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Phase change materials (PCM) are promising technology to store thermal energy at a constant temperature. A large amount of energy can be stored or released in latent heat form during the transition of material from one phase to another. Despite the great benefits, most PCMs have their own limitations i.e., low phase change enthalpy, poor specific heat and thermal conductivity, supercooling, volume change, phase segregation, etc. Consequently, efficient thermal energy storage requires improving the thermophysical properties of PCMs. The present study is a comprehensive review of existing techniques for PCMs thermophysical properties enhancement. The research progresses on adding zero, one, two, and three-dimensionally structured additives to PCM is assessed to improve the thermal transport by enhancing the PCM effective thermal conductivity. The enhancement of latent heat of fusion and specific heat using various additives is also discussed. Further, the latest techniques on supercooling and phase segregation reduction are also presented. Last, the modelling of the novel composite materials formed by combining a PCM with other materials is presented. Despite the fact that the majority of these methods are still in the research and development stage, some of them have the potential to be commercialized in the near future. Reliable and efficient PCMs are exceptionally useful for storing solar energy and industrial waste heat, especially for constant temperature applications.

Building integrated photovoltaics (BIPV) coupled with phase change materials (PCM) (BIPV/PCM) provide opportunities for reducing the photovoltaic (PV) panel temperature to increase the overall efficiency of the BIPV, while also transferring the extracted heat for building energy load management. A comprehensive numerical study is conducted to simulate the effects of different BIPV design parameters namely, BIPV height ( H ), air gap between BIPV/PCM and wall ( δ Air ), PCM thickness ( δ PCM ), and air mass flow rate ( m ) on the maximum PV panel temperature, the power production by the PV, and the energy extracted by the air. Optimum BIPV/PCM designs are derived from the studies for three different phase change materials, with the goal of maximizing the total energy from photovoltaics (EPV) and extracted heat (Eair), subject to the constraint of keeping the maximum PV panel temperature to within acceptable values. From the obtained results it is concluded that for the selected range of parameters, the optimum values of δ PCM , H , δ Air and m are, respectively, 0.04 m, 3 m, 0.02 m and 0.18 kg/s for maximizing EPV and 0 m, 3 m, 0.08 m and 0.091 kg/s for maximizing Eair without any constraints.

The application of thermal energy storage using thermochemical heat storage materials is a promising approach to enhance solar energy utilization in the built environment. Potassium carbonate ( K 2 C O 3 ) is one of the potential candidate materials to efficiently store thermal energy due to its high heat storage capacity and cost-effectiveness. In the present study, a 3-dimensional numerical model is developed for the exothermic hydration reaction of K 2 C O 3 . The heat produced from the reaction is transferred indirectly from the thermochemical material (TCM) bed through the walls of the honeycomb heat exchanger to a Heat Transfer Fluid (HTF). A parametric study is conducted for varying geometrical parameters of the honeycomb heat exchanger. The obtained results indicate that the reaction rate and heat transport in the TCM bed strongly depends on the geometrical parameters of the heat exchanger. Reducing the cell size of the honeycomb heat exchanger up to a certain level provides better thermal transport as well as improved reaction rate of the TCM bed. The results of this study provide detailed insight into the heat release processes occurring in a fixed bed of K 2 C O 3 . The study is useful for designing and optimizing thermo-chemical energy storage modules for the built environment.

International audience; Thermal energy storage devices are vital for reducing the inconsistency between energy supply and demand as well as for enhancing the performance of solar thermal systems. The present study investigates the melting process in metallic honeycombed heat exchangers filled with n-octadacane as phase change material (PCM). Further, a parametric study is conducted for four different honeycomb cell sizes, fin thicknesses, and angles of inclinations of the computational domain. The findings are described in the form of heated surface average temperature variation, melt fraction of the PCM, and thermal energy stored. Results show that the honeycomb fin structure considerably improves the heat transfer in the PCM. Further, it was observed that the honeycomb cell size and fin thickness greatly influence the variation of the average front surface temperature, melt fraction, and energy storage rate, whereas the inclination angle doesn’t have a significant effect when cell size is less than 0.01 m. From the study, it was also observed that when the computational domain is horizontal without honeycomb cells, the pure conduction in the PCM results in much higher front surface temperature, which is greatly reduced in presence of the honeycomb cells.

