A post last year linked a PR about some research into the development of low flow energy systems that exploit "vortex induced vibrations." There's more talk of it now and seems worth another look.

Aluminum cylinders joined to built-in electromagnets form a ladder-shaped device. As flowing currents swirl past a cylinder, the vortexes that form above and below push and pull the cylinders to generate electricity. . .

Flexible plates designed like a fish’s tail could speed up cylinders in very slow-moving water or decrease the cylinder movement, which would help to protect aquatic life. “We may design a tail that’s adjustable and has sensors, but I’m not anywhere near that yet,” Bernitsas said. “Simply, we are not as smart as fish at this point.”

I wonder if there could be applications for wind too? Ungainly wind monstrosities are expensive to manufacture, install and service yet they produce a small fraction of their output potential. Perhaps less obtrusive devices that work in low wind flows would not only be cheaper, but more productive.