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Researchers Have Developed a New Material That Converts Waste Heat Into Electricity

A new source of energy.

BEC CREW
2 DEC 2016
 

Researchers have developed a new material that can capture waste heat - the heat emitted from a car's tailpipe or an industrial smokestack that gets seeded into the atmosphere - and convert it into electricity. 

The so-called thermoelectric material generates four times more energy than similar materials, and the team behind it says it could be used to boost mileage in vehicles or pump energy back into power plants using their own waste.

 

"The majority of industrial energy input is lost as waste heat," the researchers report. "Converting some of the waste heat into useful electrical power will lead to the reduction of fossil fuel consumption and CO2 emission."

The new compound is made from niobium, iron, antimony, and titanium, and is produced using a technique called hot-pressing - using an hydraulic press to apply high levels of heat and pressure to a material. 

The team from Houston University found that when they applied extremely high temperatures to their new material - around 2,000 degrees fahrenheit, or 1,093 Celsius - they were able to produce an unusually high power factor.

The power factor of a material is the ratio of the power that it draws from the mains supply versus the power that it actually consumes.

If a material has a power factor of 1, that means it consumes all of the power it draws from its supply. But this new material has a power factor of 55.

"For most thermoelectric materials, a power factor of 40 is good," says lead researcher Zhifeng Ren. "Many have a power factor of 20 or 30."

 

Thermoelectric materials produce electricity by directing the flow of a heat current from a warmer area to a cooler area, converting the temperature difference into a voltage.

"To obtain that voltage, thermoelectrics must be good electrical conductors but poor conductors of heat, which saps the effect," Robert F. Service reports for Nature

"Unfortunately, because a material's electrical and heat conductivity tend to go hand in hand, it has proven difficult to create materials that have high thermoelectric efficiency - a property scientists represent with the symbol ZT."

The ZT value indicates how efficiently your thermoelectric material converts waste heat into energy. For example, if your material draws in 100 watts of heat and produces 10 watts of electricity, it has an efficiency rate of 10 percent.

Right now, the world’s most efficient thermoelectric material can hit a ZT level of 2.6.

A ZT value of 3 is considered the benchmark for a commercially viable thermoelectric material, so we're still a long way off having a material that's efficient enough to change the energy market.

But the team from Houston says maybe we’ve been placing too much importance on ZT as a measure of a thermoelectric material’s success, because it doesn’t actually guarantee high power output anyway. 

While their material only has a ZT of 1.4, it can generate around 22 watts per square centimetre - around four times higher than the 5 or 6 watts typically produced.

"Pursuing high ZT has been the focus of the entire thermoelectric community. However, for practical applications, efficiency is not the only concern," Ren says in a press release

"High output power density is as important as efficiency when the capacity of the heat source is huge, such as with solar heat, or when the cost of the heat source is not a big factor, such as in waste heat from automobiles or the steel industry, for example."

Ren has already established a company called APower to try and get his new material ready for commercialisation.

Hopefully, this is the step in the right direction for thermoelectric materials, because with 90 percent of the world’s electricity being generated by heat energy, and around two-thirds of that being lost as waste heat, that's a whole lot of electricity we could be taking advantage of.

The research has been published in Proceedings of the National Academy of Sciences.

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