Integration of solar thermal collectors in the dairy industry: A techno-economic assessment

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Integration of solar thermal

collectors in the dairy industry:

A techno-economic assessment

– A case study of Dubai Hassim Shah

Masterprogram i förnybar elgenerering

Master Programme in Renewable Electricity Production

ELEKTRO-MFE 21002

Master’s Thesis 30 credits

June 2021

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Abstract

Integration of solar thermal collectors in the dairy industry: A techno-economic assessment – A case study of Dubai

A case study at Alstom Transportation

Hassim Shah

A predominant amount of energy needed in the industrial sector is in the form of heat. A significant number of industries in the world still relies on fossil fuels for meeting their heat requirements. A transition to renewable energy for heating needs is at a snail's pace due to fossil fuel lock-in, cost superiority of conventional fuels, and less government support for renewable technology for thermal requirements. The dairy industry is one of the sectors that need heat energy for its production process.

This study deals with a techno-economic analysis on the integration of parabolic trough collectors in the dairy industry. The thesis finds the barriers for solar thermal collectors to evolve in the dairy sector and the viewpoint of the dairy industry towards the acceptance of solar thermal for meeting their thermal needs.

From a literature review it is observed that the need for dairy product will increase in the coming year. To meet the demand, the production process has to be increased. For sustainable production, companies have to rely on environment- friendly energy sources to meet the thermal demand.

In the thesis work, it was also found that for several solar fractions, the Levelized Cost of Heat (LCoH) of solar-assisted heating system is less than the LCoH of the fossil-fueled conventional boiler. Therefore, it is economically viable to integrate solar thermal collectors in the dairy industry. The project also compares the LCoH of solar assisted heating system when solar integration is done at a) feed water heating, b) direct steam generation, and c) process integration. The effect of integration point on the solar fraction, LCoH, and carbon mitigation potential is presented for a real case dairy unit in Dubai. The simulations are performed using dynamic simulation tool. Results show that minimum LCoH and solar fraction are achieved for process integration. The process integration results in up to 90 % of the solar fraction. Through process integration, the LCoH of the conventional boiler can be reduced by 60%.

Keywords: Solar thermal, parabolic trough collector, levelized cost of heat, integration schemes

Supervisor: Puneet Saini & Carlo Matteo Semeraro Subject reader: Juan de Santiago

Examiner: Irina Temiz ELEKTRO-MFE 21002 Printed by: Uppsala University

Faculty of Science and Technology

Visiting address:

Ångströmlaboratoriet Lägerhyddsvägen 1 House 4, Level 0

Postal address:

Box 536 751 21 Uppsala Telephone:

+46 (0)18 – 471 30 03 Telefax:

+46 (0)18 – 471 30 00 Web page:

http://www.teknik.uu.se/student-en/

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Popular Scientific Summary

Global energy consumption is increasing day by day. Among the total energy consumption, half of the energy is consumed in the form of heat. Industries are significant consumers of heat energy. The temperature requirements in the industrial sector can be classified into three levels: a) low-temperature, b) medium temperature, and c) high temperature. 30% of the industrial sector need heat energy which belongs to the low-temperature category. Dairy industries require temperature in the range of 50⁰C to 200^oC and the industry belongs to the low-temperature category. Most of the dairy industries rely on fossil fuel to generate heat energy. The emission during the combustion of fossil fuels may increase the level of greenhouse gas (GHG) in the atmosphere.

An increase in GHG can negatively impact the environment through global warming, and many other hazards. GHG emission from industries can be reduced by depending on clean energy technologies for heat generation. Solar thermal technology is one of the renewable energy technologies used to generate heat for domestic, industrial and district heating purposes. Even though solar thermal technologies are gaining acceptance in society, there are still barriers for it to evolve in the industrial sector. High investment cost, long payback period, and intermittent solar power are hindrances for industrial owners to have solar thermal installations. Good availability and cheap fossil fuels drive industries to rely on conventional fuels.

For industries to switch to solar thermal power, the technology must be economically feasible and technically possible to integrate for industrial heat needs. As solar thermal technology can generate steam/hot water at the temperature and pressure required for milk processing, it is technically possible to integrate for heat needs in the dairy industry. Research papers and industrial experts have validated the technical possibility of utilization solar thermal technology for thermal needs in the dairy industry. For checking the economic feasibility of solar thermal technology, it is required to find the cost of heat generated by the technology. IEA SHC (International Energy Agency, Solar Heating and Cooling) task 54 described a parameter; Levelized Cost of Heat (LCoH). LCoH is the cost of heat generated by a heating device analyzed over a period of time. LCoH can be used to compare different technologies.

In this thesis, an industry in Dubai is selected for analysis. The LCoH of the conventional boiler used in the industry and the LCoH of solar-assisted heating system for the industry is found to check the economic feasibility. Through analysis, it is found that the LCoH of solar assisted heating system is lesser than the LCoH of conventional boiler, which shows that it is economically feasible to utilize solar thermal technology for heat needs in the dairy industry.

Regarding integrating the solar thermal system to the existing system, the solar thermal system at three integration points was analyzed in this project work. The three integration points considered are a) Direct steam integration, b) feedwater preheating, and c) process integration. Solar thermal integration at different integration points showed variation in the system LCoH, solar fraction and carbon emission of the system. Among the three integration schemes, process integration at a solar fraction of 91.2% showed the least LCoH of 26 Euro/MWh, which is 60% less than the LCoH of the conventional boiler. At the same time, the carbon emission from the system can be reduced by 77.6%.

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Acknowledgement

I would like to thank my supervisors from Absolicon Solar Collector AB, Puneet Saini and Carlo Matteo Semeraro, who gave guidance throughout the project. Without them, this project will not be a success. I am grateful to Joakim Byström, CEO of Absolicon Solar Collector, for giving me the chance to work with Absolicon to do this thesis.

I am thankful to my subject reader, Juan de Santiago, for giving me proper guidance and support throughout the project and for encouraging me to achieve heights.

I would like to thank everyone in the sales & marketing department of Absolicon Solar Collector AB for their valuable support.

Last but not least, I am thankful to my uncle Shihansha, my mother Reeja and brother Harsha for supporting me for my studies and encouraging me always. I would like to thank my family and friends for the moral support and encouragement given to me for finishing this project.

