Efficiency of hydrogen production systems using alternative nuclear energy technologies

Nuclear energy can be used as the primary energy source in centralized hydrogen production through high-temperature thermochemical processes, water electrolysis, or high-temperature steam electrolysis. Energy efficiency is important in providing hydrogen economically and in a climate friendly manner. High operating temperatures are needed for more efficient thermochemical and electrochemical hydrogen production using nuclear energy. Therefore, high-temperature reactors, such as the gas-cooled, molten-salt-cooled and liquid-metal-cooled reactor technologies, are the candidates for use in hydrogen production. Several candidate technologies that span the range from well developed to conceptual are compared in our analysis. Among these alternatives, high-temperature steam electrolysis (HTSE) coupled to an advanced gas reactor cooled by supercritical CO₂ (S-CO₂) and equipped with a supercritical CO₂ power conversion cycle has the potential to provide higher energy efficiency at a lower temperature range than the other alternatives.     

A review of renewable energy technologies integrated with desalination systems

Energy is an essential ingredient of socio-economic development and economic growth. Renewable energy provides a variable and environmental friendly option and national energy security at a time when decreasing global reserves of fossil fuels threatens the long-term sustainability of global economy. The integration of renewable resources in desalination and water purification is becoming increasingly attractive. This is justified by the fact that areas of fresh water shortages have plenty of solar energy and these technologies have low operating and maintenance costs. In this paper an attempt has been made to present a review, in brief, work of the highlights that have been achieved during the recent years worldwide and the state-of-the-art for most important efforts in the field of desalination by renewable energies, with emphasis on technologies and economics. The review also includes water sources, demand, availability of potable water and purification methods. The classification of distillation units has been done on the basis of literature survey till today. A comparative study between different renewable energy technologies powered desalination systems as well as economics have been done. The real problem in these technologies is the optimum economic design and evaluation of the combined plants in order to be economically viable for remote or arid regions. Wind energy technology is cheaper than the conventional ones, and used extensively around the world. The slow implementation of renewable energy projects especially in the developing countries are mostly due to the governments subsides of conventional fuels products and electricity. The economic analyses carried out so far have not been able to provide a strong basis for comparing economic viability of each desalination technology. The economic performances expressed in terms of cost of water production have been based on different system capacity, system energy source, system component, and water source. These differences make it difficult, if not impossible, to assess the economic performance of a particular technology and compare it with others. Reverse osmosis is becoming the technology of choice with continued advances being made to reduce the total energy consumption and lower the cost of water produced.     

A review of technology diffusion models with special reference to renewable energy technologies

Diffusion of renewable energy technologies (RETs) are driven by policies and incentives due to their inherent characteristics such as high upfront costs, lack of level playing field but distinct advantages from energy security, environmental and social considerations. Even after three decades of their promotion, only 20–25% of their potential has been realized. The theory of diffusion modeling allows analysis of diffusion processes and study of growth rates of different technologies and underlying diffusion factors. Their applications have focused on commercial and consumer products such as television, automobiles and IT products and their applications to RETs have been limited. Diffusion analysis of RETs have been based on barriers’ to RET adoption and techno–economic, learning and experience curve approaches. It is observed that these diffusion models when applied to commercial products do not deal with the issues of policy influences which are critical to RET diffusion. Since policies drive RET diffusion, the models for analyzing RET diffusion should allow establishing explicit relationships between the diffusion parameters and policies and their impact on diffusion rates. Given the potential of renewable energy technologies for sustainable development, the aim of this paper is to review different diffusion theory based models and their applicability to RET diffusion analysis.     

Proposed reference irradiance spectra for solar energy systems testing

In 1982, the American Society for Testing and Materials (ASTM) adopted consensus standard solar terrestrial spectra (ASTM E891-82, E892-82) to provide standard spectra for photovoltaic (PV) performance applications. These spectra have been also used for other applications such as solar energy systems, fenestration, and materials degradation. These reference spectra were recomputed and the standards revised in 1987. The International Standards Organization (ISO) and International Electrotechnical Commission (IEC) adopted these spectra into spectral standards ISO 9845-1 and IEC 60904-3. These reference spectra are current as of 2002, even though they are based upon spectral solar radiation models and information on atmospheric attenuation from the 1980s. We summarize important issues concerning the definition of atmospheric parameters, spectral range, accuracy and resolution, and documentation of the standards. We suggest substantial improvements to meet the current and future needs of the various technologies using the reference spectra. Modern terrestrial spectral radiation models and better knowledge of atmospheric physics and prevailing radiometric quantities in the natural environment are used to develop suggested revisions to update the reference spectra. These revisions extend and improve the documentation of the hemispherical (‘global’) tilted reference spectrum with minor modifications. They also provide a more realistic clear sky direct normal spectrum for the intended applications. The revised reference spectra would include more detailed and reliable spectral information from the UV (280 nm) to the near infrared (4000 nm). The amplitude of the proposed hemispherical tilted reference spectrum differs very little from the current standard hemispherical tilted spectrum. Conversely, the proposed direct normal reference spectrum is substantially more energetic than the current standard spectrum, and is typical of a cleaner atmosphere where solar applications can be deployed more advantageously.     

