What New Wood Stove Technology Would You Like To See?

[SpaceBus]

If TEGs ever improve they would be right at home on an appliance like a woodstove, especially a cookstove.

 

[jetsam]

There are commercial products right now that deliver useful amounts of power from a stovetop, but they can cost as much as the stove. (Also, we're talking 100w, not 10kw.)

It sounds better than it actually is,, too.. So let's say you set up a 100w liquid cooled TEG- already more complexity than most people can handle. Now you have peak 100w@12vDC. So you probably want 120vAC... and you quickly find that 100w is somewhere between 0 and 100w depending on stove output. So now you have an inverter and a deep cycle battery and a charge controller.... which is actually a pretty useful setup, but again, way more complexity than most people will be willing to take on.

 

[SpaceBus]

There are commercial products right now that deliver useful amounts of power from a stovetop, but they can cost as much as the stove. (Also, we're talking 100w, not 10kw.)

It sounds better than it actually is,, too.. So let's say you set up a 100w liquid cooled TEG- already more complexity than most people can handle. Now you have peak 100w@12vDC. So you probably want 120vAC... and you quickly find that 100w is somewhere between 0 and 100w depending on stove output. So now you have an inverter and a deep cycle battery and a charge controller.... which is actually a pretty useful setup, but again, way more complexity than most people will be willing to take on.

An air cooled TEG capable of even 25-50 watts would probably push this into the realm of practicality. That could trickle charge a solar battery bank since most of the time the stove is hot the solar panels are dark. Solar with batteries would already have the inverter and other parts. Something that could sit under the firebox in the bottom drawer of my cookstove would be pretty cool since it's not hot enough down there to require the water cooling and I can't really use that space since a bit of ash falls in when I open the loading door. Sometimes I proof bread quickly on the oven side. I would gladly sacrifice some space on the top of my Morso to generate that much power. We only use a few Kw per day, and more use in the summer than winter.

 

[TradEddie]

I just wish my stove had a finer adjustment of air supply. A separate fine tune knob that would replace that last 10% of damper adjustment. On my stove, that last 1/4" is the difference between a smouldering creosote factory and an inferno. When properly set, it's a dream.

TE

 

[jetsam]

An air cooled TEG capable of even 25-50 watts would probably push this into the realm of practicality. That could trickle charge a solar battery bank since most of the time the stove is hot the solar panels are dark. Solar with batteries would already have the inverter and other parts. I would gladly sacrifice some space on the top of my Morso to generate that much power.

https://www.tegmart.com/thermoelectric-generators/wood-stove-air-cooled-45w-teg

A deep cycle battery runs $100-$200, a small charge controller is $25ish, and then you need an inverter to run off the battery ($25-$500 depending on what you need). So you could do it without a solar setup. But you do need a ventilated place to permanently store a big battery or two. Could drill a hole in the floor and put them in the basement.

 

[SpaceBus]

https://www.tegmart.com/thermoelectric-generators/wood-stove-air-cooled-45w-teg

A deep cycle battery runs $100-$200, a small charge controller is $25ish, and then you need an inverter to run off the battery ($25-$500 depending on what you need). So you could do it without a solar setup.

Wow, I didn't realize they had become so advanced. Too bad the documentation is so minimal. I'm curious about how much power is developed at what temperature.

 

[jetsam]

Wow, I didn't realize they had become so advanced. Too bad the documentation is so minimal. I'm curious about how much power is developed at what temperature.

Well... that is well documented on the TEG datasheets, which are public and free, but commercial product makers don't tend to get so detailed. Even if you got them to disclose which TEG modules their products use and pulled the datasheets, you'd be less well informed than you might imagine. The reason is that power generation depends on the temperature differential between the hot side and the cold side. So the heat applied is one part, but the cooling on the other side is just as important. (This is why the bigger units are all liquid cooled.)

Anyway, all that means that unless the manufacturer gives you some real world test info that shows how their heat sink and fans cool the cold side of the TEG, you will be able to guess what hot side temps will be in actual usage, but not cold side temps, and you need both to figure power output.

 

[SpaceBus]

Well... that is well documented on the TEG datasheets, which are public and free, but commercial product makers don't tend to get so detailed. Even if you got them to disclose which TEG modules their products use and pulled the datasheets, you'd be less well informed than you might imagine. The reason is that power generation depends on the temperature differential between the hot side and the cold side. So the heat applied is one part, but the cooling on the other side is just as important. (This is why the bigger units are all liquid cooled.)

