The solar desalination plant in Abu Dhabi: 13 years of performance and operation history

The Abu Dhabi solar desalination plant started operation in September 1984 and is still operating until now. The plant was designed as a pilot unit for the evaluation of the technical economic feasibility of such plants for supplying fresh water to remote arid coastal areas of the UAE. The aim was to evaluate the long-term system performance and reliability and determine the optimal operating strategy and maintenance schedule. The plant consists of three subsystems: the solar collector field, the heat accumulator and the seawater evaporator. The solar collector field and the heat accumulator has experienced only a small amount of performance degradation, however, the evaporator have suffered from about 25 percent degradation in performance and is currently in need of an acid and demister cleanings to bring its performance to its original level.     

Experimental and numerical performance of a multi-effect condensation–evaporation solar water distillation system

The main objective of the work is to demonstrate experimentally and numerically the performance of a simple solar distillation unit that is based on the multiple condensation–evaporation cycle. The pilot plant was designed, fabricated, tested and simulated at the solar energy laboratory, Mattarria Faculty of Engineering, Cairo, Egypt. The distillation chamber consists of a humidifier (evaporator) and a dehumidifier (condenser) units. The circulation of air in the two units is maintained by natural convection. The cold salt water is preheated inside the distillation unit before exchanging heat with the solar collector loop. This plant has a flat-plate collector field area of 3.1 m², it constitutes a closed loop with its own storage tank. The research is then carried out to evaluate the unit performance of such design and to estimate the fraction factor of the solar system to the load. A numerical simulation was developed for the system being considered. A detailed annual performance of the system is presented. The annual variation of the temperatures and useful heat gain were estimated for the system components. In addition, the optimum collector area by which the system has the maximum life-cycle savings and solar fraction was obtained. The comparison between the numerical and experimental results are accepted. The multiple-effect distillation unit that is considered in the study produces 24 l/day of distilled water. The system performance can be accepted according to the previous edited results.     

不同地区住宅能耗与太阳能吸收式空调系统匹配性分析与模拟研究

为了满足农村住宅清洁用能的需求,多种形式的能源系统逐渐开始应用于广大的农村地区。随着太阳能集热器集热效率的提高,热驱动机组各项性能不断改善,这样有利于太阳能吸收式空调系统在农村地区的应用。为了研究太阳能吸收式空调系统与农村住宅全年能耗的匹配问题,文章首先建立了DeST住宅模型,然后利用TRNSYS软件建立了太阳能吸收式空调系统模型,最后根据模拟结果对国内不同气候区内农村住宅供热季、供冷季的平均热负荷值,以及全年的能耗进行分析。此外,文章还分析了典型日太阳能吸收式空调系统的运行策略与效果。分析结果表明:在无辅助热源的条件下,太阳能集热器的集热温度会大于80℃,满足空调机组的热驱动温度,因此可以作为太阳能吸收式空调系统的的热源;当启动温度为85℃时,空调机组的制冷量可以达到8 kW,性能系数COP为0.733。     

集成太阳能辅助供热的600 MW高背压热电联产机组的运行及优化

为了解决太阳能辅助燃煤发电系统与太阳能辅助抽汽供热系统的余热损失增多问题,提出一种太阳能辅助高背压热电联产系统的优化改造方案。利用EBSILON软件采用数值模拟的方法,对改造前后机组的整体性能和改造后机组在不同发电功率、背压、热网供回水温度工况下的收益变化进行了分析,对比了改造前后机组的(火用)效率与经济性差异。结果表明：改造后的太阳能辅助高背压热电联产系统节煤更多,机组回收了集成太阳能产生的余热后供热能力增强;改造后的机组在低发电功率、较高背压和较低热网供回水温度时节煤更多;在低发电功率、较低背压及较高热网供回水温度时机组的供热能力更强;改造后的太阳能辅助高背压热电联产系统(火用)效率更高、系统的经济效益更佳。     

Thermodynamic investigation of a concentrating solar collector based combined plant for poly-generation

