Hybrid Residential Solar and Thermoelectric Power Generation

by Ken Adler, Senior Technical Advisor at the Alliance for Green Heat

Some of you may be wondering about thermoelectric wood stoves and why we decided to include them in the 2018 Wood Stove DesignChallenge, which will be held in November 2018 on the Washington Mall.  Our goal of this competition is to support development and commercialization of a revolutionary thermoelectric wood stove that produces electricity equal to 50 percent or more of the winter time output of a residential solar photovoltaic system. By combining a thermoelectric wood stove and a residential solar PV system and home battery, like the TESLA Powerwall, we can support residential and grid-based distributive power goals, and incentivize greater investment in solar power. 

Specifically, thermoelectric wood stoves can help solve the problem of low winter time solar PV output in northern climates, where useful solar radiation is limited to 2 - 4 hours per day.

While a thermoelectric wood stove may sound revolutionary, the technology behind the stove has been used since the 1980s in oil and gas field operations, where methane gas provides a low-cost source of heat to power the thermoelectric generator. Wood stoves, like waste methane gas, can provide a free source of heat for the thermoelectric generator.

Alphabet Energy Thermoelectric Generator

Thermoelectric generators are like solar panels, however, instead of turning light into electricity they turn heat into electricity. To generate electricity, one side of a thermoelectric module is heated by the wood stove while the other side is cooled with either an air or water-cooled heat sink. For applications above 100-watts, water-cooled heat sinks are the most common approach because of their ability to extract greater amounts of heat from the thermoelectric module.

60-Watt Water Cooled Thermoelectric Generator

In northern climates like New England, Canada and northern Europe, low winter time solar radiation increases the cost and reduces the efficiency of solar PV systems, and the cost-effectiveness of battery storage systems like the Tesla Powerwall.  According to NREL, solar radiation in northern areas like Vermont peaks at 6.0kWh/m2 in June and declines to 1.7kWh/m2 in December. This means that an average 4,000-watt residential solar system will go from producing 571kWh in June to 191kWh in December--a 66% reduction is solar power output.  This project will demonstrate how a thermoelectric wood stove can cost-effectively supplement a solar PV system.

Building on our experience from 3 previous Design Challenges, we will work with wood stove manufacturers, universities and others to build and test 100 to 200-watt thermoelectric wood stoves that could effectively increase by 50% the winter time output of a 4,000-watt residential solar PV system.   

Thermoelectric generators are currently sold as accessories for wood stoves; however, these accessories are limited in size and efficiency. By integrating a thermoelectric generator into a wood stove we can achieve far greater power output, efficiency, and lower cost. For example, a wood stove with a 150 to 200-watt thermoelectric generator operating 20 hours per day could generate 93 to 124kWh of electricity per month, which compares favorably with the December solar PV output of 191kWh in Vermont.

Russian Thermoelectric Wood Stove 

(not certified for sale in the U.S.)

There are several reasons why now is the time to consider thermoelectric wood stoves. First, the price of the thermoelectric modules, which are a component of the TEG, has dropped substantially because they are now being mass produced in China.[1]  Second, the EPA’s recent wood stove NSPS regulation is helping to make new wood stoves cleaner and more efficient and, coupled with cordwood testing and automated features, a new generation of cleaner stoves could also generate electricity. Third, thermoelectric wood stoves can produce electricity up to 24 hours per day eliminating load management concerns common with solar and wind power. Lastly, the stoves are powered by local wood supplies, making their fuel low carbon and locally sourced.

The 2018 competition on the Mall will demonstrate the role thermoelectric wood stoves can play in promoting solar power, energy storage systems and biomass energy, while also reducing energy costs, supporting climate change goals, and increasing distributive power.   

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[1] The cost of a thermoelectric module has fallen below $2 per watt (uninstalled), compared with $3.50 per watt for solar panels (installed).

Preliminary Ranking of Stoves at Wood Stove Decathlon as of Sunday, Nov. 17

The Wood Stove Decathlon judges and technicians have completed one round of emissions and efficiency on 8 out of 12 of the stoves in the competition. Each stove will have at least two tests and the results will be averaged. (See our previous post explaining how the stoves in the competition are scored.) If time permits, the judges may decide to do a different type of test using a cold start to measure start-up emissions on the stoves in contention for first place.

