Design and Development of Solar-Supported Electric Three-Wheeler Compatible to Bangladesh Perspectives

1. Introduction

1.1. Background

The sustainable energy transition is a transformative move in how produced, distributed and consumed energy need to be done, and that aim to transfer away from fossil fuels towards a system centered on renewable energy sources like solar, wind, hydropower, geothermal, etc. Interestingly this shift is serious to tackling the climate crisis, as fossil fuels, which still provide around 75% of global energy supply, and releasing immense amounts of planet-warming gases, like carbon dioxide, methane, and other greenhouse gasses (GHG). Under the UN Sustainable Development Goals (SDG 7), climbing up renewable energy is the primary focus to eradicate energy poverty, improve global health, and combat climate change. As per SDG goal renewable angry should be our main focus. Consequently, the sustainable energy transition as both delivers environmental benefits and drives innovation, creates jobs and reduces energy poverty. Research based data on 2015 forecasts that coal stocks will last and well into the next century. Again, global oil and natural gas reserves or in stocks and which will be extract from in future, “will run out in the late 2060s.” On the other hand, many scientific models suggest that if we’re to limit global warming to 2 °C (the target agreed at COP26 is 1.5 °C) over 80% of coal, 50% of gas and 30% of oil reserves opens in a new window and that will need to be left anyhow without touched. [1,2].

Bangladesh needs to follow and implement SDG goal to more focus of renewable energy particular to household use and transport sector. Unfortunately, total energy sector and power supply of the country almost depends on fossil fuel [3]. Bangladesh’s power sector in 2026 reflects a growing gap between infrastructure capacity and effective electricity supply, raising concerns about energy security and system efficiency. Despite having a substantial installed generation capacity of 27,417 MW [4], and as of May 2026 the total installed capacity of BPDB Power Plants is 28,919 MW [5] But the country is unable to fully utilize this potential in practice [4]. The country has a huge potential to produce renewable energy. As per global solar atlas the daily solar generation capability from sunlight at Dhaka city (which is called Global Horizontal Irradiation is 4.497 kWh/m² per day which is 1641 kWh/m² per year and the Direct Normal Irradiation (DNI) of Dhaka and other part of Bangladesh is good for solar power generation throughout the year [6].

Figure 1. 1: The daily solar generation capability from sunlight at Dhaka City

Figure 1. 1: The daily solar generation capability from sunlight at Dhaka City

The As of March 2025, renewable energy contributes approximately 3.6 percent of Bangladesh’s electricity supplied through the national grid. Total installed renewable capacity (on-grid and off-grid) is estimated at 1,550–1,600 MW [7]. Solar power dominates the mix, representing roughly 80 percent of renewable capacity. As of 01 May 2026, the total renewable energy installed capacity of our country is 1743.8 MW [8], therefore, the total installed power generation capacity becomes 30, 662 MW.

Figure 1. 2: Total renewable energy installed capacity of Bangladesh

Figure 1. 2: Total renewable energy installed capacity of Bangladesh

A dominant share of this capacity—about 94.32%—comes from non-renewable sources, while renewable energy contributes only a small fraction of approximately 3.5% to 5.7%, indicating limited diversification in the energy mix. In reality, the actual electricity generation was 16,603 MW and the total energy generation was 101,187 GWh throughout the year [4], that means the average generation was 277 GWh/ day. As per BPDB annual report 24-25 (Maximum 14,939 MW on 05 April 2026 with average 15,000 MW up to may 2026) [6], which is significantly lower than the installed capacity and insufficient to meet national demand. With total electricity demand reaching 17,000 MW, there is a lack of around 3,804.4 MW electricity [4], leaving over one-eighth of the country’s total generation capacity unmet. This situation reveals operational inefficiencies, underuse of existing resources, and an ongoing dependence on traditional energy sources, highlighting the pressing need to enhance power generation performance and expand the use of renewable energy [5].

Figure 1. 3: Bangladesh Power Generation Capability

Figure 1. 3: Bangladesh Power Generation Capability

1.1.1. Rapid Growth of Battery Driven Three-Wheeler

In the last decades, the battery-driven auto-rickshaws in Bangladesh have become a major mode of transportation for their easy availability, affordability and huge urban mobility; again, it has become an energy concern in recent years. Different studies, newspaper reports, and institutional estimates indicate that the number of electric three-wheelers has increased dramatically from approximately 0.4 million in 2013 [9] to nearly 6 million [10] by 2025 nationwide. Similarly, Dhaka city alone currently contains around 1 million to 2 million battery-driven auto-rickshaws according to various recent reports [11,12]. For an analytical understanding of this rapid expansion, the following infographic has been developed based on available studies, research papers, newspaper reports, and institutional data.

Figure 1. 4: Growth chart of battery driven three-wheeler

Figure 1. 4: Growth chart of battery driven three-wheeler

1.1.2. Energy Consumption by Electric Three-Wheeler for Charging Battery and Its Impact on National Electricity Load

Recent studies and published reports indicate that electric three-wheelers in Bangladesh consume a substantial amount of electricity daily for battery charging, creating a noticeable impact on the national power grid. Analysis of different research findings shows that a single electric three-wheeler consumes approximately 8 kWh – 10 kWh of electricity per day on average for charging its battery pack [9]. At the national level, the cumulative electricity demand from all electric three-wheelers is significantly high. Research on Bangladesh’s power grid reported a daily electricity consumption ranging between 3679–4660 MWh/day [13], while The Business Standard estimated the demand at approximately 4000 MWh/day [11]. In addition, a BUET study identified nearly 1000 MWh/day [14] of electricity consumption associated with battery-driven three-wheelers. Combining these findings gives an estimated average national electricity demand of approximately 4226 MWh/day (≈4.23 GWh/day) for battery charging alone. In 2024-25 country’s total yearly power generation was 101,187 GWh, meaning average daily total production was 277 GWh. Therefore, it is calculated that electric three-wheelers account for nearly 1.5% of Bangladesh’s total daily electricity consumption. And the major portion of the electricity consumption for battery charging purposes is met through illegal lines. Overall, the data underscores the urgent need for strategic energy management and efficient charging infrastructure to sustain this growing sector without worsening the power deficit.

The same is also valid mathematically. In Bangladesh, a typical battery charging configuration for most electric three-wheelers uses 4–5 in number 12 V lead-acid batteries that combined battery voltage 48 – 60 v having battery capacity 100 -120 Ah. For a common setup battery of 48 V, 150 Ah the battery energy:

$$E=V\times Ah=60\times 120=7.2kWh$$

Considering charging losses (15–20%): $Actual charging energy \approx 8.5kWh$

Figure 1. 5: Energy consumption by battery-driven three-wheelers in Bangladesh

Figure 1. 5: Energy consumption by battery-driven three-wheelers in Bangladesh

1.1.3. Battery Charging Impact on Cost of Electricity

Based on the growing electricity demand from battery charging, the financial impact of this consumption is also significant. Each electric three-wheeler consumes about 8–10 kWh daily [9] for charging a 48V 120 Ah battery bank made from 4 × 12V batteries in series charging for 8-10 hours with a 20 A charger. Therefore, with an average tariff of Tk 7–10 per kWh [15], the daily charging cost per vehicle ranges from Tk 56 to Tk 100. When scaled to approximately 1 million such vehicles nationwide, total electricity use reaches around 8,000 MW to 10,000 MW per day. And considering the highest number as 6 million vehicles nationwide, the amount of electricity consumption is around 17%–22% of Bangladesh’s current daily electricity generation. Therefore, the average number of three-wheelers within the country may be considered for this research is 3.5 million and these number of three-wheelers is consuming 28,000 MW to 35,000 MW of electricity per day. The daily electricity consumption and charging cost nationwide is:

Table 1. 1: Estimated Daily Consumption and Cost of electricity

Number of Three-Wheelers	Estimated Daily Electricity Consumption	Cost in Taka 7/kWh (per day)	Cost in Taka 10/kWh (per day)
1 million Vehicles	8,000 – 10,000 MWh/day	Taka 5.6 – 7 crores	Taka 8 – 10 crores
3.5 million Vehicles	28,000 – 35,000 MWh/day	Taka 19.6 – 24.5 crore	Taka 28 – 35 crores

Table 1. 1: Estimated Daily Consumption and Cost of electricity

Number of Three-Wheelers	Estimated Daily Electricity Consumption	Cost in Taka 7/kWh (per day)	Cost in Taka 10/kWh (per day)
1 million Vehicles	8,000 – 10,000 MWh/day	Taka 5.6 – 7 crores	Taka 8 – 10 crores
3.5 million Vehicles	28,000 – 35,000 MWh/day	Taka 19.6 – 24.5 crore	Taka 28 – 35 crores

Table 1. 2: Annual Estimated Electricity Consumption and Cost (I USD=122 Taka)

Number of Three-Wheelers	Estimated Daily Electricity Consumption	Annual Cost in Taka 7/kWh	Annual Cost in Taka 10/kWh
1 million Vehicles	8,000 – 10,000 MWh/day	Taka 2,044 – 2,555 crores	Taka 2,920 crore – 3,650 crore/year
3.5 million Vehicles	28,000 – 35,000 MWh/day	Taka 7,154 – 8,943 crores	Taka 10,220 – 12,775 crores

Table 1. 2: Annual Estimated Electricity Consumption and Cost (I USD=122 Taka)

Number of Three-Wheelers	Estimated Daily Electricity Consumption	Annual Cost in Taka 7/kWh	Annual Cost in Taka 10/kWh
1 million Vehicles	8,000 – 10,000 MWh/day	Taka 2,044 – 2,555 crores	Taka 2,920 crore – 3,650 crore/year
3.5 million Vehicles	28,000 – 35,000 MWh/day	Taka 7,154 – 8,943 crores	Taka 10,220 – 12,775 crores

The rapid increase in electric three-wheelers is putting extra pressure on Bangladesh’s electricity sector and economy. While electric vehicles bring environmental and social benefits, their growing energy demand and operating costs are becoming difficult to manage. At the same time, inefficiencies in power generation continue to create a gap between electricity supply and actual demand. As a result, this issue has become more than just a challenge for the energy sector—it is now a national concern. Even with a high installed power capacity, Bangladesh still struggles to generate enough electricity efficiently. The situation highlights the need for better energy management, practical tariff policies, and greater use of renewable energy to ensure long-term economic and energy stability.