The detailed thermodynamic evaluation for combined system assisted on solar energy for poly-generation are studied in this paper. This poly-generation cycle is operated by the concentrating solar radiation by using the parabolic dish solar collector series. The beneficial exits of this integrated plant are the electricity, fresh-water, hot-water, heating-cooling, and hydrogen while there are different heat energy recovery processes within the plant for development performance. A Rankine cycle with three turbines is employed for electricity production. In addition to that, the desalination aim is performed by utilizing the waste heat of electricity production cycle in a membrane distillation unit for fresh-water generation. Also, a PEM electrolyzer sub-component is utilized for hydrogen generation aim in the case of excess power generation. Finally, the hot-water production cycle is performed via the exiting working fluid from the very high-temperature generator of the cooling cycle. Moreover, based on the thermodynamic assessment outputs, the whole energy and exergy efficiencies of 58.43% and 54.18% are computed for the investigated solar plant, respectively.     

A novel integrated solar desalination system with multi-stage evaporation/heat recovery processes

A novel small-sized integrated solar desalination system with multi-stage evaporation/heat recovery processes is designed and tested in this study. The system consists of four linked collecting units and operates under barotropic and atmospheric pressure. Each of the four units contains a seawater tank and at least one solar collecting/desalination panel mainly comprising a simplified CPC (Compound Parabolic Concentrator) and an all-glass evacuated tube collector. In the last three units, heat exchangers made of copper tubes are inserted concentrically into the all-glass evacuated tubes to recover heat. In each unit, an independent desalination process including solar collecting, heat recovery (no heat recovered in the first unit) and seawater evaporation can be carried out completely. The experimental results show that the freshwater field of the designed system can reach as high as 1.25 kg/(h m²) in the autumn and the system total efficiency is close to 0.9. Both experimental results provide a striking demonstration that the designed solar desalination system has outstanding performance in solar collecting, heat recovery and seawater evaporation.     

Experimental investigation on a combined sensible and latent heat storage system integrated with constant/varying (solar) heat sources

The objective of the present work is to investigate experimentally the thermal behavior of a packed bed of combined sensible and latent heat thermal energy storage (TES) unit. A TES unit is designed, constructed and integrated with constant temperature bath/solar collector to study the performance of the storage unit. The TES unit contains paraffin as phase change material (PCM) filled in spherical capsules, which are packed in an insulated cylindrical storage tank. The water used as heat transfer fluid (HTF) to transfer heat from the constant temperature bath/solar collector to the TES tank also acts as sensible heat storage (SHS) material. Charging experiments are carried out at constant and varying (solar energy) inlet fluid temperatures to examine the effects of inlet fluid temperature and flow rate of HTF on the performance of the storage unit. Discharging experiments are carried out by both continuous and batchwise processes to recover the stored heat. The significance of time wise variation of HTF and PCM temperatures during charging and discharging processes is discussed in detail and the performance parameters such as instantaneous heat stored and cumulative heat stored are also studied. The performance of the present system is compared with that of the conventional SHS system. It is found from the discharging experiments that the combined storage system employing batchwise discharging of hot water from the TES tank is best suited for applications where the requirement is intermittent.     

Parametrical analysis of the design and performance of a solar heat pipe thermoelectric generator unit

This paper describes a solar heat pipe thermoelectric generator (SHP-TEG) unit comprising an evacuated double-skin glass tube, a finned heat pipe and a TEG module. The system takes the advantage of heat pipe to convert the absorbed solar irradiation to a high heat flux to meet the TEG operating requirement. An analytical model of the SHP-TEG unit is presented for the condition of constant solar irradiation, which may lead to different performance characteristics and optimal design parameters compared with the condition of constant temperature difference usually dealt with in other studies. The analytical model presents the complex influence of basic parameters such as solar irradiation, cooling water temperature, thermoelement length and cross-section area and number of thermoelements, etc. on the maximum power output and conversion efficiency of the SHP-TEG. Simulation based on the analytical model has been carried out to study the performance and design optimization of the SHP-TEG.     

