For decades, roads have served a single purpose: moving vehicles from one place to another. But what if the millions of miles of asphalt and concrete crisscrossing the globe could do more than carry traffic? French infrastructure company Colas set out to answer that question by developing Wattway, a thin-film photovoltaic pavement system designed to turn road surfaces into energy-generating assets. The result was the world’s first solar panel road, installed in the small village of Tourouvre-au-Perche, France. This pioneering project represents a significant step in solar road technology, demonstrating how existing infrastructure can be retrofitted to produce renewable electricity without requiring additional land for solar farms.
The Technology Behind Wattway Solar Pavement
The Wattway system is the product of five years of research and development by Colas, a global leader in infrastructure construction, in partnership with the French National Institute for Solar Energy (INES). What sets Wattway apart from earlier solar road concepts is its approach to installation. Rather than removing existing road surfaces and replacing them with solar panels, Wattway panels are designed to adhere directly onto the top of roads that are already in place. This means no excavation, no disruption to the road base, and significantly lower installation costs compared to ground-up alternatives that require full road replacement.
Each Wattway panel system is less than one centimeter (about one-third of an inch) thick, making it barely noticeable once installed. The panel consists of multiple layers: a top layer of specially formulated resin embedded with polycrystalline silicon photovoltaic cells, a protective coating that provides grip for vehicle tires, and a base layer that allows for thermal expansion of the road material beneath. This multi-layer construction is key to the system’s durability, as roads naturally expand and contract with temperature changes throughout the seasons. The panels are designed to withstand all types of vehicle traffic, including heavy trucks, and function in a wide range of weather conditions from summer heat to winter frost. France has a long history of ambitious infrastructure innovation, and Wattway continues that tradition by reimagining what a road can be in the context of renewable energy generation.
Tourouvre-au-Perche: A Village Powered by Sunlight
The small commune of Tourouvre-au-Perche in Normandy, France, made history in December 2016 when it became home to the world’s first operational solar road. A one-kilometer (0.6-mile) stretch of road was covered with more than 30,000 square feet (2,800 square meters) of Wattway solar panels. The installation cost approximately $5.3 million (5 million euros) and was expected to handle around 2,000 vehicles per day during its two-year test period. This real-world trial was designed not only to measure energy output but also to assess how the panels held up under continuous traffic, freeze-thaw cycles, moisture, and the everyday wear and tear of a functioning roadway.
According to media reports from The Guardian, the pilot project was closely watched by energy ministries across Europe. Initial projections suggested that 215 square feet of panel surface would generate enough electricity to power the average French household. However, early results revealed a significant challenge: solar panels laid flat on a horizontal road surface capture considerably less sunlight than panels installed at an optimal tilt angle. This inherent efficiency gap has become one of the central technical hurdles facing solar road technology. The road serves as a critical testing ground for understanding how power generation pavement performs under real-world conditions over extended periods of time.
Comparing Solar Road Concepts Around the World
Colas was not the only company pursuing solar pavement technology during this period. The most prominent alternative came from the United States, where a company called Solar Roadways gained international attention after raising over $2 million through an Indiegogo crowdfunding campaign. The concept, which went viral under the nickname “Solar Freakin’ Roadways,” proposed replacing entire road surfaces with hexagonal glass solar panels embedded with LED lights and heating elements. The two approaches differ in several important ways:
- Installation method: Wattway adheres to existing roads without excavation, while Solar Roadways required complete replacement of the road surface, making it far more disruptive and expensive to deploy at any meaningful scale.
- Panel thickness: Wattway panels are less than one centimeter thick and function as an overlay, whereas Solar Roadways panels were significantly thicker glass units that needed structural support beneath them.
- Load testing: Wattway underwent extensive load testing with heavy truck traffic before deployment, while Solar Roadways panels were initially tested only in pedestrian pathways with limited traffic exposure.
- Cost per square foot: Wattway’s adhesive overlay approach reduced material and labor costs compared to replacing entire road sections with thick glass modules and their supporting infrastructure.
