Better to burn out
May 3, 2012 9:58 AM   Subscribe

A fan-forced rocket stove with an inbuilt thermoelectric generator that can charge your GPS as you cook a meal using a few handfuls of twigs for fuel: the BioLite camp stove (via Blue Economy, via Big Ideas, via ABC Radio National)
posted by flabdablet (82 comments total) 37 users marked this as a favorite

 
Very cool - preordered one for my earthquake kit.
posted by zeoslap at 10:06 AM on May 3, 2012


Cool, thanks for this! What powers the forced air fan? I don't see where that question is addressed.
posted by Daddy-O at 10:10 AM on May 3, 2012


Daddy-O, that's the thermoelectric module. From the Technology page: BioLite stoves solve this problem [lack of power to boost efficiency] by converting a fraction of the fire’s thermal energy into electricity to power our combustion improvement system.
posted by bonehead at 10:14 AM on May 3, 2012


If they made a mass-heater model for home heating and some electrical generation I'd order it today.
posted by The 10th Regiment of Foot at 10:15 AM on May 3, 2012


since you can easily spend $80 or more on a modern liquid fueled camp stove $129 aint bad
posted by Redhush at 10:19 AM on May 3, 2012


I have significant doubts.

Modern phones, GPS devices, etc. that use lithium-ion batteries actually have significant power capacities and use a lot of electricity. It takes a fairly non-trivial power generator to give them a meaningful charge. Something like this is going to be a drop in the bucket, unless it produces vastly more power than it appears to at first glance. You are better off with a solar panel, because it doesn't require tending. It's still drops in the bucket (even with a pretty significant panel) but those add up when you can leave the thing going all day.

Burning natural materials generally requires a significantly larger fire than this before the fire becomes stable and doesn't require constant attention just to keep it lit. I can't imagine this will be easy to keep burning. A few twigs like that just don't contain a lot of easily accessible energy, either. Either this will be burning a ton of them (and require constant tending) or it will be completely anemic.

Bottom line is, I can't imagine the power inputs can possibly equal the promised power outputs. If they got this thing to boil water without being ridiculously finicky and burning a ton of fuel I would be absolutely astonished, to say nothing of actually charging anything.
posted by Mitrovarr at 10:20 AM on May 3, 2012 [3 favorites]


If they made a mass-heater model for home heating and some electrical generation I'd order it today.

They seem to be working towards such a product.

They also offer some bafflegab on that page about regular wood stoves producing pollution and deforestation, but at the same time saying their product still uses 50% of the wood. It ain't no solar.
posted by fairmettle at 10:24 AM on May 3, 2012 [1 favorite]


This looks awesome but it's hard to trust people who can't toast a marshmallow properly.
posted by monkeymadness at 10:29 AM on May 3, 2012 [2 favorites]


You are better off with a solar panel, because it doesn't require tending.

Have you ever gone hiking?
posted by Threeway Handshake at 10:34 AM on May 3, 2012 [1 favorite]


Interestingly, there's a related project on Kickstarter that is almost concluded as of this writing (and has exceeded its goal). It's just a camping cookpot with a built-in thermo-electric generator.
posted by adamrice at 10:34 AM on May 3, 2012 [2 favorites]


If they got this thing to boil water without being ridiculously finicky and burning a ton of fuel I would be absolutely astonished

It's a rocket stove, not just a bunch of twigs in a tube. Have you ever used one?
posted by stbalbach at 10:36 AM on May 3, 2012 [2 favorites]


Modern phones, GPS devices, etc. that use lithium-ion batteries actually have significant power capacities and use a lot of electricity. It takes a fairly non-trivial power generator to give them a meaningful charge

Let's take the iPhone 4S, since it's got quite a beefy battery, almost certainly more than average, especially in the developing world. Its battery holds 5.3 Wh. The energy density of wood is 16.2 MJ/kg, or 4500 Wh/kg. Obviously this thing is far from perfectly efficient at converting the heat of combustion to electricity (and presumably most of the heat goes to cooking anyway), but if it can manage even 1% efficiency then it would not take an unreasonable amount of wood to charge a modern phone.

