Using waste heat to generate clean electricity
Siemens is researching technologies that would allow waste heat from vehicles and industrial facilities to be efficiently used without producing carbon dioxide. To date, exhaust gas has generally only been used if it was hundreds of degrees Celsius hot. For example, the gas turbines in natural gas power plants produce exhaust gas that is used to generate steam for the operation of a steam turbine. The chemical industry, meanwhile, uses waste heat from reactions in order to preheat other substances, for example. The "cooler" the waste heat is, however, the more difficult it is to use. Against this backdrop, Siemens' global research unit Corporate Technology (CT) is now investigating a number of possible solutions to this problem, including the use of thermoelectric generators to produce carbon-neutral electricity in environments with temperatures between 200 and 300 degrees Celsius. The technology has tremendous potential because thermoelectric components are inexpensive and can be mass produced. Unfortunately, researchers have not yet been able to create materials that can achieve a sufficiently high level of efficiency within the stated temperature range.
Electricity flows in thermoelectric materials whenever there is a difference in the temperature - for example between a hot and a cold surface. These materials can be installed in exhaust ducts and tail pipes in such a way that one side remains cool in order to generate electricity. Thermoelectric materials are solids and they don't take long to ramp up. As a result, they can even process waste heat that is only produced for a short time. This feature could be put to good use - for example in power plants that have to go online at short notice in order to offset power fluctuations caused by renewable sources of energy.
However, one of the challenges that must be overcome before thermoelectric generators can be used for industrial applications is the development of materials that operate efficiently at temperatures over 200 degrees Celsius. New kinds of joining technology have to be developed as well because conventional welding techniques cannot withstand the high temperatures and large temperature fluctuations involved. To address these issues, Siemens is working together with colleges and industrial partners in the government-funded NEXTEC project. A lab demonstration model is currently under construction at CT.
Another area of research is the use of thermoelectric generators in vehicles. Although diesel locomotives and trucks harbor the greatest potential in this regard, the technology could also benefit passenger cars - particularly given the trend toward higher gasoline prices. In this field, Siemens is cooperating with automotive companies on the EU-funded HeatReCar project. Here, a prototype is being used to study the potential of recovering heat from a car's exhaust.
Provided by Siemens
