The localisation of clean-tech industries allows developing countries to align their economic growth aspirations with efforts to reduce the associated environmental impacts. A key issue in this regard is the development of technological capabilities at local firms in these countries. Although much research has been conducted on this topic, we currently have only limited understanding of how the learning mechanisms that these so-called latecomer firms engage in change as they deepen their capability stocks. In the present paper, we offer insights into this issue by means of a comparative analysis of nine technology-supplying firms in the Thai industry for industrial-scale biogas systems over a period of about twenty years. Our results suggest that there are indeed shifts in the relative importance of different types of learning mechanisms as firms deepen their capabilities. The paper finds that such shifts tend to follow a co-evolutionary pattern involving shifts within and across learning mechanisms that involve different sources of knowledge. Based on our analysis, we provide examples of how decision-makers can adopt targeted interventions for the support of clean-tech firms and industries that are at particular levels of development.