Photo: LABOR3 Architektur
Tens of thousands of kilometers of motorways run through Germany. A project is now investigating whether these gigantic areas can be used as solar roofs. The energy efficiency would be huge, and so would the problems.
Solar energy plays an important role in the success of energy change, but space for solar parks is limited. This is because rack- mounted PV systems require a lot of floor space. A research project from the “Austrian Institute of Technology” is going to test an ingenious solution to this problem: A sunroof that stretches across motorways.
The drivers would circulate under a huge solar garage, whose solar cells should let in light.
Highways are a good place to generate solar energy because they use a limited area.
Martin Heinrich, Fraunhofer Institute for Solar Energy Systems (ISE).
Stephan Freudenstein, Director of the Testing Office for the Construction of Traffic Routes at the Technical University of Munich, also sees potential in this concept: “ Traffic areas represent 5% of the total surface area of Germany, and use them to generate Electricity has a lot of potential, ”says Freudenstein.
We do not want to build a huge tunnel, but to use modules that let in light. Although semi-transparent modules are somewhat less efficient, the difference from conventional cells is only 1% , according to Heinrich.
The first step of the research project is to develop a prototype with suitable modules, which will then be tested for one year.
But what effects would a large-scale application have?
According to the Federal Ministry of Transport, Germany has 12,993 kilometers of motorway, of which 3,383 kilometers are six or more lanes and 9,610 kilometers are four lanes. With a width of 15.75 or 12 meters per driving direction, this results in a usable area of 337 square kilometers.
How much energy could it generate?
According to information from the electricity supplier E.on, 54 square meters of photovoltaic plants generate around 9,500 kilowatt hours of electrical energy per year, but in the case of motorways, another factor must be taken into account: Roof cells are not always they can be ideally aligned with the sun.
” Performance is highly location dependent ,” admits ISE researcher Heinrich. For example, highways in the east-west direction, which are lined with mountains or tall trees in the south, only get enough sun in the morning or afternoon. ” Not all locations are ideal, but even in many comparatively poor sections, enough power is generated to make the plant worthwhile at some point, ” says Heinrich.
But even if you consider that the total efficiency is 30% lower compared to ideal conditions, the result is impressive : 41.5 terawatt hours of solar energy could be generated per year in the 337 square kilometers.
For comparison: According to the Federal Environment Agency, households in Germany consumed 129 terawatt hours of electricity in 2018 – a solar roof on a large-area motorway could therefore cover almost a third of this demand.
However, such a solar park on a highway is likely to be expensive. According to Heinrich, a square meter of photovoltaic surface costs in the end about 125 euros for large power plants, but this figure would be considerably higher for a covered highway. Because the required substructure is an important cost factor, civil engineer Freudenstein warns: “ Here you need a lot of structures to withstand the wind, and they also have to be protected against corrosion. “According to Freudenstein, this translates into considerable costs.
Solar cells on road surfaces are not yet an alternative
If, instead of 125 euros per square meter, the costs of the solar system were 300 euros per square meter, a national system of this type would have a cost of 100,000 million euros. However, ISE researcher Heinrich believes that the project is feasible. ” An expansion at the national level is more a question of will than technical and economic viability, ” says Heinrich.