By Ken Adler, AGH Senior Technical Advisor
Payback calculations are common in the residential solar photovoltaic industry where homeowners want to know how long it will take for them to recoup their initial investment. If you purchase panels outright, payback periods depend on a variety of factors including a utility’s price for electricity, tax incentives, and amount of daily sunlight hours. A range of 5 to 8 years is possible however, it can be as wide as 3 to 15 years.
Answering the payback question for thermoelectric wood stoves is one of the objectives for the 2018 Wood Stove Design Challenge. In the meantime, there are several ways to begin answering this question with information already available. It is also useful to look at how use of a thermoelectric wood stove in combination with another energy-saving system, i.e., solar, could prove beneficial to the homeowner and thus both industries as well. For example, in northern states and Canada, a thermoelectric wood stove could reduce the number of residential panels needed and thereby save the homeowner thousands of dollars in panel costs.
Early Thoughts on Payback
The retail price of a thermoelectric module is around $ 57.50 for a 22-watt module, or $ 2.61 per watt. One critical point to make here is that the power output of our 22-watt module assumes an optimal hot-side temperature of 300 C (572 F) and cool-side temperature of 30 C (86 F). This ideal temperature differential is very difficult to achieve in real world conditions, so the real-world cost per watt for thermoelectric modules will be higher. However, cost should decrease and efficiency improve with widespread adoption of thermoelectric modules, similar to what happened in the solar industry. For example, DOE estimated that the installed cost of a solar panel declined from $ 7.06 per watt in 2009 to $ 2.93 in 2016, a reduction of 60 percent. If we go back to 1977, the cost of a solar panel was $ 77 per watt. It is not unreasonable to expect a decline for the cost of thermoelectric modules as economies of scale reduce production costs.
Of course, when a thermoelectric module is placed into a wood stove there are other associated costs. The primary cost by far is the heat exchange system. As I’ve discussed in a previous post, to generate at least 100 watts of power, it’s likely that a water-cooled heat exchange will be needed. The current retail price for a 100-watt water cooled thermoelectric generator, which includes eight thermoelectric modules, is $ 599, or $ 5.99 per watt. One question the competition will attempt to answer is how much this heat exchange will cost when it is integrated into the design of the wood stove.
Secondary cost considerations include the price of the wood stove, its installation, and fuel costs. The price for a larger size 50,000 BTU wood stove can range from $ 900 to over $ 4000, and the average consumer spends about $ 2,500. Since a thermoelectric wood stove would be providing both heat and electricity, it is difficult to separate out how much of the cost of the stove is for each function. The more crucial point for now is that many larger size stoves, which can generate up to 50,000 BTUs and meet the 2020 EPA NSPS standard, are available for as little as $ 1,300. While this does not include the cost of installation, it does suggest that the wood stove portion of the costs should not be a major obstacle.
The cost of installing a thermoelectric wood stove into a home should not necessarily be that much greater than the cost of installing a traditional wood stove. One additional cost will be attaching the power outputs from the thermoelectric wood stove to an inverter. However, if we assume that early adopters will already have or are planning to get a solar PV system (more on this below) the cost of the inverter would not be a major obstacle.
Finally, one can assume that the fuel cost for a thermoelectric wood stove is essentially zero because the wood stove is already being used to heat the home. A thermoelectric module will convert only 3 to 6 percent of the heat from a woodstove into electricity, while the remaining 94 to 97 percent passes through the module and is released as heat into the home. In other words, the module is only using a very small percentage of the heat generated by the stove to produce electricity.
Value in Combining Technologies
While more in-depth analysis is needed, it’s possible that a thermoelectric wood stove could help reduce the size and cost of solar PV systems in northern climates that have limited sunlight/solar radiation in winter. For example, a typical 5000 watt solar PV system in Vermont produces 6,280 kWh of electricity per year, while the same system produces 7,913 kWh in Los Angeles. Most of this difference is due to the low winter time output in Vermont between October and February: For example, the Vermont system produces 239 kWh in December, as compared to the Los Angeles system’s 473 kWh. If the Vermont resident wanted to generate the same amount of power as in Los Angeles, they would need to increase the size of their solar PV system from 5000 watts to approximately 6300 watts. At the current cost of approximately $ 3.36 per watt installed for residential solar, this could cost the Vermont resident an additional $ 4,368 for additional solar panels.
