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).

Fourth Wood Stove Competition to focus on automation and electricity generation

Today, the Alliance for Green Heat announced the fourth Wood Stove Design Challenge, returning to

Wittus, the winning team in the 2018
Wood Stove Design Challenge

the National Mall in Washington, DC in November 2018.

[For winners and results of the event, click here.]

The 2018 event will be free and open to the public and includes rigorous testing of the next generation of technology that can make wood stoves consistently cleaner, more efficient, easier to use and, like solar energy, a renewable source of electricity.

The fourth Wood Stove Design Challenge is modeled after the Department of Energy’s (DOE’s) Solar Decathlon, a competition between teams from universities worldwide to design more efficient and cheaper residential solar power.  Like the Solar Decathlon, the Wood Stove Challenge also attracts teams from around the world and focuses energy and resources on innovation and improved performance.  The stove competitions have been in partnership with the DOE Brookhaven National Lab, the New York State Energy Research and Development Administration (NYSERDA), the US Forest Service and others, the Osprey Foundation, among others. 

Participants will compete in two events:  One is to automate the wood stove with 21^st century technology like sensors and WIFI-enabled controls that improve combustion efficiency, reduce air pollution and improve ease of use.   The second competition will focus on thermoelectric wood stoves that generate electricity to power lights, cell phones, and WIFI-enabled controls. Thermoelectric generators are similar to solar PV systems except they turn heat instead of light into electricity.  When integrated with a residential solar PV system, a thermoelectric wood stove and battery power system, like the TESLA Powerwall, could effectively double the wintertime output of solar PV system in areas like northern United States, Canada and northern Europe.

Wood stoves are still used by 30 – 60% of homes in hundreds of rural and suburban counties around the country.  Yet, the technology revolution that has swept household appliances in the last 20 years has by-passed wood stove technology. 

Teams in the 2018 stove challenge will be competing for up to $50,000 in prizes.  The teams and exhibitors will also have a chance to showcase new technology on the National Mall just blocks away from the Department of Energy, the US Department of Agriculture and the Environmental Protection Agency. 

“This is a chance for students, back yard inventors, and wood stove manufacturers to re-invent this age-old technology for today’s environmentally conscious and time-conscious consumer,” said John Ackerly, founder of the Wood Stove Competition and President of the Alliance for Green Heat.  “An affordable, smart wood stove is achievable and could help millions of families reduce their reliance on gas and oil while significantly reducing  pollution,” Ackerly added.

“This is the first Wood Stove Challenge to promote wood stoves that generate electricity to power everything from a cell phone to an entire home.  Thermoelectric wood stoves, when integrated with solar PV systems and home batteries like the TESLA Powerwall, have the potential to make solar energy more affordable, reduce air pollution, and pave the way for a more sustainable energy future, “according to Ken Adler, Senior Technology Advisor at the Alliance for Green Heat and formerly with the U.S. EPA.

Previous Stove Design Challenges brought innovative stoves and a diverse array of stove and energy experts together on the National Mall in 2013, Brookhaven National Lab in 2014 and 2016.

Further details about participating and competing in this competition will be available late March, 2017. For more information about the  2018 competition, contact John Ackerly at jackery@forgreenheat.org. 

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The Alliance for Green Heat promotes modern wood and pellet heating systems as a low-carbon, sustainable and affordable energy solution. The Alliance works to advance cleaner and more efficient residential heating technology and hosts international stove design competitions to accelerate innovative stove technology.  Founded in Maryland in 2009, the Alliance is an independent non-profit organization and is tax-exempt under section 501c3 of the tax code.

Final Report on Wood Stove Decathlon from Brookhaven Lab

Reproduced below are the absract and introduction of a 17-page paper that gives an excellent overview of the technical aspects of testing stoves on the National Mall for the Wood Stove Decathlon, held in November 2013.  To read the entire report, click here.

