Solar Thermal Input Research Articles

Investigation of a novel combined ab- and ad- sorption based thermal energy storage and upgrade system

This paper presents a novel sorption-based cycle combining energy storage with energy upgrade to store low-grade heat for long periods and transform it on demand to usable energy at elevated temperatures. The system consists of an ammonia-water absorption system coupled to a resorption thermal transformer using manganese chloride and calcium chloride as the working pair with an ammonia absorbate. The absorption and adsorption systems are charged by separating the constituent sorbent-sorbate pairs, and they remain separated during the transition season. The discharge consists of a two-stage sorption process between the two systems. This work presents a transient thermodynamic model and analysis of the two-stage sorption system. For a typical solar thermal energy input of 106 °C during charging, and ambient temperatures of 5 °C and 25 °C in the winter and summer, respectively, the system is capable of discharging at an average elevated temperature of 62 °C with an energy storage efficiency of 27 %. This system is capable of simultaneously producing heat at a lower temperature by varying the mass flow rate through the high-temperature salt. The energy storage density of the combined system under different conditions is between 71 and 185 kJ kg−1. In comparison with other conventional single-stage thermal energy storage systems, this combination of absorption and adsorption-based storage provides a higher coefficient of performance for a comparable temperature output.

Thermal Performance Assessment of a Novel Hybrid Reactor for Solar Thermochemical Processes

Solar thermochemical conversion processes offer a promising pathway for converting sunlight into clean, sustainable, and carbon-neutral fuels. A solar chemical reactor is one of the most essential components that utilizes concentrated solar energy to drive chemical reactions. In this study, a novel hybrid solar reactor is designed, fabricated, and tested to assess its thermal performance for the purpose of studying the solar thermochemical conversion processes in Thailand for the first time. It was performed under different heating modes regarding solar heat and/or electrical heat, with the aim to support day-and-night operation and variations in solar radiation conditions. The reactor was experimentally tested under on-sun, off-sun, and hybrid conditions using air as a heat transfer fluid. As a result, with one kWth solar thermal power input absorbed, the solar reactor achieved high temperatures exceeding 500 °C from the hybrid system while the reactor absorption efficiency was found to be 4%. The reactor demonstrated the possibility and reliability of performing solar thermochemical conversion processes under day-and-night and unstable solar radiation conditions.

Parametric analysis for exergetic optimisation of a solar shell-and-tube latent heat storage unit for agricultural applications

Thermal energy storage by employing phase change materials (PCMs) has gained huge attention in many fields but despite great potential, a broader implementation in agricultural processes is yet to be achieved. Therefore, a standalone system for solar thermal energy storage using a Scheffler concentrator was developed for variety of agricultural applications. This study is aimed at the exergetic optimisation of the system by assessing the impact of various intensities of solar thermal input and flow rates on the exergetic performance and exergetic distribution inside an inversely arranged shell and tube heat storage unit. The experimental setup consisted of a cylindrical heat receiver, an inversely arranged shell and tube PCM tank and a flat plate resistive electric heater for solar irradiation simulation. The tank filled with 4 kg of RT70HC PCM was subject to various charging cycles under 2.5 LPM, 5 LPM, 7.5 LPM and 10 LPM flow rates and 450 W/m2, 575 W/m2, 700 W/m2 and 825 W/m2 of simulated solar intensities. The results indicate that increasing the mass flow rate enhances the heating uniformity within the tank but also leads to higher total exergy losses. However, the difference in the rate of exergy stored in the PCM was mostly negligible. Conversely, increasing the exergetic thermal input had a significantly positive impact on the rate of exergy stored in the PCM.. The exergetic efficiency of the PCM tank varied from 17.5% to 9.2%, with its peak value recorded at a 2.5 LPM flow rate and 1070 W of exergetic input.

A rational strategy for substantially enhancing the solar-utilization efficiency and organic-pollutant-degradation rate via mediated central processing unit filling

Hybrid strategy of utilizing large solar thermal input overlaid with solar electricity for continuous wastewater purification without any catalyst.

