> 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%.
A heat pump is another common example with efficiency numbers in the same ballpark. With a heat pump, the heat is being moved from outside to inside (or vice versa for air conditioning and refrigerators). In that case, it requires, for example, 1kW of electricity input to move 3.85kW of heat.
See https://en.wikipedia.org/wiki/Coefficient_of_performance
I lost it when one of the excuses was, 3 weeks later “oh, I can’t meet for lunch on July 29th, I have to go to my mother’s funeral”
If some of the heat is instead recovered during condensation to heat up the next batch of water, then you have >100% efficiency.
As someone else already pointed out, this would be called Coefficient of Performance. Efficiency is clearly defined and cannot exceed 100% without breaking laws of physics. Call it "3.85 times more efficient than before" or something along those lines and it won't sound like a free energy claim.
the [..] device can achieve an overall efficiency of 385 percent in converting the energy of sunlight into the energy of water evaporation.
it seems quite clear how the 3.85 ratio is obtained
No it wouldn't. The equivalent for panels would be like... you want to run some number of watts through a diode, and you're using solar panels to collect this power. The diode happens to give off waste light. By aiming this light at your panels, you can recapture most of it back into electricity, and reuse it 2.85 more times.
Can't it be like the reverse of a rocket engine where they use regenerative cooling from the fuel to cool the rocket nozzle, but just in reverse.
Or like they way my grandpa was doing moonshine -- the alcohol vapors pass through a serpentine in a water tank, condense, at the end you obtain alcohol, the water in the tank gets warmer -- instead, heat water coming from the water cooling tank that is preheated by the vapors of water that is condensing in the serpentine pipe.
Really clever stuff!
Edit: mixed up evaporate/condense
At 5ATM water condenses at a higher temperature than it boils at 4ATM.
[0] https://pubs.rsc.org/en/content/articlehtml/2020/ee/c9ee0412...
It's basically vapor produced at the measured average temperature divided by energy input.
> Theoretically, with more desalination stages and further optimization, such systems could reach overall efficiency levels as high as 700 or 800 percent, Zhang says.
edit: deep as in practically having unlimited heat capacity and the heat conductivity of water.
They explain it in their article[1]:
"the solar-to-vapor conversion efficiency, defined as the ratio of total vaporization enthalpy to total solar energy input, for most previous studies has been limited to below 100% as the vaporization enthalpy is lost to the ambient environment."
[1] https://pubs.rsc.org/en/content/articlelanding/2020/ee/c9ee0...
The energy efficiency of anything cannot exceed 100% (until I missed something groundbreaking in physics).
Look up heat pumps. You can make things hotter by moving heat than you could by directly heating it by burning fuel.
Which is to say this is click bait, because saying it has a COP of 3.85 isn’t anywhere near as sexy, whilst being technically more accurate.