Water from the sun : Case study: The Abu Dhabi solar desalination plant

The Abu Dhabi solar desalination plant is situated at the Umm Al Nar Power and Desalination Station about 20 miles east of Abu Dhabi city. The design, procurement and fabrication of this plant started in February 1983 and it was commissioned in September 1984. The plant was designed as a demonstration unit aimed at evaluating the technical and economic feasibility of using this type of technology to provide remote coastal communities in the UAE with fresh water. Ali M. El-Nashar, Manager, Abu Dhabi Water & Electricity Authority provides an overview of the plant performance and presents an economic assessment of the cost of water from such a plant highlighting how solar energy has been helping to provide water to the region for over 15 years.     

Measurement of solar energy radiation in Abu Dhabi,UAE

This paper presents data on measurement of actual solar radiation in Abu Dhabi (24.43°N, 54.45°E). Global solar radiation and surface temperatures were measured and analyzed for one complete year. High resolution, real-time solar radiation and other meteorological data were collected and processed. Daily and monthly average solar radiation values were calculated from the one-minute average recorded values. The highest daily and monthly mean solar radiation values were 369 and 290 W/m², respectively. The highest one-minute average daily solar radiation was 1041 W/m². Yearly average daily energy input was 18.48 MJ/m²/day. Besides the global solar radiation, the daily and monthly average clearness indexes along with temperature variations are discussed. When possible, global solar energy radiation and some meteorological data are compared with corresponding data in other Arab state capitals. The data collected indicate that Abu Dhabi has a strong potential for solar energy capture.     

Contribution to the study of solar radiation in Abu Dhabi

Measurements of global solar radiation for 10 yr in Abu Dhabi are used to examine the suitability of a method of prediction of global solar radiation. It shows a good degree of accuracy. A correlation between the clearness index, H/H₀, and the fraction of maximum possible number of sunshine hours is obtained and found to be H/H₀ = 0.307 + 0.312n/N. The diffuse solar radiation is predicted by two methods which show almost similar results. Correlation between the diffuse solar radiation as a fraction of the global radiation, H_d/H, and the fraction possible number of sunshine hours, n/N, is established using both methods, for comparison sake, since measurements of diffuse solar radiation are not available. The comparison shows a good agreement between the two correlations. The relation between the diffuse solar radiation as a fraction of the global radiation H_d/H, and the clearness index, H/H₀, is established and compared with those obtained elsewhere in order to justify their use, since direct measurements are not available. The relation shows a latitude dependency.     

Global solar radiation: Multiple on-site assessments in Abu Dhabi,UAE

Renewable energy technology and in particular solar energy is being considered worldwide due to the fluctuations in oil prices, global warming and the growing demand for energy supply. This paper investigates the climate conditions available in the United Arab Emirates (UAE) in particular Abu Dhabi to implement Photovoltaic (PV) technology. Measured solar radiation was analyzed for five different geographical locations to ensure the suitability of this region. Hourly, daily and monthly global horizontal irradiation (GHI) were collected and processed. Statistical methods were used to evaluate the computed GHI and showed high values especially during the summer period. Moreover, clearness index was calculated to investigate the frequency of cloudy sky days and results have shown a high percentage of clear days during the year. This paper highlights a promising future for Abu Dhabi in the solar energy sector and in particular Photovoltaic (PV) technology.     

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.     

The costs and benefits of large-scale solar photovoltaic power production in Abu Dhabi,United Arab Emirates

The potential for a 10 MW photovoltaic power plant in Abu Dhabi is examined in this paper using RETScreen modeling software to predict energy production, financial feasibility and GHG emissions reductions. Initial results show high energy production potential, generating 24 GWh and saving over 10,000 tons of GHG emissions annually, but poor financial prospects yielding a net present value (NPV) of ?$51 million. Benefits of reducing GHG and air pollution emissions by replacing natural gas with PV generation are calculated to have a net present value of $47 million, with a large range of possible values. Results show that the high initial costs and low expected price for electricity generated are driving reasons why photovoltaic systems are not being implemented in Abu Dhabi. A feed-in tariff rate of $0.16/kWh is recommended to make large-scale PV systems profitable.     

