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Raphaël

(1)

Hey!
Great topic! It reminded me of the Peltier effect that was a fad in CPU cooling back in the day.
I'm wondering: could thermoelectric modules be useful if placed between a CPU and its heatsink? Like producing some of the power needed by a Raspberry Pi ? It seems those can be burning hot (but not cooking hot yet!)

M@trixX

(2)

I like the idea, but I wouldn't consider thermoelectric generators as a replacement for photovoltaic but more as a supplement to it. I'm from central Europe and the heating is in use for 6-8 months a year and not entirely regularly in spring and fall, so TEGs could cover maybe half a year. The rest - sunny days and most of summer - could be easily and practically covered by PV.
While cooking on fire makes sense during the cold winter days when one is also heating the space, it has an obvious disadvantage in summer: It heats up the interior people want to keep cool. Also, it takes up a lot of time to heat up and cool down the stove, so the interior is warmed much longer than it would be by stove that can be rapidly turned on and off like gas or electric induction.
This would be obviously different for different locations and the biomass-burning-only solution with TEGs would be perfectly adequate for subarctic climates, but it would supply too much heat and too little electricity in tropical latitudes. There, PVs are clearly better choice - doubly so, when they are used to run air conditioners peaking during the sunniest hours.
TEGs are amazing and maintenance-free, but their low efficiency limits them to rather low-power applications. If a reasonably insulated building is considered, the need for heat is relatively lower than the need for electricity even in colder climates, so scaling the heating up to provide more electricity wouldn't make sense. There might be a solution: a stirling engine. It has moving parts, so it would require some maintenance, but it could provide more electricity with less heat. Maybe something worth investigating for another article?

Rafael Carrascosa

(3)

Thanks Kris, big fan of your articles here.
Afaik TEGs do not use the electromagnetic spectrum to operate, are you sure they do?
Regards,

Rafael

Kris De Decker

(4)

Thanks Rafael. I took the sentence out.

Fred Smith

(5)

If I were to build a new home, or retrofit my existing one, I would install some version of a rocket mass heater; as it is my understanding based on my extensive research that rocket mass stoves or heaters are the most efficient wood-fired heaters, using the least amount of solid fuel. Plus they are cheap and easy to build. Of course many building codes and/or insurance companies will not approve their installation or insure against them.

Simeon Hope

(6)

Once again, this site presents some gadget as a means to avoid the reality of our high energy consumption and the political and economic changes that are required to avoid the worst of the climate disaster. All we have to do is scale this up in our imaginations and consider the consequences.

"Throughout history, the burning of wood and other biomass provided households with thermal energy" while denuding the environment of trees. During the Bronze Age in the UK, vast areas of forest were chopped down for fuel and to clear land for farming. The past is not necessarily where we should be heading.

There are nearly 68 million people in the UK. If everyone switched to wood as a fuel for home energy, where would it come from? As the recent film Planet of the Humans points out, biomass a.k.a. dead trees is not a renewable resource by any means, even though the EU classifies it as such. The USA exports much of that biomass to Europe.

"UK-based researchers found last year that burning wood is a “disaster” for climate change because older trees release large amounts of carbon when they are burned and aren’t always replaced with replanted forests. Even when trees are replaced, it can take up to 100 years to cultivate a wooded area that soaks up as much carbon as was previously released. And the fuel burned in shipping wood pellets to Europe is also a significant source of emissions."
https://www.theguardian.com/environment/2018/jun/30/wood-pellets-biomass-environmental-impact

"According to the American Lung Association, wood-burning stoves produce harmful toxins that can damage your lungs and increase the risk of cancer, heart disease, and premature death. The fumes from wood-burning stoves are especially dangerous if you have a respiratory condition, such as asthma."
https://www.verywellhealth.com/the-health-hazards-of-wood-burning-stoves-914956

"The flipside is that wood fires produce vast quantities of particulate matter, tiny fragments of soot like those emitted by diesel cars. These contribute to climate change but can also cause breathing problems or even cancer in humans. In urban areas particularly, wood-burning stoves are therefore not the greenest choice."
https://www.sciencefocus.com/planet-earth/are-wood-burning-stoves-environmentally-friendly/

kris de decker

(7)

@ Simeon

First of all, please tell me where in the article do I argue to "scale this up". The reality is that at least 40% of the global population is using biomass for cooking, water heating, space heating, and/or illumination. Adding thermoelectric generators to these existing fires would actually decrease firewood consumption and air pollution, because it allows to use electric fans that increase combustion efficiency.