Nomographs for the optimum solar pond driven LiBr/ZnBr2/CH3OH absorption-refrigeration system

The paper presents a procedure for the calculation of an absorption-refrigeration plant that uses an LiBr/ZnBr₂/CH₃OH solution and is driven throughout the year by heat received from a solar pond. The calculations for the solar pond are based on a finite-difference solution of the transient heat conduction differential equation during the year, and the operation of the refrigeration unit is simulated by the use of functions describing the thermodynamic behaviour of the working medium. On the basis of the procedure devised, correlations and nomographs are developed that describe the seasonally optimum operation of the proposed composite system. The nomographs may be employed for a first estimation in the design of such systems.     

Numerical simulation of underground seasonal cold energy storage for a 10 MW solar thermal power plant in north-western China using TRNSYS

This paper aims to explore an efficient, cost-effective, and water-saving seasonal cold energy storage technique based on borehole heat exchangers to cool the condenser water in a 10 MW solar thermal power plant. The proposed seasonal cooling mechanism is designed for the areas under typical weather conditions to utilize the low ambient temperature during the winter season and to store cold energy. The main objective of this paper is to utilize the storage unit in the peak summer months to cool the condenser water and to replace the dry cooling system. Using the simulation platform transient system simulation program (TRNSYS), the borehole thermal energy storage (BTES) system model has been developed and the dynamic capacity of the system in the charging and discharging mode of cold energy for one-year operation is studied. The typical meteorological year (TMY) data of Dunhuang, Gansu province, in north-western China, is utilized to determine the lowest ambient temperature and operation time of the system to store cold energy. The proposed seasonal cooling system is capable of enhancing the efficiency of a solar thermal power plant up to 1.54% and 2.74% in comparison with the water-cooled condenser system and air-cooled condenser system respectively. The techno-economic assessment of the proposed technique also supports its integration with the condenser unit in the solar thermal power plant. This technique has also a great potential to save the water in desert areas.     

Central solar heating plants with seasonal duct storage and short-term water storage: design guidelines obtained by dynamic system simulations

A central solar heating plant with seasonal ground storage is analysed by dynamic system simulations. A reference system, involving a collector area, water buffer storage and ground duct storage, is defined for typical Swiss conditions and simulated for several types of heat load. A methodology is established for the optimisation of the main system parameters. The thermal behaviour of such a system is highlighted. The short-term heat requirements are covered by the buffer unit, whereas the seasonal heat requirements are covered by the ground duct storage. As a consequence, a system such as this is intended to supply a large solar fraction (>50%). Optimal ratios between the main system parameters are sought for an annual solar fraction of 70%. An optimal buffer volume of 110 to 130 l per m² of collector area is obtained. The optimal duct storage volume and collector area vary respectively from 4 to 13 m³ per m² of collector area and from 2 to 4 m² per MWh (3.6 GJ) of annual heat demand. They depend mainly on the specific heat losses from the duct storage unit. A large annual heat demand (>3600 GJ or 1000 MWh) and/or low temperatures in the heat distribution are essential for satisfactory system thermal performance. The spacing of the boreholes which form the ground heat exchanger of the duct store is fairly constant and is found to be about 2.5 m for a ground thermal conductivity of 2.5 Wm⁻¹ K⁻¹. Some improvements of the system control are also investigated to assess the influence on the overall thermal performances of the system. They indicate that the system thermal performances are only slightly improved in contrast to the improvement brought by a simple but optimised system control.     

Solar sludge drying — Based on the IST process

Sludges containing water can only be dewatered to a certain extent mechanically. Beyond this level, moisture must be expelled by means of thermal processes. In the municipal sewage treatment plant in Kandern-Hammerstein, IST Anlagenbau GmbH has operated its own development, a solar dryer for sewage sludges, since December 1994. The result reveals that about 700 - 800 kg water/m² ground space and year are evaporated in southern Germany. Recycling of waste heat enabled a heating of the ground plate thus doubling or tripling the drying performance. The unit operates fully automatically with a PLC control system. Although considerably more ground space is required than in comparison to an industrial drying unit, operating costs of the solar drying system are competitive, frequently even considerably lower. In the mean time, a second drying plant has been in operation since August 1997 in Iffezheim near Baden-Baden. Many improvements were made in details of design. In principle, the process can be applied for all bulk materials containing water.     

