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Research Papers

# Exergy Analysis of the Annual Operation of a Sugarcane Cogeneration Power Plant Assisted by Linear Fresnel Solar CollectorsPUBLIC ACCESS

[+] Author and Article Information
Juan Camilo López

Department of Mechanical Engineering,
Technological University of Pereira,
Pereira 660003, Colombia
e-mail: juacamlopez@utp.edu.co

Álvaro Restrepo

Department of Mechanical Engineering,
Technological University of Pereira,
Pereira 660003, Colombia
e-mail: arestrep@utp.edu.co

Edson Bazzo

Department of Mechanical Engineering,
Federal University of Santa Catarina,
Florianopolis 88040-900, Brazil
e-mail: e.bazzo@ufsc.br

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received September 2, 2017; final manuscript received May 25, 2018; published online June 26, 2018. Assoc. Editor: Gerardo Diaz.

J. Sol. Energy Eng 140(6), 061004 (Jun 26, 2018) (9 pages) Paper No: SOL-17-1363; doi: 10.1115/1.4040534 History: Received September 02, 2017; Revised May 25, 2018

## Abstract

In this work, the exergy analysis of two configurations of hybrid solar–sugarcane cogeneration power plant is proposed in order to evaluate the overall efficiency enhancement of the cycle. Solar thermal energy was coupled to a sugarcane cogeneration power plant localized on the tropical region of Brazil, in order to preheat the feeding water supplied to the steam generators and to reduce the fuel consumption during the sugarcane-harvesting season in order to stock the unused fuel for its use during the off-season. The exergy analysis of the cycle was proposed based on a thermodynamic model, which considered real operational states, and allowed to quantify the main parameters of performance, such as the solar-to-electricity (STE) efficiency, the power generation increasing, the percentage of fuel saved, and the exergy destruction rates of the equipment. The results showed that, under design conditions, almost 10% of fuel was saved, and the overall exergy destruction decreased 11% approximately. Additionally, as a result of the hourly analysis of the annual operation, it was found that the power plant operated 331 extra hours, 8.50 GWh of electricity were generated, and due to this fact, it has attained economic benefits for the operation of the sugarcane cogeneration power plant.

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## Introduction

Modern world requires strategic actions for clean and efficient power generation to satisfy the growing energy requirements worldwide. Therefore, most countries must bear an innovative and updated strategy to achieve competitiveness on the energy utilization and the efficient usage of natural resources to guarantee low pollution rates, stability, and sustainability.

Nowadays, studies on optimal power generation and energy consumption based on nonconventional sources are among the most studied topics worldwide. IEA (International Energy Agency) [1] published that the contribution for power generation worldwide by nonrenewable and harmful environmental energy resources was 81% in 2015 (Oil 31.7%, coal 28.1%, and Gas 21.6%). Therefore, it was concluded that the matrix of energy has been completely attached to fossil fuels utilization. However, there have been developed and optimized mechanisms to acquire and store renewable energy resources, such as solar and wind, in order to diminish the dependency for power generation and energy consumption based on fossil fuels. IEA estimated a contribution of 11.2% on power generation by those technologies worldwide in 2015.

Solar energy aims to reduce the usage of fossil fuels and it has been designed in order to have a lower impact on global warming [2]. Timilsina et al. [3] said that the implementation of solar energy has experienced a strong growth last years, due to the policies instituted, which have supported the utilization of this technology for power generation and other applications. Desideri et al. [4] conducted a comparative analysis of solar concentrating technologies and pointed out that it is a promising alternative to replace conventional fuels. In general terms, the efficient utilization of renewable energy resources, like solar energy, is considered as a feasible solution for global warming and an attainable way for sustainability, due to its infinite reserves and its clean, free and renewable nature [57]. Zhou et al. [8] focused their researching studies in the existence of two widely spread technologies for solar thermal energy collecting: concentrating solar collectors and nonconcentrating solar collectors. Concentrating solar collectors are able to reach high temperatures and collect solar energy over small surfaces setup by reflecting mirrors of high thermal efficiency. Nowadays, the most studied technologies for solar concentration are parabolic-trough, parabolic dish, heliostat field collectors, and linear Fresnel reflectors. Sait et al. [9] established that linear Fresnel reflectors have been one of the most economical technologies for solar energy concentration. Reddy and Kumar [10] pointed out that those technologies have already grown up, considering them as promising technologies.

Despite some researchers have pointed out that solar concentration is a feasible methodology for power generation of high efficiency and quality [10], this technology has attained poor success in the traditional energy markets, due to the high investment cost compared to other renewable energy sources, such as wind and biomass [11]. Solar-only thermal power plants must install systems of energy storage to extend their operational times, as solar energy cannot be continuously collected [12]. Therefore, the overall investment is overloaded. Due to this fact, Hu et al. [13] established an alternative for power generation with solar thermal energy assistance or hybrid power generation, where the advantages of two mature technologies are combined: traditional Rankine cycles and solar thermal collectors. The hybridization of power generation combines the environmental benefits of the usage of solar thermal energy and the efficiency, capacity, and reliability of conventional power plants [14]. This concept owns the following advantages: (i) it does not require additional infrastructure, reducing the cost of implementation; (ii) it provides higher solar-to-electricity (STE) efficiency; (iii) thermal storage system is not necessary; and (iv) higher economic returns may be obtained as the cost of implementation is lower when it is compared with the installation of solar-only power plants [13,15]. In general, it is obtained as a positive overall effect over welfare conditions, the environment and economics. Due to these facts, some authors graded the hybrid power generation as a technological alternative of high efficiency for power generation by solar energy utilization and an effective and promising way to use the solar energy resources for power generation purposes [7,8,1619].

