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Thermoelectric Energy Harvesting

I. Introduction to Thermoelectric Energy Harvesting

In a time where people are consuming the Earth’s resources at the fastest rate ever, finding alternate power sources is a great way to help create sustainable energy. A sustainable energy solution such as energy harvesting provides an environmentally friendly way to harness natural energy. Energy harvesting provides several benefits and has become a proven solution for the rapidly depleting resources on our planet.

Energy harvesting is a method of generating electrical energy from normally unused energy sources available in the surrounding environment. It is also referred to as energy scavenging or power harvesting. Examples of energy sources that may be harvested and converted into electrical energy include radio waves, solar power, kinetic energy, salinity gradients, and temperature gradients. Energy harvesting techniques provide a great low power alternative replacing the use of batteries in many low power applications.

Energy harvesting can generate only very small amounts of power. This limits its use to low-energy electronics such as:

  • Wearable electronics / fashion technology
  • Wireless sensor networks
  • Long term low power sensors
  • Low power applications that generally extend beyond the capabilities of a typical battery.

Fuel sources needed to power energy harvesting devices are readily available and free to collect. For example, temperature gradients are created during the operation of the combustion engine; and, television and radio broadcasting creates electromagnetic energy. Both can be “scavenged” to create energy.

Energy Harvesting Then and Now
Humans have long searched for ways to harvest energy, and, in fact, have used wheels as a method to do so since early Roman times. Historically, water wheels have been used to harvest kinetic energy. Streams were dammed to harvest this energy to take advantage of their flowing waters. It was then converted into mechanical power that was used to run machinery and turn grinding stones in mills.

Today, heat is harvested through the use of large wheels, referred to as heat recovery wheels. They look very similar to their predecessor in both size and rotational speed.

The search for innovative energy harvesting devices continues in an effort to find a method to power mobile devices and sensor networks without the use of batteries.

Temperature Gradients
Two methods are employed to harvest energy using temperature gradients – pyroelectrics and thermoelectrics (also referred to as peltiers.)The application of pyroelectrics is limited because it requires a varying temperature input. Thermoelectrics turn heat into electricity utilizing a temperature gradient. Thermoelectrics are extremely stable and can provide nonstop operation for hundreds of thousands of hours. However, thermoelectrics are very inefficient, running at about 10% of photovoltaics.

Thermoelectric Energy and Energy Harvesting
Temperature differences can be seen everywhere, in both natural and manmade environments. These differences can be used to create thermoelectric energy. It is exciting that electricity can be created by utilizing otherwise wasted heat. Thermoelectric harvesting systems could be used to convert the thermal energy found in a fluid stream into electricity. Run-off from coal and nuclear power plants would be likely sources. Waste heat from solar thermal and geothermal plants could also be harvested. Exhaust streams from common household appliances could be utilized. The possibilities are endless. According to the United States Environmental Protection Agency, “The development of robust, economically viable thermoelectric power harvesting systems will reduce the consumption of fossil fuels by increasing the overall efficiency of power producing and power consuming systems.” This in turn would provide a viable solution to the problem that most current resources used to create electrical power are unsustainable.

Thermoelectric effect (TE) is the direct transformation of temperature differences into electric voltage. Its discovery nearly 200 years ago is credited to Thomas Johann Seebeck.  In a thermoelectric device, voltage is produced when differing temperatures are placed side by side. In the same way, a temperature difference occurs when voltage is applied. Because of his discovery, the ability of a material or device to generate voltage per unit of temperature is referred to as the Seebeck coefficient.

In 1834, Jean Charles Athanase Peltier found that by running an electric current through the intersection of two different conductors heating or cooling would occur. The direction of the flow determined the direction of the temperature change – up or down. The heat produced or absorbed is relative to the electrical current, and the proportionality constant is referred to as the Peltier coefficient.

Because of the discoveries of these two men, heaters, coolers, and generators (TEG’s) are created using thermoelectric materials.

Ideal thermoelectric materials will have:

  • Low thermal conductivity
  • High electrical conductivity
  • A high Seebeck coefficient

Accumulating and Storing Harvested Energy
Current applications have limitations – they must be small and require very little power. They are also limited by the need to use battery power. To overcome these limitations, the ability to harvest, accumulate and store scavenged energy, which would allow smart sensors to operate indefinitely, becomes a necessity.