This paper analyzes a novel, cost-effective planar waveguide solar concentrator design that is inspired by cellular hexagonal structures in nature with the benefits of facile installation and low operation and maintenance cost. A coupled thermal and optical analysis of solar irradiation through an ideal hexagonal waveguide concentrator integrated with a linear receiver is presented, along with a cost analysis methodology, to establish the upper limit of performance. The techno-economic model, coupled with numerical optimization, is used to determine designs that maximized power density and minimized the cost of heat in the temperature range of 100–250 °C, which constitutes more than half of the industrial process heat demand. Depending on the incident solar irradiation and the application temperature, the cost of heat for the optimal design configuration ranged between 0.1–0.27 $/W and 0.075–0.18 $/W for waveguide made of ZK7 glass and polycarbonate, respectively. A techno-economic analysis showed the potential of the technology to achieve cost as low as 80 $/m2 and 61 $/m2 for waveguide made of ZK7 glass and polycarbonate material, respectively, which is less than half the cost of state-of-the-art parabolic trough concentrators. Overall, the hexagonal waveguide solar concentrator technology shows immense potential for decarbonizing the industrial process heat and thermal desalination sectors. Published version

Floating Photovoltaic (FPV) is an emerging technology that has experienced significant growth in the renewable energy market since 2016. It is estimated that technical improvements along with governmental initiatives will promote the growth rate of this technology over 31% in 2024. This study comprehensively reviews the floating photovoltaic (FPV) solar energy conversion technology by deep investigating the technical advancements and presenting a deliberate discussion on the comparison between floating and ground-mounted photovoltaic (PV) systems. Also, the economics and environmental impacts of FPV plants are presented by introducing the main challenges and prospects. The FPV plants can be conventionally installed on water bodies/dam reservoirs or be implemented as multipurpose systems to produce simultaneous food and power. Installing FPV modules over water reservoirs can prevent evaporation but penetration of solar radiation still remains an issue that can be eliminated by employing bifacial PV modules. The salt deposition in off-shore plants and algae-bloom growth are other important issues that can degrade modules over time and adversely affect the aquatic ecosystem. The capital expenditure (CAPEX) for FPV systems is about 25% higher than ground-mounted plants, mainly due to the existence of floats, moorings, and anchors. It has been stated that the capacity increase of FPV plants (ranges from 52 kW to 2 MW) can intensely decrease the levelized cost of energy (LCOE) up to 85%. It is estimated that FPV technology can become more affordable in the future by further research, developments, and progress in both technology and materials.

Sorption heat storage attracts considerable attention because its relatively high theoretical energy density compared to other heat storage methods offers various opportunities in the design of renewable and sustainable energy systems. However, limited heat transfer in the material bed remains one of the main limitations of a successful introduction to the market. In the present study, a mathematical model of the heat and mass transfer processes inside an adsorption bed of silica gel embedded with cylindrical and rectangular fins has been developed. A systematic analysis has been conducted to augment thermal transport in the adsorption bed with rectangular and pin fin configurations. A parametric study has been conducted for both fin configurations at different bed heights (δb), fin diameters/thicknesses (ϕfin/δfin) and fin spacings (δs). Further, a design-of-experiments study is conducted to relate the energy discharge (Edis) and peak power (Wpeak) to the various governing parameters, as such identifying which parameters maximize energy discharge (Edis) and peak power (Wpeak). The design-of-experiment study reveals that the rectangular fin configuration shows better performance compared to the cylindrical fin configuration.

The renewable energy resources have high impending to offer the way out to the long-standing energy shortage difficulties being confronted through the emerging countries like India. The solar energy obtained from the sun can be an imperative part of India’s plan not only to add new capability but also to upsurge energy security, address ecological concerns, and lead to the huge market for renewable energy. The electricity generated by solar thermal which is also known as concentrating solar power is emerging renewable energy technologies and can be developed as a future potential option for electricity generation in India. In this chapter, authors have been summarizing the accessibility, present status, promotion policies, strategies, viewpoints, major achievements barriers and future perspective of solar energy opportunities in India.

