Investigation of concentrating solar-biomass-fired power technologies based on advanced exergy, exergoeconomic and exergoenvironmental analyses

ABSTRACT In this study, hybrid renewable power systems (HRPS) based on biomass-fired (BF) and concentrating solar power (CSP) technologies are investigated. Parabolic trough collector (PTC), linear Fresnel reflector (LFR) and solar tower (ST) as CSP technologies are considered. This study aims to determine and compare exergoeconomic and exergoenvironmental factors, as well as and the relative cost and environmental impact differences of three proposed HRPS options for the district of Faro in the province of Garoua, Cameroon. Also, advanced exergy destruction expressions are used. We found the optimized exergoeconomic and exergoenvironmental factors for the subsystems of HRPS to be between 0.04–0.98 and 0.05–0.98, respectively. They have the highest values for the drying system (DS), and the lowest values for the solar-biomass field (SF+BF). The relative cost and environmental impact differences for the subsystems of HRPS are in the ranges of 0.07–0.79 and 0.28–0.96, respectively. They have the highest values for the DS, and the lowest values for the power block (PB). According to the levelized exergoeconomic/exergoenvironmental performances, PTC – BF presents the worst results before the optimization. ST – BF shows the best exergoeconomic and exergoenvironmental performance in the optimization process. The results of the sensitivity and optimization analyses reveal that it is essential to conduct eco-indicator and advanced exergy analyses to avoid high environmental impact points and specific exergy destructions.


Introduction
The use of hybrid renewable power systems (HRPS) instead of conventional thermal power plants based on fossil fuels can contribute to reducing considerably the amount of CO 2 emissions during energy production.Recent studies increasingly focus on the optimal hybrid combination of concentrating solar power and biomass-fired analyses of these hybrid solar-biomass power systems for multipurpose energy generation.In addition, in the past few decades, research on HRPS has gained more interest due to global warming problems, the necessity of innovative solutions for energy efficient processes in thermal power plants, and the global increase in energy needs.Despite a rapid increase in studies of HRPS, few solar-biomass hybrid power system projects have been realized around the world.Several studies have been done to improve such systems.Seyam, Dincer, and Agelin-Chaab (2020) developed 130 MWe power plant based concentrating solar power (CSP) with the aim to produce a heating load of 248 MWt for desalination and fresh water.The combined power plant integrated the following subsystems: solar field, power block, desalination unit, electrolyzer unit, and hydrogen liquefaction unit.The economic analysis led to a daily liquefied-hydrogen production of 355 tons with a specific energy consumption of 5.24 kWh/kg-LH 2 .The overall energy and exergy efficiency were found to be 88.12% and 23.05%, respectively.Similarly, Akrami, Ameri, and Rocco (2020) conducted a comparative analysis of an integrated biomass-fueled power system (BFPS) based on thermodynamic and exergoeconomic factors.The authors studied two scenarios of a BFPS, which included a Molten Carbonate Fuel Cell (MCFC), downdraft gasifier, power block (combined power cycles), and cryogenic separation unit.A sensitive analysis was developed to monitor key parameters such as gas-turbine inlet temperature, carbon ratio, CO 2 emission, and fuel consumption in order to carry out the exergoeconomic factors of the BFPS subsystems, which are 0.81-0.87for MCFC, and 0.01-0.04for steam Rankine cycle (SRC) condenser.Alibaba et al. (2020) did an assessment of a hybrid geothermal-solar power plant based on exergoeconomic and exergoenvironmental analysis.The authors found that the highest exergoenvironmental rate belonged to the solar power plant, while its environmental destruction rate was minimized due to the use of solar as fuel.Also, an exergoeconomic analysis and a multicriteria optimization method based on a genetic algorithm was conducted by Feili et al. (2020) to evaluate the performance of a hybrid power system using exhaust gas from a marine engine to generate freshwater and power.They computed specific thermodynamic and exergoeconomic metrics.Nathan et al. (2018) reviewed the hybridization options of concentrating solar power with biomass combustion systems.They concluded that the hybridization of the solar-fossil fuel system had a potential low-cost carbon-neutral energy production in the long term.They found that the hybrid solar receiver-combustor offered up to 17% reduction in levelized cost of energy (LCOE), together with a reduction in net fuel consumption by up to 40%, relative to an equivalent hybrid from stand-alone components.They pointed out that hybridization technology had potential to decrease carbon-negative energy, which could lead to a lower energy cost.Ghorbani et al. (2020) investigated the effects of operating conditions such as process performance on a 260 MW integrated system for a multigeneration-based solar collector and on natural gas containing various units such as an air separation unit, Fischer -Tropsch synthesis unit, steam and power generation plant.The authors found that the solar collectors and heat exchangers were responsible for 61% of the total exergy destruction.The economic analysis led to a return period of 2.18 years and to a prime cost of product (liquid fuel) estimated at 444 USD/m 3 .Similarly, Selimli and Eljetlawi (2020) conducted an experimental study of an energy recovery system to determine its energy consumption and economic metrics such as amount of energy saving, payback period and saving rates.Sahoo et al. (2018) presented a thermoeconomic and optimization analysis of a multigenerational hybrid power system using solar-biomass resources.The optimization was performed using thermodynamic laws and economic data to carry out specific parameters of technical criteria.The authors concluded that the analyzed hybrid system had energy and exergy efficiency of 49.85% and 20.94%, respectively.Pirmohamadi et al. (2021) assessed a hybrid power system integrating a combined heat and power (CHP) system standing with combined power cycles which included a closed Brayton -Joule, Kalina and heat pump cycles.The assessment consisted of a thermoeconomic analysis to determine the first and second thermodynamic efficiencies and related costs.The authors found that under operating conditions, energy and exergetic efficiency of the studied HRPS were 34% and 62%, respectively.
In previously published research, the authors conducted advanced thermoeconomic assessment and comparative analysis of HRPS-based solar-biomass technologies (Biboum and Yilanci 2020;Biboum, Yilanci, and Mouangue 2023).Therefore, HRPS needs to be assessed separately considering each subsystem and environmental factors.Our primary motivation in this study is to compare alternative scenarios for an HRPS with solar-biomass field (SF+BF), power block (PB), heat recovery steam generation (HRSG), refrigeration cycle (RC), and drying system (DS).Also, we conducted a sensitivity analysis using the most relevant exergoeconomic/environmental metrics on the operative conditions, leading us to determine possible strategies for design improvements.Our objective is to show the impact of optimized thermoeconomic/environmental factors, and relative cost/environmental impact differences using specific exergy destruction forms, environmental impact points of integrated subsystems, and to highlight the effects of factors on the computed financial findings.We contribute to the selection process of HRPS by highlighting such key metrics.

