Economical and environmental analysis of thermal and photovoltaic solar energy as source of heat for industrial processes

AIP Conference Proceedings 1850, 180005 (2017); https://doi.org/10.1063/1.4984572 1850, 180005 © 2017 Author(s). Economical and environmental analysis of thermal and photovoltaic solar energy as source of heat for industrial processes Cite as: AIP Conference Proceedings 1850, 180005 (2017); https://doi.org/10.1063/1.4984572 Published Online: 27 June 2017 Elena Pérez-Aparicio, Isidoro Lillo-Bravo, Sara Moreno-Tejera, and Manuel Silva-Pérez ARTICLES YOU MAY BE INTERESTED IN Potential for solar industrial process heat in the United States: A look at California AIP Conference Proceedings 1734, 110001 (2016); https://doi.org/10.1063/1.4949198 Market potential of solar thermal enhanced oil recovery-a techno-economic model for Issaran oil field in Egypt AIP Conference Proceedings 1850, 190001 (2017); https://doi.org/10.1063/1.4984573 Techno-economic analysis of concentrated solar power plants in terms of levelized cost of electricity AIP Conference Proceedings 1850, 160018 (2017); https://doi.org/10.1063/1.4984552 Economical and Environmental Analysis of Thermal and Photovoltaic Solar Energy as Source of Heat for Industrial Processes Elena Pérez-Aparicio1,a), Isidoro Lillo-Bravo2,b), Sara Moreno-Tejera2 and Manuel Silva-Pérez2 1Andalusian Association for Research and Industrial Cooperation. Camino de los Descubrimientos s/n. 41092. Seville, Spain. Phone/Fax number: (+34)954487239/(+34)954487233. 2Department of Energy Engineering. University of Seville. Camino de los Descubrimientos s/n. 41092. Seville, Spain. a) Corresponding author: [email protected] b)[email protected] Abstract. Thermal energy for industrial processes can be generated using thermal (ST) or photovoltaic (PV) solar energy. ST energy has traditionally been the most favorable option due to its cost and efficiency. Current costs and efficiencies values make the PV solar energy become an alternative to ST energy as supplier of industrial process heat. The aim of this study is to provide a useful tool to decide in each case which option is economically and environmentally the most suitable alternative. The methodology used to compare ST and PV systems is based on the calculation of the levelized cost of energy (LCOE) and greenhouse gas emissions (GHG) avoided by using renewable technologies instead of conventional sources of energy. In both cases, these calculations depend on costs and efficiencies associated with ST or PV systems and the conversion factor from thermal or electrical energy to GHG. To make these calculations, a series of hypotheses are assumed related to consumer and energy prices, operation, maintenance and replacement costs, lifetime of the system or working temperature of the industrial process. This study applies the methodology at five different sites which have been selected taking into account their radiometric and meteorological characteristics. In the case of ST energy three technologies are taken into account, compound parabolic concentrator (CPC), linear Fresnel collector (LFC) and parabolic trough collector (PTC). The PV option includes two ways of use of generated electricity, an electrical resistance or a combination of an electrical resistance and a heat pump (HP). Current values of costs and efficiencies make ST system remains as the most favorable option. These parameters may vary significantly over time. The evolution of these parameters may convert PV systems into the most favorable option for particular applications. INTRODUCTION Global primary energy consumption is continuously increasing [1]. The analysis of global energy sources matrix shows that primary energy demand continues preferring oil with a share of 35.7% of total energy consumption. Natural gas has replaced coal as the second energy resource to meet 25.6% of demand, mainly as a result of consumption from the United States and the Middle East. Coal has been relegated as the third energy source assuming 19.3% of total consumption [2]. From these data it is extracted that fossil fuels still concentrate more than 80% of the global energy sources matrix. Thermal energy is the biggest end-use sector which represents almost half of the total consumption in the European Union ahead of transport, one third, and electricity, one fifth of the final energy consumption. Process heat constitutes a major part of the energy use by industries, it can even be several times larger than electricity used [3]. Solar energy shows one of the highest potential prospects to reduce reliance on fossil fuels in the generation of process heat, particularly ST and PV solar energy. Renewable technologies are becoming cost competitive in a SolarPACES 2016 AIP Conf. Proc. 1850, 180005-1–180005-10; doi: 10.1063/1.4984572 Published by AIP Publishing. 