HVAC systems are comprised of the heating, ventilation, and air-conditioning systems in domestic and commercial buildings. These mechanical systems provide thermal comfort and air quality in indoor spaces. Types of HVAC systems include air conditioners, heat pumps, furnaces, boilers, rooftop units, chillers, and packaged systems. The HVAC system plays an important role in the energy efficiency of buildings. HVAC systems account for 39% of the energy used in commercial buildings in the United States. Consequently, almost any business or government agency can realize significant savings by improving its control of HVAC operations and improving the efficiency of the HVAC system. The uses of high-performance HVAC equipment can result in considerable energy, emissions, and cost savings (10%–40%). Whole building design coupled with an “extended comfort zone” can produce greater savings (40%–70%). Extended comfort includes employing concepts, such as providing warmer, drier air using desiccant dehumidification in summer, or cooler air with warmer windows and walls in winter. In addition, high-performance HVAC can provide increased thermal comfort, and contribute to improved indoor environmental quality (IEQ). This chapter describes different types of air conditioning systems that are the important component of efficient HVAC systems. The chapter also focuses on the technology overview, energy consumption, energy saving strategies, and the role of HVAC system in energy-efficient buildings.

Solar photovoltaic (PV) technologies installed on building rooftops and facades are common in some parts of the world. The majority of these systems are composed of modules that are attached to the surfaces of roofs and facade by means of different types of racking hardware. The photovoltaic panels are integrated into the building fabric replacing conventional building covering materials, but with the added benefit of producing renewable electricity. PV performance considerations mostly influence systems designs with aesthetics often coming secondary. But growing consumer interest in distributed PV technologies and industry competition to reduce installation costs are enhancing the development of multifunctional PV products that are incorporated into building materials. This chapter describes the methods, development, and application of building integrated photovoltaic in various types of buildings. The chapter also focuses on the benefits of the application of building integrated photovoltaic in green buildings, which cover building as well as producing electricity.

International audience; The present study deals with the investigation of melting behaviour of phase change materials (PCMs) during the cyclic heating. For this work, a computational fluid dynamic (CFD) study of heat and mass transfer during melting and solidification of PCM is carried out for the constant and variable (sinusoidal) heat supply. For the constant heat flux a step function ranging from 500 W/m2 to −500W/m2 and for variable heat flux, a sine function having a similar area as step function was considered at one wall of the container to provide heating and cooling of the PCMs. The results are reported in terms of melting interface, melt fraction during melting and solidification, temperature variation, the variation of melted PCM velocity, and rate of energy storage and release. From the results, it is observed that the melting time is reduced with variable heat flux as compared to constant heat flux and it is also pointed out that the melting time of PCM is lower as compared to solidification time

In recent years the thermal energy storage applications with phase change materials have attracted wide interest. This has motivated a number of R&D efforts to develop novel materials and design new applications based on PCM. The efficient design of the new applications majorly depends on the quality of PCM employed. Numbers of reviews, reports have been written to compile the wide range of PCMs made available for different applications. This paper focuses on the development of next generation PCMs through the enhancement of thermophysical properties namely thermal conductivity, latent heat of fusion and sensible heat. The paper presents a detailed review of the research updates in this direction so as to produce PCMs with enhanced efficiency in terms of thermal energy storage and efficient heat transfer.

This chapter mainly describes the various numerical methods that can be used for performance evaluation of the solar drying system. The numerical techniques help to develop solar dryers to increase drying effectiveness and analyses, and they forecast the performance of dissimilar types of solar dryers. The numerical analysis is essential for forecasting the relevant parameters, which are highly required in a solar drying system. Computational fluid dynamics (CFD) can be used to analyze and investigate the heat and mass transfer inside the solar dryer. An adaptive-network-based "fuzzy" inference system (ANFIS) is able to predict the performance of the solar drying system. The artificial neural network can be applied to estimate the quantity of the dehydrated product. Fuzzy logic is an essential tool for precisely forecasting the results with the least inaccuracy.

