EU law promotes the use of renewable energy sources (RES) in Member States as a tool for sustainable development. Directive 2009/28/CE is the secondary legislation tool focused at promoting investments in RES technology and production. At the state level, legal instruments to promote the use of renewable energy include, renewable energy obligations, feed-in tariffs (FITs), green certificates, mandatory purchase prices for energy distribution enterprises. States may revoke such measures or reduce the support even significantly hindering, as a consequence, the ongoing investments.The question of who shall bear the costs of such measures may depend on the forum of resolution of the dispute. Sate measures adversely affecting investments may be challenged by private actors in several fora, at the State, EU and supra-national level. The paper investigates different protection options for investors following changes in law affecting renewable energy support schemes in Europe. The potential remedies are analyzed under both EU law and ECT.