https://hackaday.com/2026/03/14/off-grid-electricity-and-hot-water-from-scrap-wood/ Skip to content Logo Hackaday Primary Menu * Home * Blog * Hackaday.io * Contests * Submit * About * Search for: [ ] [Search] March 14, 2026 Off-Grid Electricity And Hot Water From Scrap Wood 15 Comments * by: Bryan Cockfield March 14, 2026 * * * * * Title: [Off-Grid Electricity] Copy Short Link: [https://hackaday.com] Copy [charcoal-m] Cooking with charcoal is a fairly common human activity, as much as others have come to prefer fuels like propane and propane accessories for their outdoor, summertime grilling. Although it's made from wood, it has properties that make it much more useful for cooking -- including burning at a higher temperature and with more consistent burn rates. It can also be used as a fuel for generating heat and electricity, but since it's not typically found lying around in the forest it has to be produced, which [Greenhill Forge] has demonstrated his charcoal production system in one of his latest videos. The process for creating charcoal is fairly simple. All that needs to happen is for wood to be heated beyond a certain temperature in the absence of oxygen. At this point it will off-gas the water stored in it as well as some of the volatile organic compounds, and what's left behind is a flammable carbon residue. Those volatile organics are flammable as well, though, so [Greenhill Forge] uses them to heat the wood in a self-sustaining reaction. First, a metal retort is constructed from a metal ammo box, with a pipe extending from the side and then underneath the box. A few holes are drilled in this part, and the apparatus is mounted above a small fire on a metal stand. With the fire lit the wood begins heating, and as it heats these compounds exit the pipe and ignite, adding further fuel to the fire. Eventually the small fire will go out, allowing the retort to heat itself on the gasses released from the wood alone. To generate the hot water, [Greenhill Forge] has taken an extra step and enclosed the retort in a double walled metal cylinder. Inside the cylinder is a copper tube packed in sand, which harvests the waste heat from the charcoal production for hot water. In his test runs, the water in a large drum was heated to the point that the tubing he used for the test began to melt, so it is certainly working better than he expected. After the retort cools, [Greenhill Forge] uses the charcoal in another process that generates about a days' worth of electricity and hot water. It's part of a complete off-grid system that's fairly carbon neutral, since trees are an abundant renewable resource compared to fossil fuels. Heating with wood directly is still common in many cold areas around the world, with the one major downside being the labor required to keep the stove running. But we've seen at least one project which solves this problem as well. * [share_face] * [share_twit] * [share_in] * [share_mail] Posted in green hacksTagged battery bank, charcoal, electricity, energy, fire, generator, hot water, off grid, retort, wood, wood gas Post navigation - What Is A Computer? Take Pi For A Spin In This Orbital Simulator - 15 thoughts on "Off-Grid Electricity And Hot Water From Scrap Wood" 1. Ostracus says: March 14, 2026 at 10:11 am "It can also be used as a fuel for generating heat and electricity, but since it's not typically found lying around in the forest it has to be produced..." I think 7 days to die, burnt biome has this problem licked. Report comment Reply 2. Paul says: March 14, 2026 at 10:47 am Growing up in a house heated by wood, I learned that heating with wood is very efficient: It warms you three times: Once when you cut it, once when you chop it, and once when you burn it. My house is still heated (partly) by wood, and it is my secondary backup after gas and electricity. Report comment Reply 3. Andy says: March 14, 2026 at 11:51 am Burning wood is easy, burning wood efficiency and safely is HARD. There's no shortage of poorly designed wood burning stoves either. I've cut, hauled, split, stacked, stoked, and shoveled the ashes out plenty. Heating with wood is a lifestyle. Report comment Reply 4. Dude says: March 14, 2026 at 1:20 pm There's a reason why the old WW2 era gasifiers were built in a vertical drum. The air intake is at the bottom and the combustion happens in a funnel with the syngas taken out just above the funnel. The ashes drop down through the funnel onto a grate at the bottom while the fuel is continuously replenished from above. The grate has a shaker which keeps the ashes from getting stuck, and in a moving vehicle there would be a pendulum to move the shaker. The gases emitted by the fuel as it's cooking in the hopper are taken out through a vent at the top and directed down to the combustion zone with the intake air, so the system can actually cook the charcoal while it's running and the volatile gases, tar and steam, are combusted through the fire which breaks them down and gives you more syngas. That's how they were able to run on wood chips without getting too much tar in the engine. With that design, approximately 70% of the energy contents of the wood can be converted into syngas versus about 50% for the charcoal burning version. Report comment Reply 1. Dude says: March 14, 2026 at 1:26 pm Correction: the air intake is just above the funnel and the syngas is taken out from the bottom of the funnel. That way the gases given off by the cooking fuel on top of the combustion zone are