Saving Lost Energy in Vehicles: It's Not Just About Cars and Trucks

May 24, 2007 – Vol.12 No.9

SAVING LOST ENERGY IN VEHICLES: IT’S NOT JUST ABOUT CARS AND TRUCKS.

In these times of high gas prices here’s a quick lesson in energy conservation.

It takes considerable energy to accelerate a vehicle to a given speed. The quicker we try to get to that speed the greater “considerable energy” becomes. (Which is why pushing the accelerator pedal to the floor is such a gas burner, and you shouldn’t do it.)

Once accelerated to a given speed the vehicle’s engine can slack off quite a bit, needing less power at “cruise” as it were.

Stopping and slowing a vehicle also takes considerable energy, generally speaking about the same as it took to get up to speed in the first place. (Much depends on how quickly the vehicle was accelerated.)

Land-based vehicles use brakes to convert a vehicle’s, kinetic, forward-moving energy vehicle to heat to slow it or bring it to a stop. The heat from the brakes is then dissipated into the air: Energy gone to waste, lost forever.

Now, with a number of hybrids on the road that utilize an electric drive motor (at least part time) slowing a vehicle can mean employing the drive motor as generator; switching it around from energy consumer to energy maker. As the motor-turned-generator makes electricity it can, for a few seconds, pump electricity back into the vehicle’s battery pack - reversing the chemical reaction in it. The spurt of electricity will recharge the battery a bit, thus save some, but not all, of the energy lost in braking. This you know by now is regenerative braking.

Hybrid vehicles, plug-in hybrid, fuel-cell vehicles, and all-electric vehicles mostly have the technical opportunity to use regenerative braking. But what other land-based vehicles can employ regen? According to Siemens Transportation and General Electric, vehicles on rails.

The rail vehicles being supplied by Siemens for Oslo, Norway’s subway system use regenerative braking to feed regenerated energy not to on-board batteries, but to the power grid that feeds the rail cars. Siemens says up to 40 percent of the energy generated in braking can be fed back into the power supply system. That energy can be generally dispersed through the grid, or preferably stored in what Siemens calls its SES (static energy storage) system, which appears to be a near-instantly recharged bank of ultracapacitors. Stored in the SES, other rail vehicles on the same power supply system can use the stored power for acceleration: What one vehicle gave up can be used by another.

The trains - Siemens is supplying 63 trains for a total of 189 cars - are also built of aluminum to cut weight and thus save more energy. Further, 95 percent of the materials used in the vehicles can be recycled at the end of their 30-35 year life span. (That’s long term thinking!) At today’s market prices the recycled materials would fetch about $80,000 (EUR 60,000).

With the energy savings of regenerative braking combined with light weight, the new rail vehicles will save Oslo Sporveier, the operator of the system, about 33 percent in operating costs.

General Electric has developed a hybrid, energy-storing rail vehicle for another purpose, hauling freight.

The company has introduced its one-of-a-kind road locomotive, the 4,400 horsepower Evolution (tm) Hybrid diesel-electric prototype. Evolution uses innovative, lead-free batteries that capture and store energy dissipated during braking to reduce fuel consumption and emissions by as much as 10 percent compared with most freight locomotives. The extra power on board will help the locomotive work more efficiently at higher altitudes and up steep inclines.

As an example of how much is typically lost in braking, GE says that the energy dissipated in braking a 207-ton locomotive during the course of one year is enough to power 160 households for that year.

The hybrid, energy-saving technologies applied to passenger and freight rail are an improvement upon a mode of transportation that is already considered comparatively clean and energy efficient.

Visit Siemens Transportation at http://www.transportation.siemens.com/ts/en/pub/home.htm Oslo Sporveier at http://www.sporveien.no/180/ GE Transportation at http://www.getransportation.com/