Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman Determination of key parameters for sizing the heliostat field and thermal energy storage in solar tower power plants Rui Chen, Zhenghua Rao, Shengming Liao ⁎ School of Energy Science and Engineering, Central South University, Changsha, Hunan 410083, China ARTICLE INFO Keywords: Solar tower power plants Design direct normal irradiance Solar multiple Thermal energy storage Thermo-economic analysis ABSTRACT The optimal sizing of the solar tower power plant with thermal energy storage is critical for increasing the system reliability and reducing the investment cost. However, the combined effects of key design parameters for sizing the solar tower power plants, including design direct normal irradiance, solar multiple and thermal sto- rage hours, on the thermo-economic system performance under different solar resources are still unclear. In this study, a thermo-economic model for a 50 MW solar tower power plant based on steam Rankine cycle with molten salt storage has been developed to explore the optimal combinations of these parameters at four sites in China. The coupled relationship between these parameters and their effects on the annual electricity generation, solar-to-electricity efficiency and levelized cost of energy have been identified. The results show that the optimal design direct normal irradiance for minimal levelized cost of energy depends on both the annual irradiation level and the distribution of solar irradiance, which differs from the recommended values obtained from the tradi- tional methods. It is found that the irradiation received by heliostats at the optimal design condition accounts for a specific percentage (i.e., 72–75%) of the annual irradiation for the cases in this study. The sensitive analysis by varying the main financial parameters indicates that the optimal design direct normal irradiance and the cor- responding percentage slightly vary with the heliostat cost. The results can provide a theoretical reference for determining the optimal size of the heliostat field and thermal energy storage for solar tower power systems under different solar resources. 1. Introduction Concentrating solar power (CSP) technology has been proved to be one of the most promising electricity generation alternatives with re- newable resources [1]. Compared with other renewable power gen- eration technologies, such as solar photovoltaic power [2] and en- hanced geothermal system [3], CSP technology [4] is more mature and can be utilized in most parts of world. The application of CSP has been recommended and gained considerable momentum in recent years, and the cumulative capacity of global CSP projects reached about 9.9 GW by the end of year 2017 [5]. According to the IEA’s report [6], the installed capacity would reach 982 GW when CSP becomes competitive for most of the electricity generation technologies in a carbon-constrained world by 2050. However, due to the high initial investment, the actual growth of commercial CSP plants is much slower than expected. With great potential for cost reduction, the solar tower power (STP) based on steam Rankine cycle with thermal energy storage (TES) system is one of the most commonly installed CSP technologies around the world [7]. An appropriate design for the STP system is essential to lower the capital cost and increase the annual revenue from electricity generation [8]. For a specific STP with TES system, design direct normal irradiance (DNI), solar multiple (SM) and TES hours are the main parameters to determine the size of subsystems including solar field, TES, and power block. Design DNI refers to a specific DNI at which the solar field produces the rated thermal output [9]. Due to daily and seasonal variations of irradiance, determining the appropriate design DNI is extremely im- portant and complex. A high design DNI may contribute to an under- sized solar field, resulting in the low capacity factor of plants and poor utilization of the invested capital. While a low design DNI may lead to an oversized solar field, resulting in the excessive unutilized energy and high heliostats investment. Generally, the DNI at 10:00 am or noon of spring equinox (SE) [10] or summer solstice (SS) [11] was re- commended. Sometimes, the DNI at noon of autumnal equinox (AE) [12] or winter solstice (WS) [13] was also selected as the design value. In addition, specific values of 800 W/m 2 [14], 900 W/m 2 [15], 950 W/ m 2 [16] and 1000 W/m 2 [17] were used as the design DNI. However, the design DNI is strongly dependent on the local solar irradiation, and https://doi.org/10.1016/j.enconman.2018.09.065 Received 30 May 2018; Received in revised form 17 September 2018; Accepted 19 September 2018 ⁎ Corresponding author. E-mail address: smliao@csu.edu.cn (S. Liao). Energy Conversion and Management 177 (2018) 385–394 0196-8904/ © 2018 Elsevier Ltd. All rights reserved. T