Burning natural materials generally requires a significantly larger fire than this before the fire becomes stable and doesn't require constant attention just to keep it lit. I can't imagine this will be easy to keep burning.

I assume that one of the benefits of the fan is that it makes the fire more self-sustaining.

Either this will be burning a ton of them (and require constant tending) or it will be completely anemic.

Small scale cooking usually requires constant tending anyway, so the added effort of adding fuel is not too significant.

I can't imagine the power inputs can possibly equal the promised power outputs

A standard iPhone charger outputs 5 W. Would you care to elaborate on why that seems unreasonable?
posted by jedicus at 10:38 AM on May 3, 2012 [1 favorite]


They seem to be working towards such a product.

That seems to be more designed with a cooking focus. Something like a more transportable version of this with a slick built-in thermoelectric would be super-awesome. But, no, it ain't no solar, especially $1-a-watt solar.
posted by The 10th Regiment of Foot at 10:39 AM on May 3, 2012


I have significant doubts.

Yeah. If there was any kind of information about how many ma this thing put out and how long it burns a single load of fuel, it would help. You can get little solar chargers that will, in theory, charge devices but at such a low amperage that they're next to worthless. For the same extra weight and cost that the generator adds to the stove, I suspect most people would be better off with one of the high capacity battery packs that put out USB power.
posted by Candleman at 10:40 AM on May 3, 2012


jedicus: A standard iPhone charger outputs 5 W. Would you care to elaborate on why that seems unreasonable?

I've worked with small solar panels, wind turbines, etc. designed for camping. They are hilariously inadequate to charge anything but the smallest, lowest-power device, and even for that they are finicky. Now you take this thing - it burns fuel, which is a good sign, but thermoelectric generators are pathetic, so that's ominous. Plus, the fuel it burns is neither high-energy, consistent, or reliable in either energy content or structure, so you know it almost has to be fairly inefficient. I'm not running numbers or anything, but it seems incredibly unlikely to work in my opinion.
posted by Mitrovarr at 10:47 AM on May 3, 2012


I have a back-packing stove made in the '70's that uses forced air from a PC fan and a C-battery. It is a marvel. Boil some tea water with 5 fir cones in 5 minutes. Stuff doesn't even need to be dry once you get it going. I don't think they make them anymore. This thing is much more sophisticated, and expensive, with the charging system.
posted by Mei's lost sandal at 10:48 AM on May 3, 2012 [1 favorite]


Yeah... show me some statistics about how much wood and how much time is actually required for a realistic task like boiling water for coffee and charging a dead iPhone. Also, I would like to know how much this thing weighs and whether or not it will fall apart the first time I drop it.
posted by Scientist at 10:48 AM on May 3, 2012 [1 favorite]


Same thing without the charging. I've heard it puts out a huge amount of heat/flame. Just throwing that out there.

On preview Mei's lost sandal, is this it?
posted by RolandOfEld at 10:49 AM on May 3, 2012 [1 favorite]


Here is something similar:
Zen stove

posted by Mei's lost sandal at 10:50 AM on May 3, 2012 [2 favorites]


Heh. Beat me to it.
posted by Mei's lost sandal at 10:50 AM on May 3, 2012


Also, keep in mind that twig-collecting and especially stripping wood from standing trees is a violation of leave-no-trace ethics, although obviously this is only a concern in extremely high-use or low-growth areas.
posted by Mitrovarr at 10:53 AM on May 3, 2012 [5 favorites]


The stove technology is real. The design looks sound based on the research I've done over the past couple years. There is a shit ton of energy in the fuel. A TE module works off differential heat and there's hundreds of degrees of differential available here. The device can blow air over its own cooling fins. Honestly it would be hard for this to NOT work just like they say it does.

Also if you look at the "home stove" links on their site, they've done a bunch of field trials with a bigger version that looks really nice. (And the photos show a number of different test units.)

