# The Impact of Dispatchability of Parabolic Trough CSP Plants over PV Power Plants in Palestinian Territories

Authors: Aysar M. Yasin
Journal: International Journal of Photoenergy
 (2019)

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## Abstract

This paper investigates the impacts of dispatchability of Parabolic Trough Concentrated Solar Power (PT-CSP) systems over PV power plants in Palestinian territories. Jericho governorate was taken as a case study. All conditions required for implementing PV and PT-CSP systems are verified. The capacity of each investigated system is 1 MW, and both systems are investigated in terms of technical, economic, and environmental aspects. The parametric analysis is used to identify the most feasible option of each renewable energy system by varying the cost of each option candidate and introducing thermal energy storage (TES) to the technology of PT-CSP systems with different capacities. A software based on the MATLAB environment is programmed to estimate the energy produced from each system with the important technical, financial, and environmental indicators. It is found that the alternative of installing a 1 MW PV system is the installation of 1 MWe PT-CSP systems with 14.5 h or 18.5 h TES. Introducing TES improves the dispatchability of the system and the capacity factor which consequently justifies the PT-CSP system investment. Increasing the degree of dispatchability improves the capacity factor of the PT-CSP system from 21% at 0 h TES to 57% at 18.5 h TES (24 h operation). The capacity factor of the PV system is 18.7% which is mostly similar to PT-CSP with zero dispatchability (0 h TES). The study considers the environmental benefits by estimating the amount of avoided CO2 emissions, and it was found that increasing the capacity factor augments the environmental benefits.


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## Body

## 1. Introduction

Improving the energy sector is an important pillar of the prosperity of life especially in the industrial era. The rise in energy consumption and forecast depletion of the conventional energy sources in the near future require many countries to start using alternative renewable energy sources. Meanwhile, plans and policies are established to make renewable energy a strategic choice, since it offers sustainable and dependable energy to the present and future generations. The environmental hazards caused by conventional energy sources are another motivation towards further use of renewable energy sources. Indeed, burning fossil fuels generates harmful gases like NOx, SOx, CO, and HC in addition to CO2 which plays a main role in global warming [1–3]. Many researchers predict that by 2030 the amounts of CO2 emitted will increase by 20%-25% over the present level [4].The need for renewable energy in Palestinian territories is driven by the exceptional conditions of the unstable political situation, harsh economic circumstances, and weak infrastructure [5–7]. Solar energy is the most abundant renewable energy source available in Palestinian territories. It could be used to generate electricity through solar photovoltaics (PV) and concentrated solar thermal power (CSP), which are the most promising technologies in the world [8–10].Palestinian authority buys all of its need for fossil fuels from the Israeli side and imports about 90% of its electricity demand from Israel Electricity Company (IEC) because of political and logistical factors [5, 6]. Additionally, there is a geographical disconnection from the Gaza Strip, and the complex situation of Jerusalem City obstructs and disturbs the growth of a normal energy system [5]. There is no power generation except the power plant in the Gaza Strip with a total capacity of 140 MW which covers a part of Gaza City and other surrounding areas [5, 6]. There are six distribution companies in Palestinian territories; some of them have connection points with Jordanian and Egyptian electrical networks, respectively, but with limited capacity [11]. The IEC provides electricity to Palestinian municipalities and distribution companies through three 161/33 kV substations [11]. The electrical energy supplied from IEC is insufficient and does not cover the normal expansion of the demand. So, further PV energy is being generated through different initiatives [12].The use of PV energy in the Palestinian territories has increased rapidly in the last 6 years for many reasons [6, 9, 13]: reduction in the price of PV modules and its auxiliary components, people becoming aware of PV technology, PEA has released the Palestinian Solar Initiative (PSI), PEA put important regulations and laws that organize the utilization of PV energy, and finally PEA put some motivations to connect PV systems to the grid-like Feed-in Tariff (FiT) and net-metering schemes.PT-CSP technology has received special interest from the Palestinian energy decision-makers and the researchers as well. The solar radiation is high, water is available, and the land is obtainable in some locations of Palestinian territories like Jericho, Tubas, and Jenin governorates [14]. CSP offers flexibility because of the technology’s ability to store thermal energy. Contrasting PV, which produces electricity directly from the sun, CSP plants use mirrors to focus sunlight and produce high-temperature thermal energy that can be stored cheaply. This feature makes CSP a dispatchable electricity resource available whenever there is customer demand, including at times when the sun is not shining. CSP with TES offers considerable flexibility, increasing its own value to the grid and even enabling greater grid penetration of variable-generation technologies such as photovoltaic power plants [15, 16]. Instead of examining the feasibility of implementing PT-CSP in Palestinian territories as introduced in [17–21], this paper inspects the effect of dispatchability of PT-CSP power plants over PV power systems. The electrical system in Jericho suffers from frequent interruptions in the night hours especially in summer; this makes PT-CSP power plants with TES better than the PV system. In fact, storing electricity directly to the grid is not feasible in the Jericho case as it does not solve the problem of electricity shortage in the night hours as well as cannot benefit from the change of electrical tariff as indicated in Figure 1. It is significant for energy decision-makers, researchers, and planners to recognize the effect of attaching TES to PT-CSP power plants. Depending on LCOE as an economic indicator to compare the feasibility of PV power systems and PT-CSP plants is misleading, and mostly, the results show that PV power plants give lower LCOE than PT-CSP plants. The author in [22] states that LCOE indicator would generally overestimate intermittent PV technology compared with dispatchable plants like PT-CSP plants.Figure 1
Proposed PPA agreement between the power plants and the consumer in Jericho.The CSP plants become dispatchable if they are annexed with TES; this allows CSP plants to store thermal energy during the sunshine hours and convert it into electrical energy at another time of higher prices or demand. TES offers a secure and stable capacity to the power system. The dispatchability of CSP plants with TES offers high-value auxiliary facilities such as revolving reserves [23]. Considering the economic advantages of the thermal energy storage of the CSP system is called the value of CSP dispatchability or CSP storage [23, 24].The advantage of CSP dispatchability or advantage of CSP storage becomes a significant research subject, and this is clear from the following research papers. The authors in [25] investigated the feasibility of large-scale integration of 50 MW PT-CSP and 50 MW PV systems in Sharjah (UAE). The study shows that installing 50 MWe PT-CSP with 14.5 hours of TES increases the dispatchability of the system and might be an alternative to installing 50 MWp PV system. The researchers in [24] study the effects of the integration of CSP into a nonconventional (PV and wind) power system of Morocco and Algeria. The results prove that storage-based CSP plants offer significant economic advantages over nonstorage, low-dispatchable CSP plants. The authors in [23] inspect the benefit of CSP and TES in four regions in the southwestern United States, and the results show that TES can raise the benefit of CSP by permitting more thermal energy from a CSP plant. Hess [26] found that dispatchable CSP combined with TES and cofiring options can deliver energy according to demand. Authors of paper [27] found that CSP provide dispatchable electricity at a large scale and it can play an imperative role in the future, especially to balance unstable sources in progressively renewable-based power systems. Lilliestam et al. [28] and Mehos et al. [16] found that CSP plants with TES improve the capacity factor but slightly enhance the LCOE compared to a plant without TES which consequently makes CSP plants a good choice for producing a dispatchable renewable electrical source. Green et al. [29] studied the performance of a hybrid CSP-PV system when introducing TES. A higher capacity factor is obtained than the CSP system obtained when working alone. In [30], the authors investigated the added value of TES to CSP plants. The study found that CSP with TES forms a dispatchable renewable energy source controlled by solar energy.This paper investigates the effect of dispatchability of PT-CSP plants over the PV power system in Palestinian territories, particularly in Jericho governorate to further use of solar energy and move towards sustainability. In this paper, a simulation model is programmed using MATLAB environment; the results are compared using different commercial software. Another motivation behind this work is the continuous discussion in PEA about the feasibility of implementing PT-CSP systems in Palestinian territories.