Anyway, all that means that unless the manufacturer gives you some real world test info that shows how their heat sink and fans cool the cold side of the TEG, you will be able to guess what hot side temps will be in actual usage, but not cold side temps, and you need both to figure power output.

I'm just wondering what the "sweet spot" is for heat. My wood stove cruises around 700-750 on the stove top, but the warming drawer on my cookstove is much cooler. The candle powered TEG mentions it makes most power at room temperature, which is confusing since the candle is clearly hotter. Admittedly I don't know much about TEGs, and I also have no intent on buying one soon. I was just curious about this since it seems like TEGs have great potential in off grid scenarios.

 

[jetsam]

I'm just wondering what the "sweet spot" is for heat. My wood stove cruises around 700-750 on the stove top, but the warming drawer on my cookstove is much cooler. The candle powered TEG mentions it makes most power at room temperature, which is confusing since the candle is clearly hotter. Admittedly I don't know much about TEGs, and I also have no intent on buying one soon. I was just curious about this since it seems like TEGs have great potential in off grid scenarios.

Agreed, off-grid, you could have 20 or 80 watts of battery charging even when there was no sun or wind... but honestly, dollar per watt, you are better off just getting more batteries and more solar panels. Even small wind turbines are more practical. Also, those who don't cook on their stoves won't want to burn their wood stoves in July to get 80 watts of charge.

And all of the above require a battery bank to be practical. Battery banks require regular replacement (sure hope the grid doesn't go down so I can keep buying batteries so I can be off-grid!).

 

[SpaceBus]

Agreed, off-grid, you could have 20 or 80 watts of battery charging even when there was no sun or wind... but honestly, dollar per watt, you are better off just getting more batteries and more solar panels. Even small wind turbines are more practical. Also, those who don't cook on their stoves won't want to burn their wood stoves in July to get 80 watts of charge.

And all of the above require a battery bank to be practical. Battery banks require regular replacement (sure hope the grid doesn't go down so I can keep buying batteries so I can be off-grid!).

Valid points, definitely. Currently the TEGS are pretty spendy for the power generated. Maybe it's a technological dead end?

 

[jetsam]

Valid points, definitely. Currently the TEGS are pretty spendy for the power generated. Maybe it's a technological dead end?

Not at all! Almost every person who is using a stovetop "heat powered" fan is using a TEG. (Except for the rich guys, they have a Stirling engine that costs the same as the poor guy's stove.)

A TEG on a big heat sink also would make for a very practical stovetop light fixture, though I don't know if a plastic light bulb counts as a combustible for clearance purposes!

TEG modules are cheap enough that you can buy them to make stuff with (beware of sellers who think peltiers and TEGs are the same thing- they're not). You'll need some teg modules, some steel bar stock, some heat sink, some fans, some thermal transfer compound, and ICs to do whatever voltage conversion is needed for your application (and the fans).

One thing I ran into when I was playing with this is that max hot side temp on many TEG modules is lower than woodstove stovetop temps. My BK may usually be 300 degrees, but once in a while it's 800, and that is a big swing in hot side temps!

 

[Grizzerbear]

I wish their was as a efficient and safe way of reclaiming/storing all the heat that goes up the chimney without burning the house down. I mean a totally 100% efficient system.

Edit: not one of those redneck heat reclaimers either lol.

 

[andym]

One of the old posts mentioned the dream I have: a wood furnace, stove or boiler that nly requires a plastic exhaust and intake pipe. Imagine being able to place your wood stove anywhere with the only limit of being able to run 2 pvc pipes to it!
I also echo what others have mentioned about automation of air controls. That seems like a no-brainer to me.

 

[jetsam]

One of the old posts mentioned the dream I have: a wood furnace, stove or boiler that nly requires a plastic exhaust and intake pipe. Imagine being able to place your wood stove anywhere with the only limit of being able to run 2 pvc pipes to it!
I also echo what others have mentioned about automation of air controls. That seems like a no-brainer to me.

Automatic air is already here, both mechanical systems that have been around for decades (this is why Blaze King has such a large following here), and electronic ones that are just feeling their way into the market.

PVC vent pipes are possible but won't happen because of the cost (and size) of equipment. You could make an indoor wood gasification heater, but you'd end up with the filtration tanks outside, which in turn means an outdoor firebox where the wood goes in feeding an indoor woodgas stove, which should have the same venting requirements as a propane heater.

Gasification always falls down when you get to the practicalities of filtering the goo out of it. That's why the only wood-burning cars on the road are enthusiast vehicles.