The EU’s AREUS research project (Automation and Robotics for European Sustainable Manufacturing) brought together 13 partners from industry and research facilities to test a future energy platform for automotive manufacturing facilities. The automotive industry’s goal in the project was to increase energy efficiency and ensure sustainability through the use of renewable energy sources in combination with modern energy storage units. A further objective was to optimize resource utilization for installation technologies and the electromagnetic compatibility of production equipment.
“Caution! Test run.” The sign is a warning about what goes on here, although at the moment everything is quiet. Behind a security fence, four robots stand rigidly upright, their grips holding vehicle body components in a manner that makes it seem as if their movement has been frozen in time. However, the robots will begin moving again shortly, when they’ll start welding, gluing, riveting, and placing finished door hinges for the Mercedes-Benz CLS into carriers.
In the TecFactory – an innovation and development center operated by Daimler’s Production Technology department in Sindelfingen, Germany–new manufacturing processes are being developed and tested under real-world conditions. The approach utilized for the project involves switching from an alternating current topology to a direct current topology – i.e. an industrial DC smart grid. The layout of the AREUS facility is based on a real manufacturing cell from the body-in-white shop. The cell was altered to include a DC architecture and equipped with modified components and machinery ready for connection to a DC supply.
Daimler is using a real manufacturing cell to find out in detail how production processes can be made more energy efficient and how energy from renewable sources can be easily integrated into such processes. The initial problem here should be familiar: The electricity that comes out of the socket is alternating current – but all electronic devices need direct current, which is why everyone now has lots of small power adapters that are used to recharge smartphones, laptops, etc. In addition, an increasing number of households now have photovoltaic systems mounted on their roof, some of them also have a battery in the basement, and an electric car will soon be parked in the garage. This scenario cries out for a DC grid.
Surplus energy generated during breaks or on weekends can be stored in batteries and used when needed.
The situation is similar in manufacturing facilities, but the power levels are much higher. For example, variable-speed drives need direct current to control motor speeds – a frequency converter is used to provide this by converting alternating current – but the conversion causes thermal losses. Another goal is to recover the energy released when drives are braked and then reuse it or store it temporarily in batteries, as is done in today’s hybrid vehicles.
Feeding energy from renewable sources such as photovoltaic systems or wind turbines into an industrial DC smart grid reduces conversion losses in comparison with conventional solutions. Surplus energy generated during breaks or on weekends can be stored in batteries and used when needed. In conventional solutions, the direct current from a photovoltaic system first needs to be converted into alternating current so that it can be fed into the public grid, after which energy consumers more often than not convert it back to DC.
Adding up all the requirements, it becomes clear that switching factories over to across-the-board direct current operation might make sense sooner or later. Direct current supply offers many advantages, such as more efficient utilization of energy – especially when generated from renewables. Moreover, because energy storage devices play a key role in such scenarios, a DC infrastructure would make it easier for the automotive industry to deal with the fluctuations and lower grid reliability resulting from the fact that more and more electricity is now being produced from solar and wind power sources. This issue is especially important for the automotive industry in Germany, where the country’s energy transition calls for no less than 80 percent of all electricity to be produced from renewable sources by 2050.
It is exactly this goal that was pursued by the AREUS project, which was funded by the European Union. The project brought together 13 partners, including Daimler, Siemens, and other companies and international universities, all of which helped with the simulation and construction of the modified manufacturing cell in Sindelfingen. They then measured and evaluated the energy savings achieved throughout the cell’s life cycle. The project was successfully completed in the fall of 2016, and the results are encouraging. “The use of a DC automation grid can reduce energy consumption by as much as 20 percent,” reports Matthias Jahn, who manages business development with Daimler for Siemens in Nuremberg. The goal of equalizing supply-side peak loads was also fully achieved.
The AREUS manufacturing cell at Daimler is connected to a photovoltaic system mounted on the outside of the production hall and capable of covering almost the entire base load required by the cell. Because the sun doesn’t always shine, additional electricity is provided by the public grid.
The industrial DC smart grid with its active front end is the central component for energy producers and consumers and is based on a 600V DC architecture.
In order to achieve the highest possible energy efficiency, the facility’s industrial DC smart grid is supported by several storage devices – for example a lithium-ion battery for long-term storage and a capacitor bank that manages the short energy peaks that result from the dynamic movements robots make when they accelerate or brake.
The AREUS test cell at Daimler is connected to a photovoltaic system capable of covering almost the entire base load required by the cell.
A flywheel is also installed as a further storage device in order to close the gap between the lithium-ion battery and the capacitor bank. A flywheel generally consists of a rotating mechanism and a rigidly coupled electric motor. The charge-discharge process is controlled as needed via the flywheel’s speed setting.
If all energy storage devices are fully charged, any additional energy generated from solar or wind power facilities or the industrial process can be fed back to the public AC grid via the active front end.
A separate control system is used to regulate the energy-flow management needed for the individual energy producers and the energy storage systems.
As a result of the additionally identified optimization potential, energy consumption can be reduced by as much as 20% compared to the original manufacturing cell.
AREUS has been completed but has since been replaced by a follow-up project known as DC-INDUSTRIE, which is being funded by Germany’s Ministry for Economic Affairs and Energy. The 26 partners participating in DC-INDUSTRIE are working on the development of the next generation of DC infrastructure. The focus here is outside the automotive industry, but Daimler AG and Siemens are once again leading the way with their innovations.
Certain challenges need to be overcome – for one thing, the partners will have to develop their own standards for DC components. In addition, a wave of development is needed for customized and efficient systems that can be used in both small manufacturing cells and large production halls. The manufacturing cell in Sindelfingen will remain in operation until at least 2019 and the knowledge gained through it will be applied at Daimler plants in the future. If all goes well, entire production facilities could be using industrial DC smart grids in ten years.
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