A turbine is provided having one or more vanes joined to respective balloons. Compressed or pumped gas entering the turbine is selectively directed toward desired balloons by selectively activating one or more input valves, in order to selectively inflate the balloons. Simultaneously, gas inside the balloons is selectively directed away from the balloons and out of the turbine by selectively activating one or more output valves, in order to selectively deflate the balloons. The turbine is configured for being at least partially submerged in a liquid. The selective inflation of the balloons generates buoyancy which pushes the balloons upward, thereby causing the turbine to rotate. The selective deflation of the balloons decreases buoyancy which may counter the turbine's rotation. The turbine's rotation can be converted to a desired form of energy via a suitable energy converter.

The system includes a support structure with upstream and downstream pulleys rotatably supported thereby and with cables following circuits around each of the upstream and downstream pulleys. Prime movers, such as in the form of sail members, are attached to the cable. These prime movers have surfaces which are more perpendicular to the flowing water when on a downstream leg of the cable circuit than when on an upstream leg thereof. The prime movers are configured to rotate as they pass about the downstream pulley and upstream pulley to optimize their orientation to minimize drag when following the upstream leg of the circuit and to maximize surface area against which the flowing water acts when following the downstream leg of the cable circuit. Power is outputted from the system through action of the cable upon a power output such as an electric generator coupled to one of the pulleys.

A water-driven turbine has an elongated endless conveyor with down and up streaming straightaways connected by travel-reversing turns. Paddles mounted on the conveyor present high resistance to waterflow on the downstream straightaway and low resistance to waterflow or the atmosphere on the upstream straightaway, the differential allowing the flow of water to continuously drive the conveyor which is connected to a power take-off shaft facilitating connection to a variety of energy-harnessing systems. The turbine can be towed, self-driven or mooring line manipulated to a flow site and is operable in unidirectional flows such as rivers and reversing flows such as tides at depths from surface to bottom. The paddles can be mounted or changed on shore, at the flow site and anywhere in between. The turbine is efficient in low and high velocity water flow, not easily damaged by floating debris, cavitation free and fish, mammal and environmentally friendly.