Three main issues which mankind nowadays concerned with are environment, energy and poverty. These three factors correlate very well and influence each other. Change in world energy is going to be faster and fundamental than most people can realize. Developing counties and countries in transitions faced this problem in a crude way. Using the well-developed methodology for calculating the price of energy from renewable sources, this book highlights the need for using Sun’s energy in the most primitive way-water heating. An economic analysis of solar water heating , beginning with a description of the technology, covering the factors contributing to the cost effectiveness, applications, economic criteria is done and ending with a case study. Furthermore, dramatic overgrowth of energy price can be easily taken into account to calculate cost-effectiveness of nowadays situation. A general policy for successful introduction of solar water heating systems is given.