I have just received a Gizmag e-mail telling me about, among other things, Could humidity power join the list of renewable energy sources ?
It tells the story of Dr Ozgur Sahin of Columbia University and his discovery that tiny bacteria coated silicon "planks" reacted to changes in humidity. Before he got a chance to examine the planks under a microscope, he could see the planks visibly bend. The force exerted was one thousand times that of a human muscle. What was happening was that Bacillus subtilis was drying up to a husk when it was very dry which can occur naturally, and then coming back to life when water is restored to the atmosphere. He realised that he had come across a new source of energy harvesting.
The story was presumably timed to coincide with the electronic publication (for paying subscribers) on the 26 January 2014 of a "letter" on the discovery in Nature nanotechnology, which is summarised at Bacillus spores as building blocks for stimuli-responsive materials and nanogenerators. Sahin was joined by three other authors in writing the paper.
Out of curiosity I looked and found that a World patent application had been published as long ago as May 2012, Bacterial spore based energy system, by Sahin on behalf of Harvard and, unusually, Sahin himself as co-applicants. The specification contains 28 pages of text on the concept. And all free to look at.
Normally these "World applications" are coded A1 and have a search report listing what has been done before. This A2 was published without a search report, but the A3 with a list of background references only, not judged to be similar, was published as WO 2012071426 A3. The 5 patent documents it refers to can be seen on this list.
The problem presumably will be scaling up the idea to produce sizeable amounts of power. This will include genetic engineering to make bacteria which react even better to the humidity changes.