Solar-assisted System Research Articles

A simulation study on performance improvement of solar assisted heat pump hot water system by novel controllable crystallization of supercooled PCMs

Domestic hot water (DHW) has a significant share in building’s energy consumption. In order to reduce this consumption, various solutions have been proposed such as controlling the system in an efficient way, using renewable sources and using phase change materials (PCM) in the system to increase heat capacity. However, this study is not only offering heat capacity improvement of the DHW storage unit but also proposing that energy efficiency can be improved by controlling the heat releasing time of the PCM. In this study, supercooled PCM tubes are placed in a water tank and charged with a solar assisted heat pump unit, these supercooled PCM tubes can then be discharged anytime when the hot water is required. In this paper, a transient thermodynamic model is built for the whole system including solar collector, heat pump, water tank with PCM and DHW demand profile. System components are modelled and a 24 h of demand profile is used in simulation for a UK home for summer and spring weather conditions. The results show that the PCM tubes effectively compensate the morning peak hot water demand and reduce daily energy consumption around 12.1% and 13.5% by shifting heating provision from immersion heater to solar heat pump.

Solar assisted pyrolysis system for High-Density polyethylene plastic waste to fuel conversion

Plastic products are used almost in all our daily life activities due to their characteristics such as being inert, durability, flexibility, and versatility. More than 1 million tons of plastic wastes are generated daily in Ethiopia. Unless managed it properly plastic waste affects the environment immensely since they are durable and stable. Plastic wastes stay in the environment for a long time. In this paper, a solar-assisted pyrolysis system has been designed and tested for the generation of liquid fuel from High-Density Polyethylene plastic waste. Data were collected related to the solar energy potential of Addis Ababa city of Ethiopia and the amount of plastic waste generated daily. Proximate and ultimate analysis and heating value of waste were determined experimentally. The energy requirements of the pyrolysis system were determined and the sizing of the system was performed. The model is simulated using Matlab software and a mathematical model is applied to study the performance of the system. A 4 m diameter solar parabolic dish collector with a cylindrical-shaped reactor at the focal point and dual solar tracking system is used based on Addis Ababa weather data and the required energy for the endothermic pyrolysis. Based on the result, the conversion efficiency of the system is 72% by weight. The result also shows 1360 Kwh/m2 of solar energy is required to produce 14.2 liters of liquid fuel from High-Density Polyethylene plastic waste. The heating value of the produced liquid fuel is 41.8 MJ/kg. Thus, by using a solar-assisted pyrolysis system a liquid fuel has been produced from plastic waste, income is generated from the selling of the produced liquid fuel, and the environmental impact of waste plastic is reduced.

Energy and exergy analyses of the solar assisted multigeneration system with thermal energy storage system

AbstractThe following analysis has been conducted to investigate the energy and exergy efficiencies of solar assisted multigeneration system, the system comprises of parabolic trough solar collector, thermal energy storage tank, regenerative power plant, double effect absorption cooling system, and PEM electrolyzer. The variation in energy and exergy efficiencies of the parabolic solar trough collector with respect to solar absorptivity is also shown in the analysis. The heat transfer rate, the resultant outputs, the efficiencies, and the rate of exergy destructions for each component are calculated. The freshwater is used as the primary working fluid for the overall cycle and the net power produced by the low‐pressure turbine is 1.384 MW, additionally, the rate of heat produced by the thermal storage tank is 205.7 kW and the calculated thermal efficiency of the thermal storage tank is 14.33%. The overall analysis has been done by using engineering equation solver and parametric results are shown in order to determine the variations in the system.