Exergy method for the diagnosis of energy systems using measured data

The use of exergetic and thermoeconomic analysis for the diagnosis of efficiency reductions in energy systems has been widely discussed in literature. Several procedures, based on thermoeconomic analysis with the aim of locating and quantifying malfunctions, have been proposed and applied to operating plants.     

利用PSASP进行风电并网仿真分析与关键技术研究

以蔚县风电场一期工程为研究对象,利用电力系统分析综合程序（PSASP）建立风电场接入系统仿真模型,对风电场接入电网关键技术进行研究,从而为大容量新能源接入电网技术提供理论依据。     

Metal hydride hydrogen storage and compression systems for energy storage technologies

Along with a brief overview of literature data on energy storage technologies utilising hydrogen and metal hydrides, this article presents results of the related R&D activities carried out by the authors. The focus is put on proper selection of metal hydride materials on the basis of AB₅- and AB₂-type intermetallic compounds for hydrogen storage and compression applications, based on the analysis of PCT properties of the materials in systems with H₂ gas. The article also presents features of integrated energy storage systems utilising metal hydride hydrogen storage and compression, as well as their metal hydride based components developed at IPCP and HySA Systems.     

Thermal energy storage technologies and systems for concentrating solar power plants

This paper presents a review of thermal energy storage system design methodologies and the factors to be considered at different hierarchical levels for concentrating solar power (CSP) plants. Thermal energy storage forms a key component of a power plant for improvement of its dispatchability. Though there have been many reviews of storage media, there are not many that focus on storage system design along with its integration into the power plant. This paper discusses the thermal energy storage system designs presented in the literature along with thermal and exergy efficiency analyses of various thermal energy storage systems integrated into the power plant. Economic aspects of these systems and the relevant publications in literature are also summarized in this effort.     

A new thermoeconomic methodology for energy systems

Thermoeconomics, or exergoeconomics, can be classified into the three fields: cost allocation, cost optimization, and cost analysis. In this study, a new thermoeconomic methodology for energy systems is proposed in the three fields. The proposed methodology is very simple and clear. That is, the number of the proposed equation is only one in each field, and it is developed with a wonergy newly introduced in this paper. The wonergy is defined as an energy that can equally evaluate the worth of each product. Any energy, including enthalpy or exergy, can be applied to the wonergy and be evaluated by this equation. In order to confirm its validity, the CGAM problem and various cogenerations were analyzed. Seven sorts of energy, including enthalpy and exergy, were applied for cost allocation. Enthalpy, exergy, and profit were applied for cost optimization. Enthalpy and exergy were applied for cost analysis. Exergy is generally recognized as the most reasonable criterion in exergoeconomics. By the proposed methodology, however, exergy is the most reasonable in cost allocation and cost analysis, and all of exergy, enthalpy, and profit are reasonable in cost optimization. Therefore, we conclude that various forms of wonergy should be applied to the analysis of thermoeconomics.     

PEN as substrate for new solar cell technologies

The possible use of polyethylene naphthalate as substrate for low-temperature deposited solar cells has been studied in this paper. The transparency of this polymer makes it a candidate to be used in both substrate and superstrate configurations. ZnO:Al has been deposited at room temperature on top of PEN. The resulting structure PEN/ZnO:Al presented good optical and electrical properties. PEN has been successfully textured (nanometer and micrometer random roughness) using hot-embossing lithography. Reflector structures have been built depositing Ag and ZnO:Al on top of the stamped polymer. The deposition of these layers did not affect the final roughness of the whole. The reflector structure has been morphologically and optically analysed to verify its suitability to be used in solar cells.     

Exploring past energy changes and their implications for the pace of penetration of new energy technologies

Possible growth paths for new electricity generation technologies are investigated on the basis of an empirical analysis of past penetration rates. Finding and understanding high market penetration scenarios is relevant to formulating climate change mitigation strategies. The analysis shows that under favorable growth conditions, photovoltaics and wind could produce 15% and 25%, respectively, of world electricity by 2050. Under the same assumptions nuclear power could increase to 41% of world electricity. But it is unlikely that all three technology paths could be realized up to these values simultaneously and therefore the penetration rates presented here should be considered as indicative only. The results show that under positive conditions, an embryonic technology could move as a preferred option into a mainstream energy source within half a century. The introduction of growth constraints reflecting, e.g., severe economic, technical, or political limitations could reduce the above numbers by a factor of up to 2–3. The results indicate a decline in the relative year-to-year growth of new technologies when they have higher market shares. A comparison of the results with other short-term and long-term technology scenarios shows satisfactory agreement.     

Commercialization of sustainable energy technologies

Commercialization efforts to diffuse sustainable energy technologies (SETs¹) have so far remained as the biggest challenge in the field of renewable energy and energy efficiency. Limited success of diffusion through government driven pathways urges the need for market based approaches. This paper reviews the existing state of commercialization of SETs in the backdrop of the basic theory of technology diffusion. The different SETs in India are positioned in the technology diffusion map to reflect their slow state of commercialization. The dynamics of SET market is analysed to identify the issues, barriers and stakeholders in the process of SET commercialization. By upgrading the ‘potential adopters’ to ‘techno-entrepreneurs’, the study presents the mechanisms for adopting a private sector driven ‘business model’ approach for successful diffusion of SETs. This is expected to integrate the processes of market transformation and entrepreneurship development with innovative regulatory, marketing, financing, incentive and delivery mechanisms leading to SET commercialization.     

