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January 17, 2018

MMRTG

Maybe you have noticed, the finned cylinder in the background of our website is the MMRTG (Multi-Mission Radioisotope Thermoelectric Generator, picture credit NASA). This 100 W generator is the main power/heat source of NASA's Mars Laboratory AKA the Curiosity Rover. The heat comes form radioisotope decay of Plutonium, and the material that make the energy conversion is PbTe based. NASA is working on an enhanced version utilizing skutterudite, or Zintl compound based materials. This device is a masterpiece of thermoelectric material research and system engineering, built upon decades of experience, even though it only provides about 100 Watt of power at a system level efficiency of about 10%. Efficiency is a great obstacle for the domestic application of thermoelectric power generation, as you can imagine even cost is not a concern a device with similar efficiency would still be a tremendous engineering triumph.  

Read more about MMRTGs here​ and here.

January 17, 2018

Scientist who won Nobel Prize in physics twice

Who do you think have won Nobel Prize in physics twice? Albert Einstein? Wrong. Even though Einstein advanced physics so much in so many areas, he was only awarded once. It is John Bardeen, for his invention of the first semiconductor transistor (1956), then for his contribution in the theory of superconductivity, the BCS theory (1972). In addition, he and Shockley also established the deformation potential theory that described the most important carrier scattering source in many semiconductor applications, which is the deformation potential phonon-electron scattering (acoustic phonon scattering). Any one worked on thermoelectrics should have used, or heard about it. 

BTW, it is a fortune the three scientists chose to build their first transistor out of Germanium, not Silicon. Otherwise they won't get any current rectification. This is because of the unique surface states of Germanium. I am not sure about the detailed reason here, any feedback would be much appreciated.  

January 18, 2018

Electric power

With more and more auto makers going electric, Electric power seems the solution to future transportation. Electric power makes driving pollution-free and guilt-free, or, does it? Just to illustrate how complicated things could be: if we were to get all the power for propulsion from electricity, we will need many more power plants. Let aside the demand of fossil fuel and potential pollution, in order to generate electricity, power plants need cooling water, a lot of water. According to the 2014 department of energy water-energy nexus report, cooling of thermoelectric power plants makes the single largest sector of water resource usage in the US. 41% of fresh water supply is diverted (note this is not consumption  to cooling in thermoelectric power plants, the percentage of fresh water went to agriculture, at the same time, is 40%.  The National Renewable Energy Laboratory estimated that 0.5 gallon of water is consumed by thermoelectric plants for each one kilowatt hour of electricity at the user end. If this number is not impressive enough, time it by a total of 4 trillion Watts of electricity generated in the US last year. Will we still have enough water for our agriculture, and for our industrial, commercial, and residential needs in the EV era?

 

The situation is probably worse for China. Water resource is distributed more uneven, the developed regions are all in scarce of fresh water. On top of that China's power plants use significantly more coal for fuel compared to the US, which is switching toward natural/shale gas. There will be additional water consumption, efficiency drop, and pollution associated with firing up coal-burning power plants.

Maybe photovoltaics is the answer, but can we get high enough power density, and low enough cost without subsidy with solar cells?

Speaking of water, I forget the source but remember that we normally pay for only 10% of total actual cost for tap water, and 60% for electricity. So it is not really our "right" to use as much of water or electricity as we like since we "pay" for it. 

 

Maybe as important as new energy research is the education of conservation (coupled with incentives) 

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