Innovative fine particulate measurement systems for the Wood Stove Design Challenge 

R. Trojanowski1, T. Butcher1, C. Brown1, G. Wei1, Y. Ahn2 , and J. Wong2 

1. Energy Conversion Group, Brookhaven National Laboratory, Upton, New York, USA 

2. Chemical and Molecular Engineering Department, Stony Brook University, Stony Brook, New York, USA 

ABSTRACT 

The rising price of fossil resources has contributed to the increase in the amount of wood-fired residential heating appliances. Wood stoves are often overlooked by the public as a clean and renewable source due to concerns about particulate (PM) emissions. In order to gain acceptance in the market the Alliance for Green Heat and

Popular Mechanics magazine initiated a Wood Stove Design Challenge (WSDC). The selected teams designed stoves that incorporated the best practices in design and operation to maximize efficiency and minimize PM and carbon monoxide (CO) emissions since most often high emissions are seen as a result of incomplete combustion. Further, a testing protocol for the challenge was developed specifically to measure the emissions in a non-laboratory setting. Standard testing procedures may not be representative of in-use fuel and operational practices and, due to the competition venue and schedule contstraints, could not be used for the WSDC. New portable PM sampling technology released in the European market recently was adopted for the competition and evaluated to current U.S. PM measurement methods to build a correlation. 

INTRODUCTION

Tom Butcher uses the Wohler portable
particulate sampler to test a stove.

 As the price of heating oil has increased, more residents in the northeastern region of the United States have returned to heating with wood. Most existing wood stoves date from before the Environmental Protection Agency (EPA) implemented emission certification requirements for these devices. These less efficient wood stoves often cause high amounts of smoke, yielding particulates known to trigger coughs, throat and mucosal irritation, acute respiratory infections, occurrence of asthma and other diseases over prolonged exposure. A review from Bølling et al. reported residential wood combustion has also been reported to contribute significantly to raised levels of air pollution locally, both with respect to increased levels of fine particles (particulate matter with an equivalent aerodynamic diameter < 2.5 μm; PM2.5), the organic particle fraction, particle bound polycyclic aromatic hydrocarbons (PAH) and volatile organic compounds. Even those wood stoves that do meet EPA’s Phase II requirements may have unacceptably high emissions once in use. This is due to several factors including the design of the appliance, weather patterns and location, combustion activity, wood species and quality, and operator habits. While the EPA is developing new regulations, the test method used for certification is not representative of in-use fueling and operational practices. 

Designs that improve combustion and emission performance, thermal efficiency, and operational  

The Decathlon tent on the National
Mall, in between the Capitol and
the Washington monument

variability are needed in the U.S. heating market. Modern wood stoves have shown reduced reported emission factors compared to conventional wood stoves, 34-330 mg/MJ from 50-2100 mg/MJ, respectively. However, if the modern stoves are not operated correctly the combustion performance can be compromised yielding higher emissions.

This event showcased advanced technologies that could help address the problem of increased particulate emissions and enable the continued use of wood as a renewable fuel. The teams selected came from various backgrounds, ranging from established wood stove companies to independent inventors and engineering student teams. Some of the stoves selected for the WSDC were controlled by microprocessors and connected to smartphones while others were ultra-efficient stoves based on 17th century Scandinavian designs. Several state-of-the-art hybrid stoves that are already on the market were also included4. Six of the 12 finalists were from Europe. 

Teams were judged on their innovation, emission and efficiency performance, affordability and consumer ease. In November 2013 on the National Mall in Washington D.C., ten judges (made up of leading experts from Popular Mechanics, the New York State Energy and Research Development Authority (NYSERDA), the U.S. Forest Service, Washington State Department of Ecology, DOE’s Brookhaven National Laboratory (BNL), The Biomass Thermal Energy Council (BTEC), the Osprey Foundation, the Masonry Heater Association and UC Berkeley) tested and assessed the 12 stove finalists and announced an overall winner as well as winners in specific categories. 

A key challenge in this competition was measuring the particulate emissions accurately in a field environment. This project sought to develop an energy efficiency and emissions testing protocol for the WSDC which reduces the variability due to fuel and operations. The current standard test method (EPA Method 28) involves testing stoves using a dilution tunnel. Since the WSDC was held at the mall in Washington D.C., this test method would not suit and so there was the challenge of measuring the emissions in a repeatable real-time way, in a non-laboratory environment. Recently, new portable particulate measurement systems have been introduced in Europe for field inspection of biomass heating systems. Two specific products were selected for use in this project the Testo 380 and Wöhler SM 500. Both analyzers are a low cost option and offer the advantage of ease and portability. 

To determine the accuracy, precision, instrument range, and applicability for use in the WSDC for thermal efficiency and emissions of these portable direct measure analyzers, an evaluation was conducted while simultaneously following the standard methods for determining the emissions.  From laboratory testing, BNL developed a testing protocol implementing the analyzers for the competition.

