A distributed energy system integrating SOFC-MGT with mid-and-low temperature solar thermochemical hydrogen fuel production

Solar thermochemical hydrogen production with energy level upgraded from solar thermal to chemical energy shows great potential. By integrating mid-and-low temperature solar thermochemistry and solid oxide fuel cells, in this paper, a new distributed energy system combining power, cooling, and heating is proposed and analyzed from thermodynamic, energy and exergy viewpoints. Different from the high temperature solar thermochemistry (above 1073.15 K), the mid-and-low temperature solar thermochemistry utilizes concentrated solar thermal (473.15–573.15 K) to drive methanol decomposition reaction, reducing irreversible heat collection loss. The produced hydrogen-rich fuel is converted into power through solid oxide fuel cells and micro gas turbines successively, realizing the cascaded utilization of fuel and solar energy. Numerical simulation is conducted to investigate the system thermodynamic performances under design and off-design conditions. Promising results reveal that solar-to-hydrogen and net solar-to-electricity efficiencies reach 66.26% and 40.93%, respectively. With the solar thermochemical conversion and hydrogen-rich fuel cascade utilization, the system exergy and overall energy efficiencies reach 59.76% and 80.74%, respectively. This research may provide a pathway for efficient hydrogen-rich fuel production and power generation.     

Innovative configuration of a hybrid nuclear-parabolic trough solar power plant

This paper proposes a combination of a nuclear and a concentrated solar power (CSP) plant. Most of today’s operating nuclear reactor systems are producing saturated steam at relatively low pressure. This, in turn, limits their thermodynamic efficiency. Superheating of nuclear steam with solar thermal energy has the potential to overcome this drawback. An innovative configuration of a hybrid nuclear-CSP plant is assembled and simulated. It brings together a small pressurised water reactor and a parabolic trough solar field. The solar heat is transferred to nuclear steam to raise its temperature. Continuous superheating is provided through molten salts-based thermal energy storage (TES). The results from design point calculations show that solar superheating has the potential to increase nuclear plant electric efficiency significantly. Solar heat to electricity conversion efficiency defined as the ratio of extra generated power to collected solar energy reaches unprecedented rates of 52%. An off-design model was used to simulate 24-h operation for one year by simulating 8760 cases. Due to TES non-stop operation is manageable.     

Solar thermal aided power generation

Fossil fuel based power generation is and will still be the back bone of our world economy, albeit such form of power generation significantly contributes to global CO₂ emissions. Solar energy is a clean, environmental friendly energy source for power generation, however solar photovoltaic electricity generation is not practical for large commercial scales due to its cost and high-tech nature. Solar thermal is another way to use solar energy to generate power. Many attempts to establish solar (solo) thermal power stations have been practiced all over the world. Although there are some advantages in solo solar thermal power systems, the efficiencies and costs of these systems are not so attractive. Alternately by modifying, if possible, the existing coal-fired power stations to generate green sustainable power, a much more efficient means of power generation can be reached. This paper presents the concept of solar aided power generation in conventional coal-fired power stations, i.e., integrating solar (thermal) energy into conventional fossil fuelled power generation cycles (termed as solar aided thermal power). The solar aided power generation (SAPG) concept has technically been derived to use the strong points of the two technologies (traditional regenerative Rankine cycle with relatively higher efficiency and solar heating at relatively low temperature range). The SAPG does not only contribute to increase the efficiencies of the conventional power station and reduce its emission of the greenhouse gases, but also provides a better way to use solar heat to generate the power. This paper presents the advantages of the SAPG at conceptual level.     

加快发展河北省太阳能光热发电的建议和对策

太阳能作为一种可再生的新能源,越来越引起人们的关注。我国每年太阳能资源理论储量折合标准煤达17000亿t,而包括风能、水能、生物质能、地热能在内的其它所有可再生能源折合标准煤不到60亿t,太阳能利用潜力巨大。太阳能发电主要有光伏发电和光热发电。太阳能光热发电比光伏发电具有更多的优势。阐述了太阳能光热发电的国内外发展现状,分析了河北省太阳能的资源潜力,并提出了河北省发展太阳能光热发电的建议和对策.     

