Solar energy is one of the most promising renewable energy sources. Building sector is one of the most suitable candidates for utilizing this energy source because of its abundance. More specifically, solar energy is able to be used for electricity production, as well as for covering the heating and the cooling loads of the buildings. In this chapter, new and innovative ideas about the adoption of solar energy systems in buildings are presented. Simple and low cost solar collectors which can produce heating in low and medium temperatures levels are analyzed. Emphasis is given in the utilization of Phase Change Materials, as well as in the utilization of solar assisted heat pumps. Moreover, innovative passive heating systems, as Trombe wall are presented with detail.