs to be a reliable power source (direct DC/DC conversion, no grid costs) - batteries which simultaneously enable high charging speeds using said same DC/DC converters). A gigacharger would gain even larger economies of scale.
So... "probably". But the key aspect is: you can earn drastically more revenue from your ship if you run it on electricity, by sailing faster - since your fuel is cheap, clean, and it's much cheaper to add more electric powertrain power than diesel power.
Tesla powerpack expected lifespans are 15 years.
