Greening of Ag: Renewable Energy Systems for Dairy Productions, a 2017 update

By Brad Heins, Associate Professor of Dairy Science

November 2017

The typical dairy farm uses a large amount of energy during milking activities. This is due to the frequency of milking and the energy intensive nature of harvesting milk, keeping it cool, and cleaning the equipment with hot water. Renewable energy systems generally become more economically efficient as the amount of energy used increases, making dairy farms a great place to incorporate renewable energy. 

Dairy farms have not typically been set up with energy efficiency in mind and often use relatively expensive fuel sources like heating oil or propane to heat water. One of the difficulties encountered with renewable energy systems is the intermittent generation of wind and solar energy whereas the energy load on a dairy farm is very consistent since cows are typically milked twice or three times every day (very large dairies may milk continuously). An efficient way to store energy has long been sought to tie energy production and consumption together. A dairy farm's need for both electricity and heat provides an ideal situation to generate electrical energy on-site to meet current electrical load requirements, displace conventional thermal fuels with electrical energy, and evaluate thermal storage as a solution to the time shifting of wind and solar electrical generation. 

At the University of Minnesota West Central Research and Outreach Center (WCROC) in Morris, MN, we have embarked on a new project that combines the synergies of the dairy and renewable energy programs. The goal of our project is to increase renewable electric energy generation on Minnesota dairy farms by establishing a "net-zero" energy milking parlor. We have been monitoring water and energy usage since the fall of 2013. 

The dairy operation at the WCROC in Morris milks between 200 and 275 cows twice daily and is representative of a mid-size Minnesota dairy farm. The cows are split almost evenly between a conventional and a certified organic grazing herd, and all cows spend the winter outside in lots near the milking parlor. The existing dairy equipment is typical for similarly sized dairy farms and includes none of the commonly recommended energy efficiency enhancements such as a plate cooler, refrigeration heat recovery, or variable frequency drives for pump motors. The WCROC dairy provides an ideal testing opportunity to evaluate and demonstrate the effect of on-site renewable energy generation and energy efficient upgrades on fossil fuel consumption and greenhouse gas emissions. A data logger was installed in the utility room of the milking parlor in August 2013 and has monitored 18 individual electric loads, 12 water flow rates, 13 water temperatures, and two air temperatures. Average values were recorded every 10 minutes for the last 4 years. The milking parlor has gas and electric meters that measure the total consumption of natural gas and electricity within the parlor. The data helped us evaluate energy and water usage of various milking appliances. Some small energy loads were not measured in unused parts of the barn, or were not directly related to the milking operation. 

These loads fall into miscellaneous categories and are estimated by subtracting all the measured energy use. Where the energy goes Overall, the milking parlor currently consumes about 250 to 400 kWh in electricity and uses between 1,300 and 1,500 gallons of water per day (see Figures on dairy electricity usage and dairy hot water usage). The parlor currently uses about 110,000 kWh per year (440 kWh per cow per day) in electricity and 4,500 therms per year in natural gas. A majority of the electricity used is for cooling milk (26 percent), followed by ventilation and fans and heaters (16 percent). Our dairy uses about 600 gallons of hot water per day, with a majority used for cleaning and sanitizing milking equipment, followed closely by cleaning the milking parlor. Energy and water usage fluctuates throughout the year because our dairy calves 60 percent of our cows from March to May and 40 percent from September to December. 

Therefore, water and energy use escalates dramatically during April. Our first energy efficiency 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 September 2013 installation, the vacuum pump used 12 kWh per day, a 75 percent reduction 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 upgrades. Furthermore, because of our organic and conventional systems, the dairy has two bulk tank compressors: one scroll and one reciprocating. The scroll compressor is the newest and uses 15 kWh per day versus 40 kWh per day for the reciprocating compressor. Based on milk production, the scroll compressor costs 73 cents kWh per cwt. versus $1.08 kWh per cwt., indicating the scroll compressor is more efficient. In terms of fossil energy use, milk harvesting consumed more energy than feeding and maintenance.  

During the fall of 2016, we installed a TenKSolar Reflect XTG 50 kW DC array. The annual production from this solar PV system is projected to be 70,000 kWh. The total solar system cost was $138,000 ($2.77/W), which is a 19.7-year simple pay back without incentives. However, if the Made in Minnesota incentives are added, the system would have an 8.6 year pay back. In 2017, we installed two 10 kW VT10 wind turbines from Ventera. These turbines are a 3 blade, downwind turbine model. The annual predicted generation for each turbine is 22,400 kWh. The total wind system cost was $78,400 per tower with a 35-year simple pay back without incentives. With the 30% federal credit each turbine would have a 24.5 year pay back. Read more about this phase of the project.

Our study 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. To improve energy efficiency, begin with an audit to gather data and identify energy-saving opportunities. Some energy efficiency options that may be installed on dairy farms include refrigeration heat recovery, variable frequency drives, plate coolers, and more efficient lighting and fans. A majority of these upgrades have immediate to two- to five-year paybacks. Make all electrical loads as efficient as possible, yet practical. Consider converting all thermal loads to electricity by the use of heat pumps that allow for cooling of milk. In the future, we have plans to harvest energy from our manure lagoon and store electricity as heat by use of heat pumps. Renewable energy options also can improve energy efficiency. 

We have developed a Dairy Energy Efficiency Decision Tool (.xlsm) to help provide producers a quick way to estimate possible energy and costs savings from equipment efficiency upgrades. The tool can be used to quickly see what areas of a dairy operation may provide the best return on investment. Furthermore, we have developed a U of MN Guidebook for Optimizing Energy Systems for Midwest Dairy Production (.pdf). This guidebook provides additional information about the topics that were discussed in this article, as well as the decision tool.

To complete our goals, we have secured grants from the University of Minnesota Initiative for Renewable Energy and the Environment and Minnesota Rapid Agricultural Response Fund, and Xcel Energy RDF Fund, which allowed us to introduce several energy efficiency measures into the milking parlor including equipment to convert all natural gas usage to electricity. Future projects will include monitoring energy and water usage on Minnesota dairies. Look for future updates from this project that will educate producers, energy professionals, and the general public on the implementation of renewable energy technologies for dairy production systems. 

More information about this project can be found on our Energy Systems for Dairy Production webpage.