September 18, 2006
Silicon Chip Turbine Electric Generator

Semiconductor technology advances are mostly funded by sales of computer processors, memory, and other digital computer parts. Those advances have created capabilities to manipulate small scale devices for a variety of other purposes including microfluidic devices that function as biological and chemical labs on a chip. Another application being pursued at MIT is the development of extremely small gas turbines for generation of electricity. MIT researchers expect their miniature gas turbine to eventually compete with very large natural gas burning electric generator plants in efficiency.

MIT researchers are putting a tiny gas-turbine engine inside a silicon chip about the size of a quarter. The resulting device could run 10 times longer than a battery of the same weight can, powering laptops, cell phones, radios and other electronic devices.

It could also dramatically lighten the load for people who can't connect to a power grid, including soldiers who now must carry many pounds of batteries for a three-day mission -- all at a reasonable price.

The researchers say that in the long term, mass-production could bring the per-unit cost of power from microengines close to that for power from today's large gas-turbine power plants.

Making things tiny is all the rage. The field -- called microelectromechanical systems, or MEMS -- grew out of the computer industry's stunning success in developing and using micro technologies. "Forty years ago, a computer filled up a whole building," said Professor Alan Epstein of the Department of Aeronautics and Astronautics. "Now we all have microcomputers on our desks and inside our thermostats and our watches."

Cheap mass manufactured miniature electric generators could eliminate the need to connect to the electric grid, thereby reducing vulnerability from central system failures. Distributed generation would also cut transmission line losses of electricity due to resistance in cables.. However, large electric generator plants have one really big advantage: Their emissions can be rmonitored, regulated, and controlled.

Share |      Randall Parker, 2006 September 18 10:43 PM  Energy Electric Generators

David A. Young said at September 19, 2006 9:19 AM:

This is REALLY, REALLY cool! However, I seem to be missing a link in the logic chain. I don't see how you get from something that will power your watch to something that will power your AC or fridge (the whole "getting off the grid" thing). This breakthrough would be great for portable electrohics, but I don't see how it logically amps up (get it . . . "amps" up? I kill me.) to servicing larger power requirements.

Hacklehead said at September 19, 2006 2:02 PM:

A couple of questions:

What about exhaust emissions?

Can multiple units be setup in a turbo-array?

How much heat does it give off?

What kind of fuels can it use?

Randall Parker said at September 19, 2006 4:46 PM:

David A. Young,

It scales up if the cost per kwh (kilowatt-hour) is comparable with the cost per kwh from a big turbine. Yes, the devices are small. But if they can be made real cheap (as they claim) we can just put them in a bracket that holds a lot of them. Massive parallelism.


As I mentioned in my post, emissions are exactly the problem. A power plant can capture soot and other emissions and store and dispose of them in a way that keeps them out of the atmosphere. But that wouldn't be practical if every house had its own electric power plant.

As for the heat generated: Probably similar to that of conventional power plants. So during the fall, winter, and spring the heat would become a useful heating source for buildings. That would increase overall efficiency.

jim moore said at September 20, 2006 5:39 PM:

Hey Randall
Do you have any idea how they have overcome the problem of very small parts waring out very quickly?

Perry E. Metzger said at September 23, 2006 6:54 AM:

There is a problem here.

Large plants can use very high temperatures. The laws of thermodynamics say that you can't get a generator more efficient than 1-(T_c/T_h), where T_c is the temperature of the coolant and T_h is the temperature of the "hot reservoir".

In large generating plants, extremely high temperatures and pressures are possible, which raises efficiency. In micro-turbines, I don't know if you can use temperatures that are as high. If you can't, efficiency goes down.

doctorpat said at September 24, 2006 5:09 AM:

The advantage of a large plant is heat loss. Heat loss occurs proportional to surface area, which increases with the square of the scale (twice the dimensions, 4 times the area) but total energy scales with volume, the cube of the scale.

So make something twice as long, wide and high, you get 4 times the losses, but 8 times the total power for twice the thermal efficiency. (There are other forms of loss, so the overall efficiency doesn't double.)

But the MEMS devices have their own special advantages. With a chemical reaction (combustion) the mixing times are much, much faster, to the point where diffusion can be sufficient. Material strengths are much higher: smaller parts have smaller crach lengths, the stress in the parts tends to be planar rather than 3D, and the surface finishes are much finer. It's even possible to have defect free parts, which we are decades away from with a full size turbine.

Plus MEMS systems allow changes to how things operate. Once you get small enough the effective rules of the game change, for example you can now use electrostatic or electro-diffusive pumps. Surface effects dominate, and your massive parallelism means that you can operate your turbines with a much, much smaller safety factor. (With a big turbine, one failure every few years is unacceptable. With a million microturbines, you can have one failure every few weeks, it doesn't matter.)

Result: You can't say one is better than the other without a lot of research and development.

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