Water, water, everywhere and not a drop to drink. So writes Samuel Taylor in The Rime of the Ancient Mariner. While that poem was talking about disaster at sea, it’s certainly clear that we’re all living on a sinking ship – and we’re all going to be up to our necks if we don’t start to get our acts together. Water remains one of the largest problems in the world. We have plenty of water in the world, yes – but only a tiny, tiny fraction of that water is drinkable. With pollutants and other nasty chemicals seeping into our ecosystem every day, that tiny percentage is dwindling faster and faster. Today, one-tenth of the world is still utterly without any kind of clean drinking water.
Now, however, researchers have announced a recent breakthrough in the field, using cheap, clean power to create portable drinking water for parched and impoverished lips. Deemed the “solar still,” the technology will “allow people to generate their own drinking water much like they generate their own power via solar panels on their house roof,” so claims Zhejun Liu, a scholar at the State University of New York (ironically acronym’d SUNY) in Buffalo.
Humans have relied on the sun for a long time, from growing crops to sunbathing. Even though solar energy first hit the mainstream in the 1950s, ancient people realized that the sun could also provide a source of power. Solar stills have been around for millennia; black bottomed vessels filled with water and trapped with a clear substance. As the sun heats the black container, water evaporates and gets trapped on the upper layer of the container. Dirt, gunk, and other pollutants don’t evaporate and are left behind. It’s a simple, streamlined solution – but it’s also costly, and getting a day’s drinking water can take hours, requiring 6 square meters of solar still. That’s not even factoring in extra gallons of water required for cooking, cleaning, bathing, and other wet activities.
Researchers have managed to improve stills through two approaches. First, new stills are designed in such a way that only the topmost layer of water is heated and evaporated, which means that less energy is lost overall. Solutions like nanomaterials proved prohibitively expensive, so Qiaoqiang Gan, an electrical engineer at SUNY Buffalo, developed an alternative path. Secondly, it became apparent that the material’s cost would never allow the technology to be viable, so Gan began looking for cheaper alternatives.
Gan developed the new generation of solar with three primary, cost-efficient components. Manufacturers start with a fiber-rich paper, sort of like the paper used to make currency. They coat this with carbon black, a cheap powder left over after the incomplete combustion of oil or tar. Next, they take a block of polystyrene foam—the stuff used to make coffee cups—and cut slices through it, making 25 connected sections. The foam floats on the untreated water and acts as an insulating barrier to prevent sunlight from heating up too much of the water below. The paper wets the entire top surface of each of the 25 sections. Evaporated water is trapped by a clear acrylic cover and funneled into a collection vessel. Gan and his colleagues report in Global Challenges that the setup not only works, but that it’s 88 per cent efficient at channeling the energy in sunlight into evaporating water. This allows a 1-square-meter-sized device to purify 1 liter of water per hour, which is about four times faster than commercially available versions.
Gan estimates the materials needed to build the still cost roughly $1.60 per square meter, compared with $200 per square meter for preexisting models. At that price, providing the minimal water needed for a family of four might cost as little as $5 for the raw materials per device – an innovation that’s sure to make a splash. Or, in the mangled jargon of Homer Simpson, “Water, water, everywhere, so let’s all have a drink.”
