Field Of Solar Thermal Collectors Research Articles

In-field monitoring and numerical parametric analysis of a small size adsorption solar cooling plant in Italy

Solar cooling of small buildings represents a very interesting potential market, still underdeveloped and characterized by a wide range of uncertainties, both on the technological and the economical side. Actually, there are a few low size ready-to-market adsorption/absorption chillers and their costs are significantly higher than technically mature compression systems. The combination of solar thermal systems with solar assisted chillers needs a thorough design stage to be correctly optimized and this may turn out unaffordable for a low size project. A monitoring campaign has been carried on a new building (PUEEL – Prototipo Uffici ad Elevata Efficienza in Legno, High Efficiency Wooden Office Prototype) realized at the facilities of IPLA1 in Turin, Italy. The building has a wooden highly insulated envelope, controlled mechanical ventilation with thermodynamic heat recovery, radiant heating/cooling. A solar thermal collector field is integrated in the building roof (Fig.1), used both for the building heating and cooling demand, thanks to a 9kW adsorption chiller. Dynamic simulations of the system, using software Polysun © for solar cooling plant and EnergyPlus © for building demand assessment, have also been carried on and compared with in-field measurements. The validated model has been used for a parametric evaluation of the effects of the installation of different components and control strategies.

Robustness of district heating versus electricity-driven energy system at district level: A multi-objective optimization study

This article compares the robustness of the optimal choice of technologies for two Smart Energy Systems architectures at district level, illustrated by a case study representative of a newly built district in Grenoble, France. The electricity-driven architecture relies on the national electric grid, decentralized photovoltaic panels and decentralized heat pumps for heat production building by building. The alternative architecture consists of a district heating network with multiple sources and equipment for centralized production of heat. Those are a gas boiler plant, a biomass-driven cogeneration plant, a solar thermal collector field, and a geothermal heat pumping plant (grid-driven or photovoltaics-driven). Electric and heat storages are considered in both architectures. The sizing and operation of both architectures are optimized via linear programming, through a multi-objective approach (total project cost versus carbon dioxide emissions). Both architectures are compared at nominal scenario and at sensitivity scenarios. It is concluded that the electricity-driven architecture is less robust, especially to uncertainties in space heating demands (+150%/−30% impact on costs) and in heat pump performance (+35%/−15% in costs). Meanwhile, the multi-source architecture is less sensitive to space heating demands (+110%/−30%) and has negligible sensitivity to the rest of parameters except photovoltaic panels efficiency (+14%/−7%).

Simulation Study of the Thermal Performance of MSF Desalination Unit Operating by Solar Vacuum Tube Collectors

The Center for Solar Energy Research and Studies (CSERS) has a good experience in operating and evaluating the thermal performance of small scale 5 m3/day Multi-Stage Flushing (MSF) desalination plant connected to solar pond according to the local weather conditions of Tajoura area. However, a new project has been suggested to run the desalination plant with vacuum tubes solar thermal collectors utilizing available technology and experience. In this study an attempt was made to make the best use of readily available components to operate the MSF desalination unit with field of solar thermal collectors. Several configurations of collectors and tank arrangements were designed and examined through the use of simulation software, TRNSYS. The study has shown that the layout-3 (two 500 litre storage tanks each of them connected to 9x5 vacuum tube collectors) gives the best performance with an annual solar fraction over 77% at load temperature of 70 °C with flow rate of 2500 lit/hr, and over 68% at load temperature of 80 °C for working condition of 8 hours daily. The study has also shown that running the desalination plant for 24 hours a day reduces the solar fraction of the solar collector field to 25%

Optimal exergetic, exergoeconomic and exergoenvironmental design of polygeneration system based on gas Turbine-Absorption Chiller-Solar parabolic trough collector units integrated with multi-effect desalination-thermal vapor compressor- reverse osmosis desalination systems

