Floating Solar Device Boils Water Without Mirrors (arstechnica.com)

An anonymous reader quotes a report from Ars Technica: Researchers from MIT and the Masdar Institute of Science and Technology, led by George Ni, describe a prototype design that boils water under ambient sunlight. Central to their floating solar device is a "selective absorber" -- a material that both absorbs the solar portion of the electromagnetic spectrum well and emits little back as infrared heat energy. For this, the researchers turn to a blue-black commercial coating commonly used in solar photovoltaic panels. The rest of the puzzle involves further minimizing heat loss from that absorber, either through convection of the air above it or conduction of heat into the water below the floating prototype. The construction of the device is surprisingly simple. At the bottom, there is a thick, 10-centimeter-diameter puck of polystyrene foam. That insulates the heating action from the water and makes the whole thing float. A cotton wick occupies a hole drilled through the foam, which is splayed and pinned down by a square of thin fabric on the top side. This ensures that the collected solar heat is being focused into a minute volume of water. The selective absorber coats a disc of copper that sits on top of the fabric. Slots cut in the copper allow water vapor from the wick to pass through. And the crowning piece of this technological achievement? Bubble wrap. It insulates the top side of the absorber, with slots cut through the plastic to let the water vapor out. Tests in the lab and on the MIT roof showed that, under ambient sunlight, the absorber warmed up to 100 degrees Celsius in about five minutes and started making steam. That's a first. The study has been published in two separate Nature articles: "Steam by thermal concentration" and "Steam generation under one sun enabled by a floating structure with thermal concentration."

Comments

Re:Useful for desalination plants?

[swell]

"sunshine you don't use would have been wasted anyway"

Is that so? Suppose we cover miles of oceans and lakes with these devices. Would there be no change in the ecology? No change in water or air temperature?

We dam rivers wherever possible, plant solar collectors over large areas, tap geothermal energy potential, and erect windmills wherever we can expect a breeze. There has been an effort to tap the energy of the surf and other wave action. The dams certainly have an impact on the environment and the others, well we just haven't given them much thought. If we can eventually tap 10% of some prevailing wind energy, can we say there will be no consequence? 'Green' energy sources may not be so green.