Daniel Kwasi Kpeglo just finished his physics Ph.D., and the invention he left behind could one day shade whole lakes and dams the way a hat shields a face — letting sunlight through but bouncing the heat back into the sky.
The problem he set out to solve touches every family, farm and factory that depends on stored water. In hot regions like southern Africa, water sitting in dams and reservoirs slowly vanishes into the air. Rising temperatures only make the loss worse, leaving less for drinking, crops and industry. Kpeglo's simple big idea: instead of hunting for new water, waste less of what we already have.
His answer is a floating "blanket" made of a nanomaterial — a substance built at the scale of billionths of a meter. The cover is an extremely thin layer of a material called a transparent conducting oxide, fixed onto a lightweight, flexible plastic sheet. It acts like a selective filter for sunlight: most of the visible light passes through, while most of the heat-carrying invisible rays are reflected away.
In his laboratory experiments with an artificial sun, the numbers were striking. The cover let more than 60 percent of visible light through on average while reflecting more than 80 percent of infrared radiation back at the sun. During the sunniest part of the day, the water underneath stayed 10 degrees Celsius cooler than the cover's own surface — a temperature gap that sharply slows evaporation. In fact, the water level under the coated cover barely moved during the test, while an uncovered reservoir and one topped with ordinary plastic both lost water.
Why does letting light through matter so much? Because aquatic plants and animals need it to survive. Many evaporation-blocking tricks, like palm fronds, shade cloths or chemical sunscreens, block all sunlight, which can choke life in the water. Kpeglo's design only blocks the heat, keeping ecosystems alive underneath.
The cover is also water-repellent, so water doesn't cling to it. That means it can float without needing a heavy support structure — and it picked up fewer layers of algae and natural growth in tests, hinting at easier cleaning and maintenance over time.
Kpeglo is careful about one concern: tiny particles leaking into the water. But his design keeps the nanomaterial fixed onto the plastic sheet, not floating free in the reservoir.
There is still a long road ahead. So far the cover has been tested only in a lab-scale reservoir under an artificial light source, comparing uncovered water, ordinary plastic and the new coating. The next step is real-world testing — and waiting to see whether this sunscreen for lakes can scale up from a lab bench to the vast surfaces of whole dams. If it can, southern Africa and other thirsty regions may find a lightweight, life-friendly way to hold onto the water they already have.