Space Power Generation Research Articles

Investigation of mechanical, electrical conductivity, wear and corrosion performances of traditional CuNi2Si and new high performance CuNiCoSi copper based alloys

ABSTRACT CuNi2Si copper alloy has been utilised in electronics, resistance welding electrodes, and electrical connections. The industry is seeking new copper alloys with improved strength and electrical conductivity. Cu-Ni-Co-Si alloys have been designated as the next generation of high-performance copper alloys. In this study, the cast and hot-forged CuNi2Si and CuNiCoSi alloys were solid-solution treated and aged. Under optimum ageing conditions, alloys were tested for hardness, electrical conductivity, microstructure, mechanical properties, wear resistance, and corrosion resistance. Comparing the CuNiCoSi alloy to the Co-free CuNi2Si alloy, the Co element decreased grain size, accelerating Ni2Si and Co2Si precipitates. The CuNiCoSi alloy has 23% higher conductivity, 31% higher tensile strength, and 17% higher resistance under a 5 N load, 44% higher under a 10 N pressure, and 50% higher under a 20 N load in wear tests than the CuNi2Si alloy. Potentiodynamic studies showed that the CuNi2Si alloy removed 40% more metal per unit time than the CuNiCoSi alloy. The CuNiCoSi alloy outperforms the CuNi2Si alloy in hardness, conductivity, mechanical strength, wear resistance, and corrosion resistance. Due to its outstanding performance, the CuNiCoSi alloy will be vital in industrial equipment, aviation, space, nuclear energy, and electrical power generation.

Thermal-hydraulic and load following performance analysis of a heat pipe cooled reactor

Heat pipe cooled reactors have gained attention as a potential solution for nuclear power generation in space and deep sea applications because of their simple design, scalability, safety and reliability. However, under complex operating conditions, a control strategy for variable load operation is necessary. This paper presents a two-dimensional transient characteristics analysis program for a heat pipe cooled reactor and proposes a variable load control strategy using the recuperator bypass (CSURB). The program was verified against previous studies, and steady-state and step-load operating conditions were calculated. For normal operating condition, the predicted temperature distribution with constant heat pipe temperature boundary conditions agrees well with the literature, with a maximum temperature difference of 0.4 K. With the implementation of the control strategy using the recuperator bypass (CSURB) proposed in this paper, it becomes feasible to achieve variable load operation and return the system to a steady state solely through the self-regulation of the reactor, without the need to operate the control drum. The average temperature difference of the fuel does not exceed 1 % at the four power levels of 70 %,80 %, 90 % and 100 % Full power. The output power of the turbine can match the load change process, and the temperature difference between the inlet and outlet of the turbine increases as the power decreases.

Numerical study on a nuclear-powered Stirling system for space power generation

The use of nuclear-powered Stirling systems for planetary and deep space exploration applications has drawn increasing attention in recent decades. As the critical energy conversion unit in the system, the free-piston Stirling engine (FPSE) is characterized by high efficiency, low mass, compact configuration, robustness, and long lifetime, but difficult to accurately model and analyze. A self-developed numerical model of the whole system, coupled with a third-order model of the FPSE, was proposed for the first time, and a nuclear-powered Stirling system comprising eight 1 kW FPSEs was designed. The methodology for designing a system with high efficiency, high specific power, and compact structure was proposed. Furthermore, the internal heat transfer and loss mechanisms were analyzed. The results revealed that the engines’ performance could be improved by increasing the temperature ratio of the hot end to the cold end. However, this leads to a corresponding increase in the size and mass of the heat exchangers. It was shown that the optimum hot-end temperatures for maximizing the system efficiency exist at different cold-end temperatures due to the radiation heat loss of heat pipes. When the hot-end and cold-end temperatures are respectively 1050 K and 450 K, a maximum system efficiency of 25.64% could be obtained. Moreover, the system efficiency and specific power could be increased by optimizing the FPSEs’ parameters and enhancing the heat exchangers’ heat transfer capabilities, and the adverse effect of the heat sink fluctuation could be inhibited accordingly. The distribution of the exergy losses changes greatly with the operating temperatures, and the primary parameter to be optimized also changes accordingly.

