This chapter presents the thermal energy storage technologies suitable for low temperature (up to 150 °C) solar thermal applications in buildings. In the first part, insight is provided into recent developments about systems technologies and materials, their classification, limitations, and potential solutions for their application. In the second part, special focus is given on an innovative process using absorption cycles for long-term solar energy storage. A detailed dynamic model of the system has been developed for the simulation in order to evaluate the process performance and to optimize its design. A prototype of the system has also been presented, as well as experimental results in the process charging and discharging modes.