Thermodynamic solar plants

Solar thermal power plants encompass all technologies designed to convert the sun's radiant energy into high-temperature heat, and then to convert that heat into mechanical and electrical energy using a thermodynamic cycle coupled to an electric generator. The first step—capturing solar radiation—relies on optical systems. Non-concentrating systems capture both direct and diffuse components of solar radiation and produce heat at temperatures below 250°C, for use in building heating and cooling or as industrial heat to power thermal processes. This category includes solar towers (or chimneys), which are non-concentrating solar thermal power plants. With this one exception, solar thermal power plants use concentrating systems, which enable heat to be produced at temperatures above 250 °C with excellent thermal efficiencies exceeding 70%. It should be noted, however, that these systems capture only the direct component of solar radiation. The solar heat transferred from the absorber to the heat transfer fluid can be stored temporarily to compensate for cloudy periods, or over periods of several hours to shift usage outside the sunny periods of the day. Hybridization with a fossil fuel or biomass heat source increases the availability of the facilities and ensures a guaranteed heat supply. This heat is converted into electricity through thermodynamic cycles, which are well-established in the power generation industry. Depending on the equipment used and the cycles employed, conversion efficiencies range from 23% to over 50% for combined cycles. Ultimately, the instantaneous solar-to-electricity conversion efficiency ranges from 20% to 30% depending on the size of the plant and the cycle used. On an annual average, the net efficiency of electricity production ranges from 10% to 20% depending on the technology employed. According to estimates by the GEF (Global Environment Facility [16]), the investment cost is estimated at between 2,800 e/kW _e (a 20- – 80-MW _e plant with parabolic trough collectors and a Rankine cycle) and 4,000 e/kW _e (a 40- to 200-MW _e tower plant with a combined cycle), and reaches 14,000 e/kW _e for a decentralized parabolic-Stirling unit of 10 to 25 kW _e . According to the same sources, the cost of electricity produced under favorable conditions – —that is, with solar radiation exceeding 2,000 kWh/(m ² /year) – ranges from 0.16 to 0.24 e/kWh _e for a large power plant and is around 0.30 e/kWh _e ...