Alternatively, instead of purchasing extra solar panels, the Vermont resident could invest in a thermoelectric wood stove to boost their winter time power output. As we mentioned in our previous blog, a wood stove with a 150 to 200-watt thermoelectric generator operating 16 – 20 hours per day could generate 93 to 124kWh of electricity per month, which would be a good boost to the Vermont output of 239 kWh in December. And, at 0.16 $ /kWh for electricity in Vermont, the thermoelectric wood stove could save the homeowner an additional $ 15 to $ 20 per month.
While a real payback calculation for a thermoelectric wood stove will need to wait until prototypes go through more testing and we get results from the 2018 Wood Stove Design Challenge, the available information suggests thermoelectric wood stoves could help reduce the cost of residential solar installations, and potentially save homeowners thousands of dollars.
 See our Resources page for a list of thermoelectric retailers.
 NREL. U.S. Solar Photovoltaic System Cost Benchmark. September 2016. In 1977, solar panels cost $ 77 per watt.
 NREL PVWatts Calculator
 EnergySage. Solar Marketplace Intel Report. April 2017.
by John Ackerly, President of the Alliance for Green Heat
reprinted from Biomass Magazine
Many in the biomass heating movement bemoan warm winters, low fossil fuel prices and the slow pace of conversions to biomass heating systems. But systems are being put in place to adopt renewable heating and that we can be part of, but we are not.
building or campus, it cannot use more energy than the renewable energy it generates.
Six of the nine retailers AGH contacted stopped advertising uncertified furnaces within two weeks
|Indoor furnaces are usually in the
basement, but can be in a garage. Either
option often leads to better fuel storage
practices than outdoor boilers and
greatly reduces jacket losses.
On May 15, 2017, EPA regulations took effect that required all wood furnaces to include smoke the law changed on May 15.
reduction technologies and be certified by third party test labs. Some furnace manufacturers started educating their retailers early and stopped shipping uncertified furnaces during the winter. Others continued to ship units, and many retailers continued to advertise and sell uncertified furnaces after
Indoor wood and coal furnaces—also called warm, hot air, or forced air furnaces—were very popular in the US through the early to mid-1900s, then gradually their lost market share as fossil liquid fuel furnaces gained traction in the late 1900s. Then, outdoor wood boilers gained favor, becoming a far worse threat to local air quality than indoor furnaces and boilers had been for decades.
The Alliance began contacting retailers advertising uncertified furnaces to find out whether they knew about the change in regulations and how responsive they would be to information about the change. “We believe that all manufacturers and retailers should play by the same rules, so that the ones who do follow the rules don’t get undercut by ones who do not,” said John Ackerly, President of the Alliance for Green Heat. “And, we found that many if not most retailers will stop advertising products that are not legal to sell if they are politely and professionally approached by an organization that is knowledgeable about the rules,” Ackerly said.
AGH Project Manager Melissa Bollman contacted nine retailers advertising uncertified furnaces. Of those, six stopped advertising those boilers within 2 weeks. Some of the furnaces were removed from the website entirely or are listed as unavailable, while other models that were previously advertised as capable of burning wood or coal have been rebranded as “coal only” to comply with EPA regulations. Currently, if a stove or boiler is advertised as being able to burn wood, it must be tested and certified to burn wood. (The EPA does not regulate coal heaters and some manufacturers have just added a grate and continue to sell the same unit as “coal only”.)
AGH efforts were not always effective, and a few retailers still appear to be advertising uncertified wood furnaces (see screenshots below). These include Sears’ online marketplace (orders fulfilled by the third party 123Stoves, Inc.), Homeclick, and HVAC direct. All screenshots were taken on June 22, 2017.
Houzz.com, Wayfair, and HVAC direct continue to sell uncertified wood furnaces or ones that are labeled wood/coal. The units they are selling are all made by US Stove Company, whose business model leaves it vulnerable to illegal sales of its units by multiple retailers.
AGH regularly monitors advertising by manufacturers and retailers in order to better educate consumers about misleading claims. We also publicize the names of manufacturers who provide better information and do not mislead consumers.