Nowadays, 90% of hybrid power plants utilize solar thermal energy systems coupled to Rankine regenerative cycles to preheat the feeding water suplied to the steam generators [8], which is a better option to couple solar thermal energy to power plants [20]. However, this is not the only way to utilize solar thermal energy on hybrid power plants, but also the utilization of this technology can be extended to processes of steam reheating or superheating, and air and water preheating for combustion processes and steam generation [15,21]. There exist a wide researching field for hybrid power generation. Giuliano et al. [22] analyzed the annual operation of five different solar-hybrid power plants. Suresh et al. [20] and Adibhatla and Kaushik [23] analyzed a solar thermal assited coal-fired power plant from the energy, exergy, environment, and economy viewpoints. Suresh et al. [20] concluded that if solar energy is used for preheating the feeding water, the process results to be more efficient from the viewpoint of exergy than energy. Aljundi [24] and Adibhatla and Kaushik [25] in their respective works concluded that steam generators showed the highest rates of exergy destruction in Rankine cycles (between 50% and 80% of the total exergy destroyed in the cycle). Therefore, these devices have been a key point for analysis. Aditionally, Peng et al. [26] conducted the exergy analysis for solar hybrid coal-fired and solar thermal power plants without hybridization, in order to obtain detailed data of the exergy destruction rates of each component of the cycle. Zhao et al. [27] analyzed the thermodynamic performances of a solar-coal hybrid power plant and identified that the net STE efficiency of the solar hybrid system would be 3–7% higher than that obtained by a solar-only power plant. Deng [28] proposed the implementation of solar thermal energy to preheat the secondary air of the steam generator of a coal-fired power plant and concluded that a STE efficiency of 24% could be achieved. On the other hand, Reddy et al. [29] conducted an exergy and energy analysis of each component of a solar power generation system and compared the results of two different configurations. Besides, Burin et al. [30] evaluated the integration of parabolic trough collectors to a feedwater heating scheme in a bagasse-fueled power plant located in Brazil.

Peterseim et al. [31] on their researching studies analyzed the technical, economic, and environmental performance of 17 different designs for solar–biomass hybrid power generation. The results obtained showed that countries such as Australia, Spain, Italy, India, and Brazil are the most qualified candidates to utilize high efficiency solar and biomass technologies for power generation, due to the high availability of solar and biomass resources at these locations. The results obtained by Peterseim et al. [31] pointed out that a power generation increase of 17% would be attained if thermal storage systems were attached; so, it is expected that hybrid power plants (solar–biomass) will be attached to technologies of thermal storage in 2020, due to the reduction of the cost associated for its utilization. In contrast to the important number of researches reported earlier, this study focused on the analysis of a sugarcane cogeneration power plant localized on the tropical region of Brazil by the consideration of real operational parameters and a seasonal operation scheme. The power plant analyzed utilizes the sugarcane bagasse as fuel, which is obtained during the milling stage of sugarcane in the sugar production process. Because the power plant presents a seasonal operation scheme, the inclusion of a solar concentration system was proposed to store the bagasse and to extend the annual operational time of the power plant during the off seasonal sugarcane production. In addition, the dynamics of the sunlight radiation during one year was modeled by considering real direct normal irradiance (DNI) data, and the information for the geographical region where the power plant is located was gathered to perform the hourly operation of the hybrid power plant during a typical meteorological year (TMY). In addition, the analysis of a sugarcane cogeneration power plant was performed and applied to establish the impact on the fuel consumption and the exergy performance of the system, when a linear Fresnel solar concentrating system was coupled to preheat the feedwater of the steam generators. Design conditions were established for the analytical sizing process of the solar field, given solar radiation data. The annual operation of two different configurations of solar thermal attachment to the cogeneration power plant was analyzed. The fuel consumption, net work output, exergy destruction, and the solar-to-electricity efficiency were the performance parameters to be analyzed.

## Power Plant Description

The power plant under analysis has a capacity of 85 MW of power generation and it is located in Mato Grosso State, Brazil. Figure 1 and Table 1 show the sugarcane cogeneration cycle and its operational conditions. It is a sugarcane cogeneration power plant, which produces sugar and alcohol from sugarcane. The power plant generates steam by means of burning sugarcane bagasse.

There are two steam generators, where the bagasse, whose ultimate analysis is shown in Table 2, is burned off. The steam generated is distributed and expanded throughout three turbines in the plant. Both turbines 1 and 2 generate 50 MW of mechanical power which are used in the sugarcane milling process, while Turbine 3 owns a capacity of 35 MW of electric power generation. It must be considered that sugarcane requires appropriate weather conditions for its production and harvest. Seasonal changes in the south hemisphere diminish the availability of the sugarcane required for the regular operation of the power plant throughout the entire year. Figure 2(a) shows the operational scheme of the power plant and the burning processes of bagasse, which is obtained from the milling, stage during the sugarcane-harvesting season, between April and December.

Because of that fact, the utilization of a solar collector system to preheat the feedwater of the steam generators was proposed, as a mechanism to reduce the fuel consumption during the harvesting season, and by this way, to store the bagasse for power generation during the off-season of sugarcane. Figure 2(b) shows the hybrid operational scheme of the cycle, where the upper frame represents the contribution of solar thermal energy for power generation.