Next-gen solar cell study could help resolve instability issues

UK RESEARCHERS are investigating a new type of highly versatile solar cell material that could boost power generation in space and bring about the next generation of solar panels. The University of Warwick team is undertaking a five-year study, which will delve into the atomic-level structure of the new material known as perovskite. Perovskite solar panels can be easily deposited onto most surfaces, including flexible and textured ones. The materials are Solar panels based on perovskite could be easily deposited onto most surfaces, including flexible and textured ones RENEWABLES Next-gen solar cell study could help resolve instability issues lightweight, cheap to produce, and as efficient as today's leading photovoltaic materials, which are mainly silicon. However, they currently face issues with stability and a short lifespan, which decreases further in high humidity, strong sunlight and at elevated temperatures. While the properties of perovskite solar cells change in a range of atmospheric conditions, they remain remarkably stable outside the Earth's atmosphere. This points to the potential for harvesting energy in space. The European Space Agency revealed last year that it would be investigating whether satellites could beam electricity to Earth. Using nuclear magnetic resonance (NMR, an analytical chemistry technique that harnesses high magnetic fields and radio frequencies targeted at atomic nuclei) the team hopes to uncover why perovskite solar panels degrade so quickly at an atomic level.

Research progress on nanoparticles applied in redox flow batteries

AbstractIn recent years, the focus on the utilization of renewable energy has continued to heat up. However, renewable energy has the drawbacks of intermittency and mismatch between power generation and electricity consumption in time and space, thus the energy storage system is indispensable. Redox flow batteries (RFBs), as an electrochemical energy storage system, have attracted widespread attention with the nature of flexible design and long service life. The components of RFB and the efficient combination of components play a key role in battery performance. Due to the size effect and physicochemical properties of nanoparticles, the ionic conductivity, thermal conductivity, and mechanical effects are improved in RFBs with the addition of nanoparticles, thus improving the power performance and charge–discharge cycle life of the battery. In this review paper, we mainly report the application and research progress of nanoparticles applied in RFBs. The applications of nanoparticles in electrode, electrolyte, and proton (ion) exchange membranes in aqueous and nonaqueous RFBs are briefly introduced, with emphasis on adjusting the type, size, surface treatment, loading method, and loading quality of nanoparticles. The transport property and electrochemical reaction rate of active species and charges in RFBs can be improved after the inclusion of nanoparticles, leading to the improvement of the power density, energy efficiency, and stability of the battery. The applications and research progress of nanoparticles in RFBs can be systematically and comprehensively understood via the analyses and discussions in this review. It also provides a new technical idea to promote the commercial development and deployment of high‐performance RFB.

Experimental investigation of a novel vertical loop-heat-pipe PV/T heat and power system under different height differences

For a novel vertical solar loop-heat-pipe photovoltaic/thermal system, the height difference between evaporator and condenser plays an important role in the heat transport capacity, which has significant impact on the solar thermal efficiency and parametrical optimization of this system. Therefore, based on the results derived from the authors’ previous analytical investigation and computer modelling studies, a prototype of this novel system was designed, constructed, and an experimental investigation under different height difference was undertaken to study the impact of height difference on the system performance. It was found that the relationship between the solar thermal efficiency of this vertical system and the height difference is nonlinear. In present study, the optimal height difference is around 1.1 m, which was selected as an optimal value for the following experimental investigations, and below 1.1 m, the PV module surface temperature decreased with the increase of the height difference. Furthermore, the transient solar thermal and electrical performance of this system with the selected optimal height difference were investigated under outdoor real weather condition. These results of this experimentation can help optimize the system construction and thus help to develop the high thermal performance and low-cost solar PV/T system for space heating and power generation.

