Commercial Solar Power Research Articles

Influence of the displacement of solar receiver tubes on the performance of a parabolic-trough collector

The aim of this paper is to study the influence of thermal contraction and expansion phenomenon on the behaviour of the absorber tube and its alignment along the optical focal line of a state-of-the-art parabolic-trough collector for commercial solar power plants. The study performed reveals the influence that different ranges of operating temperatures of the thermal oil used in the collectors installed in a typical commercial solar field, and other parameters such the seasonal variations of sun elevation, PTC orientation, slope error, might have in the amount and distribution of the solar energy intercepted by the receiver tube. The study was carried out by means of a ray tracing method. A decrease of the intercepted solar radiation from 2.8% to up to 38% in the range of typical operating temperatures of the solar field was revealed, the decrease even exceeded the 75% when the circulating thermal oil was assumed at lower temperatures (∼100 °C).

Commercial Scale Solar Power Generation (5MW to 50 MW) and its Connection to Distribution Power Network in the United Kingdom

Over the years, the contribution of solar photovoltaic systems to the power generation is expected to grow through household small scale, and commercial scale solar installation. Researcher pronouncing that delivering such a determination require greater motivation and innovation and much more dynamic power grid network to manage solar generation connection. This research work identifies and recommends the possibilities of applying proven technical know how to get the maximum from the existing power network economically. The simulated case study examples of various capacity connection requests was carried out to provide key insights on the problems faced by the PV farm connections in their line of business. This research is also an effort to give many answers to solar PV developers and enthusiasts who are not very technical and confused about different money saving connection options and the electrical constraints of the power grid. This study data can be used to provide recommendations to further enhance the growth of commercial scale solar power generation in the UK.

CHARACTERISTICS OF MOLTEN SALTS AND RECOMMENDATIONS FOR USE IN SOLAR POWER STATIONS

Molten salts (MS) in the 580°C range could be used to store excess energy from solar power stations and possibly from nuclear or coal. The energy can be stored up to a week in large containers at elevated temperature to generate eight hours of electricity to be used at night or during peak demand hours. This helps to reduce the fluctuation experienced at thermal solar power stations due to weather conditions. Our research supported by Office of Naval Research (ONR), presents a survey of salts to be used in molten salt technology. The physical characteristics of these salts such as density, melting temperature, viscosity, electric conductivity, surface tension, thermal capacity and cost are discussed. Cost is extremely important given the large volumes of salt required for energy storage at a commercial power station. Formulas are presented showing the amount of salt needed per required megawatts of stored energy depending on the type of salt. The estimated cost and the size of tanks required and the operating temperatures are presented. Recommendations are made regarding the most efficient type of molten salt to use. Commercial thermal solar power stations have been constructed in the US and overseas mainly in Spain for which molten salt is being considered. A field of flat mirrors together with collection towers are used in some designs and parabolic troughs used in others.

High Efficiency Photovoltaic Source Simulator with Fast Response Time for Solar Power Conditioning Systems Evaluation

Photovoltaic (PV) source simulators serve as a convenient tool for the dynamic evaluation of solar power conditioning systems and maximum power point tracking algorithms. High efficiency and fast transient response time are essential features of any PV source simulator. This paper proposes a new type of PV source simulator that incorporates the advantages of both analog and digital-based simulators. The proposed system includes a three-phase ac-dc dual boost rectifier cascaded with a three-phase dc-dc interleaved buck converter. The selected power stage topology is highly reliable and efficient. Moreover, the multiphase converter helps improve system transient response though producing low output ripple which makes it adequate for PV source simulators. The simulator circuitry emulates precisely the static and the dynamic characteristics of actual PV generators under different load and environmental conditions. Additionally, the system allows the creation of the partial shading and bypass diodes effect on PV characteristics. The paper investigates the dynamic performance of a commercial solar power inverter using the proposed PV source simulator in steady-state and transient conditions. Closed-loop output impedance of the proposed PV source simulator has been measured and verified at different operating regions. The impedance profile--magnitude and phase--matches the output impedance of actual PV generators. Mathematical modeling and experimental validation of the proposed system is thoroughly presented based on a 2.0 kW hardware prototype. The proposed simulator efficiency, including the active-front-end rectifier and the converter stages, peaks at 96.7%.