The requirement of fresh water is growing exponentially in industrial as well as domestic sector, resulting in more pollution of natural water resources and creating a scarcity of drinking water. Additionally, the number of arid and desert regions on the world map which already face the shortage of rainfalls and ground water. The problem is substantially increased as most of the water bodies like rivers, lakes are saline and brackish which are not suitable for drinking purpose. In recent past, solar desalination has been found to be a sustainable and economical way of generating the fresh water to cater the need of drinking water at large. Much technological advancement in the field of solar stills has been made which can ably produce a large quantity of fresh water depending on the availability of solar radiation. Various desalination schemes have been utilized to utilise water from such available resources to convert the available water in to the drinkable water. Additionally, attention has also been put on developing efficient solar still with latent heat based thermal energy storage systems which can work in the absence of sunlight as well. In the present paper, a short review on solar stills utilizing latent heat storage has been presented. The present study covers the design specifications, efficiency, along with the comparative analysis of solar stills with latent heat storage system, investigated in the last decade. A discussion on the future research outlook in the area of solar stills with latent heat storage has also been given, so as to make it more economically viable for generating sustainable potable water.

International audience; Solar Photovoltaic (PV) cells can absorb up to 80% of the incident solar radiation obtained from the solar band, however, only a small amount of this absorbed incident energy is transformed into electricity depending on the conversion efficiency of the PV cells and part of remainder energy increases the temperature of PV cell. High solar radiation and ambient temperature lead to an elevated photovoltaic cell operating temperature, which affects its lifespan and power output adversely. Number of techniques have been attempted to maintain the temperature of photovoltaic cells close to their nominal operating value. In the present review various cooling techniques such as natural and forced air cooling, hydraulic cooling, heat pipe cooling, cooling with phase change materials and thermoelectric cooling of PV panels are discussed at length. It is important to note that, though cooling techniques are highly needed to regulate the PV module temperature, especially for mega installations, these should be economically viable too.

Various heating systems are used to meet the heating requirements of the greenhouses. The conventional solution for this problem is the burning of some fossil fuel inside the greenhouse during cold days. The use of latent heat energy for greenhouse heating in winter days is a significant development. The storage of the excess heat in greenhouses for sunny days in a cold season is advantageous, in view of increasing concerns over usage of fossil fuel. Thermal storage plays a vital role in solar devices particularly in greenhouses to improve its performance because of the intermittent nature of solar energy. Therefore, a storage system constitutes an important component of the solar energy utilisation system. Thermal energy can be stored as sensible heat, latent heat or chemical energy. The present study is carried out to present a review of the solar greenhouse based on latent and sensible heat energy storage. The various designs and application methods are reviewed considering different thermal energy storage materials employed for building a solar greenhouse and future prospects of the same have been discussed.

Thermal energy storage (TES) systems using Phase Change Materials (PCM) are very attractive due to high storage density and economic viability. Use of fatty acids as phase change material for various TES applications: buildings, solar heating systems, air-conditioning systems have been widely accepted. It is highly desired to study the performance of PCMs for a particular application, in terms of heat transfer mechanism and geometry/structure of the container, as it helps in optimizing the cost and quality of TES systems. In the present work, authors studied the performance of five different fatty acids (Capric acid, Lauric acid, Myristic acid, Palmitic acid and Stearic acid) when used with aluminum containers. The numerical simulation of heating and cooling of PCMs has been conducted using finite element analysis (FEM). The results are reported in term of melt fraction, temperature variation, the transition of solid-liquid interface and the quantity of thermal energy stored in different fatty acids with time for melting and solidification. Based on the simulated results it can be concluded that the Capric takes minimum time for melting and solidification with the same boundary conditions, among the studied PCMs in this work. Such studies could be quite helpful in developing fatty acid based TES applications.

Solar dryer based on thermal energy storage materials is quite effective for continuously drying agriculture and food products at steady state in the temperature range (40 °C–60 °C). Such dryers have globally become a potential viable substitute to the solar dryers based on fossil fuel, due to the utilization of clean energy resources and cost-effectiveness. Storage materials utilized in these dryers can store energy during the sunshine hour and deliver the stored energy during off-sunshine. It reduces the existing load on the gap between energy demand and supply, hence plays a vital role in energy sustainability. A number of studies have been done in last few decades for drying agriculture and food products with a solar dryer based on thermal energy storage concept. This paper mainly presents a review on the important contributions made so far in the field of solar drying systems based on the thermal energy storage medium, with a focus on recent updates in thermal energy storage technology available in terms of materials capable of storing heat as sensible and latent heat.