Continuously variable transmissions with a torque sensing regulators in waterpumping windmills

One widespread application of wind energy is in waterpumping. Usually windmills are coupled to water pumps, though piston pumps are difficult to match to wind turbines. In the first approximation, the piston pump requires a constant torque to the turbine at all rotational speeds. Conversely, if the turbine were to operate at maximum efficiency levels, it would supply a torque proportional to the square of the wind speed. Hence, the combination of windmill and piston pump would be maximally efficient only for a single wind speed. This paper suggests incorporating a continuously variable transmission (C.V.T.) between the pump and the turbine to enhance the efficiency of windpumpers at different wind speeds. The feasibility of adopting automatically regulated C.V.T.s, which adjust their transmission ratio to the torque without requiring sophisticated regulators or control systems, is also examined since such a solution does not undermine the cost-effectiveness, reliability or simplicity of the system. A mathematical model has been relied on to simulate the operation of a windpumper equipped with a C.V.T. with a torque sensing regulator. The advantages in terms of efficiency and rate of flow of such a solution are demonstrated assuming that a waterpumping system equipped with a C.V.T. is installed in two locations in Somalia. Finally, the paper examines the dynamic behaviour of the system proposed