The global deployment of renewable energies has taken off and calls for a continuous increase in foreign investments and cooperation, particularly because many states cannot cover the costs and technological requirements of the energy transition on their own. Therefore, there should be policies and legal frameworks in place to protect and thereby promote foreign investments. International Investment Agreements (IIAs) can, ceteris paribus, contribute to this goal. These agreements contain a set of obligations that protect foreign investments against possible discriminatory or arbitrary conduct of the host states. This includes transparency obligations that can help to create a level playing field for national and foreign renewable energy investors. Unfortunately, the concept of transparency, and its inherent implications, has not been clearly defined to date, and its relationship with renewable energy investments is still under investigation. Therefore, it is important to realise the prevailing transparency obligations under IIAs, and the best practices that can better meet the particular requirements of renewable energy investments. Using a qualitative approach, this article intends to pursue this goal by providing an overview of the concept of transparency, exploring its status in the context of fair and equitable treatment (FET), and analysing favourable transparency clauses in the light of renewable energy investment considerations.