Environment

"Solar umbrellas" could reduce the blight of evaporation ponds

"Solar umbrellas" could reduce...
Salt evaporation ponds in Secovlje, Slovenia
Salt evaporation ponds in Secovlje, Slovenia
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Evaporation ponds south of the Dead Sea taken from a Space Shuttle mission in 1989
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Evaporation ponds south of the Dead Sea taken from a Space Shuttle mission in 1989
This illustration shows the principle behind the solar umbrella
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This illustration shows the principle behind the solar umbrella
Salt evaporation ponds in Secovlje, Slovenia
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Salt evaporation ponds in Secovlje, Slovenia

Scientists at Berkeley Lab have developed a sort of “solar umbrella” which could radically reduce the amount of land needed for industrial evaporation ponds.

Evaporation ponds are a cheap way to deal with waste water contaminated by industrial processes in various industries, including power plants, desalination plants as well as the oil, gas and lithium industries. The idea behind evaporation ponds is to create shallow expanses of waste water which is naturally evaporated by sunlight, leaving behind solid waste which can be more easily disposed of.

The largest ponds can be the equivalent of hundreds of football fields in area, sometimes laid out one next to the other forming giant mosaics occupying vast areas of land.

Evaporation ponds south of the Dead Sea taken from a Space Shuttle mission in 1989
Evaporation ponds south of the Dead Sea taken from a Space Shuttle mission in 1989

As well as the direct impact they have on the natural environment, the high concentrations of salt and elements such as selenium can pose a direct risk to birds, which can mistake the ponds for natural wetlands.

An experimental prototype of the scientists’ umbrella has seen evaporation rates more than 100 percent greater than normal, which could mean that evaporation ponds can one day be significantly reduced in size.

The umbrella works on the principle that water is much better at absorbing solar radiation in infra-red wavelengths. Whereas normal sunlight will gradually heat the whole depth of the water, infra-red intensely heats only the surface, down to a depth of a mere 100 micrometers or so.

This illustration shows the principle behind the solar umbrella
This illustration shows the principle behind the solar umbrella

By building a canopy that sits a foot above the water, the incoming sunlight is converted from wavelengths of 400 to 1,500 nanometers to 3,000 nanometers or more, and the rate of evaporation increases.

This is not the first attempt to harness solar energy to improve evaporation ponds, but to date, most proposals have involved floating sunlight-absorbing materials in the ponds themselves. According to the Berkelely Lab researchers, these have the shortcoming of becoming clogged up with contaminants so that, as time passes, their performance drops off a cliff.

With more work, the researchers think their concept has the potential to increase overall evaporation by 160 percent. They intend to do economic analyses of the technology for both lithium extraction and desalination plants. They also hope to reduce costs by making the umbrella out of an inexpensive polymer.

The research was led by Akanksha Menon and Ravi Prasher of Berkeley Lab, and was published this week in the journal Nature Sustainability.

Source: Berkeley Lab

4 comments
Douglas Rogers
This is the opposite of what you would do if you were worried about global warming.
Bruce Anderson
Evaporation ponds are pretty big. Scaling up this technology will be quite the challenge.
Chrys Alice Anderson
PLEASE ask these guys to also shape the polymer cover to capture and re-condense the separated water vapour - given the humongous GHG contribution of that vapour if released to the atmosphere (per Douglas Rogers comment!)... - should be relatively simple.
Brian M
Would have thought a way of removing the air saturated with water vapour was required as you have effectively covered the pond reducing air circulation. Plus collecting and condensing the water could be useful as a water source, especial for those in arid areas?