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Simple, solar-powered water desalination (2020)

news.mit.edu

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Re: Simple, solar-powered water desalination (2020)

#21

Post by eigart »

crackercrews wrote: post #3

For those curious what the 385% refers to > the team’s demonstration device can achieve an overall efficiency of 385 percent in converting the energy of sunlight into the energy of water evaporation. Honestly I still don't know what that means, or how efficiency can be over 100%.

My understanding: As the water condenses onto the next surface layer in the stack, the solar heat is recycled. This is because the transition from gas to liquid releases heat.

Really clever stuff!

Edit: mixed up evaporate/condense

Re: Simple, solar-powered water desalination (2020)

#23

Post by andromeduck »

hinoki wrote: post #15

It sounds like they figured out how to make the distillation version of a compound steam engine [0]. Like others, I’m confused by the efficiency number. Are they producing 385% more water for the same energy compared to the best single state result? [0] https://en.m.wikipedia.org/wiki/Compound_steam_engine

That's already a thing.

https://en.wikipedia.org/wiki/Multi-stage_flash_distillation

Re: Simple, solar-powered water desalination (2020)

#27

Post by fuzzybear3965 »

OJFord wrote: post #20
crackercrews wrote: post #3

For those curious what the 385% refers to > the team’s demonstration device can achieve an overall efficiency of 385 percent in converting the energy of sunlight into the energy of water evaporation. Honestly I still don't know what that means, or how efficiency can be over 100%.

I'm not even sure what 'the energy of water evaporation' means? Gravitational potential of the mass of water evaporated (and condensed at some height)?

I think they mean latent heat/enthalpy of evaporation.

Re: Simple, solar-powered water desalination (2020)

#28

Post by connorproctor »

sonicggg wrote: post #6

What's the point here? Is electricity even the bottleneck of water desalination? I thought the biggest issue with these plans is the brine. That is the major pollutant, and no amount of solar panels will solve that.

This doesn’t use electricity at all, the “solar power” is heat from the sun causing the water to evaporate. It’s a still, not a filter. According to the article the salt/brine freely flows back into the body of water.

Re: Simple, solar-powered water desalination (2020)

#30

Post by wcoenen »

crackercrews wrote: post #3

For those curious what the 385% refers to > the team’s demonstration device can achieve an overall efficiency of 385 percent in converting the energy of sunlight into the energy of water evaporation. Honestly I still don't know what that means, or how efficiency can be over 100%.

The 100% level refers to a system where all energy goes to heating up water in order to evaporate it, and then letting it cool down to condense it. All the energy that was spent to heat up the water, is lost to the environment in the "cooling down" step.

If some of the heat is instead recovered during condensation to heat up the next batch of water, then you have >100% efficiency.

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