When it comes to our knowledge of Earth's oceans, it's surprising that we may know more about distant planets like Mars than we do about the depths of our own seas. Actually, only 5% of the planet's seabed has been adequately mapped and explored.. And when it comes to advancing our understanding of the marine ecosystem and working towards its conservation, Technological innovations such as autonomous underwater vehicles (AUVs) are poised to play a pivotal role. However, a major challenge arises when these AUVs venture into the abyss: how to propel them efficiently? As recent research suggests, the answer may lie in the untapped potential of solar energy.
Is solar power a viable option for AUVs?
In a word, yes, but with some reservations. While the oceans offer a plethora of renewable energy sources like wave and tidal energy, these tend to be location dependent. HAS lasting power For AUVs on long-distance missions in the open sea, solar energy presents itself as a viable solution, employing two distinct methods:
- Ocean Thermal Conversion (OTEC): This technique capitalizes on the temperature gradient of water bodies, where the surface layers are generally warmer due to solar radiation.
- Photovoltaic : Photovoltaic technology, similar to its terrestrial counterpart, is used with some adaptations for underwater applications, as we will explore shortly.
Contrary to what one might think, solar radiation can reach depths of up to fifty meters, especially in the green to blue part of the spectrum. New York University has already published a study which highlights this challenge, since silicon photovoltaic cells used on earth are optimized for the red part of the spectrum. In addition, this type of electronic component is very sensitive to salt and humidity, as well as biofouling. And that's where New York University announced new developments to multiply the potential of underwater rovers.
A new generation of underwater photovoltaic cells
The team of American scientists used LED lamps in the laboratory, simulating various wavelengths of the spectrum. Their conclusions provide two main pieces of information:
- Most efficient photovoltaic cells for underwater operation incorporate materials like cadmium telluride, indium gallium phosphide, and other variants with a wider light reception range than traditional silicon cells. Perovskite cells also exhibit superior performance. However, more research is needed before commercial prototypes become reality.
- Combat biofouling is now feasible with existing commercial solutions. Previously, biofouling affected up to half of the surface area of an AUV in 30 days. Fortunately, transparent, non-toxic coatings can be applied to photovoltaic panels, effectively mitigating this problem.
Current prototypes of solar-powered AUVs
Although research into solar panels for AUVs is still in its infancy, several promising prototypes have already met these challenges head-on. MIT’s PEARL project is a striking example. In 2021, the institute unveiled a floating mothership equipped with solar panels, serving as a charging station for underwater vehicles, with integrated satellite connectivity. This innovative approach avoids the complexities linked to the exploitation of sunlight in the great depths of the ocean.
Another interesting initiative is the SAUV II, a solar-powered vehicle designed by the United States. Institute for Autonomous Underwater Systems. Resembling a manta ray, this prototype has an impressive depth capability up to 500 meters, facilitating deep underwater exploration. Just like marine mammals like dolphins or whales, the SAUV II resurfaces to recharge its batteries when energy levels are low. Made of fiberglass, it includes a full suite of equipment, including GPS, acoustic altimeters, depth sensors, gyroscopes and radio or satellite data transmission systems.
In addition to these examples, we have covered research on other AUVs. Some, like the Tunabot And robotic jellyfish, take inspiration from the natural world, mimicking the movements and shapes of creatures such as tuna and moon jellyfish. This exciting field is known as biomimicry or biomimetics, a topic we have explored extensively in previous articles. If you are intrigued, you can start your journey with this introductory article to deepen biomimetic engineering.
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Pictures
SAUVII (Wikimedia Commons)