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List of figures

Figure 1: Block diagram showing the integration of solar thermal collectors in the dairy industry [13] ...5

Figure 2: Image of a parabolic trough collector [14] ...6

Figure 3: Schematic diagram of conventional boiler system [18]. ...8

Figure 4: Schematic diagram of the heating section of pasteurizer[22]. ...10

Figure 5: Schematic diagram of direct steam integration [20]. ...11

Figure 6: Schematic diagram of integration of solar thermal collectors for feed fluid preheating[20]. ...11

Figure 7: Flow chart showing the processes in the dairy industry. ...12

Figure 8: System with two inlets and two outlets[25] ...14

Figure 9: System with inlets and outlets to the storage tank combined [25] ...14

Figure 10: System with variable storage tank [25] ...14

Figure 11: Schematic of a solar thermal system with unfired boiler [25] ...15

Figure 12: Solar thermal with flash tank[25] ...15

Figure 13: Daily load profile of the plant ...19

Figure 14: Yearly load profile of the plant ...20

Figure 15: Graph plotted between LCoH and Solar Fraction for solar thermal integration for feedwater preheating. ...25

Figure 16: A plot between solar fraction and carbon saved with the increase in solar fraction for solar thermal integration for feed water preheating...26

Figure 17: Graph plotted between LCoH and Solar Fraction for direct steam integration of solar thermal collectors ...27

Figure 18: A plot between solar fraction and carbon saved with the increase in solar fraction for direct steam generation. ...28

Figure 19: Graph plotted between LCoH and Solar Fraction for process integration ...29

Figure 20: A plot between solar fraction and carbon saved with the increase in solar fraction for process integration. ...30

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List of tables

Table 1: Table showing temperatures for different processes in the dairy industry[24]. ...13

Table 2: General information of the dairy processing plant ...18

Table 3: Technical details of the boiler used in the case ...19

Table 4: Financial details of the boiler ...20

Table 5: Data regarding the processes going on in the industry. ...21

Table 6: Technical specification of Absolicon T160 [29]. ...22

Table 7: Simulation results for solar thermal integration for feed water preheating. ...24

Table 8: Simulation results for solar thermal integration for direct steam generation ...27

Table 9: Simulation results for process integration. ...29

Table 10: Comparison between different integration points ...33

Table 11: Carbon saved for ST integration for feed water preheating ...39

Table 12: Carbon saved for ST integration for direct steam generation ...39

Table 13: Carbon saved for ST integration for process heating. ...40

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Abbreviations

GHG Greenhouse gas

PV Photovoltaic

ST Solar Thermal

DHW Domestic hot water system

PTC Parabolic trough collector

LCoH Levelized Cost of Heat

IEA-SHC International Energy Agency, Solar Heating & cooling

CSH Concentrated solar heating

CIP Cleaning in place

UAE United Arab Emirates

LPG Liquid petroleum gas

DNI Direct normal irradiation

kWh/y Kilowatt-hour per year

MWh/y Megawatt-hour per year

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1. Introduction

Renewable energy is increasingly gaining acceptance in society. Climate change due to the combustion of fossil fuels is the driving force for that. Other potential drivers for the growth of renewable energy, such as solar energy, are the fall in the solar device price due to the devices' mass production and the greenhouse gas (GHG) pricing [1]. Solar energy is used to power domestic, commercial, and industrial needs both in the form of heat and electricity. Photovoltaic (PV) and solar thermal (ST) technology are the two technologies used to harness energy from the sun. PV technology uses photons (packets of energy) from the sun to generate electricity, using PV cells. In contrast, ST technology concentrates the sun's radiation to generate heat in the form of hot water or steam [1]. Industrial process heating, domestic hot water (DHW) system, district heating is the leading solar thermal system application.

Heat energy accounts for half of the total energy consumption considering the global energy demand, and it is predicted that the demand will increase in the future [2], [3]. From that, a significant share is covered by thermal needs for industrial process heating. A split-up of temperature needs in the industries is that 30% of the total industrial needs are under 150^oC, intermediate and high-temperature requirements account for 22% and 48%, respectively [3]. Even though solar thermal energy can meet most of these industrial process heating demands, industries still rely on boilers that consume fossil fuels for combustion, which can lead to severe environmental impacts like global warming, and many adverse effects on humankind [3]. The growth in solar thermal usage for industrial process heating is at a snail pace due to barriers such as fossil fuel lock-in, cost superiority of conventional fuels, and less government support for renewable technology for thermal requirements [4].

The dairy sector or the processes starting from the farm level to customer level in the milk industry has a significant share in the total carbon footprint generated by the whole industrial sector. Several studies have been done to measure the carbon footprint of each level in the dairy sector. A study done at a prominent dairy industry in Europe in 2013 found that 7.4 kg, 6.5 kg, 8.1 kg, and 1.1 kg of carbon dioxide are emitted for per kg production of dairy products such as whey-based products, milk-based products, cheese, and butter respectively [5]. The processes involved in the dairy industry can be classified into two segments (i) pasteurization of milk and (ii) process for value-added products such as cheese, butter, etc. [6] For a dairy plant, 70% of the energy is required for process heating. The plant requires temperature in the range of 50^oC to 200^oC for various operations in the form of steam and pressurized hot water [6].

This thesis deals with a techno-economic analysis for integrating ST technology in the dairy industries in Dubai. For the investigation, Absolicon's T160 parabolic trough collector (PTC) is used. Initially, the technical and economic viability of ST integration in the dairy sector is checked. The optimal solar fraction and the best integration point in the steam network that can achieve the least Levelized Cost of Heat (LCoH) and minimum CO2 emission are found through analysis.

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2 1.1 Purpose of the thesis

The thesis aims to analyze various aspects of integrating ST technology in the dairy industry. The load profile, thermal demand, and fuel expenses of a specific industry are analyzed for achieving this. In the end, a system and optimal integration point that can achieve minimum LCoH and minimum carbon emission are proposed.

1.2 Thesis Goals

There are three goals for the thesis. The goals are formulated in such a way that it can satisfy the purpose of the study.

1. Is it viable, technically and economically, to utilize concentrated solar heating (CSH) for various thermal needs of milk processing?

