Desalination is an important technology that can help expand the world’s drinking water supply. Engineers from China demonstrated a relatively new, solar-powered desalination plant with high efficiency and low cost.
The cruel irony of our world is that the surface of the Earth is covered with water, but the vast majority of it is undrinkable. If we could find a way to remove the salt, compounds, and microbes that make seawater dangerous to drink, we could get rid of some of the most fundamental human health problems once and for all.
One of the simplest ways to do this is to use the fundamentals of the physics of evaporation and re-condensation of water, leaving behind all unnecessary fractions and inclusions. Researchers at the Dalian Maritime University in China have developed a new unit that can float above seawater, efficiently absorb solar energy, and use that heat to desalinate water through evaporation.
The block itself consists of three layers: the main part is polyethylene foam, which helps it float and acts as a heat insulator. The outside of the foam is wrapped in air-cushioned paper, an absorbent material used in disposable diapers that draws water up to the top surface. The top surface is coated with titanium nitride oxide (TiNO).
“In the solar field, TiNO is a common commercial solar absorbing coating widely used in solar hot water and photovoltaic applications,” explained Chao Chang, lead author of the study. “It has high solar absorption and low thermal emissivity, and can efficiently convert solar energy into thermal energy.”
This unit can be placed in a conventional solar distiller – a transparent plastic container with a sloping roof that captures condensed fresh water and directs it into the container. In trials, the team found that the new solar cell has a solar-to-water conversion efficiency of 46%, a decent step up from the 30-40% we get from single installations of this type.
It is important to note that the device avoids one major mistake – contamination due to the accumulation of salts on the surface, which over time significantly reduces efficiency. During testing, the team found that the salt layer did not form because the pores in the material drain the salt and dump it back into the seawater. Another advantage, according to the team, is that the paper portion of the block can be reused more than 30 times.
Unfortunately, the team does not provide one of the most important pieces of information – just how much freshwater it can produce per unit of time. The new unit outperforms competitors due to its relatively low cost and high efficiency, so the authors hope to find a commercial use for it.