# Energy Efficiency Improvement of Diesel-Electric Trains Using Solar Energy: A Feasibility Study
## 1 Introduction  
Worldwide, energy consumption is a central issue of economic activity. Over the past few months, the COVID-19 pandemic has caused an unprecedented global economic and social crisis. The pandemic has significantly affected all aspects of life, including the energy sector [1]. Due to the pandemic, many governmental decisions were made, such as the imposition of lockdowns worldwide which decimated transport-related demand. Associated events led to an unprecedented collapse in oil demand and, therefore, a drop in the global energy demand, with a rate of 4.5-6% in 2020 relative to 2019 [2, 3]. Indeed, recently, the statistical review of world energy in 2021 affirms that the carbon emissions from energy use were falling by over 6% in 2020. However, there are worrying signs that the COVID-induced dip in carbon emissions and the energy demand will be short-lived as the world economy recovers and lockdowns are lifted [3]. Regardless of the lower energy demand in 2020, renewable energy, led by wind and solar, continued to grow. In 2020, renewable energy posted a record increase in production,by 358 TWh compared to 2019 [3]. Moreover, this increase is comparable to those seen in 2017, 2018, and 2019. Thus, we noticed a relative immunity of renewable energy growth to the world political and health issue events in the last years. Remarkably, PV solar capacity in both 'OnGrid' and 'OffGrid' increased over time and reached around 710 GW and 4 GW, respectively, in 2020 as we can see in Table 1. Furthermore, there was a 125.8 GW and 0.234 GW increase in installed capacity from 2019 to 2020. Therefore, renewable energy has formed a crucial part of any viable solution to reduce primary energy consumption over the last years [4; 5; 6]. In general, renewable energy share, the energy intensity of gross domestic product, and the electrification of final uses of energy have all shown improvements in recent years. Yet, the pace is insufficient to put the world on track to meet the Paris agreement (COP21) goals. This international climate conference marks a turning point in the fight against global warming. It commits all countries to reducing greenhouse gas emissions and keep warming below 2 \({}^{\circ}\)C and, preferably, below 1.5 \({}^{\circ}\)C by 2100 [7]. Considering ample resource availability, significant market potential, and cost competitiveness, PV solar panels are expected to continue driving overall renewables' growth in several regions over the next decade. From today's levels, IRENA's analysis shows that solar PV power installations could grow almost four-fold over the next ten years, reaching a cumulative capacity of 2840 GW globally by 2030 and rising to 8519 GW by 2050. This growth implies that the total installed capacity in 2050 will be almost twelve times higher than 2020. Around 60% of total solar PV capacity in 2050 would be utility-scale globally, with the remaining 40% distributed (rooftop) [8]. Thus, to achieve the goal by 2050, the use of PV solar panels must increase enormously in all end-use sectors. One of these sectors is the transport sector, the second-largest energy consumer after the industrial sector, with a rating factor of 14% of global energy consumption [9; 10]. The transport sector is divided into six principal modes: road, maritime, air, rail, intermodal, and pipeline [11]. Our study in this paper focuses on using PV solar panels in the rail mode, mainly in diesel-electric trains. Rail is responsible for 9% of global motorized passenger movement and 7% of freight [12]. Since 2017, rail-based transport on an electric network has been a relatively low carbon dioxide emission and so-called 'green transport' mode, compared with other means of transport (such as planes and cars/trucks) [13]. On the other hand, rail-based primary fuel constitutes an essential reason for the growth of CO\({}_{2}\) emissions globally [14].