Taking the Measure of the Seebeck effect

Coming soon, The Seebeck Effect: "A physical phenomenon discovered two centuries ago may hold the key to meeting future energy needs, while reducing global warming...."

Although it sounds like the title and plotline of a summer thriller movie, the Seebeck effect is quite real, and its potential for helping to solve the energy crisis is not Hollywood hype. The Seebeck effect involves the direct conversion of temperature differences into electricity. It was first reported in 1821 by the German-Estonian physicist Thomas Johann Seebeck, who observed that a temperature difference between two ends of a metal bar created an electrical current in between, with the voltage being directly proportional to the temperature difference (the Seebeck coefficient).

Scientists have long recognized that the Seebeck effect could be exploited as an environmentally clean way of producing electricity. As yet the process is far too inefficient, however, and involves materials much too expensive for practical commercial applications.

The situation may soon be changing. Mechanical engineer Arun Majumdar and chemical engineer Rachel Segalman, who both hold joint appointments at Lawrence Berkeley National Laboratory and the University of California at Berkeley, have recorded the first measurements of the Seebeck effect in inexpensive organic molecules.

Working with Pramod Reddy, a graduate student, and Sung- Yeon Jang, a postdoctoral fellow, Majumdar and Segalman trapped electron-conducting organic molecules between a pair of gold electrodes, then measured the thermopower (voltage) at room temperature with their own technique of scanning tunneling microscopy (STM). Although this study was done on nanoscale materials, it cracks open the door to an entirely new field of thermoelectrics, which in turn could lead to a new generation of low-temperature solar cells and thin films, and low-cost plastic power generators.

"This is a significant step and major departure from traditional inorganic semiconductor materials," says Majumdar. "For the past 50 years, researchers have been working to improve the efficiency of thermoelectric materials, but progress has been extremely hard to come by, mainly due to the coupling between various properties of the material like electrical conductivity, thermal conductivity, and the Seebeck coefficient, which determines the efficiency of the device. Recently, through nanotechnology, the efficiency has been increased — but only with expensive semiconductor materials that require high-temperature processing."

Nearly all the world's electrical power, approximately 10 trillion watts, is generated by heat engines, giant gas- or steam-powered turbines that convert heat to mechanical energy, which in turn is converted to electricity. In accordance with thermodynamics, however, much of the heat isn't converted but released into the environment instead. To generate 10 trillion watts of electricity means wasting another 15 trillion watts as heat.

If even a small fraction of the lost heat could also be converted to electricity, its impact on the energy situation would be enormous. "We are talking about massive savings on fuel and atmospheric carbon dioxide," Majumdar says.

In their experimental setup, Majumdar, Segalman, and their students use an STM whose gold stylus tapers off to a single atom at its tip. The STM features a customized control circuit that moves the gold tip at a constant speed toward a substrate, also made of gold. While the STM gold tip is maintained at ambient temperature, an electric heater is used to warm the gold substrate. This creates a temperature difference between the tip and the substrate. Using chemical handles, the experimenters trap a molecule in the gap between tip and substrate and then measure the Seebeck effect.

"As we would expect," Majumdar says, "we saw a thermoelectric voltage generated across the metal/molecule junctions — which depended on the type of molecule and lasted as long as one or more of those molecules were trapped, but vanished once all of the molecules broke away."

For their organic molecules the Berkeley researchers elected to work with the benzenedithiol family. The electronic properties of these chemicals are well known, and they are easy to use.

Says Segalman, "One of the primary advantages of organics is that molecular structure is directly related to physical properties. And because we can tune the structure through synthetic chemistry, we have a seemingly infinite toolbox to tune and optimize the thermoelectric efficiency. Since organic molecules are abundant, relatively inexpensive, and easily processed, they hold great promise for widespread application."

Says Majumdar, "I am sure most conducting molecules will display the Seebeck effect when sandwiched in a metal junction. We will be measuring a number of thiol-terminated molecules in metal/molecule/metal junctions, and we will also be looking into ways to tune the thermopower, such as introducing various chemical moieties in the molecule, or controlling the metal/molecule chemical bond."

The ability to measure the Seebeck effect in metal/molecule junctions offers promise that extends beyond the field of energy, according to Majumdar and his coauthors. For example, in the emerging arena of molecular electronics, a key issue has been the alignment of electronic energy levels when new chemical bonds are formed. This is a critical factor in the operation and performance of a device, but until now it has been difficult to determine such energy alignments at metal/molecule junctions.