1.2. Problem Statement

Battery-powered three-wheelers are becoming increasingly popular in Bangladesh because they are affordable and convenient for everyday transportation. However, most of these vehicles depend completely on electricity from the national grid for charging, which is putting extra pressure on the country’s power supply system. In many cases, charging is done through unregulated or illegal connections, leading to energy wastage, overloading of the grid, and financial losses for the country. At the same time, the lack of proper regulations and sustainable charging facilities has become a growing concern. Therefore, there is an urgent need for a cleaner and more sustainable charging solution that can reduce dependence on grid electricity and encourage the use of renewable energy in electric three-wheelers. Therefore, the core problem addressed in this research is developing a solar-supported Electric Three-Wheeler that can:

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Encourage the integration of solar-assisted charging systems for electric three-wheelers in Bangladesh.

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Reduce dependency on grid-based battery charging demand.

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Promote the use of renewable energy by extending the operating range.

1.3. Advantages of Using Rooftop Solar PV

Rooftop solar PV provides a simpler, more practical, and cost-effective solution for electric three-wheelers in Bangladesh. In contrast, rooftop solar panels can make use of the existing roof space of the vehicle, eliminating the need for extra infrastructure while promoting the use of clean solar energy [16,17]. Another advantage of using rooftop solar is that the vehicle can receive charge while operating during the daytime. The solar panel will function to reduce battery discharge and slightly extends the operating time of the vehicle. This can reduce dependence on household or commercial electricity charging and help lower pressure on the national power grid [17,18]. Bangladesh also receives good sunlight throughout most of the year, which makes rooftop solar systems suitable for local conditions. Since electric three-wheelers mainly operate during the daytime and move at relatively low speeds, rooftop-mounted solar panels can provide useful supplementary energy during operation. Therefore, rooftop solar integration is considered a practical, affordable, and sustainable solution for Bangladesh [16].

1.4. Objectives

1.4.1. General Objective

To develop and evaluate a solar-supported electric three-wheeler suitable for Bangladesh by integrating solar energy with battery-powered transportation to reduce dependence on grid electricity and promote sustainable mobility.

1.4.2. Specific Objectives

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To study the current energy consumption and the impact of battery-driven electric three-wheelers on Bangladesh’s electricity system.

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To design and assess a solar-supported electric three-wheeler using rooftop-mounted solar photovoltaic panels.

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To evaluate the energy generation, energy consumption, and overall performance of the proposed system under practical operating conditions.

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To determine the potential reduction in grid electricity usage through the use of solar energy in electric three-wheelers.

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To analyze the economic feasibility and cost-effectiveness of the proposed solar-supported system in the context of Bangladesh.

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To identify the technical and operational challenges associated with implementing solar-supported electric three-wheelers in Bangladesh.

1.5. Expected Outcome

1.5.1. Relevance of the study to National Development

The study aligns with the national goal to save unauthorized and unregulated electricity consumption. Bangladesh addresses unregulated and unauthorized electricity consumption primarily through the Electricity Act 2018, Bangladesh Energy Regulatory Commission (BERC) regulations, prepaid metering systems, and utility enforcement programs. National policy focuses on reducing non-technical system losses, preventing electricity theft, improving billing efficiency, and modernizing electricity distribution through smart grid technologies [19]. It will also help contribute to increase generation of renewable as per national Draft Renewable Energy Policy 2025 [20]. The draft Renewable Energy Policy 2025 of Bangladesh proposes:

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Increasing the share of renewable energy in electricity generation to 20% by 2030 and 30% by 2041.

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Increase the renewable energy capacities of approximately 6,145 MW by 2030 and 17,470 MW by 2041, with solar energy expected to play the dominant role in the renewable energy mix.

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Planned Renewable Energy Expansion Areas by incorporating rooftop solar systems and floating solar projects.

2. Literature Review

2.1. Current Challenges of Electric Three-Wheelers in Bangladesh

The growing use of electric three-wheelers in Bangladesh has opened up new possibilities for affordable transportation and easy mobility within urban area. However, the increasing dependence on grid electricity, along with uncontrolled power consumption and illegal charging practices, has created serious challenges for the country’s power system. Researchers have therefore focused on improving vehicle efficiency and integrating renewable energy solutions such as solar-powered charging systems to support environmentally friendly and sustainable transportation.

2.1.1. Socio-Economic Importance of Electric Three-Wheelers

Nurunnahar et al. examined the environmental, economic, and social impacts of electric vehicles in Bangladesh and highlighted their role in providing cleaner and affordable transportation [21]. The study also warned that banning electric vehicles could negatively affect livelihoods and transportation access for many people. The Daily Star (2024) reported that several studies recommend regulating easy bikes instead of banning them because of their importance in supporting transportation and employment opportunities. Mahmud (2024) also discussed the gradual legalization of e-rickshaws in Bangladesh and highlighted government efforts to introduce proper regulation for the growing sector. The Financial Express (2025) stated that the government is planning stricter policies to regulate battery-run rickshaws due to concerns about illegal electricity use and road safety. Rahman (2025) further reported that a new BUET-designed battery-run rickshaw is being considered to improve safety, efficiency, and standardization within the sector.

2.2. Types of Electric Three-Wheeler in Bangladesh

Electric three-wheelers in Bangladesh are commonly grouped into low, medium, and high-powered types according to their motor capacity and performance. Low-powered vehicles (650–800 W) are usually modified pedal rickshaws used for short-distance travel with lower electricity consumption. Medium-powered vehicles (800–1200 W) offer better speed, passenger capacity, and operating range for regular urban transportation, while high-powered vehicles (1200–1500 W) are designed for higher speed, heavier loads, and longer-distance operation using larger motors and battery systems.

2.3. Electricity Consumption and Impact on the National Power System

The rapid growth of battery-operated three-wheelers has increased electricity consumption significantly in Bangladesh. Moreover, the uncontrolled and illegal charging systems are creating additional pressure on the national power grid. Rian and Rahman (2014) discussed the growing use of battery-operated auto-rickshaws in Bangladesh and highlighted concerns related to uncontrolled electricity consumption during charging [9]. Further analyzed the electricity demand of electric three-wheelers and explained how this unregulated charging practices are creating additional pressure on the national power grid [22]. The study emphasized the importance of organized charging systems and better energy management [22].

Examined the rapid increase of electric autorickshaws and discussed its effect on the country’s electricity system [13]. He also identified several challenges in adopting solar energy for charging purposes. Similarly, [14] reported that illegal charging practices are contributing to power theft and increasing additional pressure on the national electricity network. In another report, [14] highlighted environmental pollution caused by improper battery disposal and discussed the need for better battery management and renewable energy-based charging systems. Bangladesh Power Development Board (BPDB) (2025) brought the current condition of electricity generation and energy demand in Bangladesh, also shown the challenges of rising electricity consumption and system losses. The report also emphasized the importance of renewable energy integration and efficient energy management for future sustainable development in the field.

2.4. Study on Solar-Powered Vehicle Technologies

Many researchers have proposed several renewable energy-based solutions to reduce dependency on conventional electricity and improve the efficiency of electric transportation systems. [23] developed a hybrid solar and pedal-assisted electric three-wheeler to reduce dependency on conventional electricity sources. The study showed that combining rooftop solar panels with pedal support can improve vehicle endurance and overall energy efficiency.

Figure 2. 1: Previous study on hybrid solar and paddle assisted rickshaw

Figure 2. 1: Previous study on hybrid solar and paddle assisted rickshaw

[12] proposed a pedal-powered charging system for three-wheeler batteries as an alternative of using renewable energy solution. The study demonstrated that such a system could reduce necessity on grid electricity while supporting low-cost and workable transportation.

Figure 2. 2: Previous study on hardware prototype pedal charger

Figure 2. 2: Previous study on hardware prototype pedal charger

Saha, Goswami, and Ehsan (2011), BUET has developed an electric hybrid rickshaw for improving energy efficiency and reducing dependence on conventional fuel-based transport in Bangladesh. The study demonstrated the possibility of hybrid vehicle technology for cleaner and environmentally friendly urban transport. [24] proposed a solar-powered rickshaw system to reduce the physical effort of rickshaw pullers and decrease dependence on conventional electricity in Bangladesh. The study discussed the potential of integrating solar energy with electric rickshaw systems to improve energy efficiency and support sustainable transportation. The authors also highlighted the possibility of reducing pressure on the national power grid through renewable energy-based vehicle operation [24].

Figure 2. 3: Previous study on structural view of a solar charging auto rickshaw

Figure 2. 3: Previous study on structural view of a solar charging auto rickshaw

Huq et al. developed a torque sensor-based electrically assisted hybrid rickshaw to reduce rider effort and improve vehicle performance. The research showed that intelligent power assistance can improve energy efficiency and make electric transportation more effective. Khan et al. proposed a PV-assisted hybrid rickshaw-van integrated with a solar-powered battery charging station to reduce dependence on conventional electricity sources. The study demonstrated improved operating range and highlighted the potential of solar-powered transportation systems for sustainable mobility in Bangladesh. International Growth Centre (IGC) [25] investigated different ways to improve the energy efficiency of electric three-wheelers in Bangladesh through field experiments and performance analysis. The study found that using efficient charging systems, better battery management, and improved vehicle design can greatly reduce electricity consumption and help promote more sustainable transportation.

2.5. Renewable Energy Potential and Policies in Bangladesh

Bangladesh has strong potential for generating renewable energy, especially solar energy, due to its favorable weather and sunlight conditions throughout the year. The World Bank Group [18] provided solar irradiation and photovoltaic potential data for Bangladesh through the Global Solar Atlas, showing that the country has strong potential for year-round solar energy generation. Similarly, Sustainable and Renewable Energy Development Authority [8] presented updated renewable energy capacity data and highlighted Bangladesh’s ongoing efforts to expand renewable energy use. Government authorities are also focusing on renewable energy development and sustainable transportation systems to reduce pressure on conventional electricity generation and improve environmental sustainability.