Thermodynamic analysis of a CCHP system integrated with a regenerative organic flash cycle

• A new CCHP-ST-OFC system is proposed and thermodynamically analyzed. • Effects of operating parameters on system energy performance were studied. • A negative feedback operation strategy was proposed and adopted in a studied case. • The negative feedback strategy decreases natural gas consumption by 9%. Combined cooling, heating and power (CCHP) systems have received wide attention for their potential of high efficiency and energy conservation. In this work, a novel CCHP system is designed coupling the solar thermal input (ST) system and the regenerative organic flash cycle (OFC) system. The OFC subsystem could recycle two kinds of heat sources to achieve cascade utilization of heat energy. The CCHP-ST-OFC system is evaluated by comparing with the conventional CCHP system and the CCHP-ST-ORC system (organic Rankine cycle). The effects of several operating parameters on the thermodynamic performance are discussed. Based on the negative feedback regulation, an operation strategy is proposed and applied to buildings to verify the thermodynamic economy. The results demonstrate that the electricity and heat provisions are 275.0 kW and 211.5 kW, which are 4.7 kW and 19.3 kW higher than the CCHP-ST-ORC system. The electricity of the OFC subsystem is 15.0 kW and 47% higher than the ORC system. Moreover, changing the smoke outlet temperature in the waste heat recovery equipment could effectively adjust the heat provision and power generation. The trend of the day and night power generation with the mass flow rate of the heat source is reversed. The energy provision and performance increased with the increasing partial load ratio of the internal combustion engine. The building case study reveals that the exergy efficiency of the CCHP-ST-OFC system is 38.7% and the primary energy ratio is 53.1%, respectively. Meanwhile, the natural gas consumption of the CCHP-ST-OFC system is 5.14 × 10 5 m 3 /year, with a 9% reduction than the CCHP-ST-ORC system.

Performance analysis of a RDF gasification and solar thermal energy based CCHP system

Municipal solid wastes (MSW) are, through the amount generated and energy content, one of the energy resources that can successfully contribute to covering energy consumption at local or regional level. The integration of this resource in modern energy systems can increase the penetration of renewable energy resources in energy supply. One of the most promising technologies for converting waste into energy is gasification. As conventional district heating and cooling systems require decarbonization, one solution is the use of waste gasification and solar energy conversion equipment. This paper analysis from an energetic and economic point of view the possibility of using the fuel produced by the gasification of refuse derived fuel (RDF) and solar thermal energy in a gas engine based combined cooling, heating and power generation (CCHP) system to be integrated into a district heating and cooling system. The proposed system can generate 27295685 Nm3/year of producer gas, 14.57 GWh/year of electricity, 32.11 GWh/year of heat and 1.55 GWh/year of chilled water with a solar thermal energy input of 1.15 GWh/year. The capital cost of the CCHP system can be recovered in 9.62 years when solar collector are not used and in 6.19 years when solar collectors are used. By using RDF and solar thermal energy are saved 3567778 Nm3 of natural gas in a year.

Identification and techno-economic assessment of potential enhancement of existing biomass power generators with concentrated solar thermal input

Hybrid power generation systems that combine more than one renewable resource type are a potential option to improve the capability of renewable power generation systems to meet network demands reliably. This increases the system complexity and cost, so this must be compensated by achieving correspondingly higher capacity factors to achieve similar financial performance to simpler systems. In the analysis undertaken, the hybrid systems developed were limited to combinations of biomass combustion and concentrated solar thermal technology for production of steam to feed a Rankine cycle turbine system. To ensure that resource availability was realistic in the study, biomass availability was based on 5 years of historical data for an existing biomass power generation site in Australia that currently has limited seasonal operations and matching solar data for the same location. A technoeconomic assessment was undertaken in parallel with optimization of plant configurations by inclusion of additional plant components and varying sizing. This included plant designs with different storage capacities, both thermal storage for solar energy and torrefaction char from short-term surpluses of biomass. Several system options were identified where financial performance matched the simple biomass combustion system, but with significant increases in capacity factor through hybridization.

Economic analysis and experimental investigation of a direct absorption solar humidification-dehumidification system for decentralized water production

In the present work, a direct absorption solar humidifier (SH) based closed-air loop open-water loop humidification-dehumidification (HDH) desalination system is investigated experimentally. The selection of air-to-water mass flow ratios for this configuration is unknown. Hence, this work characterizes the impact of feed flowrates and recirculating air flowrates to arrive at an operating state that influences the system efficiency for a determined solar thermal input. Performance curves that directly correlate the system’s Gained output ratio (GOR) against humidity-based normalized gain are proposed to enable site selection and performance estimation. Water flowrate has optimal value for the SH-HDH desalination system highlighting a delicate balance between feed water and air flowrates that allows improved heat and mass transfer in the module while minimizing overall thermal losses. A comparison of the performance of the SH-HDH system with a conventional HDH system showed 18.4% improvement. A novel approach by storing the hot water rejected from SH-HDH configuration during on-sun hours for the off-sun operation was considered. The estimated cost of water produced was ranging from 0.007 to 0.035 USD/liter, depending on received solar irradiation and rainfall at the location. Finally, a comparison of GORsolar, cost of desalination, and productivity of the present system are compared with the literature.