This continued advertising and sale of products that are no longer compliant highlights the danger that stranded inventory can pose for retailers when deadlines pass. If the 2020 emission rules are not delayed or changed, some wood stove retailers may get stuck with inventory that they are no longer allowed to sell, but are under pressure to unload to recoup their investment.
Without regulation, wood furnaces often sold for $ 1,000 – $ 2,000, less than many certified wood stoves. Even after the 2017 rules took effect, certified wood furnaces remain affordable with most selling for $ 2,100 to $ 3,200. Ten models are now certified, ranging from a more expensive European-designed pellet furnace at 89% efficiency to a very basic US Stove model 1330E that is 33% efficient.
However, the future of this class of wood heaters is far from secure, as EPA rules require wood furnaces to emit no more than 0.15 lbs/mmBtu as of 2020. Other than the European-designed pellet furnace, the other certified furnaces are not at all close to meeting that standard. Wood furnaces saw extremely little technological development until they were required to be certified between 2005 and 2017, and the sector is far behind the levels of controls that have been built into stoves and boilers.
By John Ackerly & Melissa Bollman
Alliance for Green Heat
This paper was prepared for the Warsaw Stove Summit which brought AGH and scores of experts in coal and wood heating from 19 countries to Poland in May 2017.
The US Census Bureau estimates that approximately 127,000 households used coal as a primary heating fuel in 2015, or about 0.1% of American homes. Residential coal heating dropped rapidly until 2000 and since then has been relatively stable.
More than half of homes using coal heat are concentrated in Pennsylvania and New York, right where it is mined. It appears to be based on cultural traditions and local support for local jobs because its still a very inexpensive way to heat and easy to transport. Most of the United States has no restrictions on coal heating and there have been few attempts to restrict it. Rather, it seems to have gradually died out except in pockets of states where anthracite is mined. Bituminous and sub-bituminous coal is much more widely dispersed but it is used far less than anthracite.
Coal stoves, particularly those fueled with anthracite coal that principally comes form Pennsylvania, typically have less particular matter than wood or possibly even pellet stoves. However, their health impacts may be far worse, as coal often emits high levels of SO2 and oxides from nitrogen. In addition, coal often has poisonous toxins such as flourine, arsenic, selenium, mercury and lead. For more on health impacts of coal and wood heating in the US and Europe, we excerpted key parts of a World Health Organization report here.
Who heats with coal and why?
Homes that heat with coal tend to be concentrated near anthracite coal mines and in homes with lower or mid level incomes. In the wealthier and more urban counties of Pennsylvania that are within 100 miles of anthracite mines, virtually no households heat with coal. High use of coal heat does not correlate with high use of wood heat. Both coal and wood are favored by rural, lower-income populations but coal appears to be favored near anthracite mines, and wood is favored in nearby, rural counties, according to data from the US census. The highest percentage of homes heating with coal at the county level is about 13%.
A prominent 2008 New York Times article reported that residential coal heating was on the rise, but rise was modest, and petered out a few years later. That rise corresponded with a major recession from 2007 – 2009 during which rates of wood heat soared far higher than coal. The New York Times also reported that an additional 80,000 homes use coal as a secondary heat source and the US Census reported 104,000 used it as a secondary heat source in 2005. Only 4,000 homes use it to cook with and 22,000 used it to heat domestic hot water in 2005, according to the US Census.
In 2015, the top five states for residential coal heating were Pennsylvania, New York, West Virginia, Kentucky, and Indiana. Over 50% of US homes that heat primarily with coal are located in Pennsylvania, where anthracite coal is mined.
The primary benefits of heating with coal, compared to wood, is 1. it burns for longer periods of time, so less reloading is needed and a home can easily stay warm overnight; 2. Like pellets, it can be delivered in bags on pallets by a forklift, and does not need the time consuming splitting, stacking and seasoning that cordwood needs; 3. It is even more inexpensive per BTU (assuming you don’t cut the wood yourself); and 4. It is a very dense fuel, and takes up half the space that the same amount of wood takes, per BTU.
The downside of heating with coal is 1. The odor, which most people find moderately unpleasant; 2. The black dust which is harder to clean than dirt and wood pieces from cordwood; and 3. Its hard to light, requiring most people to start the fire with wood, before switching to coal.