## 2. Technical Assessment of the Selected Site (Jericho) for the Implementation of PT-CSP and PV Power Systems

Palestinian territories are located in the geographical region between the Mediterranean Sea and the Jordan River. It comprises the West Bank and the Gaza Strip with an estimated total surface area of 6220 km2. Palestinian territories lie on the western edge of the Asian continent and the eastern extremity of the Mediterranean Sea, between 34°20′–35°30′E and 31°10′–32°30′N which means that it lies on the sunny belt. In this paper, Jericho governorate is taken as a case study. Any candidate site for implementing PT-CSP systems has to comply with certain requirements [31, 32]. This includes solar radiation requirements, land availability and use, land slope, water availability, infrastructure requirements, and meteorological conditions. The monthly global daily solar radiation on the horizontal surface of Jericho governorate is presented in Figure 2 [33, 34] with a yearly average of 5.63 kWh/m2-day.Figure 2
Monthly average global daily solar radiation on a horizontal surface.For completeness of the analysis, the global annual solar radiation on a horizontal surface in the hourly interval is shown in Figure3 and the potential is 2053 kWh/m2 [35].Figure 3
Annual global solar radiation on a horizontal surface in an hourly interval.The average monthly direct normal irradiance (DNI) in Jericho (selected site) is illustrated in Figure4 [35].Figure 4
Monthly average direct normal irradiance (DNI) in Jericho.The annual DNI in an hourly interval used in the simulation is illustrated in Figure5, and the potential is 2071 kWh/m2 [35]. The area is exposed to sunlight solar radiation for at least 5.9 h daily in January and at maximum 11.3 h daily in July with average 8.6 h [33].Figure 5
Annual DNI in an hourly interval.CSP and PV power plants need a large land area compared to conventional power plants. The land availability to build a large CSP plant is significant and has to comply with certain natural conditions. The land areas should be suitable for construction of solar fields, and the following conditions should be verified: inhabited areas, ground structure, water bodies, land slope, dunes, protected or restricted areas, forests, mountains, agriculture, etc. [36]. The PT-CSP systems need large flat areas, and the selected plant site should have a slope ranging from 1 to 2% [37]. The suggested site in Jericho has an acceptable slope which is 1.3%. The selection is based on a detailed study of the available areas and consultation with the planning department of Jericho municipality (http://www.jericho-city.ps).Water availability for concentrating power plants is important, especially if they are equipped with wet cooling systems. Wet cooling systems are favorable for the CSP plant operation because of higher possible power plant efficiencies and lower investment costs in comparison to CSP plants with dry cooling systems [38], and this justifies the importance of water availability for such plants. The water availability for the selected site in Jericho is analysed based on data gathered from the Ministry of Local Government and National Spatial Plan. It is located close to water resources and near water connection grids. The location of the proposed CSP plant site is close to existing 33 kV power transmission lines. The CSP plant needs high voltage lines to transmit the generated electrical power to consumers. A short distance from the transmission lines is an advantage, because the investment in infrastructure is lower [38].The solar field is designed to endure wind speeds of 33.3 to 36.1 m/s, and the average annual wind speed for Jericho is 1.5 m/s [39]. The performance and efficiency of the solar power plant are dependent on the ambient temperature. For wet cooling, the efficiency of the condenser increases with decreasing wet bulb temperature, which is a function of ambient temperature and relative humidity. The average annual ambient temperature and relative humidity in Jericho are 22.8°C and 45.5% [39], respectively, which are acceptable and do not affect the efficiency of the solar field and power block. Figures 6 and 7 show the monthly average temperature [39] and the annual hourly average air temperature [35] for the selected site, respectively. Figure 6 shows that the maximum temperatures occur in June through September. Meanwhile, Figure 7 shows that during the day, the hourly average temperature is ranging from 20 to 27°C.Figure 6
Monthly average air temperature.Figure 7
Annual hourly average air temperature.