Investigating an Integrated Solar Combined Cycle Power Plant

Using solar energy standalone to generate electricity has high investment risk. This is due to the need to energy storage systems to ensure electricity generation during the night. For this reason the hybridization of renewable energy resources and fossil fuel has been motivated. In an Integrated solar combined-cycle (ISCC) the solar thermal energy is integrated into combined cycle gas turbine (CCGT) power plant. The aim of this study is to evaluate the impact of addition of solar energy to a CCGT at both design and off design conditions of solar thermal input and ambient temperature.

Modular micro-trigeneration system for a novel rotatory solar Fresnel collector: A design space analysis

The aim of this paper is to study a new modular micro-scale trigeneration system based on a rotary Fresnel collector, named “SunDial”, under a restricted design space. This system is based on the integration of an organic Rankine cycle with a vapor compression heat pump using miniaturized turbomachinery. Four layouts areoed to maximize the energy supply according to different heat management strategies, as requested by potential end-users. In addition, a working fluid screening is carried out which has lead to the selection of two candidates: isobutane and propane. A consistent system performance metric has been defined in order to coherently asses the configurations conceived. Different degrees of integration between the power cycle and the heat pump are analyzed. The influence of power, heating and cooling supply on the global metrics are studied for each design. Finally, an energy flow sizing is presented for a 15 kWth solar thermal input SunDial module applied to different industrial end-users. Results show that isobutane is preferable when high shares of heating and cooling are required, whereas propane leads to higher power outputs.

Modelling experiments with small-scale thermal system used for pig fattener heating

This study presents the ongoing research conducted in the field of thermal systems which are commonly used in agriculture and also in other fields to utilize the solar thermal energy. This paper describes a small-scale physical system that is controlled by hardware-inthe-loop (HIL) method. The solar thermal input is realized by a heating element, which can provide a 60 W power in total. The input energy is controllable via Pulse Width Modulation (PWM) to mimic the stochastic changes in weather. The heat storage unit is a 1 litre in volume isolated tank, which contains also the heat exchanger unit. The working fluid in this system is water which is forced by custom made peristaltic pumps both on the “collector” side and on the output. In this way the mass flow rate of the pump can be controlled on the heat exchanger and on the user side, as well. The user side is modelled by a water-air heat exchanger forcing cooled air by a varying speed fan. The temperatures are measured on several points of the system which are used to control the flow rates. Experiments were performed with various controlling algorithms in order to find an optimal solution to provide heat for a pig fattener. The recent status of the test results is shown in the case of On-Off and PID control methods in contrary.

The energetic performance of a liquid chemical looping cycle with solar thermal energy storage

A Liquid Chemical Looping cycle Thermal Energy Storage (LCL-TES) with a gas turbine combined cycle is assessed for two different configurations. In the first configuration, the hot gas from the LCL-TES system is transferred directly to the gas turbine, while in the second one the hot gas is heated further by an after-burner. Aspen plus software was used together with MATLAB codes to simulate the cycle for an average diurnal normal irradiance profile of Port-Augusta in South Australia, using copper oxide as the chemical looping medium. The effect of air reactor pressure, concentration ratio of the solar concentrator, conversion extent and thermal input from the after-burner on the cycle efficiency was assessed. Also reported are the solar absorption, solar to electrical efficiency, solar share, and exergy efficiency, together with their sensitivities to relevant input parameters. On this basis, the first law efficiency was estimated to be 44.9% and 50% for the cycle without and with the after-burner, with corresponding temperatures of 1200 °C and 1700 °C, respectively.