## Thermodynamic Model

###### Conventional Power Plant.

The analysis of the cogeneration power plant was conducted, based on the conservation principles of mass and energy, and exergy balances, as indicated in Eqs. (1)(3). In addition, an own thermodynamic model was developed where each component of the steam power plant was analyzed individually under steady-state conditions during the harvesting season of sugarcane according to the procedure guide of Bejan et al. [32] Display Formula

(1)$∑ m˙in=∑ m˙out$
Display Formula
(2)$∑ m˙inhin+Q˙in+W˙in=∑ m˙outhout+Q˙out+W˙out$
Display Formula
(3)$∑ E˙in=∑ E˙out+E˙d$

The exergy efficiency is calculated by the following equation: Display Formula

(4)$ε=E˙outE˙in$

The chemical exergy of the bagasse, for the exergy analysis of the steam generators, is obtained by the following equation: Display Formula

(5)$E˙bagch=m˙bagebagch$

where $ebagch$ is calculated by the following equation, which was proposed by Szargut [33] as an approximation to the chemical exergy of solid fuels: Display Formula

(6)$ebagch=(LHV+LZW)β+(eSch−CS)zS+eAchzA+eWchzW$

L is the enthalpy of vaporization of water; zw, zs, and zA are the mass fractions of water, sulfur, and ashes of the fuel, respectively. On the other hand, the standard chemical exergy ratio of the solid fuels, β, is calculated by the following equation [33]: Display Formula

(7)$β=1.0414+0.0177(zH/zC)−0.3328(zO/zC)[1+0.0537(zH/zC)]1−0.4021(zO/zC)$

where zH, zC, and zO are the mass fractions of hydrogen, carbon, and oxygen of the fuel, respectively.

###### Solar Energy Integration.

The integration of the linear Fresnel solar collectors was proposed as a reasonable alternative to solar preheat the feedwater of the steam generators and to reduce the fuel consumption of the power plant. In addition, the design conditions were established for the analytical sizing process of the solar field, given the solar radiation data for the geographical region where the power plant is located. The design of the hybrid power plant involved a solar field to supply the feedwater at 180 °C to the steam generators under peak conditions of both irradiance and optic efficiency. Thus, the reflection area of the solar field is obtained by the following equation: Display Formula

(8)$ASF=Q˙DDNIDηopt,D−Plosses$

where $Q˙D$ is the heat required to raise the temperature of the feeding water from 105 °C to 180 °C considering the design conditions; $DNID$ and $ηopt,D$ are the DNI and the optic efficiency selected for the design conditions, 900 W/m2 and 67%, respectively; and $Plosses$ represents the thermal losses per square meter of the reflectors.

After the calculation of the design area, two coupling configurations of the linear Fresnel solar collectors were analyzed: Configurations A and B (see Fig. 3). In configuration A, the solar field was coupled for preheating the feeding water supplied to the steam generators. The operational limit of this configuration was fixed to the temperature attained by the feeding water. In order to avoid the modification of the operational dynamics of the steam generators in the power plant, the specifications of the equipment establish that the feedwater must not exceed a temperature of 180 °C. On the other hand, in configuration B, the solar field was coupled for heating a feeding water fraction, in order to attain a state of saturated steam for being directly injected into the drum of the steam generators. In this case, the fuel consumption saving restrained the operation of this configuration, because according to the specifications of the steam generators, 15% of fuel consumption savings could be attained without disrupting the operational conditions of the equipment.

Once the reflection area of the solar field has been sized, the simulation of the annual operation for both configurations is conducted according to the thermal performance characteristics of the linear Fresnel solar collectors, which are provided by the manufacturer. Therefore, according to Eq. (8), the annual operation of the solar field is modeled by the following equation [34]: Display Formula

(9)$Q˙solar=ASF(DNIηopt−Plosses)$

where $Q˙solar$ is the heat supplied to the feeding water by the solar field, $ηopt$ is the optic efficiency of the solar collectors, obtained by the Eq. (10), and $Plosses$ represents the thermal losses per square meter of the reflectors, which are obtained by Eq. (11) [34] Display Formula

(10)$ηopt=η0K⊥(θ⊥)K∥θi$
Display Formula
(11)$Plosses=u0ΔT+u1ΔT2$

where $η0$ is the efficiency correction factor that equals to 0.67, $K⊥$ and $K∥$ are the transversal and longitudinal corrections factors, respectively, which are obtained by Eqs. (12) and (13), and are function of the incidence angle, $θi$, and its transversal component, $θ⊥$. On the other hand, $u0$ and $u1$ are the thermal losses coefficients provided by the manufacturer and these are equivalent to 0.056 W/m2 K and 0.000213 W/m2 K2, respectively, and $ΔT$ is the temperature difference between the mean temperature of the water which flows throughout the solar collectors and the ambient temperature [34] Display Formula

(12)$K⊥=−2.64·10−11θ⊥6+8.20·10−9θ⊥5−9.10·10−7θ⊥4+4.17·10−5θ⊥3−7.80·10−4θ⊥2+2.55·10−3θ⊥+0.9998$
Display Formula
(13)$K∥=−2.57·10−11θi6+7.27·10−9θi5−7.16·10−7θi4+3.10·10−5θi3−7.63·10−4θi2+3.40·10−3θi+0.9996$

Solar thermal configurations were analyzed varying the solar multiple (SM) and fixing the initial design conditions. As shown in Eq. (14), the SM defines the relation between the thermal energy obtained by the solar field under design conditions and the heat delivered to the feeding water by the solar field in order to attain the design temperature limit [10] Display Formula

(14)$SM=ASF(DNIDηopt,D−Plosses)Q˙D$

where ASF is the reflection solar area. The thermodynamic model considered the following performance criteria: extra operational time, extra energy trading, annual average fuel consumption saving, and the solar-to-electricity efficiency (STE). The STE represents the ratio between the extra electric power generated when the solar field is coupled to the cycle, and the total amount of solar thermal energy used in the cycle is shown in the following equation [15]: Display Formula

(15)$ηSTE=W˙solarDNITMYASF$

where $W˙solar$ is the fraction of the electric power generated by the power plant linked to the attachment of the solar field during a TMY, which is calculated by Eq. (16) and corresponds to the upper brand of Fig. 2(b). $DNITMY$ is the sum of the DNI levels per hour during the TMY analyzed and $ASF$ is the area of reflection of the solar field Display Formula

(16)$W˙solar=SFW˙generated$

SF is the Solar Factor and indicates the fraction of heat delivered to the working fluid by the solar field. SF is calculated by Eq. (17). On the other hand, $W˙generated$ is the total electric power generated by the plant Display Formula

(17)$SF=Q˙solarQ˙solar+Q˙SG$

where $Q˙SG$ is the heat supplied during the bagasse burning process into the steam generators to the water.