As of 4:00 PM Sunday 11/17, the number one stove for low emissions is the Mulciber stove by the University of Maryland.  The number one stove for high efficiency is the Wittus Twinfire.  The full rankings are:

Emissions                               
1. Un. of Maryland      
2. Woodstock Soapstone              
3. Intercontinental      
4. Wittus Twinfire          
5. Travis Cape Cod                
6. Ecolabel Tile Stove              
7. Hwam
8. SmartStove
9. Tulikivi
10. Kimberly
11. Intensifire
12. Walker

Efficiency
1. Wittus Twinfire
2. Ecolabel Tile Stove
3. University of Maryland
4. Tulikivi
5. Woodstock Soapstone
6. Travis Cape Cod
7. Intercontinental
8. Hwam
9. Intensifire
10. Walker
11. SmartStove
12. Kimberly

Meet the Contestants; The Cape Cod

With the first Wood Stove Decathlon only a couple months away, we are doing a weekly blog post to showcase the Decathlon competitors. Take this opportunity to learn more about the design teams and their stove’s innovative features. 

The Cape Cod is a powerhouse stove, weighing in at almost 600 pounds with a 3 cubic foot firebox. The Cape Cod has been officially certified by the EPA as a clean-burning large freestanding wood stove. Running at over 80% efficiency and with only .45 grams of emissions per hour, the Cape Cod produces an incredibly clean burn. This clean burn comes from the combination of Lopi’s advanced secondary combustion system along with catalytic assist to create the unique Hybrid-Fyre™ technology that makes this stove run so efficiently. 

President of Travis Industries, Kurt Rumens, along with Cape Cod designer, Alan Atemboski, created the Cape Cod with the mindset to develop the future of wood stoves. With the industry always progressing, they wanted to set Travis Industries apart with a product that would create a new standard in wood stove design, something that had not been done before. They figured out a balance between the secondary combustion and catalytic systems so that when combined, it created the best of both technologies. The hybrid of emissions produces the cleanest burn, giving it the name Hybrid-Fyre™. With over two years of extensive research and practice, they developed the clean-burning large freestanding wood stove registered by the EPA, and in December of 2012 the Lopi Cape Cod was born. 

The Cape Cod comes with several quality features, but one that makes it more efficient is the GreenStart igniter system. This new system allows the Cape Cod to be started in seconds with the push of a button. 

So far, the Cape Cod has been a success with its extreme efficiency, powerful heat output and sleek cast iron design. It has been named the winner of three prestigious Vesta Awards, including Best New Wood Stove, Best of Show- Hearth Product, and the Green Award. 

From modest beginning of its first wood stove built in 1979, Travis Industries is now the largest privately-owned wood, pellet and gas stove, insert and fireplace company in America, producing high-quality American-made products. 

We are looking forward to seeing the Cape Cod in action at the Wood Stove Decathlon November 16-19, 2013. Vote for your favorite stove at Popular Mechanics. 

Meet the Contestants; Firemaster

With the first Wood Stove Decathlon only a few months away, we are doing a weekly blog post to showcase the Decathlon competitors. Take this opportunity to learn more about the teams and their stove’s innovative features.

Jason Stewart is bringing a stove to the Decathlon with a new feature that he thinks can help clean up thousands of older stoves. The IntensiFire is a down draft insert that can be retrofitted to nearly any wood stove. The down draft redirects unburned gases back into the hot coal bed, to reignite and save heat. This also makes more efficient use of the fuel. And, a more complete combustion of the smoke also helps to reduce emissions by burning smoke particulates that otherwise would have been released into the atmosphere.

The insert is much cheaper to manufacture and to install compared to the price of a complete wood stove. Its versatility to be retrofitted to multiple styles of wood stoves makes the Intensifire a viable option in many situations.

Stewart found himself in such a situation with an old wood stove that supposedly was to heat his rental home. The old clunker smoked badly, with wasted heat rising up the flue. The landlord wouldn’t replace it and Stewart was not allowed to make any major modifications. With some tinkering, Stewart simply extended the flue into the firebox to create a down draft. It worked so well, Stewart was able to increase up to 60% of the old stove’s heat efficiency. The success of his invention surprised perhaps even himself, and Stewart decided to pause his pursuit of an Architecture Degree and start the IntensiFire business.