Performance analysis of solar assisted vapour Jet refrigeration system with regenerator (CRMC method)

There are various forms of low-grade thermal energies that could all be useful in powering an ejector refrigeration system. Effective utilization of low-grade thermal energy is feasible from many available sources from industrial areas, solar and the automobile exhausts etc, . The normal Vapour Jet Refrigeration system is compared with the efficient Vapour Jet Refrigeration system fitted with a solar assisted regenerative heat exchanger unit. The ejectoris designed using Constant Rate Momentum change (CRMC) methodology to enhance the Coefficient of Performance by the usage of the refrigerant R134a as the working medium. The ejector cycle has been recognized as the promising technology for utilization of solar energy for cooling. The heat absorbed by the solar flat plate collector is partially used to heat refrigerant in the ejector cycle. Study on the effect of refrigerant temperature due to heat provided by boiler and solar flat plate in the Vapour Jet Refrigeration system on Coefficient of Performance, pumping power, entrainment ratio, diffuser outlet temperature & heat rejected at condenser is carried out. Simulation of ejector designed through Constant Rate Momentum change (CRMC) methodology is done using FLUENT software.

A systematic review of recent air source heat pump (ASHP) systems assisted by solar thermal, photovoltaic and photovoltaic/thermal sources

The air source heat pump (ASHP) systems assisted by solar energy have drawn great attentions, owing to their great feasibility in buildings for space heating/cooling and hot water purposes. However, there are a variety of configurations, parameters and performance criteria of solar assisted ASHP systems, leading to a major inconsistency that increase the degree of complexity to compare and implement different systems. A comparative literature review is lacking, with the aim to evaluate the performance of various ASHP systems from three main solar sources, such as solar thermal (ST), photovoltaic (PV) and hybrid photovoltaic/thermal (PV/T). This paper thus conducts a systematic review of the prevailing solar assisted ASHP systems, including their boundary conditions, system configurations, performance indicators, research methodologies and system performance. The comparison result indicates that PV-ASHP system has the best techno-economic performance, which performs best in average with coefficient of performance (COP) of around 3.75, but with moderate cost and payback time. While ST-ASHP and PV/T-ASHP systems have lower performance with mean COP of 2.90 and 3.03, respectively. Moreover, PV/T-ASHP system has the highest cost and longest payback time, while ST-ASHP has the lowest ones. Future research are discussed from aspects of methodologies, system optimization and standard evaluation.

Experimental study of a pilot-scale fin-and-tube phase change material storage

The large-scale deployment of solar-assisted systems in the residential sector relies on innovative thermal energy storage units. This paper contributes to the present-day discussion by proposing a pilot-scale phase change material storage, whose size has been selected to be coupled with solar-assisted heat pumps. The storage unit consists of a fin-and-tube heat exchanger placed within a tank: water is circulated on one side of the heat exchanger and, on the other side, commercial paraffin RT26 is employed. The storage system is operated considering two heat exchanger configurations (viz., parallel and series configurations) and implementing a broad set of boundary conditions, to test the storage unit under relevant operating conditions. To this end, a novel test rig with electrical resistances (to provide the heating load) and a heat pump (to provide the cooling load) has been designed and build. The results were commented in terms of global and local performances; it was found that the proposed storage, compared with a volume-equivalent water storage, is able to store 65% higher thermal energy. In addition, the dataset obtained in this research is attractive to validate numerical codes of phase change material storage units.

Comparison of solar thermal and solar electric space heating and cooling systems for buildings in different climatic regions

Solar thermal and Photovoltaic (PV) systems can save significant amount of non-renewable energy that are utilized to satisfy the energy services for buildings. The falling prices of PV in recent years increased the attractiveness of PV systems. The purpose of this research is to develop a systematic methodology for fair technical and economical comparison of reference and solar assisted systems. For this reason, the annual energy requirements for heating, cooling and DHW for a selected dormitory building under five representative climatic conditions were evaluated using the Hourly Analysis Program (HAP). At the same time, solar thermal and PV systems have been designed and simulated for the same building using Sketchup, Trnsys and PVsyst. Finally, a systematic comparison between the solar systems and five conventional systems have been carried out in terms of primary energy ratio, and Levelized Cost Of Energy (LCOE). For the case of Amman, solar thermal and electric systems achieved a non-renewable primary energy savings of 29% and 100%, respectively, whereas, they achieved LCOE savings of 15% and 62%, respectively compared to the best conventional system. The selection of the best solution for a given project requires a full understanding of the system performance and the interaction of its components rather than the technology efficiency only. This system performance depends on the building envelope, load patterns, availability of solar radiation, roof area availability, energy prices, and policies. Thus, a case-by-case analysis should be done for each project in each climatic region.

