Use of solar energy as integrating source in a dual-purpose power plant

Power plants for electric energy production based solely on solar energy are a very attractive prospect but many physical and technological difficulties still cause low efficiencies and high costs. A combined power plant with a gas and a steam turbine is still the best solution for electric energy production on an industrial scale. In the areas with a shortage of fresh water, power plants are often combined with desalination units in order to produce drinking water from sea water (dual-purpose power plants). In particular, desalination systems based on thermal processes can be easily coupled with combined power plants for electric energy production since they need steam as their primary energy source. This steam can be spilled during the turbine expansion and redirected to the treatment unit. Starting from the consideration that the geographical areas which suffer a water shortage are often those where strong direct normal irradiation is present, the integration of solar energy in a dual-purpose power plant can be very interesting from both the technological and economic points of view. During the day, the collected solar energy can be used to produce steam that can be used in the desalination unit, thereby reducing the spill from the steam turbine and thus increasing the generated electric power. If the solar energy availability is sufficient, the spill from the steam turbine can be fully replaced by the steam produced by the solar plant. Possible solar plant steam surplus can be used to increase drinking water production. This paper investigates the best technical and operational combination of power plant, desalination system and solar plant and demonstrates that some integrated arrangements allow a conversion rate from solar energy to electric energy which proves to be more suitable if compared to photovoltaic systems or hightemperature traditional solar plants