The invention provides a fluid-dynamic renewable energy harvesting system which includes fluid-foil means for interfacing with a fluid current such as a water current or wind or both, and which includes energy harvesting means utilizing fluid current driven periodic motion of the fluid-foil means for capturing fluid-dynamic renewable energy and converting it into usable energy in a desired form such as electricity. The invention provides devices, methods and systems for harvesting renewable energy for small-scale, medium-scale and large-scale applications, to provide real and substantial benefits towards efficiently fulfilling energy needs while also more broadly serving humanity and our global environment. The various embodiments of the invention provide energy with zero consumption of fossil fuels and zero emissions of greenhouse gases, and some selectively sited embodiments can beneficially counter global warming induced ice melting.