Solar Steam Device

Would you go under the knife in a Moldovan hospital? How about at a military outpost in Afghanistan, or at a clinic in Zambia? Thousands of people do every year, and in the world's most resource-poor areas, medical personnel need a way to sterilize their equipment quickly and completely.

The World Health Organization reports that 10 percent of patients hospitalized in developing countries contract at least one healthcare-associated infection. In Intensive Care Units, the number is closer to 60 percent.

A new solar-powered device created by researchers at Rice University in Houston, Texas, uses the sun's energy to super-heat millions of tiny metallic nanoparticles. The particles, submerged in water, create scorching hot, disinfecting steam in about five minutes.

The system uses no electricity or fuel and little water, and it generates steam hot enough to kill even the most resilient microbes.

Rice researcher Naomi Halas presented her team's prototype today in a keynote address at the 246th National Meeting & Exposition of the American Chemical Society (ACS) in Indiana.

Off-the-Grid Surgery

Traditional autoclaves, the machines surgeons in the U.S. use to disinfect their equipment, rely on electricity. But a World Bank report from May of this year says that 1.2 billion people in the world aren't connected to the power grid.

"We have developed a solution, our solar steam technology," Halas said. "It is completely off-grid, uses sunlight as the energy source, is not that large, kills disease-causing microbes effectively and relatively quickly, and is easy to operate. This is an incredibly promising technology."

Halas has made one solar-powered autoclave prototype, and another model designed to sterilize human waste for families without access to plumbing or running water.

She's hopeful that the technology could also be adapted for cooking, purifying drinking water, and generating power on its own by using steam to spin small turbines.

How It Works

The autoclave looks like a small satellite dish, with a concave mirror that concentrates sunlight onto a container of water and metal or conductive-carbon nanoparticles. The particles are so tiny that it would take 1,000 of them to reach the width of a human hair, but they absorb light across the solar spectrum.

When the particles—dubbed “nanoheaters”—get hot, a layer of steam forms on their surfaces and they rise to the top of the water container, releasing steam into a collection tube. Then they sink back to the bottom to begin the process again.

"Nanoheaters generate steam at a remarkably high efficiency," Halas said. "More than 80 percent of the energy they absorb from sunlight goes into production of steam. In the conventional production of steam, you would have to heat the entire container of water until it boils, with the bubbles rising to the top to release steam. With nanoheaters, less than 20 percent of the energy heats the neighboring liquid."

The device is the first practical application of nanoparticle technology described last year in the journal ACS Nano. Funding from the Bill and Melinda Gates Foundation helped make the prototype possible.

The technology is not currently small enough, durable enough, or inexpensive enough for widespread deployment, but Halas has formed a company to develop the device for commercial use.

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