2.6. Solar PV and Battery Technologies for Electric Vehicles

2.6.1. Common Solar PV Configuration

Most residential solar modules commonly use 60-cell solar panels, which generally have dimensions around 1650 × 990 mm (65 × 39 inches) [26]. These panels are smaller, lighter, and easier to install on rooftops compared to commercial solar panels [26,27]. Their compact design makes them suitable for applications where installation space is limited. Commercial solar panels are larger and heavier and are mainly used in large-scale installations such as warehouses, factories, and utility-scale solar projects [27]. Commercial systems commonly use 72-cell modules with higher power output and larger physical dimensions [26,27]. The table below shows the key differences:

Table 2. 1: Difference between various Solar PV

Panel Type	Cell Count	Typical Size (mm/inches)	Weight (kg/lbs)	Wattage Range
Residential	60 Cells	1650 x 990 mm (65” x 39”)	18–20 kg (40–44 lbs)	100W – 400W
Commercial	72 Cells	2000 x 1000 mm (79” x 39”)	22–24 kg (48–53 lbs)	400W – 450W
Industrial (Less Common)	96 Cells	2000 x 1320 mm (79” x 52”)	28–30 kg (62–66 lbs)	480W – 550W

Table 2. 1: Difference between various Solar PV

Panel Type	Cell Count	Typical Size (mm/inches)	Weight (kg/lbs)	Wattage Range
Residential	60 Cells	1650 x 990 mm (65” x 39”)	18–20 kg (40–44 lbs)	100W – 400W
Commercial	72 Cells	2000 x 1000 mm (79” x 39”)	22–24 kg (48–53 lbs)	400W – 450W
Industrial (Less Common)	96 Cells	2000 x 1320 mm (79” x 52”)	28–30 kg (62–66 lbs)	480W – 550W

The dimensions and weight of solar panels are closely related to their wattage output [26]. A typical 300W solar panel generally uses 60-cell modules and measures around 1650 mm × 990 mm, while a 400W solar panel commonly uses 72-cell modules with dimensions near 2000 mm × 1000 mm [26]. Higher-capacity 500W panels use larger-format cells and advanced technologies, resulting in larger dimensions and weight [26,28]. These standard solar panel sizes are important for planning installation layout, structural support, transportation, and mounting system design [28]. A clear knowledge on solar panel dimensions helps optimize rooftop space utilization and improve the efficiency of solar energy systems.

Figure 2. 4: General size of solar PV array

Figure 2. 4: General size of solar PV array

2.6.2. Commonly Used Battery Pack

In Bangladesh, most electric three-wheelers use lead-acid battery packs because they are affordable, widely available, and easy to maintain. These batteries are usually connected in 48 V or 60 V configurations using several 12 V battery units. However, most of the commonly used batteries are not suitable for fast charging and slow discharging, which reduces their efficiency and overall lifespan. They also have several other limitations, including long charging time, heavy weight, low energy efficiency, and frequent maintenance requirements. Improper charging practices and overloading further reduce battery performance and durability. As a result, these low-efficiency battery systems increase electricity consumption, shorten vehicle operating range, and place additional pressure on Bangladesh’s already stressed power system.

Table 2. 2: Battery pack data

Battery Quality	Battery Type	Capacity Used	Main Features	Performance	Approximate Lifetime
Low Quality	Local Lead-Acid Battery	48–60 V, 80–100 Ah	Low cost and easily available, but heavy and requires frequent maintenance	Low efficiency with slow charging, fast discharging, and shorter backup time	1–1.5 years
Medium Quality	Standard AGM/Gel Battery	48–60 V, 100–150 Ah	Better charging capability, lower maintenance, and improved durability	Moderate efficiency with improved charging and comparatively slower discharging	2–3 years
High Quality	LiFePO4 (Lithium Iron Phosphate) Battery	48–72 V, 100–200 Ah	Lightweight, fast charging, slow discharging, long lifespan, and high energy efficiency	High performance with fast charging, slow discharging, and excellent long-term reliability	5–8 years

Table 2. 2: Battery pack data

Battery Quality	Battery Type	Capacity Used	Main Features	Performance	Approximate Lifetime
Low Quality	Local Lead-Acid Battery	48–60 V, 80–100 Ah	Low cost and easily available, but heavy and requires frequent maintenance	Low efficiency with slow charging, fast discharging, and shorter backup time	1–1.5 years
Medium Quality	Standard AGM/Gel Battery	48–60 V, 100–150 Ah	Better charging capability, lower maintenance, and improved durability	Moderate efficiency with improved charging and comparatively slower discharging	2–3 years
High Quality	LiFePO4 (Lithium Iron Phosphate) Battery	48–72 V, 100–200 Ah	Lightweight, fast charging, slow discharging, long lifespan, and high energy efficiency	High performance with fast charging, slow discharging, and excellent long-term reliability	5–8 years

2.7. Limitations of Existing Systems

Although electric three-wheelers have become a popular and affordable mode of transport in Bangladesh, the current system still faces several problems. Most of these vehicles depend fully on electricity from the national grid for charging, which increases pressure on the country’s power supply. In many places, illegal charging and unauthorized electricity use have also become common, creating difficulties for proper power distribution and management. Many existing vehicles also struggle with poor battery performance, limited travel distance, low charging efficiency, and the lack of proper standards or regulations. Earlier studies mainly focused on energy use, hybrid systems, or charging methods, while the practical use of rooftop solar technology in locally used electric three-wheelers has received less attention. In addition, growing electricity demand and concerns over battery waste make it important to develop cleaner and more sustainable transportation systems based on renewable energy.

2.8. Research Gap Identification

Previous studies have explored topics such as electricity consumption, hybrid vehicle technologies, battery charging methods, and the use of renewable energy in electric three-wheelers. Several researchers proposed solar-assisted or pedal-assisted transportation systems to improve energy efficiency and reduce dependence on conventional electricity sources. However, limited research has focused on developing a practical rooftop solar-assisted electric three-wheeler suitable for Bangladesh’s operating conditions. Most previous studies did not fully evaluate the combined performance of rooftop solar panels, battery systems, vehicle endurance, and reduction of grid electricity dependence under practical local conditions. Therefore, this research focuses on designing and evaluating a solar-assisted electric three-wheeler system that can support battery charging through rooftop solar energy, improve vehicle endurance, and reduce dependence on grid electricity in Bangladesh.

3. Methodology

3.1. System Design

The concept is to develop an electric three-wheeler that will use a roof mounted solar panel to support battery pack in addition to the existing battery capacity thereby increase its endurance. The project will keep further development option for the development of a solar charging station for the battery pack for initial charge and then supplemented by the roof mounted solar panel thereby increasing the operating range and duration. This way the solar operated three-wheeler will run completely with renewable energy. The vehicle will not take any energy from commercial or domestic charging source and save national electricity.

3.2. Material Selection

The major components of the proposed solar-supported electric three-wheeler need to be selected by considering efficiency, performance, power output, charging capability, and cost-effectiveness. Importance also needs to be given to smooth vehicle operation, proper utilization of solar energy, reliable battery performance, and suitability for the local operating conditions of Bangladesh. The key selection considerations are discussed below:

• The efficiency of the solar PV system needs to be considered to ensure maximum use of solar energy from the limited rooftop area of the vehicle.
• Battery charging and discharging performance needs to be considered to ensure reliable energy storage, faster charging, and longer operating time.
• The motor power output needs to be selected carefully to provide sufficient speed, torque, and load-carrying capability for smooth vehicle operation.
• Cost-effectiveness needs to be considered to ensure affordability, easy maintenance, and practical use under the local conditions of Bangladesh.
• The energy transmission system needs to be considered carefully, as higher motor load can increase battery discharge rate and reduce the vehicle’s operating duration.

3.2.1. Differential Motor Selection

The capacity of differential motor needs to be selected meticulously so that it can provide a good balance between performance, energy efficiency, battery usage, and operating cost for the proposed solar-assisted electric three-wheeler. For selecting the capacity of differential motor, it is important to analyze the electrical power flow and battery discharge behavior in an electric three-wheeler system. Following picture represents that an increase in vehicle speed results in higher motor power demand, which increases battery current consumption and accelerates battery discharge thereby reducing total runtime. However, more grid electricity will be required to charge a higher ampere-hour battery to drive a high-power differential motor.

Figure 3. 1: Vehicle behavior with increased speed and load

Figure 3. 1: Vehicle behavior with increased speed and load

3.2.2. Battery Pack Selection

The battery capacity in ampere-hours (Ah) determines how long the vehicle can run. Below is the comparison for a 48 V battery pack. The 4 x 100 Ah battery pack stores twice the energy of the 4 x 50 Ah pack. This gives significantly better runtime, better operating margin under passenger load, and less stress on the batteries.

Table 3. 1: Common battery used

System Voltage	Battery Arrangement	Typical Use
36 V	3 x 12 V batteries	Light-duty setup
48 V	4 x 12 V batteries	Most common and practical
60 V	5 x 12 V batteries	Higher-power configuration

Table 3. 1: Common battery used

System Voltage	Battery Arrangement	Typical Use
36 V	3 x 12 V batteries	Light-duty setup
48 V	4 x 12 V batteries	Most common and practical
60 V	5 x 12 V batteries	Higher-power configuration

Configuration	Battery Energy	Ideal Runtime at 800 W	Practical Runtime
4 x 50 Ah batteries	48 V x 50 Ah = 2.4 kWh	3.0 hours	2.0 - 2.5 hours
4 x 100 Ah batteries	48 V x 100 Ah = 4.8 kWh	6.0 hours	4.0 - 5.0 hours

Configuration	Battery Energy	Ideal Runtime at 800 W	Practical Runtime
4 x 50 Ah batteries	48 V x 50 Ah = 2.4 kWh	3.0 hours	2.0 - 2.5 hours
4 x 100 Ah batteries	48 V x 100 Ah = 4.8 kWh	6.0 hours	4.0 - 5.0 hours

3.2.3. Rooftop Solar PV Selection

Many important factors may be considered when selecting the solar PV panel for the rooftop of a three-wheeler. These include:

• Available space on the rooftop/body
• Charging efficiency
• Weight of the panel
• Angle of sunlight incidence
• Weather conditions and available sunlight hours

Among these, the most important factor is the available space on the vehicle roof. In general, a larger solar panel can absorb more sunlight and produce more electrical power. However, the rooftop area of a three-wheeler is limited, making it difficult to install more than one solar panel on a single vehicle. In general, the available roof-top area of three-wheeler varies within 1.5 m² to 2 m². Another important consideration is the physical size of commercially available solar panels. Most standard solar PV arrays are built with 60 solar cells combined in a single panel. Because of this, selecting a smaller but higher-efficiency panel becomes very important for rooftop installation on a three-wheeler. Based on market surveys and manufacturer datasheets, commonly available solar panels range between 900 mm × 650 mm to 2000 mm × 1500 mm, with power ratings ranging from 100 W to 500 W. The following values assume good sunlight, correct wiring, and use of a proper MPPT charge controller.