Going further with Fresnel Receiver: New Design Window for Direct Steam Generation

Nowadays, parabolic trough collectors constitute the first concentrating solar thermal technology regarding global installed power. Central receivers and Fresnel receivers appear with smaller value and commercial solar dishes power are practically negligible. Several features have driven parabolic troughs to this first position, but some disadvantages are appearing, i.e. the cost reduction is not as quick as expected, the flexible or ball joints constitute leak problems with high pressure and temperature, and simplification of the mechanical structures is quite difficult. At this point, Fresnel receivers appear as a main competitor with troughs, offering lower cost but also lower efficiency; if the reduction in cost is higher than in efficiency, or if Fresnel efficiency is improved, there are potential facts which can make this simpler technology more competitive than trough collectors.In order to improve the Fresnel capabilities, it could be useful to analyze its optical properties. One important feature of Fresnel solar fields is that receiver and concentrator are mechanically separated, providing the system of a new freedom degree in comparison with trough collectors. This degree of freedom can be used in multi-tube receivers, using the high intensity thermal flux impinging in the receiver to illuminate the tubes where the fluid has higher film coefficient (i.e. where the phase change occurs) to obtain a high thermal efficiency, and using the lower thermal flux for preheating and reheating.The idea presented in this paper is to use a multi-tube Fresnel receiver with an adequate optical system that permits tailoring the thermal flux mapping in the receiver in coherence with the convection process of the thermal fluid. In order to obtain this objective, the mass flow will undergo preheating through the peripheral tubes (where the radiation flux will be lower due to the tracking, mirrors shape and sun shape errors) and will be driven afterwards to the high intensity thermal flux, where boiling (that implies high film coefficient values) takes place. A four tube receiver configuration, according to these ideas, will have two main possibilities. The first one a one-way mass flow through the peripheral tubes (inlets to the receiver) and a second pass inside the internal tubes (outlets). The second possibility assumes the mass-flow inlet receiver through one peripheral tube and the exit at the other one, the mass flow passing consecutively through the other two tubes.

Solar radiation attenuation in solar tower plants

Abstract With the advent of the first commercial solar power tower plants with a rated power in the 10–20 MW range, scale-up to larger 20–50 MW commercial plants is being considered ( Lata et al., 2010 , Herring, 2009 ) in the vast arid regions of the sunbelt. In the case of single-tower plants, the heliostat field size grows considerably and the heliostat–receiver slant range distances are often over 1 km. Solar radiation attenuation over these distances cannot be neglected and must be taken into consideration during plant design. The measurement of the atmospheric attenuation is not an easy task and the use of spectral atmospheric transmission models is necessary. We used the MODTRAN (MODerate resolution atmospheric TRANsmission) code to study the solar radiation attenuation at different slant range distances in different scenarios: rural atmosphere on a clear day (visibility 23 km) and rural atmosphere on a hazy day (visibility 5 km).

Special Climate around a Commercial Solar Chimney Power Plant

A simple thermal model is developed for solar chimney thermal power system and validated by the comparison between the simulated results and those simulated by Schlaich et al. Based on a proposed 200 MW power plant in a desert in western China a special climate, which is formed around the giant solar chimney power plant by the volume of warm air flowing from the chimney outlet to a high altitude, is simulated and analyzed. An atmospheric circulation and rainfall are formed. It is found that the solar chimney power plant increases the chance of rainfall, especially for low-humidity air in the desert region, supporting the agriculture in the local area and promoting a part of the desert region to be reformed to fertile soil. Further, the effects of many factors on the rainfall area around a commercial solar chimney thermal power plant are also analyzed. It is concluded that by keeping other conditions equal, solar radiation of more than 706 W∕ m2 , a collector area of more than 10.45 km2 , a chimney height ...

