Energy Systems

Biogas & Carbon Farming – Part 2

From a Permaculture Principles Perspective

In the first article in this three part series, we discussed our decision making process to use biogas. In this second article we will discuss using biogas here at Maya Mountain Research Farm through the lens of the 12 Permaculture Principles as outlined by David Holmgren in his book “Permaculture: Principles and Pathways Beyond Sustainability”



Principle 1: Observe & Interact

In deciding if biogas is right for you and your situation, and starting with a good analysis of your needs and opportunities for biogas, the questions you might ask yourself are:

Where will your feed material come from?

If you have a small dairy operation, or raise pigs, biogas would be a fairly obvious choice. If you make coconut oil, or sacha inchi oil as we do, the pressed seed cake is fantastic feedstock.

If you end up deciding to build or obtain a biogas plant, being aware of it becomes habit. Can we cook beans on the biogas plant, today, or do we not have enough gas? what feed stock is abundant, right now? banana peels? coconut whey from making oil? avocados? breadfruit?



Principle 2: Catch & Store Energy

Because of the maturity of our system, many nutrient and energy flows that would otherwise be wasted can be slooooowed down and taken advantage of. In the case of surplus food, some of it is sold, exchanged or donated, some can be fed to animals, and some of it can be fed to the biogas plant.

There are times when markets are saturated due to seasonality. If our avocados are bruised, or if they get overripe, they have limited value as food, but are high in embodied energy. The biogas plant converts the bruised flesh into burnable methane and we still get high value fertilizer.

Much like our photovoltaic system, where the sun charges the batteries during the day, and we use the power for lights at night, a biogas plant captures and stores energy that might otherwise be lost. The bacteria work for us all day and all night, and we have access to the stored energy as needed.



Principle 3: Obtain A Yield

Biogas helps us to obtain ADDITIONAL yields. By slowing the movement of nutrients flowing through our home/farm/communities, we can obtain yields that we would otherwise not. In doing so, we obviate the need to use fossil fuel in the form of natural gas obtained from the earth, or burning fuel wood. In addition to the yield of nutrient rich effluent, and fuel, this represents a form of avoided emissions of carbon.

Kathy Puffers brilliant Solar CITIES biogas system is integrated with an aeroponics system which creates additional harvests. Her system will be one of the systems we discuss in the third article in the series.



Principle 4: Apply Self-Regulation & Accept Feedback

This is a principle one would want to look at closely before you got into biogas. To avoid enthusiasm overruling reality the questions you might ask are:
a) Is my location suitable for biogas? You would want to know if you have space, if there are codes you need to overcome, if the society you live amongst will object.

b) Will I have time to attend to the biogas plant? If you leave home for work for more than a few days, who will maintain the system?

c) Can I obtain sufficient feedstock for my needs? If you live in a rural area and produce tonnes of food, chances are, yes, you have sufficient food stock to maintain the system. If you live in an urban area with access to a bakery, or a market, or a restaurant close by you may be able to source your feedstock from excess food or waste from those locations. Since we built the system, we have noticed it loves fats, and starches, and that brassica hearts and leaves affected by bacterial wilt will boost production.



Principle 5: Use & Value Renewable Resources & Services

Biogas is a great renewable resource. Since we built the plant we have had about 700 hours of free fuel. Our results, again, are specific to our location and the age of our farm. We have a lot of surplus food and much of it has minimal market value. It would otherwise rot or be composted. Much of the surplus energy and nutrient flows that we have here can be replicated in an urban area, or tied to food processing or animal husbandry if close to the location of the biogas plant.

You might be able to make arrangements with a close by operation to retrieve byproducts, which could feed your system, and avoid becoming pollutants.



Principle 6: Produce No Waste

By converting waste material, be it food waste, byproducts of food processing such as pressed seed cake from making oil, whey from making cheese or coconut oil, peelings of cassava, banana peels, or animal or human manure, which may be pathogenic, carrying worms, bacteria or viruses, to biogas to cook with, we end up with energy in the form of gas, and fertilizer which we can move back to the soil.

Pijan rei banana, apple banana, bluggo banana and plantain skins are often used to feed the biogas plant, as are the overripe fruit. We use bananas extensively in the pioneer phase.
Image by author

One of the arguments we have heard against biogas is that the excess food would be better composted, but in the creation of biogas we still end up with a liquid fertilizer, while also accessing the energy available through burning the methane.