## 3. The Research Methodology

As introduced in the previous sections, PV energy is a promising renewable energy option in Palestinian territories. However, in contrast with CSP, it cannot support regular power, has no efficient storage system, and is not able to back up the power system with stable capacity, though the PV power plants challenge PT-CSP with lower LOCE. The question invoked by energy decision-makers is the following: Does the economic benefit of the dispatchability compensate for the drawback of PT-CSP’s higher LCOE? In order to answer the question, both PV and PT-CSP systems are simulated and the cost of the produced electrical energy unit (kWh) is calculated based on the following procedure: (i) calculate the input solar energy in the plane of PV and PT-CSP systems after reading the solar radiation (global or DNI); (ii) calculate the produced electrical energy from PV and PT-CSP systems and that delivered to the grid; (iii) calculate the cost of PV and PT-CSP systems in addition to the cost of the required area; and (iv) finally, calculate the cost of electrical energy unit produced by PV and PT-CSP systems.


## 4. Simulation Model and Assumption Data

### 4.1. Simulation Model

In order to perform the simulations required for the above optimization analysis, a software based on the MATLAB environment is designed. The software combines annual time series power production from on-grid PT-CSP and on-grid PV systems. The software estimates the LCOE and other metrics for renewable energy projects. The software simulates on-grid PT-CSP that uses solar energy to generate steam to drive an electric power generation plant.The proposed on-grid PT-CSP power plant with TES is shown in Figure8 [40]. The entire plant is mainly divided into the solar field, TES, and power block. The CSP systems make use of concentrating mirrors to collect the sunlight as heat. This collected heat raises the temperature of a working fluid significantly high. A conventional thermal power block extracts the heat from working fluid and drives a steam engine working on the Rankine cycle [20, 40]. The power block consists of a turbine coupled with a generator. The TES system consists of two tanks.Figure 8
PT-CSP power plant model with TES.The following equations and relationships are used in the software to describe the performance of the CSP system [41–43]. The global incident thermal energy (Qinċ) is calculated using Equation (1) which is a multiplication of DNI (Ibn) and the solar field aperture area (Aap,tot):
(1)Qinċ=IbnAap,tot.The total solar field aperture area is fixed during the simulation, and it depends mainly on design power cycle rating, field efficiency, and solar multiple as shown in(2)Aap,tot=Q̇inc,desIbn,des,(3)Q̇inc,des=Q̇th,desηopt,peakηcleanηgenηtherm,des,where ηopt,peak, ηclean, ηgen, and ηtherm,des are the maximum efficiency given by the user, mirror cleanness efficiency, general optical error, and thermal efficiency at design, respectively. The design of solar field thermal output Q̇sf,des is calculated based on the design power cycle output and the solar multiple Ms using
(4)Q̇th,des=Ẇdes⋅Msηcycle,des.The solar field thermal outputQtḣ is calculated by modifying the design thermal output Q̇th,des with respect to actual solar radiation Ibn, optical efficiency ηopt, and thermal efficiency ηtherm using
(5)Qtḣ=Q̇th,desIbnIbn,desηoptηopt,desηthermηtherm,des.The design of solar radiationIbn,des, the design optical efficiency ηopt,des, and design thermal efficiency ηtherm,des are defined by the user. The actual solar radiation Ibn is imported by the software. The optical efficiency ηopt is the function of solar position (azimuth/zenith) of each solar field column. The solar position is calculated using equations developed by Duffie and Beckman [41]. Values of optical efficiency ηopt with respect to zenith and azimuth angles are shown in Figure 9.Figure 9
