From pv magazine Germany
In addition to floating PV arrays and agrivoltaic systems, motorways could be an ideal solution for the surface problem of photovoltaics. By 2030, up to 200 TWh of solar power could be annually generated along Germany’s autobahn network. The implementation of such a project would result in a smart grid, but the benefits would not stop there.
The project would entail steel-grid masts erected every 15 meters along the sides of motorways. PV modules would be installed on steel lattice girders hung between the masts. “Energy bands” made up of solar modules could stretch along the traffic axes between cities, industrial areas and airports.
The energy band concept stems from the Altes Neuland Frankfurt Foundation, which has developed the project. It says that if 80% of motorways and 65% of federal roads – a combined 45,000 kilometers – were equipped with bifacial PV arrays with 25% efficiency, up to 200 TWh could be generated every year.
If the full potential is exploited and construction processes are optimized, this could also be achieved at competitive costs, the foundation argues. Although the substructure made of steel-grid masts clearly exceeds the costs of conventional substructures, the masts would also have a service life of 100 years. New modules could be added again and again during this time at very little cost.
The idea initially arose from the space requirements for PV and wind power. Current electricity consumption in Germany is 560 TWh per year. With mobility and heat gradually being electrified, by 2050 it is estimated that 2,400 TWh of electricity will be consumed yearly. The foundation assumes that 1,000 TWh of this will also be produced in Germany. The area required for this would take up 2.5% of the federal territory, or three times the area of the state of Saarland.
The energy bands are intended as a direct current system. A 110 kV high-current cable would run underground. A mains connection would have to be set every 9 km to 87 km. The different lengths per network connection depend on the use of the module assignment. So it would be conceivable to lay one, two or three rows of modules on top of each other, to install cross bridges with modules and, if necessary, even cover the masts and motorway bridges with solar modules. There is space for between 2,000 and 20,250 modules per kilometer.
The Altes Neuland Foundation has also considered scenic landscapes. If an energy band leads through a town or past a forest, avenue trees or a particularly picturesque landscape, the energy band can simply be interrupted. In this case, the project planners can omit masts and modules and only continue with the underground cable. The energy band array would only begin again behind the village or forest, while both parts would still be connected by the underground cable.
The biggest advantage of such a system would be that the electricity is already distributed during production and is thus routed to the right places, the Altes Neuland Foundation notes. Motorways connect metropolitan areas, industrial areas and airports. In addition, there is a charging infrastructure for electric cars and electric trucks along such long-distance routes. In this way, the electricity would already be produced in the right place or could at least flow to the right place.
Size vs. volatility
The energy bands would extend over hundreds of kilometers, so there would also be an opportunity to even out fluctuations in consumption and power generation across the entire system. According to the foundation's project data, if it rains in one place, the sun may shine elsewhere. Such a project is optimized even further if additional wind turbines are connected to the system. Smaller wind turbines can be placed on the masts and existing systems that are located in fields along the highways can also feed into the energy bands.
Although an expert analysis would be required for mast wind loads, it would still be easier than covering the motorway with PV systems, according to the foundation. The latter variant would require wind reports, drainage systems and lighting concepts. Researchers at the Austrian Institute of Technology (AIT), Germany's Fraunhofer ISE and Forster Industrietechnik recently teamed up on a pilot project for motorway solar generation using PV rooftops.
The initiators of the project say their plan would face fewer problems with the provision of space and permits. Arrays would only be built 1 meter to 2 meters to the sides of roads. This area is owned by the federal government, so there would be no need for permits from many different landowners.
The starting signal for the expansion of the energy bands could begin on a small scale. A huge infrastructure project would not be necessary. Municipalities and investors could develop small sections. It would only be important that they are developed in such a way that sections can be joined together at a later point in time and that there is a legal and technical basis for trading in electricity along the sections.
Peter Birkner, a professor in Bergische Universität Wuppertal’s electrical energy supply department, has followed the development of the project and the feasibility study as a member of the scientific advisory board. He is convinced of its feasibility and says it is now important to put together a suitable consortium to develop a first section.
It remains to be seen how quickly such a consortium will be formed, but investors would have little to be concerned about. All technologies that are installed are already market-ready and have been tried and tested. The foundation argues that the necessary modules, steel pylons and underground cables have all been around for decades. Annual production potential of 200 TWh could be achieved as early as 2030, it says.
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And if the efficiency of solar modules can be boosted by 50% by 2030, that’s 300 Twh a year – 1/8th of the expected demand by 2050. Then, from 2030 to 2050, another 50% = 450 Twh – more than 1/6th of expected demand…
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