Thermoelectric generator (TEG thermogenerator) is an electrical device that uses the Seebeck, Thomson and Peltier effects to generate electricity through thermo-EMF. The thermo-EMF effect was discovered by the German scientist Thomas Johann Seebeck (Seebeck effect) in 1821. In 1851, William Thomson (later Lord Kelvin) continued thermodynamic research and proved that the source of the electromotive force (EMF) is a temperature difference.
In 1834, French inventor and watchmaker Jean Charles Peltier discovered the second thermoelectric effect, found that the temperature difference occurs at the junction of two different types of materials under the influence of an electric current (Peltier effect). Specifically, he predicted that an EMF would develop within a single conductor when there was a temperature difference.
In 1950, Russian academician and researcher Abram Ioffe discovered the thermoelectric properties of semiconductors. Thermoelectric power generator began to be used inautonomous power supply systems in inaccessible areas. The study of outer space, man's spacewalk gave a powerful impetus to the rapid development of thermoelectric converters.
The radioisotope energy source was first installed on spacecraft and orbital stations. They are beginning to be used in the large oil and gas industry for anti-corrosion protection of gas pipelines, in research work in the Far North, in the field of medicine as pacemakers, and in housing as autonomous sources of power supply.
Thermoelectric effect and heat transfer in electronic systems
Thermoelectric generators, the principle of operation of which is based on the complex use of the effect of three scientists (Seebeck, Thomson, Peltier), were developed almost 150 years after discoveries that were far ahead of their time.
Thermoelectric effect is the following phenomenon. For cooling or generating electricity, a "module" consisting of electrically connected pairs is used. Each pair consists of semiconductor material p (S> 0) and n (S<0). These two materials are connected by a conductor whose thermoelectric power is assumed to be zero. Two branches (p and n) and all other pairs that make up the module are connected in series in the electrical circuit and in parallel in the thermal circuit. TEG (thermoelectric generator) with this layout creates conditions to optimize the heat flow that passes through the module, overcoming itelectrical resistance. Electric current acts in such a way that charge carriers (electrons and holes) move from a cold source to a hot source (in the thermodynamic sense) in two branches of the pair. At the same time, they contribute to the transfer of entropy from a cold source to a hot one, to a heat flow that will resist heat conduction.
If the selected materials have good thermoelectric properties, this heat flux generated by the movement of charge carriers will be greater than the thermal conductivity. Therefore, the system will transfer heat from a cold source to a hot one and act as a refrigerator. In the case of electricity generation, the heat flow causes the displacement of charge carriers and the appearance of an electric current. The greater the temperature difference, the more electricity can be obtained.
TEG efficiency
Assessed by the efficiency factor. The power of a thermoelectric generator depends on two critical factors:
- The amount of heat flow that can successfully move through the module (heat flow).
- Temperature deltas (DT) - the temperature difference between the hot and cold side of the generator. The larger the delta, the more efficiently it works, therefore, conditions must be provided constructively, both for maximum cold supply and maximum heat removal from the generator walls.
The term "efficiency of thermoelectric generators" is similar to the term applied to all other typesthermal engines. So far, it is very low and amounts to no more than 17% of Carnot's efficiency. The efficiency of the TEG generator is limited by the Carnot efficiency and in practice reaches only a few percent (2-6%) even at high temperatures. This is due to the low thermal conductivity in semiconductor materials, which is not conducive to efficient power generation. Thus, materials with low thermal conductivity, but at the same time with the highest possible electrical conductivity are needed.
Semiconductors do a better job than metals, but are still very far from those indicators that would bring a thermoelectric generator to the level of industrial production (with at least 15% use of high-temperature heat). A further increase in the efficiency of TEG depends on the properties of thermoelectric materials (thermoelectrics), the search for which is currently occupied by the entire scientific potential of the planet.
The development of new thermoelectrics is relatively complex and expensive, but if successful, they will cause a technological revolution in generation systems.
Thermoelectric materials
Thermoelectrics are made up of special alloys or semiconductor compounds. Recently, electrically conductive polymers have been used for thermoelectric properties.
Requirements for thermoelectrics:
- high efficiency due to low thermal conductivity and high electrical conductivity, high Seebeck coefficient;
- resistance to high temperatures and thermomechanicalimpact;
- accessibility and environmental safety;
- resistance to vibrations and sudden changes in temperature;
- long-term stability and low cost;
- automation of the manufacturing process.
Currently, experiments are underway to select optimal thermocouples, which will increase the TEG efficiency. The thermoelectric semiconductor material is an alloy of telluride and bismuth. It has been specially manufactured to provide individual blocks or elements with different "N" and "P" characteristics.
Thermoelectric materials are most often made by directional crystallization from molten or pressed powder metallurgy. Each manufacturing method has its own particular advantage, but directional growth materials are the most common. In addition to bismuth tellurite (Bi 2 Te 3), there are other thermoelectric materials, including alloys of lead and tellurite (PbTe), silicon and germanium (SiGe), bismuth and antimony (Bi-Sb), which can be used in specific cases. While bismuth and telluride thermocouples are best for most TEGs.
Dignity of TEG
Advantages of thermoelectric generators:
- electricity is generated in a closed, single-stage circuit without the use of complex transmission systems and the use of moving parts;
- lack of working liquids and gases;
- no emissions of harmful substances, waste heat and noise pollution of the environment;
- device long battery lifefunctioning;
- use of waste heat (secondary heat sources) to save energy resources
- work in any position of the object, regardless of the operating environment: space, water, earth;
- DC low voltage generation;
- short circuit immunity;
- Unlimited shelf life, 100% ready to go.
