Why we’re investing in biogas
Half of our team (Tim) used to design and build electric wind turbines, so our thoughts a year and a half ago were to design and build a wind turbine to power our aeration blowers, have a more sustainable farm, and save money on electricity. Then we got a year of virtually no wind at our location, courtesy of “massive global climate change”. Some people call this “global warming” but the fact is that climate is an engine driven by heat energy from the sun, and more energy means not just warmer, but more extreme weather: heat, cold, drought, flood and woe. We got dead calm and low rainfall out of the deal.
This failure of wind sent us in another direction in which we learned about biogas and wrote a successful $45,000 grant for a biogas project. Later, we got good help with this project from David House, author of “The Complete Biogas Handbook”, described by the title. We recommend it.
Biogas is mostly methane, with some carbon dioxide and a small amount of sulfur dioxide. Methane, the component of biogas that burns, can be used for virtually anything that propane or natural gas is used for, including heating, lighting, and powering internal combustion engine-driven electrical generators. You can use it to power automobiles and farm tractors. It can be made in a relatively low-tech fashion from any organic waste that was once alive, by putting that waste in a biogas digester (AKA a biogas generator) and “fermenting” it. During this process, the digester produces biogas and as a side product, a liquid concentrate that is a wonderful fertilizer. So, we are building our first biogas project now. It looks like it will save us $1,100 of our current $1,500 per month farm energy bill.
Now at this point people often ask “why don’t you just put in solar panels (AKA PV, photovoltaic, or solar electric)?” Well, we checked it out and found that we can power the farm for only $250,000 worth of PV panels and charging system. Yes, Martha, solar electric is for rich people. The biogas-powered electric generating system we’re building has a target price tag in the $25-35,000 range for a 10 kW (ten kilowatt) system, which makes it more affordable for a wider range of users than photovoltaic systems. We’ll talk a little about biogas first so you have some background, then explain why the biogas concept has so much potential for aquaponic farmers in cold climates.
The first part of our biogas project consists of building a biogas lab: we are just installing the circulating pumps this week, and should be able to charge our digesters and start our test runs sometime soon this year (2011). The lab will test different substrate recipes (the stuff the biogas digester runs on) and different techniques of making the biogas with different digester designs. It will will allow us to quantify the many variables that go into biogas production and then design a good affordable biogas digester with its attendant support systems and diesel electrical generator that is suitable for small farms. The lab will also give us data to develop methods and techniques so anyone with moderate construction and mechanical skills can produce biogas in an economical manner on a small farm for cooking, heating, and powering small engines.
A little explanation is in order here: most current biogas technology comes from from city sewage treatment plants that treat liquid wastes with 2% solids content. This is the amount of solid “stuff” in the waste stream that is fed into the biogas digester. In other words, they’re processing mostly water, and need very large (and expensive) digesters to process the huge volume of stuff that comes through their installations. A small amount of biogas technology comes from the large dairy and swine farms across the United States that often also put out liquid wastes with very low solids content. The price tag for these biogas/electrical generator installations on dairy and swine farms starts at around a half million dollars. So, the existing technology is unaffordable and also sized way too large for the average small farmer or sustainable community.
A small amount of research has been done that indicates that high solids (10% solids up to 25% solids) biogas production is feasible and also economically attractive. So, to make a biogas project for a small farm economically feasible, we need to figure out how to do higher solids and a mix of different kinds of solids such as is commonly available on a small diversified farm, rather than the steady-state and steady volume of low-solids waste that a pig or dairy farm puts out. That’s where the biogas lab comes in. It allows us to try out a lot of different ideas in a short time on a small budget to refine our digester design before we have to spend $10-12,000 on our full-size digester that we only have one shot at getting right.
To accomplish the most research economically in a short time, the lab has ten 5-gallon size digesters, six 6-gallon size digesters, and a single 500-gallon digester, with instrumentation to measure total gas production from each digester, plus analysis capabilities to measure the makeup and quality of the biogas we are generating. There are heat exchanger elements inside the digesters that circulate hot water captured from the waste heat of the electrical generator’s diesel exhaust so we can run the digesters in mesophilic mode (90-115°F) as well as psychrophilic (65-70°F) mode.
The reason for the mesophilic mode is that even though the mesophilic digester uses up energy in the form of heat to heat its contents, it produces much more biogas in the same time than the psychrophilic-mode digesters that operate at the lower temperature range. At the time of our next training this April 2011 we should have the biogas lab fully operational, and will be doing hands-on training on building and operating the various elements of a biogas digester and its associated systems.
…So: cold climates
Now that you have a basic understanding of our biogas project, we’ll explain why this is so important to aquaponics farmers in cold climates. We’re lucky to have a 365-day growing season at our farm in Hawaii, but most farmers in cold climates have a short growing season of only 5 to 7 months. They have to make all their income during this short time while having expenses that last for a full year. The two major problems these farmers face if trying to grow during wintertime are that heating greenhouses is expensive, and there’s not enough sunlight for good plant growth, resulting in a need for expensive supplemental lighting. Thus, they never even bother with the greenhouses because ultimately the cost to produce the vegetables is not tied just to the cost of building the greenhouses but also to unpredictable and continually rising petroleum-based energy costs for their heating and electricity.
Biogas offers a potential and sustainable solution to these problems. The fuel that powers the diesel engine on an electrical generator turns into about 65% waste heat that goes out the exhaust stack and through its radiator. Rather than paying for propane or heating oil to heat an aquaponics greenhouse in the cold months, the farmer can just recapture this waste heat with a very simple heat exchanger system, then affordably transfer it to the greenhouse to heat the greenhouse. If the aquaponics farmer either generates enough waste on the farm to feed his biodigester, or can cheaply transport it from a nearby free source (most farmers are happy to have someone show up to haul their piles of animal poop away for no charge), then the farmer can also have a relatively cheap source of electricity to power supplemental lighting for his aquaponic crops.
We feel that breaking food production’s current ties to petroleum costs is a good thing. It is our fondest hope that what comes out of our biogas project is a way for farmers in temperate and cold climates to grow affordably year-round, using renewable farm wastes and animal poop as a sustainable energy source, and that ultimately it will result in lower food prices for everyone.