A Floating Nanomaterial “Sunscreen” Could Help Reservoirs Lose Less Water

A thin floating sheet designed to act like sunscreen for stored water has shown promising results in laboratory experiments, according to research reported by Phys.org. The proposed cover is intended for lakes, dams and reservoirs where evaporation can reduce supplies for households, agriculture and industry. The design uses a flexible plastic sheet coated with a transparent conducting oxide only a few hundred nanometers thick. Rather than blocking sunlight altogether, the material is designed to let useful visible light pass through while reflecting much of the infrared radiation associated with heat. In the reported experiments, more than 60% of visible light passed through the cover on average, while more than 80% of infrared light was reflected. The water beneath it became about 10°C cooler during the sunniest part of the day than the upper surface of the sheet. Researchers also observed that the water level remained essentially unchanged during the test period, while uncovered water and water beneath ordinary plastic sheets fell. The light transmission is important because completely shading a reservoir could deprive aquatic plants and animals of sunlight. The coated sheet was also described as lightweight, water-repellent and less prone to accumulating algae or other natural growth during testing. Because the nanomaterial was fixed to the plastic rather than placed directly in the water, the design was intended to reduce—but does not eliminate—concerns about contamination. The research remains at an early stage. The tests used a laboratory-scale reservoir and an artificial light source designed to mimic sunlight. The cover has not yet been evaluated under real sunlight, wind, rain, changing temperatures or moving water. Before the idea could be used on a natural dam or reservoir, large field trials would need to assess its cost, durability, maintenance requirements and environmental effects. A practical installation would also require a floating system to keep the sheets in position. Researchers say durable, ultraviolet-resistant materials would be needed because prolonged sunlight can cause some plastics to become brittle, crack and break apart.