Low-cost solar device converts sunlight to steam

The device floats on water, converting 20% of incoming solar energy into steam at 100ºC without expensive optical concentration devices and is made of cheap, commercially available materials, including bubble wrap and a polystyrene (plastic) foam.

"This project is an excellent demonstration of how international collaboration and use-inspired research can yield cutting-edge scientific findings that have direct application to the sectors that are at the core of the UAE's continued evolution toward an innovation and knowledge-based economy," said Dr. Steve Griffiths, Vice President for Research and Associate Provost, Masdar Institute.

"The system we have developed enables us to generate steam with solar energy without having to rely on direct sunlight," said Dr. TieJun Zhang, Masdar Institute Assistant Professor of Mechanical and Materials Engineering.

"The technology is particularly suited for the UAE's dusty climate, as it fully uses the entire spectrum of sunlight for thermal applications rather than just the direct portion, which can be hindered by the aerosols," he added.

Dr. Zhang, MIT's Mechanical Engineering Department Head Dr. Gang Chen, PhD student Hongxia Li and Postdoc Weilin Yang at Masdar Institute, published a paper on their new floating solar receiver last week in the journal Nature Energy, along with George Ni, an MIT graduate student and the paper's leading author, and two other researchers at MIT.

The receiver's design is relatively simple: A floating, sponge-like device made of a spectrally-selective absorber allows visible light energy from the sun in, while restricting the amount of heat that radiates back out into the atmosphere. This heat-trapping effect significantly improves the device's sunlight-to-steam efficiency.

The absorber is sandwiched between a top bubble-wrap layer, which allows for sunlight absorption while reducing the amount of heat lost to the air through convection, and a bottom insulating foam layer, which floats the entire structure on a body of water and reduces the thermal loss of the generated heat to the water below.

The floating receiver acts like a sponge, constantly soaking up water and evaporating it, producing a continuous stream of steam.

The solar receiver was validated at MIT, where it demonstrated the ability to rapidly reach 100°C and generate steam during periods of low direct sunlight, such as during non-summer months and heavy cloud coverage.

"The technology we have demonstrated is particularly attractive for hot-arid region such as Abu Dhabi for potential applications in waste water treatment, sea water desalination, and even power generation," Dr. Chen said.