Irish Dairy Solar Load Shifting And Slurry Aeration Guide

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Key Takeaways

• Daily electricity demand on Irish dairy farms is concentrated during morning milking (6:00 to 8:00 am) and evening milking (3:00 to 6:00 pm).
• South-facing arrays yield up to 1,000 kWh per kWp annually, whereas east-west orientations produce around 850 kWh per kWp (a 10% reduction) but deliver superior milking self-consumption.
• Plate coolers paired with Direct Expansion bulk tanks deliver efficient milk cooling without the high capital costs and mechanical complexity of ice storage systems.
• Diverting surplus daytime generation to water heating and slurry aeration reduces expensive battery capacity requirements.
• Farm battery storage is benchmarked at 0.5 kWh per 1 kWp of PV, delivering a 10,000-cycle design lifespan, 90% depth of discharge, and 80% to 90% round trip efficiency.

Dairy Energy Profiles and Milking Load Patterns

Dairy farming in Ireland presents distinct electrical demand dynamics. According to extensive research from Teagasc Moorepark, peak electricity usage happens during morning milking (6:00 to 8:00 am) and evening milking (3:00 to 6:00 pm). The primary power consumers during these windows include vacuum pumps, milk transfer pumps, milk cooling compressors, and high-temperature water heaters.

Because traditional south-facing solar arrays generate peak power between 11:00 am and 2:00 pm, dairy operators must implement deliberate load-shifting strategies to prevent uncompensated export and maximise self-consumption savings.

Array Orientation: South-Facing vs. East-West Splitting

The physical orientation of farm building rooftops strongly influences diurnal generation alignment:

• South-Facing Generation: A south-facing solar PV system with a 20 pitch will generate the most electricity, producing up to 1,000 kWh per kWp of panels annually. This configuration maximises total energy volume but generates the majority of its yield when parlour demand is low.
• East-West Splitting: Splitting the array across east- and west-facing shed roofs reduces overall generation by about 10% (producing around 850 kWh per kWp annually). However, it shifts electricity production closer to the farm's peak demand times, improving self-consumption efficiency. The eastern panels ramp early to support morning milk cooling, while western panels sustain evening parlour wash-down cycles.

Milk Cooling Technologies and Thermal Load Diversion

Milk cooling constitutes roughly 30% of total electrical consumption on pasture-based dairy farms. Teagasc evaluates cooling strategies based on capital expenditure and thermal efficiency:

• Plate Coolers and Direct Expansion: While some dairy farms use ice storage systems for milk cooling, the most common method is using plate coolers and Direct Expansion bulk tank cooling systems. These systems are preferred because they efficiently cool milk without the high initial costs and complexity associated with ice storage systems.
• Water Heating Diversion: Farm water heaters require substantial energy to maintain wash temperatures. Farms that can divert excess solar energy to a hot water heater or an ice bank may need less battery storage, converting surplus midday solar directly into stored thermal energy.
• Continuous Load Integration: Unlike batch milking parlours, automated milking systems operate continuously, spreading electricity demand throughout the day. This consistent energy demand aligns well with solar PV generation, which typically peaks during daylight hours, allowing farms to maximise the self-consumption of solar energy.

Battery Storage Benchmarks and Cycling Performance

Where electrochemical storage is installed to support parlour startups or slurry aeration base loads, Teagasc recommends clear sizing ratios: