According to ‘’Waste Heat Recovery : Technologies and Opportunities in U.S. Industry’’ report published by the U.S. Department of Energy, 20 to 50% of all energy input in the U.S. industrial sector is lost as waste heat in the form of hot exhaust gases, cooling water, and heat lost from hot equipment surfaces and heated products.
Recovering waste heat losses and turn it into useful energy provides an attractive opportunity for an emission free and less costly energy resource.
The idea of transforming waste heat into power isn’t new. Since the 1970’s steam turbine technology has been used to transform heat losses into power at big scale. More recently, technologies based on the Organic Rankine Cycle, Kalina Cycle, and the Sterling Engine have been used to capture waste heat at lower temperatures and at smaller scales.
Meanwhile, the recent advances in nanomaterial science offer new opportunities in waste heat recovery, which are based on thermoelectric generation. Thermoelectrics are materials that can directly convert heat to electricity with no moving parts or circulating fluids, they are highly scalable and reliable. However, the use of thermoelectrics in waste heat recovery has been limited until recently, due to their relatively low efficiency.
In the past three years we could see rapid development of a group of American startups, which have pioneered different industrial applications of new nanostructured thermoelectric materials.
Alphabet Energy is commercializing a breakthrough thermoelectric technology developed at the Lawrence Berkeley National Laboratory. Company uses silicon-based materials (silicon nanowires), which allows to create the highest efficiency in waste-heat recovery while using cheap materials. Today, Alphabet Energy focuses on the development of waste-heat-to-electricity generators that utilize hot exhaust gas from heavy industrial applications and engines.
GMZ Energy was founded based on the scientific discovery made at MIT and Boston College. Company is developing a bismuth telluride thermovoltaic device that converts solar heat directly into power via the Seebeck effect. (In the Seebeck effect, a sharp temperature gradient can result in an electric charge). GMZ Energy wants to integrate its thermoelectric materials directly into conventional solar hot water collectors, enabling the production of electricity in addition to heat and hot water.
Phononic Devices is commercializing advanced thermoelectric materials and device concepts exclusively licensed from the University of Oklahoma. Thermoelectrics can capture wasted heat, and convert it into power, but they can also displace heat and maintain a cool temperature in everything from laptops to refrigerators and lasers. Phononic Devices is using thermoelectric materials for cooling applications and it has developed solid-state heat pumps that it is using in compressor-free refrigeration units.
As we can see all these startups are actually academic spin-offs, based on the scientific research, coming from university labs. In this context I would like to present five European research projects, which are seeking to make new advances in thermoelectric materials. Each of these projects has a big potential to develop breakthrough technologies in waste heat recovery, which can then be spin-out to new companies.
The NEAT project aims to develop a new class of high performance thermoelectric nanocomposites, based on eco-friendly materials. Until recently, the best known thermoelectric materials had figures of merit (so-called ZT, representing the thermoelectric performance of the material) values near 1. Structuring thermoelectrics materials at nanometric scale has been proposed in the 1990’s as a mean to enhance their performance. Later, several types of thin film nanostructured materials have demonstrated ZT values near 3. NEAT seeks to develop an innovative bulk alloy nanocomposite materials capable to attain ZT>3 for medium (300-600°C) and high (600-1000°C) temperature ranges, suitable to harvest energy in the KW range.
The ThermoMag project aims to develop thermoelectric materials and modules that are relatively inexpensive, widely available, non-toxic, lightweight, practicable in size, vibration-tolerant and scalable for industry. To meet these requirements, the project focuses on study of 3D nanocrystalline Mg2Si-based thermoelectrics. Magnesium and Silicon are both extremely abundant and relatively easy-to-extract elements and hence very inexpensive compared to other conventional, rare elemental constituents used in thermoelectrics (e.g. Bi, Te, Ge, Sb, and Se). ThermoMag seeks to significantly raise the ZT of Mg2Si-based thermoelectric materials by refining material nanostructure and doping with a wide range of elements
The objective of the H2ESOT project is the development of efficient thermoelectric modules using organic thermoelectric materials. To achieve this ambitious goal, the project will prepare, purify, fabricate, test and theoretically evolve organic polyacenes materials. Acenes or polyacenes are a class of organic compounds with strong semiconductor proprieties. Polyacenes combine high Seebeck coefficients with low thermal conductivity, which makes them potentially very interesting for low cost heat-to-electricity conversion.
The NanoCaTe project aims to develop a more efficient thermoelectric- and storage material based on nanocarbon (e.g. graphene and CNT) to reclaim waste heat by thermoelectric generators and to storage the energy in super capacitors. The main objective of the project is to develop efficient and inexpensive flexible printed thermoelectric generators and energy storage systems.
NexTec is a large scale demonstration project with the objective to find more efficient thermoelectric materials, designed for waste heat recovery. The project use nanotechnology to improve the component materials of thermoelectric devices and seeks to make cost-effective mass production of these devices. NexTec will select the best performing thermoelectric materials for fabrication of realistic devices. Then, industrial partners of the project will test and validate these devices in their areas of expertise. Finally, best-performing device designs will be chosen for licensing and mass production for niche applications.
Despite recent advances in thermoelectric energy conversion, thermoelectric technologies aren’t still mature enough to play a significant role in economy-wide energy efficiency. The above research projects can significantly improve efficiency and cost of thermoelectric materials, which can open new opportunities for waste heat recovery, especially for unconventional waste heat sources. Deployment of new technologies in thermoelectric waste heat recovery will significantly increase the efficiency of existing industrial systems and at the same time contribute to global CO2 emission reduction.