Terrestrial Solar Power Research Articles

A constellation design for orbiting solar reflectors to enhance terrestrial solar energy

Orbiting solar reflectors (OSRs) are flat, thin and lightweight reflective structures that are proposed to enhance terrestrial solar energy generation by illuminating large terrestrial solar power plants locally around dawn/dusk and during night hours. The incorporation of OSRs into terrestrial energy systems may offset the daylight-only limitation of terrestrial solar energy. However, the quantity of solar energy delivered to the Earth’s surface remains low due to short duration of orbital passes and the low density of the reflected solar power due to large slant ranges. To compensate for these, this paper proposes a constellation of multiple reflectors in low-Earth orbit for scalable enhancement of the quantity of energy delivered. Circular near-polar orbits of 1000 km altitude in the terminator region are considered in a Walker-type constellation for a preliminary analysis. Starting from a simplified approach, the equations of Walker constellations describing the distribution of the reflectors are first modified by introducing a phasing parameter to ensure repeating pass-geometry over solar power farms. This approach allows for a single groundtrack optimisation to define the constellation, which was carried out by a genetic algorithm for single and two reflectors per orbit with an objective function defined as the total quantity of energy delivered per day, to existing and hypothetical solar power projects around the Earth. When full-scale constellations are considered with a number of reflectors, the quantity of solar energy delivered is substantial in the broader context of global terrestrial solar energy generation.

A reference architecture for orbiting solar reflectors to enhance terrestrial solar power plant output

Orbiting reflectors offer the possibility of illuminating large terrestrial solar power plants to enhance their output, particularly at dawn and dusk when their output is low but energy spot prices can be high. While the concept of orbiting solar reflectors has been considered in various forms in the past, there is now a timely overlap of rapidly growing global demand for clean energy services, falling launch costs through reusability and the emergence of in-orbit manufacturing technologies to enable the fabrication of large, ultra-lightweight space structures. This paper provides an end-to-end analysis of a possible minimum initial architecture to deliver such global clean energy services. The analysis will cover orbit selection, attitude control requirements, structural analysis and economical viability, followed by a discussion on regulatory issues, future improvements and further applications.

Graphitic surface layer formation on organic substrates for electronics using a concentrated solar simulator

Heat spreading is an important attribute that improves thermal management and operation of high-performance packages, such as those for solid-state power amplifiers. This attribute can be enhanced through direct transformation of polymers into graphitic films. The present work reports a custom vacuum deposition process that synthesizes thin graphitic layers on organic substrates through direct pyrolysis via concentrated irradiation from a xenon lamp to produce a peak heated zone of approximately 3 cm diameter with a maximum heat flux of 3.2 MW/m^2. The light source, replaceable with concentrated terrestrial solar power, provides ultrafast heating of substrates through rapid flashes (< 0.5 s) and improves growth rates over relatively larger areas compared to laser processing, mitigating the issue of porosity in graphitic layers that deteriorate heat spreading capabilities. The enhanced organic substrates are analyzed using Raman and energy-dispersive X-ray spectroscopy, scanning electron microscopy, and thermal diffusivity measurements, indicating graphitic conversion.Graphical abstract

Enhancing terrestrial solar power using orbiting solar reflectors

The delivery of global clean energy services represents a key challenge for the 21st century. In order to deliver such services, it is clear that large-scale solar power farms will continue to grow both in number and size. In principle, ultralight membrane orbiting solar reflectors can illuminate large-scale solar power farms during the critical dawn/dusk hours of the day, enhancing the utility of terrestrial solar power. The key advantage is that only a relatively modest mass needs to be delivered to Earth orbit. This paper discusses the technical challenges associated with the development, deployment and operation of such a space-based energy service. Business development models are discussed along with regulatory issues and finally an integrated technology demonstration roadmap is presented.

An analytical model for solar energy reflected from space with selected applications

Orbiting solar reflectors can be employed to redirect incoming sunlight to provide/reject additional solar energy to/from a planetary body. The concept has been studied in the past for a variety of applications, among which enhancing terrestrial solar power generation, supporting lunar exploration and terraforming Mars are the most prominent. Despite the potential of the concept, previous studies have assumed a perfect reflector, and have only relied on simplified geometric analyses to calculate the quantity of energy delivered with minimal consideration of geometric and physical losses. In this paper, an analytical model is developed for a reflector in a circular orbit to calculate the total energy delivered to a stationary ground-target, such as a solar power farm. A perfectly ideal flat reflector is also assumed to avoid material specific considerations but atmospheric transmission losses, fixed ground-target size and solar panel orientation are included. Case studies demonstrate the significance of high-fidelity modelling, provide new insights into the scalability of the results to test the effectiveness of the concept at different solar system objects, including delivering solar energy at the Earth, Moon and Mars.