To read the entire PDF report, click here.

For more information about the 2013 Decathlon, click here.

For information about the 2014 Collaborative Stove Design Workshop, click here.

NYSERDA Provides Grant to Develop Automated Wood Stove

In an effort to bring more automation to the wood stove, New York State Energy Research and Development Authority (NYSERDA) is providing a $49,000 grant to support the Alliance for Green Heat to test and work towards improving automated wood stove designs.

The project will bring some of the world’s leading automated stoves and prototypes to Brookhaven National Lab in November to test their performance and assess which designs hold the most promise in smoke reduction, reliability and consumer demand.  Seven companies with different approaches to automation are competing in the event.

John Rhodes, CEO of NYSERDA
announcing Renewable Heat NY
funding in August 2014

 NYSERDA support is part of Governor Cuomo’s Renewable Heat NY initiative, which encourages the expansion of sustainable markets in New York State for high-performance wood-fired heating technology and encourages the use of renewable biomass fuel, such as cord wood and wood pellets. NYSERDA has become the largest supporter of research on residential wood and pellet heating technology in the U.S. 

This project, called the Collaborative Stove Design Workshop, is a follow-on to the successful Wood Stove Decathlon on the National Mall in November 2013 that was also supported by NYSERDA.  Unlike the Decathlon, which was a more formal technology competition, this Workshop will bring a variety of experts together to study and help improve the automated designs, some of which may be open sourced so anyone can build from them.

“A wood stove is only as good as its operator and its fuel,” said John Ackerly, President of the Alliance for Green Heat (AGH).  Automation can eliminate the widespread problem of operators who don’t give their stoves enough air at the right times, leading to excessive smoke in rural communities, suburban neighborhoods and towns.  It can also mitigate the problem of using unseasoned wood. “Pellet stove technology represents the biggest breakthrough in residential wood heating in the past quarter century but we believe more breakthroughs are possible,” Ackerly said.

The Organizing Committee that oversees the project consists of John Ackerly, Alliance for Green Heat; Ellen Burkhard, NYSERDA; Tom Butcher, Brookhaven National Lab; Craig Issod, founder of Hearth.com; Mark Knaebe, US Forest Service; Ben Myren, Myren Consulting; Norbert Senf, Masonry Heater Association; Dean Still, Aprovecho Research Center; Rod Tinnemore, Washington Department of Ecology; and Rebecca Trojanowski, Brookhaven National Lab. Additional funding comes from the Osprey Foundation and the US Forest Service.

Applications to attend and take part in the workshop are being accepted until September 1.

Testing Observations at the Wood Stove Decathlon

By Norbert Senf

The Wood Stove Decathlon was a historic event. It was the first ever attempt to gather a collection of stoves in the field (literally, in this case) and test them for particulate matter (PM) emissions.

Norbert Senf, right, with Neils Wittus,
center, and John Ackerly

For something untried until now, the side-by-side field-testing can claim several firsts. 

It successfully compared stoves within a surprising range of categories including masonry heaters as well as retrofit kits. The project was a success not only as a media event but also in advancing the real world testing of wood burning stoves.

Cordwood is an extremely complicated fuel to get repeatable data with because it is so inherently variable. To add to the challenge, PM is particularly difficult to measure, even in a laboratory. While the test results from the Decathlon were not sufficient to provide PM numbers that allowed comparison with EPA numbers, they did allow a ranking of the stoves against each other. This is a substantial achievement in itself.

PM is the wood fuel pollutant of greatest interest since it causes the most public health concerns. Carbon monoxide (CO) is another pollutant.  It is created by incomplete combustion like PM, but it is much easier to measure. It is generally not considered a health hazard in low atmospheric concentrations outside of densely trafficked urban areas, and eventually oxidizes to CO2 on its own.

Due to new wood burning emissions regulations in Germany, two new portable instruments for measuring PM in the field were recently developed there. Fortunately, this happened just in time for the Decathlon to try them out. The instruments are limited to the 15-minute test cycle that is mandated in the German regulation, and therefore can only measure what happens during a portion of the burn. Measuring an entire test cycle will certainly be a goal for future Decathlons.

