Solar Power and Which Roof to Use

A roof is more than a way of keeping the rain off. Nowadays many people think of a roof as a place to put solar panels to collect all of that free sunshine. The problem is that not all roofs are created equal. Scientists from the University of Gothenburg have launched a tool that uses the actual conditions to determine the maximum possible magnitude of solar incidence (and implied the maximum amount of time in shadow) – in a whole town, a neighborhood, or a particular roof. The scientists have surveyed Gothenburg in a pilot project.

If you have the free area at ground level this will do as well, but many houses do not have this area available and the roof is sometimes the only area that can be used. It must cost more to put it on the roof, and maintenance is going to be more difficult, against that the panels are faced with glass and this might get damaged more if it is accessible at ground level. It’s a matter for each householder to decide.

Solar power does not work if there is no sun which is why the effect of shadows must be understood. The roof must be clear of obstacles such as overhanging trees and the shadows of other buildings for the ideal effect.

On top of that the best sites need the sun rays to be presented at the optimal angle for maximal power generation.

The new tool is based on computer-based geographical information systems (GIS) that collect, store, analyse and present geographical data. This means that the tool describes real roofs in the correct surroundings. The sun in the model illuminates the three-dimensional built environment and simulates how surrounding buildings, terrain and vegetation throw shadows.

The shadow effect can be calculated for each month or for a complete year, and this means that certain parts of a roof may turn out to be unsuitable for collecting solar energy, even though the roof has both optimal direction and gradient. In this way, it is possible to calculate the total solar radiation on each part of a roof structure within a given area, calculated as kilowatt hours per square meter.

Thus, SEES can provide a map over the suitability, based on the user’s requirements for good, less good and poor annual solar incidence. Climate data (either measured or calculated values) with a resolution as high as 1 hour is used for the location at which SEES is being used, in order to obtain as accurate an estimate of solar incidence as possible.

“We have used Gothenburg as pilot town in the project, but the method can be used in all municipalities where the necessary data is made available. The users can judge the suitability of a roof for solar voltaic panels or solar thermal panels across a wide range, based on this”, says Fredrik Lindberg.

The solar energy project has been carried out by the University of Gothenburg in collaboration with WSP Analys & Strategi, and it has just presented its final report. The project has been financed by the SolEl programme, the Research Foundation of Göteborg Energi, the City Planning Administration of Gothenburg and the Region Västra Götaland County Council.

Article by Andy Soos, appearing courtesy ENN.

photo: PhOtOnQuAnTiQuE

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