Energy and environmental life-cycle impacts of solar-assisted systems: The application of the tool “ELISA”

Solar heating and cooling (SHC) systems can be relevant in the achievement of energy and climate European goals. The benefits of these technologies should be evaluated taking into account their life-cycle energy and environmental impacts, calculated by applying the Life Cycle Assessment (LCA).The development of a complete LCA can be difficult and time-consuming particularly for non-experts in LCA, discouraging them in developing the life-cycle assessments. To overcome this issue, the paper presents “ELISA - Environmental Lifecycle Impacts of Solar Air-conditioning systems”, a user-friendly simplified tool for estimating the life-cycle energy and environmental benefits/impacts of solar technologies for heating and cooling in different geographic contexts and comparing them to conventional systems.The tool was applied to analyse three systems (thermal SHC, conventional and PV assisted system) in Greece and to identify the one characterized by the best life-cycle performances. The results revealed that the impacts of PV assisted system are about 60% lower than those of the others, highlighting the advantage of using renewable electricity for building air-conditioning in locations with high solar radiation availability.ELISA can be used by researchers, designers and decision-makers to introduce the life-cycle thinking in the early design phase of heating and cooling systems.

Parameter analysis and optimization of a two-stage solar assisted heat pump desalination system based on humidification-dehumidification process

A combination of heat pump and humidification-dehumidification (HDH) process is a suitable choice to obtain fresh water for small-scale desalination applications, especially when the solar energy is used as the auxiliary heat source. In this paper, a novel two-stage solar assisted heat pump (SAHP) desalination system based on HDH, in which the humidifiers are connected in parallel, is proposed. A mathematic model is developed to improve the system performance by optimizing the operating parameters such as process air flow rate and cooling seawater flow rate, and it is also validated by the experimental results. Analysis results indicate that there exists an optimal process air flow rate in the desalination system, which does not vary with the hot seawater flow rate. However, it will be increased with the increase of cooling seawater flow rate. When the flow rates of process air and cooling seawater are 350 m3/h and 0.55 m3/h, respectively, the maximum fresh water yield is 17.94 kg/h. The corresponding gained-output-ratio (GOR) is 2.02. However, the system performance is constrained by a bottleneck: increasing dehumidifying capacity can result in a reduction in the performance of lower-temperature (LT) humidifier. Consequently, a modified system is then proposed to solve this bottleneck effectively. The maximum fresh water yield can be increased by 16.70% to 20.54 kg/h, and the corresponding maximum GOR is also increased by 18.05% to 2.42.

The validation of a novel lumped parameter model for photovoltaic thermal hybrid solar collectors: a new TRNSYS type

Decarbonisation is one of the most important challenges facing researchers, and solar-assisted systems represent an important solution to reduce the energy consumption at the household-scale. The current work contributes to existing research by proposing and validating a novel lumped parameter simulation model for photovoltaic thermal hybrid solar collectors using field measurements carried out at an experimental facility. The modelling approach, which also considers the effect of the thermal capacitances of the elements composing the photovoltaic thermal collector, used an electrical analogy method to solve the transient heat transfer problem. The results of the simulations were compared with the experimental data collected during different weather conditions; the effects of the thermal capacitances of the collector were also investigated. The results were compared in terms of both average daily performance and instantaneous values of the variables characterizing the system. Although the differences were negligible, the results of the simulation analyses matched the measurements more precisely when the thermal capacitances were taken into consideration. Finally, the simulation model was implemented as a TYPE of Transient System Simulation (TRNSYS) software, and it is made freely available to facilitate future integrated computer simulations.

