## 1 Introduction  
The recent trends in energy consumption and energy policies are shifting the focus to sustainable utilization of energy as a key issue [1, 2]. Based on an International Energy Agency (IEA) report [1], a steep increase in global primary energy consumption has been observed over the last few years. Roughly 50% of this energy is being used to heat and cool applications in the industrial and domestic sectors. Thermal Energy Storage (TES) systems are arising as key technologies to help increase energetic efficiency and enable a high share of renewable energies for future energy systems [1, 2, 3]. TES can be divided into three main categories: Sensible Heat Storage (SHS), Latent Heat Storage (LHS) and Thermo-Chemical Heat Storage (TCS). In LHS systems, heat is stored in the form of phase change enthalpy, which can be accumulated or released upon phase change of the energy-storing material [2; 3]. As such, this application requires materials with high phase change enthalpies, which are referred to as Phase Change Materials (PCM). As reported by [PERSON] et al. (2009) [PERSON] et al. (2009), due to higher compactness and higher heat storage density, LHSs allow for greater flexibility in the location selection of the storage system and minimum space usage. PCMs accumulate energy while the phase change occurs at almost isothermal conditions and over narrower temperature ranges, therefore providing higher energy efficiency with a smaller temperature difference between charging and discharging in comparison to sensible storage [5; 6; 7]. However, in addition to higher investment costs compared to SHSs, PCMs often face issues with toxicity, flammability, and possible degradation of properties after several cycles [5]. Early studies focused on salt hydrates as inorganic PCMs due to their availability, low cost, and high latent heat storage capacities. However, because of their tendency to corrode, supercool and segregate, researchers have turned their attention towards organic PCMs as well [8; 9; 10]. Paraffins are the most commonly used organic PCMs as of today; however, they are oil derivatives and are characterized by high flammability and relatively limited melting point range. Therefore, carboxylic acids and their derivatives have been selected as a more sustainable alternative [10; 11; 12]. In particular, in order to reduce environmental impact, research is being conducted on organic PCMs based on readily available natural resources, such as carboxylic esters, which naturally occur in fats and oils from renewable feedstock [10; 11; 12]. [PERSON] et al. [11] conducted preliminary studies on the environmental impact of salt hydrates and esters as PCM in house-shaped cubicles in Spain. The results showed that based on the Eco-indicator 99 method, an impact reduction of 10.5% for esters compared to paraffins was calculated. Carboxylic esters can be obtained via Fischer esterification of carboxylic acids with alcohols, and present comparable thermal and chemical characteristics to the original acids [12]. In fact, similarly to the corresponding carboxylic acids, they are reported to show low or no toxicity, no corrosivity, high enthalpies of fusion, high chemical and thermal stability, and are mainly inflammable [8; 9]. Millions of possible combinations between carboxylic acids and alcohols exist, creating endless possibilities for esters as PCMs [8]. However, despite the advantages reported above, esters as PCM have not been investigated deeply so far. As reported by [PERSON] [12] and [PERSON] [13; 14], a clear gap in the data concerning experimental thermal properties of esters derived from carboxylic esters exists. This is probably due to lack of easily available commercial products, which makes it challenging to collect experimental data. In order to allow for identification of potential esters to be used as future PCM in relevant temperature ranges, more experimental data on the thermal properties of esters is required.