Low-temperature Solar Thermal Energy Research Articles

Performance investigation and evaluation of a low-temperature solar thermal energy storage system under dynamic weather conditions

Designed and operational parameters matter greatly in how successful an energy storage system performs. However, a current challenge in matching suitable these parameters lies in the poor understanding of such systems’ performance under dynamic weather conditions. In this paper, we investigated a phase change material (PCM) storage unit that is particularly aimed for poor-solar areas, and connected the unit to a flat plate solar collector to establish a complete solar thermal energy storage system (STESS). To optimize the system performance, different grades of solar radiation and outdoor ambient temperatures are introduced, and the effects of heat transfer fluid (HTF) flow rates and solar collecting areas are investigated numerically through multiple performance evaluation parameters. The results indicate that the solar collecting area has a significant effect on the performance of the STESS compared to that of the water flow rate. And different collecting areas of 1 m2, 1.5 m2, and 3 m2 with an optimal water flow rate of 0.06 m3/h are matched to different average daily solar radiation of 203.4 W/m2, 155.2 W/m2, 92.7 W/m2, respectively. Further for the heat release process, different heat release efficiencies from 88.32 % to 97.12 % with different energy consumption of the fan from 0.003 kWh to 0.063 kWh are obtained when the air flow rate is increased from 30 m3/h to 90 m3/h. One of the air flow rates of 60 m3/h is superior for the STESS considering higher heat release efficiency and lower energy consumption of the fan. The findings of this paper will contribute to optimizing the performance of a STESS in practical applications.

Impact of Solar Thermal Energy on the Energy Matrix under Equatorial Andean Context

Low-temperature solar thermal energy is a viable and mature alternative to reduce the use of fossil fuels for domestic hot water heating. The impact of the inclusion of this technology in the energy matrix in the Andean city of Cuenca, Ecuador, is analyzed. In Ecuador, liquefied petroleum gas (LPG) is currently used to heat water due to the high state subsidy, with a cost of 0, 11 USD for an LPG kg compared to the international price of 1.18 USD a Kg of LPG in 2021. Sustainability indicators show that the urban energy matrix would be minimally affected by a high penetration of solar thermal systems. The indicators that are positively affected are related to energy self-sufficiency, emissions, and employment at the expense of an increase in the cost of energy. Moreover, the analysis of the impact on consumption exclusively in the residential sector shows that liquefied petroleum gas consumption would drop from 73 to 64%, mainly because the liquefied gas is used in cooking. However, the change in technology is limited by the subsidized cost of liquefied petroleum gas, which makes the adoption of this technology difficult in the current state

Simultaneous Production of Solar Thermal Heat and Power for Industrial Applications

Currently most of the energy production is supported by fossil fuels, however, renewable sources contribution on worldwide demand of energy has been in constantly growth. One of the main challenges in the use of solar thermal energy in industrial processes is their cost, especially when is compared to energy generation by fossil fuels. This cost delimits the investment payback time for a thermo-solar installation to be feasible. This fact makes crucial the development of methodologies for the integration of solar energy for large-scale industrial applications. This work deals with the thermo-economic evaluation of the heat and power production through a low-temperature flat-plate solar collector system. Also, strategies were developed to increase energy efficiency by evaluating different process integration scenarios. The proposed strategies for energy efficiency combined with renewable energy were applied to an integrated solar thermal energy system into a 1G and 2G (first and second generation) bioethanol process from sugarcane. It was found that to replace the fully process heat and power with low-temperature solar thermal energy, a heat recovery network ? ?? ?????? of 5 °C, a heat duty of 131 kW and a supply temperature of 105 °C are required. All these results lead to a cost of 0.2112 USD/kWh of the integrated system. The power system operates independently by mean an Organic Rankine Cycle and the heating system is supplied by a solar collector network with a cost of 0.0477 USD/kWhele.