Common wisdom holds that low carbon monoxide (CO) emissions, which are easy to measure, will also ensure low PM, which is difficult to measure. The contest results did not bear this out. The stove with the lowest PM had the second highest CO. For the stove with the lowest CO, there were 4 stoves with lower PM. To be sure, the data set is limited. The 15-minute test window did not allow for average values to be measured over the burn of an entire fuel load.

Repeatability is one of the most important measures of data quality. Since each stove in the Decathlon received two (in theory) identical test runs, we can get a brief glimpse here, as well. Discarding obvious outliers, we see a coefficient of variation (CV) in repeat runs of 43% on PM, 40% on CO and 7% on efficiency. This compares favorably with EPA inter-laboratory repeatability studies, where the two stoves with the largest data sets both came in at 44% CV on PM. For masonry heaters, an MHA (Masonry Heater Association) laboratory study on repeatability with dimensional lumber fuel cribs yielded 10% CV on PM, 1.5% on CO, and 0.26% on efficiency.

The repeatability metric provides a useful baseline for judging data quality in future decathlons. There is an ongoing fueling protocol debate in the testing community between the repeatability achievable with fuel cribs, and the real world randomness of cordwood. EPA testing is currently done with cribs. To get a repeatable EPA cordwood number may require running a large number of (expensive) laboratory test runs and taking an average. To date, very little work has been done to provide data for either side of the debate.

All in all, the Wood Stove Decathlon was a great effort towards advancing our knowledge about how wood stove emissions compare in the real world. This was particularly valuable to see for different classes of appliances with no commonly defined EPA testing methods.

Valuable lessons and insights were had for designing a future challenge. Seeing the complex testing issues play out in real life was a unique educational opportunity for contestants, organizers, judges, regulators and the testing community itself.

Norbert Senf was one of the ten judges at the Wood Stove Decathlon. He joined early efforts to write codes and standards, and was a founding member of the Masonry Heater Association of North America (MHA). He currently chairs the MHA Technical Committee.

The Costs of Running the Wood Stove Design Challenge

From inception, to announcement, to selecting the teams, to holding the Wood Stove Decathlon, the Wood Stove Design Challenge unfolded over a 2-year period.  The total cost came to about $200,000 over those 2 years, and $157,000 of that was in 2013.

In 2013, the Wood Stove Design Challenge cost about $157,000 in direct cash expenses.  In addition, tangible, in-kind donations that we would have otherwise had to pay for accounted for more than $50,000.  The largest budget items were salaries ($39,000), the tent ($33,000), prize money ($30,000) and testing ($23,000).

Overall, our largest funders were NYSERDA ($47,000), the Osprey Foundation ($40,000), and the District of Columbia ($10,000).  In addition, we had extremely large in-kind support from ICC Chimney, which was probably in the $20,000 range, the Chimney Safety Institute of America, the mobile particulate sampling companies Wohler and Testo, Brookhaven National Lab, Popular Mechanics, Travis Industries and others.

One reason the Alliance was able to hold this competition for a total cost of $200,000 is that salaries were low, and we kept many expenses to a bare minimum.  If the Alliance were to do another similar Design Challenge, we would have to plan for a total of about $300,000 over a two year period, and use at least $200,000 of that for the year of the event.

2013 Decathlon Costs Salaries  (Jan. 1 - Nov. 30, 2013)
President (50%)	$23,000
Research Fellow	$3,200
Research Fellow	$1,875
Web/IT	$1,000
WSDC assistant  (50%)	$6,000
Taxes, benefits & payroll (50%)	$4,500
Sub-total	$39,575
Prizes
First prize	$25,000
Second prize	$5,000
Sub-total	$30,000
Contractors
Brookhaven National Lab	$23,000
Media consultant	$2,500
Sub-total	$25,500
Event costs
NPS cost recovery deposit	$1,800
NPS police	$2,244
Tent, generator, tables, chairs, etc.	$33,117
Portable restrooms	$535
Signs	$690
Add’l liability insurance	$809
Lunches/food	$950
Local Travel	$200
Judges hotel	$2,300
Transport	$1,500
U-Haul Rental & scaffolding	$680
Misc. event supplies	$3,500
Sub-total	$48,325
Other costs
Jan. Brookhaven Judges Meeting	$3,000
Supplies	$1,000
Copying/printing	$600
Rent, phones, etc. (50%)	$7,450
Misc.	$1,600
Sub-total	$13,650
Total 2013  Decathlon expenses	$157,050