Secondary concentrator design of an updated space solar power satellite with a spherical concentrator

Highlights

• An updated space solar power satellite concept is proposed.

• A design methodology of secondary concentrator is presented.

• Effective energy collection and energy density distribution are simulated.

• The effective solar energy collection is up to 81.14% for the order of 5.

• Relative non-uniformity index decreases from 0.77 to 0.4 after further optimization.

Abstract

The Space Solar Power Satellite (SSPS) is a promising project to solve the energy crisis on earth. In this paper, a secondary concentrator design of an updated SSPS-OMEGA concept is proposed aiming at the problems existing in original SSPS-OMEGA concept, such as high power transmission through power brush, thermal management of the photovoltaic (PV) cell arrays and special requirements for the concentrator film brought by the inside placed transmitting antenna. Firstly, the updated concept with a secondary concentrator, a disc PV cell arrays and outside placed transmitting antenna is illustrated and main parts of it are described. Secondly, a design methodology of the secondary concentrator is presented. The characteristics of spherical concentrator are simply described. The generatrix geometry of the secondary concentrator is described using Bézier curve, and the performances of optics and energy density distribution on PV cell arrays are evaluated using the Monte Carlo Ray Tracing method. After that, a mathematical optimization model is established and the Particle Swarm optimization is used to obtain better configuration of secondary concentrator, solar energy collection performance and energy density distribution on PV cell arrays. Finally, the optimal generatrix geometry of secondary concentrator and energy density distribution under different orders of Bézier curve are investigated, the result shows that the effective solar energy collection and solar energy collection can be up to 81.14% and 87.06% respectively when the order of Bézier curve is 5. Moreover, a further energy density distribution optimization is conducted and the relative non-uniformity index of 0.4 is realized.

Introduction

Space Solar Power Satellite (SSPS) is a tremendous energy system that collects and converts solar energy to electric power in space, and then subsequently transmits the electric power to earth through wireless transmission, and finally received and rectified to the terrestrial power grid, as shown in Fig. 1. SSPS is a promising project to solve the energy crisis on the ground by using abundant, clean and sustainable space solar energy. Since proposed initially by Glaser (1968), SSPS has been developed all over the world and many typical concepts are proposed in many different countries in the last six decades, such as the SSPS reference system (DOE/NASA, 1980), Integrated Symmetrical Concentrator (ISC) (Carrington et al., 2000), sun sail (Seboldt et al., 2001) and sun tower (Mankins, 2002) SSPS, tethered SSPS (Sasaki et al., 2006), Solar Power Satellite via an Arbitrarily Large-Phased Array (SPS-ALPHA) (Mankins, 2012), and multi-rotary joint SSPS (Hou et al., 2015). SSPS is a large scale system which involves many subjects and key technologies, such as multi-system coupling and optimization, continuous transmission of high-power microwave energy, ultra-large structure design with high-precision automatic deployment, thermal management, on-orbit assembly and vibration control, et al. (Duan, 2018). Many indicators can be used to measure the performance of a SSPS system, such as power output, solar energy collection, mass and cost, et al. however, a novel and feasible SSPS concept with the high power output and low system mass is always desirable and worth exploring.

For this purpose, a novel SSPS via orb-shape membrane energy gathering array (SSPS-OMEGA) concept is proposed by our team in 2014 (Yang et al., 2014), shown in Fig. 2. It mainly consists of three parts: spherical concentrator, photovoltaic (PV) cell arrays, and transmitting antenna. According to the ideal optical design, the spherical concentrator is comprised of the semi-transparent and semi-reflecting thin film. Sunlight would pass through one side of the thin film whilst being reflected by the other side, and the incident light is focused on a line region ([0.5,1] R, where R is the radius of the spherical concentrator) (Ji et al., 2019). The PV cell arrays will rotate around the spherical concentrator along the rotation orbit when SSPS-OMEGA working on Geostationary Equatorial Orbit (GEO), and the generated direct current (DC) power is transmitted to transmitting antenna through the power brush. The transmitting antenna is placed inside the concentrator and supported by six cables hanging from the spherical concentrator.

The usage of the spherical concentrator can reduce the size of PV cell arrays, thereby reducing the mass and lunch cost. There are obvious advantages in this concept, such as thermal problem is slightly relieved by separating the sandwich structure, no light leakage, and the attitude control is simplified because only the PV cell arrays move along the circular frame orbit at a constant speed. However, there still exists three main problems, one is movement of the ultra-high power brush when transmitting DC power from PV cell arrays to transmitting antenna, one is the layout and thermal management of PV cell arrays for its complex hyperboloid configuration and inside placement of the concentrator, the other one is the problems brought by the inside placed transmitting antenna, such as incident solar energy blocking when the system is running periodically and special requirement (microwave penetration) for the concentrator film.

Furthermore, the energy density distribution on PV cell arrays is also needed to be taken into consideration. Different with the thermoelectric solar energy harvesting systems, where the solar energy collection is the foundation of the subsequent energy generation (Taneja et al., 1991, Sellami et al., 2012, Ali et al., 2014, Yu and Tang, 2015, Farges et al., 2018), the uniformity of the energy density distribution on PV cell arrays is also important and is considered in almost all photovoltaic power stations (Jones and Wang, 1995, Meng et al., 2014, Tsai, 2015, Prasad et al., 2017, Gong et al., 2017). For this concept, Yang et al. (2017) did a further design about the generatrix geometry of the PV cell arrays to obtain optimal optical performance available for efficient response to sunrays. Ji et al. (2019) conducted collection rate fluctuation analysis under different division layers of spherical concentrator with deformation. However, these two researches did not solve the problems mentioned above. Therefore, it is necessary to put forward an updated concept with better feasibility and system indicators for SSPS design and development.

To investigate the updated SSPS-OMEGA concept, a secondary concentrator design with transmitting antenna and PV cell arrays outside placement is proposed aiming at the problems existing in original SSPS-OMEGA concept in this paper. In this updated concept, the spherical concentrator is still used to collect solar energy, but a secondary concentrator is well-designed to reflect the sunlight to the disc PV cell arrays outside placed of concentrator, and then the generated DC power is transmitted to the outside placed transmitting antenna through a non-contact rotary joint. Bézier curve is used for the parametrization of the secondary geometry, and the optimum design is investigated for different order of Bézier curve. The Monte Carlo Ray Tracing method and the Particle Swarm optimization are used to obtain better configuration of secondary concentrator. In the optimization procedure, both solar energy collection and energy density distribution on PV cell arrays are taken into consideration.

This paper is organized as follows, the updated SSPS concept with a spherical concentrator and secondary concentrator is described in Section 2. Section 3 presents a design methodology of the secondary concentrator. The result of secondary concentrator design is simulated in Section 4, and a conclusion is summarized is Section 5.