Finally, the exergy analysis of the solar field was given by Eq. (18), which was obtained from the exergy balance presented in Eq. (3)Display Formula

(18)$E˙SF+E˙in,w=E˙out,w+E˙d$

The term $E˙SF$ is the solar thermal exergy received by the solar field, calculated by Eq. (19) [29,35], with Tsun being the temperature of the sun, which was assumed as 6000 K as proposed by Kalogirou [36] and Lozano et al. [37] Display Formula

(19)$E˙SF=Q˙solar[1−(43)(T0Tsun)+(13)(T0Tsun)4]$

## Results and Discussions

The hybrid cogeneration power plant was analyzed for two different configurations, considering the design conditions and the operation during the TMY. The results were obtained by the implementation of a thermodynamic model using the software Engineering Equation Solver (ees). Also, it was established that when assisted by the solar thermal energy, the steam and power generated by the steam generators and the turbines are equal to the amount produced in the conventional power plant. Additionally, out of the sugarcane-harvesting season, turbines 1 and 2 were out of line, so power generation only went through the turbine 3.

###### Conventional Power Plant.

The sugarcane cogeneration power plant was analyzed and characterized considering real operational conditions. Pressure, steam, and heat losses in pipes were supposed as negligible. Table 3 shows the performance parameters of the cogeneration cycle which operated at its initial conditions before the attachment of the solar thermal concentrating system.

The results showed that the exergy destroyed by the steam generators is highest in the cycle, and these devices performed the lowest exergy efficiency in the cogeneration power plant. Therefore, if there were a way to enhance the operational performance of these devices, the overall effect over the efficiency of the cycle would be significant. This fact makes the steam generators a key point for analysis and the main target when new upgrades for the power plant are proposed. Due to this fact, designs of solar thermal energy implementation are tied up to the operational performance of the steam generators. Additionally, the parameters of performance studied were not evaluated for the condenser because it is a dissipative device.

To evaluate the parameters of performance of both configurations for the hybrid power plant, the reflection area of the solar field was calculated from the design conditions. It was established that, for the preheating of the feeding water to 180 °C, with a DNI of 900 W/m2 and an optic efficiency of 67%, a total reflection area of approximately 56,000 m2 was required.

###### Design Conditions Analysis.

The analysis of the configuration A under design conditions showed that the fuel consumption was reduced to 9.97% points. Table 4 shows the parameters of performance of this configuration. While the exergy destroyed by the steam generators decreased to 11.50% points, the total exergy destroyed by the cycle just decreased to 1.11% points. However, if the exergy cost of the solar collectors is regarded as zero, due to the fact that solar energy is considered as a free of charge resource, as proposed by Lozano et al. [37], the exergy destruction of the solar field would not represent negative impacts over the operational cost of the power plant, thus the exergy destruction of the overall cycle would decrease to 344,100 kW, which represents a reduction of 10.83% compared to the parameters of performance of the conventional power plant. Additionally, $ηSTE$ of 16.39% was obtained, it means that16% of the solar energy available was converted into electricity when peak conditions of DNI and optic efficiency were considered.

On the other hand, the analysis under design conditions of the configuration B showed that the fuel consumption was reduced to 9.87% points. Table 4 shows the parameters of the performance of the hybrid power plant for configuration B. The exergy destroyed by the steam generators was reduced to 10.16% points and, considering the solar thermal energy as free of charge resource, the exergy destruction of the overall cycle would decrease to 349,226 kW, which represents a reduction of 9.51% points. Even though by the configuration B the phase of saturated steam for a fraction of the feedwater was attained, the preheating process, by the configuration A, leads to major benefits in terms of fuel consumption savings, and thus, a higher reduction of the exergy destruction rates in the process was obtained. Furthermore, $ηSTE$ of this configuration was 16.22%. The design parameters obtained for both configurations, under design conditions, did not hold significant differences.

###### Typical Meteorological Year Analysis.

In the analysis of the TMY, real DNI data were assessed. These data mainly consider the effects of weather changes related to cloudiness and rainfall. Besides, the overall performance of the solar field for different SM values (1, 1.1, 1.2, and 1.3) was evaluated, it means the reflecting design area was increased to 10, 20, and 30%. Table 5 shows the results obtained for both configurations analyzed. As it was expected, if the reflecting area of the solar field increased, the fuel consumption would decrease, therefore the overall capacity and the extra operational time of the power plant would increase. However, $ηSTE$ would decrease, which means that a lower amount of solar energy would be converted to electric energy. Although the results obtained by the TMY analysis for both configurations did not hold significant differences, the best performance of the solar field was attained by configuration A considering a SM of 1.3; the cogeneration power plant saved 1.48% of the bagasse consumed annually, operated 331 extra hours, and generated 8.50 GWh of additional electricity.

Figure 4 shows the average fuel saved per year and for each month and SM for each configuration. Higher fuel saved was obtained on November and December, due to higher solar radiation on these months, which belongs to the summer season in the south hemisphere.

###### Direct Normal Irradiance Versus Exergy Destruction of the Plant.

Figure 5 shows the effects due to changes in DNI over the exergy destroyed by the cycle as well as for the steam generators, during a random period of operation of 72 h, for the configurations A and B. The interval of operation to conduct the analysis was selected between 6337 and 6409 h of the year, period of time which corresponds to September, when important peaks on the DNI levels appeared. It was observed that the gap between curves of exergy destroyed by the cycle and the steam generators, it means the exergy destroyed by the other components remained constant. It means, for a stable rate production of sugar, the exergy destroyed by other devices in the plant did not change, despite fluctuations in solar radiation. Besides, the exergy destroyed did not immediately change when solar thermal radiation increased, so it was observed that a DNI level of approximately 300 W/m2 is necessary in order to have an initial reduction on the exergy destruction rates of the system.

