1. Introduction
Nowadays, the world’s population is growing unceasingly, and therefore the electricity demand is estimated to increase. It is the main reason for increasing greenhouse gas emissions. For instance, greenhouse gas emissions from electricity and heat production have contributed to the largest global greenhouse gas emissions in 2014, with a share of about 25% [
1]. To reduce greenhouse gas emissions, a large number of studies have been conducted related to the utilization of renewable energy for power generation purposes with minimum pollutants. Solar energy is the most abundant, sufficient, and cleanest available anywhere among renewable energy resources. According to the technology roadmaps of the CSP provided by the International Energy Agency (IEA) in 2010 [
2], the CSP could supply 11.3% of global electricity by 2050. In addition, the one-megawatt capacity of the CSP can avoid 1360 tons of CO
2 emission compared to the coal-fired power plant [
3].
Regarding the trend of power generation development, solar energy is undoubtedly the next generation of clean, green, and sustainable energy resource for power generation. Two main power generation methods use solar energy in power generation practice, such as solar photovoltaic (PV) [
4] and CSP technology [
5]. Moreover, solar chimney technology is one of the potential solutions for solar power generation [
6,
7]. Besides, another interesting method of solar power generation in the short and midterm is solar-assisted power generation, which is the hybridization of solar energy and fossil fuel-based conventional thermal power plants [
8]. From the future perspective of dispatchability, energy storage, and system efficiency, CSP technology is superior to PV technology [
2,
3]. Nowadays, four different types of technically mature CSP technologies, such as parabolic trough collectors (PTC), linear Fresnel collectors (LFC), solar power tower (SPT), and parabolic dish (PD) systems, are used to generate electricity using solar energy via a thermodynamic principle [
9]. Moreover, the high-temperature potential available in SPT and PD technologies can be used for fuel production via steam reforming and thermochemical approaches [
10,
11,
12]. Among these CSP technologies, the PTC technology is the most developed and commonly practiced for power generation [
13,
14].
In recent years, intensive studies on CSP plants have been investigated using different methods and technologies under various operation conditions [
5,
15]. Some researchers have studied the thermodynamic analysis of the CSP plant using first and second laws. Reddy et al. investigated energetic and exergetic analysis of the 50 MW parabolic trough-based CSP plant for two different tropical locations to optimize the operating pressures of the Rankine cycle for the maximum efficiency of the system by considering a variety of condenser pressure concerning ambient temperature [
16]. Desai et al. [
17] performed the extensive energy and economic analysis of parabolic trough collector-based CSP plants to study effects of turbine inlet pressure and temperature, design radiation, plant capacity, and various modifications of Rankine cycle on overall efficiency, as well as levelized cost of electricity (LCOE = 0.188
$/kWh).
Moreover, many studies have conducted detailed investigations on the performance analysis, techno-economic evaluation, and economic analysis of the CSP plants with various capacities using different numerical methods. Yuanjing et al. [
18] achieved the performance analysis of the 30 MW CSP plant for performance improvement of SEGS VI trough solar power plant. Sultan et al. [
19] examined the techno-economic competitiveness of the 50 MW CSP plants under Kuwait climatic conditions considering solar multiple and the number of operation hours of thermal energy storage (TES). Wang et al. [
20] conducted thermodynamic and economic analyses of the CSP plant with an air-cooled condenser, considering the effects of meteorological conditions, including DNI and ambient temperature. Praveen et al. [
21] investigated performance analysis of the 100 MW CSP plant in two different sites of the Middle East Region to optimize the initial plant design by considering variations of the solar multiple (SM) and operation hours of TES. Shafiee et al. [
22] demonstrated a life cost analysis model to support investment decision-making in CSP projects based on the net present value, internal rate of return and discounted payback period of the investment, and LCOE. Results show that the average LCOE is 0.16
$/kWh. Boukelia et al. [
23] analyzed and compared the techno-economic and environmental potential of two different CSP plants in terms of both hourly and annual performances using an ANN-based approach. Ikhlef et al. [
24] performed a techno-economic optimization of a 25 MW parabolic trough power plant in Algeria by considering the solar multiple, fossil fill fraction of the backup system, and a full load of TES.
