In one application of this method, one or more water pumps, each powered directly by a windmill, lift water from downstream of a river, stream, or creek to upstream of a dam at which a hydropower plant is installed. The windmill may be of the vertical-axis or horizontal. Upon demand, the lifted water is used to generate electricity utilizing the hydropower plant. An adjustable weir is constructed across the river, stream, or creek downstream the windmill, whose function is to create a reservoir or pool from which water can be pumped and to regulate the flow of water downstream. The adjustable weir can be raised or lowered by means of a jack or jacks that are controlled by a computer. In another application of this invention, one or more water pumps, each powered directly by a windmill is installed at sites having 2 nearby bodies of water, one higher than the other. The bodies of water may be natural or artificial. The water pump lifts water from the low water to the high water, where it is stored as potential energy. Upon demand, the lifted water can be used to generate electricity utilizing a conventional hydropower plant.