A French firm (Naval Group, formerly DCNS) has successfully tested what it calls FC2G (Fuel Cell 2nd Generation) AIP (Air Independent Propulsion) system for 18 days in a mock-up of the complete system in an 8 meter long circular structure identical to the space it would occupy in a submarine. The FC2G performed efficiently for three weeks. This test will be repeated several times as preparations are made to install FC2G in a submarine. The FC2G is safer, more efficient and easier to operate than earlier fuel cell AIP systems, including the widely used DCNS first-generation AIP.

Fuel cell tech has been around for decades, long enough to become a proven technology. But fuel cells require dangerous fuels like hydrogen. Hydrogen is currently stored in cylinders outside the pressure hull of the sub. FC2G eliminates that with a two-stage system that extracts hydrogen from diesel fuel, which is also used for the sub’s diesel engines and purifies the hydrogen to a very high degree. The high-quality hydrogen gets more electricity out of the standard fuel cell technology. At the same time, the need for hydrogen storage is eliminated because only as much hydrogen is obtained from diesel fuel as would be in the sub if the hydrogen were brought in from external storage tanks. The oxygen is obtained from the same supplies used for the crew to breathe while submerged.

FC2G also operates more quietly and expels fewer byproducts from the sub. While hydrogen is a widely used industrial product, diesel fuel is even more widely available and much safer to handle. FC2G also generates more electrical power than older AIP systems of similar size and weight. FC2G also uses more efficient control software and hardware. That means the entire FC2G system requires only one sailor to monitor it.

The developer has a lot of credibility because many subs already use the older DCNS AIP designs. China and Russia are still struggling to get first-generation fuel cell tech working in their subs. Boats that use fuel cells also have diesel engines that power the subs while on the surface or just below the surface using a snorkel to obtain fresh air and expel diesel fumes. There are also storage batteries to provide some submerged operations if the fuel cells are not working.

Japan is working on making lithium batteries safe enough to use in subs. Lithium is more efficient than current batteries used in subs but also bursts into flames under some conditions. There are also new, more efficient and safer, battery tech working in the lab. All this stuff will eventually be available for subs while right now a new generation of AIP is ready to go.

More efficient AIP means there will be more non-nuclear subs, which cost about a quarter what a nuclear sub goes for, which means even quieter and hard to find subs at sea.