Maximum power-conversion efficiency for the utilization of solar energy

The overall efficiency of solar thermal power plants is investigated for estimating the upper limit of their practical performances. This study consists of the theoretical optimization of the heat engine and the optimization of the overall system efficiency, which is the product of the efficiency of the solar collector and the efficiency of the heat engine. In order to obtain a more realistic performance of the solar thermal power plant, the solar collector concentration ratio, the diffused solar radiation and the convective and radiative heat losses of the solar collector are taken into account. Instead of the classical Carnot efficiency, the efficiency at maximum power is used as the optimal conversion efficiency of a heat engine. By means of simple calculations, the optimal overall system efficiency and the corresponding operating conditions of the solar collector are obtained. The results of the present work provide an accurate guide to the performance estimation and the design of solar thermal power plants.     

太阳能热发电厂厂用电率计算方法分析

文章主要解决了太阳能热发电设计领域的厂用电计算思路及方法的问题。太阳能热发电已成为我国新能源发电的重要发展方向,太阳能热发电厂用电率的计算目前还没有相关的规程规范。在研究过程中,采用对太阳能热发电厂的运行模式与火力发电厂运行模式进行对比分析的方法,得出火力发电厂厂用电率的计算方法不适用于太阳能热发电厂的研究结果。通过对槽式太阳能热发电厂集热场系统、吸热传热系统、储热系统、常规岛系统分别进行分析,提出了槽式太阳能热发电厂厂用电量的计算方法,得出了太阳能热发电厂应采用长序列代表年辐照值,逐时计算代表年的发电量和厂用电量,以其比值来计算厂用电率的结论;提出了槽式太阳能热发电厂厂用电率的计算思路和方法,可供塔式太阳能热发电厂参考,对我国太阳能热发电厂的设计发展起到推动作用。     

GIS-based assessment of combined CSP electric power and seawater desalination plant for Duqum—Oman

This paper investigates the potential of implementing combined electric power and seawater desalination plant using concentrated solar power technologies for Wilayat Duqum in Oman. Duqum is going through a considerable urban, touristic and industrial expansion and development. GIS solar radiation tools are used to select the most appropriate site for the plant location. There are basically two different options to combine concentrated solar electric power with seawater desalination. The first option is to combine a CSP plant with a thermal desalination unit, exploiting the exhaust heat of the steam cycle to drive a thermal desalination unit. The second option is to exploit only the electricity output of the CSP plant with a reverse osmosis desalination unit. The paper deals with both options and shows where each of the concepts has advantages considering local conditions: the quality of the input water, the demand of freshwater and/or potable water, social and economic aspects, the environment and others.     

Effect of dust deposition on the performance of a solar desalination plant operating in an arid desert area

The performance of a solar desalination plant (whether using thermal or photovoltaic collectors) is influenced by the ability of the glazing system to transmit solar radiation to the collector absorption surface. This ability is influenced by such factors as the intensity of solar radiation, the transmittance of the collector glazing, the tilt angle of the absorbing surface, the operating parameters of the plant, the properties of the materials of construction, etc. This paper discusses the influence of dust deposition on the evacuated tube collector field on the operating performance of the solar desalination plant at Abu Dhabi, UAE. This plant has a collector field area of 1864 m² of absorber surface and an MED (multiple effect distillation) unit for seawater desalination with a capacity of 120 m³/day of distilled water. The reduction in transmittance due to dust deposition on the amount of heat collected has been measured and its influence on the distillate production has been estimated using the computer simulation program SOLDES which has been verified previously as an effective tool for predicting the operating performance of similar plant designs. The frequency of high-pressure water jet cleaning on the performance of the plant was also investigated. It was found that dust deposition and its effect on plant performance depend strongly on the season of the year and the frequency of jet cleaning should be adjusted accordingly.     

