Layer-oriented adaptive optics for solar telescopes

First multiconjugate adaptive-optical (MCAO) systems are currently being installed on solar telescopes. The aim of these systems is to increase the corrected field of view with respect to conventional adaptive optics. However, this first generation is based on a star-oriented approach, and it is then difficult to increase the size of the field of view beyond 60-80?arc sec in diameter. We propose to implement the layer-oriented approach in solar MCAO systems by use of wide-field Shack-Hartmann wavefront sensors conjugated to the strongest turbulent layers. The wavefront distortions are averaged over a wide field: the signal from distant turbulence is attenuated and the tomographic reconstruction is thus done optically. The system consists of independent correction loops, which only need to account for local turbulence: the subapertures can be enlarged and the correction frequency reduced. Most importantly, a star-oriented MCAO system becomes more complex with increasing field size, while the layer-oriented approach benefits from larger fields and will therefore be an attractive solution for the future generation of solar MCAO systems.     

Photovoltaic and photoelectrochemical conversion of solar energy

The Sun provides approximately 100,000 terawatts to the Earth which is about 10000 times more than the present rate of the world's present energy consumption. Photovoltaic cells are being increasingly used to tap into this huge resource and will play a key role in future sustainable energy systems. So far, solid-state junction devices, usually made of silicon, crystalline or amorphous, and profiting from the experience and material availability resulting from the semiconductor industry, have dominated photovoltaic solar energy converters. These systems have by now attained a mature state serving a rapidly growing market, expected to rise to 300 GW by 2030. However, the cost of photovoltaic electricity production is still too high to be competitive with nuclear or fossil energy. Thin film photovoltaic cells made of CuInSe or CdTe are being increasingly employed along with amorphous silicon. The recently discovered cells based on mesoscopic inorganic or organic semiconductors commonly referred to as 'bulk' junctions due to their three-dimensional structure are very attractive alternatives which offer the prospect of very low cost fabrication. The prototype of this family of devices is the dye-sensitized solar cell (DSC), which accomplishes the optical absorption and the charge separation processes by the association of a sensitizer as light-absorbing material with a wide band gap semiconductor of mesoporous or nanocrystalline morphology. Research is booming also in the area of third generation photovoltaic cells where multi-junction devices and a recent breakthrough concerning multiple carrier generation in quantum dot absorbers offer promising perspectives.     

Supply of cooling and heating with solar assisted absorption heat pumps: an energetic approach

The primary energy consumption of two kinds of solar assisted absorption systems (solar assisted absorption chiller during summertime and heat pump during wintertime or solar assisted absorption chiller with direct gas combustion for heating during wintertime) is compared with the primary energy consumption of a compression chiller which can work as a heat pump during wintertime. For the absorption systems three technical options were considered: a single effect machine; a double effect machine with the solar energy delivered to the lower temperature desorber and combustion heat of a gas burner delivered to the higher temperature desorber; a double effect machine with both solar energy and combustion heat delivered to the higher temperature desorber. The analysis performed in this article shows that solar assisted absorption chillers, absorption heat pumps and direct solar heating systems even with low and intermediate solar fractions can operate with considerably less primary energy consumption than compression systems. Further, the necessary solar collector area to achieve that goal is compatible with roof area available in buildings. It was also verified that, for the double effect absorption machines, there is no advantage in delivering the solar energy to the higher temperature desorber, thus establishing as preferable the solution in which it is delivered to the lower temperature desorber.     

Solar Energy Materials

Solar energy materials have properties tailored to meet requirements set by the spectral distribution, angle of incidence, and intensity of the electromagnetic radiation prevailing in our natural surroundings. Specifically, the optimization can be performed with regard to solar irradiation, thermal emission, atmospheric absorption, visible light, and photosynthetic efficiency. Materials for thermal and electrical conversion of solar energy in man‐made collectors, as well as for energy‐efficient passive design in architecture, are typical examples. This paper reviews solar energy materials with emphasis on the thermal applications of a variety of types. Electrical applications are given a more cursory exposition, the reason being that a systems perspective—rather that a materials perspective—is most fruitful in this case.     

Solar absorption system for air conditioning

This Paper presents a new continous operating solar desiccant absorption system in which CaCl₂-H₂O is used as the absorbent. The flat-plate solar collector is utilized as the desorber where water from the solution is evaporated to ambient air in passing over the collector above the solution film. The plant is equipped with a latent heat accumulation system which is extremely compact in size and very efficient. The coefficient of performance—solar collector efficiency product, indicating the grade of solar energy utilized, is estimated as being the highest of all presently known systems.     

