Tuesday, December 28, 2010

Thermoelectrics: Promise and Barriers of a Potential Breakthrough

By David Cohen-Tanugi | Originally published at Americans for Energy Leadership

The term 'energy efficiency' usually brings to mind better-insulated homes and smart power meters. But emerging thermoelectric technology could give energy efficiency a whole new meaning by tackling the huge energy waste that happens before the watts even reach our homes. Yet, to reach market, thermoelectics will have to overcome a number of technological and policy related barriers.

The Promise

Thermoelectric devices, which enable the conversion of heat into electricity, are still at an early stage in the energy innovation chain, but the principle behind how they work can help to highlight a crucial aspect of energy waste across the world that is often ignored in the policy realm.

You may have heard that homes in developed countries waste 25-35 percent of their energy due to insulation problems and inefficient devices. But the lion's share of energy waste actually comes at the early stages when the electric power is generated in power plants and carried across transmission lines.

Traditional fossil fuel plants create extremely high temperatures by burning or reacting their fuel, which they use in turn to run a steam engine that generates electric power while also rejecting heat at a lower temperature. The low-temperature output typically goes to waste, often tapping precious stream water resources in the process. So not only is the output heat a waste of energy, it also causes more environmental harm by consuming large quantities of water and disturbing neighboring ecosystems. Even cleaner solar panels waste precious energy by releasing heat. Experts estimate that for every 100 kWh of primary energy that are consumed in the United States, as much as 60 kWh goes to waste before ever reaching our factories, our offices or our homes.

Thermoelectrics could become a game-changer in energy efficiency by drastically reducing this energy waste at power plants – but only if we manage to address important scientific and policy barriers first. By tapping the waste heat from power plants, thermoelectric devices could generate additional electricity for the grid while helping to reduce the environmental footprint of water-hogging thermal plants.

The Technical Barriers

Unlike high-performance glass windows and insulation materials for homes, thermoelectrics is not a market-ready technology and is still at an early stage in the laboratory. Because the science behind the devices is so complex, specialists are even debating whether or not thermoelectrics can ever become a viable technology.

Basically, a thermoelectric device works just like an engine: it converts a certain temperature difference (say, a waste heat source at 500 degrees Fahrenheit compared with room temperature at 70 degrees) into an electric potential to generate power (you can find a great review here). For a given temperature output, a very efficient system will generate a high voltage, while a low-efficiency device will only create a modest voltage. In order to achieve real energy savings, the world would need thermoelectric devices with very high efficiency.

At present, this efficiency remains discouragingly low: even state-of-the-art thermoelectric devices can only convert 10 percent of the energy from a waste heat source at 500 degrees. This is why thermoelectrics have only met success for limited ‘niche’ applications, like powering telescopes in space for NASA and marginally increasing the mileage of BMW vehicles – hardly the energy efficiency revolution we have all been awaiting.

Fortunately, this efficiency is only limited by the basic laws of thermodynamics, and there is considerable room for progress. New advances in nanostructured materials, resonant modes, insulating materials and other state-of-the-art physics could help boost thermoelectrics’ contribution to energy efficiency throughout the world.

But technology is only the first step. Suppose now that R&D efforts manage to produce a new thermoelectric technology in a few years that is scalable, economically attractive and that can efficiently tap the waste energy from power plants, what’s next?

The Policy Barriers

In the realm of clean energy, it’s been shown that energy efficiency is the most attractive investment with the shortest payback time. But even with the most proven, market-ready technologies, individuals are still slow to adapt, often at the expense of higher energy bills. How would we get power plants to use thermoelectrics, if such a technology were available?

If past experience is any judge, the wide-scale implementation of a (hypothetical) high-efficiency thermoelectric technology would be a considerable challenge. Unlike private homeowners, electric power utilities are extremely risk-averse and their learning curve is slow. And in contrast with programs such as DOE’s Home Star, there are currently no subsidies or government incentives for utilities to take advantage of their waste heat. Not to mention the fact that even residential energy efficiency has a long way to go, with 20-30 percent energy savings still untapped in the United States. In short, there is a huge energy waste in the power sector and no policy mechanisms to tackle it.

Although it’s difficult to speculate the policy implications of an unproven technology, a few policy themes deserve serious attention. First, industrial plants would think twice about releasing waste heat into the atmosphere and rivers if they could put a price on it. In particular, putting a price on water usage for power plants and factories across the United States would make an enormous difference for the economics of waste heat, as well as for the environment. Second, one could envision a series of requirements for new and existing plants, similar to the Best Available Control Technology (BACT) requirements in the Clean Air Act of 1990, that would be aimed at widening the use of energy-efficiency technology in the power and industrial sectors.

In Conclusion...

At present, the technology behind thermoelectrics isn’t mature enough to play a significant role in economy-wide energy efficiency. Some even argue that this day will never come, and that it would be a waste (no pun intended) of resources to bet on thermoelectrics as a climate change mitigation technology.

It is too early to tell whether thermoelectrics can live up to their full potential, but the basic purpose of thermoelectrics also points to other promising options, such as combined heat and power (also known as a cogeneration plant). As water becomes an increasingly scarce resource, some emerging desalination technologies might also succeed in tapping waste heat from power plants to convert seawater into clean water.

The magnitude of the energy waste problem in colossal: the example of thermoelectrics illustrates how energy efficiency extends far beyond the reaches of our homes. A more mature debate on innovative policy ideas, combined with ambitious technological research, will play a crucial role in bringing about a paradigm shift in the world’s energy landscape.

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David Cohen-Tanugi is a Policy Fellow in AEL’s New Energy Leaders Project. He writes a column on some of the most promising and game-changing clean technologies that are coming out of laboratories in Cambridge and across the United States, providing an in-depth look at the role that innovation policy for clean technologies will play in our energy future.

David is a Ph.D. student at MIT in materials science & engineering. His research there will focus on computational approaches to clean energy technology. Prior to joining MIT, David served as the China-US climate and energy policy liaison for NRDC.

Disclosure: Several members of the author's research group at MIT are working on advanced thermoelectric technology. The views expressed are those of the author and do not necessarily reflect the position of AEL.

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