Innovations

Braking Energy Recovery in a metro network

Code

PT1.7

Title

Braking Energy Recovery in a metro network

Case study/reference

http://www.eltis.org/discover/case-studies/putting-brake-energy-recovery-systems-test

http://www.tickettokyoto.eu/en/cases/braking-energy-recovery-brussels-metro-network-stib

http://www.tickettokyoto.eu/sites/default/files/downloads/T2K_WP2_Inv1_STIB_braking_energy.pdf

http://www.ingeteam.com/Pressroom/Corporate/tabid/1574/articleType/ArticleView/articleId/736/The-Brussels-metro-is-to-reduce-its-C02-emissions-by-40-thanks-to-Ingeteam-technology.aspx#.Ve6wqfTNFnl

Recommendations for the design

The methodology that is proposed for the development and implementation of this innovation is realised in three steps:

Gather: The first step is to gather all relevant feasibility studies and consider their results.
Develop: Second step is about developing tools for evaluating the several technologies available on the market.
Evaluate: The final step will be to proceed with the investments for energy recovery solutions and to evaluate the results of each investment.

However, some potential drawbacks are mentioned below:

Retrofitting of old vehicles (space availability and weight constraints)
Placement of one ESS per vehicle (increase in the costs)
Standstill of the vehicle for implementation, maintenance and repair
High safety constraints due to passengers onboard

Recommendations for the implementation

While the project has been very successful and deployment continues, those considering implementing braking energy recovery systems should keep in mind that these are technically complex projects. Despite the high number of suppliers competing in that market, only very limited systems have yet been implemented in the public transport field. The reason is that most systems are still at the prototype stage, which makes it difficult for transport operators to take investment decisions due to the lack of experience feedback and uncertainties about the return on investment. However, costs will drop when market expands due to technological improvements and elements costs reduction.

Regarding quality control checks, according to information coming from actual experiences from the implementation of the innovative measure: “After delivery and once the installation was complete, a test run was organized for each supplier during the night with only one metro running on the network. This was more secure in case of a major failure as this would no impact the daytime service. It was also easier for the supplier to test thoroughly their system and make sure it was recovering energy from the braking phase of the vehicle and not from a nearby substation. Some minor issues happened during the implementation but could easily be fixed.”

Moreover, based on STIB, the importance of fine-tuning of the system was required as STIB noticed that when defining the energy recovery threshold, a difference of 5V can result in a reduction of 20% of the energy savings. As a result, it is recommended to actively collaborate with the supplier to make sure that the system is properly set and that no modification can be made regarding the parameters.

Brief description

STIB (Public Transport Operator in Brussels) implemented braking energy recovery techniques on its network. When metros brake, the mechanical energy from braking is transformed into electrical energy that can be sent to another, accelerating, vehicle or used to light a station.

Full description

In the summer of 2010 five public transport organisations joined forces in Ticket to Kyoto, a four-year project co-funded by the EU’s Interreg IVB programme. Part of the project focused on the recovery of braking energy. Braking energy is when modern rail vehicles recycle the kinetic energy they produce when braking. However, a lot of this energy is wasted because the majority can only be re-used by a vehicle accelerating nearby.

The partners (STIB among them) invested in and tested reversible substations and a flywheel. A reversible substation uses an inverter allowing the gathered energy to flow in both directions between the high voltage grid and the vehicle electrical grid. The recovered braking energy is not stored but sent back into the network.

A flywheel is a rotating wheel spinning around an axis, used for storing energy mechanically in the form of kinetic energy. Instead of feeding it back to the network, the flywheel stores it and sends it back to another vehicle.

Based on the results of its tests, the STIB extrapolates that the traction-energy consumption of metro lines 2 and 6 will be reduced by 9 per cent. This saves approximately 3 400 000 kWh and 568 tCO2 per year. The STIB also estimates that, thanks to the future savings it will make in energy costs, the money spent on the inverters will be recouped in five years. The company considers this acceptable given that another benefit will be the reduction in CO2 emissions.

CIPTEC score

3.5