Solar-assisted System Research Articles

Performance comparison of two low-CO 2 emission solar/methanol hybrid combined cycle power systems

Abstract Two novel hybrid combined cycle power systems that use solar heat and methanol, and integrate CO2 capture, are proposed and analyzed, one based on solar-driven methanol decomposition and the other on solar-driven methanol reforming. The high methanol conversion rates at relatively low temperatures offer the advantage of using the solar heat at only 200–300 °C to drive the syngas production by endothermic methanol conversions and its conversion to chemical energy. Pre-combustion decarbonization is employed to produce CO2-free fuel from the fully converted syngas, which is then burned to produce heat at the high temperature for power generation in the proposed advanced combined cycle systems. To improve efficiency, the systems’ configurations were based on the principle of cascade use of multiple heat sources of different temperatures. The thermodynamic performance of the hybrid power systems at its design point is simulated and evaluated. The results show that the hybrid systems can attain an exergy efficiency of about 55%, and specific CO2 emissions as low as 34 g/kW h. Compared to a gas/steam combined cycle with flue gas CO2 capture, the proposed solar-assisted system CO2 emissions are 36.8% lower, and a fossil fuel saving ratio of ∼30% is achievable with a solar thermal share of ∼20%. The system integration predicts high efficiency conversion of solar heat and low-energy-penalty CO2 capture, with the additional advantage that solar heat is at relatively low temperature where its collection is cheaper and simpler. The systems’ components are robust and in common use, and the proposed hybridization approach can be also used with similar benefits by replacing the solar heat input with other low heat sources, and the system integration achieves the dual-purpose of clean use of fossil fuel and high-efficiency conversion of solar heat at the same time.

Energy Management for Households With Solar Assisted Thermal Load Considering Renewable Energy and Price Uncertainty

In this paper, we investigate the energy scheduling problem for a household equipped with a solar assisted heating, ventilation, and air conditioning, and water heating system in the real-time pricing environment. Our objective is to minimize the electricity cost while maintaining user's thermal comfort requirements. We consider different types of loads with different characteristics, detailed modeling of thermal dynamics, and uncertainty in electricity price and solar energy. The advantage of the proposed design lies in the exploitation of the solar assisted thermal system that can flexibly utilize the energy from the solar source or from the grid during low-price periods to support the home hot water demand, user thermal indoor temperature preference while reducing the electricity cost. We present numerical results to illustrate the effectiveness of our proposed design. Specifically, we show that the proposed design can achieve significant cost saving, allow flexible tradeoff between user comfort tolerance and electricity cost reduction, and efficiently adjust the electricity consumption load profile. We also analyze the influence of solar assisted thermal system factors such as the water tank temperature limit, solar collector size, and weather condition on the achievable cost.

Experimental analysis on single stage hybrid solar assisted adsorption refrigeration system

In the present energy scenario the continuous increase in the cost and demand for energy has led to more research and development to utilize available energy resources efficiently, in which solar energy is the most promising. Refrigeration systems utilizing solar energy can be effectively employed for vaccine storage, manufacturing ice etc. in rural areas without conventional energy supplies. Compared to solar refrigerator, the conventional PV refrigerator has high installed cost. In liquid absorption systems, rectification is required to avoid the problem of generation of some absorbent with the refrigerant in generator. In the case of solid absorbent systems like CaCl2/NH3 pair, it disintegrates after repeated cycles of operation. Special treatment of the absorbents is needed to obtain hard porous granules, thereby increasing the system cost. Solar adsorption systems, which do not possess these disadvantages, can be fabricated without any moving parts using locally available technology in developing countries. This paper envisages the design, fabrication and tested on the hybrid solar assisted adsorption refrigeration system. This system that combines the solar refrigeration and heating cycle uses working pair as activated carbon and methanol. It consists of a solar parabolic concentrator, water tank, adsorbent bed, condenser, expansion device, evaporator and receiver. The hybrid system has been designed for heating 50 liters of water from 25 OC to 90OC as well as cooling 10 liters water from 25OC to 10OC at a coefficient of performance of 0.85. The experiment results demonstrate that the refrigerator (5 kg activated carbon) has a cooling capacity of 40 to 50 W and COP ranging 0.146 - 0.18 at different evaporator temperature.

