The use of solar energy for existing buildings is in an early phase of development and there is a lack of common understanding about its advantages and disadvantages, including, for example thermal performance and cost. This article gives some general aspects about solar energy in building renovation, together with a summary evaluation of 15 case studies, i.e. existing solar renovation projects where the majority of the projects relate to renovation of multifamily buildings in central and northern European climates. The general discussion, as well as the case studies, deal with three major solar renovation concepts: ＇glazed balconies and galleries＇, ＇solar walls＇ and ＇solar collectors＇, basically to meet two major renovation criteria: the need to repair or improve the ＇building envelope＇ and the need to replace or improve ＇heating, ventilation and domestic hot water systems＇. Most of the case studies are judged to be successful as demonstration projects. However, a major conclusion is that most case studies include mixed renovation activities like traditional wall insulation and replacement of windows in combination with one or two solar renovation concepts, which makes it hard to evaluate thermal energy savings and cost-effectiveness related to the solar renovation concept. Experiences concerning the different aspects of renovation, such as the various features employed, the renovation process itself, thermal performance and operational experiences, as well as economics are summarised. The need for further comprehensive efforts is expressed and recommendations concerning design, construction and evaluation of future demonstration projects are discussed, in order to guide future activities in this field.