Recent Developments in Integrated Solar Combined Cycle Power Plants

Global concern for depleting fossil fuel reserves have been compelling for evolving power generation options using renewable energy sources. The solar energy happens to be a potential source for running the power plants among renewable energy sources. Integrated Solar Combined Cycle(ISCC) power plants have gained popularity among the thermal power plants. Traditional ISCC power plants use Direct Steam Generation(DSG) approach. However, with the DSG method, the ISCC plant’s overall thermal effici...     

Development of thermodynamic cycles for concentrated solar power plants

Solar thermal power is a promising ‘green’ technology that could contribute significantly – in countries where it may be applicable due to available resources – towards meeting the 2020 and 2050 targets for the free energy production of emissions [Viebahn, P., Lechon, Y., and Trieb, F., 2011. The potential role of concentrated solar power (CSP) in Africa and Europe – a dynamic assessment of technology development, cost development and life cycle inventories until 2050. Energy Policy, 39 (8), 4420–4430]. Especially for the regions where solar radiation is significant, the technology of concentrated solar power (CSP) plants seems to have a great potential, once cost-related issues are resolved. The thermodynamic process, on which the component design of the plant is based, plays a significant role in the optimisation of the efficiency of the derived configuration. This paper aims to present a route for the design of thermodynamic cycles for a CSP, starting from the simplest processes and heading towards more complicated ones. For a reference output capacity, the obtained efficiencies are presented, illustrating the technical benefits of shifting to more advanced thermodynamic processes.     

Direct energy conversion: An attractive option for developing countries

Solar energy will play a key role in direct energy conversion. The conversion efficiencies of a variety of silicon and GaAs solar cells are described. A cost comparison of silicon and GaAs hybrid solar systems shows current average costs of 4.4 ¢ and 6.75 ¢ per kWh in the U.S.A. and 11 ¢ per kWh in Nigeria.

A brief account of current developments and future prospects is given for integrated tandem solar cells (ITSC) and for electrochemical solar cells.     

Spectral beam splitting technology for increased conversion efficiency in solar concentrating systems: a review

Solar concentrating systems that employ one or more quantum receivers may realize improved energy utilization and higher electric conversion efficiency by incorporating spectral beam splitting technology. Such techniques were investigated in thermophotovoltaic conversion, introduced in the early 1960s, and in concentrating PV devices using cells of different band-gap materials, proposed as early as 1955. One major application was found in systems combining quantum and thermal receivers. This article presents a review of the various solar hybrid beam splitting systems proposed in the literature and the different spectrum splitting strategies employed.     

On the potential of solar energy conversion into hydrogen and/or other fuels

Solar energy, when used together with water for the production of hydrogen, forms an inexhaustible source of transportable primary energy. Hydrogen is also a potential means of storing solar energy. In this paper the thermodynamic and energetic conditions for the splitting of water are established. The different water decomposition techniques are discussed.Electrolysis. Electrolysis is a proven and convenient way of producing hydrogen. If the very high temperature electrolysis (80–1000°C) development is successful, heat-assisted electrolysis with electric efficiencies of 100% and more looks attractive in connection with thermo-mechanical helio-electricity conversion.Thermal conversion. Highest temperature (≈ 3000°C) direct decomposition (thermolysis) is thermodynamically interesting, but is, for the time being, technologically not feasible. Use of thermochemical cycles is mainly a question of economics and of adaptation to the high temperatures, attainable with solar concentrating devices.Quantum conversion. The thermodynamic potential of light makes quantum conversion highly attractive, requiring much basic research, though.Bioconversion. Biosystems are already operating in nature but with low and lowest efficiencies. With successful R & D to increase efficiencies, bio-energy systems seem to become a convenient way of fuel production.Economics are considered when it seems reasonable to do so, otherwise educated guesses are made as to the economics of the different decomposition techniques and their implications for the possible large-scale hydrogen production by solar energy.Some considerations are made on the influence of large-scale solar power plants on the climate.     

