Harnessing Regenerative Energy to Power Savings

Financial Daily, April 8, 2011
By Sam Tan

It is with both interest and concern that I read of the billions of ringgit poured into tapping our marginal oilfields, just offshore Malaysia. Springing to my mind are two things :one ,that our energy needs are steadily rising each year, rushing as we are, at breakneck speed to developed nation status. And two that our oil reserves are unfortunately not being replenished quick enough to service demand.

So as surely as night follows day, we can expect a couple of petrol price hikes this year, if oil prices keep rising at this rate. Just as well, then, that our government has decided to offer stamp duty exemptions on hybrid vehicles in Malaysia.Hybrid technology for cars is not really cutting edge science.In fact,the world’s first gas-electric car was unveiled by an 18-year old Ferdinand Porsche in 1898!

In today’s hybrid vehicle seen on roads in Europe and Japan, manufacturers are combining petrol-powered engines with electric motors, where the motor acts as a generator. The principle here is “regenerative braking”, where the motor operates as a generator during braking and its output is stored in a battery, recouping some of the energy lost during stopping.

This energy is saved in a storage battery and used later to power the motor.Some of today’s popular hybrid and electric vehicles use this technique to extend the range of the battery pack.

While regenerative braking is a common feature in today’s hybrid vehicles, lesser known applications exist such as in building elevators. Utilising the same principles adopted by car manufacturers, regenerative lifts generate power on downward travel, sufficient enough power elevation.

This can be explained: when a motor turns faster than the commanded speed, the motor in effect acts as a generator.In a conventional valve-controlled hydraulic elevator, when the cabin moves downwards, the entire potential energy of the cabin is wasted.It’s also consumes more energy than a regenerative lift.

Lift makers recognised this early on, and aiming to reduce the power needs, have been working on energy-regenerative hydraulic elevators since the 1990s. Today, they have reached a point where the current generation of regenerative elevator can achieve a significant amount of energy-saving compared to traditional elevators.

Advances in just this field provide building owners big opportunities to save energy and building managers really need to keep an eye on energy consumption since energy cost (in fact, all costs) are rising at a frightening pace.

Imagine the savings on offer for building owners and managers. Some of these motors can consume up to 70 percent less energy than conventional elevator solutions, and have the ability to recover up to 30 percent of the elevator system’s total energy consumption

Regenerative braking is a principle of physics that can be applied in any condition where such conditions occur, and therefore need not be limited to applications.Regenerative braking has been in extensive use on railways for many decades. The Transcaucasian railway started utilising regenerative braking in the early 1930s and was especially effective on the steep and dangerous Surami Pass.

And in Scandinavia, rail cars on the Kiruna to Narvik railway are full of thousands of tons of iron ore on the way down to Narvik, and these trains generate large amounts of electricity by their regenerative braking. The regenerated energy is sufficient to power the empty trains back up to the national border. In fact, excess energy from the railway is pumped back into the power grid to supply homes and businesses in the region, and the railway is a net generator of electricity.

There are also many other scenarios in an industrial environment where regenerative conditions occur, such as ramped stopping (or even slowing to a reduced speed) of a high-inertia load such as a flywheel or large mechanical arm. Or a sudden drop in load torque such as when an industrial saw completes a cut, or when a drilling operation completes work on a machined product.

And then there are indexing operations that repeatedly accelerate then decelerate, to stop as part of the normal process, such as that which occurs with material handling and packaging lines.

As can be seen, what all these applications have in common is the need to make the driven load move slower than the load would in an otherwise uncontrolled state, therefore offering immense opportunities to harvest this energy and thereby immensely reducing one’s power consumption.