A dairy's carbon footprint is broader than just electricity use

The University of Minnesota West Central Research and Outreach Center organized and hosted the 1st Midwest Farm Energy Conference, June 17-19 in Morris, MN. The program was developed in partnership with industry sponsors, the Initiative for Renewable Energy and Environment (IREE), and the Rapid Agricultural Response Fund and included a variety of topics related to energy systems for dairy and swine facilities. There were 13 presentations including Steve Peterson, Director of Sourcing Sustainability at General Mills. The conference included: energy optimized systems for dairy production, energy conservation and generation in swine facilities, and practical information for agricultural producers and energy experts. More information and conference presentations are available here.

The dairy operation at the WCROC milks 250 cows twice daily and is representative of a mid-size Minnesota dairy farm. The goal of our project is to increase renewable electric energy generation on Minnesota dairy farms by establishing a "net-zero" energy milking parlor. As the research goes forward, we are beginning to add new energy savings equipment, renewable energy production, and practices to help lower the energy requirements for our dairy operations. One of our goals is to conduct a life cycle assessment (LCA) study on our dairy products.

Our team at the WCROC in Morris, MN has been monitoring water and energy usage since August 2013 within our two dairy production systems. The data have included all the electricity, natural gas, and petroleum products used directly in animal care, along with the indirect energy used to grow feed for the dairy. A data logger (Campbell Scientific CR3000) was installed in the utility room of the dairy milking parlor in August 2013 and is monitoring 18 individual electric loads, 12 water flow rates, 13 water temperatures, and 2 air temperatures. Average data values are recorded every 10 minutes. The data were used to evaluate energy and water usage of the various milking appliances throughout the day and total daily usage over a month or year. After a year of baseline, renewable energy alternatives were added to the facility to reduce the carbon footprint of the dairy production system.

Figure 1. Energy use in milk harvesting at WCROC Dairy

Overall, the milking parlor currently consumes about 250 to 400 kWh in electricity and uses between 1,200 and 1,500 gallons of water per day (Figure 1). One energy efficiency upgrade was installed in the milking parlor in late September 2013. The upgrade was a Variable Frequency Drive for the vacuum pump. Before the upgrade, the vacuum pump used 55 to 65 kWh per day. After the installation, the vacuum pump uses 12 kWh per day, resulting in a 75% decrease in energy usage. The data show a large drop in daily electricity usage by the pump providing a vivid example of the kind of energy savings that can be achieved with relatively simple equipment upgrades. This example also hints at the potential for large decreases in the energy needed to harvest milk if the whole system is re-engineered with energy efficiency in mind.

Furthermore, the dairy has 2 bulk tank compressors: one scroll compressor and one reciprocating compressor. The scroll compressor is the newest compressor and uses 15 kWh per day versus 40 kWh per day for the reciprocating compressor. Based on milk production for the two dairy herds, the scroll compressor costs $0.73 kWh per cwt versus $1.08 kWh per cwt, indicating the scroll compressor is more efficient than the reciprocating compressor.

Figure 2. Carbon emissions from the WCROC Dairy

In terms of fossil energy use in the organic system (Figure 2), milk harvesting operations used more energy than herd feeding and maintenance (1.51 vs. 0.93 MJ/Kg FCM, respectively). This suggests that fossil energy use per unit of milk could be greatly reduced by replacing older equipment with new more efficient technology or substituting renewable sources of energy into the milk harvesting process. In fact, a new scroll compressor installed to replace an older failed piston compressor reduced fossil energy use per kg of milk by roughly 3%. In examining the carbon footprint, it was found that animal husbandry (enteric emissions, 1.07 CO2 eq/kg FCM) emitted more greenhouse gasses as measured by kg of CO2 equivalents than did the milk harvesting operation (0.55 CO2 eq/kg FCM).

This project will investigate an efficient energy storage technology and system that could significantly improve the feasibility of renewable energy on dairy farms. A dairy farm's need for both heat and electricity provides an ideal situation to evaluate thermal storage as a renewable energy solution.