Here is what I wrote:
I also work in this space, so the headline caught my attention. This is far from the first. Some other evaporation driven engines include:
https://en.wikipedia.org/wiki/Drinking_bird
https://en.wikipedia.org/wiki/Energy_tower_%28downdraft%29
https://en.wikipedia.org/wiki/Barton_evaporation_engine
The solar updraft tower and vortex engine also operate in a similar space, meaning that all of them operate using the temperature difference between ground and tropopause which feeds the water cycle.
It is my personal opinion that evaporation-driven engines (or something quite similar) are the most promising energy source (on this planet). Essentially, they are an alternative source of solar energy which doesn't have the problem of needing the sunlight to be present to work.
The main issues, as with most new energy sources, are efficiency and cost. The Columbia motor costs $5 for 50 microW, or $1x10^5 dollars per watt. You generally want something nearer 1$/watt for primary energy use. The efficiency in terms of water or thermal energy is not stated, but is likely similar to drinking birds, which have a thermal efficiency around 0.01%. The theoretically possible efficiency for the evaporative half of the water cycle is on the order of 12%, so there is a lot of room for improvement.
IIRC a sipping bird is powered by the heat differential caused by cooling of the evaporator. This thing seems to be powered by centre-of-gravity changes caused by motion of hygroscopic material.
I suspect that IRL it would very quickly stop working due to gunk in the water affecting the hygroscopic material, but it's a very neat hack nevertheless.
I wonder if you could build a passive humidifier out of one of these? Float one in a container of (clean) water and attach some fan blades. As it spins, it pushes water into the air. At the very least it'd make a fun executive toy.
The concept of using bacterial spores as a means of producing motion is pretty neat, though it's obviously a long way from being practical. The suggested use case (low power remote floating sensors) seems pretty suitable for solar power, which has the advantage of maturity and no moving parts.
A simple optical sensor could sense rotation, and there's probably some weird meteorological situation or chemical plant process meter that would find a rotating optically detected non powered humidity sensor to be useful.
For chemical process plant work something that measures humidity would be super boring because there's a zillion competing technologies, all mostly unpatented by now. The fun would begin with selective uptake of "weird stuff" non-water substances using the same physical design. Maybe you could detect H2S leaks or hydrocarbon leaks or ...