978-0-7354-1522-5/$30.00 180005-1 number of countries and circumstance, but public support are still required to support deployment in many others. Most of the thermal energy needs in industrial production processes is below 250ºC, a temperature level which could be well supplied by ST technologies [4]. The area of application of solar technologies is large as it allows the heat transfer fluid reaches temperatures between 45ºC and 400ºC, to cover the full range of temperatures. The selection of one or other technology depends on their cost and the thermal requirements associated with each industrial process. Recently several studies focused on analyzing the possibilities of coupling a solar system to an industrial process have been developed. These studies identify required improvements in the collectors used in solar systems responsible for generating process heat, analyze the current market and compile a series of recommendations based on knowledge acquire through experimental facilities. Barriers that still hinder the development of solar systems as high investment costs, lack of public funding and low costs of conventional energy are identified [5-8]. First solar systems coupled to an industrial process were based on conventional solar technologies but currently new developments are beginning to become available[9-10]. The broad range of possibilities offered by solar energy has raised the interest of different countries such as Australia, Germany, Mexico or Tunisia. In the case of Australia, the research, development and demonstration program in solar industrial process heating was led principally by the Commonwealth Science and Industrial Research Organization. A study developed in Australia tried to identify potential sites for utilization of ST energy. The review identified 2498 individual sites by location, industry type, energy use and characteristic process temperature [11]. German studies also have attempted to select the sectors with the greatest potential. These sectors are analyzed to identify suitable processes for the integration of solar heat. The results of this study facilitate the prioritized application of ST energy in industrial sectors and processes [12]. Meanwhile Tunisia has analyzed the feasibility of integrating thermal collectors as a source of energy supply of industrial processes. Results show that currently ST systems are not economically interesting for end users with current subsidy schemes, but they could lead to significant economic benefits for the government [13]. Solar heat for industrial processes has repeatedly been identified as an important market for solar thermal applications, proof of this are the increasing number of applications [14]. Several reports have thoroughly analyzed the contributions of solar energy in meeting the energy requirements of several kind of industries, from the oil industry to the paper, textile or pharmaceutical industry [15-21]. PV solar energy covers a wide range of applications that supply electricity; however its use has not been generalised as a supplier of thermal process heat. Historically ST systems have been used to cover these needs because of their costs and efficiencies. Solar technologies costs, mainly PV systems costs are being reduced significantly [22], it is also expected that this trend continues over the next few years [23-24]. As result of this new situation this study seeks to compare economically and environmentally the use of ST systems and PV systems as source of heat for industrial processes. DESCRIPTION OF ANALYZED ALTERNATIVES The plant that is analyzed in this paper considers that solar energy system is coupled to a previously existing industrial process. Solar system function is to supply the thermal energy required to run the plant. The conventional source of energy of the plant works as an auxiliary power system replacing the new system when solar radiation transient do not allow meeting the needs of the industrial process. The characterization of the industrial process is not the subject of this paper but its needs, especially the working temperature, determines the most appropriate solar technology. This paper assess two alternatives, the first one analyzes the possibility of include a ST system while the second one considers the idea of include a PV system. In the case of ST systems three technologies are taken into account, CPC, LFC and PTC. This paper evaluates the thermal energy at the output of the solar field. The second option includes two ways of use of the generated electricity by the PV system, an electrical resistance or a combination of an electrical resistance and a HP. The HP is used to preheating the working fluid. Next figure shows representative schemes of analyzed configurations, from left to right, ST, PV and PV-HP systems. 