I would prefer a video and a teardown showing all the bits before I order, personally, but right now my bullshit meter is hovering right around 0.25 on a scale of 10.
posted by seanmpuckett at 10:54 AM on May 3, 2012 [2 favorites]


Well, I guess it's twig-collecting versus petroleum collecting?
posted by Mei's lost sandal at 10:54 AM on May 3, 2012


The power output is the problem here. A hiker would use such a stove for a few minutes at a time, 10 or perhaps 20. One of the goals of using such stoves is to minimize fuel use compared to an open campfire.

I can't imagine that's enough time to charge a phone, running one of these stoves for a few hours. The stove technology is fine, I just can't see the thermo-electric generator producing enough power to be useful. Keep in mind that they're only 5% or so efficient.
posted by bonehead at 10:57 AM on May 3, 2012


My guess is that it will work pretty well, but that it'll burn twigs like crazy, and will be hard to keep fed for long enough to charge a phone. It'll probably take two hours of near-constant tending to get a phone fully charged. It's better than NO charger, but I think it'll be a very high-attention device.

I haven't really examined it to check the idea for safety, but it might work better if you were to stick it in the edge of a regular, large campfire. That should still give it the heat to run the generator, without needing constant fuel loading.
posted by Malor at 10:58 AM on May 3, 2012 [1 favorite]


Burning the thing for 2 hours to charge your phone could be a drag.
posted by Mei's lost sandal at 10:58 AM on May 3, 2012


You know, a "charging stick", that you just stick into a fire, with a USB port on one end, might work pretty well. But now that I think about it, I'm not sure how much heat these things need -- maybe they're doing the forced air thing because that's the only way to get the flame hot enough?
posted by Malor at 11:00 AM on May 3, 2012



Burning the thing for 2 hours to charge your phone could be a drag.


well, yes, but on the other hand, if you're out in the middle of nowhere, with no other source of power, and you NEED to make a phone call (assuming cell service, but that's another issue), this could be a lifesaver, even if you had to tend the fire for a few hours.
posted by HuronBob at 11:01 AM on May 3, 2012 [1 favorite]


I've been on the pre-order list since they started offering it a year ago. The last word I heard was "ready for the 2012 camping season", which is about now. I'm still waiting :(
posted by Popular Ethics at 11:08 AM on May 3, 2012 [1 favorite]


I'd imagine the electronic charging feature works in a similar way that a solar system works: the energy trickles into a battery for storage and then that battery, once full, has enough energy in it to charge an iphone or similar small device. So it's not a real-time transfer of energy from flame to phone. If you were out for a week-long camping trip, you'd be filling up the on-board battery with each use and by the time your iphone was running low (you did remember to charge it before you left for the trip right?) you'd have enough power in the stove battery to charge your phone up.

Or do TE panels not work that way? I'm just guessing here based on experience with solar systems...
posted by jnnla at 11:09 AM on May 3, 2012


Also, keep in mind that twig-collecting and especially stripping wood from standing trees is a violation of leave-no-trace ethics, although obviously this is only a concern in extremely high-use or low-growth areas.

Well shit! I guess we all should just stay indoors.
posted by c13 at 11:09 AM on May 3, 2012 [2 favorites]


As a backpacker who frets over every ounce in his pack, I'd probably make a little room in the weight budget for this to replace my tin can rocket stove. Not that I'd be planning to charge my phone from empty to full in one go, but if I have to fire up my pack stove anyway to cook a meal, why not throw a little juice at the phone while I'm at it?

I leave my phone off while I'm camping/hiking, only turning it on for brief periods to check in. That kind of usage paired with a 10~20-minute topoff (with the phone off) every time I cook a meal... shoot, that'd be more than enough to keep my phone charged nearly indefinitely.
posted by xedrik at 11:09 AM on May 3, 2012 [3 favorites]


Seeing the quantity of fuel burned over time to make your device go would give some pretty good direct insight into what is happening behind the scenes to keep all our devices running.
posted by Mei's lost sandal at 11:10 AM on May 3, 2012


I notice they don't list any sort of amperage or wattage output of their thermoelectric generator.

However, as stoves go rocket stoves are amazing. They are far more advanced than an open pit campfire, or even some fueled stoves. They're incredibly efficient and basically operate on the same principles as a blowtorch. They're basically Venturi burners.