drawn down through the fire and contribute to the combustion. There is no separate top vent for the gases. Report comment Reply 2. Dude says: March 14, 2026 at 1:56 pm https://www.researchgate.net/figure/ Downdraft-gasifier_fig1_289685682 Another advantage of the funnel shape is that you can build a lot of insulation around it and conserve heat. This is called a downdraft gasifier. It works on charcoal as well, and charcoal was used in the cities because it generates less smoke out of the exhaust and it's easier to start, but the fuel economy was far worse and reloading the hopper was dirty business. When used in trucks and buses, wood chips were used instead because it goes further on a charge and refueling stations could be set up along the roads without the need to maintain charcoal burning fires. The wood chips could be made into fairly large chunks because they break down through the pyrolysis zone. Coincidentally, they now sell wood gasifying stoves for heating homes in Europe, for the point that the gasifying process can be slowed down inside a well insulated box and the same load of wood can burn for more than a day, so you don't need large hot water tanks to moderate the heating. It burns cleaner and more efficiently without a big draft up the chimney. I bet you could tap some of the syngas out of the stove and run the generator on it as well. Report comment Reply 5. SpillsDirt says: March 14, 2026 at 2:26 pm Wood might be a renewable resource, but its slow. ' One acre of well-managed forest typically produces about 2.5-3 tons of firewood per year on a sustainable basis. Clearcutting an acre typically yields 80-105 tons of timber but is only possible after a 15-80 year growth period depending on species, whereas thinning (removing selected trees) provides roughly 25-40 tons, every 10-15 years after an initial 30-50 year growth period. A well-managed bamboo plantation can yield between 10 to 20 tons of fresh bamboo per acre every year after an initial growth period of around 5 years. Report comment Reply 1. SpillsDirt says: March 14, 2026 at 2:38 pm Forgot to add... 10 tons of fresh bamboo can produce approximately 2 to 3 tons of fuel pellets. So production per acre for fuel purposes falls roughly between equal and double per acre by weight. Bamboo fuel pellets generally offer better combustion properties--higher heat value and lower emissions compared to pine Report comment Reply 1. Dude says: March 14, 2026 at 3:10 pm better combustion properties Bamboo is a grass so the ash content is greater. Commonly about 2-3 times more. Report comment Reply 1. SpillsDirt says: March 14, 2026 at 3:20 pm Yes, compared to pine pellets (around 0.83%), bamboo fuel pellets typically have a higher ash content (around 1.1-1.64%), still relatively low compared to other agricultural residues like rice husk and straw which can exceed 20% ash or corn stalks (and related stover) which typically ranges from 3.6% to 13.2% on a dry matter basis,and can spike higher (up to 23%) depending on soil condition. Report comment Reply 1. Dude says: March 14, 2026 at 3:33 pm From what I can find, Bambusa balcooa is around 0.84% while Bambusa vulgaris is 1.84% while Bambusa tulda is up to 4.5% ash. Pine on the other hand averages closer to 0.5% and tops off at around 0.9% depending on soil conditions. Another difference is that wood ash is mostly potassium and calcium, while bamboo ash contains a lot of fine silica dust which is a health hazard when inhaled. Report comment 2. SpillsDirt says: March 14, 2026 at 3:57 pm Bamboo fuel pellets are almost exclusively produced from Bambusa balcooa as its significantly more productive per acre than B Tulda, or Vulgaris. Bamboo ash Also contains calcium (Ca), potassium (K), and magnesium (Mg). While the high silica content of stem based wood pellet ash is up to 50%, and that is certainly higher than wood based ash production, its far lower than other agricultural residue. Rice Husk ash is 97-99% silica. Rice straw ash often contains 60-75% silica, wheat straw ash typically ranges around 65-73%, Corn stalk ash often contains around 64-79% None of this changes the fact that Wood is a SLOW renewable with longer production time, and lower fuel production per acre. Report comment 2. Dude says: March 14, 2026 at 3:12 pm higher heat value and lower emissions compared to pine According to what? For what I can find, bamboo averages 18 MJ/kg while pine goes for 21 MJ/kg. Report comment Reply 1. SpillsDirt says: March 14, 2026 at 3:24 pm Liu et al. (2016) reported that calorific value of bamboo pellets was 18.5 MJ/kg which was higher than pine wood of 18.3 MJ/kg. Only high resin pine hits 21Mj/kg, those species/cuts are typically avoided in fuel pellet production due to the fouling deposits it creates during combustion. Report comment Reply 2. Podstawek says: March 14, 2026 at 3:46 pm If renewability is of concern, why not use human fat extracted from corpses before they're buried? While I find regular burial stupid because today's cemeteries bring tommorow's abundance (as new oil/gas fields), cremation is even dumber since it wastes all that potential energy into plain CO2. If we could obtain corpses from developing countries with large populations (like India, China or Africa) then we could fuel our economies without relying on Middle East. Report comment Reply Leave a ReplyCancel reply Please be kind and respectful to help make the comments section excellent. 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