###### Direct Normal Irradiance Effects Over STE Efficiency.

The STE efficiency allowed to determine the contribution of solar energy collecting for power generation, so, Fig. 6 shows the fluctuation of $ηSTE$ due to variations in the DNI levels, for each configuration.

Figure 6 shows a similar behavior for both configurations of solar assistance during the operational period analyzed before. However, between 6370 and 6380 h for configuration B, some differences are observed. Configuration B shows a higher peak value than configuration A, reaching a $ηSTE$ of 15% approximately. Besides, it is highlighted that the efficiency did not immediately increase due to the increasing of DNI, but a delay of reaction would be detected that could be observed if horizontal parallel lines were compared.

###### Direct Normal Irradiance Versus Fuel Consumption.

Figure 7 shows the effect of DNI over sugarcane consumption for both configurations. The rate of bagasse consumption decreased after DNI increased. Finally, configuration A showed higher reduction on fuel consumption of 45 kg/s approximately, while configuration B attained a value of 47 kg/s.

## Conclusions

A linear Fresnel solar thermal concentrating system coupled to a sugarcane cogeneration power plant was analyzed and evaluated for two different configurations. Configuration A was coupled to pre-heat the feeding water of the steam generators under design conditions in order to raise up the temperature of water in 75 °C. Configuration B was coupled to change the phase of a mass flow fraction of feeding water from liquid at the inlet of the solar collectors to saturated vapor at the output, in order to inject it afterward, into the drum of the steam generators.

To evaluate the system of solar collectors, two operational conditions were considered, as well as the design conditions, and the TMY. As a result of the design conditions, configuration A showed greater performance than B; the fuel consumption decreased 9.97%, and the solar field contributed with 16.39%. In addition, the exergy destroyed by the steam generators and the overall cycle decreased 11.51% and 11.10%, respectively. In addition, the results of the TMY analysis for both configurations were compared, where SM values were also evaluated. It was obtained that the maximum difference of operational extra time attained was 5 h, for configuration A.

The exergy destruction rates associated with the operation of the solar field were excluded from the calculation of the overall exergy destroyed by the power plant. As the solar exergy flow is considered as a free of charge resource, those destruction rates do not generate over cost, even though the exergy destruction ratio of the solar concentration system is higher than the ratio of other devices.

The best performance of the solar field was attained by configuration A where a major rate of extra electric power generation was detected. In addition, fuel consumption was saved during the year, with a SM of 1.3; it means, when solar collectors preheated the feedwater of the steam generators. Because of that, the cogeneration power plant could be operated for 331 extra hours, 8.50 GWh of extra electricity was generated and there was a total fuel consumption savings of 1.48% during a TMY. Finally, it must be mentioned that the feasibility of the project and the final election between the configurations A and B will depend on the ratio cost/benefit for the implementation of each design.

## Acknowledgements

The authors want to acknowledge the Gestión Energética research group – Genergética of the Technological University of Pereira and the Laboratório de Combustão e Engenharia de Sistemas Térmicos – LabCET of the Federal University of Santa Catarina. Also thanks to the program “Jóvenes Investigadores” of COLCIENCIAS – Colombia and to the Santander Bank for the financial support to this project.

## Funding Data

• Banco Santander (Becas Santander Iberoamérica).

• Departamento Administrativo de Ciencia, Tecnología e Información de Colombia Jóvenes Investigadores.