Besides, many studies related to the operation conditions of the CSP plant have been performed under different geographical locations with various climate conditions. Teleszewski et al. reported the analysis of the applicability of the parabolic trough CSP plants in the temperate climate locations. Results revealed that geographical location was strongly affected by the operating performance of the CSP plant [
25]. Aqachmar et al. presented a detailed investigation of the Noor-I parabolic trough CSP plant located in Morocco [
26]. Mohamed et al. studied the effects of plant site location on the performance of CSP plants with molten salt TES under three different locations in Egypt [
27].
Furthermore, numerous studies have been conducted on the operation conditions of the solar field (SF), TES system, and power block (PB) to improve the operating performance of the CSP plant. Mokheimer et al. [
28] analyzed the techno-economic performance of the PTC solar field in Dhahran, Saudi Arabia by considering average hourly, daily, monthly, and annually-averaged weather data. Wang et al. [
29] examined the daily performance of PTCs in three different regions of China under different seasons, considering cosine effect, shadowing effect, end loss effect, and optical efficiency. González-Portillo et al. [
30] performed the analytical optimization of the TES system for LCOE reduction in CSP plants considering the costs and efficiencies of the three main parts (SF, TES, and PB) of the CSP plant. Topel et al. [
31] investigated performance improvement of the CSP plant by increasing steam turbine flexibility during start-up. Schenk et al. [
32] developed the dynamic model to evaluate and optimize the transient behavior of PB in the CSP plant during normal, warm, and hot start-up operation modes. Gonzalez et al. performed a simulation of a solar steam generator in the CSP plant via machine learning using a complete year of data from a commercial CSP plant [
33]. Salazar et al. performed analytic modeling of the energy flow in parabolic trough solar thermal power plants under low-latitude locations, considering the effect of solar field operation on the turbine power and efficiency [
34].
As can be seen in previous studies, the performance analysis of the CSP plant located in warm climate conditions with higher DNI was mainly investigated under nominal load. Therefore, it is significantly important to investigate the performance of the CSP plant located in temperate climate conditions under part-load conditions. The novelty of this study lies in the following several aspects:
- (1)
Performance analysis of the 50 MW CSP plant is performed in the nominal and part-load conditions;
- (2)
Effect of power output on the operating performance of the power block is investigated considering the variation of power output caused by the variation of DNI;
- (3)
Effect of variation of DNI on the operating performance of the solar field is considered in the design-point condition;
- (4)
Effect of outlet temperature of the heat transfer fluid (HTF) on the operating parameters of the solar field is examined in the design-point condition;
- (5)
The aperture area of the solar field is optimized using a solar multiple considering the minimum LCOE;
- (6)
Effect of daily DNI on the operating performance of the solar field and CSP plant system is considered under four different reference days.
4. Conclusions
In this study, the performance analysis of the 50 MW CSP plant was investigated for four different reference days (i.e., 22 March, 22 June, 22 September, and 22 December). Numerical simulation of the 50 MW CSP plant was performed both at nominal and part-load conditions, considering the effects of several variations, including the power load and solar radiation. The results show that the operating performance of the CSP plant was strongly affected by the solar radiation and solar incidence angle. Moreover, the operating performance of the CSP plant in the part-load conditions was significantly reduced compared to the nominal load. For instance, the efficient and economical mode of the CSP plant is near the nominal load, which is around 50 MW.
The results also show that, except for the winter season, the rest of the reference days represent the best period with higher operating performance for the 50 MW CSP plant. For example, the highest value of the operating performance of the 50 MW CSP plant is for the 22 June and the lowest value for the 22 January. Moreover, the operating performance on the 22 March is almost similar to the 22 September. Although the results revealed that the 50 MW CSP plant could operate well throughout the year, the winter season has been expected to significantly affect the operating performance of the CSP plant due to the solar incidence angle, duration of sunshine, and ambient temperature. Except for the winter season, the power generation of the CSP plant can be significantly increased due to the TES system. For instance, the 50 MW CSP plant can produce 295 MW·h, 75 MW·h, and 107 MW·h of additional power generation with the aid of the TES system on the 22 June, 22 September, and 22 March, respectively. In addition, the minimum LCOE was 0.214 $/kWh, considering the optimal aperture area of the solar field (523,200 m2).