The Heating Coefficient Experimental Analysis of Solar Water-Assisted Low Temperature Air Source Heat Pump System

In winter,Many families use air source heat pump because of the low evaporation temperature of the system, resulting in lower heating efficiency of system. To solve this problem, the low temperature solar assisted hot water was added to the project which is on the basis of air source heat pump, and the system has been tested. After analysis of the collection efficiency of solar collectors at low temperatures and comparative analysis of the temperature cycle, pressure, energy consumption of the low-temperature solar-assisted systems and air source heat pump system, the optimal collector temperature and law of heat pump refrigerant cycle changes of the system were obtained. Theoretically, comparative analysis of low temperature air source heat pumps and solar hot water secondary air source heat pump compression ratio and COP. It gives the key parameters affecting the compression ratio and COP, pointing out ways to improve the heat pump COP. Finally, a key measure to improve the thermal performance of the unit system is proposed, to provide a reference for future practical applications and research. Foreword Air source heat pump in ambient air contains rich low grade solar potential as a source of heat, it has inexhaustible characteristics [1] . The main reason for restricting the use of air source heat pump in northern area of our country is when the outdoor air temperature is low in winter, the outdoor coil frost severe heating efficiency air source heat pump is greatly reduced. Martinez suggested experimental study on the application of solar radiant floor heating systems , solar water temperature is 50-60°C, low efficiency, especially when overcast snow lower system efficiency [2] .In view of the outdoor coil frosting problem, direct expansion solar assisted heat pump water heater system using the proposed by Li Yuwu, from a certain extent alleviated the problem of heat in winter for coil winter fros, improving the heating coefficient and improved the operating characteristics of the unit. However, this system requires the direct absorption of heat in air tube, and the specific heat of air is small, difficult to heat storage, illumination by solar radiation impact, unstable system operation [3]. Based on the above issues, for the low-level office building , the new rural residential , this study presents low temperature solar auxiliary air source heat pump system , the device uses low-temperature solar hot water heat pump system as low , both full use of solar energy , but also eliminates the original system frost problems and improve the efficiency of solar collectors and heat set to improve the evaporation temperature of the evaporator , thereby increasing the compression ratio of the heat pump unit .

Cooling performance and energy saving analysis of cascade refrigeration system powered by solar energy for Riyadh region (Saudi Arabia)

Energy saving and reduction in the green house gas emissions are key to the growth of the economy of a country. The study's objective is to develop a solar-powered cascade refrigeration system. The solar assisted cascade system is the combination of electricity-powered conventional vapour compression refrigeration system (VCRS) and solar-powered vapor absorption refrigeration system (VARS), connected in series. The system performance is analysed based on the solar thermal energy potential available at Riyadh region of the Kingdom of Saudi Arabia (KSA). NH3 − H2O mixture is used in VARS and three different refrigerants of highest performance are selected for VCRS. Thermal Energy Storage (TES) is used to store potential energy to keep the system operating round the clock continuously. The results indicate that the coefficient of performance (COP) of the proposed system is superior compared to the conventional VCRS and has a 44.7% saving in electrical energy consumption during peak load demands. It is notice...

Control Aspects of Decentralized Solar Thermal Integration into District Heating Networks

This paper consists of two parts. In the first part a numerical model describing the thermo hydraulic behavior of district heating (DH) networks has been used to investigate the pressure and temperature profile within a solar assisted system. The network description is based on a graph-theoretical method and the Newton algorithm was used for solving the system of nonlinear equations. A direct integration without heat storage is implemented here for an existing network topology in South Germany. The simulation shows that critical differential pressure driven operation of the district pump is not realizable with a reasonable number of pressure transmitters. The volume flow driven control provides more stability but has to be optimized by means of pressure measurements. The second part of the paper presents the new test facility built for decentralized solar heat integration. It also gives an overview about the design topics that will be investigated during the next test period: component suitability for bidirectional heat exchange, station control, net metering and handling both solar and load sides.

