Highway Solarisation in Sri Lanka: A GIS-Based Evaluation of Solar Energy Potential on the Southern Expressway

Sri Lanka, with its equatorial location, receives abundant solar energy resources, ranging from 1,247 kW h/m2 to 2,106 kW h/m2 throughout the year. Despite this potential, the utilisation of solar energy has been narrowed to small-scale rooftop solar installations. Consequently, this study investigates the concept of ‘highway solarisation,’ which integrates solar photovoltaic (PV) technology into the highways, with solar panels placed along their paths to capture sunlight and generate electricity. The Southern Expressway in Sri Lanka emerges as an optimal candidate for this initiative owing to its heightened solar intensity and minimal shading. Thus, this research aims to analyse the feasibility of implementing highway solarisation along the Southern Expressway, employing a Geographic Information System (GIS). The study area covers a 200.5 km long expressway, extending from Kottawa to Mattala, accompanied by a 250 m buffer on both sides. Various datasets encompassing Photovoltaic Power Potential (PVOUT), Direct Normal Irradiation (DNI), Global Horizontal Irradiation (GHI), Digital Elevation Model (DEM), and land use were collected and processed using ArcGIS 10.8.2. Subsequent to the generation of maps delineating PVOUT, DNI, GHI, elevation, aspect, and land use, the Multicriteria Decision Making (MCDM) technique was employed to identify suitable sites for solar panel deployment. Analysis of PVOUT revealed a variation of 3.95–4.25 kW h/kWp while peak and lower values concentrated between 130–200 km and 40–111 km markers along the highway. Notably, the distribution of DNI exhibited similar trends, with a peak in proximity to the Mattala Interchange (IC). The GHI ranged from 5.05–5.50 kW h/m2, with an upward trend from 130–200 km. Elevation and aspect profiles highlighted the predominantly flat terrain of the expressway, which increases the direct solar irradiation. Challenges were identified particularly from Kottawa to Kokmaduwa IC, notably in urbanised and densely vegetated areas. However, the open land cover segment beyond Kokmaduwa to Mattala IC in the Southern Expressway portrayed moderate to high suitability for solar panel installation, highlighting its substantial potential for highway solarisation and contributing to sustainable energy generation in Sri Lanka.