1 Performance Assessment of Solar Thermal Power Plants: A Case Study in Queensland Rakibuzzaman Shah, Ruifeng Yan, and Tapan Kumar Saha Power and Energy System Research Group School of Information Technology and Electrical Engineering The University of Queensland Brisbane, QLD, Australia e-mail: [email protected]; [email protected]; [email protected] Abstract—Recent and ongoing improvements make the generation comes from renewable energy sources [3]. concentrated solar thermal power (CSP) as one of the Australia has the highest average solar radiation per square promising sources to replace fossil fuel based power plants. meter in the world, but yet to be a major player in the CSP CSP plants are already commercially being exploited in some industry. A recent study shows that it would be technically countries such as Spain and USA. Australia is also expecting feasible to integrate 15 GW of CSP plants in the Australian increasing penetration of CSP in near future in order to meet electricity network with a modest expansion of the grid [4]. the renewable energy target of 20% by 2020. Among the states With the Mandatory Renewable Energy Target (MRET) of and territories of Australia, Queensland is one of the promising ensuring 20% of Australian electricity supply from states for the large-scale deployment of CSP plants. In such a renewable energy resources by 2020 [5], an increased case, it is important to analyze the performance of different investment in large-scale solar thermal installation is likely CSP technologies in Queensland’s climatic condition. Therefore, this paper compares the performance of four to be seen in near future. available large-scale CSP technologies at some potential sites Recently, much research efforts have been made towards for CSP deployment in Queensland. The aim of this paper is to revealing different aspects of CSP integration into the power report the performance of these technologies by means of grid [6]-[10]. Research works in [6], [7] have proposed the output analysis. The effects of different design parameters on optimized operational planning of CSP plants with thermal the performance are also analyzed and reported in this paper. storage for maximizing the revenue of the CSP systems. Sarkar and others [8] have proposed a stochastic planning Index Terms—Performance assessment, solar thermal power plants, solar yield. approach for assessing MW level resource of wind and solar hybrid system. Moreover, it is worth noting that all of the I. INTRODUCTION above stated research works have only considered the parabolic trough CSP system for their studies. There are In recent years, growing concern for clean energy in an other sets of research works devoted in revealing the techno- effort to reduce emissions and minimize the reliance on economic performance of CSP technologies in different fossil fuels have led to worldwide integration of renewable locations in power systems [9], [10]. With the addition of energy generations. Essentially, there are two major new technology such as Linear Fresnel Reflectors (LFR), an technologies, which cover renewable energy sources: - Wind extensive technology comparison has been done in [9] with and Solar. There are two distinct methods for solar power the most mature and lowest cost CSP technology: parabolic generation: solar photovoltaic and concentrated solar thermal trough. However, there is not much published works, which power (CSP). Unlike solar photovoltaic, a CSP plant use assesses and compares different CSP technologies in a direct normal irradiance (DNI) to convert solar energy into complete system within a consistent framework. This paper heat energy through focusing a receiver, which is then used aims to fill this gap, and provide a comparative performance in the thermodynamic cycle to produce electricity through a assessment of different CSP technologies by using location conventional generator. Recently, CSP plants have gained specific climate data. Among the states of Australia, considerable importance around the world as one of the Queensland has a huge potential for solar power resources. promising and viable options for bulk power generation. The This study is conducted for CSP potential sites in worldwide installed capacity of CSP plants is escalating Queensland. rapidly and expected to reach 2 GW by the end of 2013 [1]. As of now, Spain and United States are the two leading The rest of the paper is organized as follows. Section II nations in CSP installations [1], [2]. According to “CSP briefly explains the CSP generation potential in Queensland. Global Outlook” the concentrated solar thermal power could Section III briefly reviews the available CSP technologies for meet 7% of the world’s power by 2030 and 15% by 2050 [1]. power generation. Section IV presents the simulation results and discussion. Conclusions are drawn in Section V. Australia is the world’s ninth largest energy