Design and Techno-economic assessment of a new hybrid system of a solar dish Stirling engine instegrated with a horizontal axis wind turbine for microgrid power generation

Highlights

• A new hybrid solar dish/Stirling and wind system is proposed and modelled.

• A techno-economic assessment of the system has been carried out.

• A sensitivity analysis is performed to investigate the effects of design parameters.

• The levelised cost of electricity is between 0.13 $/kWh and 0.155 $/kWh.

• A theoretical foundation for designing and operating the hybrid system is developed.

Abstract

The increasing interest in renewable microgrids have motivated the exploration of more sustainable alternatives to traditional energy supply. In this study, a novel hybrid renewable energy-based microgrid power system is proposed, designed and techno-economically assessed. The system consists of a concentrated parabolic solar dish Stirling engine and a horizontal axis wind turbine integrated with a battery bank. The novelty of the study lies in replacing conventional hybrid systems, such as a typical photovoltaic/wind assembly, with a novel solar dish/wind turbine system that has the potential to achieve higher efficiencies and financial competitiveness. The solar dish Stirling engine serves as the primary source of electrical power generation while the horizontal axis wind turbine, in conjunction with a battery bank, supplies backup electricity when the primary source of power is unavailable. The system has been designed through advanced modelling in the MATLAB/ Simulink® environment that efficiently integrates the individual energy technologies. A technical sensitivity analysis has been performed for all the units in order to reduce the respective design limits and identify optimum operational windows. Further, the performance of the model has been tested at two locations in Jordan, and a thorough techno-economic analysis of the integrated system has been conducted. The simulation results show that at the optimal design point the efficiency of the Stirling engine is 37% with a net output power of 1500 kWe. For the horizontal axis wind turbine, a module of 100 kWe with a power coefficient of 0.2–0.24 is suitable for operation in terms of cost, power, torque and farm size. Also, two economic indicators, namely, the levelised cost of electricity and hourly cost, have been calculated. The levelised cost of electricity lies between 0.13 and 0.15 $/kWh while the hourly cost is found to be around 4 $/h. Thus, the economic evaluation revealed that the proposed system is very competitive with other integrated renewable energy technologies.

Introduction

In this section, a general overview of the factors that drive hybrid renewable energy technologies are presented as well as some of the benefits and features that the implementation of concentrated parabolic solar dish Stirling engines (CPSD-SE) can offer. Further, a summary of published works related to the development of CPSD-SE and their integration into microgrids is investigated along with the research gaps that the current study aims to fill. Finally, the main objectives of the research are discussed.

Due to the damaging effects on the environment from the worldwide consumption of conventional energy resources, it has become paramount to find renewable energy-based systems to mitigate greenhouse gas emissions and, at the same time, to provide cost-effective solutions to protect against any future inflation in energy prices [1]. Nevertheless, all renewable energy technological solutions bring with them certain disadvantages. In particular, the majority are stochastic, dispersive, and in general are not easily accessible, and they come with distinct regional variabilities [2]. For these reasons, hybrid renewable energy systems (HRES) have been proposed by experts to eliminate the intermittent output of individual systems and enhance their efficiency [3].

Hybridisation by integrating various energy resources has many advantages, including the reduction of specific capital costs, an increase in the capacity of power generation, enhancement of reliability and overall efficiency as well as it provides more flexibility to the optimisation of the design [4]. The most common hybridisation configuration is combining solar and wind energies. Further, a microgrid system comprising of HRES is one of the most efficient energy alternatives that are expected to satisfy the energy demands of remote regions. In general terms, microgrids can be defined as clusters of electrical energy generators, energy storage and controllable loads in combination with a central control system to monitor their operation and distribute generation sources that operate in both grid-connected and off-grid modes [5]. Moreover, the small-scale decentralised distributed generation systems are now becoming a promising alternative to the typical large-scale centralised power plants [6] at remote locations [7]. Most of the hybrid microgrids generations are accomplished by integrating photovoltaic (PV) arrays with wind turbines (WT) [8]. Nassar et al. [9] applied techno-economic optimisation of a stand-alone hybrid PV/wind power system to electrify an urban community in Libya. Based on the cost analysis, the levelised cost of electricity (LCOE) was estimated to be 0.236 $/kWh. An alternative solution to PVs is the concentrated solar power (CSP) plants, especially dish concentrators that have higher electrical efficiency than PV plants of similar size. For example, the CPSD-SE has the highest conversion efficiency, ranging from 16% to 31%, among the CSP based technologies [10]. In comparison, the most efficient commercial solar PV has an efficiency that ranges between 13 and 20% [11]. Further, a CSP plant can harness direct normal solar irradiation (DNI) that is usually more than 2000 kWh/m², (greater than5 kWh/m²/day [12]). Moreover, CSP plants typically possess lower environmental impacts than PV plants over their entire life cycle due to the less intensive assembling and decommissioning phases [13]. In summary, the CPSD-SE system has the potential to become an attractive solution due to its great potential in enhancing the microgrids performance as well as providing an eco-friendly energy conversion system. As a result, the scope of the present research is to assess a hybrid system based on the CPSD-SE technology.