Table 3. 2: Factors for selecting roof top solar PV

Panel Rating	Typical Real Output	Useful Daily Energy	Effect on Runtime
330 W	about 250 W	about 1.25 kWh/day	about +1.5 hours
400 W	about 300 W	about 1.5 kWh/day	about +1.9 to 2.0 hours

Table 3. 2: Factors for selecting roof top solar PV

Panel Rating	Typical Real Output	Useful Daily Energy	Effect on Runtime
330 W	about 250 W	about 1.25 kWh/day	about +1.5 hours
400 W	about 300 W	about 1.5 kWh/day	about +1.9 to 2.0 hours

Operating Condition	Expected Runtime	Comment
Battery only	about 4.0 - 5.0 hours	Suitable for regular use without solar support
Battery + 330 W solar panel	about 5.5 - 6.5 hours	Less efficient for solar support
Battery + 400 W solar panel	about 6.0 - 7.0 hours	Best balance of roof size, weight, and useful support

Operating Condition	Expected Runtime	Comment
Battery only	about 4.0 - 5.0 hours	Suitable for regular use without solar support
Battery + 330 W solar panel	about 5.5 - 6.5 hours	Less efficient for solar support
Battery + 400 W solar panel	about 6.0 - 7.0 hours	Best balance of roof size, weight, and useful support

3.2.4. Final Recommendation

This combination is expected to provide reasonable battery capacity, improve daytime runtime, and a realistic solar contribution without making the roof system heavy. In simple terms, the system should be described as a solar-assisted battery-electric three-wheeler. The battery remains the main energy source, while the rooftop solar panel acts as a range extender and reduces battery discharge during sunny daytime operation. Based on the full discussion, the recommended setup is:

Battery: 4 x 12 v, 100 Ah batteries

Solar array: 1 x 400 W

Differential Motor: 48 v, 800 watts

MPPT Charge controller: 20 Amps

3.3. Design Modeling

The design modeling process may be performed to develop the structural layout of the rooftop solar panel system while considering the aerodynamic effect on the vehicle. Separate electrical connections and control circuit arrangements to be designed for proper system integration. Different software tools need to be used during the design and analysis stages to evaluate the overall system performance.

➢

AutoCAD: AutoCAD will help prepare the rooftop solar panel layout, component positioning, and structural dimensions of the proposed electric three-wheeler.

➢

MATLAB: MATLAB may be used to study battery performance, solar power generation, energy management, and the overall behavior of the system under different operating conditions.

3.4. Fabrication

A lightweight support frame will be required as per the roof dimensions of the vehicle to ensure stable fitting of the solar panel system. An aerodynamic fiberglass roof structure will reduce air resistance and improve the appearance of the vehicle; this will support better solar energy absorption. A compact lightweight body with 14-inch wheels, front and rear disc brakes, and a modified display system for solar charging information may be assembled and finally tested for stability, alignment, vibration resistance, and overall operating performance.

3.5. Power Transmission and Efficiency Consideration

In a solar-supported electric three-wheeler system, electrical energy needs to be generated from the solar PV panel and stored in the battery through an appropriate charging system. The stored energy is then used to operate the motor controller and DC motor for running the vehicle. Since the motor requires more power at higher speed and load conditions, the battery discharges more quickly, which reduces the vehicle’s operating time. Therefore, proper selection of the motor rating, battery capacity, and solar PV size is important to improve energy efficiency and achieve a longer driving range.

3.6. Testing and Validation

To validate the system operation and efficiency following tests will be required:

➢

Battery Charging with Solar Energy: The solar charging system needs to be analyzed to understand how effectively the rooftop solar panel can charge the battery under normal sunlight conditions. Factors such as charging time, voltage stability, and charging performance need to be considered to ensure efficient transfer of solar energy to the battery pack.

➢

Endurance Test: The endurance performance of the electric three-wheeler needs to be evaluated to determine how long the vehicle can operate using combined support from the battery pack and the solar energy system. Operating time, driving range, and overall vehicle performance need to be observed under normal running conditions.

➢

Safety Test: The safety performance of the proposed system needs to be considered to ensure reliable and secure operation during regular use. Special attention needs to be given to electrical connections, battery protection, motor performance, and the structural stability of the roof-mounted solar panel system.

➢

Battery Charging with Solar Energy: The solar charging system needs to be analyzed to understand how effectively the rooftop solar panel can charge the battery under normal sunlight conditions. Factors such as charging time, voltage stability, and overall charging performance need to be considered to ensure proper transfer of solar energy to the battery pack.

➢

Endurance Test: The endurance performance of the electric three-wheeler needs to be evaluated to determine how long the vehicle can operate using combined support from the battery pack and the solar energy system. Vehicle running time, driving range, and overall performance need to be observed under normal operating conditions.

➢

Safety Test: The safety performance of the proposed system needs to be considered to ensure reliable and secure operation during regular use. Special attention needs to be given to electrical connections, battery protection, motor performance, and the structural stability of the roof-mounted solar panel setup.

Figure 3. 2: Conceptual framework

Figure 3. 2: Conceptual framework

3.7. Data Analysis

The data collected during the testing phase needs to be analyzed to evaluate the overall performance of the proposed solar-supported electric three-wheeler. Parameters such as solar charging performance, battery charging and discharging behavior, vehicle running time, motor performance, and energy consumption need to be considered to understand the system efficiency and operating capability. Graphs, tables, and charts also need to be prepared to present the results clearly and in an easy-to-understand manner. The overall system design needs to focus on achieving safe, efficient, and environmentally friendly operation suitable for practical use in Bangladesh. Importance also needs to be given to improving renewable energy utilization, reducing dependence on conventional grid electricity, and increasing vehicle endurance and performance. Repeated testing and data analysis need to be considered to further improve the system for reliable and sustainable green transportation.

4. Design and Construction

4.1. Design and Construction

This chapter outlines the process to be followed in the design and developing a solar supported electric three-wheeler. The methodology focuses on conceptualizing, designing, and electrical integration of the solar panel with the control circuit. The approach involves selection of suitable major components and mathematical calculation to determine the desired outcome.

4.1.1. Key Assumptions. There Are Few Assumptions Has Been Considered as Follows

➢

Motor rated power: 800 W

➢

Average draw assumed 560 W depending on load and road (70% load).

➢

Approximate total system losses (controller, wiring, drivetrain): : 15–20%.

➢

Bangladesh/Dhaka solar yield: ~4.5 kWh/ m². [18]

➢

Solar panel Efficiency: 18-22%

➢

Solar panel system loss: 15-20%

➢

Total Sun hour 5 hours

➢

Approximate passenger load: 3 x 70 kg = 310 kg

➢

Vehicle speed: 20-25 km/ h

4.2. Power Transmission of the Solar-Supported Electric Three-Wheeler System

4.2.1. Combined Power Flow Block Diagram

The following block explains the general provision to transmit power up to the motor for varying load

Figure 4. 1: Combined power flow block diagram

Figure 4. 1: Combined power flow block diagram

4.2.2. Electrical and Control Configuration

The electrical integration of the solar panel is as follows:

Figure 4. 2: Electrical and Control Configuration

Figure 4. 2: Electrical and Control Configuration

4.2.3. Motor Capacity and Power Consumption

Common Gear Ratios and Type for 800 W Motors as shown below.

➢

Motor rated power = 800 W

➢

Gear ratio = 1:10

➢

Tyre size = 14 inch

➢

Typical full-load motor speed ≈ 4500 RPM

➢

Speed proportional to motor RPM/ load

Estimated speed at different motor loads for 800 W motor:

Table 4. 1: speed at different motor loads for 800 W motor

Motor Load	Output Power (W)	Current Draw (A)	Estimated Motor RPM	Estimated Speed (km/h)	Power Consumption (kWh/h)
30%	240 W	5.0 A	1350 rpm	9.0 km/h	0.24
40%	320 W	6.7 A	1800 rpm	12.1 km/h	0.32
50%	400 W	8.3 A	2250 rpm	15.1 km/h	0.40
60%	480 W	10.0 A	2700 rpm	18.1 km/h	0.48
70%	560 W	11.7 A	3150 rpm	21.1 km/h	0.56
80%	640 W	13.3 A	3600 rpm	24.1 km/h	0.64
90%	720 W	15.0 A	4050 rpm	27.1 km/h	0.72
100%	800 W	16.7 A	4500 rpm	30.2 km/h	0.80

Table 4. 1: speed at different motor loads for 800 W motor

Motor Load	Output Power (W)	Current Draw (A)	Estimated Motor RPM	Estimated Speed (km/h)	Power Consumption (kWh/h)
30%	240 W	5.0 A	1350 rpm	9.0 km/h	0.24
40%	320 W	6.7 A	1800 rpm	12.1 km/h	0.32
50%	400 W	8.3 A	2250 rpm	15.1 km/h	0.40
60%	480 W	10.0 A	2700 rpm	18.1 km/h	0.48
70%	560 W	11.7 A	3150 rpm	21.1 km/h	0.56
80%	640 W	13.3 A	3600 rpm	24.1 km/h	0.64
90%	720 W	15.0 A	4050 rpm	27.1 km/h	0.72
100%	800 W	16.7 A	4500 rpm	30.2 km/h	0.80

4.2.3.1. Battery Energy Calculation (48 V, 100 Ah pack)

This battery configuration provides sufficient stored energy to satisfy the estimated vehicle runtime and range requirements [29]. The nominal energy content can be calculated as:

E_battery = V × Ah

E_battery = 48 V × 100 Ah = 4800 Wh = 4.8 kWh

(Considering system losses; approx 85% usable then)

Effective usable energy becomes: $E\_usable\approx 4.8kWh\times 0.85\approx 4.1kWh$

4.2.3.2. Solar Energy Requirement and PV Output Estimation

Considering approx. 20% charging and conversion losses, the total electrical energy required from the PV system to fully recharge the 4.8 kWh battery pack becomes:

$$E_{required}={\displaystyle \frac{E_{battery}}{0.8}}={\displaystyle \frac{4.8}{0.8}}=6.0\mathrm{kWh}$$

Therefore, approximately 6.0 kWh of solar-generated electrical energy is required to fully recharge the battery from a fully discharged condition.