While the above pros and cons are widely agreed upon, other less tangible factors play a role. Coal has increasingly gained a stigma as a dirty, non-renewable fuel, whereas wood is regarded as far more environmentally friendly (even though particulate matter from wood can be equally high). On the other hand, the dwindling economic prospects of coal towns and counties tends to make those populations want to support the fuel to combat what they often see as an unfair bias against coal.
Coal and coal stoves
Coal stoves are either stokers or batch. Stokers automatically feed coal pellets (much like pellet stoves) into the stove, require electricity and only use anthracite. Batch stoves are loaded by hand and can take anthracite or bituminous.
Most coal used for heating in the US is anthracite but anecdotal estimates by experts say that no more than 25% is bituminous, primarily in areas where its abundant.
The EIA stopped collecting data on residential coal consumption in 2008. In 2007, the EIA reported that US residents consumed 353,000 short tons (320,171 metric tons) of coal, which represented only 0.03% of the nation’s annual coal use (1.1 billion short tons or around 1 billion metric tons). The overwhelming majority of course (93%) of US coal is used to generate electricity.
Usually coal is sold in 40 or 50 pound bags or by the ton. Coal may be sold directly to consumers from the mine, a fuel supplier, or a hardware store. Blaschak is one of the largest suppliers of bagged anthracite coal and sold 374,000 tons in 2014. Forty pound bags of anthracite coal (any size) from Pennsylvania usually run $ 6-$ 8. A ton of anthracite typically costs between $ 190 and $ 210 per ton, before delivery charges (which can increase price to $ 250-$ 300). One fuel seller, Central Maine Coal, sells about 200 short tons (181 metric tons) of residential coal per heating season.
Bituminous coal is usually considered a better coal for blacksmithing than heating, but can be burned in some coal stoves and is often only $ 80-$ 100 per ton.
Institutional heating with coal is somewhat relevant to residential coal heating and data indicates that institutional coal heating is declining much more rapidly that residential heating.
According to the EIA, US educational institutions consumed 700,000 short tons (634,900 metric tons) of coal in 2015, down from 2 million short tons (1.8 metric tons) in 2008. Twenty of the 57 US educational institutions that used coal in 2008 reported not using it 2015 due to sustainability initiatives. It is likely that most of the coal consumed at educational institutions is used to generate heat. Most US schools no longer heat with coal. Recent (2015-2016) news articles report that only five public schools heat with coal in West Virginia and four schools heat with coal in Cumberland, Maryland. One of the Maryland schools uses 517 tons of coal annually at a cost of $ 120 per ton.
Coal stove companies
Most coal stoves are made in Pennsylvania except for one big producer, Hitzer stoves located in eastern Indiana. Sales of coal stoves are reported to average 4,000 to 7,000 a year, but in 2008 they may have topped 10,000. In comparison, about 140,000 wood stoves are sold each year. There are about a dozen companies making coal stoves and one notable trend is that the larger wood stove companies are getting out of the coal stove business. Vermont Castings, Harman and Moreso used to sell coal stoves and now don’t. The one company that still focuses on both fuels is US Stove Company, based in Tennessee. Coal stoves cost about the same as wood stoves and range between $ 2,000 – $ 3,500.
Coal stoves remain exempt from EPA emission regulations. Coal stoves have never had a certification program at the EPA or at any state level, although the federal government and some states have indicated an interest in developing emission regulations. Regulation would likely drive up the cost of coal stoves and may reduce sales of coal stoves but other strategies may reduce their use faster and more economically. But without emission regulations, there is little data on coal stove emissions from various types of coal stoves, and there is little incentive for stove companies to try to produce cleaner stoves. Tests conducted in the 1980s suggested that wood stoves emitted higher levels of particulate matter than anthracite stoves, but lower levels than bituminous stoves (Houck, 2009). Of course, wood emits fewer other toxic chemicals than coal.
One significant policy change in 2015 was the ban on advertising dual coal/wood use in stoves unless the stove was certified with wood, and the company also tested for coal emissions and provided that data to the EPA. To our knowledge, no company has done this so no stove should advertise the ability to burn wood and coal any more.