In the recent years, considering aridity problem of the country and high potential of desalinating the seawater in the southern and northern coasts, focusing on the poly-generation cycles of power and distillate with the lowest possible cost and emission of the pollutants has been increased. In this research, the study of the trigeneration system of power, heat and desal water located in the Qeshm island has been conducted. The potentials of the existing unit have been evaluated and the different scenarios have been proposed to improve the performance of the system. Setting the inlet air cooling system up to the gas cycle is one of the schemes proposed to diminish the undesirable effects of the ambient conditions. Also integrating the existing MED desalination unit with RO system and using solar thermal collector field in order to improve the performance of the system and to propose the optimal scheme for the operating unit has been investigated. The conventional and the advanced exergy, exergo-economic and exergo-environmental analyzes based on life cycle assessment have been used to evaluate the existing and the proposed systems. The multi objective optimization process has been performed to maximize the exergetic efficiency and to minimize the cost and environmental impact of the product of the system. Considering the complexity of the problem, using the genetic programming to generate the objective functions has been conducted. In order to apply the optimization process on the existing and the proposed system, multi objective genetic algorithm (MOGA) and multi objective water cycle algorithm (MOWCA) have been used. Multi objective water cycle algorithm has been performed for the first time at the energy problems in this research. The results shows that using the inlet air cooling system has decreased the fuel consumption, total costs and environmental impacts of the system by 1019 tons/year, 914 k$/year and 197 kpts/year, respectively. Also integrating the existing unit with the solar thermal collector field to achieve an increase of 4.77% in efficiency of the system has been investigated. Five different types of STC at two configurations have been evaluated and the thermodynamic, economic and environmental optimal solution has led to calculate 9081 m2 area of required collectors. Using RO desalination unit in the downstream of MED has prevented the energy leakage and increased the distillate production rate by 255.12 tons/h. The optimization processes using two methods shows the capability of the MOWCA and lead to an increase of 12.66% in exergetic efficiency and decreased the total cost and environmental impact rate of the system by 47.4$/h and 49.2 pts/h, respectively.

Solar thermal wastewater evaporation for brine management and low pressure steam using the XCPC

In this manuscript, the performance of a commercial thermal evaporator powered using solar energy is described. The solar collector, known as the external compound parabolic concentrator (XCPC), is an emerging technology which combines nonimaging optics and metal-glass vacuum tube technology to provide high operating temperatures from a stationary collector. Paired with a commercial thermal evaporator, it provides a renewable heat alternative to fossil fuels for wastewater volume reductions. To assess performance, the team at UC Merced installed a 10 gallon-per-hour (0.037 m3/hr) thermal evaporator and connected it to a 30 kW solar thermal collector field. The solar array operates between 130 and 150 °C, providing thermal energy to drive evaporation for 8 h each day. The single-stage thermal evaporator has a specific energy consumption of 776 kWh/m3. Performance of the array was then used to develop an annual performance model to extrapolate performance for different locations and thermal loads (e.g. other commercial and emerging water treatment and desalination technologies). Extrapolating performance yields an annual thermal generation of ~500 kWhth useable heat delivered to the process load at 150 °C per square meter of solar field, although the team estimates a commercial installation can generate closer to 625 kWh/m2/year. Thus a commercial installation could process 2.5–3 m3 of product water per square meter each year. At these temperatures the thermal energy can also be used to decarbonize a number of other industrial processes such as evaporation, desalination, drying, and more.

Potential for solar thermal energy in the heap bioleaching of chalcopyrite in Chilean copper mining

Bioleaching of chalcopyrite is only possible in the presence of thermophilic micro-organisms. While suitable conditions can be generated within a heap naturally through the exothermic reaction, the effectiveness of the process can be improved with an additional heat source. Chilean copper mines are primarily located in the Atacama Desert, which has the highest solar irradiation levels on the planet. Solar thermal energy can be incorporated into the heap bioleaching process to raise the temperature in the heap and increase the copper extraction rates.A heap bioleaching system, including ponds and a solar thermal collector field, has been simulated over one year using HeapSim and TRNSYS. The maximum copper extraction achievable for the system without a solar thermal field is 67% with a 7kg/hm2 solution flow rate. A maximum extraction of 85% over one year could be achieved with a collector field to heap area ratio of 1:1 and a 10kg/hm2 solution flow rate.An economic analysis compares the capital cost of the solar thermal system to the revenue from additional copper extraction. The net present value and internal rate of return were positive for collector areas in the range of 10,000–150,000m2 for a heap area of 200,000m2. The peak NPV occurs at 50,000m2 at which point an extractionof 76% is achieved over one year of leaching.