Several models later, Stewart is gearing up for the Decathlon and expanding his market to the United States. This further extends Stewart’s commitment to protecting the environment. In 2009, he sailed around New Zealand as a volunteer on Earthrace, a boat run on biodiesel, to highlight important environmental issues. The next year, he once again boarded Earthrace, renamed Ady Gil, to oppose Japanese whaling.

The biggest issue opposing Stewart now is the financial costs to attend the Decathlon. Stewart must ship himself and his IntensiFire from New Zealand to Washington DC.  If you are able to help Stewart reach his goals, he can be contacted here.

We are looking forward to seeing IntensiFire in action at the Wood Stove Decathlon November 16-19, 2013. Vote for your favorite stove at Popular Mechanics.

NYSERDA provides funding for Wood Stove Design Challenge

The New York State Energy Research and Development Authority (NYSERDA) has awarded nearly $50,000 to support the technical aspects of the Wood Stove Design Challenge, contest officials have announced.

The purpose of the contest, which is run by the Alliance for Green Heat, is to inspire engineers and manufacturers to create more efficient wood stoves, which can produce more heat with reduced emissions.

Funding from NYSERDA, which will go towards technical support and operations costs, comes from the Biomass Heating R&D Program, which takes a comprehensive approach to developing a high efficiency and low emissions biomass heating industry.

NYSERDA works with manufacturers, universities, engineering firms, research institutions, and federal and private labs to improve wood combustion designs and conduct third party evaluations. Additionally, NYSERDA supports studies to investigate the air quality and public health impacts of wood combustion.

Much of the technical preparation for the Wood Stove Design Challenge will happen at the Brookhaven National Laboratory, where NYSERDA funding will enable testing and calibration of the test equipment and the fueling protocols. Dr. Thomas Butcher and his team will be testing portable emission analyzers next to a dilution tunnel to determine their applicability for on-site testing at the National Mall in Washington D.C. in November.

Biomass heating has increased over the past decade as the price of home heating oil has increased. But much of that increase comes from older, less efficient wood burning technologies that can cause high wood smoke concentrations, especially in rural valley communities.

The Wood Stove Design Challenge is using cordwood to test the stoves, so it’s representative of how the stoves are used in homes. Traditionally, stoves have been tested with 2 x 4s in an attempt to maximize consistency and replication of the results.

The grand prize winner will receive a $25,000 cash prize. Between two and five prizes for second place will share a $10,000 pot. Awards will be based primarily on such attributes as innovation, emissions, efficiency, affordability and most consumer friendly. Prize money was raised through various private sponsors.

The winning stoves will receive extensive publicity, and Popular Mechanics, who helped design the Challenge, will cover the winning designs in its magazine and website.

Prof. Hopke Becomes Judge of Wood Stove Design Challenge

Professor Philip Hopke, of Clarkson University, has become the 10th judge of the Wood Stove Design Challenge. Dr. Hopke is the Bayard D. Clarkson Distinguished Professor at Clarkson, the Director of the Center for Air Resources Engineering and Science (CARES), and the Director of the Institute for a Sustainable Environment (ISE).

For the past 5 years, he has been actively studying solid fuel combustion systems with an emphasis on emissions and efficiency. “We can take advantage of our large wood resources if it can be burned more cleanly,” Prof. Hopke said. Clarkson University is located in northern New York, surrounded by communities that heavily rely on wood and pellet heating.

As a Jefferson Science Fellow at the U.S. Department of State in 2008-09, he advised the Department on strategies to support the development of cleaner wood cook stoves in the developing world. In that capacity, he also worked with Prof. Kirk Smith of University of California Berkeley who is also a judge in the Wood Stove Design Challenge.

Dr. Hopke is also the past Chair of EPA’s Clean Air Scientific Advisory Committee (CASAC), and has served on the EPA Science Advisory Board (SAB).

Professor Hopke received his B.S. in Chemistry from Trinity College (Hartford) and his M.A. Ph.D. degrees in chemistry from Princeton University and had a post-doctoral appointment at M.I.T

For more information on the Wood Stove Design Challenge and the judges, click here: http://www.forgreenheat.org/stovedesign/judges.html