As a rule, energy is stored in batteries, capacitors or super capacitors. If an application requires huge energy spikes, a capacitor is used. If a steady flow of energy is needed, a battery is utilized.

The Future of Energy Harvesting
Energy harvesting and the opportunity it creates to use components continuously, off grid and for extended periods of time, has garnered much attention in commercial as well as military use. Future applications may include designs of high-powered output devices for use in remote locations. Additionally, the wearable electronics industry looks to find ways to create harvesting devices that can recharge or power radio communications equipment, cellphones, mobile computers and more. The ability to harvest energy from the temperature differences between night and day may one day be used to power outdoor applications. One of the challenges faced in applications such as these is creating a device robust enough to withstand long-term exposure to harsh settings. Their designs would also need to incorporate the ability to harvest energy from multiple sources of ambient energy.

Thermoelectric energy is fascinating and has great potential for future applications, both big and small. Heat sources abound and can be easily scavenged by thermoelectric generators (TEGs) for use in these applications. II-VI has lead the way for providing thermal energy harvesting products to power wireless sensors and other microdevices, thereby eliminating the need for battery-powered solutions. The EverGen series from II-VI offers a low-cost and zero-maintenance solution for wireless sensor technology.

II. What is the Seebeck Effect?

Similar to Christopher Columbus navigating the vast waters of the Atlantic, Thomas Seebeck helped to plot the way for the field of thermoelectrics. Seebeck’s discoveries in the 19th century have stood the test of time and continue to be used to this day.

Along with fellow physicists Jean Peltier of the Peltier effect and Lord Kelvin of the Thomson effect, Seebeck created the foundation for the field of thermoelectrics as we know it today.

(Image source: sciencestruck.com)

What Is The Seebeck Effect?
Thomas Seebeck discovered that when dissimilar metals are exposed to a variance of temperature with distance, they produce an electric current. The Seebeck effect (also known as the Peltier-Seebeck effect) is the foundation of thermocouples and thermopiles. The metals that are commonly paired together to create the Seebeck effect are constantan with copper, iron, chrome, or aluminum. However, there are also a number of other wire pairings that can be used to create this particular effect. Together with the Peltier and Thompson effects, the Seebeck effect completes the triad that is the basis for thermoelectrics.

Seebeck Effect Equations
There is more than one Seebeck effect equation and the equation a person uses will naturally depend on the type of Seebeck device one is using and how much voltage he or she needs the device to produce.

The Seebeck effect is calculated using a reversible closed Carnot cycle. Put in simple terms, it looks like this: dQ / dt = (Пa – Пb)1. This calculation is used to determine the heat rate for the electric current. To determine the co-efficient calculated by the model, the following equations are used: Пa = kTln (ɳL) and Пb = kTln (ɳR). Other equations can be found here and here.

How are Seebeck Devices Used?
Seebeck generators are also commonly known as thermoelectric generators (TEG’s). They convert heat into energy and are used for low power remote applications and applications that would not be able to support a large heat generator. Seebeck generators do not have moving parts, operate 24/7 and can be used in all types of weather. What is more, they do not require battery back up.

Companies that build and/or manage gas pipelines use thermoelectric generators in a number of ways. These generators provide cathodic protection, make radio communication a possibility and can be used for telemetry. Thermoelectric generators are also used as off-grid power generators in remote areas and as back-up generators for solar panel energy creation devices.

Seebeck Devices in Consumer Products
Automotive thermoelectric generators are used in many types of cars. They take waste heat produced by the engine and turn it into energy, thus increasing a car’s efficiency. Given the fact that 40% of a car engine’s energy is lost via exhaust gas heat, it is clear that using a thermoelectric generator inside a car can represent significant energy savings. What is more, thermoelectric generators also drastically reduce the amount of emissions that a car produces, thus helping to make vehicles much more environmentally friendly than they were in times past.

Industrial Uses of Seebeck Devices
Seebeck generators are becoming increasingly popular in the manufacturing industry. Because they can take waste heat (that would have been released into the environment) and turn it into energy, they are extremely useful for any company that generates heat in the creation of its products and/or services. Increasing the efficiency of generators can save a company money and also reduce CO2 emissions, which helps protect the environment.