Let us determine the total area required to produce 6 kWh of electricity from solar energy.

The average daily solar energy availability in Dhaka is approximately [18]:

$$4.5{\mathrm{kWh}/\mathrm{m}}^2/\mathrm{day}$$

Assuming:

PV module efficiency: ${\eta }_{panel}=20\mathrm{\%}=0.20$

Overall system efficiency: ${\eta }_{system}=90\mathrm{\%}=0.90$[30]

The usable electrical energy generated per square meter of PV area per day becomes:

$$E_{m^2}=4.5\times 0.20\times 0.90=0.81{\mathrm{kWh}/\mathrm{m}}^2/\mathrm{day}$$

Therefore, the total PV area required to generate 6.0 kWh/day is: $A_{total}={\displaystyle \frac{6.0}{0.81}}\approx 7.4{\mathrm{m}}^2$

Thus, approximately 7.4 m² of solar PV area would theoretically be required to fully recharge the battery within one sunny day under the stated assumptions. However, a typical electric three-wheeler rooftop provides only approximately 1.5–2.0 m² of usable installation area, allowing practical installation of only 300–400 W of PV capacity. Therefore, the rooftop solar system should be considered as a supplemental daytime energy source and range extender rather than the sole charging source.

4.2.3.3. Daily Energy Generation from 400 W PV Array

With a 400 W (0.4 kW) PV array and an assumed average of 5 peak sun hours per day, the daily energy production by solar panel is:

E_PV_daily ≈ 0.4 kW × 5 h = 2 kWh per day

In reality: considering 80% efficiency

E_PV_day ≈ 0.4 kW × 5 h × 0.8 = 1.6 kWh/ day

Therefore, the number of ideal days required to generate the 6.0 kWh (for battery) needed to charge the battery from empty is:

Theoretically, Days_to_full_charge ≈ 6.0 kWh ÷ 2 kWh/day ≈ 3 days

Practically, Days_to_full_charge ≈ 6.0 kWh ÷ 1.6 kWh/day ≈ 3.75 days

In other words, if the vehicle were left stationary with the 400 W rooftop PV system and experienced good sunshine, it would take approximately 3 - 4 sunny days to charge the battery from 0% to 100% using solar energy alone.

4.3. Energy Flow

Here the motor will require a total of 560 W to keep the vehicle moving at a certain speed and load condition. This total power requirement would come from the available energy sources connected to the system. In a conventional electric three-wheeler without solar support, the entire 560 W would be supplied only by the battery pack. In the proposed solar-assisted system, the rooftop solar panel will generate approximately 300 W during good sunlight conditions. This solar power would be supplied through the MPPT charge controller directly into the electrical system while the vehicle is operating. Therefore, the solar panel would share part of the motor’s power demand and reduce the amount of power that must be supplied by the battery.

Figure 4. 3: Energy flow chart

Figure 4. 3: Energy flow chart

Power required from the battery would become:

$$\mathrm{Battery}\mathrm{Power}\mathrm{Required}=\mathrm{Motor}\mathrm{Demand}-\mathrm{Solar}\mathrm{Contribution}=560\mathrm{W}-300\mathrm{W}=260\mathrm{W}$$

This means the battery would need to supply only 260 W instead of the full 560 W. As a result, the battery would discharge more slowly, increasing the vehicle’s operating time and reducing the overall depth of battery discharge.

The calculated current flow, for a 48 V battery system:

Without solar support: $I={\displaystyle \frac{P}{V}}={\displaystyle \frac{560}{48}}\approx 11.67\mathrm{A}$

So the battery alone would supply about 11.67 A continuously.

With solar support: $I={\displaystyle \frac{260}{48}}\approx 5.42\mathrm{A}$

The battery would only supply about 5.42 A, because the solar panel will be contributing the remaining energy. This will reduce current draw, lower battery stress, improve battery life, reduce heating, and increase the overall operating duration of the vehicle.

4.4. Design Overview

A simple AutoCAD design overview is shown below:

Figure 4. 4: AUTOCAD layout of different parts of the three-wheeler

Figure 4. 4: AUTOCAD layout of different parts of the three-wheeler

4.5. Runtime Analysis

4.5.1. Battery Runtime Analysis

Motor rated power = 800 W

Battery voltage = 48 V 100 Ah

Motor current from the 48 V battery pack: I_motor = P / V = 800 / 48 = 16.7 A [29].

Therefore, the rated traction current is approximately 16.7 A. In practice, the battery current may be slightly higher after controller and motor losses are considered. Again, the vehicle will not run at full load for economical speed. Here, considering a maximum 70% load. Finally, the load power becomes = 800 w x 70% = 560 W

4.5.2. Solar-Supported Runtime Analysis (1.6 kWh and 6.4 kWh).

A 400 W rooftop panel seldom delivers its full nameplate power continuously during actual driving because of panel temperature, varying sun angle, road direction, passing shade, and dust the 20%, the solar efficiency becomes 80%.

Battery runtime with solar power: $T={\displaystyle \frac{\mathrm{Battery}\mathrm{Energy}\left(\mathrm{kWh}\right)}{\mathrm{Load}\mathrm{Power}\left(\mathrm{kW}\right)}}$

Given:

Daily solar energy contribution = 1.6 kWh

Full Load = 0.8 kW (800 W), $T_{battery}={\displaystyle \frac{1.6kWh}{0.8kW}}$ = $2\mathrm{hours}$

At 70% Load = 0.56 kW (560 W), $T_{battery}={\displaystyle \frac{1.6kWh}{0.56kW}}=2.8\mathrm{hours}$

(Battery energy 1.6 kWh)

Table 4. 2: Motor load vs runtime data with Solar energy

Motor Load	Power	Current	Motor RPM	Wheel RPM	Speed	Solar Energy	Nominal Runtime
100%	800 W	16.67 A	4500	450	30.2 km/h	1.6 kWh	2.00 h
70%	560 W	11.67 A	3150	315	21.1 km/h	1.6 kWh	2.86 h

Table 4. 2: Motor load vs runtime data with Solar energy

Motor Load	Power	Current	Motor RPM	Wheel RPM	Speed	Solar Energy	Nominal Runtime
100%	800 W	16.67 A	4500	450	30.2 km/h	1.6 kWh	2.00 h
70%	560 W	11.67 A	3150	315	21.1 km/h	1.6 kWh	2.86 h

Figure 4. 5: Motor load vs runtime relation with solar energy

Figure 4. 5: Motor load vs runtime relation with solar energy

This 2.8-hour runtime was calculated at 70% load. In practical operation, the actual runtime may be slightly lower due to system inefficiencies, frequent stop-start driving conditions, and battery operating limitations. Therefore, under normal service conditions and without solar assistance, the practical operating time is expected to be around 1.5–2 hours.

4.5.3. Combined Runtime Analysis (Total Available Energy = 6.4 kWh)

Total Energy Available

Battery energy = 4.8 kWh

Solar transferable energy = 1.6 kWh

$$E_{total}=4.8+1.6=6.4\mathrm{kWh}$$

At Full Load (800 W), $T={\displaystyle \frac{6.4}{0.8}}=8.0\mathrm{h}$

At 70% Economical Load (560 W), $T={\displaystyle \frac{6.4}{0.56}}=11.43\mathrm{h}$

Combined Speed–Load Runtime Table (6.4 kWh Total Energy)

Table 4. 3: Combined Motor load vs runtime data for 64 kWh energy

Motor Load	Power	Current	Motor RPM	Wheel RPM	Speed	Total Available Energy	Nominal Runtime	Practical Runtime
100%	800 W	16.67 A	4500	450	30.2 km/h	6.4 kWh	8.00 h	6–7 h
70%	560 W	11.67 A	3150	315	21.1 km/h	6.4 kWh	11.43 h	8–10 h

Table 4. 3: Combined Motor load vs runtime data for 64 kWh energy

Motor Load	Power	Current	Motor RPM	Wheel RPM	Speed	Total Available Energy	Nominal Runtime	Practical Runtime
100%	800 W	16.67 A	4500	450	30.2 km/h	6.4 kWh	8.00 h	6–7 h
70%	560 W	11.67 A	3150	315	21.1 km/h	6.4 kWh	11.43 h	8–10 h

Additional Runtime from 1.6 kWh Solar Energy

Figure 4. 6: Runtime time improvement with solar support

Figure 4. 6: Runtime time improvement with solar support

4.5.4. Practical Interpretation

Under full load condition (800 W), the electric three-wheeler is expected to operate at around 30 km/h with a runtime of approximately 6–7 hours, while under economical load condition (560 W), the runtime may increase to around 8–10 hours at a speed of about 21 km/h. The additional 1.6 kWh solar-assisted energy can further extend the operating time. However, in practical use, the actual runtime may reduce due to motor losses, stop-start driving, road conditions, passenger load, and variation in sunlight availability.

Estimated Practical runtime

Table 4. 4: Estimated practical runtime

Case	Theoretical Runtime	Realistic Runtime considered
Full load, battery only	4 - 5 h	3 – 4 h
70% load, battery only	6 - 8 h	6 - 7 h
Full load + solar	6 - 7 h	5 - 6 h
70% load + solar	8 - 10 h	8 - 9 h

Table 4. 4: Estimated practical runtime

Case	Theoretical Runtime	Realistic Runtime considered
Full load, battery only	4 - 5 h	3 – 4 h
70% load, battery only	6 - 8 h	6 - 7 h
Full load + solar	6 - 7 h	5 - 6 h
70% load + solar	8 - 10 h	8 - 9 h

4.6. Approximate Range on Flat Roads

A more realistic practical operating duration is approximately 6–7 hours without solar assistance and 8–9 hours with daytime solar support. For a 700 kg loaded three-wheeler driven by an 800 W motor, a modest operating speed of about 20 km/h on flat roads is a realistic basis for range estimation. Assuming an average operating speed of approximately 20 km/h on relatively flat roads. However, the addition of a roof mounted solar would generate around 1.6 kWh of energy for the battery pack would drive the vehicle more 2 hours-time thereby giving a range extension of 40 km each day.

$$\mathit{R}\mathit{a}\mathit{n}\mathit{g}{\mathit{e}}_{\mathit{b}\mathit{a}\mathit{t}\mathit{t}\mathit{e}\mathit{r}\mathit{y}-\mathit{o}\mathit{n}\mathit{l}\mathit{y}}=20\times 6\mathit{t}\mathit{o}7=120\mathit{k}\mathit{m}\mathit{t}\mathit{o}140\mathit{k}\mathit{m}$$

$$Rang{e}_{solar-assisted}=20\times 8to9=160kmto180km$$

4.7. Proposed Configuration of Solar Supported Three-Wheeler

The proposed solar-supported electric three-wheeler is designed with an 800 W differential motor, a 48 V battery pack consisting of four 12 V, 100 Ah batteries connected in series, and a 400 W rooftop solar PV panel connected through an MPPT charge controller. The vehicle is mainly charged from household or grid electricity during nighttime, while the rooftop solar panel provides additional energy support during daytime operation to reduce battery discharge and improve the operating range of the vehicle.

