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There are three main alternatives for the improvement of heat transfer in phase change materials (PCM) such as the use of additives, support matrices and customized designs for heat exchangers. The first two alternatives imply incurring additional material costs, as well as a decrease in the specific heat storage capacity by using components that remain solid during the process. The present work therefore sought to study the effect of the use of a coil shell heat exchanger with a square cross section on natural convection during the melting process of hydrogenated palm stearin. Three different sections of the profile called square profile, U-profile, and L-profile and two types of material, copper, and stainless steel, were studied. A test bench was built with a capacity of 5 kg of this PCM, implementing a hot water recirculation system with flow and temperature measurement and including 9 temperature sensors inside the PCM. The melting process was conducted by recirculating water with a temperature of 75° C and a flow rate of 2 L/min. The results show a marked effect of natural convection on the melting process, presenting characteristic profiles for this phenomenon. It was found that the highest temperatures are recorded in the upper part of the PCM and that the heat transfer in the solid material is appreciably low. The results allow us to identify for each profile, the zones in which heat transfer is relatively high because of natural convection and those zones that require the use of additives or support matrices. It is therefore expected to contribute to the design of more efficient and lower commercial cost configurations. [ABSTRACT FROM AUTHOR]

The search for new phase change materials (PCM) of renewable origin and low cost, as an alternative to the use of paraffin wax, contributes to the environmental resilience of solar thermal energy systems. An important source of PCMs of renewable origin are vegetable oils and fats, especially those with established agro-industrial chains. Globally, palm oil has positioned as an indispensable product in many industrial sectors. One of the main by-products of palm oil refining is palm stearin, which can be hydrogenated to improve its thermal properties. This paper presents the results of the performance of a Solar thermal energy storage system (STESS) located in a Colombian paramo area with an altitude of 3,200 m.a.s.l. The system store heat in 550 kg of Hydrogenated Palm Stearin (HPS), contained in a rectangular vessel, which allow to supply hot water and space heating for a country house. The average ambient temperature is 12°C during the day and 7°C at night. This experimental station implements a robust measurement and control system including 39 PT-100 type temperature sensors, and different actuators connected to a control system based on Arduino and Raspberry Pi devices. This configuration permit also to implement a remote monitoring system. The constructed STESS employs 140 collector tubes, running at a maximum temperature of 95°C. According to the energy load tests during a period of 7 hours of operation, approximately 40.0 MJ were stored as heat in the hydrogenated palm stearin. For the same period, the heat transfer fluid received approximately 170 MJ of energy. In subsequent discharge tests, the heat stored in the HPS allowed the ambient temperature inside the room to be maintained 8°C above the external ambient temperature for up to 8 hours during the night, demonstrating the technical feasibility of using this new PCM from renewable sources. [ABSTRACT FROM AUTHOR]

In order to mitigate the effects of climate change, contribute to energy autarky and improve the quality of life of the population, Colombia has adopted the energy transition to renewable energy as a state policy. In this context, the use of solar thermal energy, which is abundant in the tropical zone, should be considered as one of the alternatives to be prioritised. A solar thermal energy storage system (STESS) has been developed for the supply of hot water and heating in paramo areas. The system is capable of storing energy in the form of latent heat using a renewable phase change material (PCM). The PCM reaches a maximum temperature of 70° C, allowing enough energy to be stored to take several hot showers and maintain a comfortable temperature in a room. This paper evaluates the performance of the developed STESS from a financial point of view, analysing the associated capital and operational costs. It is also compared with alternative technologies available in the area based on electric heaters and propane gas heaters. The operating cost analysis concludes that the performance of the STESS allows savings of variable operation cost up to 90 % compared to electric energy-based systems. These results become even more relevant considering that many of these areas are not connected to the national electricity grid and almost none of them have a reliable supply of propane gas. Regarding capital costs, although STESS requires an initial investment up to 20 times the value of alternative systems, its long lifetime, low operating costs and reliability make it an attractive alternative in this scenario. [ABSTRACT FROM AUTHOR]

