Progress in passive cooling strategies for silicon photovoltaic panels with incorporated phase change materials

The urgency to combat against climate change has never been more apparent, as the recent rise in global carbon dioxide (CO₂) emissions shows. In 2023, there was a 1.1 % increase in CO₂ emissions associated with energy use, reaching an unprecedented level of 37.4 gigatons (Gt) [1]. This alarming increase underlines the urgent need for more ambitious climate protection measures and firm actions. The key formal document to manage climate change is the Paris Agreement, which was concluded in 2015 following extensive international negotiations. The agreement sets the goal of becoming carbon neutral globally by 2050, which requires a profound energy transition. This transition is essential to manage the climate emergency and limiting the global temperature increase to 1.5 °C above levels seen before industrialization [2]. The rise in CO₂ emissions underscores the gap between current policies and the goals of the Paris Agreement and highlights the need for accelerated and more effective climate strategies.

A critical component to achieving climate goals is the green transition, a transformation process focused on shifting the economy from fossil fuel dependence to sustainable practices. This transition has become an important aspect of global economic strategies, in which increasing the share of renewable energy technologies is crucial [3]. Renewable energy sources such as solar, wind and hydropower are central to the green transition. This transition is crucial for reducing the carbon footprint and improving energy security. According to recent studies and data, mentioned technologies play a central role in attaining sustained environmental resilience. and meeting global emission reduction targets. In 2023, studies and reports underline the significant impact of advances in renewable energy. Global annual renewable energy additions increased by almost 50 %, reaching around 510 GW (GW), the fastest growth rate in the last two decades and a new record for the 22nd consecutive year [4]. Photovoltaics had an outstanding year with a global installed capacity of 345.5 GW, compared to 199.1 GW in 2022 [5]. There was also significant progress in wind energy, with at least 15.6 GW of new capacity installed in 2023, which refers specifically to the countries that are members of the European Union [6]. These results underline the crucial contribution of renewable energy technologies to the green transition and their essential role in achieving sustainable energy goals.

Solar energy is widely recognized for its energy potential and widespread availability as a renewable resource, making it a critical component in the transition to a sustainable energy system [7]. As the global community increasingly seeks alternatives to fossil fuels, the development and deployment of renewable energy technologies has accelerated significantly. Among these technologies, photovoltaics (PV) has emerged as a key player in the transition to greener energy solutions. Photovoltaic systems harness solar energy where sunlight is directly converted into electricity by solar cells. Of the various types of PV technologies, silicon-based photovoltaic systems are the most widespread and widely used [8]. Despite considerable progress in these technologies, improving the energy conversion efficiency of silicon-based PV panels remains a major challenge. Currently, the conversion efficiency of commercial silicon-based PV panels is typically 10–20 % under standard test conditions [9]. This means that only a small portion of the solar energy absorbed by PV panels is converted into useable electrical energy, with the remainder primarily lost as heat. Furthermore, the problem is exacerbated by the fact that the efficiency of silicon-based PV panels decreases usually in range from 0.4 % to 0.5 % for each 1 °C rise in the temperature of the cell, making it even more difficult to improve their overall performance [8].

To overcome these challenges, innovative techniques for cooling PV panels have been developed. Both active and passive cooling methods have been explored to reduce the negative effects of elevated temperatures on panel electrical efficiency [10]. Active cooling techniques involve the use of external mechanisms such as fans [11,12] or liquid cooling systems [13,14] to dissipate heat more effectively. Passive cooling methods, on the other hand, utilize design improvements and materials that dissipate heat naturally without additional energy input. Passive cooling methods can generally be divided into three main types [15]. The first type is air-based passive cooling, which enhances natural convection through components such as heat sinks and cooling fins [16]. The second type is solid-based passive cooling, which uses phase change materials (PCMs) [17] that absorb and release thermal energy during the transition between different states. The third type is thermal cooling, which includes technologies such as thermoelectric generators (TEGs) [18] and thermosyphons [19] that utilize temperature gradients for effective thermal management.

The integration of PCMs into PV panels was first investigated by Stultz and Wen in 1978 and represented a pioneering approach to increasing the efficiency of electricity generation through passive cooling [20]. This method aimed to reduce the efficiency losses caused by high operating temperatures in PV systems by utilizing the unique thermal properties of PCMs. PCMs are materials that undergo phase transitions, typically between the solid and liquid states, during which they take in and emit thermal energy [21]. Through this phase change, PCMs can act as a thermal buffer and help to maintain the temperature of PV panels within the optimal operating range, thus reducing the negative effects of elevated temperatures on performance. In addition, passive cooling systems based on PCMs have several significant advantages. These systems efficiently regulate the temperature of the PV panels and offer high heat absorption rates with minimal material usage. They operate without power consumption and without moving parts, thus eliminating maintenance requirements and operating costs [22]. These characteristics make PCM-based cooling systems an attractive, cost-conscious way to enhance the sustainability and performance of photovoltaic systems.

This comprehensive review is motivated by the significant advances and growing interest in passive cooling strategies for silicon-based PV panels, particularly using PCMs, with final goal to improve energy conversion efficiency as well as longevity. A comprehensive review [23] published in 2016 highlighted various passive cooling techniques, such as heat pipe systems and cooling fins, but did not address PCMs. Since then, two recent studies have focused on the application of PCMs for passive cooling of PV panels. However, one of these studies [24] focused on photovoltaic/thermal (PV/T) systems, while the other [10] looked at concentrated photovoltaic (CPV) systems, both of which are outside the scope of this review. Subsequent reviews [25,26] have looked at both active and passive cooling methods and mentioned PCMs as a cooling option for PV panels. However, these reports didn’t elaborate on the specifics of passive cooling with PCMs. This points to a gap in the literature, as no comprehensive review has addressed passive cooling of PV panels with PCMs in the last five years. This gap underlines the need for a further targeted investigation of this topic, which is the main objective of this review work.

For this review work, relevant papers were identified by searching the Scopus® database using keywords such as “photovoltaic"," “PV"," “phase change material"," “PCM” and “passive cooling”. Fig. 1a shows the annual number of publications found on Scopus®, while Fig. 1b illustrates the subset of publications included in this review. Namely, studies that dealt with CPV systems, PV/T systems or sun-tracking photovoltaic panels were excluded to ensure that this review focused and limited by target on PV-PCM passive cooling systems.