4.7.1. Vehicle and Load Basis

The vehicle load condition was considered based on the typical passenger capacity and normal operating conditions commonly found in Bangladesh.

Table 4. 5: Proposed vehicle load basis

Parameter	Expression / Basis	Value
Vehicle curb weight	Given	400 kg
Additional passenger and accessory load	Given	300 kg
Included additional load	Battery 80 kg + panel 20 kg + passengers/payload	Included
Total running weight	400 + 300	700 kg
Traction motor rating	Given	800 W

Table 4. 5: Proposed vehicle load basis

Parameter	Expression / Basis	Value
Vehicle curb weight	Given	400 kg
Additional passenger and accessory load	Given	300 kg
Included additional load	Battery 80 kg + panel 20 kg + passengers/payload	Included
Total running weight	400 + 300	700 kg
Traction motor rating	Given	800 W

4.7.2. Battery Pack Configuration

The 48 V battery configuration was selected to ensure sufficient energy storage and a stable power supply for efficient operation of the 800 W motor system.

Table 4. 6: Proposed battery specification

Parameter	Expression / Basis	Value
Number of batteries	Given	4 units
Individual battery rating	Given	12 V, 100 Ah
Battery pack voltage	12 × 4	48 V
Battery pack capacity	Series connection capacity	100 Ah
Battery pack energy	48 × 100	4.8 kWh

Table 4. 6: Proposed battery specification

Parameter	Expression / Basis	Value
Number of batteries	Given	4 units
Individual battery rating	Given	12 V, 100 Ah
Battery pack voltage	12 × 4	48 V
Battery pack capacity	Series connection capacity	100 Ah
Battery pack energy	48 × 100	4.8 kWh

4.7.3. Solar Charging Configuration

A single rooftop solar panel of 400 W is connected to the 48 V battery pack through an appropriate MPPT charge controller. The panel will be a support source during daytime rather than the sole charging source. However, the rooftop-mounted solar panel was considered as an additional energy source to support daytime vehicle operation and reduce battery discharge during running conditions.

Table 4. 7: Proposed Solar configuration

Parameter	Expression / Basis	Value
Solar panel rating	Given	400 W
Panel mounting area	Given	1500 mm × 1000 mm
Average effective sun hours	Design assumption	5 h/day
Overall charging efficiency	MPPT + wiring + battery charging	80%

Table 4. 7: Proposed Solar configuration

Parameter	Expression / Basis	Value
Solar panel rating	Given	400 W
Panel mounting area	Given	1500 mm × 1000 mm
Average effective sun hours	Design assumption	5 h/day
Overall charging efficiency	MPPT + wiring + battery charging	80%

4.7.4. Proposed Technical Specification of Battery Supported Three-Wheeler

The following summary presents the main design specifications in a simplified, board-ready calculation format:

Table 4. 8: Proposed Technical Specification of the Battery supported three-wheeler

Parameter	Expression / Basis	Value
Battery pack	4 × 12 V, 100 Ah in series	48 V, 100 Ah
Motor capacity	1 x 800-watt differential	800 watt
Nominal battery energy	48 × 100	4.8 kWh
Solar panel	Single rooftop PV panel	400 W
Useful solar energy	400 × 5 × 0.8	1.6 kWh/day
Solar-only charge time	4.8 / 1.6	3 days nominal
Motor power	Given	800 W
Motor current	800 / 48	16.7 A
Net battery load during solar support	560 − 320	240 W
Battery-only runtime	4.8 / 0.56	6 -7 h
Solar-assisted runtime	(4.8 + 1.6)/ 0.56	8 – 9 h
Practical speed basis	Flat road operation	20 km/h
Battery-only range	20 km/h × 7 h	140 km theoretical
Solar-assisted range	20 km/h × 9 h	180 km theoretical

Table 4. 8: Proposed Technical Specification of the Battery supported three-wheeler

Parameter	Expression / Basis	Value
Battery pack	4 × 12 V, 100 Ah in series	48 V, 100 Ah
Motor capacity	1 x 800-watt differential	800 watt
Nominal battery energy	48 × 100	4.8 kWh
Solar panel	Single rooftop PV panel	400 W
Useful solar energy	400 × 5 × 0.8	1.6 kWh/day
Solar-only charge time	4.8 / 1.6	3 days nominal
Motor power	Given	800 W
Motor current	800 / 48	16.7 A
Net battery load during solar support	560 − 320	240 W
Battery-only runtime	4.8 / 0.56	6 -7 h
Solar-assisted runtime	(4.8 + 1.6)/ 0.56	8 – 9 h
Practical speed basis	Flat road operation	20 km/h
Battery-only range	20 km/h × 7 h	140 km theoretical
Solar-assisted range	20 km/h × 9 h	180 km theoretical

The proposed system is designed as a solar-supported battery-electric three-wheeler in which the battery pack is mainly charged from household or grid electricity during nighttime. During daytime operation, the rooftop solar PV panel provides additional energy support, which helps reduce battery discharge, improve overall efficiency, and increase the practical driving range of the vehicle.

5. Results and Analysis

5.1. On Ground Findings

5.1.1. Data from Local Easy Bike

To check the authenticity of the data regarding the technical specification on auto rickshaw/ easy bike available in the open source and in company advertisement. Several interviews were also conducted to collect various data on different the three-wheelers running in Dhaka city.

Table 5. 1: Sample data sheet based on realistic operating conditions of 48 V, 800 W three-wheeler in Dhaka city traffic

Sl. No	Time	Speed (km/h)	Motor Power (W)	Battery Voltage (V)	Current (A)	Energy (Wh/hr)	Distance (km/hr)
1	08:00	16	380	50.8	7.5	380	16
2	08:30	18	420	50.2	8.4	420	18
3	09:00	20	480	49.8	9.6	480	20
4	09:45	22	550	49.1	11.2	550	22
5	10:30	19	460	48.7	9.4	460	19
6	11:15	17	400	48.3	8.3	400	17
7	12:00	14	320	48.0	6.7	320	14
8	01:00	15	350	47.7	7.3	350	15
9	02:00	18	420	47.4	8.9	420	18
10	03:00	21	500	47.0	10.6	500	21
11	04:00	20	480	46.8	10.3	480	20
12	05:00	19	450	46.5	9.7	450	19
13	06:00	17	410	46.2	8.9	410	17
14	06:30	15	360	46.0	7.8	360	15
15	07:00	14	330	45.8	7.2	330	14

Table 5. 1: Sample data sheet based on realistic operating conditions of 48 V, 800 W three-wheeler in Dhaka city traffic

Sl. No	Time	Speed (km/h)	Motor Power (W)	Battery Voltage (V)	Current (A)	Energy (Wh/hr)	Distance (km/hr)
1	08:00	16	380	50.8	7.5	380	16
2	08:30	18	420	50.2	8.4	420	18
3	09:00	20	480	49.8	9.6	480	20
4	09:45	22	550	49.1	11.2	550	22
5	10:30	19	460	48.7	9.4	460	19
6	11:15	17	400	48.3	8.3	400	17
7	12:00	14	320	48.0	6.7	320	14
8	01:00	15	350	47.7	7.3	350	15
9	02:00	18	420	47.4	8.9	420	18
10	03:00	21	500	47.0	10.6	500	21
11	04:00	20	480	46.8	10.3	480	20
12	05:00	19	450	46.5	9.7	450	19
13	06:00	17	410	46.2	8.9	410	17
14	06:30	15	360	46.0	7.8	360	15
15	07:00	14	330	45.8	7.2	330	14

Table 5. 2: Power consumption vs speed curve of local three-wheeler

Table 5. 2: Power consumption vs speed curve of local three-wheeler

5.1.2. Data Collected Through Interview of Three-Wheeler Driver

To ascertain the various data and information obtained from mathematical derivation and other calculation several interviews were carried out of three-wheeler driver for real data collection. The data was collected through interviews with several auto-rickshaw drivers. After analysis, it was found that the calculated and estimated values were very close to the practical data, including charging and discharging time, daily runtime, and operational performance. Several important practical insights were also identified, such as daily income patterns, battery replacement intervals, and maintenance practices. These findings are highly valuable for evaluating the real-world feasibility and practical implementation of the project. However, the following table presents a summary of the operational conditions and economic information gathered from interviews with e-bike and auto-rickshaw drivers:

Table 5. 3: E-Bike Interview Range Summary

Field	Observed Range / Compiled Information
Vehicle Type	02-seat, 03-seat, 04-seat auto-rickshaw
Battery Voltage	48 Volt (all vehicles)
Number of Batteries	4 batteries
Battery Replacement Period	6 months – 1 year
Daily Operating Duration	8 – 12 hours
Charging Time	8 – 12 hours
Runtime per Charge	6 – 12 hours
Backup Charging During Power Outage	No backup charging system available
Charging Location	Garage, rented house/home
Motor Power	1500 Watt
Driver Experience	8 months – 2 years
Wheel/Tire Replacement	6 months – 1.5 years
Average Speed	15 – 40 km/h
Vehicle Ownership	Self-owned and rented
Tire Size	14 – 16
Operating Schedule	Typically, 6 AM – 10 PM (varies by driver)
Daily Travel Distance	40 – 90 km/day
Vehicle Price	Tk 70,000 – Tk 225,000
Daily Income	Tk 700 – Tk 1,300
7-Day Income	Tk 4,900 – Tk 9,100
Owner Payment / Rental	Tk 350 – Tk 550 per day; some owner-operated vehicles not applicable
Garage/Charging Cost	Tk 100 – Tk 220 per day, or Tk 6,000/month including charging