180005-2 (a) (b) (c) FIGURE 1. Representative schemes of analyzed alternatives. SELECTED SITES Geographical, radiometric and meteorological information about the five different sites selected for this study is summarized in the table below. Annual global radiation (Hgi) on the optimum inclination (I) used for PV and CPC technologies, annual direct normal radiation (Hbn) and average ambient temperature (T) are obtained from Meteonorm (version 7.1.4). It is considered that the optimum inclination is that which provides the highest annual global radiation. Aperture normal radiation (HAN) used for LFC and PTC technologies and the coefficient Hgi/HAN are included in Table 1. HAN has been calculated according to N/S axes equations on horizontal surface [25]. TABLE 1. Geographical, radiometric and meteorological data. Site Geographical Data Radiometric and Meteorological Data Latitude Longitude Hgi Hbn T HAN Hgi/HAN I [º] [º] [kWh/m2] [kWh/m2] [ºC] [kWh/m2] [-] [º] Seville 37.41 N 6.01 O 2248.2 2349.0 19.8 2039.1 1.10 32 Hong Kong 22.28 N 114.16 E 1352.2 743.6 23.9 672.7 2.01 17 Dubai 25.26 N 55.31 E 2154.5 1767.9 28.4 1612.5 1.34 25 Berlin 52.52 N 13.38 E 1214.0 938.6 11.3 779.2 1.56 37 Calama 22.50 S 68.90 O 2597.7 2884.0 16.3 2650.0 0.98 22 HYPOTHESES This section summarizes the considered hypotheses to frame the conditions in which this analysis is performed: 1. Consumer and energy price index are 3% and 1.5% respectively. 2. Annual operation and maintenance costs are 2%, 4.5%, 5%, 1% and 2% of investment cost for CPC, LFC, PTC, PV and PV-HP technologies respectively. 3. All options include thermal energy storage. 4. Replacement costs: 10% of investment cost in year 10 for ST systems, this cost is not considered for PV systems. Replacement costs are only considered in the case of ST systems due to the durability of some of their devices as insulation, mirrors or vacuum tubes. In case of PV modules their durability is usually greater than 20 years. 5. The HP cost, included in the investment cost parameter of Table 2, ranges from 750€/kWe to 1300€/kWe depending on its size. 6. It is considered Joule efficiency equal to 100%. 7. Lifetime: 20 years for all technologies [26]. 8. Working temperature industrial process: 200°C. The HP preheats the working fluid up to 60°C. 9. Typical COP of heat pumps ranges from 1.56 to 5.37 [27]. This study considers a COP equal to 3. 10. It is considered that each kWe unit consumed by the HP is linked to a PV solar field surface that varies between 5m2 and 10m2 of PV modules. It depends on the efficiency of the PV system, which according to Table 2 ranges from 10% and 20%. 11. This study considers that generated thermal energy by ST system replaces thermal energy obtained from natural gas while the generated electrical energy by PV systems replaces the consumption of grid electricity when GHG emissions are assessing. 12. Ranges of efficiency, investment costs and working temperature of each technology are established according to specified sources in Table 2: 180005-3 TABLE 2. Investment cost, efficiency and working temperature. CPC LFC PTC PV Investment Cost(1) (€/m2) 225-325 260-425 330-560 150-800 Efficiency 0.30-0.70 0.60-0.70 0.45-0.75 0.10-0.20 Working Temperature (ºC) 45-250 100-250 100-400 - Sources [5], [28] [5], [28], [26] [28], [26] [29], [30] (1) Investment costs include thermal energy storage system costs. Wide range of PV technology cost is due to the fact that PV system considers two configurations. As Figure 1 shows the consideration of HP, electrical resistance and power conditioner (PC) depends on the selected configuration. The PC device is necessary to couple the resistance and the HP to the solar field. The relationship between the solar field power and the size of the HP has been established in the hypotheses number 10.  METHODOLOGY As mentioned previously the aim of this study is to provide a useful tool to decide which kind of system, ST or PV, is economically and environmentally the most suitable alternative in each particular situation. To achieve it the first stage of the proposed methodology consists on analyze the LCOE ratio linked to ST and PV systems. This ratio depends on investment cost (CI,ST/CI,PV), energy efficiency (ŋPV/ŋST) and solar resource (HPV/HST). The second stage of this methodology compares the environmental benefit ratio related to the use of ST and PV systems through the evaluation of GHG emissions avoided. This ratio depends on the environmental conversion factor (CFt/CFe), energy efficiency (ŋST/ŋPV) and solar resource (HST/HPV). Estimation of LCOE Ratio The first stage of this methodology estimates the LCOE of ST and PV systems. LCOE parameter is often used to compare the cost of generated thermal energy when different solar technologies are