2. Comparing the utilization of solar thermal and conventional method for steam production, which method is energy efficient and cost-efficient, and what fraction of solar thermal will make the process economically feasible?

3. A comparative analysis on integrating solar thermal system in different points in the conventional steam network to study its effect on the steam system's LCoH and carbon emission.

1.3 Methodology

The research work consists of two parts: market analysis and techno-economic analysis. The first part was a market analysis. Conducting a market analysis was helpful to know about the acceptance of technology in society. In this project, market analysis was done to learn about the dairy industry owners' opinions towards ST technology for industrial heating needs. It also helped to determine the barriers and drivers for the technology to penetrate the dairy sector. For conducting the market analysis, semi-structured interviews were done in parallel with operation managers of dairy industries. The companies' viewpoint towards using solar thermal energy for their heating needs was found. In the same interview, data regarding the heat carrier, operation profile, fuel expenses, and fuel consumption were collected to be used for the next stage.

The next part of the thesis is a techno-economic analysis. The technical possibility of utilizing ST technology in the dairy industries is already proven. Therefore, in this project, it is validated using a literature review. The paper published on 2013 [7], explains the pilot installations done in dairy industries and its technical possibility. Then the LCoH of a conventional boiler was found. This was done using an excel model based on the LCoH formula proposed on task 54 of the International Energy Agency, Solar Heating and Cooling Program (IEA-SHC). With the same excel tool, the LCoH of the solar-assisted heating system was also found.

As mentioned above, an excel tool to calculate the LCoH of a heating system was developed. The excel model can be operated in multiple boundary conditions. It was required to provide certain inputs to the tool to calculate the LCoH of the system that was to be analyzed. Inputs to be given to the tool are given below.

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3 1. Initial investment cost of the system.

2. Subsidies and incentives available for the installation and maintenance of the system.

3. The corporate tax rate for the heating system.

4. The estimated residual value of the system.

5. Discount rate or inflation rate.

6. The period of analysis.

7. Carbon tax in the location.

The technical details that are needed as input are:

1. The power output of the heating system.

2. Full load and part load efficiencies of the system.

3. Turn down ratio of the system if the heating system is a boiler.

4. The maximum flow rate of the boiler.

5. Type of fuel used by the boiler.

6. Amount of fuel consumed.

7. The calorific value of the fuel.

8. Load profile of the system.

After finding the LCoH of the conventional boiler system, Absolicon Simulator was used to find the solar fraction, size of the solar field, the volume of the storage tank and LCoH of the heat energy generated from the solar heating system. The results obtained from the simulator and the excel tool were utilized to find the global LCoH or the LCoH of the solar-assisted heating system. If the global LCoH is found out to be lesser than the boiler LCoH, then it can be concluded that integrating a ST system to the existing fossil-fueled boiler is economical [8].

Similarly, Absolicon simulator was used to check the variation of LCoH when the integration was done at different points in the steam network. The variation in the LCoH values was used to find the best integrating point that can give minimum LCoH.

Literatures are available, explaining that the energy efficiency of a system can be found out using different indicators. One such indicator to calculate energy efficiency is the economic-thermodynamic indicator [9]. As per the economic-thermodynamic indicator, the input is considered to be the cost required to operate a system. The output is the energy derived from the system. The ratio of both parameters gives the energy efficiency of the system. This concept compares the energy efficiency of the conventional boiler system and solar-assisted heating system in this project.

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2 Theory

2.1 Overview on renewable energy for heating needs in the industrial sector

As mentioned above in this report, considering the end-use energy, heat is consumed the highest in the world. Renewable energy used to generate this heat energy accounts for 11% as of 2019, whereas fossil fuel is the primary source for heat generation. In 2019, 40% of the carbon emission was due to the utilization of fossil fuels [10].

Industries are significant consumers of heat energy. In 2020, 50% of the global heat consumption was accountable for industrial process heating. China, USA, India, European Union, and Russian are the major consumers of heat energy [10].

In the industries, among the renewable resources used for energy generation, bioenergy accounts for are large portion. This is because the by-product of the production process would be biofuel and used to feed the biomass boilers. Renewable electricity is another option selected by the industries due to the reduced cost of the photovoltaic system and the easy availability of labour for service. There is a rapid spread of the utilization of heat pumps for heat supply. By the end of 2019, 13.5 million heat pumps were operating in European Union [10].

As per reports, there was no significant increase in renewable energy utilization for heat generation in 2020. But the demand for heat is expected to recover by 2021-2022. Then there would be an increase in the renewable energy utilization for heat needs considered to 2019 usage. The consumption of solar thermal power is expected to accelerate during 2021 by +8%. China, USA, and European Union will be the primary consumers and responsible for the growth by 70% [10].

The major barriers to the evolving solar thermal system would be the lack of policy attention and increased interest from policymakers towards heat electrification. The driving factors for the utilization of solar thermal systems are the simplicity of the technology and minimal maintenance.

The dairy industry is one among the industrial sector the requires a significant amount of energy for heating needs. The United Nations food and agricultural organization forecasted that dairy consumption might increase to 99 kg/person/year, which is 19% more than the present value. To meet the demand, there should be an increase of 22% in global milk production by 2027. Milk processing is an energy-intensive process, requiring fossil fuel combustion for production purposes, leading to greenhouse gas emissions [11].

In this project, it is analyzed that dairy industries are ready to switch to renewable energy for the production process if the adopted technology is economically feasible. The economic feasibility of technology is influenced by fuel, processes, system efficiency, etc [12]. Industries consider the adoption of ST technology and replacement of exciting technology as expensive. Industrial owners also consider factors like the lifetime of an existing asset, cost of current fuel, utilization time, area availability, and renewable energy resources availability before selecting a solar thermal system for heating needs.

Studies done by the Australian Renewable Energy Agency (ARENA) states that solar thermal technology will become feasible, or a cost parity to the conventional fuel price can be achieved when the system size

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is large, or the annual consumption of heat is high. In several locations, medium-level systems are also economically feasible when the cost of conventional fuel is high [12].