A novel solar assisted vacuum thermionic generator-absorption refrigerator cogeneration system producing electricity and cooling

A novel solar assisted cogeneration system composed of a parabolic dish collector (PDC), a vacuum thermionic generator (VTIG), and an absorption refrigerator (APR) is proposed, in which the APR harvests the rejected heat from the VTIG for further cooling production. The equivalent power output and efficiency of the proposed system are obtained by considering various irreversible losses including radiation and convection heat losses of the PDC, radiation heat losses between the cathode and anode of the VTIG, heat transfer irreversibility, irreversible effects inside the working fluid of the APR. The maximum attainable efficiency increases from 17.21% to 27.06% as the bottoming APR is hybridized into the system. Meanwhile, the corresponding power density gains a 13.47% increase. Comprehensive sensitivity analyses are conducted to examine the dependence of the proposed system performance on some decisive design parameters and operating conditions such as absorber temperature of the solar collector, solar concentration ratio, solar irradiance, work function and anodic temperature of the VTIG, heat transfer area, heat transfer coefficient, and internal irreversibility factor of APR. The obtained results may provide some new insights into development and operation of such a solar powered cogeneration system.

Thermodynamic and economic analysis of solar assisted CCHP-ORC system with DME as fuel

A solar assisted combined cooling, heating and power system coupled with an organic Rankine cycle (SCCHP-ORC) is proposed and investigated via both experimental and simulation methods. The dimethyl ether (DME) is used as the fuel of the proposed system for the prime mover (PM) and auxiliary boiler (AB). DME was chosen based on that it is friendly to the environment and avoids low temperature corrosion. The performance of the proposed system was evaluated during typical summer and winter days via a case study using thermodynamic and economic methods. The results show that the proposed system followed by the electricity load (FEL) strategy can satisfy most of the electricity demand. The cooling and heating profiles are supplied by utilizing the PMs’ cooling water and the parabolic trough collector (PTC). Additionally, the released energy from a thermal energy storage (TES) can significantly reduce the need for grid energy during peak load hours. Moreover, the efficiency of the proposed SCCHP-ORC system is higher than that of original system by 9.87%. The minimum values of carbon dioxide emission saving ratio are of 58.14% during summer and 17.32% during winter. The total amount of carbon dioxide saved are 778.7 kg/day during a typical summer day and 358.7 kg/day during a typical winter day duo to the technologies selected in this system. Besides, the sensitivity analysis shows that the changed electricity price has a largest impact on the payback period ranging from 4.0 year to 6.5 year.

Performance analysis of solar assisted multigenerational system using therminol VP1 based nanofluids: A comparative study

The application of the nanofluids is suggested to enhance and improve the efficiency of solar thermal power system. In the present study, three different nanofluids (Fe2O3/therminol VP1, SiO2/therminol VP1, and Cu/therminol VP1) are numerically investigated in parabolic dish solar collector that is further integrated to a combined cycle for power and hydrogen production. Heat rejects from the power cycle is also utilized to drive a single effect absorption (LiBr-water) system. Furthermore, a comprehensive energy, exergy and exergo-environmental analysis are carried out by varying several input parameters and their influence on overall energetic and exergetic efficiencies, network output and rate of hydrogen generation is assessed. The engineering equation solver is employed to conduct the parametric study. Outcomes of the study demonstrate that the SiO2/VP1 has the better characteristics among the investigated nanofluids. The overall energetic efficiency of the SiO2/VP1, Fe2O3/VP1, and Cu/VP1 is almost 38.79%, 38.74%, and 37.53%, while overall exergetic efficiency is 41.72%, 41.66%, and 40.36%, respectively at 1000 Wm-2. The exergoenvironmental impact coefficient and impact index are noticed to be reduced for all the three nanofluids as mass-flow rate increases. The hy-drogen production rate for SiO2/VP1 is maximum and has observed to be increased by increasing the ambient temperature. Increase in nanoparticles concentration also rises the exergetic efficiency but reduces the thermal conductivity of the nanofluids. Coefficient of performance is noticed to be increased with rise in evaporator temperature, whereas, it is reduced by increasing the generator temperature.

