Energy Savers
South East

Gumdale Nursery

Energy Savings
Native tube stock for revegetation
Solar Photovoltaic, Heating
Capital Cost


A South East Queensland nursery producing native tube stocks for revegetation has saved money and reduced energy consumption after implementing the recommendations from a recent Energy Savers Audit. The recommendations installed included the upgrade of a heating system and a Solar PV system.

The farm consists of 3.3 ha irrigated all-year-round producing approximately 7,000 units per ha per year.

The annual energy consumption for the site during the 2018-2019 period was 64,884kWh at a cost of $17,005. Still, a new seeding/transplant machinery was installed at the time of the audit, which is estimated to increase energy consumption by at least 12%.

The energy consumption on the farm consists of:

  • Propagation system: includes biological fridges and a mist-house with an updated hydronic root-zone heating system operating for a minimum of 70 days per year during night-time between May to September.
  • 3 Office areas: including several computers, air conditioners, routers, phone systems, and water cooler.
  • Irrigation: 7 automated pumps to operate during non-business hours.
  • Staff facilities: small appliances including fridge, freezer, urn, kettles, etc.
  • Other minor uses: including a potting system, automated irrigation controls, a workshop, and a water treatment system.

A recent energy audit showed how improving the current systems can lead to energy and cost savings. The audit recommendations are:

  • Hydronic root-zone heating system upgrades: replace the heated benches with rolling benches and upgrade the hydronic heating mats, which is estimated to improve the productivity of the nursery operations.
  • A 30kW Roof Mounted Solar PV: to offset the increased electricity requirements of the newly installed automated seeding/transplant machinery and ensure the nursery is not reclassified as a high electricity user and attract demand charges. A solar system on site will require upgrading the electricity meter and power box.

Table 1. Costs and savings from audit recommendations.

Recommendations Annual Energy Savings (kWh) Annual Costs Savings ($) Emission Savings


Capital Cost ($) Payback Period (Years)
Heating system upgrade 4,143 842 3.4 22,711 20*
30 kW Solar PV 40,973 10,393 33.2 43,839 4
Total 45,116 11,235 36.6 66,550 12

* Could improve to less than 1 year if the estimated productivity increases are generated.

The nursery has proceeded with the implementation of a 39kW Roof Mounted Solar PV with a 30kW inverter, after the roof was assessed by an engineer and reinforced to accept the larger system, with a capital cost of $30,000. Also, the grower has upgraded the heating system and has added second hot water storage to take advantage of the solar energy produced to heat water during the day, reducing energy consumption from the grid at night.

The savings made have been measured in a Measurement and Verification (M&V) process, as outlined in Table 2.

Table 2. Estimated and Actual energy and cost savings from the 39kW Solar PV.

Metric Audit estimation* M&V calculation Variation (%)
Energy Savings including exports (kWh) 66,187 70,000 6
Cost Savings including exports revenue ($) 17,958 15,703 -13

* Adjusted to the 39kW solar PV system implemented.

The lower cost savings measured compared to the adjusted savings from the audit recommendations have been influenced by the lower feed-in tariff offered in 2020 compared to the evaluated in 2019.

The new rolling benches have increased the area available for plant propagation by approximately 40%, which has increased the amount of heating required and therefore the amount of energy used to heat water. This, along with the new seeding/transplant machinery installed and the replacement of 3 old biological refrigerators with more efficient units, has led to an increase in energy consumption of 33%.

From the solar energy generated, 75% or 49,109 kWh are being used onsite valued at $13,689, and 16,747 kWh are being exported to the grid with a revenue of $1,005. Considering that 48,511 kWh – 50% of the total energy use onsite – are being imported from the grid at a cost of $11,909, there are significant potential savings from shifting consumption into the solar generation period. The total power balance of the farm, including solar exports, and the energy cost distribution, are shown in the following figures.

Energy ES179

Cost ES179

The next step for the farm is to adjust energy usage to offset as much energy consumption as possible from the grid, which would lead to further cost savings. The revenue from feeding into the grid is lower than the cost savings from using the energy onsite: for every dollar of energy exported, more than $3 could be saved if the energy were consumed onsite. If the farm were to shift 16,747kWh of energy consumption per year to coincide with solar generation times, they would save an extra $3,106 per year.

Solar optimisation ES179

From the implementation of recommendations in the audit, the farm has reduced energy consumption by 72% and costs by 61%, including feed-in revenue, with Carbon emission savings of 56.7 t/CO2-e per year.

Table 3. Pre and post implementation energy consumption, costs, and energy productivity improvements.

Metric Pre-implementation Post-implementation Reduction (%)
Energy Consumption (kWh) 97,620 27,620 72
Cost ($) 25,957 10,254 61
Energy productivity (kWh/ha) 29,582 8,370 72


An energy audit is a good investment 

An energy audit is a great first step in moving a business towards a more efficient future by reducing energy use, costs, and carbon emissions on site.  

An energy auditor will review your past energy bills, your equipment, and the way your business operates. They’ll show you where you’re using excess energy and explain what you can do about it. Find out about what’s involved in an energy audit HERE. 

See our range of agricultural energy efficiency case studies HERE and Subscribe to our bi-monthly energy e-news HERE.  

If you have any energy efficiency related questions for the team, get in touch at energysavers@qff.org.au.  

The Energy Savers Plus Extension Program is delivered by the Queensland Farmers Federation with support and funding from the Queensland Department of Energy and Public Works.