[Column] Dilemma of Using Waste Heat as Energy (page 2)

Dec 25, 2008
Tetsuo Nozawa, Nikkei Electronics

LED lamp powered by candle flame

Next, please look at the photo on the right. This is a demonstration in which the heat of a candle flame was converted into electric power to turn on an LED. The photo was shot when I interviewed Nextreme Thermal Solutions Inc of the US.

"Most energy of a candle flame turns into heat," the company said. "So, an LED lamp powered by the heat glows brighter than the candle flame itself."

This technology is based on a well-known principle called "thermoelectric conversion." Many manufactures are paying close attention to it because it requires no microphone speaker or any other moving parts, making it easy to enhance durability and reduce size unlike the aforementioned thermoacoustic technology.

The technology had once been developed in Japan's national project. And it seems that it will be commercialized in several fields in the near future.

These technologies are all an effort to efficiently convert waste heat, which has been a nuisance thus far, into electricity. Potential heat sources include boilers, hot water pipes, automotive emissions and engines, ICs, microprocessors, transmitters in high-speed telecommunication devices, the sun and human bodies (body warmth).

Merely technologies for old cars?

While each of those technologies are very interesting and exciting, there is one small concern: They are useful only when applied to devices with a low energy efficiency. For example, if automotive engines become more efficient and generate less waste heat, the technologies might become unnecessary.

In fact, I heard in one of my interviews that, "Even with gasoline cars, the temperature of waste heat is decreasing as engines have been downsized and become more efficient."

When researching for the story on the waste heat utilization technologies, I found that only the US and European automakers such as General Motors Corp (GM) and BMW AG are enthusiastic about those technologies.

Should GM develop a practicable thermoelectric conversion technology or an electric vehicle? And should we reuse the heat of incandescent bulbs using a waste heat utilization technology or replace them all with fluorescent or LED lamps? The waste heat utilization technologies are not very competitive among the technologies for enhancing energy efficiency.

Nevertheless, such technologies will not disappear, either, as long as body temperature or solar heat exists. I hope these researchers take a long-term perspective on those technologies.