Energy and Exergy Analyses of a Novel Solar PTC Assisted Multi-Generation System

In this study, a solar assisted multi-generation system is presented. The exergy and energy performance analyses are the objective of this research. The multi-generation system consists of two Rankine cycles, two absorption cycles and a hot water tank. Solar parabolic trough collectors are used to generate thermal energy from the Sun which in turn is used to power the system. The multi-generation system achieves an energy and exergy efficiency of 77% and 49%, respectively without solar input. Considering the solar PTC, the efficiencies respectively are 57% for energy and 40% for exergy. The COPs for the absorption cycle and other findings from the study are presented in details in the full paper. Exergy destruction in major components is calculated and parametric studies are done to check the performance of the system under varying global solar irradiance conditions.

Energy, exergy and exergoeconomic analysis of solar-assisted vertical ground source heat pump system for heating season

The purpose of this study is to evaluate the experimental performance of a solar assisted vertical ground source heat pump system (VGSHP) for the winter climatic conditions of Mardin, which is in the South-Eastern Anatolia region of Turkey. For this aim, an experimental analysis was performed on solar assisted VGSHP system, which was designed to meet the heating needs of an experimental room, during the heating season (10.01.2013/03.31.2014). The experimentally obtained results were used to calculate energy, exergy and exergoeconomic analyses of the system and its components. The energy efficiency, exergy efficiency and exergoeconomic factors of the entire system were 67.36 %, 27.40 % and 60.51 %, respectively. In this study, the system was proposed for disseminating the use of alternative technologies supported by renewable energy systems and it has been tested for the first time in Mardin to meet its heating needs with convectional systems. The experimental results showed that the proposed solar assisted VGSHP system can be used for residential heating in Mardin and similar regions. As a result, it has been detected that the system is very effective in both reducing energy consumption and decreasing emissions of green-house gases.

A solar assisted seasonal borehole thermal energy system for a non-residential building in the Mediterranean area

Solar heating and cooling systems are reliable and feasible solutions among renewable energy technologies. Indeed, solar thermal devices help reduce primary energy consumption and can reduce electricity demand, thus representing one of the best options for satisfying heating and/or cooling energy supply. The Borehole Thermal Energy Storage (BTES) represents one of the best promising option among the various storage technologies, because the size of the storage can be easily extended by drilling additional boreholes and simply connecting the pipes to the existing boreholes; the overall energy efficiency of this system is about 40–60%. In this paper, the authors present an application of this technology for the heating system of a school building located in the Southern part of Italy. Two different energy schemes are presented: a school equipped with a conventional gas boiler system with radiators and the same school building with a low temperature heat pump system with fan-coils. All simulations were performed in dynamic state by using TRNSYS software. The results of the analysis assessing the energy and economic performances of the two systems highlighting the advantages of the BTES application in the context of Italian market.

Theoretical investigation on energy storage characteristics of a solar liquid desiccant air conditioning system in Egypt

This work presents theoretical study of a standalone outdoor liquid desiccant air conditioning (LDAC) system assisted by solar energy. The liquid desiccant dehumidification cycle was integrated with a double indirect evaporative air cooler and a regenerative air heat recovery. The double indirect evaporative air cooler was used to recover heat from the return air, while air-air heat exchanger was used to recover heat from air leaving the regenerator. A water-in-glass evacuated tube solar collector was used to supply the system with solar heat. The remaining required heat is provided by natural gas fired boiler. The system was simulated by transient model under thermal energy storage, thermochemical energy storage and combined thermal and thermochemical energy storage modes.The theoretical results show that the mean daily thermal coefficient of performance (TCOP) is a strong function of the difference between absolute humidity ratio of outdoor air and saturated air. Results also show that, each tube of solar collector can deliver 30-Watt to operate the LDAC system under thermal energy storage mode for 16 h daily. While in the LDAC system under thermochemical energy storage mode, each tube would deliver 38.5-Watt for 16 h operation.It has been found that, to rise the solar fraction from 90% to 100% in the thermal energy storage mode, the required size of tubes array will be increased by 20%. Also, an analysis was carried out on the TCOP and required storage volume of the different energy storage modes. It shows that the combined energy storage method is the most energy efficient method.Finally, life cycle cost analysis (LCCA) was carried out for the LDAC system using various types of energy storage modes. The comparison indicated that 90% solar fraction LDAC system is the most economic system related to unit prices of solar collector and gas prices in Egypt. The total annual cost for the 90% solar assisted LDAC system is found to be lower than that of a vapor compression cycle (VCC) by about 50.5%. At the second order, the thermal energy storage mode by 49%. On the other side, the thermochemical energy storage mode is the least cost saving energy storage mode.