Preliminary experiment and performance evaluation of a terrestrial solar thermoelectric generators under fluctuant solar radiation

The solar thermoelectric generator (STEG) is a promising alternative terrestrial solar power generation device due to its ability to utilize almost full solar spectrum. Many researches have been carried out to improve its efficiency. Some improved STEG has achieved remarkable efficiency in the laboratory. However, its performance in practical situations has been few studied, which limits its practical applications. In this work, the experimental investigation and performance evaluation of the terrestrial STEG system in typical days in East China are presented. Detailed changes in efficiencies and output power of the system are revealed. The results show that the performance of the system changes with the environment. The system can obtain the highest one-day electrical efficiency of 3.22% at 12:00 in the noon and thermal efficiency of 53% at 15:00 in the afternoon. The influences of solar irradiance, cooling water temperature and water cooling quality are discussed. The optimization methods of the system running in real environment are discussed and optimized to improve the average efficiency in the long run. The performances of this system and pure solar water heating system without TE modules are compared and the details are presented. The hybrid system has a higher comprehensive performance and lower thermal performance than the pure solar water heating system. This work provides a valuable reference for the design and optimization of STEG running in real environment.

Solar Power Satellite system in formation on a common geostationary orbit

The diurnal day-night cycle severely limits the Terrestrial solar power. To overcome this limitation, a Solar Power Satellite (SPS) system, consisting of a sunlight reflector and a microwave energy generator-transmitter in formation, is presented in this work. The microwave transmitting satellite (MTS) is placed on a common geostationary orbit (GEO) in the Earth’s equatorial plane, and the sunlight reflector uses the solar radiation pressure to achieve quasi-periodic orbits about the MTS, so that the sunlight is always redirected to the MTS, which converts the solar energy in electromagnetic power and transmits it by microwaves to an Earth-receiving antenna. Assuming the sun line direction constant at dierent seasons (i.e. autumn/spring equinoxes and winter and summer solstices), previous studies have shown the existence of a family of displaced ecliptic orbits above or below the equatorial plane of the Earth around a GEO. In this study, the position of the Sun is assumed on the ecliptic plane with a mean obliquity (inclination of Earth’s equator with respect to the ecliptic) of 23.5◦. A linear solution as an initial condition for the full equations of motions about a GEO, which yields bounded orbit for the sunlight reflector about the MTS in the Earth-satellite two-body problem with solar radiation pressure. To redirect the sunlight to the MTS, the law of reflection is satisfied by the space mirror attitude.

Collecting solar power by formation flying systems around a geostationary point

Terrestrial solar power is severely limited by the diurnal day–night cycle. To overcome these limitations, a Solar Power Satellite (SPS) system, consisting of a space mirror and a microwave energy generator-transmitter in formation, is presented. The microwave transmitting satellite (MTS) is placed on a planar orbit about a geostationary point (GEO point) in the Earth’s equatorial plane, and the space mirror uses the solar pressure to achieve orbits about GEO point, separated from the planar orbit, and reflecting the sunlight to the MTS, which will transmit energy to an Earth-receiving antenna. Previous studies have shown the existence of a family of displaced periodic orbits above or below the Earth’s equatorial plane. In these studies, the sun-line direction is assumed to be in the Earth’s equatorial plane (equinoxes), and at $$23.5^{\circ }$$ below or above the Earth’s equatorial plane (solstices), i.e. depending on the season, the sun-line moves in the Earth’s equatorial plane and above or below the Earth’s equatorial plane. In this work, the position of the Sun is approximated by a rectangular equatorial coordinates, assuming a mean inclination of Earth’s equator with respect to the ecliptic equal to $$23.5^{\circ }$$ . It is shown that a linear approximation of the motion about the GEO point yields bounded orbits for the SPS system in the Earth–satellite two-body problem, taking into account the effects of solar radiation pressure. The space mirror orientation satisfies the law of reflection to redirect the sunlight to the MTS. Additionally, a MTS on a common geostationary orbit (GEO) has been also considered to reduce the relative distance in the formation flying Solar Power Satellite (FF-SPS).

Sandwich module prototype progress for space solar power

Space solar power (SSP) has been broadly defined as the collection of solar energy in space and its wireless transmission for use on earth. This approach potentially gives the benefit of provision of baseload power while avoiding the losses due to the day/night cycle and tropospheric effects that are associated with terrestrial solar power. Proponents have contended that the implementation of such systems could offer energy security, environmental, and technological advantages to those who would undertake their development. Among recent implementations commonly proposed for SSP, the modular symmetrical concentrator (MSC) and other modular concepts have received considerable attention. Each employs an array of modules for performing conversion of concentrated sunlight into microwaves or laser beams for transmission to earth. While prototypes of such modules have been designed and developed previously by several groups, none have been subjected to the challenging conditions inherent to the space environment and the possible solar concentration levels in which an array of modules might be required to operate. The research described herein details our team's efforts in the development of photovoltaic arrays, power electronics, microwave conversion electronics, and antennas for microwave-based “sandwich” module prototypes. The implementation status and testing results of the prototypes are reviewed.

