Big Wind Machines

Recently I had occaision to discuss the merits of wind power with a colleague.  In particular there is a controversy between horizontal axis wind turbines, the giant propeller driven systems you see in advertisements, and vertical wind, which does not have much presence in the marketplace.  The premise is that horizontal systems can take advantage of the large swept area of the propeller blades to generate a great deal of force.  I’m not sure if this is supposed to imply that large swept areas intrinsically convert more kinetic energy from the wind into electricity.  And it is easy to conclude that this is the benefit of horizontal wind turbines.

Except that there is a fundamental mechatronic system at work.  The large propeller turns at low speeds, typically around 18 rpm on average, and there is a massive gearbox that is used to increase the speed of the output to turn a generator at high speed, which is typically where generators are most efficient.  The gear increaser has the effect of also increasing the amount of torque required at the input (propeller) by the gear ratio.  So if the gear increase is 100:1, then the propeller must be size 100 times larger in swept area in order to produce the needed torque to turn the generator.

This actually gets a bit worse since the mass, and it is very substantial, of the gear box itself represnts inertia that is resisting the turning of the blades.  And there is a generator rotor at the end of the gearbox whose mass (massive mass) is now resisting the turning of the propeller by the square of the ratio.  So if the ratio is 100:1, the inertia is increased by 10,000 times.  Even magnetic drag, or the residual attraction of the rotor to the stator, will get amplified in the same fashion, making it a significant force to contend with.

Add to this situaion a list of systems losses for overall fricitional loss of the bearings and gearbox, parasitic losses for steering and blade pitch adjustments.   Efficiency losses due to long distance transmission of power, that is a by-product of the remote sites that have favorable wind conditions.  It’s a pretty difficult situation to engineer.  And they keep proposing to build them bigger and bigger, hoping that the scale effect will overcome the problems.

All of the vertical wind systems I have seen so far are much smaller due to the fact that smaller rotors can turn at higher speed and power electric generators directly.  The flax axial generator is very popular in do-it-yourself designs that people are experimenting with in their back yards.

But vertical wind can also scale up.  And there are a few companies doing it.  With convertional wind power costing $2/watt, vertical systems could bring that price down very quickly and allow systems that can be installed close to the point of use or in offshore arrays where generation takes place almost 100% of the time.  Unlike the average 31% on the large land based systems.

Now that’s progress, 300% increase in energy generation at lower cost.  Hope it comes to market soon.

Top Ten Challenges – Energy Storage

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.

Energy

Everyone has an opinion about Energy Policy.  Just ask.  They’ll tell you!  And I am glad for the fact that there is a lot of discussion taking place.  We need good dialog and good information.

We might be a little lacking on the information side.  Nuclear power for generating electricity is not a popular topic, but worse yet, no one seems to want to talk about pebble bed reactors.  Pebble bed reactors have been around for over 25 years and represent the most stable path for producing electricity without burning fuel.  Small spheres of an enriched radioactive material are encapsulated in a ceramic insulator so that the nuclear fuel cannot accidentally achieve critical mass.  The same property of the geometry causes the “pebbles” to achieve high enough temperature to heat steam and generate electricity, but reaches thermal equilibrium at 800 degrees remaining stable without coolant.  So there can’t be a meltdown.

This makes atomic energy safe enough to locate in a major city without fear of a metldown or a chain reaction, the two weaknesses of conventional nuclear powerplants.  The fuel is encapsulated in carbide and graphite materials with processes that are very difficult to circumvent.  And because of the simplicity of the design, these reactors are lower cost than the water cooled reactors.  Could we save the environment and satisfy our energy needs at the same time?  Maybe so.

But this conversation is not part of the energy plan for the US.  Neither is drilling off the US coastlines and putting American workers back in the business of supplying our oil and gas needs in the US.  That makes no sense. The oil industry chose to import gasoline directly from the middle east 30 years ago because it was cheaper.  But we have done nothing to update our supply chain since then, and now we have to buy oil from countries that don’t like the US.

The logic seems to be about reducing our energy consumption instead of increasing our energy production.  Using less is fine until it cuts into our ability to produce necessary goods like electronics.  We don’t need to hobble the largest sector of the economy by telling semiconductor companies that we have to turn off electricity to their plants during the summer months.  They will have no choice but to locate to other countries.

You can’t “save” your way out of a recession.  You can’t save enough money to keep a company in business if it stops selling it’s products.  That’s all there is to it. And our policy leaders need to understand and apply that logic to the current situation.  The best thing to “stimulate” the US economy is to get it’s businesses producing.  Produce more energy with the resources that we have.

And when the car companies can make a competitive electric or hybrid vehicle, we will produce less gasoline and make more electricity.   There are plenty of opportunities to sell new cars to stimulate that industry too!

Facts or Fiction? Politics or Science.

I recently picked up my monthly copy of one of the pre-eminent magazines in the sciences that I have subscribed to for many years. This month’s cover article was on American energy policy. OK, fine. We are all concerned about the rising prices at the pump and impact (mostly negative) on our economy.

But it freaked me out when I tried to read the article. The entire thing was an editorial based on reader responses to a survey sent out by the magazine. No facts, no science, no specific issue really, not even any survey demographics, no factual support for several pages of random assertions about what different factions in the government are doing wrong and the havoc being wreaked in our economy.

I admit, I got a little irate. Read more

Energy Policy

Americans have been focusing on energy reduction in this country for some time. In an upcoming article to be published in Design World, I will detail some of the impact of national energy policy on how electric motors should be built, and how they should be used. The main conclusion of the article from a technical perspective, is that the big energy savings come from control system solutions, not from incremental improvements in electric motors themselves, which the Department of Energy has spent a lot of money pursuing.

It is reasonable that the government concerns itself with how energy is used. But what is appropriate for implementing policy? Is it in the national interest to develop better washers and dryers? better refrigerators? better air conditioning systems? Or is this the domain of private enterprise? Business that is for profit and normally makes the investment in product development sometimes gets a hand from government. Read more

Motors, R&D and Politics

The “Green Revolution” is under way. Regardless of how you rationalize it, there is a lot of activity around reducing the amount of energy being consumed in almost every aspect of American life. For the most part, its well intentioned. As good stewards of the resources we have, we should use them responsibly.

Energy conservation has been an active part of the mechatronics world for some time. The variable frequency drive, now a $1B+/year product is marketed and sold because of its ability to reduce electrical consumption in about 1/3 of all applications. So we who are part of the drives and controls community have been in the vanguard of energy conservation for many years. An often overlooked fact. We’ve been “Green” for decades. Read more