Wood stoves are not generally considered to be at the cutting-edge of renewable energy technology, but they remain a major part of the household energy landscape, particularly in rural communities. The Energy Information Administration reports that 12.7 million homes rely on wood for primary and secondary heating in the United States, and this includes 30 to 60 percent of homes in hundreds of rural counties, according to the Alliance for Green Heat. The recently concluded Wood Stove Design Challenge (November 9 – 13) showed how wood stoves can indeed provide renewable, clean, and affordable heat – and energy – in homes.
At the Wood Stove Design Challenge, ten teams showcased their latest advancements in wood stove technology, particularly in the areas of automation and renewable electricity generation. These new advancements in wood stove technology will enable more efficient designs that improve air quality and lower greenhouse gas emissions compared to older stoves. Additionally, design improvements are helping to mitigate some of the dangers associated with wood stoves as they become a more attractive source of heat and ancillary power in homes across the United States.
Though humans have been using wood as a fuel for thousands of years, there is still room for improvement in stove efficiency, design, and integration with emerging smart home technologies. Advancements that lower the cost of owning, operating and maintaining wood stoves are especially important to making highly efficient wood stoves more widely available to users. Over 23 million households in rural areas face some form of energy insecurity, such as being unable to use heating equipment or having to reduce food and medicine purchases to afford energy bills.
The Wood Stove Design Challenge was established by the Department of Energy (DOE) and organized by the Alliance for Green Heat to encourage technological innovation in the industry. Ten teams from around the world installed their wood stove models on the National Mall for the duration of the challenge and tested their performance in two categories: automation and thermoelectric generation. These stoves represent some of the best efforts by educational institutions and private companies to create more efficient and more intuitive products.
Winners of this year’s competition were announced on Tuesday, November 13, as the competition came to a close. First place in both categories was awarded to the thermoelectric E-Stove from Wittus-Fire by Design, a New York-based company that distributes the German-made stoves in the United States. The Alliance for Green Heat highlighted the stove’s “great performance on emissions, efficiency and safety.” Its electrical output was also noteworthy, reaching 250 watts with wood logs and over 300 watts when fueled by densified wood logs. Wittus’ E-Stove operates with a combustion efficiency of over 90 percent and employs wood gasification to produce energy: wood is cooked in a low-oxygen environment inside the stove to convert it to combustible gases which are then ignited in a separate chamber.
The Wiseway Stove, designed by Hi-Z Technology and Northwestern University, won second place in the thermoelectric category, producing 100 watts. Canadian company Stove Builders International (SBI) won second place in the automation category as well as the “Innovation Prize.” The design from Idaho-based 509 Fabrications won the “People’s Choice Award.”
Generating Power with Thermoelectric Wood Stoves
In addition to the space-heating and water-heating that a normal stove can provide, thermoelectric wood stoves are able to generate electricity. Electricity produced by thermoelectric wood stoves can be integrated into a home’s broader power system to power appliances, lights, or battery banks. Back-up power sources like this can be especially useful for homeowners during the winter months, when renewable electricity generation is at its lowest. A wood stove burning throughout the year will provide a consistent base of electricity and on some days could produce numerous times more than what residential solar panels offer. Additionally, it opens up the option for homes in colder climates to be “off grid” more regularly.
Burning fuel inside the stove creates a distribution of heat, and thermoelectric generators (TEGs) installed within the stove use the temperature differential across their conductive components to create an electric current. This is known as the Seebeck effect and allows heat from burning wood to be transformed into usable electricity. TEGs do not utilize moving parts like turbines as would be used in a large-scale hydropower or coal-fired plant and are thus more reliable – a plus for households that use wood stoves.
Several of the stoves at the 2018 Wood Stove Design Challenge demonstrated lighting up sets of lights. Thermoelectric stoves are a far more predictable and consistent source of electricity than solar or wind for homeowners interested in generating their own.
Addressing Air Quality Issues
Air quality is a major concern in wood stove design because wood combustion can release dangerous particulate matter and gases into the atmosphere and into confined spaces in homes. The Environmental Protection Agency (EPA) estimated in 2010 that over 6 million wood stoves failed to meet EPA requirements and were producing 86 percent of all wood stove emissions in the United States. Inhaling the small particles released through combustion can cause bronchitis, asthma, lung cancer, and cardiovascular diseases. In certain communities or regions where a stable layer of cold air often forms near the ground (known as a thermal inversion) and can prevent particulate matter from dissipating into the atmosphere, this hazardous material can reach dangerous concentrations.
Replacing older, less efficient wood stoves with those that burn cleaner is crucial to reducing emissions and lessening health risks. In partnership with the EPA, the nonprofit trade association Hearth, Patio, and Barbecue Association (HPBA) provides support to local organizations and agencies to establish woodstove changeout programs. These programs offer funding to homeowners to install replacement stoves that meet the EPA’s new emissions criteria and provide educational opportunities to highlight the programs. Lower-income homeowners, who might otherwise not be able to afford to purchase a new stove, benefit especially from such programs. Schott, a company that produces heat-resistant glass for fireplaces, estimates that replacing one inefficient wood stove is equivalent to removing five diesel trucks from the road.
Different types of fuel can be used in wood stoves and offer cleaner alternatives to natural wood, such as pellets or wood bricks. Traditional logs must be fully dried and properly burned to avoid incomplete combustion. When this is not achieved, considerably higher levels of deadly carbon monoxide can be released into a home. According to the EPA, carbon monoxide from heating appliances poisons and kills over 150 people each year.
Wood pellets (and larger wood bricks) serve as a drier and more intense combustion material; they burn more cleanly than cord wood. These products are created by compressing sawdust, wood shavings, or other lumber wastes. Additional types of pellet fuel are created from other forms of biomass. Particular stoves are designed to handle particular fuel sources, however, so purchasing stoves that can utilize these cleaner fuels will help to reduce health risks in the home.
Author: Patrick Teese
- November 9-13 Design Competition to Showcase Wood Stove Advancements, EESI
- Power Generation, Thermoelect GmbH
- Brief History of Thermoelectrics, Caltech Materials Science
- Stove Teams, Alliance for Green Heat
- Wood Smoke and Your Health, EPA
- Alliance for Green Heat (Facebook)
- Why Get Behind Wood Stove Changeout Programs?, Schott Robax
- Wood Smoke and Your Health, EPA
- Carbon Monoxide Poisoning, Iowa State University Department of Agricultural and Biosystems Engineering