Social opposition to renewable energy (RE) projects has become a significant issue both for the deployment of RE technologies and the social justice of this process. However, the policy tools oriented to address this issue have received little research attention, particularly in the Global South. Thus, this research analyses the effectiveness of the social impact assessment (SIA) in Mexico's RE sector. In 2014 the government of Mexico introduced the SIA in response to the social conflicts around RE projects. The SIA has generated some favorable changes in the sector's social management. Yet, its effectiveness is constrained by diverse issues related to its institutional and regulatory design, government implementation, practices of companies and consultants, and restricted social involvement. Moreover, the sector's socio-technical arrangement (priorities, organization, experience, and policies) strongly influences the performance of SIAs and accounts for the lack of consideration of social aspects in project design and planning. We argue that without a substantial internalization of the social dimension in the priorities, policy, and planning of RE, the SIA would be limited to a problem-fixing role, which would constrain the effective management of social impacts.