Optical efficiency with respect to azimuth and zenith angles.Thermal efficiencyηtherm is calculated using the product of three sensitivities, namely, sensitivity to the irradiation value Fhl,Ibn, ambient dry-bulb temperature Fhl,Tamb, and ambient wind speed Fhl,Vwind. The polynomial form for each sensitivity is given in Equations (6)–(8) [43, 44]:
(6)Fhl,Ibn=C0+C1IbnIbn,des+C2IbnIbn,des2+C3IbnIbn,des3,where C0=4.75, C1=−8.0, C2=4.5, and C3=−0.25;
(7)Fhl,Tamb=C0+C1ΔTamb+C2ΔTamb2+C3ΔTamb3,where C0=1, C1=0, and C2=0;
(8)Fhl,Vwind=C0+C1Vwind+C2Vwind2+C3Vwind3,where C0=1, C1=0, C2=0, and ΔTamb=Tamb−Tamb,des.The thermal lossQ̇hl is estimated using
(9)Q̇hl=Q̇hl,ref,desIbnIbn,desFhl,IbnFhl,TambFhl,Vwind,where Q̇hl,ref,des is the reference thermal loss from the solar field at design. It is estimated by multiplying the design solar field thermal Q̇sf,des with reference thermal loss fraction. The reference thermal loss fraction is assumed 0.063 MWt/MWtcap [43, 44]. The final power output Ẇcycle is calculated using
(10)Ẇcycle=ηturbineηelect−genηboilerQ̇th.The nominal electrical generator efficiency is 0.96, the nominal boiler efficiency is 0.90, and the nominal turbine efficiency is 0.37 [45]. The net power Ẇnet is calculated by Equation (11) which is the parasitic loss Ẇpar subtracted from the final power output Ẇcycle. The fixed parasitic fraction is assumed 0.0055 MWe/MWcap [46]:
(11)Ẇnet=Ẇcycle−Ẇpar.The software calculates the total TES capacity using Equation (12) [43]:
(12)Etes=Ẇdes·Δttesηcycle,des,where Δttes is the number of desired storage hours.On the other hand, the software calculates the amount of electrical energy produced by the on-grid PV power system using a few basic inputs. The globalI, beam Ib, and diffuse Id annual solar radiation on a horizontal surface in the hourly interval are imported by the software [35]. The optimum tilt anglein Palestine for grid-connected systems is 27°, and the azimuth is 180°, so the software estimates the global solar radiation on the tilted surface based on Equations (13) and (14) [41] assuming that the combination of diffuse and ground-reflected radiation is isotropic:
(13)IT=IbRb+Id1+cosβ2+Iρg1−cosβ2,(14)Rb=Ib,TIb=cos∅−βcosδcosω+sin∅−βsinδcos∅cosδcosω+sin∅sinδ,where Ib,T is beam annual solar radiation on a horizontal surface in the hourly interval at the tilted surface, ω is the hour angle, ∅ is the latitude angle, β is the tilt angle of the PV array, δ is the declination angle which is a function of the day number, and Iρg is the diffuse reflectance of the total solar radiation. The software user enters the PV array DC power rating at standard conditions, and the capacity of the inverter is determined accordingly. The software estimates AC electrical energy injected by the PV to the grid using Equation (15) [47]:
(15)EAC−grid=∑08760IT∗APV∗ηpv∗fman∗fdirt∗ftemp∗ηpv−inv∗ηinv∗ηinvsub,where APV is the total area of the PV array, ηpv is the efficiency of the PV module, fman is a derating factor for manufacture tolerance, fdirt is the derating factor for dirt, ftemp is the derating factor for temperature, ηpv−inv is the efficiency of the subsystem between the PV array and the inverter, ηinv is the efficiency of the inverter, and ηinvsub is the efficiency of the subsystem between the inverter and the switchboard. The software estimates the derating factors of the PV system using the equations illustrated in the guidelines of grid-connected solar PV system installers. The software calculates the capacity factor of both PT-CSP system and PV system as a performance metrics as shown in
(16)Capacityfactor=netannualenergysystemcapacity∗8760.The system capacity in the PT-CSP system is the estimated net output at design. The system capacity for PV system is the DC rating kWdc. The software estimates the LCOE as a financial metric as shown in Equation (17) [48]:
(17)LCOE=∑n=0NCn/1+dn∑n=1NQn/1+dn,where Cn is the annual project cost in year n, Qn is the electricity generated by the system in year n, d is the discount rate, and N is the project lifetime. The software requires the specifications of the inverter and module. The effect of shading and temperature is considered. The type of PV collectors used in this study is flat-plate PV modules without a tracking system.


