By using the products (and sometimes the wastes) from one part of an operation as an input to another, Integrated Food Energy Systems (IFES) simultaneously produce food and energy. The result is an exchange of energy, and sometimes of nutrients, across a farming or food processing operation, and potentially an overall reduction in environmental footprint.
IFES can include a wide range of practices and technologies, including agroforestry, biofuels, biogas systems (such as anaerobic digesters), on-farm renewable energy (wind, solar PV, geothermal, etc.); waste heat, and combined heat and power (CHP).
The USDA defines agroforestry as trees and livestock intentionally grown together to take advantage of their components as an integrated agroecosystem to boost productivity. Agroforestry has been proven to protect and enhance ecosystem services at both the local and landscape scale, producing food, feed, and wood products, thereby providing income diversification and an avenue for climate change mitigation and adaptation. In some cases, crop residues can be used for energy and nutrients, such as feeding byproducts to livestock, as compost and for fuelwood.
A hectare of an agroforestry system is estimated to contain 50 to 75 Mg carbon per hectare, as compared to row crops, which contain less than 10 Mg carbon per hectare (silvopasture.org; Bogdanski, 2012).
Over 40 percent of the global population (or approximately 3 million people) rely on wood and other biomass (charcoal, agricultural waste, and dung) for fuel.
Because carbon is released during fuel combustion, which is then sequestered by plants throughout their growth, bioenergy has the potential to reduce GHG emissions. Nevertheless, one should be aware that carbon emissions are released in the conversion of carbon-rich land to bioenergy feedstocks.
An example of a biofuel crop that serves as both a nitrogen fixer for soil health, and as an edible, nutritious food for human and animal consumption, is the pigeon pea in Malawi. The leguminous part of the plant provides a rich source of protein, while the woody stalk material is used for cooking. In addition to these multiple uses, the pigeon pea is commonly grown as an intercrop between rows of corn, sorghum, or millet, thereby allowing for further consumable crop growth without devoiding the soils of nitrogen.
Biogas / Anaerobic Digesters
Anaerobic (oxygen-deficient) digesters use microorganisms to break down biodegradable materials in the absence of oxygen, in order to manage waste, reduce odors, and/or produce fuels. China currently leads the world in biogas production, using it to serve 25% of its rural population.
An example of a biogas IFES is the Vietnamese Gardener’s Association’s (VACVINA) vegetable and fruit production. Together with fish ponds and livestock, their crops are interwoven with biogas production. “In VACVINA households, some products from the garden are used to feed the fish, while the fish pond provides water, mud and slime to irrigate and fertilize the garden. Fish waste is given to animals as feed and animal manure is used as fertilizer for plant and food for fish, as well as for biogas production” (FAO, 2012) Whatever meat, milk, fish and vegetables are not consumed by households are then sold to the local market. Additionally, these biogas digesters generate enough daily fuel for cooking and lighting, and the resultant slurry can be used as a fertilizer to improve soil quality for growing vegetables. (FAO, 2012)
Since some food is produced for home consumption, while excess is sold to market, and fertilizer costs are roughly halved, the payoff for these biogas systems is quite good. Additionally, farmers may improve their quality of life thanks to the addition of a biogas digester. “Long hours formerly needed to collect firewood can be saved, and respiratory and eye diseases related to smoke decrease significantly. The unpleasant odor of unhygienic pig and manure operations and the pollution of nearby waterways vanishes, which does not only serve the farmer but also the environment” (Bogdanski, 2012).
Renewable Energy IFES
Wind power is not a new concept in agriculture. Beginning in the late 1800s and early 1900s, American farmers ground grains by using wind energy to pump water and generate power.
Wind power currently represents the fastest growing renewable energy source. Many people like its simple design, and its benefits have affected many demographics worldwide, especially farmers because of its ability to quickly generate revenue, and because farmers are most likely to have the land base for housing wind turbines. Additionally, if the land is appropriate, wind developers are apt to jump at the opportunity to invest. Wind turbines are also appealing to farmers, because once installed, they are relatively inexpensive to maintain and operate. Energy produced once an operator breaks even can be considered profit, or at the very least, “free” energy.
However, one should note that in the short-term, wind can be unpredictable. On a year-to-year basis, estimates of potential wind power are easier to come by. Research gains still remain for figuring out how to store wind energy for later use.
Adding solar arrays to farms is appealing to farmers because their terrain tends to receive good sun exposure anyway (in order to be able to grow crops efficiently). Livestock and dairy operations make solar investments particularly sensible due to their large water heating requirements, including cleaning and sterilizing animal equipment, providing hot water for pen cleaning, as well as for warming and stimulating cow udders. Up to 40% of energy on a dairy farm is used to heat water and cool milk. Aquaculture and breweries represent additional industries that can use solar energy for hot water needs, including heating water for fish hatcheries. According to the USDA consensus, in 2009 there were 7,968 U.S. farms from all 50 states using solar panels for energy generation. Sources: (Xiarchos and Vick, 2011; USDA, 2009; http://www.usda.gov/oce/reports/energy/Web_SolarEnergy_combined.pdf; http://www.agcensus.usda.gov/Publications/2007/Online_Highlights/Fact_Sheets/Practices/energy.pdf
Heat can be recycled in a number of ways through municipal operations. Municipal waste heat recovery captures heat from industrial processes, machines, and equipment—which would usually be considered a useless by-product—and recycles it back into the system. Waste heat recovery boilers work by being placed on top of the heat source in order to generate steam, which then powers turbine generators to produce electricity.
The poultry industry is beginning to take on Waste Heat Recovery (WHR) operations as well. Heating cold fresh air accounts for approximately 80% of the fuel used in poultry farming, so this figure can diminish significantly when the heat is captured from ammonia-filled “dirty” air. The preheated fresh air is then distributed throughout the barn with “top to ground mixing,” such that warm air with uniformed distribution is able to help maintain a comfortable environment, thereby reducing the chances of respiratory infections.
Capturing and reusing heat from landfills represents yet another method of recycling “excess” heat within the solid waste industry. Chemical and biological reactions cause the waste to disintegrate within temperature ranges of 20 degrees C to over 90 degrees C. The result is about 50% methane, 42% carbon dioxide, 7% nitrogen, and 1% oxygen. The methane and carbon dioxide can then be extracted via wells dug intermittently throughout the site, and piped for combustion and/or for power generation. When methane is combusted, it is converted into carbon dioxide, which then runs through a generator to be turned into power. In additional to producing electricity and decreasing GHG emissions, capturing and converting methane from landfills also prevents volatile organic compounds and odors from being released.
Sources: http://www.carbonneutral.com/resource-hub/carbon-offsetting-explained/project-types; http://www.heartlandfarmenergy.com/products.html; http://www.energysystemsgroup.com/landfills.asp; Grillo, Robert J. Energy Recycling – Landfill Waste Heat Generation and Recovery. Curr Sustainable Renewable Energy Rep (2014) 1:150–156