The deforestation in the past had little to do with people cooking their food. Rather, it was the consequence of industrial processes (such as glass and iron production) and the search for building materials, mostly for battleships. Check out "A Forest Journey" by John Perlin.

Whether or not biomass is sustainable is all a matter of scale. If the wood for a stove comes from nearby and is harvested by the one who uses it -- the default mode in the pre-industrial household -- it is without doubt the most sustainable source of thermal energy. If biomass is traded internationally, harvested with big machines, and for profit, it is destructive. In fact, anything that is incorporated into a capitalist mindset becomes destructive.

Planet of Humans is a very inaccurate movie. Although I agree with much of the criticism on renewable energy sources, the arguments and data are often wrong.

Concerning air pollution: you are conflating two distinct concepts: health and sustainability. What's healthy is not necessarily sustainable, and the other way around.

David Bourguignon

(8)

Thanks for this interesting historical paper Mr De Decker. This system, however relevant in some situations, does not seem to be taking into account present day constraints. It is worth remembering indeed that:

1) Bioenergy requires land and water (lots of it). In fact, the physics of bioenergy production (average annual yield provided by a Fraunhofer/Chalmers study referenced in https://www.solarthermalworld.org/news/solar-thermal-shows-highest-energy-yield-square-metre) is:
Solar thermal: 150 kWhth/m²
Photovoltaics: 59.5 kWhel/m²
Biomass: 3.5 kWhth/m²

2) Burning biomasse emits GHG. The consequences of neglecting GHG emissions due to biomass burning during a climate crisis is an issue, in particular for very long recapture time (typically, with trees way more than 50 years, some research considering > 100 years). In fact, there is a current debate around this, and biomass could soon no longer be consider carbon neutral, see:
https://news.mongabay.com/2018/05/un-forest-accounting-loophole-allows-co2-underreporting-by-eu-uk-us/
https://news.mongabay.com/2019/06/carbon-to-burn-uk-net-zero-emissions-pledge-undermined-by-biomass-energy/
https://news.mongabay.com/2019/12/cop25-eu-officials-say-biomass-burning-policy-to-come-under-critical-review/

Thanks in advance for your attention.

kris de decker

(9)

Thanks, David. You're making the same argument as Simeon, so I can only repeat what I said in comment #7.

David Bourguignon

(10)

Dear Kris, I get your point fully, but I think the paragraph you wrote as an answer to Simeon and myself is missing from your article. In particular, I did not get the point regarding improved combustion using an electric fan, but it makes a lot of sense. Thanks for emphasising this.

By adding this paragraph, in my humble opinion, your article will benefit from a broader contextualisation (both historical, social, ecological, etc.) because many readers might have a tendency to over-generalise "solutions" very quickly and this shallow thinking, in addition to industrialism, may also be the root cause of problems mentioned in the Planet of Humans' documentary.

I agree, there is definitely no one-size-fits-all energy system, even though big market players promote standardised approaches a bit too often. My 2 cents: current industrial biomass approaches will hit a wall in the coming years because they ignore climate and ecosystem constraints and end up destroying the planetary life-support system. And the poorest people currently relying on biomass simply for cooking will suffer first from this situation.

kris de decker

(11)

@ David

I think it is clear enough that I'm looking at the technology in the context of the 40% of the global population that relies on biomass already (most of them in "developing" countries). The importance of the electric fan in lowering firewood use and air pollution is also clearly stated.

The points you and others make about the sustainability of biomass are valid, but it's an issue that can't be dealt with in an extra paragraph. That's why I kept it short. It deserves its own article, which I am writing now.

David Bourguignon

(12)

Thanks a lot Kris for your feedback. I am looking forward to reading your new article!

gareth

(13)

Two things about this

1) There are a lot of people literally burning sticks they pick up off the side of the road or animal dung. They are going to burn these things anyway, if all this did was provide combustion air and improve efficiency a lot of the issues around particulates and efficiencies are dramatically improved (also lessening the time to collect).

