# How much electricity can be directly generated from air humidity?

There have been some recent papers on harvesting electrical energy from air humidity using nanoengineered materials:

These articles are paywalled, but have some popular science articles, e.g.

and at least one patent application.

Can the theoretical maximum energy harvesting rate be estimated per unit area of the material, and if yes, what is it? I guess this should be calculable from the air humidity, temperature, and pressure, and the latent heat of condensation of water, possibly with some assumptions about air flow over the surfaces. (I assume the energy is coming from condensation which means the device also produces possibly useful liquid water, but I don't immediately see this mentioned in the articles.)

The EU has provided €3M in funding to the CATCHER project for developing humidity-to-electricity conversion with an objective of a power density of ~36 mW/g or 15 - 20 mW/cm$$^2$$, but I don't know if these are theoretical limits or just practical goals.

Clarification Update

Just to be clear, I am asking if there is some bound on the energy harvesting rate similar to how the solar constant sets an upper bound on solar energy, how Carnot's Theorem limits thermal generation (e.g. as discussed in this question about thermoelectric generation), or how wind turbine power is constrained by the Betz Limit. This question is not about how practical the technology is or whether it could compete against wind, hydro, or other power technologies that directly or indirectly also harvest energy from the atmosphere.

• Wasn't taking electricity from humidity the mechanism for John Galt's motor in Atlas Shrugged, or am I mistaken on that? Commented Aug 24, 2023 at 2:23
• @Kyle-Kanos It has been decades since I read Atlas Shrugged, but according to my quick online search his engine was powered by "atmospheric electricity". I would have guessed that referred to the vertical atmospheric voltage gradient and was probably inspired by Nikola Tesla's ideas. Commented Aug 24, 2023 at 2:52
• Oh right, it was static electricity in the atmosphere. I was close! Commented Aug 24, 2023 at 12:29
• They didn't say how much current per area of material, just a voltage, so we can't estimate what sort of size of device could produce what sort of power. We will have to do experiments and build our own devices to figure it out. Commented Oct 2, 2023 at 19:23
• @wordsforthewise The Yao Lab whose research triggered the recent media interest would likely know of any US efforts. This article mentions one startup in Europe that produces 10 mW at 1.5 V from a 4 cm diameter disk, i.e. 1 mW/cm^2. Commented Oct 3, 2023 at 14:44

You can find the latent energy required to condense 1 mol of water from vapor to gas, find the mols of water in a $$\rm cm^3$$ of air as a function of temperature and relative humidity, and then get the maximum energy per $$\rm cm^3$$ of air a X temperature and Y humidity. If you are simply looking for this maximum possible harvesting value, it should be relatively simple.