The researchers developed a high-precision methodology for this purpose. The free-to-use tool is innovative, it uses open-source code Geographic Information Systems and also takes into account the energy viability of the facilities.

Cities consume the most energy and emit the most CO₂. So implementing renewable energies in them is essential along the path towards decarbonisation. In urban areas, however, very little land is available for this purpose. That is why fitting photovoltaic panels onto rooftops is one of the most appropriate options.

Aware of this situation, University of the Basque Country (UPV/EHU) researchers measured the capacity of buildings in Vitoria-Gasteiz for this purpose: “In a context in which photovoltaic macro-projects located in rural areas, in particular, are in full swing, we wanted to find out the advantages and limitations of this technology in spaces that have already been humanized. That way, we could better assess whether it is possible to avoid occupying land that could be used for other purposes,” explained the researcher Alex Tro.

The UPV/EHU study concluded that 50% of the rooftop surface in Vitoria-Gasteiz is viable in energy terms for the fitting of photovoltaic panels and that, if this surface is fully exploited, it would be possible to produce 38% of the electricity consumed by the capital of Álava-Araba in one year. Alex Tro says that the estimates so far have been improved by this study: “Our methodology takes into account many local factors to make the calculations, and thanks to that, there are fewer errors. It enables us to conduct high-precision studies and rates, as appropriate, the rooftop areas that are usually rejected for the fitting of photovoltaic panels. For example, many of the west-east facing ones may be suitable for obtaining solar energy, according to our measurements.”

The study also confirmed that the outskirts of the city have a greater potential for generating electricity using solar energy. In fact, in the centre, it is more difficult to take advantage of the sun due to the accumulation of more buildings in a smaller space and the presence of taller buildings.

Innovative, free-to use, high-precision, methodology

The methodology used to reach these conclusions was developed by Ekopol itself and, as already mentioned, means that it is possible to measure, in a very precise way, the capacity of the rooftops in a given environment to generate solar energy because it takes many variables into consideration.

It uses open-source code Geographic Information Systems. In other words, software that is freely available to anyone and allows data on a specific area to be crossed and conclusions to be automatically drawn. For example, in this case, the researchers downloaded maps of buildings and height maps relating to Vitoria-Gasteiz from public databases and, by inputting this information into the computer program, detected the orientation, shadowing and tilt of every square meter of the city’s rooftop area. As Alex Tro pointed out, “by providing the system with many other data (average hourly temperature each month, efficiency and useful service life of the panels, etc.), the tool automatically determines how much solar radiation each roof receives and how much energy would be generated from it. That way, very detailed information is provided. Other methodologies use general data, but ours makes calculations using local values and so the results are adjusted to a considerable extent”.

In addition, the UPV/EHU methodology applies another filter to the process of measuring rooftop potential: the energy viability constraint. In other words, it compares the energy that would be invested to implement the photovoltaic panels in a given building with the energy that the installation could generate in that location during its useful service life. If it is not viable, the roof in question is ruled out. “In that respect, the assessment system we have developed is innovative; indeed, in most cases, the focus is on economic viability alone, not on energy viability,” highlighted the author of the study.

Alex Tro stressed that the methodology developed is a great contribution and offers resources whereby studies of this type can be easily reproduced in many cities. However, at the same time, he was keen to point out that change cannot come through renewable energies alone: “Rooftop photovoltaic installations are viable and necessary to a certain extent, but we have seen that this is not enough. In the most extreme case, even if all the viable rooftops of a city were covered, it would not be enough to meet the energy demands of today’s society. Renewable technologies certainly need to be used, but we have to move closer to the concept of eco-social transition by changing consumption habits and prioritizing the reduction of energy consumption.”

Additional information

Alex Tro-Cabrera is a researcher in the Department of Energy Engineering, Faculty of Engineering - Bilbao. He is a member of the Ekopol research group. He explores the photovoltaic potential of buildings and the social and environmental impacts of this technology. His research focuses on the creation of energy communities and the promotion of collective self-consumption models.