Solar energy integration is increasingly being researched as a strategy to address the growing energy demands and environmental impacts of transportation. As electric vehicles (EVs) and public transit electrification expand globally, the strain on centralized power grids and the need for cleaner energy sources intensify. Solar power, as a renewable and decentralized resource, offers a unique opportunity to complement grid electricity, reduce emissions, and enhance energy resilience. This paper investigates recent advancements in solar energy integration for transportation, with a focus on public transit and electric vehicles. Over the past three years (2021–2024), three key developments are analyzed: solar-powered electric bus depots, optimized scheduling for solar-integrated bus systems, and rooftop photovoltaic (PV) panels for range extension in electric vehicles. A case study in Yinchuan, China, demonstrates how integrating solar PV and battery storage at bus depots can significantly cut costs, emissions, and grid dependency. Similarly, modeling studies from Canada and Australia show that optimizing charging schedules to match solar availability can lead to meaningful operational savings. In electric vehicles, simulations reveal that rooftop solar panels can extend the driving range and lower reliance on grid electricity. Together, these findings confirm that solar energy, when strategically deployed in both infrastructure and vehicle design, offers measurable benefits in sustainability, cost efficiency, and grid resilience for modern transportation systems. Additionally, the paper proposes decentralized solar-powered charging stations for public transport and electric vehicles, incorporating innovative perovskite solar cell technology.

 

The decarbonization of the transportation sector is central to achieving global climate targets, but the prospect of electrical integration introduces grid stress, limited charging infrastructure, variable charging times, and increased total lifecycle emissions. As electric vehicle (EV) adoption increases as a result of the push towards renewable energies, auxiliary energy strategies are essential to support EV upkeep and charging infrastructures. Photovoltaic (PV) integration offers decentralized on-site power generation options that can supplement grid demand, offset operational loads, and improve system resilience. For both passenger and commercial usages, solar energy represents a logical and increasingly viable adjunct to electric vehicles.

However, vehicle-integrated photovoltaics suffer from insufficient surface area, low cell efficiency, and diurnal intermittency which all constrain practical applications. To address these shortcomings, recent studies have offered quantitative insight into solar integration in transportation. For example, PV-equipped bus depots with stationary battery energy storage have demonstrated notable reductions in peak grid load and charging costs [1]. Linear optimization models incorporating solar variability and ambient temperature have further enabled responsive scheduling strategies in public transit [2]. Within passenger EVs as well, limited rooftop PV systems can offer measurable range extension and cost offsets, especially under favorable conditions [3]. The intersection of these findings suggests a maturing field where solar adaptation can noticeably improve global sustainability targets.

This paper presents three focused evaluations of solar applications in transportation: (1) integrated solar-battery systems at electric bus depots, (2) solar-aware optimization of bus charging schedules across climatic conditions, and (3) rooftop PV utilization for EV range extension. Each analysis is based on simulation outputs and real-world data from recent peer-reviewed studies. The objective is not to assess solar as a wholesale replacement for traditional charging or fuels, but to quantify its contribution as a layered, complementary asset within decarbonized mobility networks.

 

As electric bus adoption accelerates worldwide, depot energy demand has grown significantly, placing increased pressure on local grids during peak hours. Conventional charging strategies rely heavily on grid electricity, which is often carbon-intensive and subject to volatile pricing structures. Integrating on-site solar photovoltaic (PV) systems at bus depots presents a promising solution to this problem by enabling self-generation of clean energy and reducing dependency on external energy sources. 

Figure 1. Configuration of bus depot in Yinchuan, showing rooftop photovoltaic (PV) array, battery energy storage system (BESS) and grid interface Adapted from [1].

