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The Spanish Royal Decree 661/2007 for the regulation of renewable energy allows operators of power plants to participate directly on the electricity market instead of reverting to flat-rate prices. The premium tariff option motivates operators of renewable energy plants to increasingly act like managers of conventional plants, selling electricity at the liberalized market. Just like a normal market participant, the operator places bids in advance on the day-ahead market and is obliged to fulfill them. Thus, there is the need for operators of renewable energy plants to be able to provide predictable and dispatchable energy in the profitable premium tariff. This legal setting motivates the following analysis on the value of irradiance forecasts for determining optimal operation strategies of solar power plants. The scientific background of this study are ongoing research activities on the use of satellite-based now casting of solar irradiance using cloud motion vector techniques and on data assimilation of aerosols into air quality models as a basis for day-ahead irradiance forecasts. The influence of a schedule based on imperfect forecasts on the daily revenue for a solar thermal power plant is assessed. Three typical weather situations are analyzed: clear-sky, overcast, and aerosol-charged situations. This paper shows the economic potential of the participation at the premium tariff with optimized operation strategies using direct solar irradiance forecasts based on Earth observation techniques.