In the face of uncertainty surrounding the debate about liberalisation of the German energy market and the future of the Renewable Feed in Tariff (REFIT), one wind lobbyist suggests a new system based on quotas of renewables in the supply mix. In this model, utilities "are obliged to supply, say, a minimum of 10% of their sales with renewable energies, but where the REFIT system remains in effect," suggests Uwe Carstensen of Winkra, a wind turbine developer based in Hannover that owns and operates several wind stations. If a utility cannot fulfil its quota, it buys the missing volume from another utility that has green power to spare. Renewable energy is bought at the REFIT rate, and the quotas can be altered each year to take account of market developments. Carstensen is president of the Federal Association of Renewable Energies; he also chairs the German wind station operators organisation, Wirtschaftsverband Windkraftwerke.