 

A study conducted in Yinchuan, China, explored the performance and cost-effectiveness of a solar-powered electric bus depot with an integrated PV system and battery energy storage [1]. The configuration of this solar-powered electric bus depot is illustrated in Figure 1, which depicts the integration scheme of rooftop PV generation, lithium-ion battery storage, and grid interaction. The system is designed to balance real-time depot energy demand with variable solar availability, while reducing peak grid draw and total electricity cost. The system included a 4.5 MW rooftop PV array installed across depot structures and a 2.6 MWh lithium-ion battery system designed to buffer energy for both operational and peak load management. 

Ma et al., the research group behind the study, simulated the system's performance over ten years, using Yinchuan solar irradiance profiles, depot load data from a fleet of 350 electric buses, and dynamic electricity pricing as recorded in Figure 3. The modeling framework was also extended to test similar configurations in different climates and economic contexts, including the United States, Europe, and Australia [1].

Figure 2 and Figure 3. Economic cost and carbon emission reductions from PV+BESS deployment across four regions: Los Angeles, Munich, Yinchuan, and Sydney. Dynamic grid pricing in Yinchuan. Adapted from [1].

 

The results of the study demonstrated substantial benefits. Total electricity costs for the depot were reduced by 37.35 percent, while carbon emissions dropped by 41.46 percent due to the system’s reduced reliance on grid electricity derived from fossil fuels. The PV and battery system also lowered peak grid load by 49.35 percent as shown in Figure 5, implying that the integration of PV significantly reduces demand on the grid during peak hours. Figure 4 shows how the charging profile aligns with solar generation throughout the day, enabling efficient the hybrid PV+BESS configuration to supply 55.7 percent of the depot's total energy demand, with the remainder covered by traditional sources.

Figure 4 and Figure 5.
Daily PV output versus electric bus charging load (Figure 3, left) and corresponding grid power demand with and without PV+BESS integration (Figure 4, right) in Yinchuan. These profiles demonstrate the temporal mismatch between generation and demand, and the effectiveness of storage in mitigating grid stress. Adapted from [1].

 

These findings highlight the viability of solar-powered depots as a sustainable backbone for future electric transit networks, as solar energy successfully offset electricity costs without significantly hindering performance. Transferability of this system model, however varies depending on solar resource availability and local energy prices. The key enabling factors for success included sufficient rooftop surface area for PV deployment, accurate load forecasting, and an appropriately sized BESS for balancing energy generation and consumption [4]. Specifically, the 4.5 MW PV array supplied over half of the depot’s energy demand. Load forecasting ensured that solar and battery dispatch aligned with real-time charging needs of 350 electric buses. Additionally, the 2.6 MWh battery enabled the depot to store excess solar power and use it during peak pricing or low irradiance periods, maximizing cost savings and grid independence.

As more transit agencies adopt solar-integrated depot models, the cumulative benefits could be substantial. Widespread deployment would not only reduce dependence on grid electricity but also help stabilize local energy systems by offsetting peak demand through intelligent energy storage. Additionally, the impact on carbon emissions could be profound, helping cities meet aggressive climate targets while modernizing public transit infrastructure. If supported by policy incentives and falling PV and battery costs, solar-powered depots may become the standard for sustainable urban mobility.

 

In 2025, a multi-scenario optimization study conducted by researchers from the Indian Institute of Technology Madras investigated the impact of solar-aware scheduling for electric bus fleets. Baldua et al. implemented a two-stage linear programming model to optimize both the infrastructure size (PV area and battery capacity) and the daily charging schedules of battery electric buses (BEBs) [2]. As shown in Figure 6, the model determines how energy should flow from both the grid and the solar PV system to meet charging demands while minimizing cost. The optimization considers not only when buses should charge, but also which energy source (traditional or solar) should supply the energy, and whether the battery energy storage system (BESS) should be charged or discharged at a given time. This behavior ensures that charging is aligned with solar generation windows and avoids expensive grid periods, resulting in more cost-effective and energy-efficient operations.

