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[en] Recent advances in science and technology of materials fabrication, engineering of work functions, and micrometer gap machining between emitter and collector are making thermionic conversion/converter (TEC) of solar energy an emerging technology. As the converter is the lightest of all devices with highest direct power conversion density (per unit area of the converting surface), it has, potential for substituting photovoltaic technology to a large extent and for deployment in space as a power source. This article summarizes the current efforts/technologies in the field, and discusses their inherent merits and demerits towards realizing the goal of achieving high conversion efficiency and simulation of performance evaluation of a solar TEC. We also discuss the use of both metals and nanomaterials, critical roles of work functions of both emitter and collector, collector temperature, absorptivity and emissivity of the surfaces, radiation losses, and use of both metals and nanomaterials in the efficiency of conversion of solar energy. We further deal with the role of correcting thermionic emission current density equation in the simulation of solar TEC performance. We discuss briefly the possible methods of space-charge control in future in a solar TEC. (author)
[en] Highlights: • Steam generation is due to boiling/vaporization in localized solar absorption area. • Hypothesized nanobubble is unlikely to occur under normal solar concentrations. • A photothermal efficiency of 80.3% was achieved for 12.75 ppm GNP dispersion. • A specific absorption rate of ~50 kW/g was achieved for 1.02 ppm GNP dispersion. Steam production is essential for a wide range of applications, and currently there is still strong debate if steam could be generated on top of heated nanoparticles in a solar receiver. We performed steam generation experiments for different concentrations of gold nanoparticles dispersions in a cylindrical receiver under focused natural sunlight of 220 Suns. Combined with mathematical modelling, it is found that the initial stage of steam generation is mainly caused by localized boiling and vaporization in the superheated region due to highly non-uniform temperature and radiation energy distribution, albeit the bulk fluid is still subcooled. Such a phenomenon can be well explained by the classical heat transfer theory, and the hypothesized ‘nanobubble’, i.e., steam produced around the heated nanoparticles, is unlikely to occur under normal solar concentrations. For future solar receiver design, attention should be paid to focus and trap more solar energy at the superheated region while minimizing the temperature rise of the bulk fluid.
[en] Highlights: • Physics of black material for light-to-heat conversion. • The absorbers using various black materials are identified. • The state-of-the-art design of the photothermal sheets. • The devices with their steam releasing property are highlighted. Solar energy-to-heat conversion for steam generation is an essential metrology for power generation, water purification and desalination. Harvesting light energy and converting it to heat as terminal energy by black photothermal sheets is a novel strategy to attain this goal. This technology rely on use of black nanomaterials as light absorber to increase the absorption and conversion efficiency of solar energy. Fundamental understanding of their structure-property has to be fully exploited for further developing efficient solar-to-heat systems. This report summarizes physical understanding and experimental advances in development of black photothermal sheets for solar water evaporation. We examine the popular photothermal systems with remarkable vapor generation performance to identify the state-of-the-art of the device design. Three groups of the photothermal sheet are discussed in terms of different light-harvesting materials, such as carbon-based sheets, plasmonic sheets as well as semiconducting sheets. The physical difference of these novel devices with their steam releasing property are also highlighted.
[en] Highlights: • We examined the attainment of the Conical Intersection (CI) in Hipoxantine (Hx). • Charge transfer in the molecule is very important in the evolution of S0 and S1. • Aromaticity impairment and push pull systems in Hx are crucial in attaining its CI. • QTAIM offers valuable tools to study the photostability of nucleobases. We analyzed the evolution of the electron density across the S0 and S1 states potential energy curves of hypoxanthine (Hx) using the Quantum Theory of Atoms in Molecules (QTAIM). Examination of QTAIM energies and electronic populations indicates that charge transfer processes are important in the stabilization of the S1 state towards the Conical Intersection (CI) which confers to Hx its photostability. Our results point that the rise of energy of the S0 state approaching the CI is accompanied by a loss of aromaticity of hypoxanthine. Overall, the analyses presented herein give important insights on the photostability of nucleobases.
