Most rail mass-transit systems use electricity for motive power. The electric motors that accelerate the train can also be reversed to slow the train and generate electricity, which is called regenerative braking. Unless this energy is used immediately (another train is leaving the station at the same time as one is arriving), it typically is shunted to a bank of resistors and wasted as excess heat. However, a couple transit systems are finding economical ways to use this energy.
Philadelphia’s Southeastern Pennsylvania Transportation Authority (SEPTA) installed a lithium-ion battery system to store the excess power. They are able to make the investment profitable by accessing the frequency-regulation market. Not to get too technical, but the market prices for electricity greatly depend on the desired use. Base-load electricity (from traditional power plants) is cheap, but cannot accommodate sudden changes in demand. Frequency-regulating power is used to respond to sudden spikes or dips in consumption. (If this power is not available, the system cannot maintain the desired 60 Hz current, hence the name, frequency regulation.) Utilities will pay a premium for this short-term power supply to keep the overall system running smoothly. SEPTA now earns up to $200,000 per year as a power provider and has reduced energy use by 20 percent. The Scientific American article also discusses other storage technologies in Los Angeles and Portland.
The Dutch train system, Nederlandse Spoorwegen (NS), faces a similar dilemma to find a profitable use for their excess energy. Netherlands heavily subsidizes their commuter electrical costs to make transit affordable. NS pays approximately 1.5¢ per kWhr instead of the market rate of about 20¢ per kWhr. While this is great for Johann and Jaantje Commuter, there is little incentive for NS to implement new programs or systems to reduce consumption. As an alternative, NS is looking to convert 30 diesel buses operating out of the Apeldoorn station to electric. The engineers cited in the Climate Progress article estimate that this will save about €8 million (US$11 million) over the next 12 years. Unfortunately, the article did not contain any specifics on whether this is an actual project or merely an engineer’s dream.
Hopefully, projects like these demonstrate viable ways to creatively use readily available but wasted energy.