Renewable Energy Sources (RES) offer a key transformative potential from a social point of view due to their modularity and capacity to generate energy at local level, allowing for the development of democratic and participative bottom-up initiatives. Spanish RES cooperatives, unlike other European countries, are few in number. Here, we review their development by applying the Multi-Level Perspective approach. Spanish RES cooperatives have recently come up against a hostile regulatory and economic context, which has induced specific organizational and operating structures such as the application of innovative participation methods and investment tools. Spanish RES cooperatives regularly collaborate in sharing learning processes and experiences, having also demonstrated their capacity to spread new ideas at both social and political levels. However, despite their growth and territorial spread over the last few years, RES cooperatives still have a minor presence in the Spanish energy system. Although some internal factors may limit their potential as an active instrument towards the transition to RES in the country, the regime's resistance is found to be the main barrier. This paper concludes with some recommendations for policy makers and RES cooperatives to enhance its potential role in the forthcoming energy transition process.