Energy suppliers were forced, by German law, to buy energy from renewable energy producers in Germany at a minimum price that was considerably higher than the cost of buying from non-renewable energy producers. It was acknowledged by ECJ and AG that this was contrary to article 28 (as stating that a certain proportion of energy must be bought from national producers reduces the scope for imports), and the real question was whether a defence under article 30 could be made out. ECJ held that the desire to promote renewable energy was was a defence under article 30. This is because article 6 EC says that environmental protection requirements must be integrated into the definition and implementation of EU policies, and makes environmental protection a general principle of EU law.
AG Jacobs (more radical line than the court): There is an unwritten exception to article 28 (de facto extending art 30) that discriminatory measures may be used for environmental protection