You literally can boil water in just a few minutes with a handful of twigs. Once they get going and properly tended they'll burn damn near anything short of sopping wet grass. Newspaper balls, pine cones, twigs, weeds, dried animal dung, pine needles, dried moss - damn near whatever you want.

Even without a forced air fan a rocket stove accelerates combustion by increasing draft and airflow through the combustion chamber, increasing available oxygen to the point that even light green wood can burn with almost no smoke and a whole lot of heat and efficiency.

The ash output of a properly designed and operated rocket stove tends to be super fine white powder "fly ash", even when burning something resinous like a dried pine cone.

But as for the thermoelectric generator? I have no idea, but you can probably get a lot more wattage out of one of the newer thin film or monocrystalline portable solar panels designed for backpacking and emergency use, even on a cloudy day.

I have a much older DIY panel made from polycrystalline elements that's about 2-3 square feet and it'll charge phones and AA batteries just fine. In bright sun it'll theoretically power/charge a netbook.

As a camping tool/toy, I'm more interested in the weight and size per watt. Roll-up solar panels aren't very heavy or big and can be rolled up with a camping pad.
posted by loquacious at 11:14 AM on May 3, 2012


I wonder if it could charge my portable TV? 'Cause I like to keep up on Jersey Shore when I'm in the woods.
posted by nowhere man at 11:15 AM on May 3, 2012 [2 favorites]


Irish kettles manage to heat water very quickly using much less fuel than you'd expect, stuff that you can pretty much gather from deadfall. I can see a stove like this working. The kitchen stove seems pretty damned cool, although it looks awfully tippy with a pot on top of it. Such a timely post, I'm packing up my gear for the first camping trip of the season, and this stove looks awesome!
posted by Foam Pants at 11:17 AM on May 3, 2012


Even if the rocket stove is only 80% efficient (and I would expect it's higher, given the observed perfomance of rocket stoves boiling water, etc), you will be getting something like 1.6 KWh of thermal energy out of every pound of dry wood. Siphoning off enough to charge a ~3Wh cell phone battery or whatever is totally plausible. If an average burn is a half pound and the TE generator is 50% efficient you need to capture less that half of one percent of the thermal energy being released.
posted by aquafiend at 11:21 AM on May 3, 2012


For a power estimate: one of these stoves puts out enough heat to boil a litre of water in 10 minutes or so. That's about 500W ( (100C-20C) * 1000g * 4.2 J/gC / 600 s). At 5% efficiency there's about 25 to 30W (J/s) available in electricity.

That iPhone battery is about 5.3 Wh or 19000J.It's going to take about 750 seconds to deliver that at a power production of 25 W, say 12 mintues. Hunh. So maybe this isn't such a gimmick after all.
posted by bonehead at 11:24 AM on May 3, 2012


Similar stove review, reporting ~30 C to 100C in "4 to 6 minutes" for a quart of water, so that guesstimate will at least be in the ballpark. The efficiency of the thermo-electrics is the big question in my mind, but even at low estimates may be capable of producing usable power.
posted by bonehead at 11:27 AM on May 3, 2012


Also, for me, the dominant use won't be to charge a phone, but to run a little USB powered LED lamp. If you've ever tried to cook after dark when camping, you'd appreciate how useful an extra light would be.
posted by Popular Ethics at 11:30 AM on May 3, 2012 [4 favorites]


I have to be skeptical as well since they don't give a power output. If it was significant, you can bet they'd be trumpeting it. After all, who wouldn't be clamoring to own a place to set your iPhone down that puts it in serious danger of melting!
posted by DU at 11:31 AM on May 3, 2012 [1 favorite]


I foresee many melted cables.
posted by charlie don't surf at 11:35 AM on May 3, 2012 [1 favorite]


Burning the thing for 2 hours to charge your phone could be a drag

If, on the other hand, you had an off-the-grid log cabin with a few solar panels and/or a wind turbine charging a little battery bank, you could line the exhaust pipe of your cast iron wood burning stove with a bunch of TE panels and heatsinks and get extra watts out of otherwise wasted heat. For greater efficiency, mount the heatsinks through the cabin back so they're exposed to sub-zero winter temperatures.

