Containerize the batteries, charge them nearby the port, and load them like regular cargo

Monday, May 22nd, 2023

Batteries and cargo ships don’t seem like a natural fit, because, Austin Bernon argues, ships need cheap batteries instead of high performance ones:

Let’s examine powering a 10,000 TEU container ship from New York to Rotterdam with the cheapest volume battery chemistry we have, lithium iron phosphate (LFP). At the max continuous speed of 22 knots, power usage is ~40 MW. The trip distance is 3800 miles, so we need ~150 hours of power or 6 GWh. These ships carry ~2 million gallons of fuel, which equates to ~7.5 million liters. The latest CATL Qilin LFP packs contain 290 Wh/l. We can fit nearly 2.2 GWh just in our fuel storage space. Two-stroke marine diesel engines are massive, and we can get another ~0.5 GWh from reducing engine room space and ballast. The last 3.6 GWh can fit in less than 450 TEUs. So we can cross oceans losing only 4.5% of cargo space while gaining the benefits of electrification. The mass performance is not as good, with the batteries using 25% of the cargo mass after netting out fuel and engines. Ships carrying lighter containers would see little cargo penalty, but those carrying heavier goods would.

The startup Fleet Zero has a solution for the charging problem — containerize the batteries, charge them nearby the port, and load them like regular cargo. Ships carry so much fuel today because few fuel sales points offer the required scale, quality, and cost. Filling up at the best places and using large fuel tanks is the way to minimize cost. Recharging at each port will be the lowest cost strategy if batteries and electricity are cheaper than fuel, even if there is variation in prices between ports.

The issue with using LFP batteries is cost. 6 GWh of LFP batteries would cost over $600 million. The cost per cycle would be $110/MWh plus charging costs that could be anywhere from $30/MWh to $100/MWh. Heavy fuel oil at $80/barrel in a 45% efficient engine equates to ~$110/MWh. Business models like Fleet Zero assume multiple stops on routes (which cargo ships commonly do, anyway) and slower speeds. Ships carry fewer batteries on each leg, and the system requires fewer batteries. Cost per cycle drops to reasonable levels while cargo penalties decrease. But it would make adoption easier if cheaper batteries allowed ships to carry more batteries or increased their savings.

These numbers contrast with calculations from analysts like Vaclav Smil because he assumes a 30+ day non-stop trip from Asia to Europe. But shipping companies are in the business of making money,


  1. David Foster says:

    Charging costs $30/MWh to $100/MWh…really? How about at a German port?

  2. Jim says:

    I know this one weird trick to tap an infinite supply of available-anywhere-anytime-anywhy electricity. Capitalists HATE him. Would you like to learn more? :3

  3. McChuck says:

    Shipping companies are in the business of making money, which is why ships don’t stop in every port. That takes enormous amounts of time. Time is money.

  4. Borepatch says:

    The whole idea is stupid. It costs twice as much and has zero reserve capability – container ships are huge but a Force 8 gale will slow even something that large. What happens when your charge falls too low? Divert to the Azores to recharge? They have a lot of diesel to sell you but probably you’d use a significant chunk of the island’s generation capacity.

    The ocean is no place to assume that everything will go to plan.

  5. TRX says:

    “while gaining the benefits of electrification.”

    The benefits must be really obvious, because the author didn’t list any.

    Also, no mention of recharging time, or who would pay for the grid upgrades to provide megawatts of power, or mention that the ships would be limited only to ports with charging facilities.

    Also, packing the batteries in at the density he’s talking about is questionable. LFP batteries burn really good, and hot, and are not extinguished by water, and emit toxic gases when they burn. The propensity for sudden combustion is why it’s recommended they be spaced far enough apart to (maybe) avoid a chain reaction.

  6. Isegoria says:

    In the article he suggests iron-air batteries for their low cost, acceptable volumetric energy density, and low fire risk.

    The benefits of electrification he lists include improved hull designs and hull coatings, which could go with any new design, and electric-specific improvements:

    Optimal Propeller Design and Conditioning

    Ships can reduce fuel usage by 15%-20% by using more efficient propellers and improving the water flow conditions around them.

    Large cargo ships almost all use giant two-stroke marine engines because they are efficient and reliable. Another advantage of two-stroke engines is that their slower-than-normal speed means they can directly drive propellers without expensive and complicated gears. That speed and location are not optimal for propeller efficiency, though.

    Electric ships can use larger propellers with lower RPMs that are more efficient. They can also place the propellers further outside the wake using propulsion pods because electric motors are tiny compared to marine engines. Many cruise ships already use these because diesel-electric powertrains better match their requirements than direct-drive powertrains.

    Fins and other devices can smooth the flow around the pods, further improving propeller efficiency.

    Wider Efficiency Curves

    The flexibility of electric powertrains can provide another 5%-10% reduction in fuel usage. Engines have a very narrow range where they operate at peak efficiency. In the real world, they rarely run in optimal conditions. Electric motors have good efficiency across a wide range of speeds.

    Slow Steaming

    Ships usually slow down when fuel costs are high because reducing speed can cut fuel consumption dramatically. A problem for ships with marine diesel engines is that engine efficiency drops precipitously at lower RPMs, resulting in diminishing returns for slow steaming. Electric motors don’t share this issue, so they get the full benefits of slower travel. An electric ship will use ~1/8th of the power and ~1/4th of the energy to complete a trip if it halves its speed. Ship owners gain the ability to load up the batteries and blaze ahead if spot freight prices are high, or they can slow down to extend range and reduce costs if necessary. It is challenging to have both options with traditional cargo ships.

  7. Pseudo-Chrysostom says:

    Seems like everyone forgot the fact that diesel-electric and turbo-electric transmissions were a thing some time around 1990.

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