The Middle East and North Africa (MENA) countries have abundant solar and wind energy resources available and Jordan is considered to be a good typical example of such a region. Therefore, the MENA region has a great potential to integrate the most advanced CSP technologies [14]. Further, the German Aerospace Center (DLR) stated [15] that by 2025 the CSP technologies would play a leading role in the Mediterranean region that would promote a broad mix of renewable technologies. Consequently, CSP will have a considerable portion of the RES generation in the MENA countries. More specifically, Jordan has a relatively abundant annual DNI of 2700 kWh/m2, and in addition, the average number of sunny days per year is nearly 300 with 3311 h per year. For the wind speed, Jordan has a high potential of annual average wind speed at some locations with higher than 7 m/s and with highs of 10 m/s [16]. Thus, Jordan has been selected as a suitable region to test the performance of the proposed microgrid but it should be also highlighted that the same design and modelling approaches can be implemented in many other locations in the world.

It is apparent that there is a lack of studies that deal with the integration of HRES with solar thermal power cycles based on external combustion engines such as SE. Also, an implementation of a hybrid CPSD-SE/HWT system in decentralised microgrids for power generation has not been previously studied in the literature.

A small number of techno-economic studies exist in the literature regarding CPSD-SE systems. One of these studies was a theoretical analysis conducted by Wu et al. [17] by means of a parametric study to determine the overall performance of the CPSD-SE system. The performance evaluation results revealed that 18.54 kWe of electrical power could be generated with an overall thermal–electric efficiency of 20.6%. Another study, focusing on the techno-economic feasibility of the CPSD-SE system under varying conditions, was conducted by Poullikkas et al. [18] in a number of Mediterranean regions, but principally in Cyprus. The researchers conducted a parametric cost-benefit analysis using a special algorithm as a simulation tool. Further, a techno-economic viability of a 100 MWe CSP plant consisting of 4000 of 25 kWe CPSD-SE units in Algeria has been investigated by Abbas et al. [19]. The System Advisor Model (SAM) software, developed by The National Renewable Energy Laboratory (NREL), was implemented for a techno-economic assessment to estimate the monthly and yearly energy production.

Ruelas et al. [20] conducted a theoretical examination to assess the technical feasibility of a Scheffler-type CPSD-SE using a new mathematical model. Ruelas’s model involves three parameters namely the geometric, optical and thermal models of the receptor. Reddy and Veershetty [21] conducted a techno-economic feasibility analysis of the autonomous power plant for a 5 MWe CPSD-SE collector at over 58 locations in India. To reach high values for the average annual power generation of 12.68 GWh, the parametric analysis included such factors as the land area required and energy yield. Based on the economic performance, the minimum LCOE for CPSD-SE power plant was 0.197 $/kWh, with a payback period of 10.63 years. Bakos and Antoniades [22] conducted a techno-economic study of a large scale CPSD-SE power plant in Greece, utilising the TRNSYS software. This simulation tool was utilised to simulate the performance as well as to assess the feasibility of the proposed installation of the solar power plant consisting of 1000 units CPSD-SE, each with a nominal power of 10 kWe. The results showed that the annual energy production of the proposed power plant could reach 11.19 GWh, and achieving a 16 years pay-back period.