I think about this every time I see a campfire. Here's a generator with four 1" square TE modules that generates a little over 1 amp @ 12 volts.
posted by CynicalKnight at 11:35 AM on May 3, 2012


Apart from the woo woo around exactly how much heat this thing puts out the real issue is that it's freaking huge and heavy compared to say an MSR and a SIGG bottle - and an MSR looks after you above the snowline. I'm also concerned about how well it burns wet vegetation.
posted by fingerbang at 11:39 AM on May 3, 2012 [1 favorite]


My stove preference for indoor or emergency use is a grain alcohol stove. The fumes are non toxic and actually smell kind of nice, the fuel is readily available in large quantities at the corner liquor store, it's not petroleum thus green (though grain is grown with petroleum), and it's multipurpose (thinking of medicine as an antiseptic, but suppose could drink it). It burns extremely hot and clean, no marks on pots so can use with kitchen pots. The stoves themselves can be made from a coke can for free, but there are some nice ones for sale for under $50. I used the Brasslite for cooking at home for one person for 1 week when my power was out.

The wood stoves are great because the fuel doesn't have to be carried but wouldn't want to fool with it in a temporary emergency situation. Have to cook outdoors, smoke and fumes, carbon black pots, ashes, startup time, collecting fuel etc.. it would make sense on a long distance hiking trip where every ounce was critical so as to not carry fuel, though I think grain alcohol is very dense energy and not too heavy for 7 days of cooking needs.
posted by stbalbach at 11:41 AM on May 3, 2012 [1 favorite]


If, on the other hand, you had an off-the-grid log cabin with a few solar panels and/or a wind turbine charging a little battery bank

As I said above, a small mass-heater with a built-in thermoelectric is exactly what I would love to have for my off-the-grid cabin. Mine is in the deep woods, which means there is plenty of available biomass, but very little wind or sunlight. Something that could give me heat for warmth and cooking and run a little reading light would be great! I can't get that there from solar or wind.
posted by The 10th Regiment of Foot at 11:45 AM on May 3, 2012


I have a hand-cranked LED camping lantern with a USB port. I've never actually tried to charge something with it. But now I wonder how long a child will crank it if the reward is, say, 15 minutes of Angry Birds.
posted by Ella Fynoe at 11:46 AM on May 3, 2012 [6 favorites]


it's freaking huge and heavy compared to say an MSR and a SIGG bottle

A liter of white gas weighs a little under 2 pounds (not including a couple ounces for the stove). This thing weighs a little over 2 pounds. Not a freaking huge margin.
posted by The 10th Regiment of Foot at 11:49 AM on May 3, 2012 [1 favorite]


All I can say is if you haven't seen a rocket stove perform in real-life, it's almost impossible to believe how well well they work. Compared to a regular open fire, it's like moving from a VW bug to a Lamborghini.

A typical open fire is very inefficient. TONS of energy is lost convectively, radiantly, and in incomplete combustion. When you tune the chimney/combustion chamber you contain and direct both the radiant and convective heat, and (with the increase in air) you burn the fuel way more completely. Night and day. Truly.

I'll be buying one of these.
posted by Benny Andajetz at 11:52 AM on May 3, 2012 [1 favorite]


I have a MSR stove that burns white gas, and it's great. But I loooove my rocket stove. Really, if you haven't tried using one, you should. You can build a basic one from soup cans, to get a feel for how crazy awesome they burn. I pick up twigs and sticks as I hike, and stick them in my pack or pockets to keep them dry. A small supply of dry tinder is all that's needed, as once the stove is going it'll eat darn near anything, even wet pine cones. As you're cooking, place some more sticks/tinder around the stove to dry it out, and that's what's used to replenish your tinder supply. It's nice not to have to haul fuel around, and the major drawback to liquid-fueled stoves is that when you run out of fuel, the stove is generally useless. I've fed everything from bark to pinecones to dried manure to my rocket stove and it gobbles it all up.
posted by xedrik at 11:52 AM on May 3, 2012 [2 favorites]


