The initial investment for hydro is high to build,the dam/reservior and its power plant that may vary from 250 million dollars up to 1.25 billion dollars. the positive thing about this though is the fact that it will run about 40 to 50 years, but it also coct alot to build even though it doesnt take that long to come up with a design to build it. comparing to the cost of electricity with the initail investment the pay back period is short.