Large-scale SHS based 3D printing of high-performance n-type BiTeSe: Comprehensive development from materials to modules

Micro thermoelectric devices have a broad application prospect in confined space refrigeration and power generation of small nodes in the Internet of things. The leg performance, manufacturing efficiency and yield are very important for the industrial production of thermoelectric devices. Here, self-propagating high-temperature synthesis (SHS) and selective laser melting (SLM) technique are combined to directly form a dense and highly growth-oriented n-type BiTeSe material in large scale from raw materials of Bi, Te and Se powders. Ignoring the solid solution of a small amount of Se, the composition and structure analysis of the micro-region via transmission electron microscopy shows that Bi first reacts with Te to form BiTe compound in the molten pool of laser, and then Te reacts with the intermediate BiTe to form Bi2Te3 phase. In the next manufacturing process, a thin bulk material with a size of 60 × 30 × 0.5 mm3 can be printed out within 1 h. Because of the excellent mechanical properties, 4000 valid legs with a size of 0.4 mm × 0.4 mm in plane can be obtained successfully. Finally, a micro thermoelectric device is fabricated via using 3D-printed n-type BiTeSe and commercially hot extrusion p-type BiSbTe legs (28 pairs). For solid refrigeration, the maximum cooling temperature difference is about 44 °C and the maximum cooling power Qmax of the device is about 2.1 W when the input current Imax is about 1.1 A. For power generation, the open-circuit voltage Uoc is 324 mV and the maximum output power Pmax is 4.97 mW when ΔT is 40 K.

Infiltration-controlled combustion of magnesium for power generation in space

Chemical heat integrated power systems can potentially provide high energy densities and long lifetimes compared to the best batteries. They are of interest for space missions where the use of solar or nuclear energy is impractical. In a new concept of such a system, a metal combustor is coupled with a chemical oxygen generator, and the metal powder bed inside the combustor burns with the infiltrated oxygen. However, the infiltration-controlled combustion of metal powders is not well understood. In the present work, a magnesium powder poured in a vertical quartz tube was ignited by a laser inside a chamber filled with oxygen at pressures of 44 – 90 kPa. The ignition resulted in the propagation of a thermal wave followed by a second ignition at the other end and propagation of a thermal wave backward. High-speed and infrared video recordings as well as thermocouple measurements were used for diagnostics. The results demonstrate that if a metal with a low Pilling-Bedworth ratio (0.81 for magnesium) is used, coflow combustion is possible. The coflow combustion wave propagates at incomplete conversion, with an axial velocity being as low as 0.1 mm/s and the zone of the highest temperature traveling along a helical path. An increase in the axial velocity of the combustion wave is accompanied by an increase in the flame thickness and a decrease in the extent of conversion.

Finite-time thermodynamics and exergy analysis of a Stirling engine for space power generation

In recent years, the interest of space agencies and private companies in space exploration has increased, mainly in deep space missions. This type of mission poses great challenges due to the high energy level demanded from the power systems, requiring a more efficient and compact energy conversion system. Thus, this work carried out a finite-time thermodynamic model and exergy analysis of a Stirling cycle for nuclear space power generation. The thermodynamic model was coupled to a simple dynamic Stirling engine model and takes into account several aspects such as the thermal losses between the hot and cold side of the Stirling cycle, finite-time regeneration, temperature drop along heat pipes, and variable compression ratio. The system performance and component irreversibilities were evaluated by varying the nuclear core temperature and the cold side temperature of the cycle. Then, the figure of merit mass per power output (kg.kW-1) of the energy conversion system was computed, enabling the model to find temperature conditions for a system that aligns high efficiency and compactness. The results showed that the component with the greatest irreversibility is the reactor core with a value of 496.14 kJ, representing 68.18% of the total irreversibility. The exergy analysis showed that only 5.15% of the total exergy is used for power generation and 24.33% is rejected to space. Moreover, the cold side temperature of 352 K provided the system with the lowest value of mass per power output (87.69 kg.kW-1).

A bare-photovoltaic tether for consumable-less and autonomous space propulsion and power generation

State-of-the-art electrodynamic tethers reach a steady electric current by using a bare segment to capture electrons passively from the ambient plasma (anodic contact) and an active electron emitter or a tether segment coated with a low-work-function material (cathodic contact) to emit electrons back and close the electrical circuit. This work proposes to take advantage of recent developments on thin-film solar cells and insert a photovoltaic (pv) tether segment in between the anodic and the cathodic contacts. Since thin-film solar cells can be folded and manufactured with any desired length and the same cross-section dimensions as the bare segment, i.e. width and thickness around few centimeters and tens of microns, the resulting device is compact and preserves bare tether simplicity. Detailed analysis of the current and voltage profiles throughout the tether shows that the electrical power introduced by the pv-segment into the tether-plasma circuit improves the performance and makes them less dependent on ambient conditions. The pv-segment decreases considerably the tether-to-plasma bias at the cathodic contact, thus opening the possibility to emit substantial current while using consumable-less electron emitters like thermionic and electron field emitters. The pv-segment also favors the current collection by increasing the tether-to-plasma bias at the bare segment. Propulsion and power generation applications and alternative architectures of bare-pv tethers are briefly discussed.

