energies Review Phase Change Materials (PCM) for Solar Energy Usages and Storage: An Overview M. Mofijur 1,*, Teuku Meurah Indra Mahlia 1 , Arridina Susan Silitonga 2, Hwai Chyuan Ong 1, Mahyar Silakhori 3 , Muhammad Heikal Hasan 1,4, Nandy Putra 5 and S.M. Ashrafur Rahman 6 1 School of Information, Systems and Modelling, Faculty of Engineering and IT, University of Technology Sydney, Sydney, NSW 2007, Australia 2 Department of Mechanical Engineering, Politeknik Negeri Medan, Medan 20155, Indonesia 3 School of Mechanical Engineering, University of Adelaide, Adelaide, SA 5005, Australia 4 Department of Mechanical Engineering, Universitas Pertamina, Jakarta 12220, Indonesia 5 Department of Mechanical Engineering, Universitas Indonesia, Kampus UI Depok 16424, Indonesia 6 Biofuel Engine Research Facility (BERF), Queensland University of Technology, Brisbane, QLD 4000, Australia * Correspondence: MdMofi[email protected]; Tel.: +61-46985-1901 Received: 28 July 2019; Accepted: 15 August 2019; Published: 17 August 2019 Abstract: Solar energy is a renewable energy source that can be utilized for different applications in today’s world. The effective use of solar energy requires a storage medium that can facilitate the storage of excess energy, and then supply this stored energy when it is needed. An effective method of storing thermal energy from solar is through the use of phase change materials (PCMs). PCMs are isothermal in nature, and thus offer higher density energy storage and the ability to operate in a variable range of temperature conditions. This article provides a comprehensive review of the application of PCMs for solar energy use and storage such as for solar power generation, water heating systems, solar cookers, and solar dryers. This paper will benefit the researcher in conducting further research on solar power generation, water heating system, solar cookers, and solar dryers using PCMs for commercial development. Keywords: PCM; solar energy; renewable energy; energy storage 1. Introduction In today’s world, environmental problems and the energy crisis are two major global issues that need to be urgently addressed [1–3]. The continuous rise in the level of energy consumption, increases in fuel prices and the emission of greenhouse gases are the main forces driving the need for more effective use of renewable energy sources [4–6]. Worldwide, primary energy consumption increased by 1.5% in 2018 compared to consumption levels in 2017 [7]. Many studies on global energy consumption and emissions have been conducted and these topics are discussed at length in [8–10]. One of the solutions to greenhouse gas emissions is the use of renewable energy, and thus, renewable energy initiatives have been implemented in many countries [11–16]. However, the problem associated with some renewable energies like solar and wind, is that they are only available for a certain time period. The supply of renewable energy is difficult to control since it is based on weather-related natural phenomena such as rain, wind and solar energy. Better utilization of renewable energy is possible if it can be stored, as this decreases the demand for fossil fuels, eventually reduces the cost of system maintenance, and in turn, reduces energy waste. In order to balance energy production with consumption, it is necessary to store excess energy for the short/long Energies 2019, 12, 3167; doi:10.3390/en12163167 www.mdpi.com/journal/energies Energies 2019, 12, 3167 2 of 20 Energies 2019, 10, x FOR PEER REVIEW 2 of 20 term. However, at this time, storing excess electrical energy is quite expensive. Instead, the cost related tothe storing energy thermal grid but energy excess iselectric quite low.energy Excess can be thermal exported energy through cannot a grid be exportedconnection. to theThermal energy energy grid butstorage excess may electric be able energy to assist can during be exported electric through utility agrid grid stress. connection. In order Thermal to store energy energy, storage systems may such be ableas batteries to assist or during PCMs electriccan be utilityused. However, grid stress. as Inth ordere energy to storestorage energy, capacity systems (kWh) such of the as batteries batteries or is PCMsvery limited, can be researchers used. However, and users as the are energy opting storage for PCMs capacity as an alternative. (kWh) of the It batteriesis important is very to note, limited, that researchersenergy storage and usersis economically are opting forattractive PCMs aswhen an alternative. it reduces Itenergy is important consumption to note, and that cost energy and storage it is a isviable economically substitute attractive for another when itenergy reduces source energy [17–22]. consumption The different and cost andforms it isof a viableenergy substitute storage forare anotherpresented energy in Figure source 1 [23]. [17– 22]. The different forms of energy storage are presented in Figure1[23]. FigureFigure 1.1. ClassificationClassification ofof energyenergy storagestorage systemssystems [[23].23]. Amongst the various energy