The diffusion of renewable energy technologies (RETs) has been progressing very slowly in global scope, particularly in developing countries where the diffusion challenges for renewable are greater. Among potential actors in the promotion and diffusion of rural-based renewable energy innovations, NGOs and NPOs have been mentioned as promising actors. However, empirical studies that show the role of the actors and the way they can be system builders by diffusing existing technologies have been very rare. This paper discusses the practices of an NGO in Ethiopia (Solar Energy Foundation) and an NPO in Bangladesh (Grameen Shakti) and shows how local technological innovation systems can be built by key actors in the context of developing countries. The study sheds light on the process of system building for accelerated diffusion of RETs in the context of developing countries. Using a theoretical framework, we compared the approach, technology adoption trend (solar home systems diffusion), and common challenges facing both actors in their respective countries. The two empirical cases which are in different geographical contexts provided lessons on the similarities and differences of system building practices and emerging innovation systems for diffusion of RETs in developing countries.