Large-scale rooftop solar photovoltaic technical potential estimation using Random Forests

Photovoltaic (PV) panels are a very promising technology that answers part of the increasing need for global renewable energy production, particularly in urban areas. We present a novel methodology combining Geographic Information Systems (GIS), solar models and a Machine Learning (ML) algorithm, Random Forests, to estimate the potential for rooftop PV solar energy at the scale of a country. We use a hierarchical approach which divides the computation of the final potential into several steps. Each step is reached by estimating multiple variables of interest using widely available data, and combining these variables into potential values. The method for estimating each variable of interest is as follows: (1) collect all the data related to the variable, (2) train a Random Forest model based on the collected data and (3) use the model to predict the variables in unknown locations. The variables of interest include available area for PV installation on rooftops, shape, slope and direction of rooftops, global solar horizontal and tilted radiations, as well as shading factors over rooftops. The study focuses on Switzerland and provides the rooftop PV technical potential for each (200 × 200) [m2] pixel of a grid covering the entire country. The methodology, however, is generalizable to any region for which similar data is available and could therefore be useful for researchers, energy service companies, stockholders and municipalities to assess the rooftop PV capacity of the region. Prediction Intervals are also provided for the different estimated variables, in order to measure the uncertainty of the estimations. The results show that Switzerland has a large potential for rooftop PV installations. More specifically, for roofs orientated at ±90° from due south, the total estimated potential PV electricity production is about 16.29 TWh/year, which corresponds to 25.3% of the total electricity demand in 2017.