All I can say is if you haven't seen a rocket stove perform in real-life

I just want to put in two cents here, I took up backyard metal casting as a hobby recently and the first time I melted aluminum in what was formerly a paint can with a couple of dollars worth of kitty-litter based refractory fueled with barbecue charcoal and "blasted" by my wife's old broken hair drier, I knew there was a lot more to fires than a Franklin stove. Rocket stoves are not at all a new invention, making one hand-held with a built-in charger is just a new and thoughtful innovation.
posted by The 10th Regiment of Foot at 12:09 PM on May 3, 2012


A small length of pipe cut into the side of a Weber grille and powered with a hair dryer works awesomely for things like pizza, too.
posted by Benny Andajetz at 12:28 PM on May 3, 2012 [2 favorites]


I leave my phone off while I'm camping/hiking, only turning it on for brief periods to check in. That kind of usage paired with a 10~20-minute topoff (with the phone off) every time I cook a meal... shoot, that'd be more than enough to keep my phone charged nearly indefinitely.

This right here (along with charging any other usb things, like hiking gps) is the use case for this type of thing. Not charging an iPhone from dead to full in one sitting.
posted by Threeway Handshake at 12:35 PM on May 3, 2012


Mei's lost sandal: "Well, I guess it's twig-collecting versus petroleum collecting?"

Twig-collecting is carbon neutral, although low-efficiency campfires do produce a lot of particulate matter and noxious fumes because the burn isn't great. It sounds like rocket stoves generally solve the efficiency problem, so I'm not really seeing a downside to this. The big picture problem is much less with burning things in general and much more with burning things we dug out of the ground.
posted by wierdo at 12:48 PM on May 3, 2012


The problem isn't global impact - you will easily use enough fossil fuels getting to your camping location to completely dwarf whatever your stove burns. Even if you used public transportation, the divided impact would still be much greater. The problem is that a bunch of people camping in the same location who build campfires will eventually strip all of the accessible and flammable wood, which kind of ruins the site. Even collecting tinder can do this if enough people do it.

Like I said, it's only a concern if it's a heavily-used site or experiences very little regrowth (tundra, desert, etc.)
posted by Mitrovarr at 1:09 PM on May 3, 2012 [1 favorite]


Twig-collecting is carbon neutral,

Just to be a bit of a smart-ass here, but burning petroleum is actually carbon-neutral as well, if your time-frame is expanded enough. Not that it matters in our current situation.
posted by Mei's lost sandal at 1:38 PM on May 3, 2012


I like these but given the weight of 954g I can't really see a use for one. I just bought a NOAA/AM/FM radio with a crank charger, LED flashlights and solar charger and it only weights 657g For 50 bucks. That leaves a great deal of money and weight allowance for a nice stove. But I do hope they can sell a few and provide some of the home units to developing nations.

A quick point about the thermal energy available. You need to remember that this thing can only extract energy from the difference in temps between the air intake (above ambient as it is next to a fire) and the temp of the fire gasses. Not to say that that isn't a significant amount available but you can't just say that Xg of wood has Yj of energy where thermal engines are concerned.
posted by The Violet Cypher at 1:42 PM on May 3, 2012


Thermoelectric generators are really fascinating; Thinking of all kinds of applications. Is there a general cost per watt figure for them at this point?

Thanks for the post.
posted by Mei's lost sandal at 1:48 PM on May 3, 2012


but burning petroleum is actually carbon-neutral as well, if your time-frame is expanded enough

No, unless you got the petroleum from some sort of naturally spouting geyser of oil. Most of the time, petroleum is sequestered far underground, and would stay that way for eternity, barring any sort of event that moves it around. Many people are trying to do this same thing with carbon dioxide.

Twigs on the ground, however, have already fallen off a tree and are already beginning to decompose, releasing their carbon into the air.
posted by Threeway Handshake at 3:44 PM on May 3, 2012


Cool, thanks for this! What powers the forced air fan? I don't see where that question is addressed.