Principle 7: Design From Patterns To Details

Agroforestry System
Our multistrata agroforestry system produces surplus food for the biogas plant. In line of site we have avocado, caimito, coconut and banana, all of which we use for making biogas, as well as turmeric, cacao, coffee, psalmwood/Cordia alliadora, Mayflower/Tabebuia rosea, madre de cacao and cashew.
Image by author.

Using the Principles of permaculture, we arrived at creating a multistrata agroforestry system or food forest. Over decades this resulted in an abundant daily production of food, such as bananas and coconuts, vegetables in season and seasonal fruits and food from tropical staple trees, biogas was a great element to put into the larger system. Much of this production is cycled through our kitchen, which is the nexus of most energy and nutrient flows for the farm. Some of it is consumed on site, and some is taken off the farm to sell or donate to a feeding program we support. Some is collected for our rabbits, and some goes to the poultry. Some of it is processed, like when we make sacha inchi oil, or coconut oil, or pineapple or mango vinegars.

With all of the nutrients and energy flows going though the kitchen, putting in the single element of a biogas plant and stove was a detail that built on patterns that had been established over time. We already had used this location for cooking and for processing food. Biogas was an appropriate addition.

In some future time, we would like to build a larger and more integrated system tied to animal husbandry sheep, goats, pigs, rabbits, human manure, and vegetable waste, and with the effluent cycled through an aeroponics system, like Kathys (to be examined in Part 3).



Principle 8: Integrate Rather Than Segregate

By situating our biogas plant close to the kitchen and between the kitchen and the rabbit house and poultry system, we added an element that both provided the service of disposal and treatment of surplus food waste and limited quantities of manure, we obtained the yields of fertilizer and methane production.

The location facilitates ease of working with the biogas plant. Between the kitchen and the animals, this makes feeding the biogas plant easier as we make several trips a day to the rabbits and the poultry. Our biogas system was placed north of the kitchen, but very close, because our wind comes predominantly from the east-northeast. if there had been any smell, and there hasn’t been, it would not blow into the kitchen.

Tying the effluent back to the farm, we are collecting and dispersing nutrients to target areas.



Principle 9: Use Small & Slow Solutions

The timing on installing a biogas plant is important. It helps if other elements are in place to make it possible, especially in a rural area. If, back in 1988, when I first started farming on what was degraded citrus and cattle land, I had built the Solar CITIES biogas plant, I would have been unable to feed it, easily, especially after I got rid of the last of the cattle.

By working on other aspects of the farm, and not thinking of biogas, much, over the years, we built up our resources, eventually arriving at a place where biogas was an attractive option that clicked off on a lot of needs and opportunities.



Principle 10: Use & Value Diversity

There are many overlaps between the principles. Having multiple sources of any single service or good is an important aspect of sustainability. We have diverse ways to cook, solar cookers, wood burning cook-stove, fire hearth, cob oven, and biogas neatly compliments all of them. In this case, having this single element as part of a diversified energy portfolio, and as one of several ways to pass nutrients through the kitchen, with some food scraps going to the poultry or rabbits, some to the black soldier flies or vermi-composting bins, and some going to the Solar CITIES biogas plant, we have a diverse range of possibilities for nutrient streams.

Our biogas plant provides diverse services and products. It disposes of waste food and humanure, it creates useable energy, and it created high value liquid fertiliser.

Happily, our biogas plant loves the diet it has, this time of the year, of avocado peels, over mature avocados, bananas, pineapple skins, mango skins, breadfruit, as well as mulberry leaves, cassava peelings and a little bit of humanure.

Bananas & Avos
Banana and avocados that have been damaged or are not suited for consumption or sale are feedstock for the biogas plant.
Image by author
bread fruit
Over ripe breadfruit is excellent feedstock for the biogas plant, as are breadfruit peels. Breadfruit is also a champion of food security.
Image by author.



Principle 11: Use Edges & Value The Marginal

Some of the most marginalised people are indigenous and campesino women who use firewood on open hearths for cooking. Rural women are more likely to suffer from chronic obstructive pulmonary disease (COPD), which is one of the leading causes of death in the world due to lack of access to clean burning stoves and internal fires in houses with inadequate ventilation. Additionally ocular diseases tied to the irritants in smoke are common among women in rural households.

