This article presents the behavior of an existing system combining solar collectors and heat pumps at large scale (10'000 living m², more than 1'000 m² solar collectors) for space heating and domestic hot water production, focusing on summer period. Ongoing detailed monitoring enables to measure its energy performance. The monitoring results for 2012 show a system SPF of 2.9 (2.6 in winter and 4.4 in summer). The direct solar fraction in summer is lower than 50%, which is low considering the oversizing of the solar collector area for domestic hot water production. The high domestic hot water demand (􀁡50 kWh/m²/yr whereas the usual value is around 20) can partly explain this low value, but other factors should also be considered. The results presented in this article are part of a research project aiming to assess the relevance of the concept of coupling solar thermal and heat pumps in various types of building (especially existing buildings with low efficient thermal envelope).