For both cities, the optimized strategy significantly improved cost performance over usual scheduling, which relied on average-based charging schedules that did not consider solar availability or electricity pricing. In contrast, the optimal schedule responded dynamically to these factors. To apply this model, they used actual bus network configurations for Durham (Canada) and Canberra (Australia), integrating local solar irradiance profiles and electricity tariff structures. Both cities' fleets consisted of around 100 battery electric buses, and the model was designed to reflect realistic constraints like depot capacity, charger availability, and scheduling windows. The optimization prioritized charging during midday solar peaks and leveraged battery storage to avoid grid usage during high-cost periods. During low solar availability, the model would draw more from the grid or battery energy. 

Figure 7. Scenario-based hourly energy utilization in Durham and Canberra transit networks for representative weeks in summer, mid-year, and winter. Optimized charging shifts load toward solar generation windows, reducing grid dependency and cost. Adapted from [2].

 

As a result, Durham saw a 16.48 percent reduction in electricity costs, while Canberra -benefiting from greater solar irradiance - achieved a 32.00 percent reduction. These regional differences in performance were largely attributed to solar resource variability and local pricing structures. Simulation outputs showed that charging events were most frequently aligned with daytime solar generation windows, maximizing PV utilization while minimizing dependence on expensive grid electricity.

Optimal infrastructure sizing was derived by evaluating multiple scenarios that varied PV area, BESS capacity, and bus charging locations across both Durham and Canberra networks. Overestimating solar panel area without sufficient battery capacity results in wasted generation, while underestimating grid capacity risks power shortages during operations. Through the simulations, it was shown that PV areas between 1,500 to 1,800 m² and battery capacities between 600 and 900 kWh were the best trade-off between investment and operational savings. Figures 8 and 9 depict the relationship between solar infrastructure sizing and energy usage patterns. Most overnight charging employed contracted grid power, while daytime charging was covered predominantly by BESS powered from solar. This pattern reflects an operational strategy in which solar energy, being cheaper than grid pricing, was prioritized during the day, and grid energy was stored in BESS during low-price periods [2]. These configurations ensured high solar utilization while reducing peak grid dependency, illustrating how the optimization model adapts to local solar irradiance and pricing structures. Canberra compared to Durham, highlighting the need to account for localized consumption dynamics. 

Figure 8 and 9. Optimal PV array sizes and BESS capacities for electric bus depots in Durham (top) and Canberra (bottom) across different times of day. Adapted from [2].

 

These findings demonstrate that incorporating solar-aware charging optimization into transit fleet planning not only reduces operating costs but also enhances PV utilization and reduces grid dependency. The study emphasizes that adaptive scheduling combined with appropriately sized solar infrastructure can play a critical role in making electric transit systems more sustainable and economically viable [5]. 

 

Developing countries face barriers related to limited grid capacity, high electricity prices, and sparse charging infrastructure. In sunny, high-irradiance regions such as India, integrating rooftop photovoltaic systems directly onto vehicles offers a decentralized solution to grid-based charging. This approach leverages abundant solar resources to improve vehicle performance and autonomy in climates well-suited to solar energy capture.

To successfully integrate rooftop PV panels into EVs, several strategies can be employed.

Figure 10. Model of rooftop solar photovoltaic vehicle used. Adapted from [3]

Designing lightweight and flexible panels, such as those utilizing perovskite solar cell technology, can address the issues of weight and efficiency. Implementing advanced energy management systems will optimize the usage of solar-generated power. Conducting pilot projects to test the real-world performance of rooftop PV panels can provide valuable data for refinement and broader application. Collaboration with EV manufacturers and solar technology providers will be essential for scaling up and adopting this innovative solution. Continued research and development investments are necessary to improve the stability with reference to  SAE J2929( Provides safety standards for electric and hybrid vehicle propulsion battery systems), efficiency, and cost-effectiveness of perovskite and other advanced PV technologies.

