The Upside of the Downhill

I think about energy a lot. I’m not sure why this is, but often I see little places where energy is being squandered when it should be reclaimable. In general, any time you have something that’s hot, and you don’t want it to be hot, energy is being lost.

Some of this energy can be hard to spot. Take, for example, the fully-loaded truck at the brake-check pullout before going down a long hill. It’s not moving. Its fuel tanks could be almost empty. But it has energy. Lots of it. The driver is checking the truck’s brakes because the truck is about to turn all that energy into heat. If the driver is not careful, that heat could cause brake failure and a very dangerous situation. The driver will inch down the hill, allowing time for brakes to cool and to use the compression of the engine to slow downward progress as well (heating the exhaust).

All that energy, and we treat it like a bad thing. But energy is expensive, even now when we only pay a fraction of its true cost! What we need is a safe way to reclaim the potential energy of the truck, safely and in a useful form.

Introducing TruckGen. TruckGen is a system that uses the truck to turn a generator as it descends. The generator provides resistance to the truck, but rather than turning the energy into heat, turns at least some of it into electricity. (In fact, the generator would have to be able to provide huge resistance to the motion, but that’s OK — that’s where the electricity comes from.) The truck’s brakes are spared, saving wear and tear and making the descent safer, and as a bonus useful power is reclaimed.

I’ve considered several ideas for exactly how this would work; one of my favorites is a chair-lift-like affair with a cable that runs above the road. Descending trucks would attach to the cable with big clamps, and as they descended they would drive a capstan that turned a generator. The cable would have to be quite strong, of course, but if anything went wrong all the trucks would have nice fresh brakes.

An alternate would be to dispense with the generator and have the uphill trucks attached to the cable as well, and the descending trucks would give them a push. Cutting out the electrical generation makes this system quite efficient. (There would have to be something to prevent some uphill trucks from slacking and forcing other ascending trucks to haul them up as well while they save fuel.) In either case all trucks attached to the cable would move the same speed, improving traffic flow.

If cable strength is a problem (I’m not sure even where to start figuring that out), I imagine an alternate method with a vehicle that latches on to the front of the truck for the descent. It might look something like the tractors that push jets around at an airport, with big tires with good traction (or cogs on a rail?) which would turn a built-in generator. There would be an overhead power line, similar to the ones used to power trains, but in this case they would be receiving the power instead of providing it. The tractors would use some of that electricity to get back to the top of the hill, which cuts into the efficiency of that plan, but the descending trucks would still be a heck of a lot safer.

Next time you see a truck creeping up a steep hill, ask yourself, “what’s going to come of all that work?” With TruckGen, you have the answer.

3 thoughts on “The Upside of the Downhill

  1. Actually, you don’t need very large generators at all; they could conceiveably be installed in the trucks. This is the principal upon which diesel locomotives operate, and also the big dump trucks that work in open pit mines — even a diesel engine can’t provide the huge torque needed, but a big electric motor can.

    The engine(s) of the locomotive or truck doesn’t directly power the wheels. Rather, the engine creates electrictity that is either stored in batteries or used to power an electric motor at each of the drive wheels.

    When it’s time to slow down, the circuit is reversed, so the motors turn into electric generators and slow the train or truck down, while charging the batteries.

    Of course, this technology comes at a price, as people who bought Priuses three years ago are finding out when it comes time to replace the batteries. But for industrial applications, it’s quite efficient.

    (Odd thought: I wonder what BNSF and Phelps Dodge do with all of their worn-out batteries? There must be somebody doing recycling on a colossal scale.)

  2. I’m pretty sure modern diesel-electric locomotives don’t have batteries. I know the older ones, like the classic F9, did not. Electricity goes straight from generator to motors. Diesel trains stop using old-fashioned friction.

    So, it’s true that if trucks were fitted with massive electric motors (essentially making them hybrids), then the only part of the equation left is doing something with the generated electricity. Storing the electricity released by a laden truck going down a long hill would be impractical with modern batteries. Trains that get electricity from overhead power lines could put the juice back on the grid, for instance.

    Other vehicles use a variety of systems to store some of the energy from braking; some use compressors to put air cylinders under high pressure, for instance. (Not to be confused with air brakes.) Those systems also couldn’t deal with the very large amount of energy involved here, though.

    My goal was to build a system that did not require replacing the trucks themselves, but diesel-electric big rigs might start making sense in the future, which would certainly simplify things as you pointed out.

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