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.
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| 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.
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| 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.
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.
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Russian Thermoelectric Wood Stove
(not certified for sale in the U.S.)
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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.
[1]
The cost of a thermoelectric module has fallen below $2 per watt (uninstalled),
compared with $3.50 per watt for solar panels (installed).