Apparently it's electrical. I always thought it would be cool to make a jet engine type thing. You put wood in a container, have a fan on the exaust, which would naturally turn as hot air rises. Then, you hook that fan up to the input so it sucks air in, speeding up the combustion, which in turn spins the fan faster, sucks in more air, etc.
posted by delmoi at 3:53 PM on May 3, 2012 [1 favorite]


> Also, keep in mind that twig-collecting and especially stripping wood from standing trees is a violation of leave-no-trace ethics, although obviously this is only a concern in extremely high-use or low-growth areas.

Isn't also essentially illegal in the Sierra Nevada?
posted by danl at 4:16 PM on May 3, 2012


Cool, thanks for this! What powers the forced air fan? I don't see where that question is addressed.
Apparently it's electrical.


The fan runs off the same thermoelectric generator as the USB port. In fact, the fan is the reason the TE generator exists in the first place. It's my understanding that the addition of a port (it was absent on early models) came only after the designers realized they were generating more electricity than they needed.
posted by Popular Ethics at 4:51 PM on May 3, 2012


delmoi, a combustion system where intake gas is compressed by linked fans powered by the expansion of the exhaust is what they call a turbocharged system, and if you'd like to see one then you are going to love the Nye Thermodynamics NT6 wood burning turbine.

The rest of his site is pretty great, too.
posted by seanmpuckett at 5:50 PM on May 3, 2012 [2 favorites]


Scientist writes "Yeah... show me some statistics about how much wood and how much time is actually required for a realistic task like boiling water for coffee and charging a dead iPhone. "

Charging a dead iPhone seems like a extreme worse case. There are devices that have much lower energy requirements than an iPhone. My phone for example only has a 750mAh battery good for about 4 days of stand by and a couple hours of talk time. And it's not like you need to bring the iPhone up to 100% charge for it to be useful. I have no idea what there draw is like but if you aren't draining it dead every day then you don't need a full charge every day.

Interesting to me though is the idea of applying TE generators to freestanding wood stoves. During heating season it would be essentially free electricity. The heat used to generate electricity would later be released back into the house when the electricity is used to power whatever.
posted by Mitheral at 7:09 PM on May 3, 2012


Burning sticks and twigs is so boring. Try Plutonium.
posted by charlie don't surf at 10:13 PM on May 3, 2012


Hmm...you can buy peltier effect TE devices on ebay from a few dollars up. They are designed to cool CPUs when you apply a current, but they are reversible, so a temp difference would generate power.
I got one to play with. I hoped to power a tiny PC fan with it to spread some hot air from my woodstove around the room more efficiently. Unfortunately, the current delivered from resting on top of the stove on one side versus ambient air on the other was inadequate.
Sadly I can't remember, but milliamps, and not many.
I'm skeptical this device will work IRL.
posted by bystander at 1:38 AM on May 4, 2012


Related: the SCORE project, using a thermoacoustic generator rather than direct thermoelectric, is aiming for 150W of electricity, 1.6kW of cooking heat and 750W of simmering heat using 1 kg/hour of wood, dung and other bio-mass at a unit cost of £20 per household in 1 million quantities.
posted by flabdablet at 2:35 AM on May 4, 2012


Unfortunately, the current delivered from resting on top of the stove on one side versus ambient air on the other was inadequate.

The ambient air above a wood stove is pretty bloody hot. You might have got better results by letting the TE device occupy a hole in an insulating layer applied to the side of the stove, attaching a finned heat sink to the cool side, and blowing air picked up below the stove over that.
posted by flabdablet at 2:39 AM on May 4, 2012


Twigs on the ground, however, have already fallen off a tree and are already beginning to decompose, releasing their carbon into the air.