### 4.2. Data Assumption

In order to highlight the value of dispatchability of PT-CSP plants over PV power plants, a parametric analysis is performed by changing the capital cost of PV and PT-CSP systems in order to find out the least cost feasible option. The study proposes implementing 1 MW based on PV technology and 1 MW based on PT-CSP system. The study proposes a 1 MW capacity of PT-CSP for the sake of analysis and comparison because most of the installed PV power plants in Jericho are within this range. Using large-scale PT-CSP power plants normally gives better results than small-scale capacities. This paper justifies the need for TES for the following reasons: utilize the flexibility provided by CSP-TES in contrast to PV and wind power plants and solve the problem of shortage of electricity at peak times and consequently utilize higher electricity tariffs.The proposed initial investment cost of a PV system of 1 MW varies between 1000 and 3000 USD/kW. The initial investment cost of PT-CSP system of 1 MW varies between 3500 and 8500 USD/kW. Operation and maintenance (O&M) are important parameters. They are considered in the comparison provided that O&M costs [49] for PV systems are lower than that of PT-CSP power plants [50]. Table 1 summarizes the most important input data and assumptions entered into the software. The global annual solar radiation on a horizontal surface in the hourly interval is the main data entered to the software, and they are obtained from the solar energy for a professional website [35].Table 1
Summary of the input data and assumption of the PV system and inverter.
Parameter
Value
Technical data
PV module type
Multi-c-Si (350 Wp)
Nominal efficiency
17.13%
Temperature coefficient of power
-0.47%/°C
Module area
2.043 m2
Inverters (two inverters are used)
0.5 MW
Total system capacity
1 MW
Economic data
PV capital cost
1000-3000 USD/kW
Operating and maintenance (O&M) costs
15 USD/kW/year
The lifetime of the PV system
20 years
Annual inflation
2.5%
Real discount rate
5.5%
Income tax
0Table2 summarizes the most important input data and assumptions entered into the software. The global annual solar radiation on a horizontal surface in the hourly interval is the main data entered to the software, and those are obtained from the solar energy for professionals’ website [35].Table 2
Summary of the input data and assumption of the PT-CSP system.
Parameter
Value
Technical data
CSP system type
Parabolic trough
Thermal storage capacity
0-18.5 h/day
Heat transfer fluid (HTF)
Therminol VP-1
Total system capacity
1 MW
Economic data
CSP capital cost
3500-8500 USD/kW
Operating and maintenance (O&M) costs
66 USD/kW/year
The lifetime of the PT-CSP system
25 years
Annual inflation
2.5%
Real discount rate
5.5%
Income tax
0


### 4.3. Time of Energy Purchase

The study assumes a power purchase agreement (PPA) between the proposed PT-CSP plants, PV power plant proposed power, and the consumers. The proposed PPA adjust the price of kWh based on time of the day for a given month. Figure9 illustrates the time of purchase proposed by this study. This assumption considers the case of Jericho City in Palestine. Figure 1 shows the multiplier factor with the selling price of generated kWh at a specific time of the day for a given month.


### 4.4. TES Dispatch Control

The algorithm of charging and discharging methodology of the TES system is illustrated in Figure10. The algorithm starts by reading the state of charge (SoC) of TES and the solar radiation data. If it is sunshine time and the available solar energy exceeds the required energy, the algorithm checks the SoC of the storage system. If SoC is full, then the amount of thermal energy required to drive the power cycle at full load is consumed and the surplus is dumped. If the SoC is not full, the surplus is stored in the TES system.Figure 10
Flow chart of charging and discharging methodology of TES.If it is sunshine time and the available solar energy exactly equals the required energy, all the amount of thermal energy is consumed to drive the power cycle. If it is sunshine time and the available solar energy is less than the required energy, the algorithm checks the SoC of the storage system. If SoC is not empty, then the deficiency of thermal energy is given from the storage, but the system will work at lower capacity if SoC is empty. If it is not the sunshine time and SoC of the storage system is not empty, then TES will drive the power cycle until the SoC becomes empty.