"The ability to measure the Seebeck effect resolves this important issue and can be directly used to estimate the energy levels of the junction," Majumdar says. "This is a fundamental step in the design and understanding of molecular electronic devices for information processing and storage, and of molecular solar cells for converting sunlight to electricity."

Berkeley Lab has applied for patents on behalf of Majumdar and Segalman for the use of their metal/molecule heterojunction assemblies in thermoelectric energy conversion, batteries, and supercapacitors. The research was funded by the U.S. Department of Energy's Basic Energy Sciences program (DOEBES), the National Science Foundation, the Berkeley-ITRI Research Center (ITRI is the Industrial Technology Research Institute of Taiwan), and the Thermoelectrics Program and DOEBES Plastic Electronics Program at Berkeley Lab.

Sustainable Energy Technologies Ltd (Sustainable Energy) is offering a new inverter to deliver power from small wind turbines to electricity grids at the same high efficiencies available to solar PV applications. Using proprietary technology, the new inverter will also have the capability to provide backup power during grid outages, and to connect hybrid systems incorporating both solar and wind energy.

The first product application will be for a residential scale wind turbine developed by Japan's Zephyr Corp. The AirDolphin Mark-Zero is an ultra-quiet light-weight wind turbine which employs a number of innovative features unique to the industry that deliver lower operating costs and higher efficiencies than other small turbines and large megawatt scale turbines.

Sustainable Energy has agreed with Zephyr to adapt the Company's Sunergy inverter platform for the AirDolphine turbine. The inverter incorporates recently developed proprietary software that enables it to operate in a grid interactive mode with very high efficiencies, and to switch to battery based mode for back up power during grid outages. Under its agreement with Zephyr, the Company has also acquired the right to bundle the AirDolphin with the new inverter product for distribution in Canada.

 For about six months of the year, bursts of a hot, electrically charged gas, or plasma, swirl around a donut-shaped tube in a special MIT reactor, helping scientists learn more about a potential future energy source: nuclear fusion.

During downtimes when the reactor is offline, as it is right now, engineers make upgrades that will help them achieve their goal of making fusion a viable energy source--a long-standing mission that will likely continue for decades.

MIT's reactor, known as Alcator C-Mod, is one of several tokamak plasma discharge reactors in the world. Inside the reactor, magnetic fields control the superheated plasma (up to 50,000,000°K) as it flows around the tube.

Fusion occurs when two deuterons, or one deuteron and one triton--nuclei of heavy hydrogen--fuse, creating helium and releasing energy. The reactions can only occur at extremely high temperatures.

Although MIT's reactor is smaller than others, it has a stronger magnetic field than some larger reactors, allowing the plasma to become denser at comparable temperatures. "That positions us to provide important data you can't get anywhere else," said Earl Marmar, head of MIT's Alcator C-Mod project and senior research scientist in the Department of Physics.

One major goal of the upgrades is to create a system where plasma can flow in a steady state, rather than short pulses, or bursts. Last year, engineers added a microwave generator that creates phased waves that flow around the ring, reinforcing the plasma current. The microwaves interact with the highest velocity electrons in the plasma, pushing them around the ring.

"It's possible to use this approach to go to fully steady-state plasma," Marmar said. "As an attractive energy source, ultimately we want steady state."

Benefits of a steady-state system include a constant energy output, less need for energy storage and less stress on the system, he said.

This year's modifications include the installation of a cryopump, which will allow scientists to control the density of the plasma over a long period of time--another necessary step to achieving a steady-state flow.

Several other modifications will allow the researchers to more accurately measure properties of the plasma, such as density and temperature. The new devices will also allow them to more accurately detect and measure magnetic and electric fields generated by the plasma.

The reactor, which has been offline for upgrades since August, is expected to be ready to use again starting in March.

More than 100 MIT researchers from the Departments of Physics, Nuclear Science and Engineering, and Electrical Engineering and Computer Science, including about 30 graduate students, use the Alcator C-Mod reactor to run experiments.

On a recent morning, the control room, normally packed with scientists at about 100 computer monitors, was nearly empty while engineers, scientists and students worked on modifications to the reactor, located in the next room.

When experiments are going on, researchers from around the world can participate in and watch the proceedings through the Internet.