Unless of course they are in the process of becoming coal or oil.
posted by The 10th Regiment of Foot at 5:00 AM on May 4, 2012


Even better would be to stick the cold side of the TE into the air stream of the make up air duct of the stove. Most high effieciency stoves have the ability to introduce air from outside into the combustion chamber instead of using room air. That air is going to be plenty cool. You could connect the hot side to the stove with a bar/plate of copper clad aluminum that you could bolt right to the side of the stove.
posted by Mitheral at 8:00 AM on May 4, 2012


I can't help but wonder about the lifetime/abuse rating for the peltier TE devices. I love the concept but fear the execution.
posted by RolandOfEld at 8:30 AM on May 4, 2012


RolandOfEld, thermocouples have worked reliably for decades in deep-space probes (see the link to RTG above). There are no moving parts, and they routinely last a very long time.
posted by JMOZ at 1:05 PM on May 9, 2012


BioLite just put up a page with some specs: USB power output is 2W continuous, 4W peak at 5V (for comparison, a standard PC USB2 port is current-limited to 2.5W maximum).
posted by flabdablet at 7:07 PM on May 9, 2012


More specs here.
posted by flabdablet at 7:21 PM on May 9, 2012


Few PC USB2 ports are actually limited to 500mA except on laptops, although many Windows PCs require a driver for the device to allow more than the standard 500mA draw. I have a few ports that go up to 2A apiece, but this is a pretty modern machine.

My old Thinkpad would do up to 1A, but only when plugged in, otherwise it limited the USB ports to the standard 500mA.

To nitpick myself a bit, the standard allowed current draw is actually much less than 500mA. The USB host is only supposed to allow that much after the device has requested it. However, most computers will allow the full 500mA even when the device isn't actually a USB device at all and just uses the plug for power.
posted by wierdo at 12:24 AM on May 10, 2012


Biolite also started taking orders (instead of just reservations) yesterday. My stove is apparently due to ship June 1. Exciting!
posted by Popular Ethics at 1:52 PM on May 10, 2012


I'm more impressed with the spec for "Fire Power" output, than for electrical output. 5.5 kW is almost 20 BTU/hr, which is twice the power of most camping stoves. I wonder how much that output varies with the quality of twigs you feed it.

On the other hand, the specs say the stove can boil a litre of water in 4.5 minutes. Raising the temperature of a litre of water from 22C to 100C takes 326 kJ, or an average of 1.2 kW over 4.5 minutes. That's well within their maximum power spec, so perhaps this is closer to the average? (Biolite claims that the boil time is about the same as a fuel stove, so I'm guessing average power is about equivalent).

The specs also say that boiling a litre of water will take 46 g of wood. That's roughly equivalent to 680J worth of fuel, so we can estimate that the stove is 50% efficient at heating the water. That matches Biolite's chart pretty well, and is apparantly twice as efficient as an open fire.

A 1cm diameter x 15 cm long twig (seems about right from the video) of dry pine would weigh about 7 g, so you'd need to burn 7 twigs to boil a litre. Not much at all. It looks like you can fit that many in one fuel load, so no need to refuel half way through. I'm impressed! We'll see if I get the same performance when my stove arrives.
posted by Popular Ethics at 2:47 PM on May 10, 2012


Oooh, they even provided a pdf with references for their comparison infographic. I like these guys.
posted by Popular Ethics at 2:49 PM on May 10, 2012


Popular Ethics writes "5.5 kW is almost 20 BTU/hr, which is twice the power of most camping stoves."

I think you dropped a K there. Seeing how a candle flame is a couple hundred BTU your average camping stove must be 10K BTU with the Biolite stove being 20K BTU.
posted by Mitheral at 4:28 PM on May 10, 2012 [1 favorite]


I have absolutely no need for this, not being a camper, but I still want one. What the hell is wrong with me?
posted by wierdo at 4:38 PM on May 10, 2012


Also, I wonder how bad it would smell if I tried to burn dried shit. I have plenty of that, thanks to the dogs.
posted by wierdo at 4:43 PM on May 10, 2012


Most fuel dung is from herbivores and is therefore mainly shredded plant fibre. It makes fires that smell more like burning grass than anything else. I would expect dried dog shit to be mostly protein, and that burning it would smell more like burning hair or feathers.

I won't be putting any dried dog shit in my stove when it arrives, but would be interested to hear whether I've guessed right if you're willing to risk it.
posted by flabdablet at 5:13 PM on May 10, 2012 [1 favorite]


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