2.2 Utilization of solar thermal in industrial process

As the environmental harm is increasing due to fossil fuel utilization for energy needs, the essentiality of using clean fuels for the same is coming into the picture. In this thesis report, through literature study, section 2.3 & 2.10 explains the available solar thermal technology and the energy demand in the dairy industry, respectively. The research paper [13] shows the trend of fossil fuel consumption in the industrial sector. The technical possibility of integrating solar thermal technology in the dairy industry for the heat requirements is also shown.

In the present scenario, solar thermal collectors are mainly used for domestic heating purposes. If the solar thermal collectors are to be used for industrial processes, the collectors must generate heat in the temperature range specified for operations like sterilization, pasteurization, etc. It is tricky to integrate solar thermal collectors in the existing process line, and many dairy industries work 24/7 with continuous energy demand. As solar power is available only during the daytime, a storage unit or a hybrid system is required to tackle intermittency.

Figure 1: Block diagram showing the integration of solar thermal collectors in the dairy industry [13]

Several methodologies are available in scientific papers for integrating solar thermal collectors in the industrial process line. The literature [13] states that, for integration, it is required to find the operating temperature of all the processes in the dairy industry. According to the temperature range, the type of solar collector that can be used is then selected. The very next step is to know about the total thermal energy required for the dairy industry. This data can be used to find the area of solar collectors needed.

A proven method for the integration of solar collectors is through pinch analysis. In this method, the pinch temperature is to be found out. Data of a process is represented as a stream, which is a function of mass flow rate, specific heat capacity, supply temperature, and target temperature. The data of all the streams are combined, and a grand composite curve is formed. Hence, there will be a hot stream and a cold stream.

Conventional heat

source Process

Solar thermal source

Storage

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The minimum temperature difference between the hot stream and the cold stream is called pinch temperature. The collectors are then integrated into points of minimum temperature difference [1].

2.3 Concentrated solar thermal technology

A concentrated solar thermal technology uses a mirror or reflecting surface to concentrate solar radiation to a particular point to generate heat. Solar radiation that initially fall on the reflector surface are reflected to a receiver at the reflector's focal point. As parabolic trough collector is used for analysis in this study, the same is explained in this report.

Figure 2: Image of a parabolic trough collector [14]

Figure 2 shows the image of a parabolic trough collector. The main components in the collector are the curved reflecting back surface and the receiver tube. The solar radiation concentrated in the receiver tube will heat a mixture of water and glycol that is flowing through the receiver tube. The generated heat energy is then used to produce steam or hot water. Parabolic trough collectors' main advantage is the tracking system, a north-south aligned tracking system that will track the sun from east to west. Parabolic trough collector can generate heat up to 350^oC to 400^oC, which is suitable for most industrial applications [15].

2.4 Levelized cost of heat (LCoH)

It is a parameter used to measure the cost of heat generated by a system. For finding the Levelized cost, it is required to analyse the system over a period of time. The significance of this parameter is that it can be used to compare different heat-generating systems. Unit of LCoH is €/kWh. Below shown is the formula used for the calculation of LCoH [16].

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LCoH =

𝐼_𝑜−𝑆₀+ ∑ 𝐶𝑡(1−𝑇𝑅)−𝐷𝐸𝑃𝑡.𝑇𝑅 (1+𝑟)𝑡 −

𝑇𝑡=1 𝑅𝑉

(1+𝑟)𝑇

∑ ^𝐸𝑡

(1+𝑟)𝑡

𝑇𝑡=1 (1)

where 𝐼₀ is the initial investment cost in Euros, 𝑆₀ is the available subsidies or incentives in Euros, 𝐶_𝑡 is the operation and maintenance cost in Euros per year, 𝑇𝑅 is the corporate tax rate in percentage, 𝐷𝐸𝑇_𝑡 is the depreciation of asset is Euros per year, 𝑅𝑉 is the residual value in Euros, 𝐸_𝑡 is the final energy consumption of the system in kilowatt-hour per year, 𝑟 is the discount rate in percentage and 𝑇 is the time period of analysis in years.

(1 can be used to find the LCoH of a system that can generate heat. The terms that are used in the equation are given above. The operation and maintenance (O&M) cost of the system includes the maintenance cost, fuel expenses and carbon tax. The asset depreciation of the system can be found from the estimated residual value and by using straight-line depreciation. The fuel type, calorific value of fuel and efficiency of the boiler can be used to find the final energy consumption of the system for each year. The O&M cost can vary according to the turndown ratio of the boiler. Turn down ratio of the boiler is used to find the minimum operating capacity of the boiler. If the functional load of the boiler goes below minimum capacity, the boiler will be affected by mechanical damages, which can increase the O&M cost.

The same equation can be used to calculate the LCoH of a conventional boiler, solar thermal system and the LCoH of a solar-assisted heating system. After finding the LCoH of the conventional boiler and the solar thermal system, the weighted sum of both values is considered as global LCoH or LCoH of the solar- assisted heating system. The weighted sum is the sum of the product of LCoH of the system and the energy divided by the total energy [16].

𝐺𝑙𝑜𝑏𝑎𝑙 𝐿𝐶𝑜𝐻 = (𝐿𝐶𝑜𝐻_{𝑏𝑜𝑖𝑙𝑒𝑟}∗ 𝐸𝑛𝑒𝑟𝑔𝑦 𝑓𝑟𝑜𝑚 𝑏𝑜𝑖𝑙𝑒𝑟) + (𝐿𝐶𝑜𝐻_{𝑠𝑜𝑙𝑎𝑟}∗ 𝐸𝑛𝑒𝑟𝑔𝑦 𝑓𝑟𝑜𝑚 𝑠𝑜𝑙𝑎𝑟) 𝑇𝑜𝑡𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦

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2.5 Solar fraction

Solar fraction is the amount of energy that the ST system provides to the total energy need. It is zero if no energy is supplied by solar, and it would be 1 if the solar thermal system meets all the energy. The solar fraction of the system depends on the size of the solar field, the volume of the storage tank, the meteorological parameters of the location, and the load profile. The same system installed in different places with different weather patterns would show different solar fraction. The system at a sunny location will deliver a higher solar fraction than a system in cold weather condition [17].

In this thesis, the solar fraction is considered as the fraction of energy that the solar thermal system can contribute to the specific load. If the integration is done for feed water preheating and if the solar fraction is 20%, it signifies that the solar thermal system will meet 20% of the boiler's energy required for feed water preheating.

