Due to its high and relatively predictable electricity demand, the dairy sector has a significant opportunity to reduce operating costs and carbon emissions through solar PV.

The aim of installing a solar PV system on dairy farms is to maximise self-consumption and only exporting electricity as a last resort.

As the following two examples show, regardless of the size of the farm, solar PV can pay on dairy farms. This example will run through how solar PV can work on a 100-cow farm and a 300-cow farm.

100-cow farm with conventional milking parlour

The first example runs through an example of a typical 100 cow dairy farm with conventional milking parlour.

Note that current electricity prices vary significantly among farmers and will affect payback time. The key assumptions are below:

  • Annual electricity use: 45,741kWh.
  • Day rate for electricity: 0.25c/kWh, night rate electricity 0.15c/kWh
  • Annual electricity bill: €11,435 plus VAT.
  • Main uses: bulk tank (72%), water pump (19%), hot water (2%), lighting (4%), cubicles (2%) and sump pump (1%).
  • Area of roof space available for solar PV: 320m2 east and west.
  • ESB connection: three-phase.
  • Maximum import capacity: 29kVA.
  • Location of transformer: within 75m.
  • Battery storage: 10.2kWh storage.
  • Size of bulk tank: 25,000l.
  • ACA: 100%.
  • Electricity demand

    A system where the panels are facing east and west would suit the profile of the site better due to having two separate daytime peaks when milking.

    Spread of electricity usage through the day.

    This means that electricity generation is better spread and utilised throughout the day.

    Battery storage would be a viable option here as it would act as buffer between usage and generation.

    Once the battery is full, then the electricity would be diverted towards heating water and only when all on farm-uses are exhausted would the excess electricity be exported to the grid.

    Solar PV system

    For this scenario, a 40kWp (ie the peak output of the solar PV system) was selected. This would require around 300m2 of roof space and need planning permission and an ESB grid connection under the NC-7 process.

    The annual output of this system is expected to be 36,000kWh, generating around 79% of the farm’s electricity requirements.

    The cost of the solar PV system would be €46,000 and €8,350 for 10.2kWh battery storage. These prices are excluding VAT.

    In this example, it is estimated that around 12% of generated electricity may be available for export to the grid. That means TAMS II grant aid is not suitable here.

    The size of the system also exceeds the limit of 11kW for TAMS II funding. In this case, better energy communities (BEC) grant aid has been factored in. The cost and returns for the solar PV system are outlined on Table 1.

    Please note that annual savings may increase or decrease depending on energy unit pricing.

    40kWp payback

    This is a relatively large rooftop solar PV system and, thus, careful due diligence and planning is required.

    However, as the farmer is displacing 78% of their electricity requirements with self-generated renewable electricity, there is significant scope for savings.

    Little electricity is being exported to the grid, generating just under €600 of income per annum. But savings of nearly €8,000 are achieved each year by displacing imported electricity.

    A solar PV system can be sized based on the farm's peak demand.

    VAT can also be claimed in year one to the value of €7,337.25, while if the farmer is eligible for accelerated capital allowances, this could be up to nearly €6,800 in value. These, combined with displacing imported electricity, mean the payback period here would be an attractive five to six-and-a-half years.

    Over a 10-year lifespan, this system would offset 130t of CO2.

    300-cow farm with rotary milking parlour

    In this example, we look at a 300-cow dairy farm with a rotary milking parlour. Similar to the first example, milking times follows a pattern of morning and evening and, thus, electricity demand peaks at those times.

    The efficiency of cooling will dictate energy intensity, however, as it would be the largest user of electricity.

    In this case, an east-west-orientated system would offer a better generation profile across the day with only slightly less actual generation. Below are the key assumptions.

  • Annual electricity use: 146,000kWh.
  • Day rate for electricity: 0.25c/kWh, night rate electricity 0.15c/kWh.
  • Annual electricity bill: €36,500 plus VAT.
  • Main uses: bulk tank (48%), water pump (13%), hot water immersion (25%), lighting (5%) and rotary parlour (9%).
  • Area of roof space available for solar PV: 830m2 with east- and west-facing slope.
  • ESB connection: three-phase.
  • Maximum import capacity: 50kVA.
  • Location of transformer: within 75m.
  • Battery storage: 22kWh storage.
  • Size of bulk tank: 25,000l.
  • ACA: 100%.
  • Solar PV system

    For this scenario, a 70kWp rooftop solar PV system was selected. This would require around 525m2 of roof space. This is a large PV system and would require planning permission and an ESB grid connection.

    As the timing of peak generation doesn’t match peak loads, 22kWh battery storage is feasible. The cost of the solar PV system would be €85,000 and €11,833 for 22kWh battery storage. These prices are excluding VAT.

    The annual output is expected to be 58,800kWh and would generate around 40% of the farm’s electricity requirements. In this example, it is estimated that around 13% of generated electricity may be exported to the grid.

    TAMS II is not suitable here as the system exceeds the limit of 11kW for a dairy farm so BEC funding has been chosen. Table 2 runs through the costs and returns for the solar PV system.

    70kWp payback

    In this example, around 40% of the farmer’s electricity requirements are met by the solar PV system so there is reasonable scope for savings.

    Exported electricity to the grid provides little income, approximately €1,000 per year. Electricity savings, however, are substantial at around €13,000 per year or 36% of total electricity costs.

    VAT can also be claimed in year one to the value of €13,072.45 and accelerated capital allowances could amount to nearly €12,104 in value.

    These, combined with displacing imported electricity, means the payback period here would be an attractive five to six-and-a-half years. Over a 10-year lifespan, this system would offset 170t of CO2.