At current consumption rates fossil fuels will become supply limited, especially as global energy demand is projected to increase. Fossil fuel combustion is the leading contributor to man-made greenhouse gas (GHG) emissions and thus requires strategies to manage energy production and use to reduce environmental impacts.

Agriculture is increasingly trying to provide food in a sustainable manner. Dairy farms are especially important as they as they can both improve energy efficiency and become bioenergy producers due to the natural coupling that exists between the dairy and energy sectors. To achieve this goal, it is important to understand where energy is used, the types of fuels being used, and how bioenergy could be integrated at dairy farms.

Dairy Farm Energy Use

Dairy farming is evolving to use more energy intensive processes to improve production and revenue. This is especially true in larger operations where mechanization such as rotary parlors or manure processing (e.g. solid-liquid separation) are increasing in practice (Fact sheet on solid-liquid separation).

At a dairy farm, energy is used for crop production in a variety of ways. Farmers know how much diesel fuel is used to operate the machinery needed to plant seeds, apply fertilizers, and harvest crops, but it is easy to forget that it also took energy to produce these inputs. For most crops (other than legumes) more energy is used to make the nitrogen fertilizer than to fuel all tractor field operations. Making efficient use of manure nutrients a great way to save energy as well. At the milking center, housing facilities, and other farmstead buildings, electricity is used to operate the milking machines, for lighting, milk cooling, and ventilation, while natural gas or propane may be used for heating and pasteurization. During manure handling, energy is needed for collection with mechanical systems which use electricity or skid loaders which use fuel. When farms integrate manure processing, such as sand separation or solid-liquid separation, generally electricity is required to operate these systems. Transporting manure to storage and to land for final application also requires energy to operate pumps or tankers and other equipment.

Total energy consumption can vary significantly depending on the management practices and technologies adopted at each dairy farm. Life cycle assessment (LCA) studies have reported that total energy (energy consumed + energy needed to manufacture material and energy resources such as fertilizers and diesel) can range from 0.6 to 3.0 MJ/pound of milk produced (1.3 to 6.7 MJ/kg milk) (2, 3, 4). This number includes all forms of energy used at the dairy farm (e.g. electricity, diesel, natural gas).

Dairy Farm Energy Efficiency

Dairy farms can increase their energy efficiency by reducing total energy consumption on-farm, reducing the use of resources that demand energy to be manufactured (e.g. fertilizers), or by increasing milk production while maintaining the same energy consumption levels. Dairy farms can become energy producers by integrating bioenergy systems in their operations, which will improve both their economic and environmental sustainability.

Energy Production Opportunities at a Dairy Farm

Dairy farms have opportunities for integration of bioenergy production systems, the most common being biogas production through anaerobic digestion. Biogas, a renewable gas mostly comprised of 65% methane and 35% carbon dioxide, can be used to generate electricity, directly combusted to generate heat, cleaned and injected into the natural gas pipeline system, or cleaned and compressed to be used as a transportation fuel. The production of biogas at a dairy farm can make the farm a net energy producer, while at the same time mitigate GHG emissions from both manure storage, through methane reduction, and replacement of fossil fuel sources (Fact sheet on anaerobic digestion).

Other opportunities for integration with the bioenergy sector include (but are not limited to) the production of ethanol and biodiesel. Production of biofuels results in co-products that can be fed to dairy cows as feed supplements. For example, dry distillers grains with solubles (DDGS) are available when ethanol is produced from corn, and soybean meal is a result of the oil extraction when biodiesel is produced from soybean oil. Having a secure market as cow supplement for these products can benefit both the dairy and biofuel industries environmentally and economically.

References

1. International Energy Agency (IEA). 2017. Key World Energy Statistics 2017. https://www.iea.org/publications/freepublications/publication/KeyWorld2017.pdf
2. Cederberg, C., and M. Stadig. 2003. System expansion and allocation in life cycle assessment of milk and beef production. International Journal of Life Cycle Assessment 8:350–356. https://doi.org/10.1007/BF02978508
3. International Dairy Federation (IDF). 2009. Environmental/Ecological Impact of the Dairy Sector: Literature review on dairy products for an inventory of key issues. Bulletin of the IDF 436/2009. International Dairy Federation, Brussels, Belgium. http://www.ukidf.org/documents/Bulletin436.pdf
4. Aguirre-Villegas, HA, TH Passos-Fonseca, DJ Reinemann, LE Armentano, MA Wattiaux, VE Cabrera, JM Norman, and RA Larson. 2015. Green Cheese: Partial life cycle assessment of greenhouse gas emissions and energy intensity of integrated dairy production and bioenergy systems. Journal of Dairy Science 98: 1571–92. https://doi.org/10.3168/jds.2014-8850