Photo: LABOR3 Architektur

Tens of thousands of kilometers of motorways cross Germany. A project is currently investigating whether these gigantic areas can be used as sunroofs. The energy efficiency would be huge, as would the problems.

Solar energy plays an important role in the success of the energy change, but the space for solar parks is limited. This is because rack-mounted photovoltaic systems require a lot of floor space. A research project of the “Austrian Institute of Technology” will test an ingenious solution to this problem: A sunroof that spans highways.

The drivers would circulate under a huge solar garage, whose solar cells would let in light.

Highways are a good place to generate solar power because a limited area is used.

Martin Heinrich, Fraunhofer Institute for Solar Energy Systems (ISE).

Stephan Freudenstein, director of the test office for traffic road construction at the Technical University of Munich, also sees the potential of this concept: “Traffic zones represent 5% of the total land area of ​​Germany and their use to generate electricity has a lot of potentialSays Freudenstein.

We don’t want to build a huge tunnel, but to use modules that let in light. Although semi-transparent modules are a little less efficient, the difference with conventional cells is only 1%, according to Heinrich.

The first step of the research project is to develop a prototype with adapted 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 motorways, including 3,383 kilometers of six or more lanes and 9,610 kilometers of four lanes. With a width of 15.75 or 12 meters per driving direction, the result is a usable area of 337 square kilometers.

How much energy could it generate?

According to information from electricity supplier E.on, 54 square meters of photovoltaic power plants generate around 9,500 kilowatt-hours of electric power per year, but in the case of highways, another factor must be taken into account: roof cells do not are not always being ideally aligned with the sun.

Performance is highly dependent on locationISE researcher Heinrich admits. For example, highways running east-west, lined with mountains or tall trees to the south, only get enough sun in the morning or afternoon.Not all locations are ideal, but even in many relatively poor sections, enough energy is generated to make the facility useful at any given time.Said Heinrich.

But even if the total performance is considered to be 30% lower than ideal conditions, the result is impressive: 41.5 terawatt-hours solar power could be produced annually within 337 square kilometers.

For comparison: According to the Federal Environment Agency, German households consumed 129 terawatt hours of electrical energy in 2018 – a solar roof of a major highway could therefore cover nearly 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 ultimately costs around 125 euros for large power plants, but this figure would be considerably higher for a covered motorway. Because the required substructure is an important cost factor, warns civil engineer Freudenstein: “Here, many structures are needed to withstand the wind, in addition they must be protected against corrosion.“According to Freudenstein, this translates into considerable costs.

Solar cells on roadways 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 cost 100,000 million euros. However, Heinrich, a researcher at ISE, believes the project is feasible. “Expansion at the national level is more a question of will than of technical and economic viabilitySaid Heinrich.