There is high demand for time to run experiments on the reactor, but priority is given to projects that have high relevance to the Alcator goals and also to MIT graduate student research projects.

"One of our highest priorities is to get graduate students the run time they need," Marmar said.

Pacific Power has signed a power purchase agreement with Evergreen BioPower for a new, 10-megawatt biomass generation facility located at Freres Lumber in Lyons, Ore. It will begin providing reliable renewable energy to the utility’s customers during the fourth quarter of 2007.

“The new facility will offset our current use of approximately 2 million therms of natural gas annually while allowing us to utilize low-value residuals to generate steam. Evergreen BioPower will then use the steam to generate firm, renewable electricity for the surrounding area,” said Kyle Freres, vice president of Freres Lumber. “Throughout the company’s history, we have striven to maximize the efficiency of our operations. Cogeneration is a logical progression toward this goal.”

“The new facility at Freres Lumber will be a great addition to the local economy and a benefit to the environment,” said Pat Reiten, president of Pacific Power. “The use of woody biomass will become even more important in the very near future. We are a leader in the development of renewable energy, and we value renewable resources – including woody biomass – as an important part of our overall generation portfolio.”

Woody biomass is the residual waste wood that results from the lumber manufacturing process. Those residuals are then burned in a boiler, rather than land-filled, to generate steam that is used both in the lumber drying process and to produce electricity.

There has been renewed interest by forest products firms in developing these small biomass projects at their mills. The increase in natural gas prices along with governmental incentives has prompted several forest products firms to develop cost-effective cogeneration projects at their mills. They are sized to the mill’s thermal load and use the captive waste wood fuel.

Fairchild Semiconductor Introduces Optically Isolated MOSFET Gate Drivers

Adding to its power portfolio, Fairchild Semiconductor has released the first in a new family of high-frequency optically isolated MOSFET gate drivers capable of driving up to 30 A / 1200 V in industrial applications. Exhibiting a 200 ns (max) rise/fall time rate, the FOD3180 (2 A) and FOD3181 (0.5 A) quickly turn the power MOSFET on and off to limit power dissipation.

The FOD3180 device features high 2A peak output current that allows a wide range of MOSFETs to be driven without additional amplification. These isolated MOSFET drivers are best used for increasing system efficiency and reliability in applications such as solar inverters, high-performance uninterruptible power supplies (UPS), DC/DC converters, and plasma display panels (PDP).

“The FOD3180 and FOD3181 optically isolated MOSFET gate drivers add the key ‘isolation piece’ to Fairchild’s industry-leading power portfolio by bridging low-power logic products to high-power discrete MOSFETs,” said John Constantino, Fairchild’s optoelectronic strategic marketing manager. “This total power solution from Fairchild enables designers to streamline their supply chain while enjoying the online design tools, design centers, evaluation boards and other technical support we provide through the Global Power Resource.”

Additional reliability features of the FOD3180 and FOD3181 include a 5000 V isolation rating that meets most safety-certification standards, undervoltage lockout that protects the MOSFET by keeping it off until the voltage reaches the enabled state, as well as coplanar construction that provides fail-safe insulation. These devices also provide a wide (20 V max) operating voltage, while their PMOS pull-up and NMOS pull-down transistors provide a 17V signal swing (VCC - VEE).

Scientists Develop Portable Generator That Turns Trash into Electricity

A group of scientists have created a portable refinery that efficiently converts food, paper and plastic trash into electricity. The machine, designed for the U.S. military, would allow soldiers in the field to convert waste into power and could have widespread civilian applications in the future.

"This is a very promising technology," said Michael Ladisch, the professor of agricultural and biological engineering at Purdue University who leads the project. "In a very short time it should be ready for use in the military, and I think it could be used outside the military shortly thereafter."

The "tactical biorefinery" processes several kinds of waste at once, which it converts into fuel via two parallel processes. The system then burns the different fuels in a diesel engine to power a generator. Ladisch said the machine's ability to burn multiple fuels at once, along with its mobility, make it unique.

Roughly the size a small moving van, the biorefinery could alleviate the expense and potential danger associated with transporting waste and fuel. Also, by eliminating garbage remnants - known in the military as a unit's "signature" - it could protect the unit's security by destroying clues that such refuse could provide to enemies.

