AUVs will recharge without a mothership

The US Department of Defense is testing hydrogen fuel cells that have the potential to significantly increase the autonomy of unmanned underwater vehicles (UUVs) and minimize their dependence on shore infrastructure and mother ships. The project was launched in August 2023, and the tests are scheduled to begin in early 2024.

    image source: saab.com 

The US Department of Defense is testing hydrogen fuel cells that have the potential to significantly increase the autonomy of unmanned underwater vehicles (UUVs) and minimize their dependence on shore infrastructure and mother ships. The project was launched in August 2023, and the tests are scheduled to begin in early 2024.

The American company Hibbard Inshore has prepared a hybrid version of the Saab Sabertooth - the AUV received the Subsea Supercharger system developed by Teledyne Energy Systems. It is expected that the implementation of fuel cells will increase the autonomy and range of the system, minimize the need for support ships and cut operation costs.

The deployment of hydrogen fuel cells - enhanced AUVs is complicated by a number of issues related to the need to store hydrogen and oxygen, provide buoyancy and trim in deep-water environments. The condensate formed during the operation of fuel cells in a sealed container can easily damage electronics, and the generated inert gases increase internal pressure. Most problems occur during system startup and shutdown - the moments when gases need to be removed from the anode and cathode loops. A trivial task, long solved on land, requires fundamentally new approaches for implementation in the underwater environment, and most importantly - in the enclosed environment of AUVs.

The integration of hydrogen fuel cells into AUVs promises significant expansion of their capabilities and numerous new areas for their potential application.

Source: naval-technology.com  

Is the idea of using solar energy in underwater exploration viable?

At first glance, the idea may not seem promising. After all, how much solar energy can penetrate through the thickness of water? It is well known that eternal darkness reigns at depth. Nevertheless, researchers from Tandon University in New York have been considering the prospects of photovoltaics in exploring the world's oceans using autonomous and remotely operated underwater robots. Source: Nature Photonic https://doi.org/10.1038/s41566-023-01276-z 

Underwater robots are an excellent tool for scientists to conduct various underwater explorations. However, the autonomy of robots is limited by the need for constant recharging. Often, onboard power sources are not installed on remotely operated vehicles, forcing them to rely on power supplied through cables from accompanying vessels.

The Tandon researchers are considering creating alternative power systems for autonomous and remotely operated underwater vehicles that would allow them to surface less frequently for recharging. Moreover, underwater power sources would also be useful for underwater sensors, navigation, and communication systems, reducing their dependence on battery resources or eliminating the need to run power cables to them.

Research has shown that using waves, tides, and currents for underwater exploration has potential, but their effectiveness depends on location and can limit mobility. Thermal energy from the ocean and temperature gradients are also options, but they have limited potential for stationary underwater devices. However, sunlight has potential as visible light can penetrate up to 50 meters deep, providing energy for recharging underwater robots and electronic devices. 

One issue with using photovoltaic cells underwater is that common ones are optimized for red and infrared light, reducing their efficiency underwater. Alternative options such as gallium indium phosphide (GaInP) and cadmium telluride (CdTe) panels show higher efficiency in ocean conditions, as well as organic (OSC) and perovskite cells. 

Biofouling is another issue as research has shown that after just 30 days, over 50% of the absorbing surface of underwater panels is affected, reducing their efficiency. This problem is more significant in tropical waters but becomes less of an issue at higher latitudes, making the idea viable in Arctic waters. 

While a final answer to the question of using solar energy in underwater exploration is premature, the idea of using photovoltaics to create underwater solar power stations may be worth further investigation.  \\