Sustainable mobility: energy scheduling substantially reduces the total electricity consumption of metro systems

Context: the need to reduce the energy consumption of public transit

Public transit systems require massive amounts of energy for many functions: traction/propulsion, lighting, air conditioning in metro cars, heating metro lines in winter and more. Controlling this energy use is a major challenge for these systems. Faced with rising energy costs and the demands of the energy transition, Keolis is innovating to efficiently reduce its energy needs, notably by using energy scheduling. This innovative solution makes it possible to recycle a large portion of the energy generated by vehicle braking. 

Innovation: energy scheduling

For many years, electric traction vehicles have been equipped with two types of brakes: electric and mechanical. Electric braking – less jarring, noisy and polluting than mechanical braking – is increasingly preferred, especially since the energy used by electric braking can be recovered and reused to power vehicles. 

However, when the reused energy exceeds the energy needs of vehicles in circulation, the excess energy is dissipated in the form of heat, with no possibility of reuse. For this reason, Keolis conducted a detailed analysis of the consumption profiles of its trains to identify ways to better reuse this lost energy. 

An initial analysis and diagnostic phase

This step revealed several lessons:

-       a vehicle’s electricity use is greater during startup and acceleration, much higher than when“cruising” 

-       the energy produced during vehicle braking is more or less equal to the energy needed during startup and acceleration

-       a lot of energy is lost every day in the form of heat during vehicle braking, while improved synchronization would help to maximize the reuse of this energy 

Implementation

The innovation therefore consisted in finding a better way to manage the synchronization between trains starting up and trains that are braking. 

Keolis capitalized on a feature of metro systems with a high level of automation known as GoA4. This means they are 100% automated and driverless and thus offer precise management of train circulation down to the second. Traffic is managed with the Automatic Train Supervision (ATS) tool that unfurls the train circulation timetables with precision, like a metronome. In this way, it makes it possible to optimize the reuse of the energy produced between metro lines that are braking and those that are accelerating. 

Keolis created new optimized train circulation schedules that help to substantially reduce the energy lost during braking operations. Achieving such a precise scheduling of metro lines would not be possible without their full automation.

Benefits: a sustainable mobility solution that recycles up to 80% of braking energy 

When train startup and braking are optimally synchronized, energy scheduling can recover up to 80% of the energy used by braking, thus reducing the metro line’s total energy use and contributing to the roll-out of more energy-efficient sustainable mobility.  

Another advantage is the positive impact on air quality. By relying on electric braking, the system drastically reduces the use of mechanical brakes (and their wear), and thus also reduces the particulate emissions that lower air quality. 

In addition, energy scheduling improves passenger comfort because electric brakes are smoother and quieter than other braking systems. 

Next steps: rolling out energy scheduling solutions

Developed by Keolis for the Rennes metro system, energy scheduling is now being rolled out across all 100% automated metro systems operated by the Group (Lyon, Lille, Dubai, etc.). By equipping more and more trains with electric braking, this innovation should help improve the energy efficiency of transit systems. By highlighting the performance improvements on operated networks in calls for tenders, Keolis is showcasing its sustainable mobility innovations that combine capacity scheduling and energy scheduling – two previously unmatched competitive advantages.