太阳能-土壤源热泵联合供暖系统优化研究

针对严寒地区的气候条件,选取哈尔滨地区某居民住宅小区作为研究对象,利用TRNSYS软件对太阳能-土壤源热泵联合供暖系统(SGCHP)进行计算分析。结果表明:太阳能-土壤源热泵联合供暖系统中太阳能集热器对热泵机组的进水温度和COP以及节电量等方面有改善作用;对太阳能-土壤源热泵联合供暖系统中太阳能集热器面积与地埋管管长的最佳配比的优化结果表明,1 m~2太阳能集热器可保证17～27 m长的地埋管取热平衡。并继续模拟了沈阳地区,并以哈尔滨地区为基准,给出严寒地区该参数的推荐值。     

Performance evaluation of a thermodynamic solar power plant: fifteen years of operation history

The thermodynamic solar power plant of the National Institute for Scientific Research in Tunisia has been in operation since 1984. The plant served as a pilot unit for exploring the technical reliability and evaluating the economic feasibility of the process of converting solar thermal energy into electricity. This paper consists of a close evaluation and analysis of the long-term performance of the system and a review of 15 years of successful operation. The aim of this study was to go over the main problems and technical difficulties encountered and pinpoint the major factors affecting the plant operation in order to identify the optimal operating policies toward the enhancement of the plant efficiency. Even though the thermal performance of the plant was relatively low, the impact of such a plant on the energy sector of the country was significant in terms of energy saving and environmental protection. In regions with high solar radiation such as Tunisia with a daily mean insolation of 4.8 kWh m⁻², the use of solar power plants — similar to this one — essentially for heat production prove to be a good alternative especially for remote and rural areas.     

Experimental investigation of a solar energy heating system under the climatic conditions of Edirne

Seasonal storage of solar energy to supply the heat requirement of buildings in Edirne (41°39′54″N) has been examined experimentally. Solar energy has been stored in a cylindrical underground storage unit. Measurement values have been recorded per hour by means of a computerized recorder between July 2005 and May 2006. Monthly average temperature values of the heat storage unit and the surrounding ground have been calculated through the measurement results. The transient heat transfer which takes place between the heat storage unit and the surrounding ground has been calculated by means of the QuickField finite-element analysis program. It has been determined that the most significant deviations between the theoretical and the experimental temperature values turn out to be in question during the heating period. The annual solar fraction of the solar energy heating system has been determined as 53% for space heating and 85% for domestic water heating.     

Economic appraisal of small-scale solar organic Rankine cycle operating under different electric tariffs and geographical conditions

In the present paper, the economic feasibility of small-scale solar organic Rankine cycle power applications which are assisted with auxiliary gas heaters is investigated. The system is analyzed using three different capacities of ORC system with R-245fa (35, 65, and 110 kWe) in combination with solar water heating system (SWHS) using three models. Flat plate, compound parabolic and evacuated tube solar collectors were used to generate heat with overall heat transfer coefficient (F_RU_L) of 4.35, 1.57, and 2.23 W/m². K respectively. System Advisor Model (SAM) is used to simulate the solar water heater system and optimize the tilt angle, collector area, volume of storage tank and capacity of auxiliary heater under the climatic conditions of Abu Dhabi, New Delhi, Larnaca, Madrid and Munich. The simulation results revealed that the evacuated tube and the compound parabolic collectors performed better than the flat plate collectors. The economic analysis showed that Solar ORC Power Plant is economically and technically feasible with all types of the thermal collectors in Famagusta/Larnaca, Munich and Madrid where the electricity tariff is higher than other cities. Levelized cost of energy (LCOE) is calculated using mathematical model and it ranges between 0.07 and 0.2 USD/kWh based on the plant capacity and type of thermal collectors. Moreover, the profit increase as the plant capacity increase where SIR is 1.05, 1.71, and 2.10 for 35, 65, and 110 kW plant capacity SORC with CPC. A sensitivity analysis is also performed to investigate the effect of operating hours, electricity tariff, ORC unit cost and ORC unit type on the feasibility of the system. According to the results, the electricity tariff and operating hours are the most important parameters because they have a large effect and Play important role on the economic feasibility of the system.