The one-stop rocket stove shop!

We have come to the integrated concept of a home water & energy system, based on the rocket stove (or any other stove, in fact) and rainwater harvesting system.

It is intended to be used both in the urban and rural environment, with modifications, wherever needed.

We are going to start building the prototype during November workshop in Warsaw. Comments/contributions welcome!


  1. Rainfall harvest system (recycled advertising banners, two-step filtering, main tank, hot water tank).

  2. Solar energy converted into the electricity, using reconstructed PV panels (re-assembled from damaged ones). It powers the circulation pump in the 1st primary heat exchange circuit.

  3. Solar panel (or concentrator - heating the fluid in the 1st primary heat exchange circuit, transferring the heat to the hot water tank.

  4. Rocket (or some other) stove, providing heat for the thermoelectric generator, 2nd primary heat exchange circuit and room heating.


A. Cold water

B. Hot water

C. Electricity from the thermogenerator (and possibly other sources) stored in the intelligent battery bank (

D. Nice and cozy warmth from the stove, either direct, or through the heat accumulating mass (sand, clay, water…)

Hey Petros how’s the prototyping going?

This looks really interesting but I’m not sure why you want to build it? Is there something with existing systems that makes it a better option to build one from scratch?

Which system?


Which system(s) are you referring to? The answer for your question depends on the comparison criteria.

There are many systems, and also some off-the-grid solutions, but I do not know any integrated solution costing less than a thousand dollars.

For our design, as it is drawn here, we use mostly scrap materials:

  • used commercial banners for rainfall harvesting.
  • used plastic barrels for cold water storage
  • used metal barrels for hot water storage
  • old central heating radiators (painted black) as solar collectors
  • rocket stove made of aerated concrete
  • reused water pomps (automotive)
  • regenerated car batteries
  • custom made electronics (courtesy of Warsaw Hackerspace)

The only modules we cannot (so far) make on our own, are photovoltaic panels and the thermoelectric generator. And they are all available locally.


I read this right after you posted it, and spent some time going: WWHOOA, but can people not at all skilled in any of these learn to do it themselves? the answer seems to be yes, if you guys are around :).

But then if you set it up and test it, don’t you have to comply with some sort of regulations, don’t you need approvals to install and have it replace a whole heating/water system - given you’re also dealing with electricity and other hazards as well?

FreeLab Mission is…

  • to gather
  • to verify
  • to develop
  • to spread
practical skills for social self-organisation.


Speaking of complying - it depends on the side of the mirror you are on. :wink:

Yay for DIY!

The only modules we cannot (so far) make on our own, are photovoltaic panels and the thermoelectric generator.

Saw you intend to re-build the panels from broken ones, and so far I have no idea how to push the DIY further there :slight_smile:

For the thermoelectric generator, I once thought if it is possible to harvest the Peltier elements from broken camping fridges and cheap electric cooling boxes? They are just thermoelectric generators used in the other direction, right? But maybe their temperature rating can make it difficult to use them on your stove. Alternatively, I have once found this supplier: TEG power. Their 15 Watt High Temperature TEG Panel retails for 80 USD, or 60 USD in bulk. Or maybe you have a better source already?

All these hints are from my EarthOS project’s document, which is so far a longish but still pretty chaotic collection of free & DIY tech for all of life. (I’d like to include freelab’s energy and water system and the battery bank as well!)

And apart from the tech stuff, it seems we will meet at the December LOTE2 conference. Nice! Looking forward to some interesting talks then. :slight_smile:

Peltier !== Seebeck

As the Peltier effect (Electric Heat Pump) and the Seebeck effect (Thermoelectric Generation) are adversary (is the wording correct?) ones, Peltier units are usually composed using pairs of components to minimize Seebeck effect. That is why TEG offer seems to be the best available at the moment (while totally beyond FreeLab financial reach). If I put my hands on two TEG 15W units, I will be able to run two prototypes, possibly interesting even commercial applications (and that means donations :-))

Meanwhile, using ma hacker contacts i am digging for less known solutions, talking to Polish technical universities. If we get something, I will let you know.

If Gods of the Net send me to Brussels, It will be talking time, for sure. :smiley:

I built myself a hopper fed side draft gasifying stove (well me and my friend built it).  I’ve still got to doucment it properly somewhere.  But I discussed my initiall ideas and the build on the stoves list. Starting December 2010 and working on it that winter and last winter - testing a bit last winter and more now.