2) Common experience shows that in high energy use households such as the west, once a meter with a number goes on the wall (or an app on your phone) telling you what you are using, what surplus you have etc, it becomes a game and people generally start paying a lot of attention to use and usage patterns.

In order to consider a lot of the problems and impacts in this space requires thinking 2,3 sometimes 4 or more levels deep, simplistic thinking will not provide the analysis required to understand the possibilities.

Jay Vaughan

(14)

I have a small garden in which I can grow multiple plants that will provide a regular source for my local needs .. from hedge to hazelnut and apple tree and even a bamboo grove. Once you stop living so 'big', you can also moderate your needs and manage resources rather than necessitate consumption at scale. Most of the energy produced is used, just to get the energy system working. Local energy means less effort. As a gardener, I applaud this application of an age-old resource, near endless in supply: our Sun. Why not get a little help from healthy plants and things to solve our ills?

kris de decker

(15)

@ gareth

I don't understand what you mean (none of both "things"). Could you be more clear?

gareth

(16)

Once the burning occurs anyway, may as well take some higher order energy from the heat (with TEG) and use it to improve efficiency of the burning, or charge phones, make light for homework whatever.

Regardless, the burning is probably not going away any time soon, so previous comments about doing that might be well intentioned, but only an end goal, still need to do the steps along the way to get there, this might be one of the first ones.

People who install grid connect solar electric all of a sudden become aware of what they are using, and whether it is " free" power or not and adjust their habits, often treating it like a game.

This has become evidenced because a lot of the battery installs that went in to households and thought were going to be too small, have worked out fine, because people changed their habits.

Once something like electricity consumption/production is easily measured and known people pay more attention to it.

gareth

(17)

Coming back to this, TEG is a mature but very niche technology often used at remote locations where hydrocarbons are available - eg offshore oil/gas platforms, pipeline RTU/SCADA/valve stations, and even nav lights (eg unmanned lighthouse beacons) with refueling required to a tank.

Companies like ecogenthermoelectric in Russia and Global Thermoelectric Generators in US are almost exclusively focused on TEG.

These type of applications typically burn liquid or gas fuel to make hot internals at 350-550 DegC and heatsink to atmosphere for cold, 4-1000W in unit sizes, installations of 5000W are not unheard off.

The main selling point in these applications is they are almost totally maintenance free and therefore lifecycle cost over 25 years beats all other options, plus can be used without batteries due to constant generation, assuming fuel available.

Often TEG is used offshore on unmanned platforms to maintain the 24VDC system for nav lights and other essentials, untended.

Also volkswagon had an experimental car with TEG on the extractors, got rid of the alternator and had some fairly significant economy improvements (can't remember the number but remembering thinking it was well worth it at the time, better than getting rid of wing mirrors).

There are definitely niches where the TEG technology is viable today and if production is able to be ramped up or simplified by scales of economy, or a few percent extra efficiency comes as a breakthrough, I predict we will only see more of them around in a similar but less spectacular way than solar has grown.

kris de decker

(18)

Discussion at hackernews: https://news.ycombinator.com/item?id=23348578

'Deepak'

(19)

This is 'Deepak' writing to you, i am a German engineer, involved in renewable energy projects in India and Nepal.

ARTI-India, Appropriate Rural Technology Institute (Pune)
www.Samuchit.com
has developed a fabulous pyrolysis/ gasifier high efficient (cooking) stove: 'Sampada'

https://images.app.goo.gl/aJE5YQhWmciqPmkz9


No fan required and high combustion temperature ==> no smoke; it is sold in India for less than 3000 Indian Rupees, ~ 35€.
A very good device, which can also be used to incinerate trash, for example plastic waste:

https://m.youtube.com/watch?v=KEtqBiUvK1c

The Sampada Gasifier Stove is made by Samuchit Enviro Tech in Pune ...
https://images.app.goo.gl/tD7yQMZ9PCzpHEVX7


The thermoelectric effect could also be incorporated and this 'Sampada'.