Mitigation of Vacuum and Illumination-Induced Degradation in Perovskite Solar Cells by Structure Engineering

Summary High specific power, high stowed packing efficiency, low processing cost, and high tolerance against environmental threats (high energy and charged particle radiation) make perovskite solar cell (PSC) a promising candidate for power generation in space. However, vacuum, as encountered in space, causes perovskite outgassing, raising concern for its long-term stability. In this work, we find that PSCs (ITO/SnO2/perovskite/Spiro-MeOTAD/Au) degrade ten times faster upon reducing the pressure from 9 × 104 to 5 × 103 Pa during operation, due to acceleration of the perovskite transformation and ion migration. Gas permeability of the layers atop perovskite and mobile ion-induced chemical reactions at charge transporting layers and related interfaces are two critical factors. We develop a PSC structure (ITO/PTAA/perovskite/PCBM/ZnO/AZO/[Ni/Al grid]) that effectively mitigates vacuum and illumination-induced degradation pathways, enabling PSCs to realize a low PCE loss rate of 0.007%/h over 1,037 h at the maximum power point under 100 mW cm−2 illumination at 5 × 103 Pa.

Cold-side temperature optimization of a recuperated closed Brayton cycle for space power generation

Regarding space exploration, an adequate design of an energy conversion system for power generation is essential and plays an important role in the mission feasibility, having low total mass and size as key features that differ space power plants from grounded power stations. The waste heat system of space power plants consists of heat pipes attached to a radiator panel and, as they are responsible for the highest size proportion of the total energy conversion system, special attention must be directed to these components during the design phase. Considering these aspects, this short communication aims the optimization of the cold-side temperature of a recuperated closed Brayton cycle for space power production. For this purpose, an endoreversible thermodynamic modeling is proposed, based on overall thermal conductances of heat exchangers and heat pipes, whereas a set of algebraic equations characterized the compressor and turbine performance. The ratio of the cycle power output per radiator area was considered as the objective function which is maximized. For a fixed heat input of 157 kW and heat source and sink temperatures of 1150 K and 200 K respectively, it was evidenced an optimum operating temperature ranging from 450 to 500 K for the cold heat pipe. Based on this range of operation, heat pipes made of titanium-water with rectangular grooves as the wick structure were chosen as reference for design modeling and assembly of the heat rejection system.

Monolithic Integrated Antenna and Schottky Diode Multiplier for Free Space Millimeter-Wave Power Generation

This letter presents a novel monolithic integrated frequency multiplier circuit for free space power generation in the ${W}$ -band (75–110 GHz). The circuit is based on a submicrometer GaAs Schottky diode monolithically integrated with a slot antenna on a GaAs semi-insulating substrate. The fabricated diode with an air-bridged Schottky contact and a U-shaped ohmic contact showed an ideality factor of about 1.25 and a zero bias cutoff frequency higher than 1.25 THz. Using input signals between 15 and 50 GHz, the free space power generated in the ${W}$ -band corresponding to $\times 2$ , $\times 3$ , $\times 4$ , and $\times 5$ frequency multiplication was measured and showed minimum isotropic conversion losses (with antenna) of 11.5, 16.9, 23.7, and 26.4 dB, respectively.

Controlling the operation of the intelligent generator and energy translator integrated from space and planetary objects as the elements of a power plants in space (in orbit)

The author analyzes problems of using artificial intelligence based of monitoring systems and management, as well as the opportunities of operating performance parameters of networks transporting energy resources within a quasi-integrated electric power super-system of the gigawatt level, the space part of which consists of distributed satellite formations as quasi-integrated segments of orbital power stations. In this case, you must consider the increasing presence of intelligent control devices (e.g., cyber-physical device conversion and switching energy, intelligent management system, open service platform, etc.). The author offers to predict the dynamic characteristics of the integrated quasi-integrated electric power super-system when analyzing the interrelations of metastable states in the processes of obtaining energy from objects of space power generation in the microwave, laser or other mode and converting it into electric power by ground installations.

