How cool is this? Two subway systems on opposite sides of the Atlantic are harnessing heat and kinetic energy to generate power.

Paris Metro

All of those people in a busy underground train station emit quite a bit of heat. Combine that with heat coming from the trains themselves, and you have a significant amount of calories going to waste. Using technology based on geothermal heating, they're going to pump the heat from down in the Metro station up into the building instead of using a boiler to help heat things up.

According to Reuters, those underground stations maintain a temperature between 57 F and 68 F. Why not use that excess warmth to reduce heating costs?

The project is going to heat 17 residences in a central Paris building, and it's projected to reduce the energy needs for heating by almost a third!

The downside to this project is that it may not be feasible on a larger scale. This experimental setup works because there was already a stairwell that connected the station to the building. In order to pump in the heat, the building and the train station need to be connected in some way, and constructing something like that is a little bit cost prohibitive right now.

Philadelphia, PA

Heat is a great energy source, but over in Philadelphia they're going a different route, harnessing the kinetic energy from braking trains. Every time a train throws on the brakes, that creates energy, and Philadelphia's Southeast Pennsylvania Transit Authority (SEPTA) is installing a battery large enough to capture it.

They're estimating that they can cut power bills by 40 percent and even sell some of that power back to the grid for a profit.

If the project is a success, they're planning to install more of these batteries to cut their energy consumption even more and bring in further revenue for the transit system. Just the single battery is expected to make them $500,000 each year. Imagine if they installed batteries in all 38 substations!

As Technology Review points out, innovations like this are a great way to cut emissions while giving transit systems an additional revenue stream. Are you listening, MARTA?

Image Credit: Creative Commons photo by premshree

h/t Reuters and Technology Review