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8 2.6 Conventional steam network in the industry

Figure 3: Schematic diagram of conventional boiler system [18].

Figure 3 illustrates a conventional steam network. The treated water is fed to the deaerator, where the corrosive gases present in the water are removed. Deaeration protects the boiler system from corrosion and can be done in both chemical and mechanical ways. From the deaerator, water is transferred to the economizer, where the water temperature is adjusted to a level that is suitable for the hot boiler. This helps to reduce mechanical vibrations that may occur in the system when cold water falls in the hot boiler. The boiler would then increase the temperature of the water, and hence steam is generated. The generated steam is used for different industrial processes, and a part will be used for the boiler system for the economiser operation [19].

In the diagram, several points are indicated with numbers from 1 to 6. These are the points where solar thermal collectors can be integrated to supply heat. Integrating the solar thermal collector at those points can create significant variations in LCoH and CO2 emission from the boiler system [20].

2.6.1 Condensate tank

A condensate tank is an optional part of a boiler system. The tank collects the condensate of the steam after the process. Condensate will have an energy that can be used to heat the makeup water. Adding a condensate tank won't affect the output of the steam system; instead, it helps to reduce the fuel required to preheat the feed water to the boiler [19].

2.6.2 Deaerator

A feedwater tank is employed to meet three needs of a boiler system. It will act as a water reservoir for the boiler, remove the corrosive components in the water, and preheats the water to increase overall efficiency and avoid mechanical shocks [19].

There are two types of deaeration, mechanical deaeration and chemical deaeration. In a chemical deaerator, chemicals are added, which reacts with oxygen, forms harmless oxygen compounds, and keeps the boiler safe from corrosion. In mechanical deaeration, the water temperature is increased to decrease the level of oxygen. A feedwater tank that uses mechanical deaeration is called a deaerator [19].

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9 2.6.3 Economizer

The flue gases that comes out from the boiler will have a high amount of temperature. An economizer will act as a heat exchanger and recovers a significant portion of that heat from the flue gas. The recovered heat is given to the feed water. It is mandatory to keep the flue gas temperature above a particular level before passing to the feed water. The reason is to avoid the mixing of Sulphur trioxide in the water, which is produced during the combustion of fuels [21].

2.7 Different integration points in the steam network

In section 2.6, different integration points in the steam network are mentioned. Among the six integration points mentioned, three points are selected for the study, and those are process integration (point 6), steam integration to the network (point 4), and feed fluid preheating (point 3). Among the other possible integration point, makeup fluid preheating is not selected for study because the demand at that point is highly variable. It is expected to have a variation in the LCoH when the solar thermal system is integrated into each point. An overview of each point, its advantages and disadvantages are explained in the sections below.

2.7.1 Process integration

There will be a single boiler or multiple boilers that supply steam or hot water for all the processes in the dairy industry. The mainstream will carry the total steam output from the boiler, and derivatives will be taken at different processes as per requirements. For process integration, the steam/hot water generated by the solar collector will be integrated directly into the process level to meet the heat demand of each process.

Pasteurization and cleaning in place (CIP) are the primary processes that demand heat for the dairy industry.

Both water and steam can be used as the heating medium for pasteurization. Due to high differential temperature, hot steam is not used commonly. Steam at 3 bar to 4 bar is used as a heating medium. Steam will heat the water, which in turn heat the product to the required temperature. Figure 4 shows the closed heating system for the pasteurization unit. It consists of valves to regulate steam, heat exchanger, a centrifugal pump that circulates the service water, and an expansion vessel to compensate for the increase in the circulating medium volume.

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Figure 4: Schematic diagram of the heating section of pasteurizer [22].

With the help of temperature sensors, the holding tube's temperature is measured, and the steam regulating valve is adjusted to maintain the required temperature in the holding tube. For cooling the milk to a lower temperature, a cooling system is also needed. In most cases, ice water is used to cool down the milk. Other coolants such as brine solution and alcohol can also be used to avoid the cooling medium's freezing.

While integrating at the process level, the main advantages are the requirement of low temperature and pressure heating medium, which can increase the performance of the solar collector field. At the same time, the integration method for the different process would vary, which can be considered as a drawback for this case.

2.7.2 Steam integration to the network

In this type of integration, steam from the solar thermal collectors is directly delivered to the steam drum of the boiler. The feed fluid is fed to the solar collector loop, where it is partially evaporated. The mixture of steam and water is passed to the steam drum. In the drum, the water and steam will be separated. When the steam attains the required pressure, it is fed to the main steam line. Figure 5 shows the schematic diagram of steam integration in the main steam line. In the industry together with the above-mentioned system, steam is produced in the steam boiler and supplied to the main steam line in which the ST thermal system supply heat. A derivative from the steam boiler is given to the degasification tank to remove corrosion creating gases in the feed water. The input to the degasification tank is the condensate that is formed when steam is used in the process section.

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Figure 5: Schematic diagram of direct steam integration [20].

2.7.3 Feed fluid preheating

In a conventional steam boiler, the boiler feedwater is degasified and preheated to protect the boiler from corrosion and avoid vibration occurring in the boiler when low-temperature water is fed to the boiler. This is done in a degasification section that uses steam from the boiler to remove the gases that cause corrosion and preheat the water. Solar thermal collectors can be integrated at this point to preheat the water, thereby reducing the utilization of the boiler for feed fluid preheating. Figure 6 shows the schematic diagram of the integration of solar thermal collectors for the feed fluid preheating. The orange colored block visible in the Figure 6 is the heat exchanger of the ST system that heats up the water from degasification tank and supply to the boiler.

Figure 6: Schematic diagram of integration of solar thermal collectors for feed fluid preheating [20].

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12 2.8 Carbon tax

It is an indisputable fact that CO2 emission has to be leashed to an extent to protect the planet from climate change. Emission trading systems, energy tax, emission standards, and carbon tax are some of the policy methods adopted to reduce carbon emissions. Among this carbon tax is an additional amount imposed on fossil fuels-related fuels depending on the fuel's carbon content [23].

