Thinking about the top challenges we face in mechatronics there is one that’s connected and not really obvious. It’s energy storage. Our tendency is think in terms of batteries because that’s the form of energy storage that we are most familiar with. Cell phones, laptop computers and many other portable gadgets of the Internet Age are very dependent on energy storage systems for their size, weight and hours of service. But of course, these are all battery applications.
So our first reaction to energy storage as a mechatronic challenge might be that it’s really just a chemistry problem and not mechatronic at all. But energy storage comes in many forms and applications. Energy storage is a requirement of almost every form of energy and control systems. Hydraulic and Pneumatic systems require accumulators to store energy so that short term loads don’t use up enough power to make the system unable to respond to demands placed on them. Energy rate over time is a governing principle in all these systems.
The initial linkage in my thinking was the electric car. As someone who worked in the electric car field many years ago, it was that the battery that killed the electric car. Carrying 2200 pounds of lead acid batteries to make a car go from here to there simply didn’t make sense.
There has been a lot of debate on that subject and a LOT of incomplete information offered which clouds our understanding of the social or political problem. But the cost and energy density of the battery pack is making sufficient progress to insure that quite a few new vehicle options will be available in 2010 and 2011.
In normal batteries energy densities of 30 Watt hours per kilogram of weight are common. Nickel metal hydride doubled the energy density to about 80Wh/kg. But the real improvements are coming from the lithium chemistries at 130+Wh/kg. There are more dense chemistries around, but they are typically very high temperature or otherwise very expensive, and so not practical for widespread use.
But the energy storage problem is not limited to chemistry. The flywheel energy storage system has been a topic of engineering development for decades. Energy density in these systems is in the range of 100 to 130 Kilowatt hours per kilogram, a thousand times more power.
So why aren’t we working on that for cars? It’s been done several times and never quite works out. Chrysler had a prototype K type car with a Garrett flywheel system. Couldn’t make it small enough to be cost effective. And there were issues of life expectancy and failure modes due to the fact that flywheel was operating on magnetic bearings in a vacuum housing.
The national power grid has exactly the same problem at orders of magnitude more power. If there is to be any hope of an intelligent national power grid, storage systems of this kind are needed to act as a buffer between demand and supply.. Solar power is only available when it is daylight and there are no clouds. Wind power only happens when the wind is blowing. This means that supply is intermittent over time. So if there are big fleets of electric cars charging overnight, there have to be storage systems that can manage the energy storage requirement.
So mechtronic challenge #4 – Energy storage. Large and small, high efficiency and long term.
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