Solar Assisted Absorption Machine for the Fermentation Cooling and Maceration Heating Processes in the Winemaking Industry

Two of the key processes in winemaking are alcoholic fermentation and must maceration, both of which have a high demand of energy. Fermentation is an anaerobic process carried out by the metabolic action of a microorganism. During this process the temperature has an important effect on the fermentation kinetics [1,2]. As the fermentation is exothermic, most of the wineries use a cooling system composed of mechanical refrigeration cycles and cooling towers in order to control the process temperature. After the fermentation, the must is macerated at temperatures close to 30°C, during which the phenolic materials (e.g. tanins and coloring agents) are leached and balanced. The aim of this study is to assess the thermal performance of a novel system composed of an absorption machine driven by solar and biomass energy sources, thus investigating the behavior of the system in an industrial winemaking process. This system consists of a lithium bromide absorption machine, a solar thermal collector field and a biomass water heater. The system operates in different modes during summer and winter seasons, taking advantage of the seasonality of both the solar resource availability and the heating and cooling demands of the processes. The results indicate that the proposed system is able to supply 25% of the cooling demand during the summer and between 30 to 50% of the heating demand during the winter.

Simulation Study of the Thermal Performance of MSF Desalination Unit Operating by Solar Vacuum Tube Collectors

The Center for Solar Energy Research and Studies (CSERS) has good experience in operating and evaluating the thermal performance of small scale 5 m3/day Multi-Stage Flushing (MSF) desalination plant connected to solar pond according to the local weather conditions of Tajoura area. However, a new project has been suggested to run the desalination plant with vacuum tubes solar thermal collectors utilizing available technology and experience.In this study, an attempt was made to make the best use of readily available components to operate the MSF desalination unit with field of solar thermal collectors. Several configuration of collectors and tank arrangements were designed and examined through the use of simulation software, TRNSYS. The study has shown that the layout-3 (two 500 liter storage tanks each of them connected to 9x5 vacuum tube collectors) gives the best performance with an annual solar fraction over 77% at a load temperature of 70 °C with a flow rate of 2500 lit/hr, and over 68% at load temperature of 80 °C for working condition of 8 hours daily. The study has also shown that running the desalination plant for 24 hours a day reduces the solar fraction of the solar collector field to 25%

Sol–gel silica antireflective coating with enhanced abrasion-resistance using polypropylene glycol as porogen

Silica antireflective (AR) coatings with high transmittance and enhanced abrasion-resistance were synthesized by sol–gel process using polypropylene glycol (PPG) as porogen. The effects of molecular weight of PPG and weight ratio of PPG to SiO2 on the refractive index and abrasion-resistance of the coating were systematically studied and compared with those of polyethylene glycol (PEG). Experimental data showed that the refractive index decreased with increasing the weight ratio to SiO2 and molecular weight of both PEG and PPG, but PPG was much more effective than PEG. In the case of same molecular weight, PPG modified coating has the higher porosity than PEG modified one. When the weight ratio of PPG to SiO2 is in a low level, the PPG-containing silica AR coatings exhibit the good abrasion-resistance. PPG is liquid at room temperature and the better solubility than PEG. These effective and economic AR coatings with enhanced abrasion-resistance have potential value in the field of solar thermal collectors.

Parametric study and exergy analysis of solar water-lithium bromide absorption cooling system

This paper presents the energy and exergy analysis of single–effect water–lithium bromide absorption cooling system driven by the heat supplied by a field of solar thermal collectors with a cooling capacity of 10 kW. The work is devoted to the study, the evaluation and distribution of the destroyed exergy for each component constituting this kind of system. The thermodynamic models have been derived using the first and second laws of thermodynamics. These models are employed in a computer program using the engineering equation solver (EES) software to perform the calculations and a sensitivity analysis to parameters is also presented. The results indicate that the contribution of some components to the overall exergy loss is very important. Exergy analysis also illustrates that the distribution of the destroyed exergy in the system between components depends strongly on the working temperatures.

Domestic hot water consumption vs. solar thermal energy storage: The optimum size of the storage tank

Many efforts have been made in order to adequate the production of a solar thermal collector field to the consumption of domestic hot water of the inhabitants of a building. In that sense, much has been achieved in different domains: research agencies, government policies and manufacturers. However, most of the design rules of the solar plants are based on steady state models, whereas solar irradiance, consumption and thermal accumulation are inherently transient processes. As a result of this lack of physical accuracy, thermal storage tanks are sometimes left to be as large as the designer decides without any aforementioned precise recommendation. This can be a problem if solar thermal systems are meant to be implemented in nowadays buildings, where there is a shortage of space. In addition to that, an excessive storage volume could not result more efficient in many residential applications, but costly, extreme in space consumption and in some cases too heavy.A proprietary transient simulation program has been developed and validated with a detailed measurement campaign in an experimental facility. In situ environmental data have been obtained through a whole year of operation. They have been gathered at intervals of 10min for a solar plant of 50m2 with a storage tank of 3m3, including the equipment for domestic hot water production of a typical apartment building.This program has been used to obtain the design and dimensioning criteria of DHW solar plants under daily transient conditions throughout a year and more specifically the size of the storage tank for a multi storey apartment building.Comparison of the simulation results with the current Spanish regulation applicable, “Código Técnico de la Edificación” (CTE 2006), offers fruitful details and establishes solar facilities dimensioning criteria.

