A solar collecting device with mirrors around a central core, framed against a blue sky.

A copper collecting plate (long central structure) paired with a transparent, heat-trapping material (white strip, top) harvests enough solar heat to make steam. Credit: Lin Zhao

Renewable energy

Technology for sterilizing medical instruments goes solar

A sunlight-powered device equipped with an a lightweight gel makes steam hot enough to kill dangerous microbes.

An airy insulating material doubles the efficiency of a device that converts sunshine to heat, enabling solar-powered production of steam suitable for sterilizing medical equipment.

Medical sterilization to prevent infections is routine in high-income nations, but less so in countries where people lack reliable access to energy. Existing solar absorbers can collect heat from sunlight but do not concentrate it well enough to create steam.

Evelyn Wang at the Massachusetts Institute of Technology in Cambridge and her colleagues modified an off-the-shelf solar absorber by adding a thin layer of foam tiles to the absorber’s copper heat-collecting surface. The foam contains nanometre-scale silica particles that confer transparency, and is riddled with pores that help to trap heat, allowing light to pass through but preventing heat from leaving.

On a rooftop in Mumbai, India, water in a sealed chamber connected to the absorber began boiling within five minutes. For 30 minutes, the solar absorber produced steam at a temperature and pressure high enough to kill microorganisms.

The researchers hope their inexpensive device could help people in resource-poor regions to avoid infections acquired in medical settings.