Carbon pricing or carbon tax is a method that imposed a price on the carbon emitted by a firm. The system aims to motivate the industries to switch to renewable energy or a strategy to reduce their carbon emission.

The significant benefits of the carbon tax are increased promotion of substituents for fossil fuels and investment or revenue that can be used for subsidizing the project to protect the environment. On the other hand, it can create a negative impact also on economic growth [23]. Countries like Sweden, Norway, Finland, New Zealand, and Switzerland have already adopted carbon tax. Studies say that a carbon tax at the rate of "$65 per ton of CO2 could stabilize the emission rate of Norway in 2020 at the 1989 level" [23].

2.9 An overview of the processing steps in the dairy industry

A dairy processing unit is where the milk produced in the dairy farms is collected and processed to store it and obtain other milk products like cheese, milk powder, etc. The processes and temperature requirement in the dairy industry vary according to the final product. In this section, different processes undergone in the dairy industry are discussed.

Pasteurization and homogenization are the two essential processes in the dairy industry. Both the above two methods require heat. Pasteurization is done to kill the pathogens living in the milk, whereas by homogenization, the milk's fat content is broken down into smaller molecules. Below given flow diagram shows various steps done for both processes.

Figure 7: Flow chart showing the processes in the dairy industry.

2.10 Heat Requirements in the dairy industry

Heat treatment is done in milk to avoid the growth of microorganisms. Through studies in the mid-19^th century, Louise paster found that heat treatment can be considered a preservative technique for milk.

Pasteurization is a heat treatment process that destroys bacteria like tubercle bacillus in milk without any change in milk's physical and chemical properties [24]. But high heat treatment can cause foreign taste

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and facilitate the growth of bacteria. At the same time, mild heat treatment helps in the preservation of milk.

Now heat treatment is adopted in all dairy plants as it helps to retain the constituents in milk from degrading and to keep optimum pH [24]. Pasteurization is a heat treatment method. In this process, milk is heated to a temperature not below 72^oC for 15 seconds and rapidly cooled down [22]. Apart from this, heat is used to produce other milk products such as cheese, whey powder, milk powder, etc.

A vital factor to be considered during heat treatment is the relation between temperature and holding time.

Table 1 shows the temperature required for each process and the holding time of heat [24].

Table 1: Table showing temperatures for different processes in the dairy industry [24].

Process Temperature Holding time

LTLT pasteurization of milk 63 30 min

HTST pasteurization of milk 72 - 75 15 – 20 s

HTST pasteurization of cream >80 1 – 5 s

Ultra-pasteurization 125 - 138 2 – 4 s

UHT (flow sterilization) normally

135 - 140 A few seconds

Sterilization in containers 115 - 120 20 – 30 min

From Table 1, it is inferred that most of the dairy industry process needs moderate temperature, and all those temperature needs can be met with the parabolic trough collector, which is taken for the study.

2.11 Design of solar industrial process heating system

Checking the feasibility of the solar thermal system

While designing a solar thermal system for the industrial process, it is essential to check whether the system is suitable or feasible for the location and end-user. For the suitability or the feasibility assessment, it is necessary to know about the solar radiation of the site, ambient temperature, load profile, load return temperature, availability of space for the installation, etc [25].

Economics also plays a vital role in the selection of a solar thermal system. If the system's present fuel is of lower cost and if the industry does not bother the effects of using the current system, then installing a new solar thermal system won't be a feasible option for the industrial owner.

Different solar thermal system configurations

Several configuration schemes can be adapted for the solar thermal system according to the end user's need, application, and type of storage etc. Figure 8 shows a simple configuration with a mixed storage tank. Storage units can be used in a solar thermal system to store hot water or steam when the solar

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radiation is available and supply the same when there is the absence of solar radiation. Suppose there is a thermal battery or a heat storage system in between the collector and the load. In that case, the collector can transfer heat to the storage without considering whether the load is connected or not. The system has two inlets and outlets. This type of system is mainly used for small loads. That is, this type of system suits best when the difference between the supply temperature and the return temperature (T) is small. There are chances for the collector inlet temperature to be higher than the required temperature if (T) is large or when the load is a constant. This issue can be because the inlet water to the collector is supplied from the tank that supplies water to the load [26]. For obtaining better performance of the system, those two inlet and outlet pipes can be combined as shown in Figure 9, making it a two-pipe system. For a two-pipe system, the cold return water from the load will go to the collector. If the load is operated for most of the time of the day, this could aid the system's efficiency, and the load requirement can be met with the hot water present at the top of the storage tank. But the charging and discharging of the storage will be the same as the four-pipe system [26]. But the drawback is that the system requires additional control devices.

Figure 8: System with two inlets and two outlets

[25] Figure 9: System with inlets and outlets to the storage tank combined [25]

Figure 10: System with variable storage tank [25]

Other options to improve the system's performance are maintaining a thermocline in the storage tank or using a tank with variable volume. A system with a variable volume tank is suitable for the case when the

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load is operated mainly at a time when the collector doesn't produce heat, say from afternoon to late night [26]. Figure 10 shows a system with a variable volume storage tank.

The configurations discussed above are mainly used to get hot water. For steam generation, the solar collectors can be configured with an unfired boiler system or a flash tank [25]. Figure 11 shows the configuration of a solar thermal system with an unfired boiler. The solar collectors will concentrate the solar radiation to increase the temperature of a working fluid. The working fluid used in the system can be water, but a non-freezing liquid with low vapour pressure is usually used. The tubes that carry this working fluid are made in contact with feed-in water in the boiler where the steam is generated. For an unfired boiler system, the collector's operating temperature must be higher than the steam delivery temperature. The flow rate through the collector is varied to achieve the required temperature at the collector outlet.

Figure 11: Schematic of a solar thermal system with unfired boiler [25]

On the contrary, the collector heats pressurized water. With the help of a throttle valve, the liquid's pressure is reduced and flashed to steam. This is the method used in the system with the flash tank [25].

Figure 12: Solar thermal with flash tank [25]

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16 System sizing

The system sizing is done on in-house developed tools. It consists of a component analysis using TRNSED, and then system simulations using OCTAVE. The TRNSED is used to get results for solar collector output for each hour, without any system connected to it. The output from this tool used as in input to the OCTAVE script. The tools are combined in an MS visual studio. The tank sizing is based on a techno-economic optimisation to minimise the LCoH. Various tank volumes are iterated to see the system output and compare the LCoH based on variation in production and demand for each hour of the year. The output of the tools is in the form of a word file, which contains all the techno-economic output parameters.

