Examination of a solar-powered freezer truck with connected vehicle technology

1 Introduction

The global demand for perishable goods, including fresh produce, meat, dairy, seafood, and pharmaceuticals, is consistently high and growing. Freezer trucks form the critical backbone of the food-supply chain, ensuring that temperature-sensitive products remain safe. A significant portion of global food waste occurs due to a lack of proper refrigeration during transport. Mobile freezer storage directly addresses this by maintaining optimal temperatures throughout the journey. The rise of e-commerce and online grocery shopping has created a massive demand for “last-mile” cold and fresh delivery. Mobile freezer units are essential for enabling direct-to-consumer delivery of frozen meals, meal kits, and fresh groceries, meeting modern consumer expectations for convenience. The power of the refrigeration/freezer unit in conventional refrigeration/freezer trucks in the market still arises from the fuel engine. On the one hand, the fuel engine needs to run to power the transportation refrigeration/freezer unit while driving. On the other hand, the fuel engine still needs to remain idle to power the transportation refrigeration/freezer unit while parking for a long time. However, such operation of the fuel engine leads to emissions, fuel consumption, and noise. Due to the conventional use of diesel-engine vapor compression refrigeration units, their greenhouse gas emissions can be as high as 40% of automobile emissions (Poff and Hargrove-Leak, 2023).

Solar photovoltaic (PV) energy is a clean, sustainable, renewable energy source and an accessible technology with relatively low cost. Reports on solar-powered transportation have provided examples such as solar hover vehicles (Afaga and Cheng, 2022), electric vessels (Leung and Cheng, 2017), solar aircraft (Wang et al., 2015), solar space vehicles (Goh et al., 2026), and solar vehicle charging (Zhang et al., 2026). These design examples demonstrate that solar-powered transportation can provide an additional free energy source and offer convenient supplementary power input. Although solar power alone is not sufficient to supply 100% of the traction energy, it can still contribute a substantial portion of the energy required for transportation.

Therefore, solar energy is the most popular and mature renewable energy source all over the world. The integration of renewable solar photovoltaics with transportation refrigeration/freezer units is gaining popularity, in which the solar photovoltaics power the transportation refrigeration/freezer units instead of the conventional diesel engines. Additionally, battery energy storage is needed as it can mitigate the uncertainty and intermittency associated with photovoltaic generation. Consequently, the photovoltaic–battery energy systems have become a simple and feasible technical solution applied to solar-powered refrigeration/freezer vehicles (Xue et al., 2024). Obviously, solar PV-powered refrigeration/freezer units can improve the sustainability of refrigeration/freezer transportation.

In comparison with conventional refrigeration/freezer trucks, the advantages of the solar-powered refrigeration/freezer trucks can be summarized as follows.

• Reduced energy consumption and cost due to renewable solar energy compared to energy from fuels or the grid.
• Cost-savings on fuel due to the elimination of idling and additional engine load (compressor, bracket, and belt assembly).
• Improved reliability since vehicle engine failure does not affect the refrigeration/freezer units.
• Removal of emissions associated with diesel consumption.
• Low noise-pollution due to solar-powered refrigeration/freezer unit without engine operation.
• Less maintenance due to fewer moving parts.
• Prolonged battery lifetime due to renewable solar energy.

The study, design, development, experiment, and assessment of solar-powered refrigeration/freezer vehicles have been described in some publications. Poff and Hargrove-Leak’s study focused on the design and implementation of a solar-powered transportation refrigeration unit. Their experiments showed that the desired temperatures could be reached and maintained and that a solar-powered unit would be able to power a transportation refrigeration unit (Poff and Hargrove-Leak, 2023). Xue et al. reviewed the energy management technologies of PV–battery energy systems, which are applied to transportation refrigeration units, microgrids, EV charging, and water pump systems, among others (Xue et al., 2024). Bahaj presented a photovoltaic–battery system that replaced the diesel generator utilized in conventional refrigeration trailers, which matched the design demand of the daily required deliveries of refrigerated produce throughout the year (Bahaj, 2000). Bahaj and James conducted the economic assessment of PV-powered refrigerating delivery, in which the PV-powered refrigeration units were compared with the diesel-powered ones. Their analysis indicated that the payback period of 18 years for the PV-powered refrigeration supermarket trailer can be attained in the United Kingdom (Bahaj and James, 2002). Rossetti et al. developed a solar-powered refrigeration unit, in which photovoltaic panels were built on top of the refrigerated container. Their experimental data showed that the developed solar PV system contributed 94% of the energy required by the refrigeration unit between 6:00 and 18:00 under early summer conditions in northern Italy’s climate (Rossetti et al., 2022).