Even more marginalised people, such as people who scavenge dumps, destitute people who live on the edge of society, are more likely to end up in hospital for untreated chronic pulmonary and ocular problems tied to smoke exposure than other working class people with access to LPG. Part of it is that dumps frequently catch fire or are set on fire, and the other is that people who scavenge dumps are less likely to have access to clean burning stoves.

A recent visit to the dump in Belmopan here in Belize, we met several families of scavengers, refugees from El Salvador and Honduras. Diverting a few buckets of biomass from the dumps they scavenge, would be enough to fuel 2-3 hours of cooking, if small biogas plants were made available to them.

This is a project we are looking at.



Principle 12: Creatively Use & Respond To Change

In 1989, I saw a system fed by pig manure at a farm called “Dem Dats Doing”, owned by Yvonne and Alfredo Villoria. Their system has a floating gas container. I found it appealing, but in the early years, a biogas plant would have been more work and the supporting infrastructure was not there.

It was not till 1991 that I took my PDC with Michael Pilarski, Chuck Marsh, Rick Valley Jose Caballero and Marc D. Cohen. Applying the principles of permaculture to the landscape, we arrived at the concept of what would now be called a “food forest”, “stacked polyculture” or “multistrata agroforestry system”.

Our harvests started to be larger than we could consume, feed to animals or donate, and larger than we had markets for. That created the niche for a biogas plant.

Biogas is now part of a larger system, one element in the system that provides multiple services and goods, fuel creation, waste management and fertiliser creation. It is also one of the multiple ways that we are able to cook our food.

In closing, Biogas is a tool that should be in the permaculture tool kit. It is not a universally applicable tool, but it is a tool that is worth considering as part of a diversified energy portfolio, and as an additional way to deal with waste that compliments composting. Systems can be large, to accommodate municipal or community waste management or for large scale animal husbandry or vegetable or fruit production, or small, to facilitate home scaled food and waste disposal.

In Part 3 we will look at different designs for small scale biogas plants, and discuss their Pros and Cons.

Christopher Nesbitt

Christopher Nesbitt has run the Maya Mountain Research Farm, an ongoing permaculture project in southern Belize, Central America, since 1988. Former degraded citrus and cattle land, the farm is focused on the intersection of agriculture and ecology. He managed the Toledo Cacao Growers Association in cooperation with UK based Green & Blacks from 1997 to 2004. Since 2004, the Farm has been working on specific ways to draw down carbon, with an emphasis on food security, degraded land repair, multistrata agroforestry systems and staple tree crops. The work done at MMRF clicks off on all 17 of the Sustainable Development Goals. In 2019, the farm won the Commonwealth Secretary Generals Innovation for Sustainable Development Award under the Prosperity category. Christopher runs the farm with his wife, Celini Logan Nesbitt


  1. Bob,

    We use a Flexpower One power center with an MX80 controller. Its Maximum Power Point tracking lets you take high voltage, 118vdc, and drop it to meet your batteries set points.

    Our NiFe batteries are 500 amp hours at 24vdc. We changed the set points to 29v for bulk charge and maximum charge at 33 volts. This keeps the batteries full.

    We have discharged it to 20 volts wiht no damage to capacity.

    They are expensive, but we have not had to change them and it is going on 5 years since we got them.
    We bought ours from Iron Edison, but they are Chinese. You might get a better deal on Alibaba, but maybe not, with shipping. Our abattery bank was donated, so we went with what was easy and fast.

    They are fantastic batteries.

    Best wishes,


  2. What are the differences between slurry ,gas
    – as far odour, bacterial count, chemical composition, manure content, NPK Content, calorific value coming out of biogas plant having following raw materials
    1) Cow Dung
    2) Human Excreta
    3) Kitchen Waste
    4) Agriculture Waste
    5) Ripen fruit waste
    6) Poultry Waste
    7) Pig Excreta

    1. Slurry is the feedstock that goes into the biogas digester. Our slurry tends to be mixed food scraps and human feces. I am not sure on the value of the different feedstocks in terms of caloric energy, but food waste has more embodied energy than manures of any kind.

      Our digester is a small one designed primarily for food waste. It can accept up to 30% manure, including human feces, but more than that the short retention time would perhaps not fully digest the manure. As it is, the effluent has an agreeable smell, not unpleasant, which fades quickly when applied to the soil.

      I have read that the effluent has much of what went into the digester, so if you wanted more phosphorous, for example, using banana peels and bruised fruit would increase the amount of that nutrient.

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