European research on solar-assisted air conditioning

The utilization of waste heat, on the one hand, and solar heat, on the other, in order to energize sorption chillers is an important issue for increasing the energy efficiency of cooling machines. Especially in the air-conditioning business, a tight correlation often exists between insolation and cooling requirements. Therefore, the interest in solar cooling by sorption systems has prevailed for several decades. Some hundred systems have been installed all over the world and operate satisfactorily. However, no really cost-competitive system for widespread application exists. A step forward can only be expected by innovative design of the collectors, chillers, or both.This paper reports on trends which might lead to such innovations. The sources are mainly papers and discussions at workshops held in 1994 in Dresden and 1995 in Freiburg and Garching, Germany. Although in these workshops mainly European experiences have been discussed, the conclusions are valid world-wide: generally, it can be stated that several new ideas, both in collectors and chillers, have gained ground. Cheaper collectors providing higher temperatures have become available and specially designed chillers for use with low-grade heat as input are being investigated.In this paper we highlight the most important developments reported on in the workshops mentioned above.     

Organic photovoltaic films

Organic electronic materials are of interest for future applications in solar cells. Although results for single layer organic materials have been disappointing, high photocurrent quantum efficiencies can be achieved in composite systems including both electron donating and electron accepting components. Efficiencies of over 2% have now been reported in four different types of organic solar cell. Performance is limited by the low red absorption of organic materials, poor charge transport, and low stability. These problems are being tackled by the synthesis of new materials, the use of new material combinations, and optimisation of molecular design, self assembly and processing conditions to control morphology. Power conversion efficiencies of over 5% are within reach, but the fundamental physics of organic donor–acceptor solar cells remains poorly understood. Within the last 18 months, power conversion efficiencies of over 2% have been achieved in four different types of organic solar cells. All are composite systems including electron donating and electron accepting components. Performance is limited by weak absorption in the red, poor charge transport, and low stability, but improvements are available through optimisation of materials and device structures.     

Energie- und CO2-Bilanzen von Solarkollektoranlagen

Energy systems based on solar collectors or other renewable energy sources are normally regarded as CO₂ zero-emission systems because nearly no fossil fuels are used to operate the systems. But the complete evaluation of an energy system concerning its CO₂ reduction potential must not be restricted to the emissions during the operation of the system. The cumulative energy demand and the cumulative CO₂ emissions during the life cycle have to be considered. In case of a solar collector system, in particular the production-determined emissions and emissions due to the requirement of auxiliary electric power for the collector pump are important. An energy analysis is this kind was performed for solar domestic hot water systems. It is shown that the consideration of the life cycle emissions reduces significantly the CO₂ reduction potential of solar collector systems whereby the design of the system has a major influence.     

Storage of solar energy

A framework is presented for identifying appropriate systems for storage of electrical, mechanical, chemical, and thermal energy in solar energy supply systems. Classification categories include the nature of the supply system’s setting; the type of energy supplied ; the type of solar energy collection system used (including ‘ indirect ’ solar energy, such as wind and hydropower) ; the type of energy stored ; and some other characteristics of the storage system. A global insolation summary is used to exhibit the diversity of requirements for solar energy storage in different settings. Comments are then made on the need and opportunities for 24 hr storage of electrical energy in batteries; backup systems that use stored chemical fuel derived from solar energy; storage of intermediate temperature heat as heat of hydration of compounds such as sulfuric acid; annual storage of low temperature heat in fresh water ponds or aquifers; and annual storage of ice produced in places with cold winters. Arguments are presented for using a systems approach to the selection of solar energy storage methods appropriate for use in specific types of settings.     

Optimal design and integration of solar systems and fossil fuels for sustainable and stable power outlet

Widespread industrial utilization of solar energy is an important goal that requires overcoming several technical challenges. One of the key hurdles is the need to address the temporal fluctuations in incident solar power (e.g., on an hourly basis or seasonally) which lead to variations in the outlet power. This work is aimed at the development of a systematic design procedure providing a stable power outlet while using solar systems. First, the dynamic performance of solar collectors is parametrically modeled. Next, an optimization formulation is developed as the basis for the design procedure which accounts for the integration of solar and fossil energy sources in a power system. The procedure determines the optimal mix of energy forms (solar vs. fossil) to be supplied to the process, the system specifications, and the dynamic operation of the system. The developed procedure includes gathering and generation of relevant solar and climatic data, modeling of the various components of the solar, fossil, and power generation systems, and optimization of several aspects of the hybrid system. A case study is solved to demonstrate the effectiveness and applicability of the devised procedure.     