Table 5. 3: E-Bike Interview Range Summary

Field	Observed Range / Compiled Information
Vehicle Type	02-seat, 03-seat, 04-seat auto-rickshaw
Battery Voltage	48 Volt (all vehicles)
Number of Batteries	4 batteries
Battery Replacement Period	6 months – 1 year
Daily Operating Duration	8 – 12 hours
Charging Time	8 – 12 hours
Runtime per Charge	6 – 12 hours
Backup Charging During Power Outage	No backup charging system available
Charging Location	Garage, rented house/home
Motor Power	1500 Watt
Driver Experience	8 months – 2 years
Wheel/Tire Replacement	6 months – 1.5 years
Average Speed	15 – 40 km/h
Vehicle Ownership	Self-owned and rented
Tire Size	14 – 16
Operating Schedule	Typically, 6 AM – 10 PM (varies by driver)
Daily Travel Distance	40 – 90 km/day
Vehicle Price	Tk 70,000 – Tk 225,000
Daily Income	Tk 700 – Tk 1,300
7-Day Income	Tk 4,900 – Tk 9,100
Owner Payment / Rental	Tk 350 – Tk 550 per day; some owner-operated vehicles not applicable
Garage/Charging Cost	Tk 100 – Tk 220 per day, or Tk 6,000/month including charging

5.2. Software Simulation and Result Analysis

5.2.1. MATLAB Simulation

Following description is a MATLAB simulation result for 1.5 m² area PV generation profile explaining the solar power behavior with motor demand.

Monthly Average PV power Profile for 1.5 m² solar panel: The graph shows how solar PV power changes during the day for different months. Power increases after sunrise and reaches its maximum around noon; then drops to zero in the evening. Summer and spring months produce more power because of longer daylight hours, while winter months generate less. The average PV power is around 118–120 W.

Figure 5. 1: Monthly average PV power vs Power profile

Figure 5. 1: Monthly average PV power vs Power profile

PV Power Generation vs Motor Demand: The first pie chart compares the yearly PV power generation with the total motor power demand. The motor requires about 1434.7 kWh annually, while the solar PV system generates 394.1 kWh. This means the PV system supplies around 22% of the total energy demand, while the remaining 78% is required by the motor load. On the other hand, the second pie chart shows the contribution of the solar PV system toward meeting the total energy demand. Out of the total demand, 394.1 kWh is supplied by the PV system, while the remaining 1044.9 kWh must be provided by the grid.

Figure 5. 2: Annual PV Power Generation vs Motor Demand

Figure 5. 2: Annual PV Power Generation vs Motor Demand

Total Solar PV Generation: In one year, the roof-top solar PV can generate around, 394.1 kWh power, out of which 326.2 kWh will directly be used by the motor, 43.4 kWh will be stored in the battery and rest 24.5 kWh will be the energy loss.

Figure 5. 3: Annual Total Solar PV Generation

Figure 5. 3: Annual Total Solar PV Generation

The daily Power Uses profile: The following graph shows daily battery discharge in blue, solar direct use in red and curtailed power in orange colour. The maximum battery discharge remained within 1.5 kWh.

Figure 5. 4: The daily Power Uses profile

Figure 5. 4: The daily Power Uses profile

5.3. Performance Analysis

5.3.1. Motor Load vs SPEED

The performance analysis showed that the selected 48 V, 800 W differential motor provides a good balance between vehicle speed, passenger carrying ability, energy consumption, and battery usage. Under normal operating conditions, the vehicle was able to run smoothly at a speed of around 20–21 km/h while carrying typical urban loads. The overall system proved to be practical, reliable, and efficient for everyday three-wheeler transportation in Bangladesh.

Figure 5. 5: Motor load-speed performance characteristics

Figure 5. 5: Motor load-speed performance characteristics

5.3.2. Solar Contribution

The rooftop 400 W solar panel supports the battery during daytime operation by supplying additional electrical energy through the MPPT charge controller. Under good sunlight conditions, the panel can provide around 300 W of power and generate nearly 1.6 kWh of energy per day. This additional solar support helps reduce battery discharge, improve battery lifespan, and lower dependence on grid electricity.

Figure 5. 6: Total Solar Contribution

Figure 5. 6: Total Solar Contribution

5.3.3. Runtime Analysis

The runtime analysis showed that the vehicle can operate for approximately 6–7 hours using battery power alone under moderate driving conditions. With solar assistance, the operating time increases to around 8–9 hours because the rooftop solar panel helps reduce the battery load while driving. This additional support also increases the overall driving range and improves vehicle endurance during daytime operation.

Figure 5. 7: Runtime performance: Battery only vs Solar -supported operation

Figure 5. 7: Runtime performance: Battery only vs Solar -supported operation

6. Commercial Proposal

6.1. General Analytical Base

Let us analyze the commercial proposal for battery-driven easy bikes/ auto rickshaws all over the country. This will be done based on the followings:

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Cost of a three-wheeler with a lead-acid battery and solar panel.

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Average income from a single three-wheeler with battery only per day (Use runtime) and per year in Dhaka.

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Average income from a single three-wheeler with solar-supported battery per day (Use runtime) and per year in Dhaka.

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How much time it will take to recover the additional cost of a solar-supported three-wheeler?

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Total Energy generation from a charging station and single solar-supported three-wheeler (4.8 kW + 1.6 kW) and its value in taka and the same amount for 6 million three-wheelers.

6.2. Commercially Used Proposal

6.2.1. Solar-Supported Electric Three-Wheeler

48 V, 100 Ah lead-acid battery pack, 800 W motor, 400 W rooftop solar panel, MPPT controller, battery-only runtime 6–7 h, solar-supported runtime 8–9 h, and daily solar contribution about 1.6 kWh as discussed in the project paper. Estimated cost of three-wheeler with lead-acid battery and solar panel has been shown in Table 6.1 below. So, the additional cost for solar support is approximately Tk 35,000–80,000. A 400 W solar panel is listed around Tk 10,400 in Bangladesh, while MPPT controllers vary widely depending on quality and rating.

Table 6. 1: Cost comparison between solar-supported vs non-solar three-wheeler

Item	Estimated Cost
Electric three-wheeler body, motor, controller and fittings	Tk 1,80,000–2,20,000
4 × 12 V, 100 Ah lead-acid batteries	Tk 60,000–80,000
400 W rooftop solar panel	Tk 15,000–50,000
MPPT charge controller, wiring, frame and installation	Tk 20,000–30,000
Total battery-only vehicle (No solar and MPPT)	Tk 2,40,000–3,00,000
Total solar-supported vehicle	Tk 2,75,000–3,80,000

Table 6. 1: Cost comparison between solar-supported vs non-solar three-wheeler

Item	Estimated Cost
Electric three-wheeler body, motor, controller and fittings	Tk 1,80,000–2,20,000
4 × 12 V, 100 Ah lead-acid batteries	Tk 60,000–80,000
400 W rooftop solar panel	Tk 15,000–50,000
MPPT charge controller, wiring, frame and installation	Tk 20,000–30,000
Total battery-only vehicle (No solar and MPPT)	Tk 2,40,000–3,00,000
Total solar-supported vehicle	Tk 2,75,000–3,80,000

6.1.2. Income from single three-wheeler

For Dhaka operation, a practical battery-only runtime of 6–7 hours/day is used. Assuming average net earnings of Tk 120/hour:

Table 6. 2: Income from single three-wheeler with battery only

Parameter	Battery-Only Three-Wheeler	Solar-Supported Three-Wheeler	Improvement / Benefit
Practical Runtime per Day	6–7 hours	8–9 hours	+2 hours operating time
Average Runtime Used for Calculation	6.5 hours	8.5 hours	+30.8% increase
Average Income per Hour	Tk 120/hour	Tk 120/hour	Same earning rate
Daily Income Calculation	6.5 × 120	8.5 × 120	—
Estimated Daily Income	Tk 780/day	Tk 1,020/day	+Tk 240/day
Operating Days per Year	330 days (Non ops: 30 days)	330 days (Non ops: 30 days)	Same
Annual Income Calculation	780 × 330	1,020 × 330	—
Estimated Annual Income	Tk 2,57,400/year	Tk 3,36,600/year	+Tk 79,200/year
Additional Solar System Cost	Not Applicable	Tk 80,000 (Max)	Initial investment

Table 6. 2: Income from single three-wheeler with battery only

Parameter	Battery-Only Three-Wheeler	Solar-Supported Three-Wheeler	Improvement / Benefit
Practical Runtime per Day	6–7 hours	8–9 hours	+2 hours operating time
Average Runtime Used for Calculation	6.5 hours	8.5 hours	+30.8% increase
Average Income per Hour	Tk 120/hour	Tk 120/hour	Same earning rate
Daily Income Calculation	6.5 × 120	8.5 × 120	—
Estimated Daily Income	Tk 780/day	Tk 1,020/day	+Tk 240/day
Operating Days per Year	330 days (Non ops: 30 days)	330 days (Non ops: 30 days)	Same
Annual Income Calculation	780 × 330	1,020 × 330	—
Estimated Annual Income	Tk 2,57,400/year	Tk 3,36,600/year	+Tk 79,200/year
Additional Solar System Cost	Not Applicable	Tk 80,000 (Max)	Initial investment

6.1.3. Payback period for additional solar cost

If the additional solar system cost is assumed as Tk 80,000, then:

Payback period = 80,000 ÷ 240 = 333.33 operating days

So, the additional solar investment can be recovered in approximately 11 months of regular operation. After this period, the extra income becomes direct financial benefit to the owner/driver.