Biogas...if biogas is converted into electric power per combusting engine motor, there is always an excess of heat, which cannot be used. Another perfect use for TEG elements.
Great work, you do!
Your truly big fan, during this lockdown, from Nepal, watching the 8000m+ Annapurna range.
Yours, 'Deepak'

Tony-the-tiger

(20)

Excellent article. Obviously, this is a small scale technology. Useful for providing small quantities of high value electricity where wood is used for space heating, water heating, or both. Especially useful where a grid connection is not available and you need 100W of dispatchable power for things like lighting. A lot of the comments about sustainability don't seem to me to be very valid. This is clearly not intended to be a solution for everyone. More a niche solution, for people that cannot draw kWs of power from the grid but have wood around them and need to keep a few lights going. Those people will be burning wood, or coal or animal faeces anyway and none of that is going to stop anytime soon. A thermo electric device allows them to get more out of the same input.

Sorin Trimbitas

(21)

Great article :D Thank you for it.

What, almost all people from hackernews, didn't understood is that you are not burning wood to get electricity but you get electricity as a by-product of your wood burning :)

Tom Antero

(22)

I have thought about harnessing my wood burning, water circulating oven to electric generation. 5 years ago I even ordered bunch of tecs to give them a try. energy generation was just as weak as was conveyed in this article.

From my experience, when it comes to energy-generation from oven, stirling engines are way to go. It can reach efficiency comparable to diesel engine. problem is that there´s no stirling engine designed and sold for that purpose. The economics just don´t make sense. Even on the darkest times in northern Finland, solar panels generate enough energy for my western comfort devices. Panels combined with hot water energy storage from oven, and lion batterypack are working too nicely for me to start developing oventop stirling generator.

toby

(23)

Here is an interesting article about themo-voltaics. This uses specially produced pv cells designed to harvest 'low' temerature infra-red photons.

https://www.pnas.org/content/116/31/15356#sec-4


Abstract
Thermophotovoltaic power conversion utilizes thermal radiation from a local heat source to generate electricity in a photovoltaic cell. It was shown in recent years that the addition of a highly reflective rear mirror to a solar cell maximizes the extraction of luminescence. This, in turn, boosts the voltage, enabling the creation of record-breaking solar efficiency. Now we report that the rear mirror can be used to create thermophotovoltaic systems with unprecedented high thermophotovoltaic efficiency. This mirror reflects low-energy infrared photons back into the heat source, recovering their energy. Therefore, the rear mirror serves a dual function; boosting the voltage and reusing infrared thermal photons. This allows the possibility of a practical >50% efficient thermophotovoltaic system. Based on this reflective rear mirror concept, we report a thermophotovoltaic efficiency of 29.1 ± 0.4% at an emitter temperature of 1,207 °C.

------------------------

This is like replacing the sun with a gas heater and then totally enclosing the heating-element (substitute sun) with pv cells and then enclosing this whole set up with mirrors to reflect back the lower wavelength photons back onto the heater.

Like a micro dyson-sphere enclosed in a mirror.

I wonder if you could use a system based on this with the cold side of the thermo-voltaic being used to heat water or an oven?

kris de decker

(24)

Discussion at Resilience: https://www.resilience.org/stories/2020-06-09/thermoelectric-stoves-ditch-the-solar-panels/

Marcos Buenijo

(25)

I wish to point out the rated conversion efficiency of a thermoelectric module does not imply 5% of the heat released by a furnace used to power these modules is converted to electricity. Of course, the figure applies only to the heat that actually moves through the modules.

For a typical installation, the proportion of the heat released by the furnace actually transferred to the hot side of these modules is appallingly low. For this reason, most applications will see extremely low net conversion efficiencies - quite literally on the order of a small fraction of 1%.

kris de decker

(26)

@ Marcos

Obviously. But now you pretend that the stove is used only for electricity production. That is not the concept.

The stove is already being used for cooking, heating and/or lighting. Adding one or more thermoelectric modules simply adds some electricity to that output.

Lighting up a thermoelectric stove only to produce electricity would be a very inefficient way of using resources.