Technical and economic evaluation of a solar thermal MgO electrolysis process for magnesium production

We present a techno-economic analysis of a 17,000–18,000 metric tons per year electrolytic process for producing Mg from MgO with and without out a concentrated solar thermal input. The solar thermal input is delivered via power tower technology and the evaporation and condensation of sodium. Energy requirements for the process at scale were based on thermodynamics and an extrapolation of laboratory measurements of the electrochemical kinetic and mass transport parameters via a finite-element numerical model. While technically possible, integrating a solar thermal input does not make economic sense without crediting avoided CO2 emissions. A solar thermal input reduces energy operational costs from $0.654/kg to as low as $ 0.481/kg, but it also lowers the Mg production rate of the electrolytic cells such that more cells are required to achieve production capacity, which, in turn, increases capital and maintenance costs. The net operational savings are negligible. The estimated operational costs to produce Mg are ∼$2.46/kg. At this cost, the process without a solar thermal input is economically tantalizing vis à vis the current commercial processes for producing Mg, and its CO2 emission level is 46% lower than that of the Pidgeon process, currently the predominant method for producing Mg.

A Thermodynamic Model of Solar Thermal Energy Assisted Natural Gas Fired Combined Cycle (NGCC) Power Plant

A solar thermal energy assisted NGCC power plant was modeled to investigate the impact on plant efficiency, output and CO2 emission with solar thermal energy addition. In this particular model, with 23.7 MWth solar thermal energy input to the HRSG, the duct firing could be shut off, 2337.5 kg/h natural gas would be saved, and 6.2 t/hr CO2 emission would be eliminated. However, there would also be a 4.07 MWe loss in power from the combined cycle. Another solar input approach shows 14.35 MWe additional electricity would be generated with 35 MWth solar thermal energy addition. The thermodynamic analyses in this paper demonstrated the possibilities to utilize the solar thermal energy to reduce fuel consumption and CO2 emission, or to increase the NGCC power plant efficiency and output, while taking advantage of the already existing power plant infrastructure.

Analysis of a feasible trigeneration system taking solar energy and biomass as co-feeds

The trigeneration systems are widely used owing to high efficiency, low greenhouse gas emission and high reliability. Especially, those trigeneration systems taking renewable energy as primary input are paid more and more attention. This paper presents a feasible trigeneration system, which realizes biomass and solar energy integrating effective utilization according to energy cascade utilization and energy level upgrading of chemical reaction principle. In the proposed system, the solar energy with mid-and-low temperature converted to the chemical energy of bio-gas through gasification process, then the bio-gas will be taken as the fuel for internal combustion engine (ICE) to generate electricity. The jacket water as a byproduct generated from ICE is utilized in a liquid desiccant unit for providing desiccant capacity. The flue gas is transported into an absorption chiller and heat exchanger consequently, supplying chilled water and domestic hot water. The thermodynamic performance of the trigeneration system was investigated by the help of Aspen plus. The results indicate that the overall energy efficiency and the electrical efficiency of the proposed system in case study are 77.4% and 17.8%, respectively. The introduction of solar energy decreases the consumption of biomass, and the solar thermal energy input fraction is 8.6%. In addition, the primary energy saving ratio and annual total cost saving ratio compared with the separated generation system are 16.7% and 25.9%, respectively.

Thermal window insulation

A definite requirement of the building envelope is to separate the natural environment from the indoor environment. Energy is one component of the environment that we sometimes wish to capture, harness, or reject. How can these actions be best performed to yield passive benefits such as solar heating or shading?This research focuses on control of solar radiation, and the role windows play as transfer medium between indoor and outdoor environments. A timely control of solar thermal energy input, and building thermal energy output with the use of operable window insulation is investigated during the heating season in the local Toronto climate.This is done through a combination of 3D finite element mathematical model and field performance tests. Model results and field tests reveal an energy imbalance attributed to unpredictable solar gains and spectrally-dependent emissivity of materials. Simulation results of the daily control show little improvement over use of a static system for a western building façade. The negligible difference versus a static system is attributed largely to human-error deficiencies associated with timely controls.

Thermodynamic evaluation of solar integration into a natural gas combined cycle power plant

The term integrated solar combined-cycle (ISCC) has been used to define the combination of solar thermal energy into a natural gas combined-cycle (NGCC) power plant. Based on a detailed thermodynamic cycle model for a reference ISCC plant, the impact of solar addition is thoroughly evaluated for a wide range of input parameters such as solar thermal input and ambient temperature. It is shown that solar hybridization into an NGCC plant may give rise to a substantial benefit from a thermodynamic point of view. The work here also indicates that a significant solar contribution may be achieved in an ISCC plant, thus implying substantial fuel savings and environmental benefits.