## Nomenclature

• A =

reflection area, m2

• DNI =

• e =

specific exergy, kJ/kg

• $E˙$ =

exergy flow, MW

• h =

specific enthalpy, kJ/kg

• K =

correction factor

• L =

vaporization enthalpy, kJ/kg

• LHV =

lower heating value, MJ/kg

• $m˙$ =

mass flow rate, kg/s

• $Q˙$ =

heat flow rate, MW

• s =

specific entropy, kJ/kgK

• SF =

solar factor

• SM =

solar multiple

• T =

temperature, K

• u =

thermal losses coefficient

• $W˙$ =

power, MW

• z =

mass fraction, kg/kg

Greek Symbols
• β =

ratio of standard chemical exergy

• ɛ =

exergy efficiency

• η =

efficiency

• θ =

incidence angle

Subscripts and Superscripts
• A =

ashes

• bag =

bagasse

• C =

carbon

• ch =

chemical

• cond =

condenser

• d =

destruction

• D =

design point

• H =

hydrogen

• in =

inlet

• O =

oxygen

• opt =

optical

• out =

outlet

• P =

pump

• proc =

process

• Q =

heat

• S =

sulfur

• SF =

solar field

• SG =

steam generators

• STE =

solar-to-electricity

• T =

turbine

• TMY =

typical meteorological year

• W =

water

• 0 =

environment conditions

• $⊥$ =

transversal component

• $∥$ =

longitudinal component

Abbreviations
• DNI =

• EES =

Engineering Equation Solver

• IEA =

International Energy Agency

• SM =

solar multiple

• STE =

solar-to-electricity

• TMY =

typical meteorological year

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Wu, J. , Hou, H. , and Yang, Y. , 2016, “ Annual Economic Performance of a Solar-Aided 600 MW Coal-Fired Power Generation System Under Different Tracking Modes, Aperture Areas, and Storage Capacities,” Appl. Therm. Eng., 104, pp. 319–332.
Zhou, L. , Li, Y. , Hu, E. , Qin, J. , and Yang, Y. , 2015, “ Comparison in Net Solar Efficiency Between the Use of Concentrating and Non-Concentrating Solar Collectors in Solar Aided Power Generation Systems,” Appl. Therm. Eng., 75, pp. 685–691.
Sait, H. H. , Martinez-Val, J. M. , Abbas, R. , and Munoz-Anton, J. , 2015, “ Fresnel-Based Modular Solar Fields for Performance/Cost Optimization in Solar Thermal Power Plants: A Comparison With Parabolic Trough Collectors,” Appl. Energy, 141, pp. 175–189.
Reddy, K. S. , and Kumar, K. R. , 2012, “ Solar Collector Field Design and Viability Analysis of Stand-Alone Parabolic Trough Power Plants for Indian Conditions,” Energy Sustainable Dev., 16(4), pp. 456–470.
Peterseim, J. H. , White, S. , Tadros, A. , and Hellwig, U. , 2014, “ Concentrating Solar Power Hybrid Plants—Enabling Cost Effective Synergies,” Renewable Energy, 67, pp. 178–185.
Soltani, R. , Mohammadzadeh Keleshtery, P. , Vahdati, M. , KhoshgoftarManesh, M. H. , Rosen, M. A. , and Amidpour, M. , 2014, “ Multi-Objective Optimization of a Solar-Hybrid Cogeneration Cycle: Application to CGAM Problem,” Energy Convers. Manage., 81, pp. 60–71.
Hu, E. , Yang, Y. , Nishimura, A. , Yilmaz, F. , and Kouzani, A. , 2010, “ Solar Thermal Aided Power Generation,” Appl. Energy, 87(9), pp. 2881–2885.
Hou, H. , Xu, Z. , and Yang, Y. , 2016, “ An Evaluation Method of Solar Contribution in a Solar Aided Power Generation (SAPG) System Based on Exergy Analysis,” Appl. Energy, 182, pp. 1–8.
Hou, H. , Yang, Y. , Hu, E. , Song, J. , Dong, C. , and Mao, J. , 2011, “ Evaluation of Solar Aided Biomass Power Generation Systems With Parabolic Trough Field,” Sci. China Technol. Sci., 54(6), pp. 1455–1461.
Hou, H. , Wu, J. , Yang, Y. , Hu, E. , and Chen, S. , 2015, “ Performance of a Solar Aided Power Plant in Fuel Saving Mode,” Appl. Energy, 160, pp. 873–881.
Zhong, W. , Chen, X. , Zhou, Y. , Wu, Y. , and López, C. , 2017, “ Optimization of a Solar Aided Coal-Fired Combined Heat and Power Plant Based on Changeable Integrate Mode Under Different Solar Irradiance,” Sol. Energy, 150, pp. 437–446.
Wu, J. , Hou, H. , and Yang, Y. , 2016, “ Comparison Analysis for TES System in Solar-Aided 600 MW Coal-Fired Power Generation System and Solar-Alone Power Generation System,” ASME Paper No. ES2016-59491.
Sheu, E. J. , Mitsos, A. , Eter, A. A. , Mokheimer, E. M. A. , Habib, M. A. , and Al-Qutub, A. , 2012, “ A Review of Hybrid Solar–Fossil Fuel Power Generation Systems and Performance Metrics,” ASME J. Sol. Energy Eng., 134(4), p. 041006.
Suresh, M. V. J. J. , Reddy, K. S. , and Kolar, A. K. , 2010, “ 4-E (Energy, Exergy, Environment, and Economic) Analysis of Solar Thermal Aided Coal-Fired Power Plants,” Energy Sustainable Dev., 14(4), pp. 267–279.
Hong-juan, H. , Zhen-yue, Y. , Yong-ping, Y. , Si, C. , Na, L. , and Junjie, W. , 2013, “ Performance Evaluation of Solar Aided Feedwater Heating of Coal-Fired Power Generation (SAFHCPG) System Under Different Operating Conditions,” Appl. Energy, 112, pp. 710–718.
Giuliano, S. , Buck, R. , and Eguiguren, S. , 2011, “ Analysis of Solar-Thermal Power Plants With Thermal Energy Storage and Solar-Hybrid Operation Strategy,” ASME J. Sol. Energy Eng., 133(3), p. 031007.
Adibhatla, S. , and Kaushik, S. C. , 2017, “ Energy, Exergy, Economic and Environmental (4E) Analyses of a Conceptual Solar Aided Coal Fired 500MWe Thermal Power Plant With Thermal Energy Storage Option,” Sustainable Energy Technol. Assess., 21, pp. 89–99.
Aljundi, I. H. , 2009, “ Energy and Exergy Analysis of a Steam Power Plant in Jordan,” Appl. Therm. Eng., 29(2–3), pp. 324–328.
Adibhatla, S. , and Kaushik, S. C. , 2017, “ Exergy and Thermoeconomic Analyses of 500 MWe Sub Critical Thermal Power Plant With Solar Aided Feed Water Heating,” Appl. Therm. Eng., 123, pp. 340–352.
Peng, S. , Wang, Z. , Hong, H. , Xu, D. , and Jin, H. , 2014, “ Exergy Evaluation of a Typical 330 MW Solar-Hybrid Coal-Fired Power Plant in China,” Energy Convers. Manage., 85, pp. 848–855.
Zhao, Y. , Hong, H. , and Jin, H. , 2013, “ Proposal of a Solar-Coal Power Plant on Off-Design Operation,” ASME J. Sol. Energy Eng., 135(3), p. 031005.
Deng, S. , 2013, “ Hybrid Solar and Coal-Fired Steam Power Plant Based on Air Preheating,” ASME J. Sol. Energy Eng., 136(2), p. 021012.
Reddy, V. S. , Kaushik, S. C. , and Tyagi, S. K. , 2012, “ Exergetic Analysis and Performance Evaluation of Parabolic Trough Concentrating Solar Thermal Power Plant (PTCSTPP),” Energy, 39(1), pp. 258–273.
Burin, E. K. , Buranello, L. , Lo Giudice, P. , Vogel, T. , Görner, K. , and Bazzo, E. , 2015, “ Boosting Power Output of a Sugarcane Bagasse Cogeneration Plant Using Parabolic Trough Collectors in a Feedwater Heating Scheme,” Appl. Energy, 154, pp. 232–241.
Peterseim, J. H. , Hellwig, U. , Tadros, A. , and White, S. , 2014, “ Hybridisation Optimization of Concentrating Solar Thermal and Biomass Power Generation Facilities,” Sol. Energy, 99, pp. 203–214.
Bejan, A. , Tsatsaronis, G. , and Moran, M. , 1996, Thermal Desing and Optimization, Wiley, New York.
Szargut, J. , Morris, D. , and Steward, F. , 1988, Exergy Analysis of Thermal, Chemical, and Metallurgical Processes, Hemisphere Publishing, New York.
NOVATEC-SOLAR, 2009, “ NOVA-1,” NOVATEC, Karlsruhe, Germany.
Petela, R. , 1964, “ Exergy of Heat Radiation,” ASME J. Heat Transfer, 86(2), p. 187.
Kalogirou, S. A. , 2004, “ Solar Thermal Collectors and Applications,” Prog. Energy Combust. Sci., 30(3), pp. 231–295.
Lozano, M. A. , Serra, L. M. , Mancini, C. , and Verda, V. , 2014, “ Exergy and Thermoeconomic Analysis of a Solar Air Heating Plant,” ASME Paper No. ESDA2014-20152.
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## References

