According to the two researchers, the link between the renewable energy industry and renewable energy policies is caused by feedback effects that reinforce policies. Laime Eicke states that "actors who benefit economically from changes in the value chain invest those resources in political processes to promote favourable policies.” Furthermore, the authors looked at the specific fragments of the value chain and suggest that manufacturing and research & development both contribute to a more ambitious renewable energy policy. However, their data also indicates that the effect caused by the manufacturing segment may be higher than the effect caused by R&D. Silvia Weko and Laima Eicke are both scholars at the IASS (Institute for Advanced Sustainability Studies) in Potsdam, as well as members of EIPCC (Effective and Innovative Policymaking in Contested Context), a graduate center of the University of Erfurt. You can find the original paper as well as more information on the publication.