High Flux Central Receivers of Molten Salts for the New Generation of Commercial Stand-Alone Solar Power Plants

Molten salt technology represents nowadays the most cost-effective technology for electricity generation for stand-alone solar power plants. Although this technology can be applied to both concentrating technologies, parabolic through and central receiver systems (CRSs), CRS technology can take advantages from its higher concentration, allowing to work at higher temperatures and therefore with a reduction in the size and cost of the storage system. The receiver system is the “door” for which the energy passes from the field collector to the thermal-electric cycle; it represents, therefore, the core of the CRS and its performance directly affects plant production. Starting from the published lessons from SOLAR TWO receiver technology, the validation of an improved receiver for molten salt technology was assumed as part of the SOLAR TRES solar thermal power commercial plant development. Main challenges for the new receiver were to increase its allowable peak flux up to 1MW∕m2 in order to maximize the thermal efficiency of the CRS solar power plant, and to improve its safe life without limiting the incident fluxes that the field of heliostats is able to deliver with an optimized pointing strategy. Several advanced features in geometric and thermodynamic aspects and in its material selection have been implemented on the receiver. With the results of a sensitivity analysis carried out with an own code developed by SENER (SENREC), a prototype receiver panel was designed, fabricated, and installed in a proper test bed at the PSA. Test validation on this panel was carried out in 2007. The initial test results show a very good behavior of the prototype receiver, which allows to anticipate that the objectives of its design can be fulfilled. SENER and CIEMAT have joined forces to face up the challenge of sizing and designing a new molten salt receiver of high thermal efficiency, able to operate at high fluxes without compromising its durability (at least 25years). Main challenges for the new receiver design were to optimize the receiver dimensions and receiver tube sizes and material selection to surpass the operating conditions in the new plants with respect to SOLAR TWO.

Survey of Thermal Energy Storage for Parabolic Trough Power Plants

A literature review was carried out to critically evaluate the state of the art of thermal energy storage applied to parabolic trough power plants. This survey briefly describes the work done before 1990 followed by a more detailed discussion of later efforts. The most advanced system is a 2-tank-storage system where the heat transfer fluid (HTF) also serves as storage medium. This concept was successfully demonstrated in a commercial trough plant (13.8MWe SEGS I plant; 120MWht storage capacity) and a demonstration tower plant (10MWe Solar Two; 105MWht storage capacity). However, the HTF used in state-of-the-art parabolic trough power plants 30-80MWe is expensive, dramatically increasing the cost of larger HTF storage systems. Other promising storage concepts are under development, such as concrete storage, phase change material storage, and chemical storage. These concepts promise a considerable cost reduction compared to the direct 2-tank system, but some additional R&D is required before those systems can be used in commercial solar power plants. An interesting and likely cost-effective near-term option for thermal energy storage for parabolic trough power plants is the use of an indirect 2-tank-storage, where another (less expensive) liquid medium such as molten salt is utilized rather than the HTF itself.

Wireless power transmission: the key to solar power satellites

Maturing of the enabling technologies has provided much of the infrastructure to support the development of a commercial Solar Power Satellite program. Solar Space Industries was formed to accomplish this goal. The basis of their development plan is to build a Ground Test Installation that will duplicate, in small scale on the Earth, all aspects of the power generating and power transmission systems except for the space environment and the range and size of the energy beam. Space operations issues will be separated from the power generation fixation and verified by testing. Doing the developmental testing on the ground instead of in space will result in a low cost program that can be accomplished in a very short time. The concept is to build a Ground Test Installation that couples an existing 100 kW terrestrial solar cell array to a phased-array wireless power transmitter based on a subarray. Power will be transmitted over a 1- 1/4 mile range to a receiving antenna and then fed into a commercial utility power grid. The objective is to demonstrate the complete function of the Solar Power Satellites, with the primary issue being the validation of practical wireless power transmission. The key features to demonstrate are: beam control, stability, steering, efficiency, reliability, cost, and safety.