Closed Brayton Cycles for Power Generation in Space: Modeling, simulation and exergy analysis

The opportunity of producing power in space seems to be attractive considering the exponential growth of the human population and the renewed interest in space missions. Space Solar Dynamic Systems promise to be a better alternative to PVs by eliminating the need for batteries, offering lower drag problems and high efficiencies taking advantage of the lower temperature of space. In this paper the modeling, simulation and exergy analysis of a Closed Brayton Cycle (CBC) for power generation in space driven by a solar parabolic collector is presented. The main objective has been the investigation of a “reduced weight” configuration, to reduce the launch costs, one of the most critical issues for the system feasibility. The investigation of a “reduced weight” configuration has been performed identifying the key process parameters: the compressor inlet temperature and its pressure ratio and the receiver diameter. Starting from the NASA Freedom data, the results have shown a weight reduction of 21% and an exergy efficiency increase of 7.4%. A comparison with a CBC driven by nuclear power has been then performed, showing the thermodynamic conditions for which the solar dynamic systems could get the recommended specific weight of 30 kg/kW.

Electrostatic Discharge Threshold on Coverglass Used to Protect Solar Cells in the Low Earth Orbit

Coverglass has been widely used to cover the solar cells of solar arrays for space power generation. Coverglass with high antireflection is widely used to protect the solar arrays from performance deterioration due to irradiation of space ultraviolet, protons, electrons, atomic oxygen (AO), and so on. Along with these, thermal cycles and/or shock may accelerate the decay synergistically affecting the threshold voltage of electrostatic discharge (ESD) on the coverglass. In order to reveal the effect of aging due to AO interaction on the ESD threshold, several coverglass samples have been exposed to low earth orbit grade AO generated by the CO2 laser on the ground. Later, both pristine and AO-exposed coverglasses have been irradiated by energetic electrons to generate artificial arcing (ESD) under high vacuum system. Statistical analysis and Weibull distribution confirm that the threshold voltage of ESD is lower on the aged coverglass than virgin.

(Invited) Flexible Thermoelectric Nanogenerator Based on MoS2 Nanomaterials and Its Application for Self-Powered Temperature Sensor

In the past decades, the energy and environment issues have become increasingly urgent and attracted a great deal of attention. New energy technologies, aiming to harvest ambient energy in clean and sustainable way, have emerged and developed rapidly to become important alternatives to fossil fuels. Recently, nanogenerator (NG), which utilizes nanomaterials for converting environmental mechanical energy into electricity based on piezoelectric and triboelectric effects, has been demonstrated as an effective and efficient approach with huge practically-applicable potentials since 2006 [1-5]. In addition to mechanical energy, heat energy also exists ubiquitously and usually goes to waste in our living environment. If waste heat could be efficiently harvested, it could not only increase energy efficiency in many areas, but also power portable electronic devices independently and sustainably. In this regard, NG based on pyroelectric effect has been developed for harvesting thermal energy and self-powered sensors [6-7]. However, the energy output of pyroelectric NG is very low and requires further improvement for practical applications. Besides pyroelectric effect, thermoelectrics is another significant option for recovery of waste heat and has been used in the field of space power generation because of its high reliability and simplicity [8]. Thermoelectric effect refers to a phenomenon in which a temperature gradient across a material will produce an electric potential to drive electric current, usually called the Seebeck effect [9]. Based on the thermoelectric effect, thermoelectric devices can generate electricity from the hot exhaust stream of cars, solar energy, wood stoves, and many other situations. Nevertheless, today thermoelectric devices are not yet in common use. The most critical reason is low efficiency, represented by the dimensionless figure of merit (ZT) of thermoelectric materials [8]. To improve ZT, we need materials with high electrical conductivity, high Seebeck coefficient, and low thermal conductivity. Unfortunately, the strong interdependence of these three parameters severely limits maximizing ZT in homogeneous bulk materials [10]. Recently, thermoelectric nanocomposite has been developed to resolve the above issue by combining different nanomaterials with respective excellent electrical and thermal properties to simultaneously improve the ZT [10-12]. In addition, two-dimensional (2D) nanomaterials have attracted a host of attention because of their unique electronic structures and excellent physical properties since 2004 [13-14]. Among the 2D nanomaterials, MoS2 is a promising thermoelectric material due to its low thermal conductivity and theoretically-predicted high Seebeck coefficient and ZT [15-16]. However, for pristine MoS2, it has a large direct bandgap of 1.2-1.9 eV, which renders it insulating and therefore requiring a strong external electrical field to realize higher electrical conductivity [17]. Unlike MoS2, graphene is a gapless semimetal with high electrical conductivity [18-19]. Yet, unfortunately, it also has high thermal conductivity. A nanocomposite based on the above two materials would be favorable for high-performance thermoelectric devices by integrating the advantages of both materials and avoiding the weaknesses of each. In this work, we report a flexible thermoelectric nanogenerator (TENG) based on MoS2/graphene nanocomposite. The nanocomposite TENG shows an enhanced energy output compared with that of pristine MoS2 TENG, possibly resulting from the improved electrical conductivity which is confirmed by I-V characteristics. The as-developed TENG can be further applied as a self-powered sensor for temperature measurement.