Recyclable photo-thermal conversion and purification systems via Fe3O4@TiO2 nanoparticles

In recent years, nanoscale particles have been applied in the utilisation of solar energy due to their excellent properties. In light of the multiple functions of composite nanoparticles, some solar-assisted systems have been developed and exhibited comprehensive photoelectric and photo-thermal transformation effects. However, the presence of nanoparticles in these systems can cause secondary pollution and severely limit large-scale application of the solar technology. Herein we developed a recyclable photo-thermal conversion and purification system based on Fe3O4 nanoparticles decorated with TiO2 nanoparticles, which could be separated from water under the action of a magnetic force. Under the solar illumination power of 1 sun (1 sun = 1000 W·m−2), thermal receiver efficiency of 76.4% and Rhodamine B degradation efficiency of 85% were obtained with a 0.1 g/L Fe3O4@TiO2 nanofluid. With the increase of the solar illumination power, the degradation efficiency has been increased to 94%. The recovery rate and efficiency could be controlled by adjusting the magnetic field strength and the magnetic property of Fe3O4@TiO2 nanoparticles. This study provides an approach to not only significantly reduce material consumption in the design of solar devices, but also to realise broad solar energy applications for water purification and photo-thermal conversion.

Thermodynamic Analysis of a Solar Assisted Combined Cooling, Heating and Power System with Different Cooling Cycle Configurations

In recent times, there is an upsurge in research on renewable energy based combined cooling, heating and power (CCHP) using natural working fluids such as NH3, CO2 etc. Supercritical carbon dioxide (S-CO2), when compared to other working fluids, offers some unique properties like low critical temperature (31.1 °C), non-toxicity, non-flammability, zero ODP and a GWP of 1. Hence it is found to be a promising working fluid for advanced power and cooling cycles. This paper presents a comparative study between two solar assisted CCHP systems, one operating with a throttle valve, and other operating with an expansion turbine. Based on the comparison, it is observed that the cooling user output and electrical power output improve by using an expansion turbine while the heating user output remains the same for both the configurations.

Experimental investigation on a solar assisted heat pump desalination system with humidification-dehumidification

In this study, a novel solar assisted heat pump desalination unit for drinkable water is proposed and investigated experimentally. The experimental unit, which mainly consists of compressor, condenser, evaporator, packing humidifier, centrifugal fan, precooler and seawater tank, et al., was designed and fabricated. The effects of the cooling seawater, the process air, the mixture ratio (the ratio of the remaining seawater flow rate from the humidifier to total hot seawater flow rate) and the thermodynamic cycle on the system performance were investigated. The experimental results show that there exists the optimal flow rate of the process air corresponding to the studied unit under given conditions. The maximum productivity of the unit is 12.38 kg/(kWh) when the flow rate of cooling seawater and process air are 0.3 m3/h and 450 m3/h respectively, which is higher than those of other solar assisted heat pump desalination units in previous works. A big mixture ratio is preferred for improving the system performance. A further performance comparison between open cycle and closed cycle indicates that the yield of the open cycle increases with the increase of the cooling seawater flow rate, which is opposite to that of the closed cycle.