Future of underwater craft may be hydrogen
Spanish firm Jalvasub Engineering is working with a number of partners on providing hydrogen and fuel cell power systems for a range of autonomous underwater vehicles (AUVs).
Currently, most AUVs are battery powered. But battery arrays are heavy – and fall short in the trade-off between onboard load and the energy necessary to push it through the water.
The answer, however, could be on its way in the form of Jalvasub Engineering’s Hycogen unit.
Hydrogen fuel cells, combine fuel and oxygen electrochemically to produce electricity. To outline the difference, Juan Alvarez Abad, CEO of Jalvasub explains: “One of the more advance li-ion batteries...provides 225Wh from a 1.5kg battery. An AUV that demands 900Wh would require four batteries. This means an electrical generation systems that weights 5.6Kg.”
By comparison the Hycogen unit developed for AUV use, just coming off the test-bench, will “provide at least 500Wh/Kg... [so] a 900Wh system will weigh only 1.8Kg. This means less than a third of the weight for the same autonomy”. Further, a 5.6Kg propulsion unit will consequently have 2,800Wh of energy.
However, there are more advances underway. Jalvasub is exploring both PEM and the higher temperature (HT) PEM fuel cells. However, up till now, one of the largest inhibitors has been the cost of the precious metal catalysts. Now the price is set to drop with the entrance of ultra-low platinum content, high performance fuel cells.
Then there’s the hydrogen feed itself: always a tricky subject, not just because hydrogen at normal pressure is incredibly bulky, but also because the fuel has to be pure, high quality hydrogen or risk ‘poisoning’ the PEM cell.
There are a couple of potential answers. While the first, most obvious solution is to hold hydrogen under pressure this limits the length of the duty cycle. The second option is to create hydrogen on-demand through mixing a reagent with water: Jalvasub and its technology partners are using a proprietary mixture, held in a cartridge, based on alkaline and alkaline earth metals that are both cheap and easily obtainable.
However, as this is an electrochemical reaction that requires oxygen at the cathode, fuel cells also require an oxygen feed. At the moment, the most usual solution is a liquid oxygen tank stored in or outside the pressured hull. However, the Hycogen unit will, again, create it in situ by a peroxide reaction. Further, in a neat twist toward efficiency, the pure water necessary for the fuel cells is obtained from the by-products.
High performance batteries remain an important element of the system, used for peak shaving and absorbing the excess charge. Another of Jalvasub’s high-tech partners is working on a battery that could substantially raise the energy capacity compared to those presently on the market.
The system doesn’t just win on lower weight and volume, it also is almost noiseless, giving only a very small acoustic or infrared signal. More, this technology is out of the carbon economy cycle: there are no CO2 emissions. So, the Hycogen system is entering the market with a convincing set of advantages: not least of which is that it’s modular and easy to scale up or customise, plus it’s also simple to maintain.
It should soon prove its capability. One of the first installations of the Hycogen modules promises to be onboard the high-endurance AUV Siroco. While existing craft of the same-size can only mange six hours of operation at a stretch, the projected duty cycle of Siroco will be more than ten hours.
Apart from Hycogen products, Jalvasub Engineering is also currently developing other products based on hydrogen technologies and fuel cells that could be applied to larger platforms like submarines.
By Stevie Knight
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