(If the complete system receives an electric charge from home-based charging station or from a commercial charging station)

6.3. Comparison of Energy Generation and National-Scale Economic Value

Following is a comparison between the Energy Generation and National-Scale Economic Value of Battery-Only and Solar-Supported Electric Three-Wheeler Systems:

The proposed system uses:

Battery charging energy = 4.8 kWh/day

Rooftop solar contribution = 1.6 kWh/day

Total available daily energy = 6.4 kWh/day per vehicle

Using the average retail electricity tariff of about Tk 8.95/kWh:

Table 6. 3: National-Scale Economic Value Between Battery-Only and Solar-Supported Electric Three-Wheeler Systems

Case Category	For 4.8 kWh		For 1.6 kWh		Total For 6.4 kWh
	Energy Use/ Expense Battery-Only System	Electricity Value (Tk)	Energy generation from roof top solar panel	Electricity Value (Tk)	Energy Generation Solar-Supported System	Electricity Value (Tk)
Single Vehicle / Day	4.8 kWh/day	Tk 42.96/day	1.6 kWh/day	Tk 14.32/day	6.4 kWh/day	Tk 57.28/day
3.5 Million Vehicles / Day	16.8 GWh/day	Tk 15.04 crore/day	5.6 GWh/day	Tk 5.01 crore/day	22.4 GWh/day	Tk 20.05 crore/day
3.5 Million Vehicles / Year	6,132 GWh/year	Tk 5,488 crore/year	2,044 GWh/year	Tk 1,829 crore/year	8,176 GWh/year	Tk 7,318 crore/year

Table 6. 3: National-Scale Economic Value Between Battery-Only and Solar-Supported Electric Three-Wheeler Systems

Case Category	For 4.8 kWh		For 1.6 kWh		Total For 6.4 kWh
	Energy Use/ Expense Battery-Only System	Electricity Value (Tk)	Energy generation from roof top solar panel	Electricity Value (Tk)	Energy Generation Solar-Supported System	Electricity Value (Tk)
Single Vehicle / Day	4.8 kWh/day	Tk 42.96/day	1.6 kWh/day	Tk 14.32/day	6.4 kWh/day	Tk 57.28/day
3.5 Million Vehicles / Day	16.8 GWh/day	Tk 15.04 crore/day	5.6 GWh/day	Tk 5.01 crore/day	22.4 GWh/day	Tk 20.05 crore/day
3.5 Million Vehicles / Year	6,132 GWh/year	Tk 5,488 crore/year	2,044 GWh/year	Tk 1,829 crore/year	8,176 GWh/year	Tk 7,318 crore/year

Solar only: 2336 – 1752 kwh/ day = 584 kWh/Day per year

MATLAB simulation data = 326 kWh/Day per year

6.4. Income Growth Trend over the 8-Year Commercial Life

Battery-only annual income = Tk 2,57,400/year

Solar-supported annual income = Tk 3,36,600/year

Additional yearly income from solar = Tk 79,200/year

Ina a total lifespan of 8 years the solar supported electric three-wheeler will have total income Tk 26.9 lakh which is around 07 lakh taka more than the income of a battery only three-wheeler. (The graph is displaying income in millions of Taka, where 1 USD= 122 Taka)

Figure 6. 1: Income growth trend over the 8-year commercial life

Figure 6. 1: Income growth trend over the 8-year commercial life

6.5. Summary

A solar-supported three-wheeler requires about Tk 35,000–80,000 additional investment, but it can increase daily operating income by around Tk 240/day and recover the extra cost within lowest 5–6 months or highest 11 months. At national scale, if 3.5 million vehicles used the same 6.4 kWh/day energy model, the total daily energy value would be approximately 16.8 GWh/day, having value Tk 15.04 crore/day and Tk 7,318 crore/year; showing strong commercial and energy-saving potential. Discarding Electricity bill, maintenance and parts replacement cost for 8 years. Here, it can be mention that, the below income remains same for both with solar-supported electric three-wheeler and without solar-supported battery three-wheeler.

Table 6. 4: Income remains same for both type of electric three-wheeler.

Expense Category	Annual Cost (Tk)	Duration	Total Cost (Tk)
Electricity Use (1752 kWh/year)	15,680	8 years	1,25,440
Battery Replacement (4 in no)	40,000	8 years	3,20,000
Tyre Change (3 in no)	12,000	8 years	48,000
Minor Maintenance	1,000	8 years	8,000
Grand Total			5,01,440

Table 6. 4: Income remains same for both type of electric three-wheeler.

Expense Category	Annual Cost (Tk)	Duration	Total Cost (Tk)
Electricity Use (1752 kWh/year)	15,680	8 years	1,25,440
Battery Replacement (4 in no)	40,000	8 years	3,20,000
Tyre Change (3 in no)	12,000	8 years	48,000
Minor Maintenance	1,000	8 years	8,000
Grand Total			5,01,440

Net Income comparison has been shown in Table 6.5 below. The cumulative income increases steadily throughout the 8-year service life for both types of vehicles. However, the solar-supported electric three-wheeler generates higher overall income, reaching approximately Tk 26.9 lakh after 8 years, compared to around Tk 20.6 lakh for the battery-only vehicle. This shows that the use of solar support can provide an additional profit of nearly Tk 5.4 lakh over the vehicle’s lifetime, excluding electricity and maintenance costs.

Table 6. 5: Net Income Comparison Net Income Comparison.

Comparison Item	Solar-Supported Electric Three-Wheeler	Battery-Only Electric Three-Wheeler
8-Year Income	26.0 lakh Tk	20.6 lakh Tk
8-Year Expense	5.0 lakh Tk	5.0 lakh Tk
8-Year Net Profit	21.0 lakh Tk	15.6 lakh Tk
Profit Difference	+5.4 lakh Tk higher profit with solar-supported model

Table 6. 5: Net Income Comparison Net Income Comparison.

Comparison Item	Solar-Supported Electric Three-Wheeler	Battery-Only Electric Three-Wheeler
8-Year Income	26.0 lakh Tk	20.6 lakh Tk
8-Year Expense	5.0 lakh Tk	5.0 lakh Tk
8-Year Net Profit	21.0 lakh Tk	15.6 lakh Tk
Profit Difference	+5.4 lakh Tk higher profit with solar-supported model

7. Challenges and Limitations

7.1. Challenges and Limitations. There Are Few Challenges and Limitation as Mention Below

➢

Limited Roof Space: The roof area of an electric three-wheeler is relatively small, which limits the size and capacity of the solar panel that can be installed. Because of this, the solar panel can only provide additional energy support and cannot fully power the vehicle by itself.

➢

Limited Charging During Operation: The rooftop solar panel cannot supply enough power to fully charge the battery while the vehicle is running. Therefore, the vehicle still mainly depends on charging from household or commercial electricity sources.

➢

Solar Panel Efficiency: The efficiency of commonly available solar panels is usually around 20–25%. Although higher-efficiency panels exist, they are costly and less practical for low-cost transportation systems.

➢

Effect of Weather and Environment: Solar power generation depends heavily on weather conditions. Cloudy skies, rain, and monsoon seasons can reduce solar charging performance. Dust, shading, and changes in the vehicle’s direction during movement may also affect energy generation.

➢

Additional Weight of the Solar System: The solar panel and its supporting structure add extra weight to the vehicle. This additional weight may slightly affect the vehicle’s balance, speed, and overall operating efficiency.

➢

Battery Performance and Lifespan: Battery performance and service life are influenced by temperature, charging and discharging conditions, depth of discharge, and proper maintenance.

➢

Variation During Vehicle Movement: The amount of solar energy generated changes continuously while the vehicle is moving because the angle and intensity of sunlight vary depending on road direction and vehicle position.

➢

Difference Between Theoretical and Actual Performance: The estimated runtime, driving range, and charging performance in this study are mainly based on theoretical calculations. In real operating conditions, factors such as traffic, road conditions, weather, and driving patterns may affect the actual performance. Therefore, practical testing and long-term evaluation are necessary for accurate validation.

7.2. Future Scope

Further study can be done to improve the design and manufacturing of aforementioned three-wheeler.

➢

Improving onboard rooftop solar support: The successful integration of rooftop solar panels in this study shows the potential for improving energy independence in electric three-wheelers. Future research may focus on using high-efficiency monocrystalline solar panels to increase solar power generation from the limited rooftop area of the vehicle.

➢

Developing external solar charging stations: Another possible improvement is the development of solar-powered charging and battery-swapping stations. A dual-battery system could be introduced, where one battery powers the vehicle while another charges at a solar station. The use of IoT monitoring and advanced MPPT technology could further improve energy management and charging efficiency. Together, these developments could help reduce dependence on grid electricity and support a more sustainable renewable transportation system.

8. Conclusions and Recommendations

8.1. Conclusions

The current energy system of the globe is a major driver of global climate change, accounting for around 75% of GHG emissions. We need to more focus of renewable energy particular to household use and transport sector. The growing use of battery-driven electric three-wheelers in Bangladesh has created new challenges for the country’s electricity sector. Although these vehicles are popular because they are affordable, easy to operate, and more environmentally friendly than fuel-based vehicles, their increasing demand for battery charging is placing extra pressure on the national power grid. Since Bangladesh is already struggling to meet its rising electricity demand, finding a sustainable and practical solution has become increasingly important. This research investigated the use of solar energy to support the operation of electric three-wheelers. A solar-assisted system was developed using a rooftop solar panel, a 48 V battery pack, an 800 W differential motor, and an MPPT charge controller. The study found that the rooftop solar panel can provide useful additional energy during daytime operation, helping reduce battery discharge and dependence on grid electricity.

The results showed that a 400 W rooftop solar panel can generate a significant amount of energy under Bangladesh’s sunlight conditions and can extend the vehicle’s operating time by several hours per day. Although the solar panel alone cannot fully operate or continuously charge the vehicle, it works effectively as a supporting energy source that improves vehicle endurance and reduces electricity consumption from conventional charging methods. The study also confirmed that the proposed system is practical, environmentally friendly, and suitable for local conditions in Bangladesh. By reducing pressure on the national power grid and encouraging the use of renewable energy, solar-assisted electric three-wheelers can contribute to developing a cleaner and more sustainable transportation system. In conclusion, we may say that, integrating rooftop solar technology with electric three-wheelers offers a practical and sustainable approach to addressing Bangladesh’s growing transportation and energy challenges. The proposed system not only promotes the use of renewable energy but also supports energy efficiency, environmental protection, and long-term sustainable development.

8.2. Recommendations

Based on the above analytical discussion, the following recommendations are made.

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Carry out further research to use more area around the vehicle with flexible and transparent solar technology to increase solar support runtime.

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The project may be used as a signature vehicle to promote solar energy in battery supported transport system thereby encouraging people/ entrepreneurs in development of solar-powered charging hubs in urban areas to reduce the total dependency of electric power through national power grid.

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Bangladesh needs to use and utilize the solar energy in the best and optimum way as a suitable country of available solar energy throughout the year.

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Flexible and reliable solar panel will be the best option in transport sector.