RETRACTED: Development of correlations for Nusselt number and friction factor of packed bed solar thermal energy storage system having spheres with pores as packing elements

Solar energy is an emerging alternative of fossil fuels to fulfill the global energy demand as it is available in plenty and eco-friendly in behaviour. However, solar energy systems requires storage unit due to its intermittent nature. The packed bed storage system (PBSS) as storage unit is considered to be a feasible option for solar thermal energy systems having operating temperature range under 100°C. The heat transfer and pressure drop within PBSS are influenced by shape of packing element as convective heat transfer coefficient is a function of it. Under the current study, correlations are developed for Nusselt number as well as friction factor using the results obtained through experimental investigation for the PBSS built up of spherical shaped packing elements having pores on the surface. The developed correlations are the function of Reynolds number, ratio of pore diameter to sphere diameter (d/D), perforation index (PI) and ratio of pore depth to sphere diameter (t/D) within range of 200 to 800, 0.066 to 0.2, 0.06 to 0.22 and 0.05 to 0.2, respectively. Values obtained from the developed correlations are compared with the values obtained through experimentations and it is found that the correlations for Nusselt number and friction factor can predict the values with mean absolute deviation of 6.7% and 7.5%, respectively. These correlations may be helpful for the researchers working in the same research area and manufacturers developing the low temperature solar thermal energy systems. This study may also be useful to investigate the effect of similar shape of packing elements in latent heat based PBSSs.

Energy and exergy parameters of low-temperature solar thermal energy storage systems: empirical estimation and optimisation

This study presents the energy and exergy analyses of three low-temperature solar thermal energy storage (STES) systems. These STESs were of the same design but, contained different heat storage materials (benzoic acid, stearic acid and palm olein) evaluated during heat charging and discharging periods. The energy and exergy inputs and outputs were analysed and factored to estimate the efficiencies during heat charging, while the energy and exergy drop during heat discharge were also estimated. The energy and exergy outputs were optimised using a set constraint employed on Design-Expert 11 software. The energy and exergy outputs ranged between 25.89-95.96 W and 13.15-52.37 W, respectively, depending on the type of heat storage materials used. Under optimised conditions, the energy and exergy outputs increased to 117.1-202.7 W and 81.2-107.5 W, respectively. The STESs were found to have a positive and significant effect on the energy and exergy efficiencies and the energy and exergy drop. The quantity of water heated only affected the energy and exergy drop. This paper reveals that the energy and exergy parameters of a solar thermal system can be optimised by the integration of a STES.

Energy and exergy parameters of low-temperature solar thermal energy storage systems: empirical estimation and optimisation

This study presents the energy and exergy analyses of three low-temperature solar thermal energy storage (STES) systems. These STESs were of the same design but, contained different heat storage materials (benzoic acid, stearic acid and palm olein) evaluated during heat charging and discharging periods. The energy and exergy inputs and outputs were analysed and factored to estimate the efficiencies during heat charging, while the energy and exergy drop during heat discharge were also estimated. The energy and exergy outputs were optimised using a set constraint employed on Design-Expert 11 software. The energy and exergy outputs ranged between 25.89-95.96 W and 13.15-52.37 W, respectively, depending on the type of heat storage materials used. Under optimised conditions, the energy and exergy outputs increased to 117.1-202.7 W and 81.2-107.5 W, respectively. The STESs were found to have a positive and significant effect on the energy and exergy efficiencies and the energy and exergy drop. The quantity of water heated only affected the energy and exergy drop. This paper reveals that the energy and exergy parameters of a solar thermal system can be optimised by the integration of a STES.

Performance Results of a Solar Adsorption Cooling and Heating Unit

The high environmental impact of conventional methods of cooling and heating increased the need for renewable energy deployment for covering thermal loads. Toward that direction, the proposed system aims at offering an efficient solar powered alternative, coupling a zeolite–water adsorption chiller with a conventional vapor compression cycle. The system is designed to operate under intermittent heat supply of low-temperature solar thermal energy (<90 °C) provided by evacuated tube collectors. A prototype was developed and tested in cooling mode operation. The results from the testing of separate components showed that the adsorption chiller was operating efficiently, achieving a maximum coefficient of performance (COP) of 0.65. With respect to the combined performance of the system, evaluated on a typical week of summer in Athens, the maximum reported COP was approximately 0.575, mainly due to the lower driving temperatures with a range of 75 °C. The corresponding mean energy efficiency ratio (EER) obtained was 5.8.