Global environmental issues and space solar power generation: promoting the SPS 2000 project in Japan

The approach to solving the global warming problem, suggested at the COP3 conference, proposed merely a treatment of symptoms; a fundamental solution of the extensive environmental problems facing the earth cannot be expected as an extension of this approach. What is required is nothing less than treatment of the fundamental causes of the problems. This article considers space solar power generation—a source of clean energy with unlimited capacity. There are problems to be overcome in order to realize this idea, the most significant being cost, which is largely determined by the cost of launching a solar power satellite into orbit around the earth. Efforts to overcome this high cost have already been initiated through private sector attempts to develop single-stage reusable launch systems. An additional approach to solving the global environmental problem is also presented here: the use of macro-engineering diplomacy to promote a pioneering project called SPS 2000 being planned in Japan. This project calls for the world's first space solar power satellite pilot plant. Such a project will catalyze the creation of a new industry that will employ a wide range of advanced technology in space. In addition, the potential for a “Copernican”-type revolution of the world's industrial economy—this one heliocentric—is suggested.     

Sorption heat pumping technologies: Comparisons and challenges

Heat pumping devices which are operating on sorption effects comprise at least two times two categories, namely liquid or solid sorption cycles on the one hand, and open or closed cycles on the other hand. For the benefit of energy saving and the environment as well as for the further development of the technology it is important to be able to compare and evaluate these options in the context of the respective application. Some ideas to this end are shown in this paper.First the meaning of temperatures and humidity for the difference between open and closed systems is discussed, and there are a lot of similarities. Then some differences between solid and liquid sorption which are especially important for the question of minimum operating temperature and part load behavior are being reviewed, and we find that there is something to learn, mutually. Finally the consequences of solar fraction, auxiliary power consumption, and cogeneration efficiency are being highlighted, in order to check the perception of sorption systems to be environmentally benign. These consequences are important for all kinds of sorption cooling systems. It can be expected that there are significant improvements in the efficiency of power plants and compression cooling systems; consequently we find that sorption technology must improve its performance considerably also in order to stay competitive.     

浅谈太阳能在夏热冬冷地区典型既有居住建筑中的应用

在夏热冬冷地区太阳能的利用主要以太阳能热水为主,在国家政策的扶持下,在既有居住建筑安装太阳能热水系统是老房节能改造的一种有效措施。本文主要针对在夏热冬冷地区的既有建筑进行安装太阳能热水系统的实施背景、现状及技术难点进行分析,提出一种适合于既有居住建筑的太阳能热水系统形式,并通过假定案例对节能潜力进行分析确定其可行性及可复制性,最终达到全面推广及实施的目的。     

Performance Maintenance of Dye-Sensitized Solar Cells Using a Latent Heat Storage Material

Recently, there has been considerable interest in various renewable energies. Among them, solar cell production has increased markedly because the photovoltaic is a clean and safe power generation method. The dye-sensitized solar cell (DSSC) has attracted much attention as an alternative to silicon solar cells due to lower manufacturing costs and plentiful resources for DSSC production. However, the performance of DSSCs has been limited by their durability and low photoelectric conversion efficiency. Temperature control of DSSCs via phase-change materials (PCMs) is expected to improve performance. In this study, DSSCs were heated or cooled with a heat exchanger copper block that was in contact with a PCM (heptadecane), while being irradiated by a solar simulator light source. The durability and photoelectric conversion efficiency of the DSSC improved under PCM temperature control.     

A solar-powered solid-absorption refrigeration system

A solar-powered solid-absorption refrigerating system is being developed for use in areas where the complexity of conventional refrigerating systems is impractical, but solar energy is abundant. An initial investigation showed that a solid absorption process offered the best compromise between simplicity of the system and a reasonable coefficient of performance when operated with flat-plate solar collectors.An experimental investigation of the absorption and desorption of ammonia in calcium chloride and strontium chloride was carried out to establish suitable design parameters.To serve as a demonstration plant a small drinking-water cooler with a 4 m² collector area was built. On a clear day in Denmark an overall coefficient of performance of 10% was obtained, corresponding to an ice production of 6 kg m⁻² of collector area. The demonstration plant is presently being treated at the University of Khartoum.     

