The Direct and Indirect Roles of Solar Power in Moving People and Goods
Solar energy is used in transportation in two primary ways: directly, by powering vehicles with onboard or integrated photovoltaic (pv cells), and indirectly, by generating electricity for the grid that charges electric vehicles (EVs) or powers electric public transit systems. While the concept of “solar roads” has captured public imagination, it represents a niche and technically challenging application; the most significant and scalable impact of solar power on transportation today comes from stationary solar farms and rooftop installations that feed clean energy into the transportation ecosystem.
The most straightforward application is on the vehicles themselves. Solar panels are increasingly integrated into the roofs of electric and hybrid cars, buses, and even trucks. Their role is not typically to provide 100% of the propulsion energy but to serve as an auxiliary power source. This supplementary energy can significantly extend the vehicle’s range by powering climate control systems, lighting, and infotainment, thereby reducing the drain on the main battery. For example, the Lightyear 0 car, though now discontinued, demonstrated the potential with claims of up to 70 km (43 miles) of range per day from solar energy under ideal conditions. In the commercial sector, companies like Trailer Dynamics are developing semi-trailers with large-surface solar roofs that can generate enough electricity to power the trailer’s refrigeration unit or assist the truck’s drivetrain, potentially saving thousands of liters of diesel annually on long-haul routes.
The potential of solar-powered vehicles is highly dependent on surface area and efficiency. The table below illustrates the typical energy generation potential for different vehicle types based on high-efficiency solar cells covering available roof space.
| Vehicle Type | Approximate Roof Area | Potential Daily Energy Generation (Ideal Sunlight)* | Equivalent Electric Vehicle Range Added** |
|---|---|---|---|
| Passenger Car | 2.5 sq meters | ~2.5 kWh | 15-20 km (9-12 miles) |
| City Bus | 20 sq meters | ~20 kWh | N/A (powers auxiliary systems) |
| Long-Haul Truck Trailer | 40 sq meters | ~40 kWh | Assists drivetrain; powers refrigeration |
*Assumes 20% cell efficiency and 5 peak sun hours. **Varies greatly by vehicle efficiency.
Beyond individual vehicles, solar energy is revolutionizing public transportation. Cities around the world are building solar-powered charging stations for electric bus fleets. These installations can be built over bus depots or on adjacent land. A prime example is the city of London, which has installed over 4.4 MW of solar panels on bus station roofs, generating electricity that is directly fed into the grid to offset the power used by its expanding electric bus fleet. This model decouples energy generation from the vehicle’s limited surface area, allowing for much larger, more efficient solar arrays. Similarly, India’s Cochin International Airport boasts a 40 MW solar plant that generates more energy than the airport consumes, making it “grid-positive” and indirectly powering the electric vehicles and ground support equipment used on-site.
This brings us to the concept of solar roads. The idea of replacing asphalt with durable, glass-covered solar panels that generate electricity while supporting traffic is technologically fascinating but fraught with practical and economic challenges. Prototypes, such as the Wattway in France, have faced significant issues. The panels must be strong enough to withstand constant traffic loads and weather extremes, provide sufficient traction to prevent accidents, and remain clear enough for light penetration. They are also exponentially more expensive than conventional asphalt and typically generate less power than rooftop panels due to suboptimal angles and soiling from dirt and tire wear. Most energy experts agree that a far more effective approach is to install solar panels alongside infrastructure—on noise barriers, on the roofs of roadside buildings, and on dedicated solar farms—where they can be positioned for maximum efficiency and maintained easily.
The most profound impact of solar on transportation is indirect. The rapid growth of electric vehicles is only as “clean” as the grid from which they draw power. Solar energy is a critical component in decarbonizing the electricity grid. Large-scale solar farms are now among the cheapest sources of new electricity generation in many parts of the world. When an EV is charged by electricity from a solar farm, its lifecycle carbon emissions plummet compared to a gasoline-powered car. According to the National Renewable Energy Laboratory (NREL) in the US, an EV charged on a solar-heavy grid can have emissions equivalent to a gasoline car that gets over 100 miles per gallon. The synergy between solar power and EVs creates a virtuous cycle: more solar energy reduces the carbon intensity of the grid, which increases the environmental benefits of EVs, which in turn creates a larger, more flexible demand for solar electricity.
Looking forward, the integration is set to deepen. Vehicle-to-Grid (V2G) technology will allow EVs to act as mobile energy storage units. During the day, solar farms can generate excess power that charges millions of EVs parked at offices and homes. In the evening, when solar generation drops but electricity demand peaks, these EVs could feed a portion of their stored energy back into the grid, stabilizing it and maximizing the utilization of solar power. This turns the entire transportation fleet into a distributed battery system, a crucial asset for managing the intermittency of renewable energy sources like solar. While regulatory and technological hurdles remain, pilot projects are underway globally, pointing to a future where our vehicles are not just consumers of energy but active participants in a cleaner, more resilient energy system.