IEA, 2017, “ Key World Energy Statistics,” International Energy Agency, Paris, France.
Pons, M. , 2012, “ Exergy Analysis of Solar Collectors, From Incident Radiation to Dissipation,” Renewable Energy, 47, pp. 194–202.
Timilsina, G. R. , Kurdgelashvili, L. , and Narbel, P. A. , 2012, “ Solar Energy: Markets, Economics and Policies,” Renewable Sustainable Energy Rev., 16(1), pp. 449–465.
Desideri, U. , Zepparelli, F. , Morettini, V. , and Garroni, E. , 2013, “ Comparative Analysis of Concentrating Solar Power and Photovoltaic Technologies: Technical and Environmental Evaluations,” Appl. Energy, 102, pp. 765–784.
Tian, Y. , and Zhao, C. Y. , 2013, “ A Review of Solar Collectors and Thermal Energy Storage in Solar Thermal Applications,” Appl. Energy, 104, pp. 538–553.
Wang, Y. , Xu, J. , Chen, Z. , Cao, H. , and Zhang, B. , 2017, “ Technical and Economical Optimization for a Typical Solar Hybrid Coal-Fired Power Plant in China,” Appl. Therm. Eng., 115, pp. 549–557.
Wu, J. , Hou, H. , and Yang, Y. , 2016, “ Annual Economic Performance of a Solar-Aided 600 MW Coal-Fired Power Generation System Under Different Tracking Modes, Aperture Areas, and Storage Capacities,” Appl. Therm. Eng., 104, pp. 319–332.
Zhou, L. , Li, Y. , Hu, E. , Qin, J. , and Yang, Y. , 2015, “ Comparison in Net Solar Efficiency Between the Use of Concentrating and Non-Concentrating Solar Collectors in Solar Aided Power Generation Systems,” Appl. Therm. Eng., 75, pp. 685–691.
Sait, H. H. , Martinez-Val, J. M. , Abbas, R. , and Munoz-Anton, J. , 2015, “ Fresnel-Based Modular Solar Fields for Performance/Cost Optimization in Solar Thermal Power Plants: A Comparison With Parabolic Trough Collectors,” Appl. Energy, 141, pp. 175–189.
Reddy, K. S. , and Kumar, K. R. , 2012, “ Solar Collector Field Design and Viability Analysis of Stand-Alone Parabolic Trough Power Plants for Indian Conditions,” Energy Sustainable Dev., 16(4), pp. 456–470.
Peterseim, J. H. , White, S. , Tadros, A. , and Hellwig, U. , 2014, “ Concentrating Solar Power Hybrid Plants—Enabling Cost Effective Synergies,” Renewable Energy, 67, pp. 178–185.
Soltani, R. , Mohammadzadeh Keleshtery, P. , Vahdati, M. , KhoshgoftarManesh, M. H. , Rosen, M. A. , and Amidpour, M. , 2014, “ Multi-Objective Optimization of a Solar-Hybrid Cogeneration Cycle: Application to CGAM Problem,” Energy Convers. Manage., 81, pp. 60–71.
Hu, E. , Yang, Y. , Nishimura, A. , Yilmaz, F. , and Kouzani, A. , 2010, “ Solar Thermal Aided Power Generation,” Appl. Energy, 87(9), pp. 2881–2885.
Hou, H. , Xu, Z. , and Yang, Y. , 2016, “ An Evaluation Method of Solar Contribution in a Solar Aided Power Generation (SAPG) System Based on Exergy Analysis,” Appl. Energy, 182, pp. 1–8.
Hou, H. , Yang, Y. , Hu, E. , Song, J. , Dong, C. , and Mao, J. , 2011, “ Evaluation of Solar Aided Biomass Power Generation Systems With Parabolic Trough Field,” Sci. China Technol. Sci., 54(6), pp. 1455–1461.
Hou, H. , Wu, J. , Yang, Y. , Hu, E. , and Chen, S. , 2015, “ Performance of a Solar Aided Power Plant in Fuel Saving Mode,” Appl. Energy, 160, pp. 873–881.
Zhong, W. , Chen, X. , Zhou, Y. , Wu, Y. , and López, C. , 2017, “ Optimization of a Solar Aided Coal-Fired Combined Heat and Power Plant Based on Changeable Integrate Mode Under Different Solar Irradiance,” Sol. Energy, 150, pp. 437–446.
Wu, J. , Hou, H. , and Yang, Y. , 2016, “ Comparison Analysis for TES System in Solar-Aided 600 MW Coal-Fired Power Generation System and Solar-Alone Power Generation System,” ASME Paper No. ES2016-59491.
Sheu, E. J. , Mitsos, A. , Eter, A. A. , Mokheimer, E. M. A. , Habib, M. A. , and Al-Qutub, A. , 2012, “ A Review of Hybrid Solar–Fossil Fuel Power Generation Systems and Performance Metrics,” ASME J. Sol. Energy Eng., 134(4), p. 041006.
