In the previous decades, people raised the awareness of the shortage of fossil fuel in the coming forty to fifty years. Besides, the reduction of CO2 emission is paid attention. Among the renewable energies, solar energy has the highest potential to be the main energy source in the future to solve the mentioned problems.
In the last few ten years, the technologies of solar energy were improved and used more widely as an energy source. The solar energy is used in several different ways. It can be used as heat energy for water heating or space heating. The solar thermal energy can be used with active or passive design. There are direct and indirect designs regardless the active or passive energy system. The efficient and the cost effectiveness are according to the designs of the systems. The places and the climate of the buildings where they locate are the main considerations of the system design. With understanding more about the differences of the existing solar energy systems, they can be applied in more efficient, cost effective and environmental friendly.
Regardless the dimension of the system, solar energy is the trend of the energy source for heating and electric power. It is not only used in building, it can also used for producing hydrogen fuel cells which will be using in transportation.