The ocean, with its vast mysteries hidden in its depths, has long captivated human curiosity. From ancient maps adorned with dragons and sea monsters to modern-day technology, we've made limited progress in uncovering the secrets of the deep blue. Despite the technological advancements to date, only around five percent of the world’s oceans have been mapped.

Solar power illuminates ocean exploration

A recent press release revealed research delving into the potential of solar power for underwater vehicles to overcome the limitations of underwater exploration.

Their work, detailed in a research paper published in Nature Photonics titled "A dive into underwater solar cells," led by Jason A. Röhr and André Taylor from the Department of Chemical and Biomolecular Engineering, NYU Tandon, sheds light on the challenges and opportunities of this burgeoning field.

While marine technologies like wave and tidal power show promise, they are often location-dependent and lack portability. One exception is oceanic thermal energy conversion (OTEC), which harnesses temperature gradients between the sea's surface and deeper waters.

However, OTEC's reliance on specific diving patterns and limited suitability for tropical and subtropical regions hinder its application for fixed underwater devices.

Solar power, on the other hand, offers a ubiquitous and powerful energy source, even beneath the ocean's surface. Sunlight, particularly in the green-to-blue spectrum, can penetrate waters up to 50 meters deep, providing ample energy to operate basic appliances.

Challenges and solutions

The NYU Tandon researchers explored the potential of solar cells for underwater applications, highlighting successful implementations in powering AUVs and communication devices while addressing the hurdles.

One of the primary challenges lies in the design of existing silicon solar technology, which is ill-suited for underwater environments. Beyond moisture and salt content detrimental to electronics in general, silicon solar cells are optimized to absorb red and infrared light, which do not penetrate water effectively.

Alternative technologies like gallium indium phosphide (GaInP) and cadmium telluride (CdTe) have shown higher efficiency and potential for optimization in oceanic conditions. Next-generation solar cells, such as organic and perovskite solar cells (OSCs and PSCs), are also under consideration.

Another critical issue underwater solar cells face is biofouling—the gradual accumulation of organic substances, including microorganisms and plants, on the cells. This buildup obstructs light access, impeding the photovoltaic process and performance.

Furthermore, it affects the submerged vehicles themselves, increasing weight and generating hydrodynamic resistance. Previous experiments revealed that biofouling covered over 50 percent of the surface after just 30 days underwater, severely hampering solar cell operation.

In their research, the team also tackled practical challenges in designing and testing underwater solar cells. They devised innovative solutions, such as using LED lights to simulate the light spectrum at various depths, eliminating the need for water during testing.

These experiments demonstrated that silicon-based solar cells performed better in shallow depths, while other cell types proved more efficient below two meters. The researchers also explored additional testing options.

Although these specially designed underwater solar cells are still in their early stages of development, these contributions could lay the foundation for groundbreaking technologies that illuminate both the potential of solar energy and the enigmatic depths of our unexplored oceans.

Study Abstract

Our oceans are vast, mostly unexplored and difficult to monitor. Large-scale implementation of a fully autonomous ‘Internet of Underwater Things’ would transform how we collect and share data from this domain; however, deployment is prohibited by the lack of persistent power sources. In principle, underwater solar-energy generation can complement the use of batteries and provide a solution, although dedicated research is needed since traditional silicon solar cells do not perform well underwater due to water’s strong absorption of near-infrared light. In this Perspective we present examples of solar-powered underwater applications and discuss which types of solar-harvesting materials could be appropriate, including GaInP variants, CdTe, organic semiconductors, and perovskite semiconductors. We also discuss challenges that need to be addressed, such as the development of effective antifouling coatings and new certification standards given that underwater conditions are starkly different from those in terrestrial environments.