Energy challenges and the production of electricity from waste heat

The Nobel Peace Prize 2007 was awarded jointly to Intergovernmental Panel on Climate Change (IPCC) and Albert Arnold (Al) Gore Jr. “for their efforts to build up and disseminate greater knowledge about man-made climate change, and to lay the foundations for the measures that are needed to counteract such change”.

The prediction of climate changes induced by CO2 emission into the air is as scary as the book of revelation: “The seventh angel poured out his bowl into the air,… then there came flashes of lightning, rumblings, peals of thunder and a severe earthquake… Every island fled away…From the sky huge hailstones, each weighing about a hundred pounds, fell on people.” 1

The human conscience is enhancing in a new direction: all of us need to face the same global problem, the human-induced climate change. We realized that we are the threat to our own planet as a consequence of lack of knowledge. But in the near future, the consequences will originate from a lack of reaction; inertia leads in secret by the “ego” of most people. I can detect that in my-self, this “ego” is seeking comfort, recognition, and power. If I can feel it at my level, how much more is the temptation of that ego at high political levels?

Thanks to the Nobel prize’s impact, everybody knows that burning fossil energy leads to climate change via CO2 emission 2. What is the status of our energy portfolio? The world energy consumption is about 15TW. 87% of that energy is coming from fossil energy sources (coal, oil, gas), 6% from hydroelectricity, 6% from nuclear power plants, and only 1% from green energy sources.

The good news is that there are enough green energy sources to replace totally the fossil energies and cover all our needs in the future. Indeed, the sun is by far the largest source with 1 x 105 TW of radiation reaching the earth surface. So, in theory, we could stop the CO2 emission without stopping the development of our society.  But the real challenge is in the rapid implementation of green energy sources to stop the global temperature rises of 1-2 °C per 30 years 2. Few people really appreciate the magnitude of the problem we need to face. We are about 7 billions of inhabitants on earth and the expected population in 30 years is about 10 billions 3. With an average power consumption of 3kW/person, the expected world power consumption should increase from 15TW in 2013 to 24TW in 2050.

What does it imply to produce an extra 9TW in practice? 9TW is equivalent to 9000GW. What would mean 9TW in term of nuclear power? One nuclear reactor generates about 1GW, so it means we would need to fabricate 9000 nuclear reactors in the coming 30 years. This corresponds to 1 reactor every day for 30 years! Of course, a mass implementation of nuclear power would create a major issue with radioactive waste.

What about photovoltaics, i.e. solar cells? Those electronic devices transform the solar radiation into electricity with an efficiency of about 20%. The sun is irradiating the surface of the earth with a power per area of 1000 W/m2 during the half-day. So, the surface area that needs to be covered with solar panels to produce 9TW is 90 000 km2. For the sake of comparison, this corresponds to three times the surface area of Belgium. To make that possible, a solar cell stripe of 100 m wide and 82 km long should be manufactured and installed every day for 30 years.

Note however that this scenario is still conservative since today’s 15TW consumption would remain mostly from fossil energy sources. In other words, the CO2 production rate would not decrease and global warming would not be stopped. But these simple illustrations on the additional 9TW needed clearly reveal that a drastic implementation of green energy technologies is crucial and a true challenge. Technology-wise, it would require extremely low-cost manufacturing technologies and conversion devices composed of materials with atomic elements of high natural abundance. Due to the complex political and economic situations, Europe is not ready to take drastic measure to tackle this problem despite our full dependence on Russian gas.

Noteworthy, there are other possible energy scenarios for the future. Indeed, gas is to Russia as the sun is to Africa. The other communist power, China, is aggressive and realizes that the many resources including solar radiation are in Africa. China is giving present to countries like Burundi, constructing a road in the capital for “free”. But “there is nothing like a free lunch”…. Despite previous tensions between Africa and

Europe, the African population (not the politicians) is really welcoming ideas see the European coming back with fair deals and promote the development of their countries as brothers. Beside awareness of political investments, Europe has maybe little gas and sun, but it has brains. Exploratory research has still a major role to play and many exciting initiatives are emerging, for instance using printing technologies for creating large area solar cells.

Finally, another key eye-opening fact is how the energy is actually converted. Using fossil energy sources, nuclear power or even solar radiation, the energy conversion to other more practical energy forms (such as electricity) is mostly realized via thermal energy with a mean efficiency of about 40% or less 4. Hence, 60% or more of all energy sources is lost in heat! The major part of the thermal energy produced is rejected in the atmosphere and oceans as waste heat. Hot gases (T>600°C) can typically produce electricity via heat engine (thermodynamic cycle), however it becomes less economically advantageous for hot gases and warm fluids in the low and medium (20°C<T<600°C) temperature ranges. Thermoelectric generators (TEGs) are explored as a potential technology to transform part of this waste heat and natural heat source in the 20-600°C into electricity. If via these TEGs, which are semiconducting devices, we could recover a mere 1% of the primary energy contained in coal, natural gas, oil, and nuclear energy that we consume in the UE-27, we would get 191 TWh/y of electricity 5.

Also, if one could improve by 1% the efficiency of all engines thanks to TEGs implemented in vehicles, the CO2 emission would reduce by 42 million tons CO2/year 6. Those numbers imply a massive implementation of TEG co-generators in Europe. Massive implementation of TEGs put requirements on the thermoelectric (TE) materials and thermoelectric generators. TE materials must be efficient, stable, environmentally friendly, composed of elements abundant in nature, and synthesized with a scalable method. Also, the low-cost manufacturing process of the TEGs must be addressed. Nowadays manufacturing constitutes 50% of the cost for a TEG. At the moment, such materials and manufacturing method do not exist and constitute the main bottleneck for using this technology.

In my project entitled “Organic Thermoelectric Generators” financed by the European Research Council, my team at the Laboratory for Organic Electronics of Linköping University (Sweden) is developing plastics that conduct electricity. We are optimizing their thermoelectric properties and demonstrated that thin films of conducting polymers possess efficiency for heat-to-electricity conversion about five times less than the best inorganic thermoelectric materials based on non-abundant element: bismuth and telluride 7. It took us a few more years to understand the reason and discovered that those samples are the first semimetallic polymers 8.

The beauty of using polymers compared to inorganic materials is that can be processed from solution and do not require high-temperature sintering. Today, many challenges remain to create a viable technology and we still do not know the exact potential of this new class of thermoelectric materials. We are working closely with the research institute ACREO, a key player in printed electronics (, and hope to be able in few years to replicate micro thermoelectric generators on large areas with low-cost printing techniques. This is just our tiny contribution to the hope for a green world.

1 The holy bible, Revelation 16: 17-21

2 Global Climate Change Impacts in the United States . Thomas R.Karl, Jerry M. Melillo, and Thomas C. Peterson (eds.). United States Global Change Research Program. Cambridge UniversityPress, New York, NY, USA. (

3 US Census Bureau, International dataBase (

4 Bernard Durand, ”Energie et Environnement” (ISBN : 978-2-7598-0001-8).


6 ”EU energyand transport in figures” (ISSN 1725-1095).

7 O. Bubnova et al., Nature Materials 10, 429 (2011).

8 O. Bubnova et al., Nature Materials 13, 190 (2014).


Professor Xavier Crispin

Organic Thermoelectric

Generators project

Linkopings University

Tel: +46 1136 3485


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