The use of compliant surfaces for harvesting energy from water streams

The possibility for hydrokinetic energy harvesting from small water streams by using compliant surfaces is considered. The basis of the proposed idea is the deliberate bifurcation of a water stream into two streams separated by a compliant or membrane surface keeping an equalized static pressure in both sides but, however, with a relative velocity between both channels. Then, owing to this relative velocity of the water stream Taylor instabilities appear which set in oscillatory motion the membrane. This motion can be converted into a small electrical output power. Utilizing a linearized flow theory an analytical expression for the attainable power as function of several parameters was derived. Actual experimental investigations were undertaken which show a good agreement with the theoretical predictions. It was found that for a water stream with velocity around 2 m/s an output power around 30 mW/cm 2 of area of the membrane is attainable. Because large areas can be covered inexpensively by the use of membranes, the concept is worthy to be considered for hydropower harvesting in water flows which are not suitable to be turbined either because a reduced pressure or little depth which prevents the use of turbines. Additional R&D is required in order to arrive at a reliable practical and commercial design.