I am planning ot rig up a water tank to heat from the stove, will suply hot water for the shower but also be sized to act as heat mass for the small, well insulated truck it is all fitted in.

Last year I also ordered from Germany a high temperature TEG for a friend -

With postage to UK it ended up being in the price range Neo suggests (although the postage was expensive)

It was a year ago I last looked at the site and things were changing fast - regular new products, new prices.

The first time my friend properly tested it he put lots of smal wood in his stove to get the heat up.  He placed the TEG on the top of the stove, checking the output as the stove got hotter and hotter… He was looking in amazement as the output grew bigger and bigger - then he melted the solder in it :(  Generally he has very little money and as far as I know, although he is still very intersted, he has not purchased another.

Hopper pics, please!


We are right now (this weekend) building a hopper-ish fed rocket water/mass heater, quite similar to the one you did. The system is build around 40 l water barrel, dual role as well, plus a brick-made bed for better heat absobtion.

Pictures will be available soon.

Would it be possible to get a picture or video of yuk stove? I am specially interested in the hopper/side draft operation.


The hopper really needs to have an airtight lid/door so that the fire does not spread up into the fuel in the hopper.

The way my stove is built its really hard to see the design form looking at it (also any photos / videos)

There are more on the mailing list.

This is the most recent post where I documented the most recent modifications that I have made to hopper design and it appears to be working well now.

check this post and the attached/linked picture - also the same for the previous post I linked above.  this will hopefully give a good idea of how it is put together.

Compaed to cutting logs with a chainsaw it does take some time to prepare fire wood, but then I don’t use power tools, and I use branches that would normally not be used for a fire (up to about 4 cm diameter)

I would suggest that if possible have verticle walls for your hopper (no sloping sides) so that any fuel in it will fall down into the fire and not get stuck in the hopper.

Because we can! (and we should)

The short answer is: “because we can!”

The longer and more on-topic here answer would be: show me a single well-tested and documented such design with instructions on building your own. I know of none. And that means somebody has to do it and release it, so that places like FreeLab or UnMonastery, or squats, or any other community, can build their own themselves instead of buying a ready-made one – as this will lead to more self-sufficiency, reduce the dependance on money, empower more communities to hack around and do more stuff themselves.

And, as a hacker, I can tell you this is inherently good. :wink:

That’s my man!

The intelligent battery bank Mk 1 explained.

In our preparation for energy self-sufficient settlement, we realised that a reasonable size battery bank is going to be quite expensive - both initially, and periodically, if you need to replace worn-out batteries with new ones.

The key thing is that, if you want to have a decent battery capacity (say, 500 Ah @ 12V) you need several typical batteries to be connected in parallel, or you have to look for specialist, high capacity single battery, which is rare and expensive.

Even if you couple standard batteries, to get the capacity, at the beginning, you will need to replace the whole bank, even if just a single battery gets damaged. Otherwise, you’ll end up with a set of batteries with various capacities (each battery ‘matures’ sightly different way), whch means a lot of parasite currents flowing among them, thus a lot of energy wasted. That is exactly why industrial UPSes (Uninterruptible Power Systems) always have all their batteries replaced - not just the one that failed.

Well, having in mind that we are preparing a solution for people who have strict budget and will likely need their batteries being replaced quite often (continous power cycling instead of stand-by regime), we defined our needs as follows:

  • We need to have a battery bank capable to adopt various batteries (while all lead-acid type - that’s for Mark I), with various capacity. Ideally, it will adopt recycled batteries, being available at a fraction of cost (in Poland it is ~$7 vs. ~$75).

  • We need to have a technology to recycle lead-acid batteries, either newly obtained, or those aalready being used, if their capacity drops below accepted level.

  • The bank has to maintain all batteries equally charged (measured by their output voltage), and to produce designed energy (be it @12V DC, or a multiplication of it, for the serial/parallel combination).

So, thanks to our friends from Warsaw hackerspace, we got to the following design:

  1. We have two know-hows for battery recycling. One is simply a specialised charger. The worn-out battery is being charged several times, according to the regenerative algorythm. It will help in most cases, at least to keep battery going for a year or so.

For serious cases, we shall use ‘wet’ technology, which uses special regenerative electrolyte, another charging regime and finally, fresh electrolyte replacement. This is rather heavy chemstry, which includes also problems of acid neutralisation and disposal - however, fully doable.