Suresh, M. V. J. J. , Reddy, K. S. , and Kolar, A. K. , 2010, “ 4-E (Energy, Exergy, Environment, and Economic) Analysis of Solar Thermal Aided Coal-Fired Power Plants,” Energy Sustainable Dev., 14(4), pp. 267–279.
Hong-juan, H. , Zhen-yue, Y. , Yong-ping, Y. , Si, C. , Na, L. , and Junjie, W. , 2013, “ Performance Evaluation of Solar Aided Feedwater Heating of Coal-Fired Power Generation (SAFHCPG) System Under Different Operating Conditions,” Appl. Energy, 112, pp. 710–718.
Giuliano, S. , Buck, R. , and Eguiguren, S. , 2011, “ Analysis of Solar-Thermal Power Plants With Thermal Energy Storage and Solar-Hybrid Operation Strategy,” ASME J. Sol. Energy Eng., 133(3), p. 031007.
Adibhatla, S. , and Kaushik, S. C. , 2017, “ Energy, Exergy, Economic and Environmental (4E) Analyses of a Conceptual Solar Aided Coal Fired 500MWe Thermal Power Plant With Thermal Energy Storage Option,” Sustainable Energy Technol. Assess., 21, pp. 89–99.
Aljundi, I. H. , 2009, “ Energy and Exergy Analysis of a Steam Power Plant in Jordan,” Appl. Therm. Eng., 29(2–3), pp. 324–328.
Adibhatla, S. , and Kaushik, S. C. , 2017, “ Exergy and Thermoeconomic Analyses of 500 MWe Sub Critical Thermal Power Plant With Solar Aided Feed Water Heating,” Appl. Therm. Eng., 123, pp. 340–352.
Peng, S. , Wang, Z. , Hong, H. , Xu, D. , and Jin, H. , 2014, “ Exergy Evaluation of a Typical 330 MW Solar-Hybrid Coal-Fired Power Plant in China,” Energy Convers. Manage., 85, pp. 848–855.
Zhao, Y. , Hong, H. , and Jin, H. , 2013, “ Proposal of a Solar-Coal Power Plant on Off-Design Operation,” ASME J. Sol. Energy Eng., 135(3), p. 031005.
Deng, S. , 2013, “ Hybrid Solar and Coal-Fired Steam Power Plant Based on Air Preheating,” ASME J. Sol. Energy Eng., 136(2), p. 021012.
Reddy, V. S. , Kaushik, S. C. , and Tyagi, S. K. , 2012, “ Exergetic Analysis and Performance Evaluation of Parabolic Trough Concentrating Solar Thermal Power Plant (PTCSTPP),” Energy, 39(1), pp. 258–273.
Burin, E. K. , Buranello, L. , Lo Giudice, P. , Vogel, T. , Görner, K. , and Bazzo, E. , 2015, “ Boosting Power Output of a Sugarcane Bagasse Cogeneration Plant Using Parabolic Trough Collectors in a Feedwater Heating Scheme,” Appl. Energy, 154, pp. 232–241.
Peterseim, J. H. , Hellwig, U. , Tadros, A. , and White, S. , 2014, “ Hybridisation Optimization of Concentrating Solar Thermal and Biomass Power Generation Facilities,” Sol. Energy, 99, pp. 203–214.
Bejan, A. , Tsatsaronis, G. , and Moran, M. , 1996, Thermal Desing and Optimization, Wiley, New York.
Szargut, J. , Morris, D. , and Steward, F. , 1988, Exergy Analysis of Thermal, Chemical, and Metallurgical Processes, Hemisphere Publishing, New York.
NOVATEC-SOLAR, 2009, “ NOVA-1,” NOVATEC, Karlsruhe, Germany.
Petela, R. , 1964, “ Exergy of Heat Radiation,” ASME J. Heat Transfer, 86(2), p. 187.
Kalogirou, S. A. , 2004, “ Solar Thermal Collectors and Applications,” Prog. Energy Combust. Sci., 30(3), pp. 231–295.
Lozano, M. A. , Serra, L. M. , Mancini, C. , and Verda, V. , 2014, “ Exergy and Thermoeconomic Analysis of a Solar Air Heating Plant,” ASME Paper No. ESDA2014-20152.

## Figures

Fig. 1

Sugarcane cogeneration cycle

Fig. 2

Operational scheme of the plant: (a) conventional power plant and (b) hybrid power plant

Fig. 3

Solar field integration: (a) configuration A and (b) configuration B

Fig. 4

Fuel saved per month: (a) configuration A and (b) configuration B

Fig. 5

DNI versus exergy destruction: (a) configuration A and (b) configuration B

Fig. 6

DNI versusηSTE: (a) configuration A and (b) configuration b

Fig. 7

DNI versus fuel consumption: (a) configuration A and (b) configuration B

## Tables

Table 1 Operational conditions of the power plant
Table 2 Ultimate analysis of the sugarcane bagasse
Table 3 Parameters of performance—conventional power plant
Table 4 Parameters of performance
Table 5 Results of TMY analysis

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