Welcome To The Sovereign Energy Series
The Sovereign Energy series is a collection of articles examining different to design and build energy sovereignty at the homestead and local community scale. These posts detail appropriate technologies for generating, storing and using energy in a multitude of forms in ways that reduce or eliminate reliance upon centralized industrial supply chains and global commodity inputs (i.e. control points). In general, this means a focus on biomass, moving water and solar technologies and their relevant design considerations.
This series is organized into three primary categories – 1) Moving Heat, 2) Moving Things/Substances, and 3) Electricity Generation, Storage And Use, borrowed from the energy framework laid out by Toby Hemenway in The Permaculture City.
Moving Heat
- Cooking Systems
- Wood
- Biogas
- Solar Direct
- Space Heating / Cooling
- Passive Solar Design Principles
- Heating
- Rocket Mass Heaters
- Woodstoves
- Cooling
- Geothermal Air Conditioning
- Earthtubes
- Windscoops
- Solar Chimneys
- Water Heating
Moving Things / Substances
- Water
- Water-Powered Pumps
- Animal-Powered Pumps
- Electricity-Powered Pumps
- Transportation of People, Animals, Materials
- Animal Transportation
- Diesel/Gas Powered Vehicles
- Electric Vehicles
- Refrigerant
- Air
Electricity Generation, Storage And Use
- Electricity Generation
- Electricity Storage
- Lighting
- SolaTubes
- Appliances and Devices
Sovereign Energy
~ Moving Heat ~
Grid-Independent Cooking Systems
Introduction to Grid-Independent Cooking Systems
Cooking food is an activity shared by all of humanity on a daily basis. We either do it ourselves or have someone (or increasingly, some thing) do it for us.
It’s fun to cook hot dogs on a stick over a campfire, but it is hardly feasible as a daily option for the vast majority of people – slow, messy, smoky and inconsistent. Cooking food efficiently and cleanly requires utilizing a concentrated energy source paired with a means of optimized heat delivery to whatever is being cooked.
Wood, coal, liquid, and gas fuels are the primary concentrated energy sources for residential and small-scale use. Of these, wood and biogas renew the most quickly and have the greatest range of technologies already developed, and thus are the best options in terms of renewability, efficiency, and cleanliness (of food and environment). Propane and/or natural gas has the largest selection of turnkey residential appliances (ranges, ovens, furnaces, water heaters etc.), which can be converted to be fueled by biogas.
Wood
Systems For Cooking With Wood
Rocket Combustion Cooking Systems
Rocket stove technology is an important technology for maximizing the use of the energy contained in wood and making it a feasible replacement for the more modern conventions of gas-fired cooking.
Rocket stoves burn wood at very high efficiency (90-95%) assuming dry wood is being used/ This is the percentage of the energy contained in the wood that is converted to heat and is thus potentially transferrable to the cooking vessel. The remaining 5 – 10% is lost as heat or smoke (uncombusted gases) to the surrounding environment. Rocket mass combustion technology can be compared with traditional wood burning stoves that burn larger logs and generally operate at ~50% efficiency (and this is under ideal laboratory conditions). If the wood is wet and air flow is not managed properly, the efficiency of traditional wood stove systems can drop into the teens, creating a “cold” fire that makes a smoky, toxic and inefficient mess – yikes!
The high efficiency characteristics of rocket combustion systems is the result of a design that creates both a high temperature burn and efficient air mixing, followed by secondary combustion of wood gases (smoke). Rocket stoves are so efficient that they do not emit smoke when constructed and operated properly. Most of what leaves the chimney is CO2 and water, as all the smoke that would typically be visible coming out of a standard chimney has been combusted and converted to useful heat! Rocket stove technology can be utilized to replace the typical cooking appliances, including cooktops and ovens.
Tim Barker gives an excellent overview of the difference between rocket style combusion vs. conventional combustion systems.
Walker Stove Riserless Core Rocket Cooktop
Matt Walker’s riserless core rocket stove designs have enabled a flat metal cooktop to be the main radiating surface for the rocket stove while still maintaining the high efficiency burn characteristic of rocket stoves, all without the large riser and bell so common with rocket mass heater builds. The metal cooktop, on which pots, pans and kettles can be placed and moved around to find exactly the right temperature for the culinary task at hand, makes for a very flexible and easy to intuit cooking set up. Units can be quite small, and could be a good fit for some of the smaller spaces, and can also be quite large and capable of cooking for larger groups.
- Very clean and efficient burn.