  1. We have designed a ‘matrix’ of chargers, being independently controlled by the software, taking indvidual care of every battery in the bank. Diagnostics, charging and monitoring will be done real time from a dedicated laptop. This will compensate all individual discrepancies among batteries, making them work like a set of brand new cells. The solution is scalable from 8 up to 32 batteries, which means the possible saving is ~$550 to ~$2200 (Polish price level, again).

Now, what we need to do is:

A. Set up a ‘dry’ and ‘wet’ battery regeneration workplaces, including all necessary consumables and proper waste disposal.

B. Set up a small-scale, 8 batteries ‘matrix’, with control circuits, laptop and software, with internet monitoring access for interested viewers.

C. Get 8-10 disposed car (or similar) batteries, regenerate them, using both technologies and install them in the matrix.

D. Run a mid-term test (up to 3 months), using the matrix for daily activity, batteries being charged from various sources, if possible.

E. Finally, make a report and full-blown documentation and publish it (as we always do) as CC-BY-SA.

In the project, all labor will be provided free. We shall only need to buy electronics and chemical equipment. Batteries - by default - will be bought from the scrapyard.

If you decide to support the project, we shall produce and share quality output that will save every sustainable settler buckets of bucks, and help them to be even less dependent from the battery manufacturers. The solution will be scalable and transferable worldwide.

Very nice!

Now this is a very nice project: using nearly free stuff for input, very DIY, and very flexible and scalable, and being open hardware. Such stuff provides what I call “freedom” :slight_smile:

Also, I was looking for something like this for my home (which happens to be in a truck, using 24 V DC). Would it be possible though to use your matrix charger for less than 8 batteries? In my case, I will have 4 or 6 I think.

Here’s some more stuff on recycling batteries (some things I found on the net one day, some ideas by me – you’ll know most of it already, but maybe it offers some inspirations):

  • Desulfating agent: In my experience, most lead-acid automotive batteires die by silfatation of the lead material. There is a substance called EDTA, to be added to the electrolyte, which people use as a kind of emergency measure for sulfated batteries, with good and not so good results (see instructions, better instructions, experiences and a critical analysis). As an alternative, there is the commercial ThermOil Battery De-Sulfater but I have no experience with it.
  • Battery preservation chemicals: I once found ThermOil Battery De-Mister, which is a commercial battery preservation agent. I did not yet test it myself, just read these "miracle stories" about it. Depending on if it works and what it is, maybe it can be replaced with a DIY substance.
  • Dendrite short-circuit repair: Another mode of failure is where a lead-acid battery developed so long dendrites that they cause an internal short-circuit. Reportedly, some people use an electric arc welder on both terminaly of the battery to burn these away – just read that on the net somewhere, but I lost the info on how to do it exactly and what can go wrong. (As with all the battery stuff, there is some risk from acid, gas explosions and the like, so if anybody else reads this: be very careful and know what you're doing before.)
  • Separating into single cells: All the 6 cells within a 12 V battery also age differently, and in case that a battery dies, mostly only one or a few cells are dead. So I thought once about separating batteries into individual cells, and managing these independently in a grid like you intend for the batteries. But that might be overkill. It is also possible to exchange the cell internals with healthy ones after opening the battery case (other readers: beware of acid etc.). A brother of mine repaired some AGM (absorbed glas mat) batteries that way in Congo, by creating a working one from two defective ones and re-sealing the case afterwards.
  • Using DC-DC step-up converters: One of my truck batteries had one cell short-circuit, so it had lost 1/6 of its voltage. Not usable for the truck any more, but for lower-current home applications I thought about using it by adding a step-up converter to bring the voltage again to 12 V (or in my case, better directly to 24 V). These accept a wide range of input voltage, produce a fixed output voltage and are up to 95% or so efficient. They do not allow much current mostly (or will be costly), but if one has an array of batteries in parallel, that would be compensated ...

Great inspirations, indeed. :slight_smile:

And this is the essence of hacker culture. We both multiplied our knowledge by sharing it. :slight_smile:

I will run details through our friend, who is professional electro-chemist. Will get back with comments, if any.

Nice! what a great invention.

Nice! what a great invention. You gave me an idea of recreational activity for our family this summer. Want to entertain the children with affordable science this summer? Sure, we all do. Why not make a water rocket to launch in the yard? I’m sure it would be a lot of fun.