Ammonia has two chief advantages over hydrogen as an energy carrier. One is the fact that it’s a liquid at ambient temperature and pressure levels, making it a ton easier to store, transport and handle; hydrogen either needs to be heavily compressed to around 700 bar, or else kept cryogenically cooled as a liquid, to just 20.28 K (−252.87 °C; −423.17 °F) – both of these are energy-intensive processes. The second is how much energy it carries: by volume, nearly three times as much as hydrogen gas, and by weight, more than 20 times as much as today’s lithium batteries.

It can be produced cleanly, and it can be used as a fuel in many different ways, many of which create zero harmful or climate-relevant emissions. And while it does have certain drawbacks, green ammonia is viewed as a promising clean fuel alternative for industries like shipping, aviation and other applications where batteries and hydrogen gas simply can’t carry enough juice to get the job done.

Amogy was founded in 2020 to accelerate the development of green ammonia as a power source for clean transport. The company says it had a 5-kW ammonia drone flying by July 2021, followed quickly by a 100-kW ammonia tractor in May 2022.

Now it’s scaled-up its ammonia powertrain to 300 kW, and presented it in what it claims is the “world’s first ammonia-powered, zero-emission semi truck” – a 2018 Freightliner Cascadia Class 8 truck that’s been retrofit with an ammonia fuel system slung under the cabin and stacked up behind it, appearing to add little in the way of bulk to the standard truck.

It fills up in eight minutes, to carry around 900 kWh of “total stored net electric energy” – roughly the same amount of energy as the Tesla Semi stores in its lithium battery packs. Amogy says its “carbon-free energy system … has 5X higher system-level energy densities compared to lithium batteries,” so it’s reasonable to expect this cab will be significantly lighter than the Tesla.

The truck has been built, filled up and “tested for several hours on the campus of Stony Brook University,” and it’s scheduled for full-scale real-world performance evaluation on a test track later this month.

So how would we expect it to compare to the Tesla Semi? Does ammonia look better than batteries for this kind of heavy transport? That’s very hard to say; Amogy doesn’t provide performance or range estimates at this stage.

We do know there’ll be inefficiencies to deal with here that don’t apply to battery-electric vehicles. Amogy’s powertrain features an ammonia cracker that converts the ammonia back into hydrogen. It then runs that hydrogen through a fuel cell to create electrical power, and uses that power to drive electric motors.

So if Amogy’s “total stored net electric energy” of 900 kWh simply means there’s enough ammonia on board to theoretically store 900 kWh, it doesn’t mean 900 kWh will reach the motors. There’ll be losses in the onboard ammonia cracking reactors, further losses in purification stages that make sure the hydrogen’s ready for use in the fuel cell, and further losses at the fuel cell stage.

We don’t know what technologies Amogy is using, or the efficiency factor at any of these stages. We can try to guess, though. The Ammonia Energy Association cites a best case ammonia cracking efficiency of 76%, but that’s likely at industrial scale – we wouldn’t expect a cracking reactor that fits on a truck or a tractor to operate that efficiently. Still, if we use that figure, some 684 kWh of energy will reach the fuel cell in the form of hydrogen. If we take a high-end estimate for PEM fuel cell efficiency at 65%, then 444.6 kWh of energy will make it through to the motors. That’s a little under half of the original 900 kWh, so in this optimistic scenario, the Amogy truck will travel about half as far as the Tesla Semi.

That doesn’t sound great. But on the other hand, you could easily add range by sticking another couple of ammonia tanks somewhere – and that’ll be a much less painful process than trying to extend the range of a lithium-battery-powered semi. Plus, this is a retrofit; designing a new truck around the ammonia concept would let you do all sorts of things.

Source: Amogy

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