Design and Preparation of High-Performance Bulk Thermoelectric Materials with Defect Structures

Thermoelectric is a key technology for energy harvesting and solid-state cooling by direct thermal-to-electric energy conversion (or vice versa); however, the relatively low efficiency has limited thermoelectric systems to niche applications such as space power generation and small-scale or high-density cooling. To expand into larger scale power generation and cooling applications such as ATEG (automotive thermoelectric generators) and HVAC (heating, ventilation, and air conditioning), high-performance bulk thermoelectric materials and their low-cost processing are essential prerequisites. Recently, the performance of commercial thermoelectric materials including Bi2Te3-, PbTe-, skutterudite-, and half-Heusler-based compounds has been significantly improved through non-equilibrium processing technologies for defect engineering. This review summarizes material design approaches for the formation of multi-dimensional and multi-scale defect structures that can be used to manipulate both the electronic and thermal transport properties, and our recent progress in the synthesis of conventional thermoelectric materials with defect structures is described. Key words: Thermoelectric, Solid-state cooling, Energy harvesting, Defect engineering

Thermophotovoltaic energy in space applications: Review and future potential

This article reviews the state of the art and historical development of thermophotovoltaic (TPV) energy conversion along with that of the main competing technologies, i.e. Stirling, Brayton, thermoelectrics, and thermionics, in the field of space power generation. Main advantages of TPV are the high efficiency, the absence of moving parts, and the fact that it directly generates DC power. The main drawbacks are the unproven reliability and the low rejection temperature, which makes necessary the use of relatively large radiators. This limits the usefulness of TPV to small/medium power applications (100We-class) that includes radioisotope (RTPV) and small solar thermal (STPV) generators. In this article, next generation TPV concepts are also revisited in order to explore their potential in future space power applications. Among them, multiband TPV cells are found to be the most promising in the short term because of their higher conversion efficiencies at lower emitter temperatures; thus significantly reducing the amount of rejected heat and the required radiator mass.

Analysis and comparison of solar-heat driven Stirling, Brayton and Rankine cycles for space power generation

This paper presents an analysis of solar-heat driven Brayton, Rankine and Stirling cycles operating in space with different working fluids. Generation of power in space for terrestrial use can represent a great future opportunity: the low-temperature of space (∼3 K), allows the attainment of very high efficiency even with low-temperature heat inputs, and the solar energy input is higher in space than on earth. This paper shows a comparative analysis of advanced Brayton, Rankine and Stirling cycles to improve the understanding of the optimal trade-off between high efficiency and the smallest needed heat rejection area. The effect of the main cycles' operational parameters and plant layouts on efficiency and power to radiator area ratio have been analyzed. The thermal efficiency of regenerative-reheated-intercooled Brayton cycle was found to be the best among the investigated configurations. The power to radiator area ratio was found to increase with the introduction of reheating for both the Rankine and Brayton cycles. Stirling cycles efficiencies are lower than those obtained by the Brayton and Rankine cycles but with values of power to radiator area ratio equal to about half of those obtained by Brayton cycles but much higher than those obtained by the Rankine cycles.