Energy Consumption of Solar-assisted Internally Cooled/Heated Liquid Desiccant Air-conditioning System in Hong Kong

Solar-assisted liquid desiccant air-conditioning system (SLDAC) has been considered as a promising application as traditional AC systems have many problems. In this paper, the operation performance of the SLDAC of a typical commercial building in Hong Kong was investigated, for evaluating the energy-saving potential. Combing the numerical model of individual component and inputting the weather data and load profile, the annual energy consumptions of SLDAC and traditional system could be obtained. The simulation results show that the electricity driven LDAC is not suitable for the commercial building due to the high energy demand in the regeneration. But, the solar-assisted system with thermal storage could provide promising energy saving potential. However, with the cooling tower as the only cooling source of the dehumidifier, the dehumidification capacity could not satisfy the requirement and only up to 12.5% of electricity consumption could be saved annually compared to traditional systems. Therefore, to improve the energy-saving potential, extra cooling source should be supplied for the application of SLDAC of buildings in Hong Kong.

Life cycle performance assessment of small solar thermal cooling systems and conventional plants assisted with photovoltaics

Starting from the results of a Life Cycle Assessment of small solar assisted heat driven chillers, the application of such methodology has been extended to systems with a conventional compression chiller assisted by a photovoltaic plant (PV). This study aims to provide a comprehensive compared investigation of these two families of solar assisted cooling systems (with solar thermal or PV). Results indicate that, in many cases, the systems with the PV grid connected plant performed best. In addition, two more configurations were investigated to further define the PV assisted systems, which minimise their interaction with the grid through the use of electricity storages. These systems performed worse than the PV grid connected systems and the solar thermal assisted systems in nearly all the analysed cases.

An economic optimization of evaporator and air collector area in a solar assisted heat pump drying system

This paper presents an economic optimization of evaporator and air collector area of a solar assisted heat pump drying system. Economic viability of solar heating systems is usually made by comparing the cost flows recurring throughout the lifetime of the solar and conventional alternative systems. Therefore, identification of optimum variables by using a simulation program and an economic analysis based on payback period of the system are presented in this paper. FORTRAN language is used to run the simulation. Effect of load and different economic variables on payback period is also investigated. Economic analysis reveals that system has sufficient amount of savings during the life cycle with a minimum payback period of about 4years.

ADVANCED SOLAR ASSISTED DRYING SYSTEMS FOR MARINE AND AGRICULTURAL PRODUCTS

Solar assisted drying systems are cost effective and suitable for drying of various marine andagricultural products. The way forward for advanced solar assisted drying systems is compact collector design,high efficiency, integrated storage, and long-life systems. Air based solar collectors are not the only availablesystems. Water based collectors can also be used whereby water to air heat exchanger can be used. The hot airfor drying of agricultural produce can be forced to flow in the water to air heat exchanger. The hot water tankacts as heat storage of the solar drying system. Heat pump drying system can be effective use for as part of solarassisted drying systems. Moreover, innovative applications of photovoltaic thermal system for simultaneousproduction of heat and electricity are suitable as standalone applications and totally operated on solar energy.The Solar Energy Research Institute has developed four advanced solar assisted drying system suitable fordrying of various marine and agricultural products namely (a) the solar assisted drying systems with thedouble-pass solar collector with fins (b) solar assisted dehumidification system (c) solar assisted chemical heatpump system and (d) solar assisted heat pump with photovoltaic thermal collectors.DOI: http://dx.doi.org/10.3329/jme.v42i1.15912

Energy and exergy performance investigation of transcritical CO2-based Rankine cycle powered by solar energy

A comprehensive performance evaluation of a solar assisted transcritical CO2-based Rankine cycle system is made with exergy analysis method. The actual thermal data taken from the all-day experiment of the system are utilized to determine energy transfer and the exergy destructions in each component of the system. In addition, a hypothetical carbon dioxide expansion turbine is introduced, then two thermodynamic models for solar transcritical carbon dioxide Rankine cycles with a throttling valve (experiment) and with an expansion turbine have been established with exergy analysis method. The obtained results clearly show that solar collector contributes the largest share to system irreversibility and entropy generation in the all-day working state, and the exergy improvement potential of solar collector is the maximum in the working state. So this component should be the optimization design focus to improve system exergy effectiveness. For the cycle with the turbine, the energy efficiency and the entropy generation are not much higher than the cycle with throttling valve, but the exergy efficiency of the cycle with turbine is twice of the cycle with throttling valve. It provides more guidance when the transcritical CO2-based Rankine system is in a large-scale solar application.