Operation of Large-Scale Pumps and Valves in Molten Salt

The molten salt pump and valve (P&V) test loops at Sandia National Laboratories (SNL) National Solar Thermal Test Facility (NSTTF) operated between Jan. 1988 and Oct. 1990. The purpose of the P&V test was to demonstrate the performance, reliability, and service life of full-scale hot and cold salt pumps and valves for use in commercial central receiver solar power plants. The P&V test hardware consists of two pumped loops; the “Hot Loop” to simulate the hot (565°C) side of the receiver and the “Cold Loop” to simulate the receiver’s cold (285°C) side. Each loop contains a pump and five valves sized to be representative of a conceptual 60-MWe commercial solar power plant design. The hot loop accumulated over 6700 hours of operation and the cold loop over 2500 hours of operation. This project has demonstrated that standard commercial scale pump and valve designs will work in molten salt. The test also exposed some pitfalls that must be avoided in specifying such equipment. Although certainly not all of the pitfalls were discovered, careful design and specification should result in reliable or at least workable equipment.

Solar Energy Utilization - The Revitalization of the World†

Summary Solar energy research and development is 12 years old. It was the challenge of the oil crises of the early and mid-seventies, not so much the will of men which gave rise to the first solar energy programs. The physical and technical knowledge of the properties of solar energy and the design and behavior of related equipment have substantially improved since; quite a number of utilization experiments have left the laboratory scale: Thermal conversion is economically viable under certain circumstances; so are wind converters; photovoltaic panels are marketed with a yearly capacity of 20 – 30 MWp; hydro-power and biomass energy are the back-bone of energy supply in developing countries. Engineers in the US and Europe are preparing for the first commercial solar tower power plants in the 100 MW range; European and Arabian engineers have agreed upon first solar-hydrogen demonstration plants both in Europe and in Arabia. What turned out, however, to be almost insurmountable barriers for solar energy utilization so far, were not so much technical as non-technical, political-economic and social barriers: As long as the supply-mindedness of men continues to be dominant, decreasing energy intensities cannot show their significance; as long as governments cling to energy conservatisms and leave the addition of new energies practically to the market, it is particularly difficult for solar energy to compete; for as long as the world economy sticks to the obsolete GNP as an indicator of economic welfare, so long will (positive) autonomous economic growth and the repair of ecological damage in the political economic accounting system be treated identically. Defensive or compensatory costs for the prevention or removal of environmental damage are not distinguished from intentional autonomous costs. These potentially perilous environmental damages and dangers are, however, just the reason which may enforce a withdrawal from the traditional fossil or nuclear energies and turn the world energy supply towards the ecologically benign solar energy utilization: Solar energy utilization has what it takes to contribute to the “revitalization of the biosphere of the world”. Solar energy research and development go on. What lies ahead is the worldwide dialog across professional borders; it is insufficient to be properly understood only by “solar people”. What lies further ahead are the design, erection and operation under long-term field test conditions of first commercial solar thermal plants; what is foreseeable is the first production unit of photovoltaic cells and panels in a semi-commercial capacity size of ≤ 100 MWp/a; what is under construction are the first photovoltaic hydrogen plants in the 100 – 500 kW range, one in Saudi-Arabia, one in Europe; what is in a study phase is a first transatlantic hydropower-hydrogen energy “bridge” between Canada and Europe. In the early years of the European Community two energy-related treaties were signed: The MONTANUNION-Treaty of 1952 dealing with coal and steel, and the EURATOM-Treaty of 1958 comprising the agreements of the contracting parties on research and development for the peaceful use of nuclear energy. An “EUROSOLAR”-Treaty does not exist so far. EUROSOLAR, with the objective to prepare another element of the Community's energy supply in the 21st century, would unite the low insolation but capital and technology rich countries of central and northern Europe with high insolation Mediterranean countries and would introduce a further element of commitment into the Community of the Twelve: A step into the right direction. A formalized forum for discussion, exchange of views, interfacultative talk is needed: The establishment of the German Solar Forum (Deutsches Solarforum) is suggested which would bring together scientists, engineers, economists and politicians. Solar energy utilization is 12 years old. Roughly one fourth of its development history lies behind, three fourths of the way remain ahead, until solar energy will have become an essential part of man's energy supply. In case of doubt continuity stands first and foremost!