Harvesting solar energy as heat has many applications, such as power generation, residential water heating, desalination, distillation and wastewater treatment. However, the solar flux is diffuse, and often requires optical concentration, a costly component, to generate the high temperatures needed for some of these applications.
MIT engineers have invented a bubble-wrapped, sponge-like device that soaks up natural sunlight and heats water to boiling temperatures, generating steam through its pores.
This device is capable of generating 100 ∘C steam under ambient air conditions without optical concentration.
The design, which the researchers call a “solar vapor generator,” requires no expensive mirrors or lenses to concentrate the sunlight, but instead relies on a combination of relatively low-tech materials to capture ambient sunlight and concentrate it as heat. The heat is then directed toward the pores of the sponge, which draw water up and release it as steam.
From their experiments — including one in which they simply placed the solar sponge on the roof of MIT’s Building 3 — the researchers found the structure heated water to its boiling temperature of 100 degrees Celsius, even on relatively cool, overcast days. The sponge also converted 20 percent of the incoming sunlight to steam.
The high temperatures are achieved by using thermal concentration and heat localization, which reduce the convective, conductive and radiative heat losses.
The low-tech design may provide inexpensive alternatives for applications ranging from desalination and residential water heating, to wastewater treatment and medical tool sterilization.
