Electric buses are becoming ever more prevalent in the public transport sector. However, the rising number of electric vehicles is not only due to municipal efforts to enforce the protection of the environment, but it is also explicitly part of the political agenda. The Clean Vehicle Directive of the European Union sets national targets for the public procurement of low- and zero-emission vehicles and will be implemented in national legislation in August 2021. This is why electromobility is not only a sustainable trend but also a clear growth market for companies such as SBRS. The company, with its headquarters in Dinslaken, is a turnkey charging infrastructure supplier for the public transport sector. SBRS supplies its solutions to bus manufacturers, which often act as general contractors during municipal projects and — in the case of public tenders — also directly to the municipalities.
The success of the company is mainly based on its technical expertise as well as on the development of customized applications. As far as the public transport sector is concerned, SBRS usually relies on charging concepts with two central pillars.
"A combination of depot-based and route-based charging is the future of sustainable mobility," said Andreas Stahl, head of sales at SBRS.
The two concepts differ from one another in terms of the charging rate. While electric buses in the depot are usually charged for several hours overnight, several fast-charging points along the route can be used to provide the vehicles within minutes with a sufficient amount of power for several kilometres.
Fast Charging Is Impossible Without Cooling
Cooling the charging points is a must, as fast charging generates more heat than the slower depot charging process. The reliability and availability of the cooling technology as well as the charging infrastructure as a whole are clearly the most important criteria.
"It's simple: The cooling system must work so that the buses can be charged and are ready for use," said Bastian Thiel, sales manager at technotrans.
This is why SBRS relies on solutions made by the fluid technology specialist with its headquarters in Sassenberg. The cooperation began in 2017 when technotrans provided solutions for four fast-charging points along the bus route and one depot charging station for a project in Osnabrück. In 2019, an additional 16 fast chargers with 300 kW each and 50 depot charging stations with 150 kW each were ordered. This means that, by the end of 2021, approximately 80% of the entire fleet of the city of Osnabrück will be battery-powered.
Osnabrück, Venice, or Brussels: The fast-charging points made by SBRS usually use the pantograph collector technology.
"The charging process starts automatically after 5-10 seconds after a bus has reached the fast-charging point and has made contact with the pantograph,” said Stahl. “There is no need for manual activation."
Within this short period of time, the vehicle and the electronic charging system establish a communication link and exchange performance parameters, e.g., concerning the battery status by handshaking. The battery management system transfers the requirements of the vehicle to the charging station which, in turn, supplies the necessary charging power. Then, the charging process begins. The length of the stop of the bus depends on the vehicle type, battery system, and distance to be covered.
For all of the projects, technotrans has developed customized concepts that fulfill the requirements specified by SBRS down to the last detail. The example of a project in Düsseldorf shows that sometimes highly specific solutions are required. In this case, technotrans has installed a passive, liquid-based central cooling system that works without a compressor. This means that a pump is used for the circulation of the cooling medium through the charging points. In addition, the medium is cooled in an air/water heat exchanger (i.e. the recooler) with regard to the ambient air before it flows back to the charging point. The recooler is installed on the roof of a small concrete building accommodating 10 charging points and the pumps. All of the charging points are supplied centrally via a recooler. The cooling capacity per charging point is approx. 6.5-13 kW.
To ensure optimum availability, SBRS and technotrans use redundant systems in all critical areas. As far as the above-mentioned central cooling system is concerned, technotrans has equipped the recooler with several frequency-controlled fans. Even if one of them fails, cooling is still provided. In addition, the pump station has a total of two pumps that run in alternation to ensure the supply of the charging points with cold water. However, technotrans also achieves a certain level of overall redundancy with the distributed cooling solution, thereby avoiding downtimes.
A High Level of Energy Efficiency and a Low Level of Noise Emissions
For SBRS, an energy-efficient design was a major aspect.
"The technotrans cooling systems have relatively low energy demands in terms of the withdrawal of the resulting waste heat. The actual advantage is not the energy saving potential but rather the fact that this energy does not need to be 'generated' at all," said Stahl.
technotrans achieves this by using speed-controlled components for its cooling solutions. They provide power even during partial-load operation, which is also beneficial in terms of the noise emissions.
"When it comes to these projects, we often speak of an urban integration in residential areas,” Stahl said. “These areas, however, are subject to several technical instructions concerning protection against noise. In other words: We need to comply with the specified noise limits while taking into account the acoustic directivity of the sound-emitting sources."
The noise level of the cooling system depends on the fan speed which, in turn, is determined by the ambient temperature and set target temperature. To keep the noise level as low as possible, technotrans has developed a special concept for demand-based power requests.
"The higher the ambient temperature is, the higher the tolerance in the target range will be,” said Thiel. “This is important to ensure that the fan speed increases slowly up to a certain point."
This means: If the temperature of the cooling medium is 26°C due to the ambient conditions, while the target temperature is 25°C, the fan will not run straight away at 100% power to compensate for the temperature difference. Instead, it will start in the low — and thereby noise-reduced — power range.
A Promising Cooperation
The specific design of the cooling system was what SBRS was convinced by in taking the technology supplier from Sassenberg on board.
"On the one hand, technotrans clearly stands out on the market but, on the other hand, the company also uses a solution-oriented approach and has no problem with adapting its systems to our systems, and so that was the decisive factor for us,” said Stahl. “We are very happy as far as the technology is concerned.”
In addition, technotrans is a one-stop shop supplying everything from the conceptual study and the technological design to the final solution. The company was also responsible for installing the pipe components. Today, technotrans has developed several series based on the originally highly specific devices. These series have been deployed in other projects since 2018. Both companies have made it clear that they want to continue their partnership in the future. Several projects throughout Europe are already in the pipeline.