This article focuses on the development of a solar-powered freezer truck, including the design of the energy system, the analysis of energy management, and the experiments on the developed prototype.

2 Design of the energy system

2.1 Proposed multiple energy inputs

To implement flexible energy control and optimal energy management and ensure the reliable operation of the transportation refrigeration/freezer unit, multiple energy inputs are proposed in this article, which consists of solar energy from the onboard PV panels, the battery energy from the onboard battery, the plug-in energy from the off-board AC supply, and the battery energy from the external battery, as shown in Figure 1. The external battery may be the on-board battery in another solar-powered freezer truck for the concept of connected vehicle development.

2.2 Proposed energy system

The energy system for the solar-powered freezer truck is proposed, which includes the PV panels, the maximum power point tracking (MPPT) controller, the DC–AC inverter, the variable speed drive (VSD), the AC compressor, the onboard Li-ion battery, the AC–DC converter, the DC–DC converter, two controllable switches, the off-board plug-in AC supply, and the off-board external battery, as shown in Figure 2. The black arrows represent the allowed power flow.

Referring to Figure 2, the PV panels are fixed on the roof of the freezer truck and can convert solar energy to electric energy, which is allocated to the MPPT controller; the MPPT controller is the unidirectional DC–DC converter with MPPT control and can capture the maximum DC power output by the PV modules, charge the onboard battery via the switch S1, and output the DC power to the DC–AC inverter and the DC–DC converter; the onboard battery is the battery energy storage in the solar-powered freezer truck, and via the switch S1, it can output the DC power to the DC–AC inverter and the DC–DC converter and absorb the DC power provided by the PV panels via the MPPT controller, by the plug-in AC supply via the AC–DC converter, and by the external battery via the DC–DC converter. S1 is the DC switch; S2 is the AC switch. The DC–AC inverter can convert the DC power to the AC power with rated three-phase voltage of 380 V, which is allocated to the VSD. The VSD can implement variable-frequency/variable-voltage control. The AC compressor is driven by the three-phase motor that is controlled by the VSD. The AC–DC converter can convert the AC power to the DC power, of which the former is provided by the off-board plug-in AC supply and the latter can be allocated to the onboard battery via S1. The DC–DC converter is a bidirectional converter and can allocate the DC power from the external battery to the onboard battery via S1 and the DC–AC inverter, the DC power from the onboard battery via S1, and the PV panels via the MPPT controller to the external battery that may be the onboard battery storage in another solar-powered freezer truck. The plug-in AC supply can directly power the AC compressor via S2 and charge the onboard battery via the AC–DC converter and S1.

It can be seen from the aforementioned analysis that the proposed energy system has flexible energy storage, offers additional solar energy to the freezer truck, can capture the maximum solar PV power, and provides connectable and exchangeable energy storage between two electric vehicles. Figure 3 illustrates the energy flow of the proposed energy system.

3 Design of optimal energy management

3.1 Objective of the proposed optimal energy management strategy

The optimal energy management strategies of energy systems in solar-powered freezer trucks are to achieve high-efficiency operation of energy systems, reduce emissions, and ensure reliable operation of solar-powered freezer units. The objective of the proposed optimal energy management strategy can be summarized as follows.

• Optimally allocating the energy from the multiple energy inputs for matching the energy demand of the AC compressor.
• Maximizing the output power of the PV panels.
• Maintaining the high-efficiency operation of the onboard battery.
• Extending the service lifetime of the onboard battery.
• Improving the refrigeration performance of solar-powered freezer trucks.
• Improving the operating efficiency of the energy system.

3.2 Proposed optimal energy management strategy

To fulfill the optimal energy management strategy, the energy control is designed as shown in Figure 4. The controlled components include the MPPT controller, the DC–AC inverter, the VSD, the DC switch S1, the AC–DC converter, the DC–DC converter, and the AC switch S2.

By using the aforementioned controllable components, the proposed energy management can achieve four types of energy allocations, which are the charging of the onboard battery, the powering of the AC compressor, both the charging of the onboard battery and the powering of the AC compressor, and the charging of the external battery.

3.2.1 Charging of the onboard battery

Five proposed energy management modes (EMMs) can implement charging of the onboard battery, including EMM A1, EMM A2, EMM A3, EMM A4, and EMM A5, as illustrated in Figure 5. The purpose of these five EMMs is to ensure that the SOC of the onboard battery is not less than its minimum value and not more than its maximum value and to try to maintain the SOC of the onboard battery within its normal range, in which the onboard battery runs at high efficiency.