## 4.1. Simulation Model

In order to perform the simulations required for the above optimization analysis, a software based on the MATLAB environment is designed. The software combines annual time series power production from on-grid PT-CSP and on-grid PV systems. The software estimates the LCOE and other metrics for renewable energy projects. The software simulates on-grid PT-CSP that uses solar energy to generate steam to drive an electric power generation plant.The proposed on-grid PT-CSP power plant with TES is shown in Figure8 [40]. The entire plant is mainly divided into the solar field, TES, and power block. The CSP systems make use of concentrating mirrors to collect the sunlight as heat. This collected heat raises the temperature of a working fluid significantly high. A conventional thermal power block extracts the heat from working fluid and drives a steam engine working on the Rankine cycle [20, 40]. The power block consists of a turbine coupled with a generator. The TES system consists of two tanks.Figure 8
PT-CSP power plant model with TES.The following equations and relationships are used in the software to describe the performance of the CSP system [41–43]. The global incident thermal energy (Qinċ) is calculated using Equation (1) which is a multiplication of DNI (Ibn) and the solar field aperture area (Aap,tot):
(1)Qinċ=IbnAap,tot.The total solar field aperture area is fixed during the simulation, and it depends mainly on design power cycle rating, field efficiency, and solar multiple as shown in(2)Aap,tot=Q̇inc,desIbn,des,(3)Q̇inc,des=Q̇th,desηopt,peakηcleanηgenηtherm,des,where ηopt,peak, ηclean, ηgen, and ηtherm,des are the maximum efficiency given by the user, mirror cleanness efficiency, general optical error, and thermal efficiency at design, respectively. The design of solar field thermal output Q̇sf,des is calculated based on the design power cycle output and the solar multiple Ms using
(4)Q̇th,des=Ẇdes⋅Msηcycle,des.The solar field thermal outputQtḣ is calculated by modifying the design thermal output Q̇th,des with respect to actual solar radiation Ibn, optical efficiency ηopt, and thermal efficiency ηtherm using
(5)Qtḣ=Q̇th,desIbnIbn,desηoptηopt,desηthermηtherm,des.The design of solar radiationIbn,des, the design optical efficiency ηopt,des, and design thermal efficiency ηtherm,des are defined by the user. The actual solar radiation Ibn is imported by the software. The optical efficiency ηopt is the function of solar position (azimuth/zenith) of each solar field column. The solar position is calculated using equations developed by Duffie and Beckman [41]. Values of optical efficiency ηopt with respect to zenith and azimuth angles are shown in Figure 9.Figure 9
Optical efficiency with respect to azimuth and zenith angles.Thermal efficiencyηtherm is calculated using the product of three sensitivities, namely, sensitivity to the irradiation value Fhl,Ibn, ambient dry-bulb temperature Fhl,Tamb, and ambient wind speed Fhl,Vwind. The polynomial form for each sensitivity is given in Equations (6)–(8) [43, 44]:
(6)Fhl,Ibn=C0+C1IbnIbn,des+C2IbnIbn,des2+C3IbnIbn,des3,where C0=4.75, C1=−8.0, C2=4.5, and C3=−0.25;
(7)Fhl,Tamb=C0+C1ΔTamb+C2ΔTamb2+C3ΔTamb3,where C0=1, C1=0, and C2=0;
(8)Fhl,Vwind=C0+C1Vwind+C2Vwind2+C3Vwind3,where C0=1, C1=0, C2=0, and ΔTamb=Tamb−Tamb,des.The thermal lossQ̇hl is estimated using
(9)Q̇hl=Q̇hl,ref,desIbnIbn,desFhl,IbnFhl,TambFhl,Vwind,where Q̇hl,ref,des is the reference thermal loss from the solar field at design. It is estimated by multiplying the design solar field thermal Q̇sf,des with reference thermal loss fraction. The reference thermal loss fraction is assumed 0.063 MWt/MWtcap [43, 44]. The final power output Ẇcycle is calculated using
(10)Ẇcycle=ηturbineηelect−genηboilerQ̇th.The nominal electrical generator efficiency is 0.96, the nominal boiler efficiency is 0.90, and the nominal turbine efficiency is 0.37 [45]. The net power Ẇnet is calculated by Equation (11) which is the parasitic loss Ẇpar subtracted from the final power output Ẇcycle. The fixed parasitic fraction is assumed 0.0055 MWe/MWcap [46]:
(11)Ẇnet=Ẇcycle−Ẇpar.The software calculates the total TES capacity using Equation (12) [43]:
(12)Etes=Ẇdes·Δttesηcycle,des,where Δttes is the number of desired storage hours.On the other hand, the software calculates the amount of electrical energy produced by the on-grid PV power system using a few basic inputs. The globalI, beam Ib, and diffuse Id annual solar radiation on a horizontal surface in the hourly interval are imported by the software [35]. The optimum tilt anglein Palestine for grid-connected systems is 27°, and the azimuth is 180°, so the software estimates the global solar radiation on the tilted surface based on Equations (13) and (14) [41] assuming that the combination of diffuse and ground-reflected radiation is isotropic:
(13)IT=IbRb+Id1+cosβ2+Iρg1−cosβ2,(14)Rb=Ib,TIb=cos∅−βcosδcosω+sin∅−βsinδcos∅cosδcosω+sin∅sinδ,where Ib,T is beam annual solar radiation on a horizontal surface in the hourly interval at the tilted surface, ω is the hour angle, ∅ is the latitude angle, β is the tilt angle of the PV array, δ is the declination angle which is a function of the day number, and Iρg is the diffuse reflectance of the total solar radiation. The software user enters the PV array DC power rating at standard conditions, and the capacity of the inverter is determined accordingly. The software estimates AC electrical energy injected by the PV to the grid using Equation (15) [47]:
(15)EAC−grid=∑08760IT∗APV∗ηpv∗fman∗fdirt∗ftemp∗ηpv−inv∗ηinv∗ηinvsub,where APV is the total area of the PV array, ηpv is the efficiency of the PV module, fman is a derating factor for manufacture tolerance, fdirt is the derating factor for dirt, ftemp is the derating factor for temperature, ηpv−inv is the efficiency of the subsystem between the PV array and the inverter, ηinv is the efficiency of the inverter, and ηinvsub is the efficiency of the subsystem between the inverter and the switchboard. The software estimates the derating factors of the PV system using the equations illustrated in the guidelines of grid-connected solar PV system installers. The software calculates the capacity factor of both PT-CSP system and PV system as a performance metrics as shown in
(16)Capacityfactor=netannualenergysystemcapacity∗8760.The system capacity in the PT-CSP system is the estimated net output at design. The system capacity for PV system is the DC rating kWdc. The software estimates the LCOE as a financial metric as shown in Equation (17) [48]:
(17)LCOE=∑n=0NCn/1+dn∑n=1NQn/1+dn,where Cn is the annual project cost in year n, Qn is the electricity generated by the system in year n, d is the discount rate, and N is the project lifetime. The software requires the specifications of the inverter and module. The effect of shading and temperature is considered. The type of PV collectors used in this study is flat-plate PV modules without a tracking system.