considered. The LCOE is evaluated according to the following expression [31] in which the numerator considers the expenses that take place throughout all the useful life and the denominator considers the energy generated over the same period. Variables r and s of this expression represent the average rate of consumer price index and the average energy price: 00 (1 ) (1 ) nn jj j j jj CE LCOE rs              (1) Life cycle costs (Ct) of this expression are calculated as the sum of investment cost (CI), annual values of operation and maintenance costs (CO&M) and replacement costs (CR): &tIOMR CCC C   (2) To evaluate the LCOE parameter it is also necessary to assess the generated energy. In the case of ST system the thermal energy (Et,ST) is obtained using area (A), the solar radiation (H) and the characteristic energy efficiency (ŋST). The value of H depends on the technology, Hgi values are employing when PV and CPC technology are evaluated while HAN values are use in case of LFC or PTC technologies (Table 1). Values used for energy efficiency have been obtained from cited sources in Table 2.The generated electrical energy by PV system (Ee,PV) is evaluated using global radiation and its characteristic efficiency (ŋPV). ,·· tST ST EAH   (3) ,·· ePV PV EAH   (4) When PV system is used two configurations are considered. In the first one thermal energy (Et,PV) required by the industrial process is generated by an electrical resistance. The power supply for this resistance comes from the PV system. The second configuration involves the use of a HP also powered by the PV system. HP is used to preheat the water to about 60ºC. In order to reach the temperature required by the industrial process, alleged in this case 200ºC, 180005-4 also an electric resistance is used. F1 and F2 factors indicate the percentage of electrical energy used by the HP and the electric resistance respectively.   ,12 ·· · · · t PV PV Joule EAHFCOPF   (5) General relationship between the LCOE of ST and PV systems is shown below:    &, 00 , & 0 0 (1 ) (1 ) · (1 ) (1 ) nn IOMR tPV ST j j jj ST n ntST PV IOMR PV j jj j CC C E rs LCOE E LCOE CC C s r            (6) The relationships between CO&M, CR and CI are specified in the third and fourth hypotheses. These relationships are used to obtain the LCOEST/LCOEPV ratio only in terms of CI.   &,, 000 ,, & 00 0 (1 ) (1 ) (1 ) ··· (1 ) (1 ) (1 ) nnn IOM R tPV tPV ST jj j I jjj ST ST nn ntST tST PV I IOM R PV PV jj jjj j CC C EE C rs s LCOE B EE LCOE C CC C s s r              (7) Table 3 shows the coefficient B of the expression above for all ST and PV combinations: TABLE 3. Coefficient B. Thermal System CPC LFC PTC Photovoltaic System PV 1.19 1.52 1.58 PV-HP 1.06 1.34 1.40 Generated thermal energy terms of ST and PV systems are substituted according to equations 3 and 5. LCOE ratio expression is as follows:         12 & 00 12 & 00 ·· · · · (1 ) (1 ) ······· ·· (1 ) (1 ) nn PV Joule IOM R ST PV jj I jj ST ST PV PV J oule nn PV I IOM R ST PV ST ST PV ST jj jj AH F COP F CC C CH rs LCOE BFCOPF LCOE C H CC C AH rs               (8) Estimation of GHG Ratio The second stage of this methodology evaluates the environmental advantages associated with the replacement of conventional sources of energy by solar systems. The relationship of the environmental impact avoided by the use of these renewable energies is evaluated in terms of GHG emissions avoided. It is considered that generated thermal energy by ST system replaces thermal energy obtained from conventional fuels while the generated electrical energy by PV system replaces the consumption of grid electricity. The expression below shows this relationship in terms of irradiance, efficiency and conversion factor coefficients. CFt represents the conversion factor from thermal energy to GHG emissions while CFe represents the conversion factor from electrical energy to GHG emissions. Characteristic values of both parameters allow the calculation of CFe/CFf ratio, which ranges from 1 to 4 [32]. Nevertheless, the CFe/CFt ratio is highly dependent on every country and year. In the case of Spain, in 2014, CFt is 204grCO2/kWht produced with natural gas and CFf is 649grCO2/kWhe, providing a CFe/CFf ratio of 3.18. 