producer, which produces 2.4 % of the energy production of the world II. SOLAR THERMAL POTENTIAL IN QUEENSLAND [3]. Australian electricity generation predominantly depends Recent studies have revealed that among the states of on fossil fuels based generation technologies (i.e., coal and Australia, Queensland will experience considerable load gas). Currently, only 8% of Australia’s total electricity 978-1-4799-6415-4/14/$31.00 ©2014 IEEE 2 growth in foreseeable future [11]. The load of Queensland is mostly supplied by the fossil fuel based plants with limited hydro and solar based power plants. It is anticipated that this practice is going to be changed due to the retirement of some aged coal fired power plants in the region and the commonwealth government MRET. Solar power is the most promising and viable resources for electricity generation in Queensland [12]. Fig. 1 shows the solar resource map of Queensland. From Fig. 1 it can be seen that Central and North-West Queensland have the best annual solar DNI followed by Northern and South East region of the state. The studies in [4] and [12] reveal that there are seven potential sites in Queensland for large-scale (50 MWe to 150 MWe and above) CSP deployment. In addition, there are other nine potential sites in Queensland for large-scale Fig. 2. CSP technologies: (a) parabolic trough, (b) power tower, (c) linear hybrid CSP plants [4]. Currently, a CSP project (30 MWe) is fresnel, (d) parabolic dish [1], [14]. at a feasibility study phase for Central Queensland- (c). Linear Fresnel Reflectors: Linear Fresnel Collinsville region [13]. reflectors as shown in Fig. 2 (c) create a linear focus for a downward facing linear receiver. It has long rows of flat or slightly curved mirrors with one axis tracking facilities to track the daily movement of the sun [15], [16]. (d). Parabolic Dishes: This type of CSP technology concentrates sun rays at a focal point placed above on the centre of the dish as shown in Fig. 2 (d). The entire system (dish and receiver) moves in tandem to track the sun. Parabolic dish technology offers the highest conversion efficiency among all CSPs. However, individual parabolic dish has lower power capacity; thereby requires hundreds and thousands of dishes to be installed for a large-scale plant like Fig. 1. Solar resource map of Queensland [11]. other CSPs [15], [16]. III. CSP TECHNOLOGIES IV. NUMERICAL RESULTS At present, there are four available CSP technologies For this study, we have modeled solar thermal plants by under development and/or exploited as shown in Fig. 2: using Solar Advisor Model (SAM), developed by National parabolic trough, power tower, linear Fresnel, and parabolic Renewable Energy Laboratory (NREL) [17]. SAM is an dish system. Among the available CSP technologies, open source software, has extensively been used for parabolic trough and power tower are the two most performance and financial modelling of CSP, PV, and wind developed technologies at this moment. Moreover, parabolic generation system. For this particular study, solar thermal trough is the most matured one, thereby, shares 95.3 % of the power plants are considered at four different locations in CSP market followed by power tower, linear Fresnel, and Queensland, as summarized in Table I. All the plants are dish technology [14]. A brief description of these CSP simulated with the solar data obtained from the US technologies is given next. EnergyPlus website for those locations [18]. (a). Parabolic trough: In a parabolic trough system TABLE I. LOCATION OF CSP SITES IN QUEENSLAND [18] (Fig. 2 (a)), parabolic trough shaped mirrors CSP site Location DNI (kWh/m2/yr) produce linear focus on the absorber tube that placed on the focal line of parabola. It has a Longreach 23.450 S; 144.250 E 2564.4 tracking capability to track the daily movement of Townsville 19.250 S; 146.810 E 1897.3 the sun path. Synthetic oil is widely used as a heat transfer fluid (HTF) [15], [16] for this technology. Gladstone 23.840 S; 151.260 E 2063.9 (b). Power tower: A power tower system (Fig. 2 (b)) Oakey# 27.450 S; 151.700 E 2071.1 uses heliostat field collectors (large mirrors with # two axis tracking) which reflect and concentrate the Represent South/South East of Queensland sun rays on to the fixed receiver positioned on top The following CSP technology options are considered of the tower. Molten salt is widely used as storage for this study: for this technology. However, direct steam generation type power tower is also commercially ¾ Power tower (direct steam) (Tower-DSG). available [15]. ¾ Power tower (molten salt) (Tower-MT). 3 ¾ Parabolic trough (Trough). day, the electrical output of the tower technologies ¾ Linear Fresnel reflectors (LFR). outperforms that of the LFR and parabolic trough systems. The main goal of this comparative study is to analyze different CSP systems on equal footing, thereby, choice of design point parameter is important.