The operation of a power plant based on solar energy can vary significantly with time because of the intrinsic intermittency of the energy resource. Hence, a smart management is required to deal with the complex dynamic variations of the different subsystems. In order to do that, different control logics can be implemented but their effectiveness strictly depends on the temporal evolution of the parameters considered. For a given plant configuration, their exact estimation can be obtained through experimental tests during the commissioning of the plant. However, any change in the design parameters of the plant reflects in a different time constant, whose preliminary knowledge may be of support in tuning the control logic of the plant during the design stage. Therefore, based on the configuration of a small-scale concentrated solar combined heat and power plant as designed and built under the EU funded project Innova MicroSolar by several universities and companies, in this study a prediction of the time constant of several plant configurations with varying solar multiple and size of the storage tank is performed. By making use of the dynamic simulator previously developed by some of the authors, an estimation of such characteristic is assessed in case of potential redesign of the plant, providing also useful suggestions into the design of the control logic.

Despite the rapid growth in the uptake of renewable energy technologies, the educational profile and the skills gained at University level do not always comply with the practical needs of the organisations working in the field. Furthermore, even though the residential sector has very high potential in curbing its CO2 emissions worldwide thus meeting the challenging goals set out by the international agreements, such reduction has been limited so far. Within this context, the ‘Skybelt’ project, co-funded by the EU under the framework of the Erasmus + programme aims at enhancing in several Universities of Asia and Europe the engineering skills of students of all level for application of sustainable renewable energy solutions in the built environment. With the target of increasing the employability of graduates and the impact of the project, a survey on the labour market needs for specialists with enhanced knowledge and skills in the topic of the project has been conducted in the related Asian countries. Hence, relevant industries, labour market organisations and other stakeholders have been interviewed and the main results of this analysis is reported in the present paper. As first outcome of this activity, the obtained results have been considered in the selection of the modules to be improved according to a student centred study approach.

Many energies management and storage technologies use phase change materials (PCM) to increase process efficiency. Technologies such as solar thermal energy storage, passive temperature management in buildings, even the development of high-performance sportswear employ various types of PCM. Phase change materials can be classified according to the working temperature, their nature or the phase transition, highlighting the use of materials of renewable origin. There are different methodologies to modify the properties of PCM, among which the preparation of eutectic mixtures stands out. This is a technique that allows obtaining PCM with a lower melting temperature than that of the initial components. Considering the above, this work presents the thermal characterization of mixtures of palm stearin, hydrogenated palm stearin, beeswax, and paraffin wax in order to evaluate the heat storage potential of the resulting products. Mixing ratios of 80:20, 65:35, 50:50, 35:65 and 20:80 were evaluated. Melting and crystallisation temperatures and enthalpies and their solid and liquid heat capacities were measured by differential scanning calorimetry. The thermal stability of the mixtures was also determined by thermogravimetric analysis. From the results obtained, the PCM obtained by mixing beeswax and hydrogenated palm stearin, which presents its eutectic melting point for the mixture ratio of 50:50 with a temperature of 56 °C and an enthalpy of fusion of 264 kJ/kg, stands out. [ABSTRACT FROM AUTHOR]

Palm stearin is the heavy fraction obtained during palm oil refining. It consists mainly of saturated fatty acids and is often an unwanted by-product that reduces the economic efficiency of the processes. Although it is currently used in the manufacture of margarine or industrial vegetable fats, the increase in palm oil production will lead to higher production of palm stearin. The composition, low cost and physicochemical characteristics of palm stearin make it an ideal raw material for obtaining phase change materials for thermal energy storage in solar thermal energy systems. This work explores the esterification of hydrogenated palm stearin (HPS) for obtaining phase change materials with suitable properties for application. The esterification conditions were studied using low and high molecular weight alcohols, like ethanol, butanol and cetyl alcohol, according to Fischer's esterification principles. The esters formation was characterized by attenuated total reflectance infrared spectroscopy. For both HPS and products obtained, melting and solidification temperatures and enthalpies, and heat capacity were determined by DSC according to ASTME793-06(2018) and ASTME1269-11(2018). A crude wax was obtained by esterification of the fatty acids present in palm stearin in all cases. Among the esters produced, the one obtained by using cetyl alcohol, which has a melting temperature of 55.9 °C and an enthalpy of fusion of 257.26 kJ/kg, stands out. This novel PCM is presumed to have an optimal performance for heat storage applications in low temperature solar thermal systems (50°C - 90°C), for hot water supply and space conditioning. [ABSTRACT FROM AUTHOR]