The EPA is currently funding research on coal emissions and has developed an unofficial, draft test method at Robert Ferguson’s lab. However, this is being undertaken only because of an EPA program to change out coal stoves on the Navajo Indian reservation, not because it has any apparent mandate or serious plan to start regulating coal stoves.
It is unlikely under the Trump administration that any certification program would be initiated by the EPA, and the only state with enough coal stoves to justify the effort would be Pennsylvania, which is unlikely to do so.
Restrictions of the use of coal stoves
Unlike the United Kingdom, there has never been any national effort in the US to reduce reliance on coal stoves. Krakow, a major Polish city is banning coal stoves in 2019, after a multi-year effort to provide subsidies for alternative heating sources.
Two states – Washington and Oregon – effectively ban them because they only allow stoves that meet specific emission requirements, but those states would have very little coal heating anyway.
Many air districts that have poor air quality and high particulate matter levels employ temporary burn bans apply to coal stoves and well as wood stoves. A few jurisdictions, such as Fairbanks, Alaska, offer homeowners financial incentives to recycle their solid fuel burning appliance (including coal stoves) or replace it with a less polluting appliance (coal stoves are not eligible). However, most change out programs only remove old wood stoves and do not allow coal stoves to be replaced with wood stoves. A Pennsylvania county offered $ 200 to trade in old wood or coal stoves, but that program has been suspended.
Oregon is the only state where it is illegal to sell a coal stove, or any other uncertified solid fuel burning appliance. Oregon also requires uncertified solid fuel burning appliances, including coal stoves, to be removed and destroyed when a home is sold. According to the latest (2015) Census data, only 143 homes rely on coal for primary heat in Oregon.
At the local level, there may be a number of cities or counties that do not allow coal stoves, but the only one we could find is Summit County, Colorado that forbids the installation of a coal stove (uncertified solid fuel burning device) in a new home or as a replacement unit for an existing non-certified stove.
Dr. James Houck, “Let’s Not Forget Coal,” Hearth & Home Magazine, December 2009, pp.
World Health Organization, “Residential heating with wood and coal: Health impacts and policy options in Europe and North America,” 2015.
Tom Zeller, “Burning Coal at Home Is Making a Comeback,” New York Times, Dec. 26, 2008
|Alphabet Energy Thermoelectric Generator|
|60-Watt Water Cooled Thermoelectric Generator|
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.)
Living off the grid has its challenges, but having an alternative power sources has made our winters much brighter (pun intended). Do you generate power? What are some of the solutions that have worked for you? — Margy
Congratulations to Wayne and Margy on their thermoelectric wood stove. In a follow-up communication with Wayne, he reported that they are no longer using the system because the thermoelectric modules failed. Wayne doesn’t know why they failed, however, the most common reason for failure is overheating. The modules can also fail if Bellville washers are not used to allow the module to expand and contract during heating and cooling. Wayne also reports,
|A stove being tested at
Omni lab, where Jim
Houck used to work.
|Extensive round robin testing in Europe
coordinated by BeReal should expand our
understanding of repeatability.
Universities or labs could develop of a better test method, but stoves do not have the same level of R&D support from Congress, DOE or other potential major funders that other renewables have. In Europe, there is more public funding and the BeReal project is doing far more extensive round robin testing than what Houck describes in the US. Some agencies and groups prefer to see stove technology stagnate and have its market share wither, due to antipathy or ambivalence toward this complicated creature that can be affordable to homeowners but too often noxious to neighbors.
|Ben Myren, owner of one of the EPA
approved test labs, is a leader in
developing cord wood testing. Here
he starts a cord wood test at the 2013
Wood Stove Design Challenge.
A response from Scott Nichols on boiler repeatability
Scott Nichols, owner of Tarm Biomass that distributes European made boilers sent in a response to this blog and we reproduced it below. Scott is also on the Board of Advisors of the Alliance for Green Heat.
|Scott Nichols has been a leader in
installing modern, automated boilers
in institutions and homes in New England.
|The cleanest and most efficient
forced air furnace is the Maine
Energy System Auto Pellet Air.
It delivers 89% efficiency.
|The US Stove 8500 pellet
furnace is the least efficient
certified furnace at 48%, but sells
for less then $ 3,000.
furnaces is 66%.