3.2.2 Powering of the AC compressor

Four proposed EMMs can implement the powering of the AC compressor, including EMM B1, EMM B2, EMM B3, and EMM B4, as shown in Figure 6. The purpose of these four EMMS is to power the AC compressor, which can run at high efficiency due to the variable speed control via the VSD.

3.2.3 Charging of the onboard battery and powering of the AC compressor

Three proposed EMMs can implement both the charging of the onboard battery and the powering of the AC compressor, including EMM C1, EMM C2, and EMM C3, as illustrated in Figure 7. The purpose of these three EMMs is to charge the onboard battery and power the AC compressor simultaneously.

3.2.4 Charging of the external battery

Three proposed EMMs can implement the charging of the external battery, including EMM D1, EMM D2, and EMM D3, as shown in Figure 8. The purpose of these three EMMs is to charge the external battery, which may be the onboard battery in another solar-powered freezer truck.

3.2.5 Connected vehicles

The external battery concept discussed above is connected vehicle technology. Several vehicles can be connected so that their energy storage can be inter-supported. Energy can be shared in order to strengthen the overall energy storage utilization (Dong et al., 2025). The purpose of this connection is to enlarge the freezer storage system. Presently, the freezer storage available in buildings is limited due to the high land and building costs. Because food delivery is in demand, more food storage will be needed. Single or small food storage systems are often insufficient to handle unpredictable scenarios. By grouping several freezer trucks, their energy storages are shared. Thereby, it improves their overall effectiveness and survival. The connected vehicle can operate in various states, such as when stationary, idling, or parking. They can be organized at a site for large-scale food storage with separate compartments and across different vehicles for better temperature and food segregation.

Figure 9 illustrates the connected system. The system can be integrated with the power distribution network, which will enable the power grid to provide additional power. Surplus energy generated from solar energy during the day can be fed into the power grid. The battery energy storage units in the truck can contribute to the overall energy distribution and energy storage of the grid.

The design of the energy storage system can be illustrated as follows in Equation 1:where

n P F 24 − T o + n P o T o − n T P V P P V = 24 P G + T D P D , (1)

n is the number of vehicles,

P_F is the average power of the freezer system in the truck,

P_o is the power of the freezer system in the vehicle when the freezer door is open,

T_o is the duration of the freezer system in the vehicle when the freezer door is open,

T_PV is the duration of the solar time,

P_PV is the average solar power during the solar time,

P_G is the average power drawn from the power grid,

T_D is the period of the operation of the diesel generators in the vehicle, and

P_D is the generation power of the diesel generators in the vehicle.

Usually, P_D is only needed when sufficient power from the PV is not available. It can be seen that when the freezer door is open, the power P _o increases rapidly. However, if the freezer is always used for storage, or when the duration of the door being open, T _o, is zero, and the diesel generator is not in use, the equation can be reduced to Equation 2:

n 24 P F − n T P V P P V = 24 P G . (2)

When T P V P P V > 24 P F 24P_G is negative, it means that power is fed to the grid, and vice versa.

During the transient condition, P_PV is the instantaneous power from the PV. Then, the energy obtained from the PV is shown in Equation 3:

T P V P P V = ∫ 0 T P V p P V d t . (3)

The battery energy storage content for the battery set in a vehicle E _B can be expressed in Equation 4 as the 1 C power P _{1C_B}:

E B = P 1 C _ B · 1 h . (4)

The above equation means that 1 h duration of 1 C power of the battery is the energy content of the battery. The requirement of the C-rate of the battery set in a vehicle can be calculated as Equation 5:where p _F is the transient power of the freezer unit in the vehicle.

C r a t e = Max p p v − p F P 1 C _ B , (5)

E B = T P V P P V − 24 P F , (6)

According to Equation 6, when E_B is positive, the PV energy is sufficient and is used to power the freezer. When the power from the PV is not sufficient to power the freezer, battery energy storage is needed to store the energy from the connected vehicle, the external battery, the diesel generator, or the power grid. Then, E_B is negative and is the energy content needed for the battery to accommodate for 1 day. E_B can be increased to a larger number of days N_day as shown in Equation 7:

E B = N d a y T P V P P V − 24 P F . (7)

However, if the power grid is constantly connected to the freezer truck, the required battery energy E_B becomes less critical. Nonetheless, battery energy is still essential during off-grid situations, such as when traveling for food delivery. If T_T is the maximum travel time during each trip, the battery must provide sufficient energy to cover the needs during this period. In addition, during that time period, solar power may not be available while traveling through urban areas due to shade from the buildings or variability in solar illumination. Therefore, E_B is calculated as follows in Equation 8:where T_T is in the unit of the number of days, and it is usually small and in a small fraction of a day.