Al-Dafaie et al. [23] proposed a mathematical model of a CPSD-SE system based on the average hourly data across six different days measured from the Energy Center of the Jordan University of Science and Technology, Jordan. A techno-economic performance analysis has been carried out to investigate the potential of utilising the rejected heat from the cold chamber in the solar Stirling engine (SE) for potable water production in the distillation process. Further, a mathematical model was utilised by Mendoza et al. [24] in order to identify the maximum geometric configuration parameters of the solar tracking system control that is designed to improve the solar system efficiency of a CSPD-SE system. The performance results indicated that a maximum thermal efficiency of 25% could be reached at a solar radiation of 1000 W/m² and diameter at 10.5 m. Bataineh and Taamneh [25] simulated a stand-alone CPSD-SE with a battery bank using the SAM software tool. The results revealed an overall net system efficiency of approximately 21% and a lowest LCOE of about 0.102 $/kWh. Zayed et al. [26] established and thermodynamically modelled a new commercial Solar Dish/Stirling system with a rated power of 25 kWe; the levelized energy cost of the system was found to be ∼ 0.256 $/kWh. Buscemi et al. [27] investigated and optimised the energy performance of a 32kWe CPSD-SE system. Shaikh et al. [28] investigated a performance model of a 25 kWe stand-alone CPSDS-SE system. The results indicate that the system could produce annual electricity of 38.6 MWh with a net efficiency of 23.39% and LCOE of 0.13 $/kWh.

In the future, it is expected that more CPSD-SE applications will be commissioned due to the technology’s suitability for hybridisation [29]. Nevertheless, only a few studies have addressed the hybridisation of a CPSD-SE with other power generation systems in microgrids. Guo et al. [30] established a new hybrid steam/air biomass gasification integrated with CPSD-SE for combined cooling, heating and power (CCHP) system in China. The authors conclude that this novel hybrid system obtains an energy efficiency of 51.34%. Mastropasqua et al. [31] have studied the integration of CPSD-SE with a solid oxide electrolysis cell to produce electricity, thermal energy and hydrogen. It has been shown that the system can be operated at a nominal solar-to-hydrogen efficiency of above 30% and producing 30 kWe and 150 kg/d of hydrogen.

For the hybridisation of CPSD-SE/HWT, Shariatpanah et al. [32] introduced a new grid-connected hybrid power system coupled with a typical CPSD-SE and a WT. The results of the simulation indicated that a new hybrid on-grid CPSD-SE/WT could provide an acceptable performance. Rahman et al. [33] investigated the automatic generation control of a hybrid CPSD-SE and a WT by assessing the generation rate and speed governor dead band constraint. Kadri and Hadj Abdallah [34] conducted a technical performance analysis of a hybrid CPSD-SE/WT connected to the electricity distribution grid in a coastal area located in Tunisia. It is clear from the literature that the power range (10–50 kWe) of the CPSD-SE system is suitable and decentralised for the small and micro scales (residential and small commercial applications) of power generation.

Based on the literature review, it is clear that there exists a lack in the literature of studies dealing with the modelling and the techno-economic design of the CPSD-SE/HWT integrated solution. The present study aims at filling this knowledge gap and adopts a comprehensive approach in assessing the feasibility of the proposed novel system. The new assembly configuration has a number of important features: (a) the generator position, usually placed in the receiver of each dish, helps to mitigate heat losses and provides flexible modular operation (typical sizes varying between 5 and 50 kWe) and hence it is ideal for distributed generation of various scales, (b) the CSPD-SE collectors do not require large cooling systems (e.g. cooling towers) and therefore electricity can be supplied in regions that water supply is restrained, (c) CSPD-SE has a low noise engine and simple structural design with fewer moving parts than other CSP systems, (d) CSPD-SE systems achieve high concentration ratios (more than 3000) and high efficiencies of about 30%. Due to these features, the CPSD-SE/HWT has the potential to be economically attractive and this is thoroughly investigated within this study.

An innovative and user-friendly modelling approach has been applied that facilitates the interaction among the different assembly components, i.e. CPSD-SE, HWT and battery bank and this fosters the optimisation of the microgrid. The CPSD-SE is the prime mover in the absence of solar irradiation, the HWT and the battery bank operate to provide the required electricity. The design procedure and the assessment performance of the microgrid have been exemplified in two regions within Jordan, namely Madaba and Mafraq. The main objectives of this work are as follows:

• Design of the proposed system through advanced modelling to integrate the decentralised microgrid system. Models have been developed in the MATLAB/Simulink® environment and have been used to evaluate the size and design of the system and to ensure that the electrical demand of the end-user is met.

• Construction of a sensitivity assessment on the developed system to investigate the effects of various design parameters on the system performance.

• Implementation and in-depth testing of the system in two regions in Jordan.

• A detailed techno-economic assessment of the proposed hybrid CPSD-SE/HWT system with energy storage for microgrid applications.