System description
Cameroon has agricultural products with the potential to generate thermal energy considering their thermophysical properties.The biomass potential of agricultural waste in Cameroon is estimated to be 576.5 MWe (Biboum and Yilanci 2020).Our study focuses on the use of maize/sorghum waste mixture (50:50) as biomass feedstock for the power capacity of 5 MWe.
The study is conducted in the district of Faro, province of Garoua, with the coordinates of 8° 29'0'" North, 13° 15'0"' East.Annual solar irradiation is about 2140 kWh/m 2 (Biboum and Yilanci 2020).The region has a significant agricultural potential due to pastoral activity and a large amount of cereal production, especially maize, sorghum and cotton.The proposed hybrid solar-biomass-fired power system is a kind of cooling, heating and power generation system.It is considered with three scenarios based on parabolic trough collector (PTC), linear Fresnel reflector (LFR), and solar tower (ST) technologies connected to the BF system.For each scenario, input and output energy, and exergy of subsystems have been assessed in the previous study (Sargent and Lundy LLC Consulting Group 2013;Biboum, Yilanci and Mouangue 2023).These values are displayed in Figure 1.The networks of working and heat transfer fluid used in each scenario are highlighted to evaluate the type of steam generation process (indirect/direct steam generation).The hybrid system can be divided into three major subsystems: a solar-biomass field, cooling and heating systems, and a power block system which integrates the HRSG subsystem.

Environmental analysis
The environmental approach in the current study takes into consideration CO 2 emissions, quality and quantity of fuels consumed, and fuel costs related to the duty-cycle operation, by using parameters such as brake-specific fuel consumption (BSFC), carbon tax (CERTAX), fuel cost per mass flow rate (C f/m ) and exergy production ( _ E P ).Brake-specific fuel consumption can be expressed as follows (Al-Hamed and Dincer 2020): The following expressions are used to determine the CO 2 emissions and fuel costs per duty-cycle operation: Table 1 presents the key parameters of the hybrid power systems.

Economic analysis
The conventional economic analysis uses the cost balance equation as presented below for the overall system cost operating at steady-state (Biboum and Yilanci 2020;Petrakopoulou et al. 2011Petrakopoulou et al. , 2011;;Petrakopoulou, Tsatsaronis, and Morosuk 2012).