Optimization of a solar powered absorption cycle under Abu Dhabi’s weather conditions

In order for the solar absorption air conditioners to become a real alternative to the conventional vapour compression systems, their performance has to be improved and their total cost has to be reduced. A solar powered absorption cycle is modeled using the Transient System Simulation (TRNSYS) program and Typical Meteorological Year 2 data of Abu Dhabi. It uses evacuated tube collectors to drive a 10 kW ammonia–water absorption chiller. Firstly, the system performance and its total cost are optimized separately using single objective optimization algorithms. The design variables considered are: the collector slope, the collector mass flow rate, the collector area and the storage tank volume. The single objective optimization results show that MATLAB global optimization methods agree with the TRNSYS optimizer. Secondly, MATLAB is used to solve a multi-objective optimization problem to improve the system’s performance and cost, simultaneously. The optimum designs are presented using Pareto curve and show the potential improvements of the baseline system.     

Improving the performance of solar desalination systems

Two modifications for solar desalination systems are presented. The first modification, using a packed layer that installed in the bottom of the basin to increase the efficiency of the still. A packed layer is formed from glass balls which is considered as simple thermal storage system. The second modification, using rotating shaft installed close to the basin water surface. The target of using the rotating shaft to break the boundary layer of the basin water surface, thus increasing the water vaporization and condensation, the performance of the present solar desalination system may also be increased. The numerical analysis presented the equations of the direct coupling of the selected PV-solar panel, DC-motor and inverter for small PV-system. The characteristics of PV array and the DC-motor are presented for the specific PV–DC power. The performance of the two modified solar stills and the conventional one is compared. Three experiments were carried out using the climate conditions of Cairo site, Egypt. Transient temperatures of the two modified solar stills and the conventional one are measured from sunrise to sunset with the same operating parameters. The energy equations that governed the present solar desalination system are presented. Energy absorbed by glass cover, basin water, packed layer and the required power of the rotating shaft are calculated to obtain the water productivity and efficiency of the present systems. The results show that the two modifications enhanced the performance of the solar desalination system. The efficiency of the modified solar desalination system using packed layer thermal energy storage was increased by 5% at May, 6% at June, and 7.5% at July, while it was increased by 2.5% at May, 5% at June, and 5.5% at July for the modified one using rotating shaft and PV-system.     

Designing a sustainable house in the desert of Abu Dhabi

In light of Estidama Guidelines, assessment method, and other documents (building code, standards, and design guidance), a sustainable house was designed following an integrated process of design and performance evaluation. The design achieved considerable improvement over a typical Emirati house case; 59% reduction in the greenhouse gas emissions and utility bill. Such a methodology could be valuable to other building professionals in the UAE who might search for a clear application model.     

TVC在MED海水淡化装置中的作用和性能分析

建立了蒸汽热力压缩器(thermal vapor compressor,TVC)和多效蒸发(multi-effect distillation,MED)海水淡化装置热力过程数学模型,计算分析了TVC对MED海水淡化装置性能的影响,讨论了对于一定设计条件下的海水淡化装置,蒸发器效数,TVC引射蒸汽、工作蒸汽及抽汽位置和装置的造水比、蒸发器传热面积、喷射系数的关系。结果表明:蒸发器效数、TVC吸入蒸汽温度的增加都会升高造水比;根据造水比和蒸发器传热面积,适当设置TVC在多效蒸发海水淡化装置中的抽汽位置,海水淡化装置的能效可以有很大的提高。     

System design, operation and performance of roof-integrated desalination in greenhouses

This paper is focused on applications in remote and arid locations where the source water is assumed to be brackish. In this concept the roof transmission is reduced as solar irradiation is absorbed by flowing water on a glass sheet covered by a top glass sheet. Fresh water is evaporated, condensed on the top glass and collected at the roof eaves.For the assessment of this concept compared to conventional, single glassed greenhouses, extensive computer simulations and field experiments were performed in Tunisia. Considerably less extreme climate conditions were registered in an experimental greenhouse with roof desalination compared to a conventional house. The simulation inaccuracy was around 5% for the water demand and production. In a more general analysis, various design cases, including crop cultivation examples were simulated. A system integrated in 50% of the roof area had the capacity to cover the annual demand for a low canopy crop. A similar capacity for a high canopy crop requires asymmetrical roof design and desalination system in the whole roof area.The yield problem could be solved with more light selective glass materials (NIR-absorption). Interesting future prospects are expected for electrochromic glasses with dynamic absorptance control. This could improve crop yields and eliminate the seasonal storage demand.     

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.     

Local model predictive controller in a solar desalination plant collector field

This paper proposes a new predictive control strategy for a distributed collector field of a solar desalination plant. The main purpose of the controller is to manipulate the water flow rate to maintain constant the outlet-inlet temperature gradient in the collectors in spite of disturbances. The controller is based on a filtered Smith predictor generalized predictive control algorithm and a simple procedure to update the linear model used in the predictor as well as the tuning parameters, in such a way that non-linear optimization is avoided. The controller copes with the process non-linearities, constraints, dead time and plant-model mismatch obtaining the desirable performance both, in the reference tracking and in the rejection of strong irradiance disturbances. Simulations and real experimental tests in AQUASOL desalination plant solar field are presented to show the advantages of the proposed controller.     

