Within a strong tradition of active and constructive pedagogy, a major concern for education is to help the younger generations become familiar with knowledge of science and technology in formal and informal settings. A theoretical framework regarding informal learning and agency in a sociocultural perspective is proposed to interpret the activities and their consequences. We try to demonstrate that a "photovoltaic" informal setting, organised out-of-school and oriented towards building a personal project, can help young people to discover an exciting world of "bricolage" and to better understand solar technologies. Children (8 to 13 y.o.) participated in engineering activities offered in a summer holiday play-scheme. The activities were organised by experts in photovoltaic research and development, and offered the possibility of building a personalised solar toy. We suggest that this informal context of activity may be an opportunity for children to develop a sense on engineering activities, and to develop meaningful representations and conceptions of photovoltaic technology. Interviews and observations allowed us to analyse children’s involvement and learning.