Evaporation in Solar Thermal Collectors During Operation—Reasons and Effects of Partial Stagnation

Evaporation in solar thermal collectors normally takes place when the collector pump is not running—the so-called full stagnation. But it is possible that part of the heat transfer fluid evaporates inside a solar thermal collector field although the pump is operating and the collector field outlet temperature is significantly below the evaporation temperature. This operating status is called partial stagnation since only parts of the collector are affected by evaporation. Partial stagnation happens at a pronounced nonuniform temperature distribution in combination with a low mass flow rate and/or a high temperature level. A main reason for an irregular temperature distribution is a nonuniform flow distribution inside the solar thermal system. The paper presents an experimental investigation that analyzes the reasons and effects of partial stagnation occurrences. For this, outdoor measurements were made with a direct-flow vacuum tube collector. Criteria that promote partial stagnation have been identified, such as a coaxial tube design, a low system pressure, and a high gas content of the fluid. Performance measurements show no efficiency reduction during partial stagnation in the system investigated at a horizontal or positive collector slope. A high degree of partial stagnation, however, might pass into a complete evaporation of the collector volume although the collector pump is still running. This could lead to a complete blockage of the flow and a high thermal load of the system components. In all cases, partial stagnation leads to an unstable operation and a high load of the collector fluid and should, therefore, be avoided by design measures. A minimized risk for evaporation during operation is achieved by a more equal flow distribution inside the collector and the whole collector field, air bubbles, and solid particles should be completely removed. In addition, the gas content dissolved in the fluid may be reduced and the system pressure level may be increased in order to raise the boiling temperature.

Cost effectiveness of decentralized energy supply systems taking solar and wind utilization plants into account

In this article, results are presented of annual simulations of a decentralized (regional) plant for the power and heat supply of a residential complex. This complex consists of four houses with 40 flats all in all. The annual power consumption of the complex is 157 MWh and the heat requirement is 325 MWh. The concrete dynamics of the energy demands over the year is taken into consideration. The energy supply system is composed of a power-controlled combined heat and power (CHP) plant (55 kW), a photovoltaic plant (PV array or PV plant) array for power generation as well as a field of solar thermal collectors with a short-term accumulator for water heating and a long-term accumulator for supplying heat for domestic heating purposes. Simulation results demonstrate that synergetic effects result from the combination of a CHP plant with wind power and PV plants of varying sizes, which have an effect on the cost effectiveness of the plant as a whole with the different dynamics of energy sources (wind and solar energies) and of the consumption of power and heat being the decisive factors. The power deficits of wind power and PV plants are compensated through the application of a natural gas-operated CHP plant. In almost all variants, the demand for fossil energy carriers is distinctly less than in conventional energy supply plants.

Compressors driven by thermal solar energy: entropy generated, exergy destroyed and exergetic efficiency

This work is devoted to the study of the entropy generated, the exergy destroyed and the exergetic efficiency of lithium-bromide absorption thermal compressors of single and double effect, driven by the heat supplied by a field of solar thermal collectors. Two different applications have been considered and compared: air-cooled and water-cooled units. Water-cooled compressors work with temperatures and pressures lower than air-cooled compressors considering, in both cases, the same suction temperature, equal to 5°C. While the absorption temperature in water-cooled compressors can reach 40°C, in air-cooled systems it can vary between 30°C and more than 50°C. Under these conditions, the discharge temperature (boiling temperature within the desorber) of a single effect air-cooled unit lies between 65 and 110°C, the maximum discharge pressure being around 0.12 bar. The discharge temperatures (boiling temperature within the high pressure desorber) of the double effect air-cooled thermal compressor lies between 110°C for a final absorption temperature of 30°C, and 180°C for a final absorption temperature of 50°C. Discharge pressures can reach values of 0.3 and 1.5 bar, respectively. The lithium-bromide air-cooled thermal compressors of double-effect can be viable with absorption temperatures around 50°C, when the temperature difference between the lithium-bromide solution and the outside air is about 8°C. The double effect thermal compressor generates less entropy and destroys less exergy than the single effect unit, leading to a higher exergetic efficiency. In both cases, the compression process of the cooling fluid occurs with entropy reduction.