Solar thermal electric power systems in Japan

The major subjects of this paper are to report the outline of the recent basic research and technical development for solar thermal electric power systems in Japan. Solar thermal electric power systems are presently being developed as one of the most important systems in Sunshine Projects which were initiated in 1974 to develop the utilization systems of new energy resources. Conceptional designs of solar thermal power systems were already done on the basis of the results of the supporting researches and two pilot plants of solar thermal electric power systems of a capacity of 1000 kWe are under construction on the basis of the conceptional and detailed designs and would be constructed by 1981. The present conditions of these pilot plants and the major researches which are thought to be most important subjects in the basic researches and technical developments for solar thermal electric power systems are described in this paper.     

Solar assisted air conditioning of buildings – an overview

Goal of this contribution is to draw a picture about some general issues for using solar thermal energy for air conditioning of buildings. The following topics are covered:

• –A basic analysis of the thermodynamic limits for the use of heat cooling in combination with solar thermal energy is drawn; thereby fundamental insights about control needs for solar thermal driven cooling are obtained.
• –A short overview about the state-of-the-art of available technologies, such as closed thermal driven cooling cycles (e.g., absorption, adsorption) and open cooling cycles (e.g., desiccant employing either solid or liquid sorbents) is given and needs and perspectives for future developments are described.
• –The state-of-the-art of application of solar assisted air-conditioning in Europe is given and some example installations are presented.
• –An overview about new developments of open and closed heat driven cooling cycles for application in combination with solar thermal collectors is given and some of these new systems are outlined more in detail.

     

Preliminary design study for a lunar solar power station using local resources

A preliminary design study of the viability of a megawatt-class power plant based on concentrated solar thermal energy by means of high concentration parabolic dishes and appropriate volumetric receivers (due to the fact that this provides high temperatures and modularity to be applied in the Moon’s surface exploitation industry) is considered. This consists of standalone power plants operating under optional thermodynamic cycles including the closed Brayton cycle, Rankine cycle, and combined cycles operating with and without heat storage as source and heat sink energies. Since some tenuous atmospheric components are relatively abundant on the Moon’s surface, such as argon and helium, and hydrogen obtained from electrolyzed water in the event that frozen water is available, taking advantage of the presence of these components as working fluids in thermal cycle-based energy conversion processes appears to be a viable task. The key idea deals with applying the afore-mentioned available working fluids to the appropriate thermodynamic cycles to achieve high efficiency power conversion under acceptable specific power. Furthermore, the possibility of taking advantage of the existence of high solar radiation flux (which allows high temperatures associated with low ambient temperatures), means that the main ingredients necessary to achieve acceptable thermal efficiencies without harmful emissions exist.A study of the thermal efficiency of the existing working fluids, pressure ratios and power ratios is performed. The results show that the proposed power plants are technically viable since most of the ingredients required are present in the Moon’s tenuous atmosphere and on its surface.     

Development of solar thermal systems in China

China has an abundant solar energy resource. Solar thermal conversion systems have been studied for 25 yr, and solar thermal industry has developed rapidly for 10 yr. There are various solar thermal systems, with an area of around 10 million m² in 2002. These systems mainly provide domestic hot water, but some other applications are under extensive study and development as well. The purpose of this paper is to present the developments that have taken place and that are under way.     