Evolution of the Seebeck Effect
While Thomas Seebeck was the first to discover that dissimilar metals can, under the right circumstances, create an electrical current, he was by no means the last person to be interested in this phenomenon. The discovery of the Peltier Effect and Thomson Effect were made based on Seebeck’s work. In 2008, physicists discovered the Spin Seebeck Effect, which can be applied to a magnetized metal and causes electrons to rearrange themselves in accordance with their spin. The Spin Seebeck Effect has the potential to enable companies to create faster, smaller and more energy efficient microchips and spintronic devices.
Thermoelectric energy generation has a great deal of potential. At present, it can enable companies as well as average individuals to save a great deal of energy and reduce emissions. It can be used to generate power in instances where other generators would not be able to operate. However, there is much more in store for the future. As ongoing research enables the scientific community to discover new uses for Seebeck devices, they are certain to become both more commonplace and more efficient.

Using the Seebeck effect, II-VI has created thermoelectric modules designed for temperature cycling applications where high reliability is essential. These power generators utilize existing temperature differentials to provide reliable, renewable energy for projects from low-power wireless sensors to large-scale electricity generation.

III. How Do Thermoelectric Power Generators Work?

Seebeck Effect
The Seebeck Effect produces an electric current when dissimilar metals are exposed to a variance in temperature. Seebeck effect applications are the foundation of thermoelectric generators (TEGs) or Seebeck generators which convert heat into energy. The voltage produced by TEGs or Seebeck generators is proportional to the temperature distance across between the two metal junctions.

Thermoelectric generators are solid-state heat engines made of pairs of p-type and n-type elements. The p-type elements are made of semiconductor materials doped such that the charge carriers are positive (holes) and Seebeck coefficient is positive. The n-type elements are made of semiconductor material doped such that the charge carriers are negative (electrons) and the Seebeck coefficient is negative.

Energy Generation
When a p-type element electrically connects to the n-type element, the mobile holes in the p-type element “see” the mobile electrons in the n-type element and migrate just to the other side of the junction.

When one electrically connects a p-type element to the n-type element, the mobile holes in the p-type element “see” the mobile electrons in the n-type element and migrate just to the other side of the junction. For every hole that migrates into the n-type element, an electron from the n-type element migrates into the p-type element. Soon, each hole and electron that “switch sides” will be in equilibrium and act like a barrier, preventing more electrons or holes from migrating. This is called the depletion zone.

IV. Industrial Applications of Thermoelectric Power Generators

Thermocyler Application Of Thermoelectric Generator Modules

Because Solid state Thermoelectric Generator (TEG) modules are designed to provide DC power to a wide range of devices with high reliability. TEGs utilize unique construction techniques to survive a high number of thermal cycles and 200°C continuous hot side operation. TEGs are applicable in a variety of industries including automotive, medical, industrial, oil, gas, and mining, and telecommunications.

EverGen® Series

II-VI’s EverGen® Series Thermoelectric Generators is a complete range of thermoelectric-based energy harvesting devices that offer customers a low-cost, zero-maintenance power solution for wireless sensor applications. By converting small degrees of temperature difference into milliwatts of electrical power, II-VI’s line of thermoelectric energy harvesting solutions can perpetually power wireless sensors for the lifetime of the application. This green innovation offers a solid-state, reliable energy source for sensors, actuators, valve solenoids and other small devices by recycling wasted heat.

 
 
V. What is EverGen® PowerStrap® Generator?

EVERGEN® POWERSTRAP™ Generator
EverGen® PowerStrap™ Generator technology is designed for industrial, steam, and oil & gas industries. These devices can provide electrical power in remote areas for sensors and monitors. The generator is a medium power output product designed as a power source solution for the industrial, commercial, and oil & gas industries. Designed to be used in place of, or complimentary to solar power systems for a constant source of electrical energy. Easily attaches to a hot pipe, such as an exhaust stack, to convert waste heat into usable DC electrical power.


Benefits

  • Class 1 Division 2 certified product.
  • Non-invasive single bolt installation design.
  • Multiple sizes to accommodate common pipe diameters.
  • Works in combination with solar power systems.

Uses

  • Powering of Burner Management & SCADA Systems.
  • Remote/off-grid power source.
  • Lead-acid battery bank charging system.
  • AC line back-up power system.
VI. Advantages and Benefits of EverGen® PowerStrap® Generator

Advantages and Benefits
The EverGen® PowerStrap™ Generator is a revolutionary product utilizing thermoelectric technology to harvest thermal energy and convert it into an economical and perpetual form of electrical energy. The EverGen® PowerStrap™ Generator provides an off‐grid electrical power source in place of, or complementary to solar power; for industrial, commercial, oil & gas applications.