- Creates a gradient of heat across the cooktop – from very high to warm. Watch Matt’s introduction and overview video of this stove in operation.
- Can be built from common and easy-to-acquire materials.
- Can be integrated with a mass bench to store additional heat in colder climates, similar to how a rocket mass heater would be set up.
- Indoor and outdoor (covered) applications.
- Do-it-yourself plans are available from WalkerStoves.com for three different sizes of riserless core rocket cook stoves – Continental, Full and Tiny.
Rocket Powered Barrel Ovens
Barrel ovens that utilize rocket designs, like the one shown in Figure 6.1.X, are quick to heat (unlike traditional cob ovens), entirely wood fired, excellent for baking, and cheap and inexpensive to build. These systems can be used indoors as well as outdoors. They rely on a continuously burning fire for heat and do not have thermal mass storage like a cob oven.
Tim Barker’s plans for constructing both a barrel style oven and converting a more typical oven to take advantage of a wood-burning rocket engine are excellent and very approachable for the DIY enthusiast. For the more visual DIYer, the Permies.com Rocket Ovens video manual will walk through all the steps to building one of these ovens start to finish.
- Very clean and efficient burn.
- Quick to reach desired baking temperatures.
- Can work for indoor or outdoor applications.
- Can be built from common and easy-to-acquire materials without welding.
DUal Chamber Cob Oven
Dual-chamber cob ovens eliminate the smokiness typically associated with these types of ovens, allowing the chef to breathe clean air while tending the fire. Essentially, these ovens employ a two-door system linked with a strategically placed chimney that improves draw and airflow and makes for a cleaner, hotter, faster burn. These ovens get up to temperature faster and have a four times cleaner burn that traditional cob ovens.
Cob ovens store heat in their massive walls, and are well suited to cooking pizzas and calzones, baking bread, and various types of slow cooking where the fire is lit, the mass brought up to temperature, and then the item to be slow cooked is set inside and the door shut for however long it needs to cook. Slow-cooked beans and yogurt making are good examples, and when not in use, the dry, dark, and potentially cool inside can be used for curing ferments when outside temperatures fluctuate too wildly. Pizza ovens are also an excellent community building tool and have a gravity all their own when organizing a work party with the promise of wood-fired pizzas at day’s end.
- Burn is much cleaner and more efficient than a single chamber cob oven due to enhanced air mixing.
- Healthier for the chef because the smoke is vented out the chimney instead of through the door used by the chef.
- Gets up to temperature much faster than a single chamber cob oven, makes better use of wood fuel.
- DIY plans developed by Ernie and Erica Weisner are available here.
Cast Iron Cookstoves
Cast iron cookstoves have come a long way with improvements in function and efficiency since the days when they were the primary cooking element in most homes. Best suited for colder climates where homes require some form of supplemental heating for better than half the year.
- More than just a cookstove with range and oven functionality, these stoves can also:
- Dry clothing and foodstuffs
- Heat the home
- Passively heat all of the home’s hot water.
- If applicable in your context, look into brands like…
Ben Falk’s videos on this subject are highly recommended if you are looking to learn more and assess your own context for a potential wood cookstove. Ben also offers a Wood Heating Intensive online class that goes into depth on his cookstove / home & water heating / drying rack set up and how he gets the most out of his fuel that is well worth the price of admission.
Champion ND-TLUD Biochar Micro-gasifier Cookstove
The “Champion” Biochar Cookstove was developed by Paul S. Anderson in 2005, and later updated in 2008, as a wood burning single burner portable cookstove that also produces charcoal as a byproduct of the cooking process. The Champion is classified as an ND-TLUD stove, ND standing for “natural draft” (the stove design creates its own draft) as opposed to forced air (a secondary power source and fan push air through the system), and TLUD standing for Top-Lit Up-Draft (the manner in which the fire is lit, at the top of the fuel column and burning downwards). Initially designed for use in Haiti as part of on-going disaster relief efforts, the Champion ND-TLUD aims to replace open fire cooking in the home – a major health hazard and inefficient use of available fuel wood (often in short supply).
The Champion Biochar Cookstove does not actually support the weight of the pots or cooking implements – those are instead supported by a pot stand or other cooking surface. This is critical as it allows the cookstove to be removed from underneath the pot or cooking surface once pyrolysis has completed and combustion of the charcoal has begun, enabling the user to preserve the charcoal. To allow for continuous cooking Champion stoves are used in tandem, so that a second fuel cylinder can be lit and swapped out with the first once pyrolysis is complete. The fuel cylinders act like batteries that can be quickly changed in and out to cook for however long is needed, and each cylinder yields charcoal at about 25-40% the original dry fuel volume.