storage systems, thermal energy storage exhibits the highest Amongst the various energy storage systems, thermal energy storage exhibits the highest efficiency [24]. A thermal storage system can utilize the solar energy and excess thermal energy that is efficiency [24]. A thermal storage system can utilize the solar energy and excess thermal energy that generated throughout the day and can be stored for either short or seasonal periods [25]. Both seasonal is generated throughout the day and can be stored for either short or seasonal periods [25]. Both storage and diurnal storage can be combined to achieve an efficient system. Diurnal thermal energy seasonal storage and diurnal storage can be combined to achieve an efficient system. Diurnal thermal storage takes the form of chilled water and ice storage for cooling and hot water tank storage for energy storage takes the form of chilled water and ice storage for cooling and hot water tank storage heating, with greater energy transfer rates [26]. Seasonal thermal storage helps to avoid energy for heating, with greater energy transfer rates [26]. Seasonal thermal storage helps to avoid energy shortage during a period when there is limited sun exposure and lowers high energy costs by storing shortage during a period when there is limited sun exposure and lowers high energy costs by storing thermal energy when solar radiation or other energy sources are abundant or inexpensive [27,28]. thermal energy when solar radiation or other energy sources are abundant or inexpensive [27,28]. Therefore, coupling solar energy with sensible storage for diurnal and seasonal periods is important Therefore, coupling solar energy with sensible storage for diurnal and seasonal periods is important for distributed generation [25,28]. In order for the PCM system to accomplish seasonal heat storage, for distributed generation [25,28]. In order for the PCM system to accomplish seasonal heat storage, insulated thermal mass and stable super-cooling are required. Super-cooling is a unique property of insulated thermal mass and stable super-cooling are required. Super-cooling is a unique property of PCM storage whereas insulated thermal mass is common to all heat storage media. Stable supercooling PCM storage whereas insulated thermal mass is common to all heat storage media. Stable PCMs readily supercool, and can remain supercooled at ambient temperatures for seasonal durations. supercooling PCMs readily supercool, and can remain supercooled at ambient temperatures for This enables long-term storage without heat loss (i.e., no self-discharge) [29]. seasonal durations. This enables long-term storage without heat loss (i.e., no self-discharge) [29]. PCM is a particularly attractive material because it is able to store a high density of energy and PCM is a particularly attractive material because it is able to store a high density of energy and keep a constant temperature or an amount of heat through its heat-storing characteristics [30,31]. keep a constant temperature or an amount of heat through its heat-storing characteristics [30,31]. The The storage of thermal energy can be further classified into three groups: sensible, latent (PCMs) and storage of thermal energy can be further classified into three groups: sensible, latent (PCMs) and chemical heat storage [32–34]. Other classifications of the application and characteristics of thermal chemical heat storage [32–34]. Other classifications of the application and characteristics of thermal energy storage can be found in the literature [35–37]. energy storage can be found in the literature [35–37]. The aim of this paper is to provide a critical review of recent studies of solar energy storage The aim of this paper is to provide a critical review of recent studies of solar energy storage using using PCMs. It discusses the classification of energy storage, PCMs integrated with solar power PCMs. It discusses the classification of energy storage, PCMs integrated with solar power generation, generation, solar water heating systems and solar cookers, and ends with an application of PCM as solar water heating systems and solar cookers, and ends with an application of PCM as solar dryer solar dryer energy. A similar study conducted a review of solar dryers with PCM as an energy storage energy. A similar study conducted a review of solar dryers with PCM as an energy storage medium medium [38,39]. However, that review focused only on using PCM for the solar dryer while the current [38,39]. However, that review focused only on using PCM for the solar dryer while the current one one examines numerous applications of PCM for solar energy storage. examines numerous applications of PCM for solar energy storage. 2. Phase Change Materials (PCMs) 2. Phase Change Materials (PCMs) The use of PCMs has recently gained more research interest and importance in the optimal use of The use of PCMs has recently gained more research interest and importance in the optimal use energy. The theories, design and analysis of PCMs to store latent heat have been explored thoroughly of energy.