Life Cycle Assessment Performance Comparison of Small Solar Thermal Cooling Systems with Conventional Plants Assisted with Photovoltaics

Life Cycle Assessment (LCA) allows for the consideration of energy consumption and environmental impacts associated with all the stages of a product's life, from the cradle to the grave. Starting from the results obtained in the IEA SHC Task 38 framework for the LCA of small solar assisted heat driven chillers, the application of such methodology has been extended to systems with a conventional compression chiller assisted by a photovoltaic plant. This study aims to provide a more comprehensive investigation through a comparison of these two families of solar assisted cooling systems (with solar thermal or PV), which is an important topic for studies concerning the research of effective and environmentally friendly systems that exploit solar radiation for cooling and heating purposes. In hot climates, the systems with the PV grid connected plant performed best. Anyway, a comparison of this system with the other systems is not meaningful because the strength of the solar thermal H/C system is the ability to reduce the dependence from the electric grid and to avoid peaks, overloads and power quality variations. Thus, two more configurations were investigated to further define the PV assisted systems, which minimise their interaction with the grid through the use of electricity storages. These systems performed worse than the PV grid connected systems and the solar thermal assisted systems in nearly all the analysed cases.

Uniform Representation of System Performance for Solar Hybrid Systems

Energy efficient HVAC solutions may be obtained by combining different energy sources – fossil and renewable – into single hybrid systems. This leads to a variety of system concepts with specific boundary conditions. As a consequence, the definition of a unique representation method and a standardized performance evaluation procedure is a challenging task.Currently, two international projects promoted by the IEA are dealing with the representation and the performance calculation of a particular category of hybrid systems, i.e. integrated solar assisted systems. The HPP Annex 34 “Thermally Driven Heat Pumps for Heating and Cooling”, whose goal is to reduce the environmental impact of heating and cooling by the use of thermally driven heat pumps, has solar cooling as one of the systems under investigation. The joint project between SHC and HPP Task 44/Annex 38 “Solar and Heat Pump Systems” is focused on different system combinations of solar thermal collectors and heat pumps.The scope of the present paper is to show a systematic methodology to represent and evaluate the energy performance of complex hybrid systems. The proposed approach is a joint effort of the on-going IEA activities and will be discussed regarding the mentioned solar hybrid systems. However, the final goal of the work is to provide a basis for a simple, fair and transparent comparison of all systems for heating and cooling, regardless of the technology.

Performance evaluation of solar-assisted air-conditioning system with chilled water storage (CIESOL building)

This study presents the performance of solar-assisted air-conditioning system with two chilled water storage tanks installed in the Solar Energy Research Center building. The system consists mainly of solar collectors’ array, a hot-water driven absorption chiller, a cooling tower, two hot storage tanks, an auxiliary heater as well as two chilled storage tanks. The chilled water storage tank circuit was further investigated in order to find the optimum solar system’s operation sequence while providing the best energy performance. Firstly, we carried out a study about the dynamics of building’s cooling load and the necessity of the integration of chilled water storage tanks to solar system. Subsequently, the new system’s operation mode was proposed to reduce the energy consumption. The results demonstrate that we can save about 20% of the total energy consumption and about 30% of water consumption applying the new operation sequence, which takes into account the chilled water tanks action. Moreover, it was demonstrated that the integration of chilled water storage tanks allows to reduce the sudden absorption chiller on/off cycles, thereby improving the efficiency of the solar-assisted system.

Study of Seasonal Storage in Ground-Source Heat Pump with Solar Collector

Aimed to ground source heat pump’s low coefficient of performance in severe cold climate areas, solar assisted GSHP system with seasonal soil heat storage has been advanced. Simulation analysis was done for the underground heat exchanger using finite element method. Changing types of soil and material of U-tube, suitable kind of soil and material of U-tube were found for GSHP system. The analysis result shows that seasonal soil storage can solve the problem of large heat load in heating period and little cold load in cooling period for severe cold areas. It provides theoretical basis for residential use.