This paper presents the feasibility analysis of a small-scale low-temperature solar organic Rankine cycle power system. The heat transfer fluid for running the organic Rankine cycle system is hot water with a temperature of 120 °C provided by an array of evacuated tube solar collectors. The performance of the solar organic Rankine cycle system was investigated using two different working fluids over a wide range of the evaporation temperature. Technical and economic indicators such as the required solar collector aperture area, the total heat transfer surface area of the heat exchangers and the volume flow ratio between the outlet and inlet of the expander are among the key parameters used to evaluate the solar organic Rankine cycle. Thermolib toolbox 5.2 in conjunction with MATLAB/Simulink was used to predict the variation of the system performance. The results showed that the solar organic Rankine cycle system is able to achieve an overall system efficiency of 6.75% using a relatively low-temperature heat source. The results also showed that the solar organic Rankine cycle system requires smaller evacuated tube solar collector and heat exchanger areas when R245fa is used as the working fluid. [ABSTRACT FROM AUTHOR]

Thermal energy storage is considered as one the most perspective technologies for increasing the efficiency of energy conversion processes and effective utilization of available sources of heat. Advantages and technical attractiveness of the thermal energy storing have resulted in continuously increasing numbers of research activities, especially in the last four decades. Among various applications of thermal energy storage, the heat or cold accumulation in the temperature range from −50 °C to 120 °C has a greater market potential and this can be carried out using a wide range of phase change latent heat materials. Among these materials the salt hydrates deserve a special attention and currently a large number of phase change compositions based on salt hydrates are produced commercially and available on the market. However, reliable data on thermophysical properties as well as their thermal stability over their lifetime is required to build effective storage systems. Currently this data is insufficient and is scattered across numerous sources that are often difficult to access for potential consumers. This paper summarises practically all available original experimental data on the phase change diagram of salt–water systems, melting temperatures, heat of fusion, specific heat, density, thermal conductivity, and thermal diffusivity in solid and liquid states and viscosity in the liquid state for 18 salt hydrates. The above information is provided for major market products on the basis of the salt hydrates for latent heat storage. The wholesale prices for pure salt, salt hydrates, and salt hydrate heat storage compositions are also additionally discussed. [ABSTRACT FROM AUTHOR]

Pakistan is among the countries that have already crossed the water scarcity line, and the situation is worsened due to the recent pandemic. This is because the major budget of the country is shifted to primary healthcare activities from other development projects that included water treatment and transportation infrastructure. Consequently, water-borne diseases have increased drastically in the past few months. Therefore, there is a dire need to address this issue on a priority basis to ameliorate the worsening situation. One possible solution is to shift the focus/load from mega-projects that require a plethora of resources, money, and time to small domestic-scale systems for water treatment. For this purpose, domestic-scale solar stills are designed, fabricated, and tested in one of the harshest climatic condition areas of Pakistan, Rahim Yar Khan. A comprehensive overview of the regional climatology, including wind speed, solar potential, and ambient temperature is presented for the whole year. The analysis shows that the proposed system can adequately resolve the drinking water problems of deprived areas of Pakistan. The average water productivity of 1.5 L/d/m2 is achieved with a total investment of PKR 3000 (<$20). This real site testing data will serve as a guideline for similar system design in other arid areas globally. [ABSTRACT FROM AUTHOR]