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3 Industry's view on solar energy

As a part of the project work, four interviews were done with different dairy industries from different parts of the world. The interview aims to know about the technical possibility and economic viability of utilizing concentrated solar thermal power for the heat needs in the dairy industry. A discussion was done with the operations manager from a firm in UAE, aimed to collect steam data and fuel data of the industry to simulate and find the best integration point in the steam network that gives minimum LCoH. The questions that are asked to the respondents are included in Appendix A.

Among the four respondents, two people mentioned that the firms use diesel for their daily production process, while an industry in Qatar uses liquid petroleum gas (LPG) and diesel as the fuel for the steam boiler. Due to the minor steam requirement and the low price of electricity, a Norwegian company is using an electric kettle for steam production. The rest of the firms are using diesel and LPG as fuel because of cheap fuel availability. The scientific research paper published on 2017 [27], is used in this project work to validate their statement.

Three out of four companies showed reluctance towards having an additional renewable energy technology for the production process. Companies are afraid of the intermittency in the availability of sunlight, and some industries have production 24 hours a day. The research work done on 2017 [13], regarding solar energy process heating describes the same fact that the intermittency of solar irradiance can affect the smooth operation of the production process. Using a ST storage system can be an option to eliminate the issue, but solar thermal storage may increase the investment cost of the solar thermal system [13]. Another economic issue that pulls back industries from opting for the solar thermal system is the system's high cost [13]. A point raised by a respondent from a dairy in UAE is that ''the cost of installing photovoltaic power plants is cheap in the location. The area is available with a strong power grid, so opting for a PV powered electric boiler could be a good option". In 2016, a research work on ‘Competitive Assessment between Solar Thermal and Photovoltaics for Industrial Process Heat Generation’ was published [28]. The research work showed that the solar thermal system is a preferred choice for the low- temperature application, whereas, for high-temperature application, photovoltaic heating shows better results [28]. It was mentioned by the operations manager of an industry located in UAE that the government is providing subsidies and incentives to solar PV, and solar thermal is getting less attraction.

An idea about the process that requires heat for the operation was obtained. It was observed that pasteurization and cleaning are the two essential processes that demand heat in the dairy industry.

Regarding the technical possibility of integrating solar thermal for heating needs in the dairy industry, all the respondents provided a similar response. If the technology can deliver steam or hot water at the required temperature, it is technically possible to integrate with the dairy industry. In the dairy processing handbook [22], each process's temperature requirement is mentioned. It is lesser than the maximum temperature that the concentrated solar thermal collector considered in this study could generate.

The information needed for the simulation such as technical and financial details regarding the boiler, different process, process temperature, details about fuel, and time profile of operation were collected in the same interview.

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4 Case Study

Two factors are considered for selecting the test case. The industry must be located in a place where there is enough solar radiation required for the solar thermal collectors to operate. The industry must be using steam or hot water generated from a boiler that uses fossil fuel or electricity generated from a conventional source.

After selecting the location, data required for analysis were collected through semi-structured interview.

To study the integration at three points in the steam network, namely process integration, steam integration, and feed fluid preheating, the data regarding the mentioned points were collected. The temperature of the heating medium, flow rate of the heating medium, time profile of operation, temperature of the condensate are the main details that are used for the analysis.

4.1 Background of the industry

The case is a dairy industry located in Dubai, where the available direct normal irradiation (DNI) is good enough for the solar thermal collectors to generate heat for industrial processes. The primary significance of this case is that the operations that require heat are performed when the radiation from the sun is available. The details regarding the selected industry and the data of the three integration points are shown below.

4.1.1 General information regarding the case

Table 2: General information of the dairy processing plant

Type of industry : Dairy Industry

Location : Dubai, UAE

DNI of the location : 1883 kWh/m²

Milk intake to the plant : 15000 L/day

Type of fuel used in the boiler : Diesel Average fuel cost at the location : 0.45 €/L

4.1.2 Boiler system

The plant uses a boiler system that generates steam. The generated steam is carried in the main steam line, and it is then derived at various locations. The temperature, time profile of operation, flow rate of the heat carrier medium and details required for LCoH calculation are shown below.

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19 Technical details of the boiler

Table 3 shows the technical details of the boiler used in the dairy processing plant. The information provided is essential do simulation to find the different solar fractions and the LCoH corresponding to those solar fractions.

Table 3: Technical details of the boiler used in the case

Heat carrier coming out of boiler : Steam Temperature of the heat carrier coming out of the boiler : 110 ^oC Temperature of the feed fluid to the boiler : 60^oC

Heat carrier pressure : 3 bar

Max flow rate of the heat carrier : 7000 Kg/h

Fuel consumption of the boiler : 150 L/h

The plant's daily and yearly load profile are collected through the semi-structured interview, and collected data is illustrated in Figure 13 & Figure 14, respectively. In both figures, Y-axis show the flow rate of the boiler. In Figure 13, X-axis shows the time of the day, and in Figure 14, it shows the month. From the load profile, it can be seen that only 48% of the total capacity is used in a day. The reason behind this is, the boiler is oversized on an expectation that there will be an expansion in the future. Oversizing of the boiler can help to reduce the investment cost during development and ensure a possibility if overproduction is required.

Figure 13: Daily load profile of the plant

0 1000 2000 3000 4000 5000 6000 7000 8000

Flow rate of heat carrier (kg/h)

Time of the day

Operating load Max load

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Figure 14: Yearly load profile of the plant Financial details of the boiler

Table 4: Financial details of the boiler

Initial investment cost of boiler : 16887 €

Subsidies or incentives available : 0 €

Operation & maintenance cost : 337 €

Corporate tax rate : 2%

Discount rate : 4%

Estimated residual value of boiler : 10132 €

Asset depreciation : 270 €/year

Average fuel cost : 0.45 €/L

Carbon tax in the location : 0 €

Table 4 shows the financial details of the boiler used in case 1. The data are collected through semi- structured interview. From the information given by the respondent, the initial investment cost of the boiler is found out to be 16887 €, and the O&M cost of the boiler is considered as 2% of the initial investment cost. The industry is located in a country where the government is not providing any subsidies or incentives to install and maintain boiler running in fossil fuel. Straight-line depreciation is considered for the asset value of the boiler. The analysis period is deemed to be 25 years, and the boiler is expected to have a residual value of 10132 € after 25 years, which is 60% of the initial cost of the boiler. The

38 40 42 44 46 48 50 52

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Percenatge flow rate (%)

Months

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respondent mentioned in the interview that the average fuel cost of the location is 0.45 €/L, and the government is not imposing any carbon tax on CO2 emission from the boiler.