Efficient Production of Biogas through Heating the Substrate with Low Temperature Solar Thermal Energy

Este proyecto de investigación tiene la finalidad de mejorar la producción de biogás mediante el calentamiento del sustrato (lodo), con energía solar térmica de baja temperatura inferior a los 100°C. Para calentar una masa biodegradable de 693 kg, compuesta por estiércol de vacuno, pennisetum clandestinum, urea y agua, se utilizaron 6 colectores planos (CSP) con potencia térmica total de 6000 W, orientados al sur y ángulo de inclinación de 20°en una región de latitud −0.3°. El agua caliente sanitaria (ACS) ingresa a la región anular del digestor a una temperatura promedio de 35°C logrando mantener la fermentación anaeróbica durante el día y la noche a una temperatura cercana a los 26°C, dentro del rango mesofílico. El equipo utilizado para el ensayo es un digestor de cilindros concéntricos construido en acero al carbono. El sustrato y el gasómetro se localizan en la parte interna del recipiente y el agua caliente circula por la pared anular del tanque que se encuentra aislado por el exterior para reducir las pérdidas térmicas al ambiente. Por otra parte, para determinar de manera indirecta la producción eficiente de biogás, se utiliza una variable física: la presión interna del recipiente que contiene el gas generado. En el trascurso de 30 días de retención hidráulica (TRH), se logra un incremento en la presión interna de 4.8 PSI/día, en forma lineal. Esta nueva alternativa para producir biogás puede ser útil en los sectores agrícolas y ganaderos para la obtención de biocombustible.

Experimental investigation on a novel triple heat sources-driven absorption heat pump system

This paper presents a novel triple heat sources-driven absorption heat pump system. The exhaust gas is used as the heat source for a high-pressure generator. The superheated refrigerant vapor generated by the high-pressure generator is used for heating the solution in the low-pressure generator 1 by releasing the latent and sensible heat. The low-temperature solar thermal energy serves as the heat source of the low-pressure generator 2. The geothermal energy supplies heat to the evaporator. Heat discharged from the condenser and the absorber is supplied to the air conditioner heat medium water. The high- and low-pressure generators are coupled to each other through an ejector. The introduction of the ejector reduces the pressure of the low pressure generator 2 below the condensing pressure so that the lower temperature solar thermal energy can be utilized. An experimental setup for this heat pump cycle is built, and an experimental investigation is carried out. The influences of the independent variables on the key internal operating parameters and heating performance have been investigated. Experimental studies show that when the hot air temperature is 213 °C and the temperature of the hot water is 43.5 °C, a heating capacity of 26.6 kW can be achieved with a heating performance coefficient greater than 1.7. In this way, an efficient and full use of waste heat is realized, and the results can provide an important basis for the design and wide application of low-temperature solar thermal and geothermal energy.

Modelling and dynamic simulation of a hybrid liquid desiccant system regenerated with solar energy

The combination of liquid desiccant systems with conventional vapour compression chillers, usually known as hybrid liquid desiccant systems (HLDS), is a promising alternative when temperature and humidity need to be controlled in air conditioning applications. One of the advantages of this technology is that different kinds of energy can be integrated, particularly low temperature solar thermal energy, which can reduce the electrical consumption of the system. These kinds of systems are typically analysed by discrete steady-state simulations, which show how the system behaves in design conditions. However, dynamic simulations can provide information about the seasonal performance and help to set an appropriate control strategy. This paper describes the modelling and dynamic simulation of an HLDS using Trnsys. Because there are non-standard components for the main elements of a liquid desiccant subsystem (LDS), an alternative modelling method based on performance tables has been developed. The simulation is carried out for Kuala Lumpur, a city with high humidity and ambient temperatures, where air conditioning is required throughout the year. The control strategy is also defined. Finally a sensitivity analysis is performed for the case analysed.

