Technical analysis of a solar-aided thermal power plant

Turkey, especially in recent years, in electricity production aims to increase the use of domestic coal and renewable energy sources. Greater use of coal in electricity generation will cause increase of emissions of harmful to the environment. Renewable energy sources can be used to reduce these problems caused by coal. In this study, the thermodynamic and economic analysis of the conversion of an existing coal-fired thermal power plant to a solar-aided hybrid power plant was conducted. The basic plants are Yatağan and Çan Thermal Power Plants. At first in this study, the size of the solar field is optimized. Feed water and number of modules were taken as optimization parameters. When optimization is done, it is considered that there is no power increase in the hybrid power plant, only fuel saving. The boundary condition of the optimization is the value of the solar field which will make zero the extraction steam flow for the feed water preheaters. As a design condition for a solar-aided hybrid power plant, it is assumed that the longest daytime in the northern hemisphere is 21 June, at which time the sun is at its highest point 13.00, with a radiation value of 900 W/m2 and the plant operates under 100% load conditions. Specific dates (21 March, 21 June and 21 December), time, solar radiation value, solar field and load factor are taken as parameters. According to the parameters considered, energy and exergy efficiency of the hybrid power plant and the specific fuel consumption of the hybrid power plant was calculated and the changes according to the reference plants were examined. Then, at 100%, 75% and 50% load conditions, firstly annual fuel savings was calculated then annual carbon dioxide emission reduction was calculated based on annual fuel savings. Lastly, for economic calculations, the emission, solar and YEKDEM electricity unit prices have been taken as parameters and the payback times of the investments have been examined. As a result of the thermodynamic analysis, it has been found that for both power plants, it is the most feasible solution to place the solar field parallel to all of the high-pressure preheaters. In the scenario where the solar field is installed parallel to all of the high-pressure preheaters, annual fuel saving reached its highest value by taking 16.513,3 t/year for Yatağan Thermal Power Plant and 7,003,7 t/year for Çan Thermal Power Plant. For these scenarios, annual fuel savings and annual emission reductions were achieved at 0.95% at Yatağan Thermal Power Plant and 0.61% at Çan Thermal Power Plant. In the design conditions, the annual thermal efficiency of the Yatağan Thermal Power Plant decreased by 8,9% and Çan Thermal Power Plant by 7,2% in the scenario where annual fuel saving is the highest. Even for the best scenarios, seven-year payback time could be achieved if the unit price of the solar field drops to 138,9 €/m2 for Yatağan Thermal Power Plant and 127,1 €/m2 for Çan Thermal Power Plant. If the electricity unit price of YEKDEM is 0,24 €/kWh for the Yatağan Thermal Power Plant and 0,26 €/kWh for the Çan Thermal Power Plant, the same seven-year payback time can be provided. As a result, in the coming years from a financially point of this hybrid system to be implemented in Turkey it has been shown to be much more economical.