III-V Semiconductor-Based Multi-Junction Solar Cells for Space and Terrestrial Solar Power Applications

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Studies on competitiveness of space and terrestrial solar power plants using global energy model

Global energy model GEM-10R has been used to analyse the possible conditions and scale of using space and terrestrial solar power plants in the long-term perspective (up to the end of the 21st century). Different external conditions, when these alternative energy technologies may be feasible, have been revealed and discussed.

Utilities in the sky?: Comparison of space-based and terrestrial solar power systems

Could huge arrays of space-based solar power systems one day supply utility scale electricity to the electric power grid on earth? How realistic a possibility is this option for alternative energy supply at the moment? Finley R. Shapiro, USA compares space-based and terrestrial solar power systems.

Power potential of a terrestrial solar-radiant Stirling heat engine

SYNOPSIS The output power and thermal efficiency of a finite-time optimized terrestrial solar-radiant Stirling heat engine is studied. The thermodynamic model adopted is a regenerative gas Stirling cycle coupled to a heat source by radiant heat transfer. Both the heat source and heat sink have infinite heat capacity rates. Mathematical expressions for maximum power and the efficiency at maximum power are obtained for the cycle based on higher and lower temperature bounds. The results of this theoretical work provide a base line criteria for use in the performance evaluation and design of such engines as well as for use in performance comparisons with existing terrestrial solar power plants.

Alkali Metal/Halide Thermal Energy Storage Systems Performance Evaluation

Materials compatibility and durability of advanced salt/alkali metal slurry thermal energy storage systems has been demonstrated [1]. Applications are being evaluated for both space and terrestrial solar thermal power conversion [2]. High energy density of these thermal storage systems is achieved by colocation of heat input and extraction within the slurry mixture which is overwhelmingly phase-change salt. This paper addresses performance testing of these systems. Understanding of mechanisms of both micro and macro stratification of the slurry is necessary to fully predict system performance as a function of gravity and system geometry. If it can be shown the gravity stratification effects are secondary to a combination of: (1) liquid metal film adhesion (wetting) to the heat exchange surfaces and solidified salt particles, (2) solubility of alkali metal in the salt-rich phase, and (3) stirring produced by liquid to vapor conversion of the alkali metal, then system geometry limitations are greatly relaxed for space application. Performance testing was accomplished using a sodium heat pipe to transfer heat from the slurry canister to a gas gap calorimeter. Testing was accomplished with the heat pipe installed only in the vapor space above the alkali metal/salt slurry and with an increase heat pipe and minimum vapor space. This testing conclusively demonstrated the effectiveness of the pseudo-heat-pipe type heat transfer mechanism operating in the slurry system under terrestrial conditions.

High-Temperature Solar Photon Engines

High temperature heat engines designed to make maximum use of the thermodynamic potential of concentrated solar radiation are described. Plasmas between 2000 K and 4000 K can be achieved by volumetric absorption of radiation in alkali metal vapors, leading to thermal efficiencies up to 75% for terrestrial solar power plants and up to 50% for space power plants. Two machines capable of expanding hot plasmas using practical technology are discussed. A binary Rankine cycle uses fluid mechanical energy transfer in a device known as the 'Comprex' or 'energy exchanger.' The second machine utilizes magnetohydrodynamics in a Brayton cycle for space applications. Absorption of solar energy and plasma radiation losses are investigated for a solar superheater using potassium vapor.

A terrestrial solar energy power system

Development of an effective solar energy utilization technique is of prime importance in solving the energy crisis mankind is confronted with today. In recent years advancements have been made in high temperature measurements, high efficiency selective radiation materials, high temperature heat pipes, heat storage medium, semiconductor manufacturing techniques, space technology, etc. In this article the authors outline a solar energy utilization system (a terrestrial solar energy power system) and discuss the feasibility of a solar energy power system.

New Sources of Power—Solar Energy

In the very near term, solar energy can provide hot water and space heating, and in the intermediate term, space cooling for both commercial and residential buildings. In the longer term, terrestrial solar power systems based on focused solar energy, wind energy, or ocean thermal gradients are possible regional sources of auxiliary power. Photovoltaic conversion of solar energy to electricity with solar cells could provide supplemental power if the costs of solar cells are reduced. By the year 2000, a satellite solar power station could be a technically and economically viable continuous source of primary electric power whenever needed throughout the world. It will use solar cells to collect the solar radiation, which would then be converted to microwave energy. The microwaves will be beamed to a receiving antenna on earth and be reconverted to electricity. Such solar systems can help meet future energy demands without significant detriment to man’s environment.

Optimization of Solar Terrestrial Power Production Using Heat Engines

Mathematical model and computer programs have been developed for the analysis of the economic performance of a terrestrial solar power system using heat engines. Various combinations of cycle, collector, engine, storage system, and sink have been studied and the influence of design parameters on power costs examined for both the steady and unsteady state cases. Typical minimum power costs under central Australian conditions for units of 12 kw capacity at current levels of materials and labor costs range from 7 to 47 U. S. cents per kwh, according to the specific design of installation.