Fields of application of thermoelectric generator
The advantages of TEG determined the development prospects and its near future:
- study of the ocean and space;
- application in small (domestic) alternative energy;
- using heat from car exhaust pipes;
- in recycling systems;
- in cooling and air conditioning systems;
- in heat pump systems for instant heating of diesel engines of diesel locomotives and cars;
- heating and cooking in field conditions;
- charging electronic devices and watches;
- nutrition of sensory bracelets for athletes.
Thermoelectric Peltier converter
Peltier element (EP) is a thermoelectric transducer operating using the Peltier effect of the same name, one of the three thermoelectric effects (Seebeck and Thomson).
Frenchman Jean-Charles Peltier connected copper and bismuth wires to each other and connected them to a battery, thus creating a pair of connections of twodissimilar metals. When the battery was switched on, one of the junctions would heat up and the other would cool down.
Peltier effect devices are extremely reliable because they have no moving parts, are maintenance-free, emit no harmful gases, are compact and have bi-directional operation (heating and cooling) depending on the direction of the current.
Unfortunately, they are inefficient, have low efficiency, emit quite a lot of heat, which requires additional ventilation and increases the cost of the device. Such devices consume quite a lot of electricity and may cause overheating or condensation. Peltier elements larger than 60 mm x 60 mm are almost never found.
Scope of ES
The introduction of advanced technologies in the production of thermoelectrics has led to a reduction in the cost of production of EP and expansion of market accessibility.
Today EP is widely used:
- in portable coolers, for cooling small appliances and electronic components;
- in dehumidifiers to extract water from the air;
- in spacecraft to balance the effect of direct sunlight on one side of the craft while dissipating heat to the other side;
- to cool the photon detectors of astronomical telescopes and high quality digital cameras to minimize observational errors due to overheating;
- for cooling computer components.
Recently, it has been widely used for domestic purposes:
- in cooler devices powered by USB port to cool or heat drinks;
- in the form of an additional cooling stage for compression refrigerators with a temperature drop of up to -80 degrees for one-stage cooling and up to -120 for two-stage;
- in cars to create autonomous refrigerators or heaters.
China has launched the production of Peltier elements of modifications TEC1-12705, TEC1-12706, TEC1-12715 worth up to 7 euros, which can provide power up to 200 W according to the “heat-cold” schemes, with a service life of up to 200,000 hours of operation in the temperature zone from -30 to 138 degrees Celsius.
RITEG nuclear batteries
A radioisotope thermoelectric generator (RTG) is a device that uses thermocouples to convert heat from the decay of radioactive material into electricity. This generator has no moving parts. RITEG was used as an energy source on satellites, spacecraft, remote lighthouse facilities built by the USSR for the Arctic Circle.
RTGs are generally the most preferred power source for devices requiring several hundred watts of power. In fuel cells, batteries or generators installed in places where solar cells are inefficient. A radioisotope thermoelectric generator requires strict radioisotope handling duringlong time after the end of its service life.
There are about 1,000 RTGs in Russia, which were mainly used for power sources on long-range means: lighthouses, radio beacons and other special radio equipment. The first space RTG on polonium-210 was Limon-1 in 1962, then Orion-1 with a power of 20 W. The latest modification was installed on the Strela-1 and Kosmos-84/90 satellites. Lunokhods-1, 2 and Mars-96 used RTGs in their heating systems.
DIY thermoelectric generator device
Such complex processes that take place in the TEG do not stop the local "Kulibins" in their desire to join the global scientific and technical process for the creation of the TEG. The use of homemade TEGs has been used for a long time. During the Great Patriotic War, partisans made a universal thermoelectric generator. It generated electricity to charge the radio.
With the advent of Peltier elements on the market at affordable prices for the household consumer, it is possible to make a TEG yourself by following the steps below.
- Get two heatsinks from an IT store and apply thermal paste. The latter will facilitate the connection of the Peltier element.
- Separate the radiators with any heat insulator.
- Make a hole in the insulator to accommodate the Peltier element and wires.
- Assemble the structure and bring the heat source (candle) to one of the radiators. The longer the heating, the more current will be generated from the home thermoelectricgenerator.
This device works silently and is light in weight. The ic2 thermoelectric generator, according to the size, can connect mobile phone charger, turn on a small radio and turn on LED lighting.
Currently, many well-known global manufacturers have launched the production of various affordable gadgets using TEG for car enthusiasts and travelers.
Prospects for the development of thermoelectric generation
Demand for household consumption of TEGs is expected to grow by 14%. Thermoelectric generation development outlook was published by Market Research Future by issuing the paper “Global Thermoelectric Generators Market Research Report - Forecast to 2022” - market analysis, volume, share, progress, trends and forecasts. The report confirms the promise of TEG in the recycling of automotive waste and co-generation of electricity and heat for domestic and industrial facilities.
Geographically, the global market for thermoelectric generators has been divided into America, Europe, Asia-Pacific, India and Africa. Asia-Pacific is considered the fastest growing segment in the implementation of the TEG market.
Among these regions, America, according to experts, is the main source of income in the global TEG market. The increase in demand for clean energy is expected to increase demand in America.
Europe will also show relatively fast growth during the forecast period. India and China willincrease consumption at a significant pace due to the increase in demand for vehicles, which will lead to the growth of the generator market.
Automobile companies such as Volkswagen, Ford, BMW and Volvo, in collaboration with NASA, have already begun developing mini-TEGs for the heat recovery and fuel economy system in vehicles.