## 4.2. Data Assumption

In order to highlight the value of dispatchability of PT-CSP plants over PV power plants, a parametric analysis is performed by changing the capital cost of PV and PT-CSP systems in order to find out the least cost feasible option. The study proposes implementing 1 MW based on PV technology and 1 MW based on PT-CSP system. The study proposes a 1 MW capacity of PT-CSP for the sake of analysis and comparison because most of the installed PV power plants in Jericho are within this range. Using large-scale PT-CSP power plants normally gives better results than small-scale capacities. This paper justifies the need for TES for the following reasons: utilize the flexibility provided by CSP-TES in contrast to PV and wind power plants and solve the problem of shortage of electricity at peak times and consequently utilize higher electricity tariffs.The proposed initial investment cost of a PV system of 1 MW varies between 1000 and 3000 USD/kW. The initial investment cost of PT-CSP system of 1 MW varies between 3500 and 8500 USD/kW. Operation and maintenance (O&M) are important parameters. They are considered in the comparison provided that O&M costs [49] for PV systems are lower than that of PT-CSP power plants [50]. Table 1 summarizes the most important input data and assumptions entered into the software. The global annual solar radiation on a horizontal surface in the hourly interval is the main data entered to the software, and they are obtained from the solar energy for a professional website [35].Table 1
Summary of the input data and assumption of the PV system and inverter.
Parameter
Value
Technical data
PV module type
Multi-c-Si (350 Wp)
Nominal efficiency
17.13%
Temperature coefficient of power
-0.47%/°C
Module area
2.043 m2
Inverters (two inverters are used)
0.5 MW
Total system capacity
1 MW
Economic data
PV capital cost
1000-3000 USD/kW
Operating and maintenance (O&M) costs
15 USD/kW/year
The lifetime of the PV system
20 years
Annual inflation
2.5%
Real discount rate
5.5%
Income tax
0Table2 summarizes the most important input data and assumptions entered into the software. The global annual solar radiation on a horizontal surface in the hourly interval is the main data entered to the software, and those are obtained from the solar energy for professionals’ website [35].Table 2
Summary of the input data and assumption of the PT-CSP system.
Parameter
Value
Technical data
CSP system type
Parabolic trough
Thermal storage capacity
0-18.5 h/day
Heat transfer fluid (HTF)
Therminol VP-1
Total system capacity
1 MW
Economic data
CSP capital cost
3500-8500 USD/kW
Operating and maintenance (O&M) costs
66 USD/kW/year
The lifetime of the PT-CSP system
25 years
Annual inflation
2.5%
Real discount rate
5.5%
Income tax
0


## 4.3. Time of Energy Purchase

The study assumes a power purchase agreement (PPA) between the proposed PT-CSP plants, PV power plant proposed power, and the consumers. The proposed PPA adjust the price of kWh based on time of the day for a given month. Figure9 illustrates the time of purchase proposed by this study. This assumption considers the case of Jericho City in Palestine. Figure 1 shows the multiplier factor with the selling price of generated kWh at a specific time of the day for a given month.


## 4.4. TES Dispatch Control

The algorithm of charging and discharging methodology of the TES system is illustrated in Figure10. The algorithm starts by reading the state of charge (SoC) of TES and the solar radiation data. If it is sunshine time and the available solar energy exceeds the required energy, the algorithm checks the SoC of the storage system. If SoC is full, then the amount of thermal energy required to drive the power cycle at full load is consumed and the surplus is dumped. If the SoC is not full, the surplus is stored in the TES system.Figure 10
Flow chart of charging and discharging methodology of TES.If it is sunshine time and the available solar energy exactly equals the required energy, all the amount of thermal energy is consumed to drive the power cycle. If it is sunshine time and the available solar energy is less than the required energy, the algorithm checks the SoC of the storage system. If SoC is not empty, then the deficiency of thermal energy is given from the storage, but the system will work at lower capacity if SoC is empty. If it is not the sunshine time and SoC of the storage system is not empty, then TES will drive the power cycle until the SoC becomes empty.


