Siward Zomer serves as the chairman of Energie Samen, the sector cooperative of energy cooperatives, and as the secretary of the European federation of Energy Cooperatives REScoop.eu. Additionally, he holds a position on the board of the NVDE. He is responsible for advocating for community energy initiatives both in the Netherlands and across Europe. Previously, Siward held the position of chairman at De Windvogel and played a pivotal role in the development of several community-owned wind parks. In his free time, he is involved as a board member of a local energy cooperatives in Amsterdam, namely De Groene Hub (Gaasperdam).