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Innovative renewable energy generation and storage for dairy farms

Brad Heins
Assistant professor - Organic dairy production
September 28, 2013

The typical mid-sized 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. Essentially, we want to remove our milking parlor from the electric grid. To complete our goals, we have recently secured grants from the University of Minnesota Initiative for Renewable Energy and the Environment and Minnesota Rapid Agricultural Response Fund, which will be used to introduce several energy efficiency measures into the milking parlor including equipment to convert all natural gas usage to electricity. A thermal storage system employing an electric heat pump will also be installed to recover heat from the milk refrigeration system and solar thermal collectors. A system schematic is shown in the accompanying graphic. Recently, we have been recommended for funding from Xcel Energy to add a 20 kW small wind turbine and a 54 kW solar photovoltaic array to the dairy.

The dairy operation at the WCROC in Morris milks between 180 and 240 cows twice daily and is representative of a mid-size Minnesota dairy farm. 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. 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. We have started to instrument the current milking system with data loggers to establish baseline energy usage. The milking parlor currently consumes about 110,000 kWh per year in electricity and 4,000 therms per year in natural gas. After the existing milking components of the dairy enterprise have been characterized, renewable energy and energy efficient upgrades will be introduced into the system. Demonstrating practical and economical ways to introduce renewable energy generation on dairy farms could produce large benefits for the farmer and electric utilities since dairy farms typically present a large electric load during peak times in the late afternoon and early evening.

Also with this project, life cycle analysis will be conducted on dairy productions systems (conventional and organic) by using measured inputs and outputs of agricultural products such as milk and meat from calves and cows to calculate greenhouse gas emissions. During June 2015, we will host a national/international agricultural energy conference at the WCROC in Morris. Participants at the conference will experience innovative and globally unique agricultural energy-optimized systems. 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.

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