Palmitic acid/polypyrrole composites as form-stable phase change materials for thermal energy storage

In this study a novel palmitic acid (PA)/polypyrrole (PPy) form-stable PCMs were readily prepared by in situ polymerization method. PA was used as thermal energy storage material and PPy was operated as supporting material. Form-stable PCMs were investigated by SEM (scanning electron microscopy) and FTIR (Fourier transform infrared spectrometer) analysis that illustrated PA Particles were wrapped by PPy particles. XRD (X-ray diffractometer) was used for crystalline phase of PA/PPy composites. Thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC) were used for investigating Thermal stability and thermal energy storage properties of prepared form-stable PCMs. According to the obtained results the form stable PCMs exhibited favorable thermal stability in terms of their phase change temperature. The form-stable PCMs (79.9wt% loading of PA) were considered as the highest loading PCM with desirable latent heat storage of 166.3J/g and good thermal stability. Accelerated thermal cycling tests also showed that form stable PCM had an acceptable thermal reliability. As a consequence of acceptable thermal properties, thermal stability and chemical stability, we can consider the new kind of form stable PCMs for low temperature solar thermal energy storage applications.

El uso eficiente de la energía eléctrica en los ingenios azucareros como contribución al desarrollo sostenible de Nicaragua

<p>En este artículo se aborda cómo el uso eficiente de la energía eléctrica contribuiría al desarrollo sostenible de Nicaragua y, por ende, a un cambio en la cultura de su utilización por parte del sector industrial, específicamente en los ingenios azucareros. En la actualidad, en Nicaragua se usan principalmente combustibles fósiles para generar energía eléctrica, lo cual causa contaminación ambiental, así como dependencia económica y tecnológica. Esto evidencia la necesidad de gestar un cambio de cultura que implique una forma de consumo eficiente y racional de la energía eléctrica. Para mejorar la eficiencia en el consumo de energía eléctrica y disminuir la alta intensidad energética, se requiere una gestión integral de energía que permita su ahorro. Además, se propone el empleo de tecnologías alternativas, tales como la cogeneración, la energía solar pasiva o la arquitectura bioclimática, domótica y la energía solar térmica de baja temperatura. Por lo tanto, se plantea el cambio de la cultura del uso de la energía, con el fin de emplearla eficientemente y, además, aprovechar otras formas alternativas de energía. Finalmente, se considera necesario educar con nuevos valores a los consumidores para construir una nueva cultura energética y ambiental que permita el aumento de la productividad, la competitividad y la reducción de impactos ambientales negativos derivados de la generación de energía eléctrica usando combustibles fósiles.</p>

Preparation and thermal energy storage behaviour of stearic acid–TiO2 nanofluids as a phase change material for solar heating systems

This paper investigates the phase change behaviour of newly prepared stearic acid–TiO2 nanofluids as composite phase change materials (PCMs). TiO2 nanoparticles of 0.05, 0.1, 0.15, 0.2, 0.25, 0.3wt% were dispersed in stearic acid, individually. The phase change temperatures and latent heats of nanofluids for melting and solidification processes were determined by differential scanning calorimetry (DSC). The complete melting and solidification times of nanofluids were reduced by 7.03, 12.56, 19.59, 28.64, 35.17, 43.72% and 6.62, 13.57, 20.53, 26.82, 34.11, 41.39% for 0.05, 0.1, 0.15, 0.2, 0.25, 0.3wt% TiO2 nanoparticles, respectively. Time reductions of both the processes proved thermal conductivity enhancement of nanofluids and it was ascertained with laser flash analyzer (LFA) measurements. Based on the results, stearic acid based composites could be recommended as potential candidate for low temperature solar thermal energy storage applications due to their better thermal reliability, chemical stability and heat transfer characteristics.