Biochar cookstoves are still relatively unknown, and cannot yet be purchased, however they are easy to make. For construction plans detailing four different methods for construction a Champion-style ND-TLUD biochar cookstove see Paul S. Anderson’s Construction Plans for the “Champion-2008” TLUD Gasifier Cookstove PDF on the topic on his website.
- Quick to start cooking ~ 3-5 min wait time for fuel chamber to get going.
- Suited for outdoor / open air ventilated cooking situations.
- Produces a small but significant quantity of charcoal at the end of each pyrolysis phase, which can be saved and utilized as biochar, sold as high quality cooking fuel, or be left in the canister to continue cooking.
Systems For Cooking With Biogas
Biogas Primer
Anaerobic digestion is a simple biochemical process by which organic waste products (food scraps, animal manures, human wastes, crop residues, other organic “waste” materials) are broken down by microbes in an oxygen-free environment. This is the same process used in septic tanks and sewage treatment plants to break down waste. The byproducts of this decomposition include biogas – generally a mix of methane (CH4), carbon dioxide (CO2), water vapor (H20), hydrogen sulfide (H2S), and in some cases ammonia (NH3) – and a nutrient rich anaerobic leachate. Biogas, and specifically the methane it contains, can be burned in similar fashion to propane and natural gas, and most appliances can be converted to burn biogas. The nutrient-rich anaerobic leachate is a high value fertilizer for gardens, tree crops and main crop plantings. There is no odor when a biogas system has been set up and is running properly.
Biogas is most commonly used for cooking, but can also be used for heating. It can also be used to power an absorption refrigerator, similar to the propane powered refrigerators commonly used in RVs and off-grid scenarios. The potential to use biogas to power off-grid cooling systems for farms and homesteaders remains a largely undeveloped niche in the West.
Anaerobic digestion has four general stages: hydrolysis, acidogenesis, acetogenesis and methanogenesis.
- Hydrolysis: Enzymes break down and liquefy the smaller molecules and break down large polymers in the material.
- Acidogenesis: The products of the hydrolysis (soluble monomers) are fermented to volatile fatty acids (or VFAs) and alcohols.
- Acetogenesis: Acetogenic bacteria break down the VFAs and alcohols, acetic acid, carbon dioxide and hydrogen.
- Methanogenesis: The methanogenic bacteria convert acetic acid and hydrogen into CO2 and methane. (Note: The three earlier stages can take place at lower temperatures than methanogenesis.
Temperature & pH
Temperature and pH are the two most critical factors to monitor to maintain the digester in an optimal state for maximum methane production. Most anaerobic bacteria perform best in warmer temperatures, therefore, depending on the climate, additional steps may need to be taken to insulate the digester or even heat it in colder climates to maintain methanogenesis.
pH needs to be regulated to prevent the digester from going either too acidic or basic depending on what phase of the digestion process it is in. Balancing pH becomes less of an issue when a system is well buffered (a measure of its ability to resist changes in pH). In small, home or farm scale digesters, pH imbalances can be treated relatively easily and cheaply. A high acid condition (acidosis) can be corrected by adding small amounts of lime, ammonia or bicarbonates such as baking soda.
Carbon:Nitrogen (C:N) Ratios
Anaerobic bacteria generally require a C:N ratio of their feedstock to be around 30:1 – very similar to a typical thermophilic compost pile. Feedstock ratios will need to be adjusted based on their approximate C:N ratios to maintain an approximate 30:1 ratio overall.
| Feedstock | C:N Ratio |
| Cow Manure—Alfalfa | 16:1 |
| Cow Manure—Dairy (with bedding) | 21:1 |
| Pig Manure | 14:1 |
| Coffee Grounds | 20:1 |
| Sheep Manure | 20:1 |
| Chicken Manure | 15:1 |
| Oat Straw | 48:1 |
| Turnip Tops | 19:1 |
| Corn Stalks | 53:1 |
| Grass Clippings | 19:1 |
| Sunflower | 30:1 |
HOME BioGAS Units
The HomeBioGas company produces done-for-you biogas fermentation units for small scale household and farm use cases. Most notably, they have a Bio-toilet integration – a low-water use flush toilet that captures “the final frontier” of waste streams – your poop – and turns it into cooking fuel and garden fertilizer.
