Today, energy needs are increasing rapidly. Since our country imports a large part of its energy resources, it is extremely important to use energy efficiently and protect the environment in order to leave a livable world to future generations. One of the losses in energy transmission is transmission loss. In order to prevent this loss all over the world, "distributed energy production" method should be encouraged. Through combined heat and power systems, we can generate heat and electricity and save energy. Cogeneration systems can generally pay for themselves within 1.5-4 years. The aim of this study is to contribute to science with a broad literature review including the design of combined power systems and the technical and economic evaluation of their most efficient applications. The systems in the literature are investigated and comparisons are made. Hydrogen fuel cell types for domestic applications are detailed and hydrogen is considered to be a logical choice. The effects of design and performance parameters are analysed. This combined power system does not harm the nature; it utilises natural resources such as wind, sun and hydrogen, which can also be obtained by electrolysis of water.