SunRays Aqua System Solar-Thermal Control of Invasive Aquatic Weeds A Distributed Heliostat Approach for Chemical-Free Freshwater Management

This study aimed to determine whether a distributed, non-focusing solar-thermal system could deliver weed-lethal temperatures to floating aquatic weeds without chemicals or sediment disturbance. The SunRays Aqua System uses a bank-mounted array of flat-mirror heliostats to project a broad, non-focusing thermal field onto a receiver, carried either by a screw-pontoon platform that lifts and partially dewaters the weed mat to overcome the water’s heat-sink effect, or by a drone for otherwise inaccessible sites. The prototype was evaluated through thermal calibration trials and mesocosm experiments on Azolla filiculoides. Calibration confirmed 20 heliostats as the minimum to reliably exceed 60 °C, and high-dose treatment reduced dry biomass to 17% of control at day 14, outperforming both mechanical removal (72%) and low-dose treatment (54%). SunRays Aqua is a viable proof-of-concept for chemical-free aquatic weed control in sensitive wetlands, with future work needed on field-scale trials, repeated treatments to manage regrowth, and biomass management to address post treatment nutrient release.