- HomeBioGas units are done-for-you – only minor assembly required to get up and running.
- Bio-toilet integration uses a hand pump system to flush the toilet and solid and liquid wastes into the digester bag. Recommend using a bidet to eliminate toilet paper.
- Purpose-built burners are included that are optimized to burn biogas from a low-pressure system.
- Integrated sandbags in the gas bag allow pressure to be adjusted as required.
- May require additional insulation and/or supplemental heat depending on climate – see the HomeBioGas Booster Kit.
- On-demand biogas hot water heater integration for water heating applications using biogas.
Visit the HomeBioGas YouTube Channel for more helpful and education videos on how their product works and the variety of situations to which it can be adapted.
DIY Biogas Systems
Biogas is a very accessible form of home-scale energy production and nutrient cycling. You can build your own anaerobic digester from commonly available materials just about anywhere in the world. There are two main types of small scale anaerobic digester designs; continuous flow digesters and batch digesters.
Continous flow digesters require daily feeding to maintain the anaerobic decomposition process. They produce biogas continually, and tend to be well suited to animal manures as their primary substrate inputs. The addition of new substrate pushes more “finished” slurry out of the digester at the other end.
Batch digesters are loaded once and allowed to complete all four stages of anaerobic decomposition, after which the effluent and is removed and the process is repeated. Batch digesters may be more effective with unprocessed plant-based substrates.
There are three categories of small batch digesters commonly built throughout the world; 1) the in-ground bag or tube style (continuous flow), 2) the in-ground dome style (semi-continous batch), and 3) the floating top/tank design (batch or semi-continuous).
The In-Ground Bag
Consists of a long trench (~ 20′) lined with a 48″ polyethylene tube to form the bag. An inlet is installed at one end, an outlet at the other, and a gas outlet fitting on top. Using a double layer of 6-8 mil poly plastic will help to reduce risk of puncture. A pressure-relief valve at the gas outlet will also ensure that gas can’t build up to too high a pressure and burst the bag. Requires approximately 100 gallons of manure slurry to charge initially, and then 10 gallons of slurry per day to maintain in continuous operation.
- Used commonly throughout Central America, well suited to more equatorial climates where supplemental insulation or heating is not required. Will work in some of the southernmost U.S. states.
- DIY installation plans available HERE.
The In-Ground Dome
This design involves a cast concrete, brick, or masonry tank buried in the earth with a cap on top. Initial construction expense is much higher than the bag style digester, however the rigid sides allow it to be buried deep enough to use the heat stored in the earth to maintain its temperature. This design holds a lot of promise for more northerly climates.
Floating Drum Digester
This design involves a lower container for the slurry and a floating upper container for containing and pressurizing the gas. This design has been utilized extensively throughout India. The
Solar Cookers
Solar ovens use reflective material to focus the radiant heat of the sun towards an enclosed pot containing the food to be cooked. Solar cookers have a bit of a reputation for being a novelty item that sounds good in principle but doesn’t work well, but they have come a long way in recent years. Some, like the Hanes Solar Cooker 2.0 shown below, have a cooking sleeve that insulates and elevates the pot so sunlight can be reflected onto the bottom of the pot. The adjustable sleeve eliminates the need for plastic cooking bags. This model boils a liter of water in about 50 minutes, is adjustable for high and low sun, and is packable and lightweight.
- Solar cookers only work when the sun is shining.
- Very easy to use.
Use caution when approaching as reflected light can be painful if looked at directly.
SOlar Dehydrators
Solar dehydrators use heat-absorbing surfaces to heat air and create a convection current the circulates hot air over the food to be dried. There are many different designs, and most all of them work to one degree or another. Solar dehydration is a great food preservation method for fruits, certain vegetables, mushrooms, herbs and more.
Downdraft solar dehydrators are an excellent design that works with fact that the heated air passing over food will be increasing in moisture content and progressively cooling, leading it to fall. Downdraft solar dehydrators work with this natural pattern by introducing the hottest, driest air at the top of the dehydration rack, allowing the air to cool and humidify as it passes down through the food racks, and is ultimately drawn out of the unit by a solar chimney on the backside of the unit.
- Solar dehydrators only work (well) when the sun is shining.
- DIY Plans Combo Package for the Missoula1 and WheatonATC1 models of solar dehydrators.
- DIY Plans for the HotAussie1 solar dehydrator – a smaller dehydrator for less intensive use than the Wheaton and Missoula models linked above.