Product Features

  • Non‐invasive thermal energy harvesting power source
  • Available for 6”, 8”, 10”, 12”, & 14” NPS pipe sizes
  • Ideal complement to solar; providing uninterruptible power year‐round
  • Specifically suited for cold environments
  • Single bolt compression installation
  • Configurable for vertical and horizontal pipes
  • Modular design for multiplicative power output
  • Class 1, Division 2, group A‐D certified
  • Patented – US 8,933,317
  • Standard 1 Year warranty
  • EU RoHS compliant
  • EU REACH compliant

Technical Data Sheet For EHBMS
View the detailed EverGen® PowerStrap™ Generator Technical Data Sheet for more detailed information. Be sure to also view the EverGen® PowerStrap™ Controller Technical Data Sheet for additional information.

VII. Installation of EverGen® PowerStrap® Generator
EverGen® Powerstrap™ Generator is designed for industrial, steam, and oil & gas industries. The generator can be easily attached to a hot pipe, such as an exhaust stack, to convert waste heat into usable DC electrical power. The device will provide electrical power in remote areas for sensors and monitors. View the product video walkthrough below and learn more about this product.

VIII. Successful Uses of Thermoelectric Power Generators

Successful Uses & Applications


II-VI provides thermal energy harvesting products that power wireless sensors and other microdevices, thereby eliminating the need for battery-powered solutions. EverGen® technology can improve energy efficiency by harvesting heat waste produced by the industrial, oil & gas industries.

The EverGen® PowerStrap™ Generator provides an off-grid electrical power source in place of, or complementary to solar power; for industrial, commercial, oil & gas applications. Applying the EverGen® PowerStrap™ Generator to a hot pipe, such as an outdoor exhaust stack, creates a power source that pays for itself in a single winter season.

The PowerStrap™ Generator is especially effective in northern climates and is a fully certified Class 1 Division 2 product, supporting the implementation of the CSA B149 gas safety code for Burner Management Systems. The EverGen® PowerStrap™ Generator is non-invasive and easy to install. With our single bolt hinged construction design installation only takes five minutes. The EverGen® PowerStrap™ Generator fits an array of standard pipe diameters. Also available is the EverGen® PowerStrap™ Generator charge controller. This controller is optimized for use with the PowerStrap™ Generator for maximizing battery power storage. 

IX. Environmental Benefits of Thermoelectric Energy Harvesting

Environmental Benefits
Thermoelectric generators are low maintenance and generate zero emissions, they are also have very low maintenance costs. The vast majority of government-sponsored research in the field of thermoelectrics over the past 10-15 years has been in the area of thermoelectric power generation. The driving force behind most of this research seeks ways to improve our utilization of energy. Consider that less than a fourth of the energy content in the gasoline in your car actually goes into useful work to move the vehicle. The majority of the energy escapes as heat loss to the ambient primarily through the vehicle exhaust and radiator. Likewise, the U.S. manufacturing industry discharges roughly one-third of the energy consumed as thermal losses to the atmosphere or to cooling systems. This heat loss is measured in Quads (1015 BTU) and represents a huge opportunity for thermoelectrics to someday impact national energy consumption and our dependence on foreign fuel.

Thermoelectric waste heat recovery is the process of recapturing this lost heat and converting it to electrical power. This is the primary focus of most DOE, DARPA and DoD research for new, more efficient power generator materials and devices.

Energy harvesting and the opportunity it creates to use components continuously, off grid and for extended periods of time, has garnered much attention in commercial as well as military use. Future applications may include designs of high-powered output devices for use in remote locations. Additionally, the wearable electronics industry looks to find ways to create harvesting devices that can recharge or power radio communications equipment, cellphones, mobile computers and more. The ability to harvest energy from the temperature differences between night and day may one day be used to power outdoor applications. One of the challenges faced in applications such as these is creating a device robust enough to withstand long-term exposure to harsh settings. Their designs would also need to incorporate the ability to harvest energy from multiple sources of ambient energy.