180005-5 , 12 , ····[··] tST ST t ST ST t J oule ePV e e PV PV PV GHG H ECF CF FCOP F GHG E CF H CF     (9) RESULTS AND DISCUSSION This section presents the most outstanding results of this study. The influence of the parameters previously specified on LCOE and GHG ratios is analyzed. Figure 2 includes graphs that show the evolution of the LCOE ratio depending on the investment cost and the efficiency ratios considering the case in which CPC and PV alternatives are used. Grey planes, LCOECPC/LCOEPV/PV-HP equal to 1, added in these two graphs indicates the conditions under which both technologies are economically similar. The surfaces below these planes specify the conditions to obtain higher benefits using a CPC system than a PV system. a) (b) FIGURE 2. LCOE ratio of CPC and PV systems depending on investment cost and efficiency ratios. When LCOECPC/LCOEPV ratio is lower than one, a ST system is more interesting than a PV system from an economic viewpoint. For PV systems without HP and CPC technology, as Figure 2.a shows, most combinations of CI,CPC/CI,PV and ŋPV/ŋCPC ratios provide a LCOECPC/LCOEPV ratio lower than one. Therefore, CPC technology is favorable against PV. For ŋPV/ŋCPC ratio values lower than 0.38 and any value of the CI,CPC/CI,PV ratio or ŋPV/ŋCPC ratio values higher than 0.38 and CI,CPC/CI,PV ratio values lower than 0.75, CPC technology is always favorable against PV. In the remaining cases, there are values for which PV may be the most favorable option. For PV systems with HP and CPC technology, as Figure 2.b shows, CPC technology viability against PV system viability is reduced. The above values go from 0.38 to 0.21 and from 0.75 to 0.51. Results of previous graphs are generalized for LFC and PTC technologies, Figure 3. The LFC technology is considered in the left graph while the right graph analyzes the PTC technology. ST systems are compared to PV systems in both cases. Blue crosses of the following graphs show results when PV systems employ a HP while red dots show results when the HP is not used. Results of these graphs are particularized for the case of Seville. (a) (b) FIGURE 3. LCOE ratio of LFC, PTC and PV systems depending on investment costs and efficiency ratios for Seville. 180005-6 Analyzing LFC technology against PV systems, the LCOELFC/LCOEPV ratio is lower than one when the ŋPV/ŋLFC ratio ranges from 0.1 to 0.4 and CI,LFC/CI,PV ratio is lower than 1.49. This value decreases to 0.65 when the PV system includes a HP. In the case of PTC technology against PV systems, the LCOEPTC/LCOEPV ratio is lower than one when the ŋPV/ŋPTC ratio ranges from 0.1 to 0.5 and CI,PTC/CI,PV ratio is lower than 1.15. This value decreases to 0.50 when the PV system includes a HP. Graphs of Figure 4 generalize these results for specified sites in Table 1. When CPC technology is used this step is not necessary because solar resource ratio of equation 8 is equal to 1. Next graphs show results for an efficiency ratio equal to 0.3. (a) (b) FIGURE 4. LCOE ratio of LFC, PTC and PV systems depending on investment costs for several sites. These graphs show that LCOEST/LCOEPV ratio values increase when a HP is included in a PV system. Among all sites, Hong Kong stands out as the one that provides the highest LCOEST/LCOEPV ratio values; Calama is on the other side. The most influential parameter on LCOE ratio is the solar resource coefficient, Hgi/HAN in Table 1, 2.01 in case of Hong Kong and 0.98 in case of Calama. To assess possible improvements that would equal ST and PV systems the following graphs are provided. The LCOEST/LCOEPV curves equal to 1 for each alternative are shown in these graphs. (a) (b) FIGURE 5. Investment cost ratio of CPC and PV systems depending on efficiency ratio for LCOECPC/LCOEPV equal to 1. In this paragraph an example of using of graphs above is analyzed. It is considering a ŋPV and a ŋCPC of 0.15 and 0.5 respectively. The CI,PV and the CI,CPC are 300€/m2 and 275€/m2 in each case. The obtained LCOE ratio is 0.298. If the CI,PV is reduced from 300€/m2 to 150€/m2 the LCOE ratio changes to 0.592. The two options analyzed are plotted in Figure 5.a, points 1 and 2 respectively. Both points are included into the ST system region. Another example is arisen, in this one the PV system includes a HP. CI,PV in this case ranges from 350€/m2 to 200€/m2, points 1 and 2 of Figure5.b respectively. The LCOE ratios obtained in this example are 0.67 and 1.18. Point 1 is included into the ST system region while point 2 is included into de PV region. This means that, from an economical point of view, in the first case is more interesting to dispose of a ST system while in the second case this situation changes to a PV system. Previous results of Figure 5 are extended for LFC and PTC technologies and all sites of Table 1. 180005-7 (a) (b) FIGURE 6. Investment cost ratio of LFC and PV systems depending on efficiency ratio for LCOELFC/LCOEPV equal to 1. (a) (b) FIGURE 7. Investment cost ratio of PTC and PV systems depending on efficiency ratio for LCOEPTC/LCOEPV equal to 1. Next graphs show, in the case of Seville, the evolution of GHG ratio depending on efficiency and conversion factor ratios for CPC, LFC and PTC technologies. FIGURE 8. GHG ratio of CPC and PV systems depending on investment cost and efficiency ratios for Seville. FIGURE 9. GHG ratio of LFC and PV systems depending on investment cost and efficiency ratios for Seville. 180005-8