Exergoeconomic analysis
The relative cost difference r k for the k th component is defined by the equation below (Pirmohamadi et al. 2021): The cost optimization of the component leads to a reduction in the relative cost difference rather than reducing the cost per exergy unit.To do this, Eq. ( 6) above becomes (Pirmohamadi et The exergoeconomic factor assesses the performance of component, and can be expressed as (Pirmohamadi et al. 2021;Tsatsaronis and Morosuk 2010;Tsatsaronis, Kelly, and Morosuk 2006;Tsatsaronis, Morosuk, and Kelly 2006):

Exergoenvironmental analysis
The overall environmental impact rate refers to its life cycle, which considers the manufacturing and installation process, operation and maintenance conditions, and disposal of each component, as shown below (Al-Hamed and Dincer 2020; Alibaba et al. 2020;Naeimi, Yazdi, and Salehi 2019): The exergoenvironmental factor (f � k ), and the relative environmental impact differences (r � k andr � 0 k ) highlight the environmental improvement which can be realized on each component and expressed using equations (Al-Hamed and Dincer 2020; Alibaba et al. 2020;Naeimi, Yazdi, and Salehi 2019).

Advanced exergo -economic/environmental analysis
The optimized relative cost/environmental impact difference and exergo-economic/environmental factor for the k th component are grouped in Table 3.

Results and discussion
Table 4 presents the amount of Therminol VP-1 used, LCOE and quantity of CO 2 produced per kWh according to concentrating solar power technologies and specific criteria.As seen in Figure 2, the ranges of LCOE are between 141.9-146.2USD/MWh, 189.2-252.6USD/MWh, and 220.7-231.3USD/MWh for LFR-BF, PTC-BF, and ST-BF, respectively.Their average levelized costs were estimated as follows: 143.4 USD/MWh, 214.2 USD/MWh, and 226.2 USD/MWh for the LFR-BF, PTC-BF and ST-BF, respectively.The LFR-BF power system achieves a payback return of 8.40 years, which is less than others by more than 2.20 and 6.30 years for the PTC-BF and ST-BF, respectively.The comparative analysis of LCOE calculation of hybrid power plants highlights specific periods of the systems' lifetimes which need to be considered for eventual external subvention and their impact on cumulative cost savings calculation.
The economic, exergoeconomic and exergoenvironmental key findings of the studied HRPS are given in the supplementary file.The financial, and exergo-economic metrics for cost data and evaluation models were taken from (Vogel and Kalb 2010;Sargent and Lundy LLC Consulting Group 2013).The levelized costs of electricity of the studied HRPS are between 141.9 and 252.6 USD/MWh for the period of the power system life.The advanced exergy analysis of the subsystems leads to the determination of optimized exergy destruction (E 0 D , and E 00 D ).As seen in Figure 3, the solar-biomass field (SF+BF) of the LFR-BF, PTC-BF, and ST-BF systems has the highest value of the optimized exergy efficiency for an optimization processes range, expressed as follows: 94.43% for [7.65-13.79],91.06% for [12.67-16.27], and 97.37% for [13.96-24.88]as shown in Figure 3a-c, respectively.The solar-biomass subsystem has the highest intrinsic optimization value followed by the refrigeration cycle, HRSG, drying system and power block.
Figure 4a represents the environmental impact point share of the PTC-BF and LFR-BF subsystems.As seen in the figure, the combination of a solar-biomass field and power block (including heat transfer fluids used) has more than 75% of the overall environmental impact points.Figure 4b represents the environmental impact point share of the ST-BF subsystems where the combination of the solar-biomass field and power block totals less than 65%.
Figures 5a-c present the main results obtained from the exergoeconomic modeling and analysis for the CSP and biomass-fired hybrid power system.The relative cost difference and exergoeconomic factor of integrated subsystems are key parameters of the study, which reveals the influence of costs, such as the cost rate of exergy destruction and the total cost rate of the subsystem.The highest exergoeconomic factor was for DS in PTC-BF and LFR-BF power systems (Figure 5a,b), and for HRSG in the ST-BF power system (Figure 5c).It becomes crucial to pay more attention to subsystems having high relative cost difference r k such as solar and BF, PB and DS in HRPS (Figure 5a-c).
Figure 6 presents the cumulative exergoeconomic key performance (f k , r k ), which highlights the efficiencies of some subsystems, as indicated by the below-mentioned data.The r k value's decrease can be observed in the solar-biomass field subsystems of the HRPS as follows: 0.99-0.53for ST-BF, 0.72-0.38 for PTC-BF, and 0.62-0.22 for LFR-BF.Also, the highest f k increase is identified in the HRSG and RC subsystems as 0.64-0.75 and 0.22-0.26,0.48-0.59and 0.47-0.64,0.68-0.75 and 0.21-0.41for ST-BF, LFR-BF, and PTC-BF.The optimized exergoeconomic performance, r k , and f k, of the overall power systems is found as follows: 1.67-3.05and 2.87-3.05,1.68-1.35and 2.40-2.72,2.47-1.10 and 1.46-2.06for ST-BF, LFR-BF, and PTC-BF, respectively.The PTC-BF system presents the worst exergoeconomic performance before optimization; the relative cost difference rate (0.495) is higher than the exergoeconomic factor (0.294).
The ST-BF presents the best exergoeconomic performance (r: 0.33-0.07and f: 0.57-0.61)during the optimization process, followed by the LFR-BF (r: 0.33-0.10 and f: 0.48-0.54),and the PTC-ST (r: 0.49-0.22 and f: 0.29-0.41),due to the positive impact of the findings (decrease in exergy destruction).Table 5 regroups key findings from the literature and environmental analysis of the hybrid power systems.
Figure 7 shows the computed results using the exergoenvironmental modeling and analysis of the HRPS.The optimized exergoenvironmental performance (r* and f*) for PTC-BF, LFR-BF, and ST-BF are 2.50-1.89and 0.56-0.66;2.55-2.13 and 0.50-0.55;1.48-1.25 and 0.60-0.64,respectively.As shown during exergoeconomic data analysis, the levelized exergoenvironmental findings contribute to a rapid assessment of subsystems and selection of an appropriate multigenerational hybrid power technology.