Noel Putaansuu

(27)

This article is on point for the subject matter. We are researching these TEGs in use with our smoke measurement instrumentation. We find that a wood stove stack and TEG can generate enough to power some sensors. It helps to not run wires along a hot sheet metal pipe. One to 2 net watts is not something most people get interested in, however, modern sensors and micro controllers can work with this power level. For more information our website is www.smokelesschimney.com

Randy Berg

(28)

"If a module is only 5% efficient in converting heat into electricity, the other 95% comes out as heat again." ... "With appropriate stove design, the heat from electricity conversion can also be re-used for cooking or domestic water heating."

While the above statements are true the actual amount of electricity produced is very small. The hot side of the module must be within it's capabilities and the cold side of the module must be at a hot enough temperature for effective hot water heating. All of this reduces the module's temperature difference hence it's efficiency.

hugh sheehy

(29)

The emissions from wood stoves are a disaster.

Arturs

(30)

It would be more beneficial to run a steam turbine of a stove or use gasification and run an ICE generator instead. It would add complexity to the build. Jet with electricity one can harvest 3x more heat or more depending on the source temperature. At minimum using electricity for computing, it would turn in to heat anyway. So basically using the same energy twice!

Himbeerkuchen

(31)

Tile ovens are not as popular as they once were (e.g. in the 1800s), yet many people (in moderate and colder climate zones) in the west still associate them with comfort and coziness. I imagine there might be a case for a TEM ceramic tile module to convert an existing tile oven to an energy-generating one. The outside of the tiles could be finned or otherwise structured to encourage air flow, while they should probably have a surface glaze and glaze color that maximizes infrared emission. Each tile might incorporate a small electronics module so that you can easily interconnect them. Hmm... should I start a small business?

Olivier Hannoun

(32)

Any thoughts on using TEG modules not with fire but with hot water generated from solar thermal panels?

kris de decker

(33)

@ Olivier

That's not going to work unless you use ice for the cold side of the module. The temperature of water cannot surpass 100 degrees while thermoelectric modules need a large temperature difference to produce electricity.

Pekka

(34)

@Raphaël

This is the Peltier effect. What the author is talking about are what the PC modding scene used to call peltier coolers. However, rather than using electricity to generate a temperature differential they're using a temperature differential to generate electricity.

Janine Mesu

(35)

@34 so, using the Peltier-element backwards....

Martin

(36)

I really enjoy the concept of your blog, with this topic and especially with your argumentation I do not agree. You can not dismiss the critics by arguing that the biomass and resulting heat energy is used anyways, so there is no reason to care for efficiency.

Specifically in your outlined scenarios the people use the stove mainly for cooking not for heating their house in their hot climate. And even if they do, most of the energy gets wasted through the chimney and poor insulation.

If you add complexity and investment in an established system you are solidifying the underlying technology and change will occure even more difficult. That is exactly not intentional. There is good reason to bring the missing 40% of people also the opportunity to live without gathering and burning carbon sources and increase their total energy efficiency of their lifestyle. With millions of burning stoves you reach the same "glass ceiling" like millions combustion cars reach. They will never be as efficient because they constantly need fuel that you need to gather and waste energy through their small scale. So in mid-term perspective I see that minimal efficiency increase from these electric elements counterproductive because the sustainable fixing of the energy problem gets delayed.

kris de decker

(37)

Hi Martin,

Thanks for your comment and of course we can disagree. However, because I received other comments that make more or less the same arguments, I have decided to address them extensively in a new article, which should be online later this month.

Meanwhile, I would like to ask you what is your alternative? I have posed the same question to some critics at Hackernews and all I got as an answer was a "large central non combustion power plant that doesn't emit air pollution or carbon". Sounds great, but what energy source does it run on?

Martin

(38)

Hi Kris,
thanks for the reply and the detailed question. I orient myself on some ongoing developments. At first, there are of course these big central power plant projects like the huge ethiopian river dam project. Those projects have reasonable critics, and I am also questioning if such projects can serve the majority of people. So I would more focus on small scale grass roots movement. Something that your proposal meets as well. We can both agree that electricity is essential for development and value built-up. But big grids are commonly fragile for external disruptions whereas internal disruptions decrease. Also the public cost is huge for a big grid. Developing countries have big external disruptions and small budget. So even in cities, the grids are basic. I would suggest that the grid is more compartmentalized and stabilized by individual power storage/supply technology. In some regions it might be better to store the energy in the individual mobility devices, essentially in lithium batteries, in some regions it might be better to produce from trash some fuels. Maybe even biogas is an option.
Power production mainly through solar effects like thermal, wind, photovoltaic (all locally small scale).
From that basis there will be potential for investement in local bigger power production, like a solar heat farm for bigger manufacturers.