## 5. Simulation of Results and Discussion

The electrical energy produced from the proposed PV power plant and PT-CSP systems is mainly dependent on the available solar energy in the selected area in addition to the amount of thermal storage. The amount of average annual electrical energy produced from the proposed power station PV and PT-CSP systems is illustrated in Figure11.Figure 11
Total annual electrical energy generation from the PV and PT-CSP systems.Figure11 shows that the annual average electrical energy generated by implementing a power station based on the PT-CSP system in Jericho with zero dispatchability is equal to 1743 MWh. This is approximately equal to the annual average electrical energy generated from a PV system in the same location.It is clear from Figure11 that introducing TES increases the energy produced from the PT-CSP system which seems strange as any storage system decreases generation from the whole power station because of losses generated from charging and discharging cycles. This is true, but in this study, introducing TES reduces the field thermal power dumped (MWt). The solar field in some periods of the day especially in summer produces thermal energy greater than the capacity of the power cycle. This surplus in thermal energy is dumped and considered losses in case of 0 h TES, while the surplus in thermal energy goes to storage if the plant includes the TES system. Numerically, the field thermal power dumped in case of 0 h TES is 1322 MWt while it is 457.65 MWt in case of 4.5 h TES. The flow chart of charging and discharging methodology of TES shown in Figure 1 illustrates this case. Another fact to be considered is that in introducing higher TES, as in the case of 14.5 h and 18.5 h, the solar field area increases even when the capacity of power cycle remains 1 MW.Figure12 shows the annual capacity factor of the different simulated systems. The annual capacity factor for the PV system is 18.7% while it is 22% for PT-CSP at zero dispatchability (CSP-0 h TES).Figure 12
Annual capacity factor of PV and PT-CSP systems.The annual capacity factor for the PT-CSP plant increases with the degree of dispatchability of the PT-CSP plant. The annual capacity factor increases to a high level with sufficient TES capacity. For example, it reaches 47.3% at 14.5 h TES. Figure12 also shows a simulation assuming the highest degree of dispatchability (24 h operation or 18.5 h TES) which raises the annual capacity factor to 57.1%.Figure13 shows the cost of electricity produced with respect to the initial investment of each solar energy system under investigation. The capital cost of the PV system is based on the local prices in Palestinian territories in 2018.Figure 13
Capital cost (USD/kW) of PV and PT-CSP systems.The results presented in Figure13 show that the cost of electrical energy produced from the PT-CSP plant is competitive to that produced from the PV system especially when the dispatchability feature is used. It is clear that LCOE is decreased with the degree of dispatchability. It is clear that the substitute cost-effective technology to the installation of a 1 MWp PV system might be installing a 1 MWe PT-CSP system having 14.5 h or 18.5 h thermal energy storage.To calculate the amounts of the avoided CO2 emissions by implementing PV and PT-CSP technologies, it is a good practice to assign the CO2 emissions per kWh produced from PV, PT-CSP, and the replaced conventional energy sources which are mostly based on coal and natural gas. The study considers coal and natural gas as reference conventional energy sources because coal and natural gas are the fuels mostly used in the countries on which the Palestinian territories rely on for its electricity needs. In this study, the emissions caused during the entire lifespan of PV and PT-CSP systems are considered. The associated emissions from PV and PT-CSP systems are 98 [51] and 22 gCO2/kWh [52–54], respectively. The associated emissions from coal and natural gas are 1000 and 469 gCO2/kWh [55, 56], respectively. The study assumes that 50% of the imported electrical energy is from coal and 50% from natural gas. Figure 14 shows the amount of CO2 emissions avoided by introducing PV and PT-CSP plants with different capacities of TES.Figure 14
Annual avoided CO2 emissions.The annual amount of the avoided CO2 emissions by using PT-CSP is ranging from 1241 tons CO2 to about 3204 tons CO2 depending on the capacity of the introduced TES while it is 1188 tons CO2 in the case of PV technology as shown in Figure 14.In order to validate the results obtained from the software, the study utilizes RETScreen™ International Clean Energy Project Analysis Software [57]. It is used for estimating the annual electrical generation from PT-CSP and PV systems. The PVsyst simulation software [58] is utilized as well to validate the results obtained in the designed software taking into consideration similar input data. Figure 15 shows great similarities between the results obtained in the designed MATLAB software, RETScreen™, and PVsyst simulation software.Figure 15
Comparison between different software.Figures16 and 17 show the output power profile of the PV system and PT-CSP systems with different TES capacities. It is clear from Figure 16 that the annual output net power profile of the PV power plant and PT-CSP plant with zero dispatchability is approximately similar to each other as both systems start producing energy at about 8:00 AM and stop at 16:30, and this is because both are depending on the solar radiation.Figure 16
Typical annual net power output profile of PV and PT-CSP systems without TES.Figure 17
Typical annual net power output profile of 1 MW PT-CSP system.Introducing TES to the PT-CSP plant extends dispatchability of the system for further hours as shown in Figure17. It is a good practice to note that the analysis shows the average net power produced in summertime and wintertime, which means that net power produced in the summertime is better and more dispatchable.Figure17 shows the simulation of operating the 1 MW PT-CSP system for 24 hours (18.5-hour TES). The system is fully dispatchable, but it is clear that the annual net power produced in some hours is slightly lower than midday hours. This is because the analysis shows the average annual net power produced.In order to further highlight this point, one can refer to Figure18 that shows the power produced in July (maximum power) and January (minimum power) and the average net annual power in the case of 24-hour operation (18.5-hour TES).Figure 18
Typical monthly net power output profile of PT-CSP.It is important to note that having the PT-CSP system with 18.5-hour TES system is not commercially available. This is due to size, some operational concerns, and the increasing cost of the thermal storage tanks essential for operating 18.5 hours of the thermal storage [59]. Scientific research efforts are being employed for using different storage media that allow this technology to be possible and economically feasible [60, 61].


## 6. Conclusion

Dispatchability of CSP plants is a significant feature that distinguishes it from other intermittent renewable energy sources like PV systems. This feature can be employed to compensate for higher LCOE of CSP plants.The substitute cost-effective technology to the installation of a 1 MW PV system might be the use of 1 MW PT-CSP with a specific degree of dispatchability, either 14.5 h or 18.5 h (24 h operation).Increasing the degree of dispatchability improves the capacity factor of the PT-CSP system. The capacity factor is 21.1% at 0 h TES and increases to 57% at 18.5 h TES (24 h operation). The capacity factor of the PV system is 18.7 which is mostly similar to PT-CSP with zero dispatchability (0 h TES).The improvement of a capacity factor increases the annual energy output from the system which consequently reduces the CO2 emissions avoided. The amounts of avoided CO2 emissions are 1241 tons at 21% capacity factor (0 h TES) and increase to 2656 tons at a capacity factor of 47.3% (14.5 h TES) considering that coal and natural gas are the substitute energy source with 50% mix.Small-scale PT-CSP power plants with TES is feasible as a starting up project in Jericho. This moves the country to further use of solar energy and move towards sustainability. This result encourages investing in large-scale PT-CSP power plants.



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*Source: 4097852-2019-10-14.xml*