Conclusion
In this study, we present an advanced analysis and optimization method of the hybrid concentrating solar-biomass-fired power systems.To make some key findings and achieve fixed targets, we performed a 5E-analysis of hybrid systems.Based on the results of energy, exergy, economic, exergoeconomic and exergoenvironmental analysis, the following conclusions can be drawn: • The energy, environmental and economic analyses permit a determination of the average levelized costs and a payback return estimated as follows: 143.4 USD/MWh and 8.40 years, 214.2 USD/MWh and 10.62 years, and 226.2 USD/MWh and 14.71 years for the LFR-BF, the PTC-BF and the ST-BF, respectively.Their levelized cost and impact rate were ranked as follows: 15.17 USD/h and 88.83 mPts/h for the PTC-BF, 14.33 USD/h and 107.34 mPts for the LFR-BF, 12.93 USD/h and 71.92 mPts/h for the ST-BF.
• The exergoeconomic and exergoenvironmental analysis contributes to carry out the cost rate associated with exergy destruction impacts of the overall HRPS, which is specified by a computed ratio of exergoeconomic factors and relative cost difference (fh, rh) ranges as follows: 0.04-0.05and 0.53-0.99 for ST-BF, 0.05-0.06and 0.38-0.72 for LFR-BF, 0.05-0.07and 0.22-0.62 for PTC-BF.
• The exergoenvironmental analysis consists in highlighting the technology requirements of the HRPS scenarios and their main subsystems: the SF+BF subsystem requires an interest in optimization while the HRSG system does not, due to a low relative cost and environmental impact difference estimated in the following range of 0.07-0.08 and 0.28-0.44,respectively.• It can be concluded that the environmental impact points of HRPS-based CSP -BF technologies and their subsystems will affect significantly the exergoenvironmental performance if designers select another architecture, type or technology of solar collector assemblies (SCAs), heliostats, transfer fluids and combined power cycles.
Further research will focus on exergoenvironmental and economic analyses with the aim to optimize design parameters and provide the most suitable conceptual design of a selected scenario.

Figure 1 .
Figure 1.Schematic view of the hybrid concentrating solar-biomass-fired power system.

Figure 6 .
Figure 6.Levelized exergoeconomic factor and relative cost difference of the HRPS.

Table 1 .
Techno-economic and environmental parameters of the hybrid power systems (Al-Hamed and Dincer 2020).

Table 4 .
Main parameters of the HRPS.
The initial investments of the studied HRPS based on PTC, LFR, and ST are estimated at 45.87 million USD, 33.27 million USD, and 51.47 million USD, respectively.The payback periods without any incentives are Figure 2. Levelized cost of energy (LCOE) and Earning after Interest and Taxes (EAIT) of PTC-BF, LFR-BF, ST-BF power systems (Lifetime: 25 years, 5-year MACRS depreciation, Amortization over 20 years).destruction is between 31.67 and 25.54 MWt for PTC-BF, 27.56 and 23.96 MWt for LFR-BF, and 29.26 and 18.34 MWt for ST-BF.Their levelized cost and impact rate are carried out as follows: 15.17 USD/h and 88.83 mPts/h for PTC-BF, 14.33 USD/h and 107.34 mPts for LFR-BF, and 12.93 USD/h and 71.92 mPts/h for ST-BF.
Exergoenvironmental factor and relative environmental impact difference of the HRPS.