Solar powered vapor absorption system using propane and alkylated benzene AB300 oil

This paper describes experimental work on a solar assisted vapour absorption air conditioning system using Propane (refrigerant) and Alkylated Benzene (AB300–refrigeration lubrication oil, absorbent). Preliminary experiments to assess the miscibility of propane in various lubricating oils namely Shell Clavus oils 32 and 64 and Alkylated Benzene oils AB150 and AB300 indicated that Propane is most miscible in Alkylated Benzene AB300. The vapour absorption system is a single stage absorption consisting of evaporator, absorber, generator and condenser. The system is equipped with heat pipes installed between the absorber and the pre-generator to recover the heat of absorption. The heat applied to the generator replicated the solar thermal energy based on the climatic conditions of Jamaica using flat plate collectors commonly used in Jamaica. Experiments at various evaporator, absorber and generator temperatures showed that the coefficient of performance of the system increases with increasing the generator temperature and with decreasing the absorber temperatures. The solar fraction for the flat plate collectors to produce the generator temperature needed to drive the absorption system is up to 50%.

Experimental investigation on a solar assisted heat pump in-store drying system

Solar powered drying is an environment-friendly technique utilized to dry grain. A novel in-store drying system composed of flat-plate air collectors, a heat pump, fans, air ducts, and grain stirrer is proposed to make full use of solar energy and to reduce the consumption of electricity. A demonstration system was built and tested in Kunming, China. The experimental data was compared with the results derived from a mathematical simulation. The experimental and simulated data demonstrate that the solar assisted heat pump drying system improved the performance of the in-store drying process. An average temperature rise of 8.9 °C for the granary inlet air was achieved. The drying rate was increased and the uniformity of grain moisture content was improved. In addition, the grain was maintained in good quality and the level of power consumption was reduced.

A solar assisted heat pump drying system for grain in-store drying

For grain in-store drying, a solar assisted drying process has been developed, which consists of a set including a solar-assisted heat pump, a ventilation system, a grain stirrer, etc. In this way, low power consumption, short cycle time and water content uniformity can be achieved in comparison with the conventional method. A solar-assisted heat pump drying system has been designed and manufactured for a practical granary, and the energy consumption performance of the unit is analyzed. The analysis result shows that the solar fraction of the unit is higher than 20%, the coefficient of performance about system (COPS) is 5.19, and the specific moisture extraction rate (SMER) can reach 3.05 kg/kWh.

Modeling of a solar-assisted HVAC system with thermal storage

A numerical model of the solar-thermal-assisted heating, ventilation and air conditioning system in a 7000 m 2 educational building, situated in a high-desert climate, is used to predict performance and optimize control parameters. Heating, cooling and shoulder seasons are considered in the study. It is found that the solar assist can account for over 90% of the total heating requirements if certain energy conservation strategies are adopted. The solar cooling assist can reduce the total external cooling energy requirement by between 33% and 43%, the latter result achieved, surprisingly, at lower solar array operating temperatures. In the shoulder season, it is possible to operate the building without any external contribution, by heating the building in the coldest hours of the day, and using any excess heat to produce chilled water, to be stored and used when required. Operation of the solar-assisted system within a much larger district energy system makes it possible to achieve maximum performance.

Optimization of serial combined system of ground-coupled heat pump and solar collector

A mathematical optimization model was set up for a ground-solar combined system based on in-situexperimental results, in which the solar collector was combined serially with a ground-coupled heat pump (GCHP). The universal optimal equations were solved by the constrained variable metric method considering both the performance and economics. Then the model was applied to a specific case concerning an actual solar assisted GCHP system for space heating. The results indicated a system coefficient of performance (COP) of 3.9 for the optimal method under the serial heating mode, and 3.2 for the conventional one. In addition, the optimum solution also showed advantages in energy and cost saving, leading to a 16.7% improvement in the heat pump performance at 17.2% less energy consumption and 11.8% lower annual cost, respectively.