 

A MATLAB-based simulation study by Eragamreddy, a research scholar at the PES College of Engineering, investigated the potential of rooftop PV panels to extend the driving range of compact electric vehicles while reducing grid dependency [3]. The model used in the study included an 800 kg light-duty electric car powered by a 1 kW brushless direct current (BLDC) motor and fitted with a 315 W PV module on its roof. The simulation was preformed using real solar irradiance data for Hyderabad, India, obtained from the U.S. National Renewable Energy Laboratory (NREL) over a one-year period.

A comparative analysis of vehicle performance with and without rooftop solar photovoltaic (RTSPV) panels reveals tangible benefits to both range and energy efficiency, as shown in Table 1. The vehicles equipped with RTSPV exhibited a 19 percent increase in range from 56.6 km to 67.1 km alongside an increase in energy consumption due to extended travel distance from 1.44 kWh vs. 1.707 kWh. Despite this extended use, the solar-assisted system reduced the cost per kilometer

travel from ₹0.20 to ₹0.17, a 15 percent decrease and a marked improvement over traditional energy sources. Additionally, travel time per full charge rose from 2.5 hours to 2.99 hours, reflecting the extended range afforded by PV charging. These findings highlight the practicality of integrating RTSPV into compact EVs, especially in regions with high solar availability, by improving range and reducing energy cost per kilometer. 

The effectiveness of vehicle-integrated photovoltaics (VIPV) depends heavily on the efficiency of the solar panels, the vehicle's typical driving cycles, and the regional climate. In this study, a 315 W rooftop panel delivered significant range gains under high irradiance levels typical of Hyderabad. The panel’s efficiency determined how much usable energy was harvested, which was especially impactful during longer daytime cycles when solar output aligned with travel. Additionally, the region’s stable climate minimized efficiency losses from extreme temperatures, helping maintain optimal battery performance.

The relationship between usage patterns and environmental conditions shows how even modest PV systems can provide practical performance gains. Looking ahead, widespread implementation of VIPV technologies in sunny, arid regions - such as parts of India, the American Southwest, North Africa, and Australia - could offset a meaningful portion of their daily energy needs, reducing electricity costs for consumers and alleviating pressure on local charging infrastructure. This could promote more sustainable urban transportation models by lowering lifecycle emissions and increasing energy autonomy, particularly in areas with underdeveloped grid access.

 

The integration of solar energy into transportation systems offers measurable improvements in sustainability, energy efficiency, and cost reduction. Through analysis of solar-powered electric bus depots, optimized charging schedules, and rooftop PV for EVs, a targeted deployment of photovoltaic and battery systems can demonstrably reduce grid dependency, lower operational costs, and extend vehicle range. The results range from cost savings of up to 37.35 percent in depot operations to a 19.60 percent range increase for VIPV-equipped vehicles. These improvements demonstrate that solar energy is no longer limited by theoretical potential but is achieving practical and applicable solutions.

These advancements may shift in the optimization processes infrastructure and vehicle design. As the electrification of transport continues to increase, solar technologies provide a complementary solution to conventional grid charging. The integration of high-efficiency, flexible solar panels, coupled with advanced energy management systems can significantly enhance the sustainability and appeal of electric vehicles. Strategic implementation and ongoing research will be crucial in realizing the full potential of rooftop PV panels, encouraging widespread adoption and contributing to the global shift towards sustainable transportation. The benefits are especially compelling in regions with favorable solar conditions and dynamic pricing structures. Future work should explore larger-scale integration to evaluate system performance under more complex constraints and higher energy demands. Additionally, long-term battery degradation [6] must be studied to understand how BESS lifespan and efficiency evolve over time, especially under daily cycling and dynamic thermal conditions. Material innovations that enhance PV efficiency such as flexible or high-efficiency solar cells [7] could address modern constraints in vehicle-mounted PV systems, where surface area reduce practicality. These potential advancements can help close the gap between simulation performance and real-world deployment. Solar transport is no longer an emerging concept; it is a catalyst for reimagining the future of mobility as cleaner, smarter, and more resilient.