Measurement of solar-energy (direct beam radiation) in Abu Dhabi, UAE

This paper presents actual measurements of direct solar radiation in Abu Dhabi (24.43°N, 54.45°E) with the existing meteorological conditions encountered during the measurement throughout the year. High resolution, real-time solar radiation and other meteorological data were collected and processed. Daily and monthly statistics of direct solar radiation were calculated from the one-minute average recorded by a Middleton Solar DN5-E Pyroheliometer. The highest daily and monthly mean solar radiation values were recorded as 730 and 493.5 W/m², respectively. The highest one-minute average daily solar radiation was recorded as 937 W/m². In addition to direct beam radiation, the daily average clearness indexes, surface temperature variations, wind speeds and relative humidity variations are discussed. When possible, direct beam radiation and some meteorological data are compared with corresponding data of the 22-year average of NASA's surface meteorology and solar-energy model. The measured data (direct beam radiation and meteorological) are in close agreement with the NASA SSE model with some discrepancy.     

The thermal characteristics and economic analysis of a solar pond coupled low temperature multi stage desalination plant

The paper discusses optimisation of the size of the pond and the number of stages for three different storage zone temperatures taking into account the large variation in quantity of energy supplied by the pond between summer and winter. One result is that over-sizing the pond, leading to some rejection of the heat collected during the summer (which is referred to as peak clipping), will result in a higher utilisation factor of the desalination plant and a reduction in the summer/winter yield ratio. Optimum peak clipping days, leading to the minimum product water cost, for each storage zone temperature and performance ratio is presented.The sensitivity analysis of the various factors affecting the overall water costs show that the capital costs comprise about two thirds (2/3) of the total desalinated water costs. This demonstrates and re-emphasises the inherent and basic fact that solar desalination is a capital intensive enterprise. Each 1% increase in interest rate increases solar pond thermal energy costs by about 13-15% and desalinated water costs from SP/MSF combination by about 10-13%.     

Status of solar desalination in India

The work was motivated by the increasing awareness of the need for enhancing water supplies schemes in arid lands featuring an appropriate technology for solar energy use in the desalination field in India. The fresh water crisis is already evident in many parts of India, varying in scale and intensity at different times of the year. India's rapidly rising population and changing lifestyles also increases the need for fresh water. Fresh water is increasingly taking centre stage on the economic and political agenda, as more and more disputes between and within states, districts, regions, and even at the community level arises. The conventional desalination technologies like multi stage flash, multiple effect, vapor compression, iron exchange, reverse osmosis, electro dialysis are expensive for the production of small amount of fresh water, also use of conventional energy sources has a negative impact on the environment. Solar distillation represents a most attractive and simple technique among other distillation processes, and it is especially suited to small-scale units at locations where solar energy is considerable. India, being a tropical country is blessed with plenty of sunshine. The average daily solar radiation varies between 4 and 7 kWh per square meter for different parts of the country. There are on an average 250–300 clear sunny days in a year, thus it receives about 5000 trillion kWh of solar energy in a year. In spite of the limitations of being a dilute source and intermittent in nature, solar energy has the potential for meeting and supplementing various energy requirements. Solar energy systems being modular in nature could be installed in any capacity as per the requirement. This paper consists of an overall review and technical assessments of various passive and active solar distillation developments in India. This review also recommended some research areas in this field leading to high efficiency are highlighted.     

Experimental study of the performance of multieffect solar thermal water desalination system

The pilot project of a multistage solar thermal water desalination system has been developed, and experimental investigations have been carried out. This paper presents the results of the testing of the system under laboratory conditions. The results show that the productivity of the developed system is two times higher than that of the conventional solar distillers of the greenhouse type. The text was submitted by the authors in English.     

低温多效蒸发海水淡化系统的变工况性能分析

建立了低温多效蒸发系统在变工况运行条件下的数学模型,分析了加热蒸汽温度、加热蒸汽流量和供入海水流量对系统的蒸发产物负荷率和单位蒸发产物热耗率的影响,探讨了各效蒸发器中海水的温度和浓度的变化与装置结垢问题的关系。结果表明,在控制结垢发生的前提下,即盐水浓缩比不超过2.5、顶值盐水温度低于75℃时,降低供入海水流量、增加加热蒸汽流量和提高加热蒸汽温度有利于系统运行。