Thermodynamic and exergo-economic analysis of a solar-biomass hybrid power plant for multi-energy generation

Cameroon, is located in the western part of Central Africa, has a good geographical position in terms of the potential of biomass sources and solar energy. However, there are still some regions in Cameroon without access to commercial electricity, especially in the northern part of the country. Using biomass and solar energy sources together can be considered as one of the most suitable options to provide uninterrupted energy supply. Potentials of these sources are sufficient to generate energy for the northern part of Cameroon. The hybridization of energy sources is a promising alternative to increase the conversion efficiency of the power system, constitutes an attractive option which can ensure low cost of energy demand. In this study, solar-biomass hybrid energy systems, which are combinations of three different Concentrating Solar Power (CSP) technologies with biomass-fired (BF) technology, are investigated. Parabolic Trough Collector (PTC), Linear Fresnel Reflector (LFR) and Solar Tower (ST) are selected for solar energy conversion as CSP technologies. For each hybrid system with an installed capacity of 5 MWe and which contains four subsystems, solar and biomass field, power block, heat recovery steam generation (HRSG) and multigeneration energy system using absorption refrigeration and drying systems, are configured and analyzed. Comprehensive economic and thermodynamic analyses in terms of energetic, exergetic and exergoeconomic analyses for each system and its components are conducted to minimize the cost and increase the performance. Initial investment costs required for the hybrid energy systems based on PTC, ST and LFR are obtained to be 38.47 Million USD, 51.47 Million USD and 25.23 million USD, respectively. From the techno-economic evaluations of the hybrid energy systems, levelized cost of electricity values for LFR-BF are found to be the lowest varying from 76.4 to 143.4 USD/MWh. According to the payback period, LFR-BF has a short return on investment with 8.4 years, followed by PTC-BF having 10.62 years while ST-BF has the highest payback period of 14.71 years. Also, LFR-BF seems to be the most profitable investment among three hybrid energy systems based on internal rate of return values for PTC-BF, ST-BF, and LFR-BF which are 13.79%, 12.64%, and 16.49%, respectively. It is found from the advanced exergy analysis of the hybrid energy systems that exergy destruction from the solar field alone (86.3% for PTC-BF, 92.2% for ST-BF and 85.4% for LFR-BF) is responsible for the most of all exergy destructions. For PTC-BF, it is obtained from exergoeconomic analysis that the value of the total cost associated with the avoidable-endogenous exergy destruction of the regenerator 1, the intermediate heat exchanger connected to power block and the steam turbines are 7.33 USD/hour, 4.17 USD/hour and 4.49 USD/hour, respectively. For ST-BF, the value of cost associated with the avoidable–endogenous exergy destruction of the regenerator 1, the volumetric receiver connected to power block and the steam turbines are found to be 3.87 USD/hour, 84.75 USD/hour and 3.94 USD/hour, respectively. For LFR-BF, the value of cost associated with the avoidable–endogenous exergy destruction of regenerator 1, the intermediate heat exchanger connected to power block and steam turbines are calculated as 4.11 USD/hour, 1.76 USD/hour and 2.84 USD/hour, respectively. Total costs associated with avoidable-endogenous exergy destructions for PTC-BF, ST-BF, and LFR-BF are around 21.7%, 26% and 24.5% of the total cost required for system optimization, respectively. In this study, the maximum monthly expenditures required to optimize three hybrid energy systems are also investigated. They are found to be 41553.30 USD for the solar field, 1715.28 USD for the power block and 2997.41 USD for the HRSG in PTC-BF system; 24695.10 USD for the solar field, 1362.57 USD for the power block and 1230.32 USD for the HRSG in ST-BF system, and 18987.90 USD for the solar field, 926.60 USD for the power block and 1218.34 USD for the HRSG in LFR-BF system. The results of the advanced exergy and exergoeconomic analysis reveal that it is essential to recover endogenous-avoidable exergy to improve the overall efficiency of the hybrid energy systems. According to the main findings of the study, it can be said that the hybrid energy system based on LFR presents the best techno-economic results and it is followed by the system based on PTC