Experience on the Development of a Thermo-chemical Storage System Based on Aqueous Sodium Hydroxide

Closed sorption heat storage opens up a way to achieve seasonal thermal storage without loss during storage. Thermal energy is not stored as sensible heat or latent heat, but by the separation of substances. In this manner it is possible to store heat, or better said, the potential to regain heat.Such a system functioning as an absorption heat pump with intermediate storage is well suited for long term thermal energy storage. Nevertheless, the conversion losses in both the regenerating and heating process make it inferior to sensible thermal storage for short storage cycles. For this reason a hybrid system including a water tank as sensible thermal storage to cover the thermal demands of several days, and a closed sorption heat storage to cover longer periods of insufficient solar thermal input is proposed.The storage system energy density is directly proportional to the sorbate mass difference between regenerated and diluted sorbent. In order to reach high utilization, a large dilution in the sorbent must be reached during heating mode. Thus, the operating temperature parameters must be adjusted and regulated accordingly.In the scope of the EU funded project COMTES, a prototype system based on the working pair sodium hydroxide and water is under construction. The system is dimensioned to cover space heating as well as domestic hot water in a single family house in Zurich, built to passive energy standards. The prototype is starting operation in spring 2014 whereby the system is regenerated to be ready to cover the heating demands the following winter.

Effect of Variable Guide Vanes and Natural Gas Hybridization for Accommodating Fluctuations in Solar Input to a Gas Turbine

In recent years, several prototype solar central receivers have been experimentally demonstrated to produce high temperature and high pressure gas capable of driving a gas turbine engine. While these prototype receivers are generally small (<1 MWth), advancements in this technology will allow for the development of solar powered gas turbine engines at a commercial level (sizes of at least several megawatts electric (MWe)). The current paper analyzes a recuperated solar powered gas turbine engine, and addresses engine considerations, such as material limitations, as well as the variable nature of solar input. In order to compensate for changes in solar input, two operational strategies are identified and analyzed. The first is hybridization, meaning the solar input is supplemented via the combustion of fossil fuels. Hybridization often allows for an increase in net power and efficiency by adding heat during periods of low solar thermal input. An alternative strategy is to make use of variable guide vanes on the compressor of the gas turbine engine, which schedule to change the air flow rate into the system. By altering the mass flow rate of air, and assuming a fixed level of heat addition, the operating temperature of the engine can be controlled to maximize power or efficiency. The paper examines how to combine hybridization with variable guide vane operation to optimize gas turbine performance over a wide range of solar thermal input, from zero solar input to solar-only operation. A large material constraint is posed by the combustor, and to address this concern two alternative strategies—one employing a bypass valve and the other a combustor modified to allow higher temperature inlet air—are presented. Combustor modifications could include new materials and/or increased cooling air. The two strategies (bypass versus no bypass) are compared on a thermodynamic basis. It is found that it is possible to operate the gas turbine across the entire range without a significant drop in performance in either design through judicious adjustment of the vanes, though both approaches yield different results for certain ranges of solar input. Finally, a yearly assessment of solar share and thermodynamic performance is presented for a 4.3 MWe gas turbine to identify the overall benefits of the operational strategies. The annualized thermodynamic performance is not appreciably different for the two strategies, so that other factors such as mechanical design, operational issues, economics, etc. must be used to decide the optimal approach.

Thermal analysis and measurement of a solar pond prototype to study the non-convective zone salt gradient stability

Solar ponds combine solar energy collection with long-term storage and can provide reliable thermal energy at temperature ranges from 50 to 90°C. A solar pond consists of three distinct zones. The first zone, which is located at the top of the pond and contains the less dense saltwater mixture, is the absorption and transmission region, also known as the upper convective zone (UCZ). The second zone, which contains a variation of saltwater densities increasing with depth, is the gradient zone or non-convective zone (NCZ). The last zone is the storage zone or lower convective zone (LCZ). In this region, the density is uniform and near saturation. The stability of a solar pond prototype was experimentally performed. The setup is composed of an acrylic tube with a hot plate emulating the solar thermal energy input. A study of various salinity gradients was performed based on the Stability Margin Number (SMN) criterion, which is used to satisfy the dynamic stability criterion. It was observed that erosion of the NCZ was accelerated due to mass diffusion and convection in the LCZ. It can be determined that for this prototype the density of the NCZ is greatly affected as the SMN reaches 1.5.