Abstract: In a venturi-shaped wind tunnel, a wind is generated by a wind generating device in the larger end of wind tunnel. Wind thus generated is caused to speed up by the venturi and drives a rotatable wind responsive device in the smaller end of the wind tunnel. The wind responsive device, in turn, drives an alternator which produces an alternating current, preferably at a fixed frequency determined by speed of rotation. The output of the alternator drives a load. The output of the alternator can also be put through a converter and converted to d.c. which drives a variable speed d.c. motor supplying power to the input fan. A monitoring means sensing the air flow may then cause a regulator to adjust the speed of the d.c. motor to maintain alternator speed constant.