REVIEW: DAIRY FARM ELECTRICITY USE, CONSERVATION, AND RENEWABLE PRODUCTION-A GLOBAL PERSPECTIVE

This review summarizes electricity use on dairy farms, with a focus on how energy is used, energy use indices (EUI), conservation strategies, and generation of renewable energy to reach net zero. EUI of electricity consumption varied between the identified studies primarily based on farm management system (confined, pasture-based), housing type (tie-stall, free-stall), and region (North America, Europe, Asia, Africa, Oceania). The highest electricity usage was associated with milking and milk cooling systems, which, on average, accounted for 23% and 22% of total electricity use, respectively. Energy use scaled per cow (EUIc) was lower, on average, for pasture-based dairy systems than for confined systems (475 vs. 769 kWh cow(-1) y(-1)). Considering milk production, the average EUI scaled to milk (EUIm) was lower for pasture-based systems (6.6 kWh 100 kg(-1)) than for confined systems 9.2 kWh 100 kg(-1). Considering all non-irrigated farm types, EUIm averaged 7.7 kWh 100 kg(-1) and EUIc averaged 612 kWh cow(-1) y(-1). There was a large range of EUI, with higher values associated with automated milking systems and irrigation. Electricity consumption by the global dairy sector (excluding irrigation) was estimated using the average EUIm at approximately 64.2 TWh y(-1). The main conservation technologies include variable speed drives (milk vacuum pumps, milking systems, fans), pre-cool heat exchangers, refrigeration heat recovery systems, energy-efficient light fixtures (compact fluorescents, light emitting diodes), and efficient ventilation (high-volume low-speed fans). Theoretical savings of up to 32% overall could be achieved by combining several technologies. Feedback from electricity monitoring can inform dairy farmers of their energy use pattern to guide decisions to reduce consumption. Tools for predicting energy use and related costs on dairy farms, which can indicate potential energy savings from operational changes, were reviewed. By combining conservation methods with renewable energy from biogas or solar, many dairy farms can produce enough electricity to reach net zero electricity. For example, a hypothetical barn-based 250 milking-cow dairy farm consumed 1021 kWh cow(-1) y(-1), on average, and could produce approximately 1095 kWh cow(-1) y(-1) using a biodigester or 960 kWh cow(-1) y(-1) using rooftop photovoltaic solar panels.