E B = T T T P V P P V − 24 P F , (8)

4 Developed prototype and experiment

4.1 Developed prototype

A prototype of the proposed solar-powered freezer truck was developed, as shown in Figure 10. There are two PV modules, one of which is fixed on the roof, and the other is movable, which is driven by the actuation unit. These two PV modules are controlled by two MPPT controllers, respectively. The movable PV panels are located below the fixed PV panels, and only the fixed PV module may run when the truck is being driven. The movable PV panels may be located beside the fixed PV panels (see Figure 10), and the fixed and movable PV modules may run when the truck is parked. The freezer unit includes the AC motor, compressor, condenser, fan, evaporator, protection components, and temperature sensor and meter, and it can display the cooling temperature inside the refrigeration chamber and provide protection for the motor (such as under-voltage, phase sequence, phase failure, etc.). The specification of the prototype is described in Table 1. The integration of the main onboard components in the developed prototype is illustrated in Figure 11.

TABLE 1. Specification of the prototype of the solar-powered freezer truck.

4.2 Design

The design of the overall system is illustrated as follows. The present PV power is not sufficient to power the freezer system, and battery energy storage is needed to store energy from the power grid and the diesel generator. For a two-day N_day of energy storage, P_F is 2.6 kW, T_PV is 5.8 h, and P_PV is 2.52 kW; using equation (7), it follows that:

E B = 2 × 5.8 × 2.52 − 24 × 2.6 = 96 k W h .

As the present design is to design a battery to cover for delivery traveling, for a traveling time of 0.2 h, the equation gives:

E B = 0.2 × 5.8 × 2.52 − 24 × 2.6 = 9.6 k W h .

4.3 Experimental validation and comparative performance analysis

4.3.1 Prototype validation and test

The basic test on the developed prototype was carried out to demonstrate the proposed solar-powered freezer truck. Various experiments on the AC–DC converter, onboard Li-ion battery, DC–DC converter, DC–AC inverter, VSD, two MPPT controllers, and cooling temperature inside the refrigeration chamber were conducted. The experimental results are shown in Table 2, in which the external battery is the onboard battery in another EV, the rated external battery voltage is 48 V, and the rated external battery energy is 5 kWh. It can be seen that the experimental results verified the developed solar-powered freezer truck.

TABLE 2. Experimental results of the developed prototype.

The connected vehicle concept is to link the present solar-powered freezer truck to another vehicle for the benefit of shared battery usage. We tested this concept using a 5 kWh external battery from another electric vehicle, which confirmed the effectiveness of the battery energy sharing. Additionally, we evaluated the system with 0.2 h of battery energy storage for the freezer truck, allowing for offline operation studies. Both experiments demonstrated the successful operation of the solar-powered freezer truck and validation of the connected vehicle.

While the primary energy source for the system is solar, auxiliary fuels are utilized when sunlight is insufficient. The key contribution of this work lies in the optimization of solar power usage and the quantification of reduced emissions compared to that with the traditional counterparts. Furthermore, the proposed work demonstrates the implementation of an energy management system specifically designed to support the vehicle’s requirements. This work represents a low-cost application that is specifically tailored for freezer trucks.

4.3.2 Comparative analysis with conventional diesel-driven refrigeration systems

To evaluate the performance of the proposed solar-powered freezer truck against conventional diesel-driven refrigeration systems, a comparative analysis was carried out based on the operational data from published literature and industry trials. Table 3 summarizes the key comparison metrics.

TABLE 3. Comparison between the proposed solar-powered system and conventional diesel-driven refrigeration.

Based on the diesel consumption reported in published literature, a conventional diesel-driven freezer truck consumes approximately 3 L of diesel per hour of operation (Greenhalgh, 2026). Assuming an average operation of 2,500 h per year for one truck, the annual diesel consumption V _{*Die_yr*} is estimated to be 7,570 L. The carbon footprint can be estimated using the emission factor EF _{*CO2_Die*} of 2.68 kg of CO₂ per liter of diesel. This gives:

Annual CO₂ emission E C O 2 _ y r = E F C O 2 _ D i e V D i e _ y r = 2.68 kg/L × 7,570 L = 20,300 kg.

The proposed solar-powered freezer truck with battery energy storage produced zero emissions of CO₂ during the refrigeration process. Compared with a diesel counterpart, this represents a 100% reduction.