Thermoelectric energy is fascinating and has great potential for future applications, both big and small. Heat sources abound and can be easily scavenged by thermoelectric generators (TEGs) for use in these applications. II-VI has lead the way for providing thermal energy harvesting products to power wireless sensors and other microdevices, thereby eliminating the need for battery-powered solutions. The EverGen series from II-VI offers a low-cost and zero-maintenance solution for wireless sensor technology.

X. Technical Specifications of EverGen® PowerStrap® Generator


The EverGen® PowerStrap™ Generator is a revolutionary product utilizing thermoelectric technology to harvest thermal energy and convert it into an economical and perpetual form of electrical energy. The EverGen® PowerStrap™ Generator provides an off‐grid electrical power source in place of, or complementary to solar power; for industrial, commercial, oil & gas applications.

Electrical Technical Specifications

Product Features

  • Non‐invasive thermal energy harvesting power source
  • Available for 6”, 8”, 10”, 12”, & 14” NPS pipe sizes
  • Ideal complement to solar; providing uninterruptible  power year‐round
  • Specifically suited for cold environments
  • Single bolt compression installation
  • Configurable for vertical and horizontal pipes
  • Modular design for multiplicative power output
  • Class 1, Division 2, group A‐D certified
  • Patented – US 8,933,317
  • Standard 1 Year warranty
  • EU RoHS compliant
  • EU REACH compliant

View the detailed EverGen® PowerStrap™ Generator Technical Data Sheet for more detailed information. Be sure to also view the EverGen® PowerStrap™ Controller Technical Data Sheet for additional information.

XI. What is the EverGen® Plate Exchanger?
 

The EverGen® Plate Exchanger is a high watt density, compact thermoelectric energy harvesting liquid-to-liquid exchanger. It can be used for applications that require higher power outputs.

Benefits & Uses
The Plate Exchanger has a compact, high energy density format for converting waste heat in liquid loops to electrical energy.
Potential applications include large engine/process waste heat recovery, self-powered hydronic heating systems and self-powered pump applications.

Frequently Asked Questions
At what temperature does it operate and at what temperature range?
The Plate Exchanger max temperature of operation would be limited to the type of gasketing used as well as the thermal fluid.  Practically, the max limit would be around 165C while the lower limit is mostly defined by the thermal fluid freezing point.

What are the dimensions of one standard unit?
Since this product does not exist, there are no set dimensions.  Unit size is also dependent on the needs of each application.  Prototypes we have built have been 5” wide x 8” tall x 12” deep.

Can you get this in a brazed format?
No.

Are commercial versions offered using gaskets?
This product is not commercially available, but prototypes built have used gaskets.

What are the power requirements?
Power requirements are customer dependent since these Plate Exchangers are custom built.

BTU/ Hr? BTU Output?
In power gen mode, this product does not produce heat but rather converts heat inputs into electrical power.

How is pricing for this determined?
Since this is not a commercially available product, significant NRE development must be undertaken to bring to market.  Investment dollars and sale prices are dependent on the business case of the application.

What is the nominal efficiency, etc.?
The heat to electrical conversion efficiency is a function of temperature differential. Maximum practical efficiency (assuming Tc=0C and Th=165C) is around 5%.

Does it come with the Evergen Unit?
We should be clear to state that the EverGen is a family name given to different products. This family of products includes the EverGen Plate Exchanger, EverGen PowerStrap, EverGen Facet, and the EverGen Controller.

Is this product corrosion resistant?
The Plate Exchanger is constructed of stainless steel or aluminum plate construction, depending on a customer’s needs. These materials are corrosion resistant.

How much energy can be harvested per day?
This depends on temperature differential and parasitic losses, such as pump losses.

What is the average lifespan of this product?
Lifespan depends on the fouling factor of working fluids and the temperature of operation.  Since this product is not commercialized, reliability parameters for the full system have not been established.  The expected thermoelectric modules reliability at the maximum stated operating temperatures would be 10 years, with failure defined as a 10% drop in initial power output.

Are there routine maintenance requirements?
The only routine maintenance required would be anti-fouling cleaning and flushing.

Can the generator be dismantled for cleaning?
No, but you will not need to dismantle it in order to get sufficient cleaning.

What materials is the generator made of and what types of plates or pipes does it utilize?
Again, this product is not yet commercialized.  Materials and plates are likely to be tailored for application requirements.