Economical and clean power solution for huge peak demand in the city centre of Utrecht

Light rail 60 is an important part of the infrastructure in Utrecht. This tram, which runs on electricity supplied by high-voltage cables, transports thousands of passengers every day between Utrecht Centraal and Nieuwegein. Last summer, however, problems arose here, when a number of high-voltage cables were damaged during excavation work. The recovery was expected to take several weeks, with the tram unable to be powered. Of course, it is not desirable to shut down such an important tram line, so an alternative power solution had to be sought. The City asked the help of Engie Bredenoord for this.

The challenge: high peak demand in the inner city

"We knew beforehand that we were looking for a special solution," says John Poulissen, Electrical Engineering Installation Manager for the Province of Utrecht Department of Regiotram. "Because of Engie Bredenoord's extensive fleet, we then chose them. Because the project takes place in the city center, it is important that the energy solution is as quiet as possible."

The location of the project site also creates another challenge, namely strict rules on nitrogen oxide emissions (NOx). A generator with a Denox installation could comply with this, but this poses another problem. The Denox installation requires a minimum exhaust gas temperature of 180-200 °C, which is achieved when the generator operates at 60% minimum load. This poses a problem for the tram line, as the power requirement varies greatly; only when a tram passes demand reach up to 1600kW depending on the length of the tram. This lasts only a few seconds and occurs sixteen times an hour. This is very unfavourable for both the generator and the Denox installation.

At the point where more trams were going to run, Engie Bredenoord was able to scale up the necessary energy supply very quickly.

The challenge: high peak demand in the inner city

"We knew beforehand that we were looking for a special solution," says John Poulissen, Electrical Engineering Installation Manager for the Province of Utrecht Department of Regiotram. "Because of Engie Bredenoord's extensive fleet, we then chose them. Because the project takes place in the city center, it is important that the energy solution is as quiet as possible."

The location of the project site also creates another challenge, namely strict rules on nitrogen oxide emissions (NOx). A generator with a Denox installation could comply with this, but this poses another problem. The Denox installation requires a minimum exhaust gas temperature of 180-200 °C, which is achieved when the generator operates at 60% minimum load. This poses a problem for the tram line, as the power requirement varies greatly; only when a tram passes demand reach up to 1600kW depending on the length of the tram. This lasts only a few seconds and occurs sixteen times an hour. This is very unfavourable for both the generator and the Denox installation.

The solution: energy storage in batteries

The situation in Utrecht is fairly similar in terms of energy demand to a festival. Again, there is a lot of variation in power requirements, for example, with large peaks during the main performances. Due to the proximity of the public, it is also desirable to reduce emissions as much as possible. Engie Bredenoord's energy solution for the tram line in Utrecht therefore takes the experience from the festival industry with it, resulting in a combination of aggregates and energy storage in batteries.

Engie Bredenoord's Battery Box can store up to 600 kW of energy from a source of your choice and then release this energy completely silently and without emissions. In Utrecht, it was decided to use three parallel Battery Boxes, with a combined power of 1800 kW. The high voltage transformer of the 10kV station of the tram management was therefore powered. When the energy stored in the batteries dropped to a certain level, the existing generators automatically turned on to recharge the batteries. For this purpose, three twinsets of 400kVA were set up with a combined power of 2400kVA, each equipped with a Denox installation. These aggregates could run at 75% of their power. This is not only the most efficient load in terms of emissions and fuel consumption, but also results in the right exhaust gas temperatures for the Denox installations to work optimally. With this method, NOx emissions could be reduced to 0.3-0.4 g/kWh, meeting the requirements.

"An additional advantage of the use of batteries is that they work completely silently," poulissen said. "During the day, the generators only ran to recharge the batteries, which then release the power completely silently. By cleverly planning, it was also possible to ensure that the batteries were full at the beginning of the evening, so that the generators did not have to run at night. This prevented noise pollution for local residents."

The result: the tram could continue for the entire period

During the work on the high-voltage cables, the tram was able to continue running, thanks to a smart combination of batteries, efficient running generators and purifying Denox installations. As a result, a sharply changing energy demand could also be met here, in the city centre.

"The collaboration was very pleasant from the first contact," says Poulissen. "Even when more equipment started to run on the tramway at some point, the energy supply could be scaled up very quickly by Engie Bredenoord. " This project, started in the autumn of 2020, is still in full swing. The inhabitants of the district, because of the use of silent batteries, do not notice this.