Protection of wind energy systems against the indirect effects of lightning

This paper is concerned with the protection of wind energy systems against the indirect effects of lightning. As wind energy is gaining increasing importance throughout the world, lightning damages involving wind energy systems have come to be regarded with more attention. Nevertheless, there are still very few studies in Portugal regarding lightning protection of wind energy systems using models of the Electro-Magnetic Transients Program (EMTP). Hence, a new case study is presented in this paper, based on a wind turbine with an interconnecting transformer, considering that lightning strikes the soil near the tower at a distance such that galvanic coupling occurs through the grounding electrode. Computer simulations obtained by using EMTP-RV are presented and conclusions are duly drawn.     

Transition to renewable energy systems with hydrogen as an energy carrier

Unlike the present energy system based on fossil fuels, an energy system based on renewable energy sources with hydrogen and electricity as energy carriers would be sustainable. However, the renewable energy sources in general have less emergy than the fossil fuels, and their carriers have lower net emergy. Because of that they would not be able to support continuous economic growth, and would eventually result in some kind of a steady-state economy. An early transition to renewable energy sources may prove to be beneficial in the long term, i.e., it may result in a steady state at a higher level than in the case of a transition that starts later. Once the economy starts declining it will not be able to afford transition to a more expensive energy system, and transition would only accelerate the decline. Similarly, if a transition is too fast it may weaken and drain economy too much and may result in a lower steady state. If a transition is too slow, global economy may be weakened by the problems related to utilization of fossil fuels (such as global warming and its consequences) before transition is completed and the result again would be a lower steady state. Therefore, there must be an optimal transition rate; however, its determination would require very complex models and constant monitoring and adjustment of parameters.     

Green vertical systems for buildings as passive systems for energy savings

This paper presents a classification of green vertical systems for buildings. The aim of this classification is to facilitate the identification and differentiation between systems. This classification is also essential to compare future research results relating to their operation. In addition, the mechanisms by which green facades can be used as passive energy savings systems are reviewed: shadow produced by the vegetation, insulation provided by vegetation and substrate, evaporative cooling by evapotranspiration, and the barrier effect to the wind. Finally, the paper describes the first results about the behaviour of a double-skin green facade or green curtain in Dry Mediterranean Continental conditions. It is verified that a microclimate between the wall of the building and the green curtain is created, and it is characterized by slightly lower temperatures and higher relative humidity. This means that the green screen acts as a wind barrier and confirms the evapotranspiration effect of the plants.     

Techno-economic analysis of the integration of hydrogen energy technologies in renewable energy-based stand-alone power systems

A large number of stand-alone power systems that are based on fossil fuel or renewable energy (RE) based, are installed all over Europe. Such systems, often comprising photovoltaics (PV) and/or diesel generators provide power to communities or technical installations, which do not have access to the local or national electricity grid. The replacement of conventional technologies such as diesel generators and/or batteries with hydrogen technologies, including fuel cells in an existing PV-diesel stand-alone power system providing electricity to a remote community was simulated and optimised, using the hybrid optimisation model for electric renewables (HOMER) simulation tool. A techno-economic analysis of the existing hybrid stand-alone power system and the optimised hydrogen-based system was also conducted. The results of the analyses showed that the replacement of fossil fuel based gensets with hydrogen technologies is technically feasible, but still not economically viable, unless significant reductions in the cost of hydrogen technologies are made in the future.     

The layer perovskites as thermal energy storage systems

A series of compounds of the general formula (n-C_nH_2n+1NH₃)₂MCl₄ (where M is a divalent metal atom and 8 n 18) undergoing high enthalpy reversible solid-solid phase transitions is considered. Although their transition enthalpy values are lower than those of the corresponding normal paraffins, the advantage of remaining solid after the phase change, together with other properties, makes these compounds of potential interest in the field of thermal energy storage systems.     

A review of wind energy technologies

Energy is an essential ingredient of socio-economic development and economic growth. Renewable energy sources like wind energy is indigenous and can help in reducing the dependency on fossil fuels. Wind is the indirect form of solar energy and is always being replenished by the sun. Wind is caused by differential heating of the earth's surface by the sun. It has been estimated that roughly 10 million MW of energy are continuously available in the earth's wind. Wind energy provides a variable and environmental friendly option and national energy security at a time when decreasing global reserves of fossil fuels threatens the long-term sustainability of global economy. This paper reviews the wind resources assessment models, site selection models and aerodynamic models including wake effect. The different existing performance and reliability evaluation models, various problems related to wind turbine components (blade, gearbox, generator and transformer) and grid for wind energy system have been discussed. This paper also reviews different techniques and loads for design, control systems and economics of wind energy conversion system.