直接吸收式太阳能集热系统研究综述

对直接吸收式太阳能集热系统及其所用集热介质的研究现状进行了综述。用于直接吸收式太阳能集热系统的集热介质主要有黑色液体、气-固或液-固悬浮体系、熔盐及其三者的相互混合物。在直接吸收式太阳能集热系统中,由于集热介质既是吸热材料也是传热材料,因此,要求集热介质应具有吸收率高、稳定性好、热导率高、与容器相容性好等性能,但是目前传统的集热介质都存在较多的不足,难以推广应用。提出了使用纳米流体作为新一代直接吸收式太阳能集热介质,并对其进行了初步实验,得到了较好的效果。     

The Italian national survey of aircrew exposure: II. On-board measurements and results

The Italian survey of aircrew exposure has been carried out with different advanced dosimetric systems, as described in part I of this paper. The key strategy of the survey was to obtain on-board comparison of measurements for both passive and real-time detectors flown together with passengers. The survey has been carried out in the period of solar minimum (1995-1997), in which the exposure to galactic cosmic rays reaches its maximum value. Even though carrying out the survey in the period of solar minimum was entirely coincidental, this circumstance has been used to good advantage to obtain a comprehensive set of data of the galactic cosmic radiation with little or no disturbance by the solar activity modulation. This comprehensive set of data covers flight routes between -20 degrees and 75 degrees geographic latitude at different civil aviation altitudes. The survey obtained with different advanced dosimetric systems has been supplemented by a large variety of data gathered with passive stacks on different short-range and long-range flights at supersonic and subsonic altitudes. Some of the most important conclusions which can be drawn from the survey are: (i) aircrew of civil aviation receive annual doses within the range of 1 mSv to 6 mSv; (ii) data from different periods of solar minimum agree well, since the discrepancies encountered seem mainly due to the different dosimetric systems used; (iii) repeated measurements on the same route are highly consistent.     

可展开薄膜结构折叠方式和展开过程研究

薄膜材料广泛运用于太空可展开航天器,薄膜的折叠和展开分析是其中的关键技术。从树叶的仿生学出发,提出薄膜结构的几种折叠方式。建立弹簧-质点系统描述薄膜材料,模拟薄膜结构的展开过程。薄膜展开过程中薄膜不可避免地发生自身的接触碰撞,提出了自接触对的判别准则,采用罚函数法有效地解决薄膜自接触问题。分析了三种折叠方式的薄膜的展开过程,并进行比较,叶外折叠方式和Miura折叠法比较适合平面薄膜的折叠。     

Line-focusing concentrating solar collector-based power plants: a review

Concentrated solar power (CSP) plant is an emerging technology among different renewable energy sources. Parabolic trough collector (PTC)-based CSP plant, using synthetic or organic oil as a heat-transfer fluid, is the most advanced technology. About 87 % of the operational capacities of CSP plants worldwide are based on PTC technology. Direct steam-generating linear Fresnel reflector (LFR) systems have been developed as a cost-effective alternative to PTC systems. Line-focusing concentrating solar collectors (PTC and LFR), with single-axis tracking, are simple in design and easy to operate. Prior to the detailed design of a CSP plant, it is necessary to finalize type of the solar field, type of the power-generating cycle, overall plant configuration, sizing of the solar field and the power block, etc. The optimal design of a CSP plant minimizes the levelized cost of energy for a given site. In this paper, a detailed review of important design parameters which affect the design of line-focusing concentrating solar collector-based power plants is presented. This includes parameters for solar collector field design, receiver, heat-transfer fluid, thermal energy storage, power-generating cycle, sizing and configuration of the plant, etc. This review may provide a reference for designing CSP plants. Future research directions are also identified.     

Toward clean environment: evaluation of solar electric power technologies using fuzzy logic

The rapid expansion of the use of solar energy power plants worldwide is a subject that is being followed with interest. Fuzzy logic methodology is used for evaluating the solar thermal power technology, it compresses huge amount of data into smaller sets, and it has the ability to decide between different solar technologies on the basis of their benefits and costs. The most often considered solar technologies were parabolic trough, central receiver, dish sterling engine, compact linear Fresnel reflector (CLFR), solar chimney, photovoltaic (PV), and solar pond. The aim of our research is to provide the needed information to make a judgment or a decision of adopting the most preferred solar technology in terms of installation and development using fuzzy set methodology. The criteria of the evaluation were based on different parameters, i.e., power capacity, efficiency, availability, capacity factor, storage capability, cost, maturity, water usage, land usage, and safety. The key barriers and features for each technology on the basis of benefit-to-cost ratios are addressed. The results showed that CLFR was found to be the best choice in terms of research, development, and implementation, followed by parabolic trough technology, then the central receiver technology, dish sterling engine, solar chimney, PV, and solar pond, according to the order of preference.