Martin

(39)

For those who wonder why solar before renewable resources? Because renewable resources have four major disadvantages. 1. You need to gather those physical fuels, transport them, store them. Either it takes time from you to collect everyday or you need to invest in storage, protection,...
2. In most parts of the world even those seemingly redundant fuels, like sticks or scrub or animal manure are a limited ressource. It just works with a small volume rate and following very timely and locally limited usage (nobody would fire the whole day a bigger place). The interchangeability of energy forms is very limited (in efficient manner). Our economical system has done a huge shift from mechanical power to electrical power. If you want to buy any machine, device, tool, there will always be an electrical version available.
3. You produce even though there is some theoretical zero emission balance many unhealthy gases in the house but also in the environment, because particles are distributed.
4. The total efficiency will in most cases rise if you shift from burning things to producing electricity and heat right out of the sunlight and its results. Just if that free fuel is missing you should count on relatively clean alternatives which result in more power conversions and losses. Even heat production can be more efficient either by direct sunlight collection or by heat exchangers (they are not a crazy complex device to be unsuitable for most countries).

All these technologies can be part of a different low tech future with less power conversion (sun-plant-fire-mechanical power-heat/electricity-mechanical power), less losses, simpler problems (reduced widespread effects like deforestation, dependencies, emissions), less use of materials (fuel is material), better readaptation with the environment. Even if it means to have some high tech devices (repairable,recycleable).

Martin

(40)

Ah I am not good at making a point. Here condensed:
1. difference between physical and "non physical" energy source
2. limited availability of energy source and "resulting energy form" usage devices
3. widespread (not concentrated like a photovoltaic production plant) environmental damage through millions of inefficient energy production processes
4. major efficiency increase only by sun/electrically possible as a result of point 1 and 3.

kris de decker

(41)

@ Martin, and others

Here's my answer to the sustainability of wood production: https://www.lowtechmagazine.com/2020/09/how-to-make-biomass-energy-sustainable-again.html

Rob

(42)

@kris
Thank you for showcasing this possibility for improvement. I am wondering if anyone has thought of using TEG tech with a rocket mass heater as promoted by Paul Wheaton. The RMH is designed to burn sticks about the diameter of your thumb. Sticks burn at about 800 degrees f., as opposed to firewood that burns at about 600 degrees f.
People in Europe used to manage coppiced woodlands that gave them all of the sticks they needed to make heat and to cook with. Perhaps the old ways are still the best. Using a RMH with coppiced wood will be more efficient than cutting trees and splitting it for heat (at a lower burning temp). I like the fact that TEG is not limited by weather events or sun/no sun limits. Also of note the RMH does not emit smoke like a conventional fireplace or woodstove. Due to superior design this stove actually burns the smoke before it is discharged. This advantage eliminates the previous "emissions disaster" concerns entirely.

Darkest Yorkshire

(43)

One of the interesting things about a stove generating electricity is it could charge the battery of an electric fire lighter. That can then light the stove the next time it's needed, breaking the dependence on matches or other lighters.

Kevin

(44)

While glad you mention the backpackers cook stove, there are commercially available modules in the United States that produce up to 100 watts on a wood stove. This can be great in an Alaskan Cabin where there is a wood stove and little sun all winter. It can also lower the need for batteries at night in an off grid electric system. The most popular application to date seems to be the small fans that circulate heat around the cabin, now available for <$40 USD. It should be pointed out that commercially available modules are sold at max power output, but realistically wood stoves are not run at highest heat all the time. For a while the a device called the Devil Watt that produced 100 watts for with an $800USD device. (I am unsure of current availability.) These devices have also been used to pump hot water around a cabin greatly increasing comfort. This small amount of power is easily enough to light several LED lights bulbs around a home and power small electronics.
https://www.tegmart.com/

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