Efficient solar desalination unit uses titanium-coated diaper material
Desalination is an important technology that may help expand the world’s supply of drinking water. Now, engineers in China have demonstrated a new, relatively simple design for a solar still with a high efficiency and low cost.
It’s a cruel irony that Earth’s surface is covered in water, but that the vast majority of it is undrinkable. If we could find a way to remove the salt, compounds and microbes that make so much of it unsafe for consumption, we might be able to chip away at some pretty fundamental human health concerns.
One of the simplest ways to do so is to tap into the basic physics of evaporating and recondensing water, leaving behind all the nastiness. In the new design, researchers from Dalian Maritime University in China developed a new unit that can float on top of seawater, efficiently absorb solar energy and use that heat to evaporate the water.
The unit itself consists of three layers: the bulk is a polyethylene foam that helps it float and acts like a thermal insulator. The outside of the foam is wrapped in airlaid paper, an absorbent material used in disposable diapers that wicks water up towards the upper surface. The top face is coated in titanium nitride oxide (TiNO).
"In the solar energy field, TiNO is a common commercial solar absorbing coating, widely used in solar hot water systems and in photovoltaic units," says Chao Chang, lead author of the study. "It has a high solar absorption rate and a low thermal emittance and can effectively convert solar energy into thermal energy.”
This unit can then be placed in a familiar solar still – a transparent plastic container with a sloped roof, which catches the condensing fresh water and directs it to be collected. In tests, the team found that the new solar still has a solar-to-water efficiency of 46 percent, which is a decent step up from the 30 to 40 percent expected from single stills of this kind.
Importantly, the unit manages to avoid one major pitfall – fouling by salt building up on the surface, which can reduce efficiency over time. In tests, the team found that no salt layer was formed, suggesting that the pores wick salt away and dump it back in the seawater. Another advantage, the team says, is that the paper material can be reused over 30 times.
Unfortunately, the team doesn’t give one of the most crucial pieces of information – just how much fresh water it can produce.
While there’s no shortage of other solar desalination systems in the works, this new one earns its keep with its relatively low cost, high efficiency, and reduced fouling.
The research was published in the journal AIP Advances.