The average NOx emission factor is 0.232 g/km for a heavy-duty vehicle (Zou et al., 2025). For an urban delivery route of 100 km per day operating 250 days per year, a diesel refrigeration unit would emit approximately:

Annual NOx emission E N O x _ y r = E F N O x _ D i e V D i e _ y r = 0.232 g/km × 100 km/day × 250 days = 5.8 kg NOx.

Our prototype results align with these industry benchmarks, achieving −35 °C cooling capability and successful solar/battery integration. The connected vehicle (V2V) battery sharing feature demonstrated in our experiments (using a 5 kWh external battery) represents an additional capability that has not been reported in existing commercial systems.

Similar figures can be drawn from other similar developments. The Sunswap Endurance Trial (Thompson, 2024) achieved 22 h of frozen cooling on a single charge over 2 days. The proposed prototype aligns with the industrial benchmarks, and our system achieves −35 °C cooling capacity and successful solar and battery integration, together with V2V that features an additional capability that has not been reported in existing commercial systems.

4.4 AI control in energy management and predictive control

Artificial Intelligence (AI) can be integrated to intelligently manage the hybrid photovoltaic–battery system (Sammar et al., 2024). AI algorithms can predict upcoming refrigeration demand based on driving routes, weather forecasts, and the number of planned door openings, thus optimizing battery usage and ensuring that the unit never runs out of power. The next stage of development is to develop an AI dynamic routing for energy efficiency and develop predictive maintenance of the system. Predicted thermal load estimation is implemented. It predicts that the freezer needs to work based on external factors. The historical data can be used to train the AI coefficients:where

P cooling t = k 1 · Δ T t + k 2 · Q solar t + k 3 · N doors t + C ,

• Δ T t = difference between the outside temperature and the desired internal temperature of the freezer units.
• Q solar t = solar irradiance (sun heating up the truck walls).
• N doors t = predicted number of door openings (based on delivery stops in the route plan).
• k 1 , k 2 , k 3 = coefficients learned by the AI from past trips (e.g., “when it is 32 °C outside, the freezer uses 2 kW”).
• C = baseline thermal loss constant of the freezer truck.

The accumulation of data necessary for accurate predictive modeling is in progress. The training process necessitates a comprehensive dataset that includes detailed operational metrics alongside daily and seasonal weather patterns. Preliminary findings demonstrate that the vehicle operates effectively, with the data showing a marked decrease in the overall fuel requirements.

5 Conclusion

A solar-powered freezer truck with multiple energy inputs and optimal energy management was proposed in this article. Consequently, the emission and noise arising from fuel engines that drive the refrigeration/freezer units in conventional freezer trucks can be eliminated and considerably reduced, respectively. The proposed multiple energy inputs and optimal energy management strategy are analyzed in detail. The former can offer flexible energy control for the optimal energy management strategy, and the latter can implement the reliable operation of transportation refrigeration/freezer units, the maximization of energy system efficiency, and the extended service lifetime of the onboard battery. The design equation and method have been presented. Using the connected vehicle concept, several freezer trucks can be connected for sharing their energy storage. This will present a large freezer-storage network system and could replace a fixed freezer storage warehouse with flexible location, reduce licensing and approval requirements, and reduce food transportation. The prototype of the proposed solar-powered freezer truck was developed successfully. The experimental results verified the developed solar-powered freezer truck and the extension of the work using connected vehicle energy-storage development. This article is significantly valuable for the application of solar-powered freezer trucks.

The novelty of this work lies in the integration of a movable solar energy system with a freezer truck. Unlike existing approaches that typically rely on a fixed solar unit, our design enables the solar components to be repositioned as needed, allowing more efficient capture of available solar energy over time. In addition, the system utilizes AI-based energy control, including energy management and predictive control, and it leverages connected-vehicle capabilities, which are also novel in this application.

6 Impact

This research can improve the practicality and sustainability of refrigerated transportation by reducing the reliance on grid power or fossil-fuel generators. By increasing the utilization of solar energy and intelligently coordinating the power flows to the refrigeration load, the proposed solution has the potential to lower operating costs and emissions while maintaining the required cooling performance. The connected vehicle and predictive control developed for the freezer truck allow flexible energy transfer among vehicles that optimizes the overall performance.

Generative AI statement

The author(s) declared that generative AI was not used in the creation of this manuscript.

Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If you identify any issues, please contact us.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Footnotes

Edited by: Yiqi Liu, South China University of Technology, China

Reviewed by: Yuguo Gao, North China University of Water Conservancy and Electric Power, China

Zachary Schreiber, Purdue University, United States