Outdoor Hybrid Solar Road Demonstrator Monitoring Using Infrared Thermography with Embedded Local Probes for Energy Harvesting Performance Evaluation ^†

Abstract

This study investigates, in a natural environment, the thermal behavior of an innovative pavement system with thermal and solar energy collection functionalities. The whole structure is continuously monitored using temperature and heat flux sensor probes integrated inside the structure. Local weather conditions are also monitored. Infrared Thermography is used as a complementary non-invasive technique to monitor temperature surface distributions with time and assess the efficiency of heat transfer within the pavement structure. All sensors are connected to a newly developed platform that centralized data access, visualization, and storage, enabling seamless management and user interactions. The obtained results are presented and discussed.

1. Introduction

Road networks are exposed daily to sunlight radiation and can coexist with some energy harvesting technologies. According to [1], the total length of the pavements in the world is around 22 million km; assuming an average width of 6 m for roads, the total surface area would cover around 0.25% of all land on Earth, which is comparable with Lewis’s results [2].

Solar radiation intercepted by road networks could be converted into electricity through solar cells, or it could be harvested through a heat-exchange fluid, based on the principle of solar thermal collectors.

Obviously, the addition of these new features would require to re-think the design, the manufacturing, the installation, and the maintenance of road infrastructure.

To this end, academia and industry are conducting R&D works on two solutions: photovoltaic pavement and asphalt solar collectors.

Using solar cells requires adding a semi-transparent layer on the wearing course while keeping skid resistance for vehicles and the load-bearing capacity of the pavement structure. On the other hand, many works have focused on embedded pipes for solar collectors to harvest thermal energy or deliver energy for de-icing in winter conditions. An average efficiency of 26% was observed in different systems studied, as presented in the literature.

As an alternative, research works were conducted on replacing asphalt base course with integrated pipes by a porous one [3,4,5]. An average efficiency of 38% was observed in different systems studied.

More recent R&D works [6] have proposed replacing porous asphalt layer with porous cement concrete layer in combination with a new approach for such hydraulic layer in situ impermeability to enhance the thermal fluid flow rate and conductive heat transfer inside the structure.

The present study investigates the thermal behavior of such innovative pavement systems integrating thermal and solar energy collection functionalities in real outdoor conditions with dedicated integrated instrumentation.

Previous numerical modeling [5] and laboratory-scale experiments [7] validated the feasibility of this concept, demonstrating promising thermal performance under controlled conditions. The transition to outdoor testing aims to evaluate the system’s response to real environmental factors, including solar radiation, ambient temperature variations, and convective exchanges.

In the present study, the prototype pavement mock-up is continuously monitored using temperature and heat flux sensors probes inserted in the structure. Local environmental conditions are monitored through the deployment of a local weather station and a pyranometer. Finally, Infrared Thermography is used as a complementary non-invasive technique to monitor temperature surface distributions with time. All sensors are connected to a newly developed platform that centralizes data access, visualization, and storage, enabling seamless management and user interactions.

We first present the instrumented mock-up, the outdoor test site, and the new monitoring system. Preliminary results are shown and discussed, followed by conclusions and future directions.

2. Instrumented Outdoor Test Site

We first introduce the instrumented outdoor test site and present the hybrid solar road mock-up built with its integrated instrumentation. Then, the new architecture of the H24 monitoring system is introduced, with emphasis on the generic management of the infrared camera and its data acquisition platform.

2.1. Designed and Built Instrumented Mock-Up

A mock-up of the SUNROAD system [6] of 2 m × 1 m dimension was built in our laboratory facilities, allowing instrumentation integration in various layers and locations inside the structure. The system was implemented in an outdoor test site equipped with additional local weather and sun illumination sensors. Figure 1 presents a schematic view of the test site and a view of the built system.

Five rows of solar cells were integrated below a semi-transparent layer in the first part of the hybrid road system surface. The second part is only covered by the semi-transparent layer. The thermal fluid flows first below the solar cells (inside the porous layer and by natural gravity). At the outlet, it flows to a hydraulic underground storage. A pump is used to raise the thermal fluid at the inlet of the system. The control command with the monitoring system connected to all sensors was integrated in a dedicated protective housing located on the shoulder of the system (see Figure 1)

2.2. H24 Monitoring System: Supervisor

A chain of various software programs called “Supervisor” have been designed [8] as a “system of systems” to support the development and operation of Structural Health Monitoring (SHM) Digital Twins. These software programs are managed by a central supervisor that handles the data collection from various sensors and sources (such as meteorological data from various providers), while a recorder handles data and metadata storage using the HDF5 format. One of the key components of the Supervisor is to embed data assimilation capabilities combined with specific physical or statistical models, including inverse models (thermal and/or mechanical) or even predictive models. It therefore interconnects hardware and software layers to enable the extraction and provision of key parameters essential for Digital Twin-based decision-making tools or predictive control monitoring application.

As illustrated in Figure 2, the Supervisor natively integrates data collection from both local sources and external systems, supporting real-time synchronization and updates. Its Model-View-Controller (MVC) design pattern ensures extensibility, customization, and interoperability with existing applications.

The Single-Writer/Multiple-Readers feature of HDF5 allows real-time visualization and live computation of Digital Twin models. Supervisor’s flexible data handling supports various sensor types, and its deployment capabilities are reinforced by Ansible automation and GitLab automatic updates. As a cornerstone in the SHM Digital Twins research framework, Supervisor also contributes to maintenance planning by providing insights on both monitored structures and deployed sensors, with future improvements aimed at broader data integration and more generic configuration mechanisms.

2.3. Infrared Images Acquisition Platform: Diarit

As part of the Supervisor toolchain, the ‘Diarit’ module [8] manages and schedules the acquisition of infrared images, supporting a variety of camera vendors. Diarit is built around a generic abstract class for infrared cameras, which serves as a high-level API. This design facilitates the integration of new camera vendors and provides standardized functionalities such as a unified user interface for camera control, live stream visualization, and the ability to plan and manage image recordings. Its integration with the Supervisor toolchain enables advanced in situ monitoring capabilities across diverse camera vendors, SDK providers, and data structures, while addressing challenges related to data synchronization, storage, and visualization.

3. Results and Discussion

Figure 3 presents the thermal fluid temperature evolution over 4 days: at the inlet, the outlet, and in the underground storage. The solar irradiance received at the mock-up surface is also shown.

Figure 4 shows an example of thermal energy harvested by the fluid loop over 9 days.

On 5–6 and 10-11 June, it can be observed that there was a decay in the amount of solar energy harvested, with low solar irradiance available on these particular days.

Figure 5 presents infrared images acquired at different time steps showing the rise of apparent surface temperature over the photovoltaic part of the mock-up with no fluid flow in the porous layer.

Supervisor’s connection with Diarit, the infrared image acquisition platform, allows for measurement correction [9] induced by variable environmental conditions measured on site.

4. Conclusions and Future Directions

This study contributes to the development of sustainable pavement technologies by optimizing energy efficiency, durability, and performance under real-world conditions. It also addresses the monitoring architecture and standard data format management of research works carried out to allow large-scale deployment on real structures or transport infrastructures. The obtained preliminary results have been promising.

As a future direction, data collected from IRT measurements and embedded temperature and heat flux sensors will be used to refine the existing numerical models, ensuring greater accuracy in predicting long-term thermal behavior.