Solar cells stay 100% powerful underwater with US Navy’s new coating tech

US Navy-funded researchers have created a new coating for underwater solar cells that prevents biofouling without compromising visible light transmission.

Biofouling is a process that prevents underwater solar cells that are not shielded from becoming covered in biological growths like algae and barnacles. This reduces their electrical or operational efficiency and is costly to remove.

A team at the Technical University of Denmark has created a new approach that combines an organic biocide, a fast-polishing binder, and ultra-low quantities of nano-sized, seawater-soluble pigments.

Researchers have found that when these coatings come into contact with seawater, the pigment particles disintegrate and form a porous layer that lets seawater seep into the coating.

Biofouling defense

Unmanned Underwater Vehicles (UUVs) and solar-powered Autonomous Underwater Vehicles (AUVs) rely on solar panels to extend mission times by converting sunlight into electricity while at the seawater surface.

However, biofouling, the attachment and growth of organisms, reduces the optical efficiency of these solar panels over time, impacting vehicle maneuverability and hydrodynamics.

Current antifouling coatings, including easy-slip silicon-based fouling release coatings (FRCs) and biocidal cuprous oxide (Cu2O), either require mechanical cleaning or block visible light, limiting their effectiveness for UUVs and AUVs.

Researchers aimed to develop a self-polishing antifouling coating that maintains visible light transmission while preventing biofouling. By investigating nano- and micron-sized pigment particles, the coating could achieve high biocide release rates and minimal light scattering.

According to the team, the goal is to create a coating that ensures over 80 percent light transmission and 90 percent solar power generation for at least three months without mechanical intervention.

Clear coating innovation

The innovative approach employs ultra-low concentrations of nano-sized, seawater-soluble pigments like cuprous oxide (Cu2O) and zinc oxide (ZnO), combined with an organic biocide and a fast-polishing binder.

When exposed to seawater, these pigments dissolve, forming a porous layer that allows seawater diffusion into the coating. This leached layer facilitates the release of biocidal compounds into the seawater. The binder matrix reacts with seawater ions, forming soluble compounds that regulate the polishing rate.

According to researchers, as hydrolysis progresses, the coating erodes, exposing fresh layers of acrylate polymer and pigments, resulting in a consistent self-polishing effect.

The research team experimented with different binder systems, using silyl acrylate (SA) alone or with rosin (SA-R) at a 70:30 ratio. They tested particle mixes including nano-sized cuprous oxide (NC), nano-sized zinc oxide (NZ), micron-sized cuprous oxide (MC), and the biocide SeaNine 211 (SN).

Coating smooth, translucent polycarbonate panels, the substrates were immersed in Hundested Harbor, Denmark, for two and a half months, with inspections and photographs taken at two, six, and ten weeks.

The combined effects of NC, NZ, and SN in an SA-R coating delivered significant fouling resistance over a 12-week exposure, thanks to the synergistic dissolution and rapid polishing of the binder.

The champion coating had an NC PVC of 0.04 percent, NZ PVC of 0.08 percent, and SN at 3 percent. After 12 weeks, the coating polished through at a rate of 1.4 μm/day. Further testing in Florida showed excellent biofouling resistance, maintaining nearly 100 percent solar power efficiency over 13 weeks.a

According to reseachers, underwater cameras and sensors on UUVs need optically clear coatings, but current coatings become hazy over time, limiting their effectiveness. Developing coatings that retain clarity while resisting fouling during extended seawater exposure is a key challenge.

Additionally, these coatings only work in seawater, as ions are needed for binder hydrolysis and pigment dissolution.

The details of the r esearch were published in the journal Progress in Organic Coatings .