The Solar Roadways trial in Sandpoint, Idaho, installed panels on a pedestrian-only pathway and encountered manufacturing defects that the company struggled to resolve. This contrast highlights the engineering rigor that Colas and INES brought to the Wattway project from the very beginning of the development process. The comparison also raises important questions about whether solar roof tiles on buildings might offer a more practical and immediate return on investment than solar pavement on roads.
Performance Metrics and Energy Generation Benchmarks
Early performance data from the Tourouvre-au-Perche installation provided valuable benchmarks for assessing the viability of solar road technology. The table below summarizes the key metrics collected during the initial testing phase:
| Metric | Value | Notes |
|---|---|---|
| Total panel area | 30,000 sq ft (2,800 sq m) | Covering a 1 km stretch of road |
| Installation cost | $5.3 million (5 million euros) | Including panels, labor, and grid connection |
| Daily traffic volume | ~2,000 vehicles | Mix of cars and light trucks |
| Panel efficiency (flat vs tilted) | Estimated 15 to 18 percent less | Horizontal orientation reduces light capture |
| Area per household | 215 sq ft per French home | Theoretical projection pending validation |
| Test duration | 2 years | Durability and energy output assessment |
| Panel thickness | Less than 1 cm | Thin-film overlay on existing road surface |
One of the most important findings from the early data was that horizontally mounted solar panels produce significantly less electricity than panels angled toward the sun. While a typical rooftop solar array in France might achieve a capacity factor of 12 to 15 percent, a flat road-mounted panel may only reach 8 to 10 percent under similar sunlight conditions. This has led some energy analysts to question whether the high cost of solar pavement can be justified by its energy output, especially given the rapidly declining cost of traditional rooftop solar panels. The National Institute for Solar Energy continues to monitor the data to determine whether incremental improvements in cell technology can close this efficiency gap over time.
Challenges and the Road Ahead for Solar Infrastructure
The Wattway pilot project in Tourouvre-au-Perche has surfaced several challenges that must be addressed before solar roads can be deployed at a meaningful scale. The first and most obvious is cost. At $5.3 million for a one-kilometer stretch, solar pavement costs roughly ten to fifteen times more than conventional asphalt resurfacing. Without a dramatic reduction in panel manufacturing costs or a substantial increase in energy output per square meter, solar roads remain difficult to justify on purely economic grounds in most locations.
Durability under heavy traffic is another open question that requires longer study. While Wattway panels are engineered to handle vehicle loads, road surfaces experience constant wear from tire friction, debris abrasion, water infiltration, and de-icing salts in winter climates. Over the two-year test window, some surface scratching and minor delamination at panel edges were observed, although the panels remained functionally intact throughout the trial period. Longer-term monitoring spanning five years or more will be needed to determine whether the panels can match the 10 to 15 year lifespan of standard asphalt before requiring replacement or refurbishment.
Despite these challenges, the Wattway project has already contributed valuable knowledge to the field of integrating photovoltaic systems into building and infrastructure design. The lessons learned in Tourouvre-au-Perche about panel adhesion techniques, thermal expansion management, and traffic resistance have directly informed subsequent solar pavement trials in other countries, including pilot projects in Switzerland, the United States, and Japan. Colas has since refined the Wattway system based on these early findings, with newer versions featuring improved surface grip textures and enhanced cell encapsulation to resist moisture penetration.
The debate over whether solar roads will ever become economically viable continues among energy experts and infrastructure planners. Proponents argue that the vast surface area of existing roads represents an enormous untapped resource for renewable energy generation that could supplement grid capacity without competing for agricultural or natural land. Critics counter that rooftop solar, utility-scale solar farms in sunny regions, and building-integrated photovoltaics all offer substantially better energy returns per dollar invested with proven technology and established supply chains. What is not in dispute is that the Tourouvre-au-Perche installation marked a genuine world first and provided civil engineers with irreplaceable real-world data about the intersection of road construction and renewable energy. Whether solar roads become a mainstream infrastructure solution or remain a niche experimental technology, the work done by Colas and INES has permanently broadened the conversation about what roads can contribute to a sustainable energy future.