The sun deposits 10,000 times more energy on earth than mankind currently uses. Martina Klärle, head of the Weikersheim-based Steinbeis Transfer Center Geoinformation and Land Management joined forces with researchers at the Osnabrück University of Applied Sciences to identify a method to calculate the full potential of solar energy. In practical terms, the method makes it possible to evaluate solar panel locations using laser scanning data.
The SUN-AREA research project looks at the best way to use solar energy captured by photovoltaic devices on the roofs of buildings. The aim of the project is to use existing laser scanning data across whole areas to pinpoint the best location to site solar panels for the generation of solar energy. This is now possible thanks to the development of computer-aided evaluation techniques which work out the shape, inclination, direction and shade on individual rooftops by using geographical information systems. The system can reliably predict the resulting energy potential of huge areas. The test region used was the town of Osnabruck, an area of 120sq km.
A key feature of SUN-AREA is that it only uses existing data (height = laser scanning data; position = footprint/ALK). So the research forms a link in a value chain, enabling business to make use of high resolution laser scanning data. Data is captured by flying over the area to be analyzed using specially equipped airplanes with a sensor under the fuselage which scans the entire area.
Based on a “digital surface model”, the laser scanning data is used to calculate and model the total roof area. Roofs stands at different heights so this has to be converted into a height value and x-y coordinates. The scanner can take in about four points per square meter with a height accuracy of about 15cm. By measuring more than one reflection of impulses (first pulse and last pulse) a concentration of points can be broken down into ground points and high points (vegetation and buildings). The system provides so much detail over such a large area that for the first time it is now possible to analyze local areas. A number of German Federal States such as Baden-Wurttemberg now have extremely precise three-dimensional aerial scanning data. Within the foreseeable future data should be available for the whole of Germany.
SUN-AREA allows you to work out how well, in which way and whether buildings and facilities would be suitable for solar panels. In the test region the team drafted a rulebook using a geographical information system that examines the suitability of rooftops for solar panels. Using a fully automated sequence of algorithms consisting of raster and vector functions the system assesses every rooftop for size, shape, inclination, direction and shade. An intersection average of individual scores is then used as a basis for calculating the potential energy of a whole area of a town as well as individual buildings.
In the first stage of the project algorithms were developed to calculate location parameters: inclination, aspect and area. The second stage analyzed shade. The direction the roof is pointing in has a key influence on the use of overall radiation. A south-facing roof can make 100 per cent use of energy. Even if a roof is facing east or west it can exploit up to 80 per cent of energy. The level of solar yield is closely linked to the angle at which the sun strikes the surface of the solar panel. The maximum value is achieved when the sun hits the panel at 90°. This is why the solar yield of a roof at an angle varies in the course of a year. Ideally, for a good annual yield, the roof needs to be set at an angle between 30° and 40°. A flat roof or changing the inclination by anywhere up to 70° will reduce the yield by up to 20 per cent.
The scanning data is so precise in terms of height and position that it is possible to calculate the shade for an individual roof by the time of day, time of the year and the latitude of the area. The direct solar radiation is calculated using the difference between the angle of rays striking the panel and the perpendicular to the surface of the roof or building. To calculate shade, the area of the surface is rasterized. Each cell within the raster is then checked to see if it fit will fall into the shade.
To calculate the average annual solar energy potential in kWh, you use the module efficiency, the size of the area in sq m, the overall average annual radiation, shade, roof inclination and aspect. Individual results are taken as pooled averages and then mapped.
To evaluate economic viability it is crucial to select the right location for solar panels. Positioning factors such as the angle of inclination, aspect, potential solar radiation and roof size are central to the successful operation of any photovoltaic installation. It is only by taking such factors into consideration that you can maximize the solar energy potential in built-up areas.
This method was first used in five test areas of up to 1sq km in the region around Osnabruck using conventional geographical information systems. Once the SUN-AREA rulebook has been applied to individual communities, one of the research project goals is to make it available for use for larger areas, including rural districts and entire Federal States.
The solar energy potential has already been successfully calculated for the test area. The 1sq km area (holding a total of 933 buildings, with an average annual energy consumption of 1500 kWh per person), had solar energy potential of around 3 GWh from all of the usable solar panels on roofs. The potential investment lay at 15 million euros. This would allow you to answer the energy requirements of around 2115 people per year, i.e. 48 per cent of the population living in the test area.
To make the results available to a wider audience the team plans to post them on the Internet. To present data for the test region of Osnabruck the team are using a geographical information system on the Internet. In a similar way to online maps, users can go to a specific location on the map and call up individual buildings, streets and even complete districts. Apart from the authorities, users could be private building owners, citizen and even whole sectors of industry such as the solar panel industry and associated sales channels.
A number of communities and rural districts have already expressed a strong interest in the SUN-AREA method. This shows on the one hand how important it is to public authorities to calculate the energy potential of areas reliably. On the other, there is a need for meaningful maps. Ultimately, practice will show whether and to what extent the SUN-AREA method will improve the spread of solar energy throughout Germany – and achieve this more economically.
Prof. Dr. Martina Klärle
Steinbeis Transfer Center Geoinformation and Land Management (Weikersheim)
stz1072@stw.de