Building-Integrated (BI) solar thermal are systems which are integrated into the building, they are a new tendency in the building sector and they provide multiple advantages in comparison with the Building-Added (BA) solar thermal configurations. The present investigation is a critical review about Life Cycle Analysis (LCA) studies of solar systems. Emphasis is given on the BI solar thermal installations while studies about BA configurations as well as about solar systems which produce electrical (or electrical/thermal) energy are also presented in order to have a more complete overview of the current literature. The influence of the BI solar thermal systems on building environmental profile is also examined. Critical issues such as ongoing standardization and environmental indicators are discussed. The results reveal that there is a gap in the field of LCA about real BI solar thermal (and solar thermal/electrical) installations. Thus, there is a need for more LCA studies which examine the BI solar thermal system itself as well as for studies which examine the solar system in conjunction with the building. Active systems which could provide energy for the building would be interesting to be investigated. Concentrating solar systems and alternative Photovoltaic cell technologies with low environmental impact could be also examined. Finally, investigations about the influence of the BI solar thermal systems on building life-cycle performance could also provide useful information for the design of future solar buildings in the frame of a more sustainable built environment.