Off-design performance analysis of a closed-cycle ocean thermal energy conversion system with solar thermal preheating and superheating

This article reports the off-design performance analysis of a closed-cycle ocean thermal energy conversion (OTEC) system when a solar thermal collector is integrated as an add-on preheater or superheater. Design-point analysis of a simple OTEC system was numerically conducted to generate a gross power of 100 kW, representing a base OTEC system. In order to improve the power output of the OTEC system, two ways of utilizing solar energy are considered in this study: (1) preheating of surface seawater to increase its input temperature to the cycle and (2) direct superheating of the working fluid before it enters a turbine. Obtained results reveal that both preheating and superheating cases increase the net power generation by 20–25% from the design-point. However, the preheating case demands immense heat load on the solar collector due to the huge thermal mass of the seawater, being less efficient thermodynamically. The superheating case increases the thermal efficiency of the system from 1.9% to around 3%, about a 60% improvement, suggesting that this should be a better approach in improving the OTEC system. This research provides thermodynamic insight on the potential advantages and challenges of adding a solar thermal collection component to OTEC power plants.     

Solar energy in India: Strategies, policies, perspectives and future potential

Renewable energy sources and technologies have potential to provide solutions to the longstanding energy problems being faced by the developing countries like India. Solar energy can be an important part of India's plan not only to add new capacity but also to increase energy security, address environmental concerns, and lead the massive market for renewable energy. Solar thermal electricity (STE) also known as concentrating solar power (CSP) are emerging renewable energy technologies and can be developed as future potential option for electricity generation in India. In this paper, efforts have been made to summarize the availability, current status, strategies, perspectives, promotion policies, major achievements and future potential of solar energy options in India.     

Performance assessment of concentrated solar power plants based on carbon and hydrogen fuel cells

In spite of the recent success on the implementation of Concentrating Solar Power (CSP), still this technology needs a substantial enhancement to achieve competitiveness. This paper provides thorough insight after previous analyses on an alternative concept for higher efficiency CSP systems based on the replacement of the power block by an electrochemical conversion system. Concentrating solar energy is herewith used to decompose methane into hydrogen and carbon, which are used in hydrogen and carbon fuel cells for electricity generation. This approach envisages modular, efficient and flexible generation plants. Dispatchability can be achieved by storing the solid carbon. Solar-to-electricity efficiency was calculated assuming thermodynamic equilibrium composition and experimental data available from literature, and compared with those of conventional power generation systems and commercial CSP plants. It is concluded that this new-generation CSP concept is potentially able to produce power more efficiently than the current state-of-the art solar thermal power plants.     

太阳能光热低温利用发展与研究

太阳能具有分散性强、能流密度低、适合得到中低温热源的特性,太阳能低温热利用是人们最早认识和利用的太阳能转换手段,也是将来太阳能低成本、规模化应用的最重要的领域。本论文针对太阳能集热、太阳能采暖、太阳能干燥、太阳能热泵、太阳能空调、太阳能低温热发电等几个当前太阳能低温热利用的主要技术,介绍了各种技术的应用原理和背景,分析了各种已有技术的研究现状和社会需求,讨论了部分新技术的未来发展方向。同时介绍了中国科学技术大学在该领域的一些研究进展。     

A new hybrid ocean thermal energy conversion–Offshore solar pond (OTEC–OSP) design: A cost optimization approach

Solar thermal electricity (STE) generation offers an excellent opportunity to supply electricity with a non-CO₂ emitting technology. However, present costs hamper widespread deployment and therefore research and development efforts are concentrated on accelerated cost reductions and efficiency improvements. Many focus on the latter, but in this paper we rather focus on attaining very low levelised electricity costs (LEC) by designing a system with very low material cost, while maintaining appreciable conversion efficiency and achieving low maintenance cost. All investigated designs were dimensioned at a 50 MW scale production. Calculated LECs show that a new proposed hybrid of ocean thermal energy conversion with an offshore solar pond (OTEC–OSP) may have the lowest LEC of 0.04 €/kWh. Addition of a floating offshore solar pond (OSP) to an OTEC system increases the temperature difference in the Rankine cycle, which leads to an improved efficiency of 12%, while typical OTEC efficiencies are 3%. This higher efficiency leads to much lower investments needed for power blocks, while the OSP is fabricated using very low-cost plastic foils. The new OTEC–OSP design can be located in many sunny coastal areas in the world.