Researchers tested the first tactical biorefinery prototype in November and found that it produced approximately 90 percent more energy than it consumed, said Jerry Warner, founder of Defense Life Sciences LLC, a private company working with Purdue researchers on the project. He said the results were better than expected.

The U.S. Army subsequently commissioned the biorefinery upon completion of a functional prototype, and the machine is being considered for future Army development.

The tactical biorefinery first separates organic food material from residual trash, such as paper, plastic, Styrofoam and cardboard. The food waste goes to a bioreactor where industrial yeast ferments it into ethanol, a "green" fuel. Residual materials go to a gasifier where they are heated under low-oxygen conditions and eventually become low-grade propane gas and methane. The gas and ethanol are then combusted in a modified diesel engine that powers a generator to produce electricity.

Ladisch and Warner said the machine eventually could be deployed in disaster situations, similar to Hurricane Katrina, or at any crisis location where people are stranded without power. Emergency crews could then use the machine to turn debris such as woodchips into much-needed electricity, Warner said.

The refinery also could provide supplementary power for factories, restaurants or stores, Ladisch said.

"At any place with a fair amount of food and scrap waste the biorefinery could help reduce electricity costs, and you might even be able to produce some surplus energy to put back on the electrical grid," he said.

Much of the fuel the system combusts is carbon-neutral, said Nathan Mosier, a Purdue professor of agricultural and biological engineering involved in the project. Carbon-neutral fuels like ethanol do not cause an appreciable net increase in atmospheric levels of the greenhouse gas carbon dioxide. This is because the fuel releases carbon that has only recently been taken up by plants during photosynthesis, the process by which plants convert carbon dioxide to oxygen and sugars. The same is not true for petroleum, in which the carbon contents were removed from the atmosphere millions of years ago.

The biorefinery generator initially runs on diesel oil for several hours until the gasifier and the bioreactor begin to produce fuel, Warner said. In the initial commissioning test, researchers measured the amount of diesel oil burned and electricity produced to calculate its efficiency.

The machine produces a very small amount of its own waste, Warner said, mostly in the form of ash that the Environmental Protection Agency has designated as "benign," or non-hazardous. Any leftover materials from the bioreactor are put into the gasifier, which has to be emptied every two to three days.

GE is supplying its ecomagination-certified solar energy modules and water filtration technology to a new initiative, launched by Dynoil LLC, to increase the availability of clean drinking water in rural areas of India and in other developing countries of southeast Asia and Africa.

The use of solar energy technology to power water filtration systems will enable Dynoil to install equipment in remote areas that lack direct access to transmission grids. Such self-sustaining, clean water systems are seen as crucial in the global fight to reduce the spread of diseases and improve mortality rates in developing countries.

"We are very pleased and excited to have the opportunity to demonstrate how GE's ecomagination products can enable projects like Dynoil's alternative energy/clean water initiative. These projects will help improve the health and safety conditions of areas lacking adequate infrastructure, transmission grids and direct access to safe water supplies," said Victor Abate, vice president - renewables for GE Energy.

As part of the U.S.$93 million agreement, GE is providing Dynoil with 200-watt solar modules and 5,000 water filtration units that are capable of providing 7.57 cubic meters (2,000 U.S. gallons) of water, or enough water to meet the daily requirements for 500 people. By utilizing GE's solar energy and water filtration technologies, Dynoil will be able to reach many remote and rural areas throughout India, Bangladesh, Nepal, Malaysia and Africa.

"By 2020, much of the world is expected to confront severe water shortages and countries, like India, will face a lack of water coupled with unprecedented infrastructure issues, shifts in population and rapid industrial growth rates," said Jeff Garwood, president and CEO of GE Water & Process Technologies. "Innovative alternative energy and clean water technologies, such as the solar-powered water filtration systems, provide customers with a real way to cultivate energy resources and water supplies for regions in need of a sustainable solution."

To ensure the longevity of the project, Dynoil is forming an installation and training organization to help empower host communities. The installation and training teams will offer training on how to install, operate and maintain the systems.

GE's solar modules are being built at GE Energy's solar energy facility in Newark, Del., while GE's Homespring water filtration system units are manufactured at GE Water & Process Technologies' facilities in Canada and Hungary.

The solar-powered water filtration systems will be packaged by Trunz Water Systems, an ISO 9000-certified company. Shipment of the equipment is scheduled to begin in the first quarter of 2007, while project installation is scheduled over the next 24 months.