[en] Highlights: • Triplex loop heat pump system for ventilation heat recover is proposed. • Mass flow rate in heat pump system can be improved by triplex loop system. • COP of triplex loop is increase with the decrease of outdoor temperature. • The performance of triplex system is higher than traditional system in most cases. - Abstract: Ventilation heat recovery is an important means of effectively reducing the energy consumption of buildings. To improve the performance of a heat pump heat recovery system under large temperature difference conditions in winter, a triplex loop heat pump system, which contains three independent heat pump cycles, is proposed in place of its single loop counterpart. Operating characteristics and system performance were analyzed while indoor temperature was constant at 20 °C and as outdoor temperature dropped from 15 °C to −20 °C. Results showed that with the decrease of the outdoor temperature, the mass flow rate and temperature effectiveness of the triplex loop heat recovery system decreased whereas the heating capacity and the coefficient of performance (COP) increased. Under the experimental conditions, the COP of the triplex loop system had an advantage over the traditional heat pump system when the outdoor temperature was below 2.5 °C. When the outdoor temperature was −20 °C, the COP of the triplex system could reach 9.33, which was 23.1% higher than that of the traditional system.
[en] The past fifty years have witnessed the advent of a new energy source and the beginning of yet another in the series of energy-use transitions that have marked our history since the start of our technological development. Each of these transitions has been accompanied by adaptive challenges. Each unique set of challenges has been met. Today the world faces the need for another transition. This paper outlines some of the associated challenges that lie ahead of us all, as we adapt to this new and exciting environment. The first step in defining the challenges ahead is to make some form of prediction of the future energy supply and demand during the period. Herein, the future up to 2010 is presumed to include two major events – first, a decline in the availability and a rise in price of petroleum, and second a need to reduce greenhouse gases in our atmosphere. Both of these events are taken to be imminent. Added to these expected events is the assumption that the total of wind, solar, and other such energy sources will be able to contribute, but only in a relatively small way, to the provision of needed energy to our ever-expanding human population. (author)
[en] Highlights: • A novel integrated system of solar energy and air source heat pump was proposed. • The novel system was compared with other two typical existing systems. • I-T diagram was proposed to divide the optimal working condition ranges. • Effect of different factors on the dividing lines in the I-T diagram was analyzed. - Abstract: Integrated systems consisted of solar energy and air source heat pump have been a hot research topic in recent decades due to their high efficiency and low environmental pollution. Recently, much attention has been paid to the performance characteristics of these systems, however, scarce of attention has been paid to indicate which kind of integrated systems have the optimal performance under different working conditions. For the integrated system of solar heating independently, the solar collectors have high heat-collecting temperature and high heat loss to ambient, so it has advantages in high solar radiation. For the integrated system of solar energy used for the low temperature heat source of heat pumps, the solar collectors have low heat-collecting temperature and low heat loss, so it has advantages in low solar radiation. But for the condition of medium solar radiation, both the above existing two types of systems may not be the optimal ones. Therefore, in this study, a novel integrated system was put forward for this condition. The characteristics and optimal working condition range of this novel system were comparatively studied by the simulation method. By comparison with the above existing two types of systems, the results proved that for most conditions of medium solar radiation, the novel system has the optimal performance, and its COP can be about 55% higher than that of the two types of existing systems when the outdoor temperature is −25 °C. An I-T diagram was proposed in this study to quantificationally divide the optimal working condition ranges of the three types of systems. This study can effectively guide the selection of optimal systems under different working conditions.
[en] This WEMO edition reviews an exceptional period with two distinctive phases: - In 2019 worldwide economic slowdown combined with energy transition measures resulted in some improvements regarding climate change objectives. However, the world was not on track to meet the 2015 Paris agreement objectives. - In 2020 our planet suffered from the COVID-19 pandemic and the economic crisis that followed, plunging our world into a long period of uncertainty. This year's World Energy Markets Observatory report explores how the energy sector can balance these competing priorities. Here we present practical ideas for how utilities, policy-makers and private companies can embrace a strategy that builds short-term resiliency while improving long-term sustainability.
[en] The time has come to put an end to the oil nightmare, and to free ourselves from our dependence on the countries that sell it to us. Let's put into new energies the means that we used to devote to the 'deregulation' or privatization of energy. Then they will quickly take over
[fr]Le temps est venu de mettre fin au cauchemar du petrole, et de nous liberer de notre dependance aux pays qui nous le vendent. Mettons dans les energies nouvelles les moyens que nous consacrions jusqu'ici a la 'deregulation' ou la privatisation de l'energie. Alors elles prendront rapidement le relais
[en] This report proposes an inventory of knowledge in geothermal energy (high and low enthalpy) in 55 countries of the world concerned by this resource. For each country, a sheet briefly indicates currently exploited and potential fields, produced and foreseen powers, and some field characteristics (fluid nature, temperature, number of drilled wells), proposes a brief overview of the sector organization (indication of national bodies, and of foreign companies intervening in the country), and states some general remarks related to the local energy policy, and, in some cases, research orientations