4.1.3 Process details

The heat consuming processes in the considered industry can be categorized into three; these are sterilization at the milk reception, pasteurization and cleaning in place (CIP). The above mentioned three processes use steam as the heating medium. At the same time, for pasteurization, steam is used to heat water, and hot water is used for process heating. For CIP, steam is used to heat water, acid and caustic soda. Steam increases the temperature of the above-told cleaning agents, and the hot solutions are used for CIP.

Table 5 shows the process names, process temperature, feed water temperature, condensate temperature, the pressure of the heat carrier, the flow rate of the heat carrier, and operation time profile.

Table 5: Data regarding the processes going on in the industry.

Process - 1 Process - 2 Process - 3 Process - 4

Process name At milk

reception (Cleaning)

Pasteurization CIP 1 CIP 2

Heat carrier Steam Steam Steam Steam

Process temperature (^oC) 95 78 95 95

Feed water temperature (^oC) 70 55 70 70

Condensate temperature (^oC) 75 60 75 75

Pressure of the heat carrier (bar)

1 or 2 3 1 or 2 1 or 2

Flow rate of the heat carrier 430 kg/h 3 tons/h 750 kg/h 750 kg/h Time profile of operation 6:00 -9:00 6:00-900 &

14:00-17:00

9:00-11:00 17:00-19:00

What percentage of total flow rate capacity is used (%)

5 38 10 10

4.1.4 Feed water details

While feeding water to the boiler, it is required to preheat the water to reduce boiler vibration. In case 1, the condensate itself is used as feedwater. The temperature of condensates after various processes are given in Table 5. At the same time, there will be condensate losses. To compensate for the condensate loss and to maintain the boiler's required water level, freshwater will be added to the condensate.

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4.2 Technical specification of the solar thermal collector

For the case study, Absolicon T160 is used for analysis. T160 is a medium-sized parabolic trough collector. The collector has the capability of sun-tracking, which will help to increase the DNI falling on the collector. The tracking system will protect the collector from overheating by moving out of the sun's direction if needed. Table 6 shows the technical specification of T160, which are used for the sizing of the solar thermal system.

Table 6: Technical specification of Absolicon T160 [29].

Model name : Absolicon T160

Collector type : Glass covered collector with single axis tracking.

Heat transfer fluid : Water, Propylene Glycol Volume of heat transfer fluid : 2.2 liter

Operational temperature : 60 – 160 ^oC

Stagnation temperature : 460 ^oC

Maximum operating pressure : 8 bar

Receiver : Stainless steel, optically selective coating

Glass : 4 mm hardened glass, anti-reflective

coating

Reflector : Polymer embedded silver on steel sheet

Weight : 148 kg

Dimensions : 5508 mm x 1094 mm x 343 mm

Collector aperture area : 5.5 m²

Optical efficiency : 0.766

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5 Results

5.1 LCoH calculation of conventional boiler

The Levelized Cost of Heat of the conventional boiler was calculated using the excel tool developed for the project. The inputs were collected through the semi-structured interview, and the cost of heat generated was obtained in Euro/MWh. Information that was used for the calculations is mentioned in section 4. The period of the analysis was considered to be 25 years. The operation and maintenance cost, asset value, residual value and energy consumed for generating the required heat were calculated for the period of analysis. LCoH for the boiler is calculated using the formula showed in Eqn 1.

The LCoH calculator showed that the energy consumed by the boiler is increasing for each successive years. An increase in energy consumption reflected an increase in fuel consumption and, in turn, the money spent to purchase fuel in each consecutive years. As the boiler in the industry considered for the case study was oversized, the equipment was operating in part-load efficiency, which is less than the full load efficiency.

During the calculation, the term 'initial investment cost' of the boiler was considered zero because the firm already has a boiler. From the article [30], it was found that there is no carbon tax in the country where the industry is located. From the article [31], the amount of CO2 emitted per litre combustion of diesel is found out to be 2.66 kg/L. The excel tool shows the litres of diesel consumed in a year. It is observed that the industry emits 855.20 tons of carbon in the first year of analysis, and it is increasing every year due to increased fuel consumption of the boiler. For meeting the thermal demand of the industry, the boiler is consuming energy of 3239.37 MWh at a fuel cost of 145,771 €/year.

Certain assumptions were made for the calculation of LCoH. The boiler is assumed to have an asset of 60% of the initial cost during the last year of analysis. Therefore, during the 25th year, the boiler will have a residual value of 10132 €. The boiler asset will have a straight-line depreciation, and in the last year, the asset value will be equal to the assumed residual value. Another assumption made is the 2% tax rate for the boiler.

Using the information shown in section 4 and considering the assumptions, the LCoH of the conventional diesel boiler in the industry was found out to be 43.9 €/MWh. As per the journal published by International Monetary Fund (IMF), carbon tax can be up to 62 € per ton of CO2 by 2030 [32]. In that case the LCoH of the conventional boiler will be 60 €/MWh.

5.2 LCoH of the solar-assisted heating system at different integration points

Absolicon Simulator was used to simulate the variation of LCoH of the solar thermal system. Later, those values are imported into the LCoH excel calculator to find the LCoH of solar-assisted heating system.

While doing simulation, it was required to specify certain parameters in the simulating tool. It was needed to specify the heating medium of the process, either steam or hot water. Inputs such as the pressure of the heating medium and load profile of the boiler decided the required storage tank size. For this case study, it is assumed that there will be no depreciation in the asset value of the solar thermal system. The simulator collected the weather data from the database when the latitude and longitude of the location were given.