Experimental investigation of methanol decomposition with mid- and low-temperature solar thermal energy

Mid- and low-temperature solar thermal energy can be transformed into chemical energy of the syngas by the endothermic reaction of the methanol decomposition. This process can overcome the disadvantages such as the low energy density, the intermission and the unequal distribution in the utilization of solar energy. In this study, a mid- and low-temperature solar receiver/reactor prototype of 5 kW was fabricated, which was installed along the focal line of a one-axis parabolic trough concentrator. The integration principle of the solar thermal energy and the thermochemical process for the solar receiver/reactor was also proposed. The kinetic characteristics of the methanol decomposition and the energy conversion in the mid- and low-temperature solar thermochemical process were investigated. Some encouraging results, such as the methanol conversion could reach more than 90%, the H2 selectivity is in the range of 50–99%, the mole concentration of syngas is about 35–95% and the efficiency of the solar thermal energy converted into the chemical energy approximates 60%, are obtained. As a result, the promising approach can be introduced for effectively utilizing the mid- and low-temperature solar thermal energy by means of the solar thermochemical process. Copyright © 2010 John Wiley & Sons, Ltd.

Performance analysis of a mid- and low-temperature solar receiver/reactor for hydrogen production with methanol steam reforming

Mid- and low-temperature solar thermochemical hydrogen production is considered as a promising field in the utilization of solar thermal applications. In this paper, a novel solar thermochemical receiver/reactor, which combines a tubular reactor and a parabolic trough collector (PTC) with the evacuated tubular receiver, was investigated. A non-isothermal model, based on a model of thermal energy loss from a PTC and a complex kinetic model of methanol steam reforming employing the Cu/ZnO/Al2O3 catalyst, was developed to analyze the performance of the mid- and low-temperature solar receiver/reactor for the new approach to solar hydrogen production. It is found that the catalytic bed temperature increased with the increment of the solar radiation. The factors influencing the hydrogen production, such as the feeding rates of the reactants, the solar radiation, the inlet temperature of the solar receiver/reactor, and the mole ratios of water to methanol, were investigated in detail. In the range of the solar radiation considered in this work, the solar thermochemical efficiency exceeds 50%, which is very competitive when compared with other high-temperature solar reactors. The inlet temperature of the solar receiver/reactor has a small impact on the hydrogen production for the whole solar reactor. At a mole ratio of water to methanol of 1, solar collector area of 600 m2 and a reactant feeding inlet-temperature of 423 K, the maximal hydrogen production capacity of the whole solar receiver/reactor can reach 54 kmol h−1 under the solar radiation intensity of 1000 W m−2. The encouraging results indicate a promising approach for the effective utilization of mid- and low-temperature solar thermal energy via the solar thermochemical process. Copyright © 2010 John Wiley & Sons, Ltd.

Use of flat plate solar collectors and parabolic trough concentrators for greenhouse soil disinfestation

The aim of the present work was to investigate the use of low and medium temperature active solar energy systems for the disinfestation of greenhouse soils. Four flat plate solar collectors (low-temperature solar thermal energy devices) and six parabolic trough concentrators (medium-temperature solar thermal energy devices) were used to heat water, which, via a buried heat exchange system, was used to heat the soil of greenhouse plots. These treatments were compared to no solar (control) and solarized (using a 50 micro m-thick transparent polyethylene sheet) plots. Experiments performed in the summers of 2004 and 2005 showed that: 1) the temperatures reached and the energy accumulated in the soil - and therefore the disinfestation capacity - were greater with either of the active solar treatments (40-60 deg C and 10.222.438-18.102.054 J, respectively) than with solarization (< 40 deg C and 6.628.760 J, respectively) and 2) the temperatures reached using the parabolic trough concentrators (50-60 deg C) were higher than those achieved with the flat plate solar collectors (40-50 deg C). The soil temperatures reached suggest these systems could be used to disinfest greenhouse soils.