Energy Savers
South East

Carbrook Nursery

Energy Savings
Bore, Centrifugal
Solar Photovoltaic
Capital Cost


A South East Queensland nursery growing ornamental plants has saved money and reduced energy consumption after implementing the recommendations from a recent Energy Savers Audit. The recommendation installed included a Solar PV system.

The farm consists of 4 ha with a production area covering 0.8 ha, which are irrigated all-year-round producing around 700,000 units per ha per year.

The annual energy consumption for the site during the 2018-2019 period was 47,351kWh at a cost of $11,432, and energy consumption on the farm consists of:

  • Propagation system: includes a 30-year-old hydronic heating system operating on average 16 hours during night-time from May to September, a small circulation pump, a temperature triggered control unit, an automated extraction fan, and a 22-year-old domestic refrigerator used as biological seed storage.
  • Irrigation: 7 automated pumps to operate during non-business hours, depending on plant requirements.
  • Office: several computers, air conditioner, router, printers, and lights.
  • Residence.
  • Dispatch shed: lighting and fans.
  • Other minor uses: including potting shed, staff facilities, water treatment system, growing structures, and a small workshop.

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

  • Biological refrigerator upgrade: replace the biological refrigerator with a more efficient unit.
  • Hydronic heating system upgrade: the auditor has evaluated 3 alternative solutions to upgrade the heating system:
    1. pipe insulation to reduce heat loss;
    2. install a hot water system to reduce overnight energy demand and insulate the pipes;
    3. replace the heating system with a solar evacuated tube heater and hot water storage, which could support an increase in production given the heating capacity of the solar system.
  • A 20kW Roof Mounted Solar PV connected to the grid: to offset most of the nursery energy consumption. Although the optimal array size to offset the maximum daily electricity demand should be 39kW, the roof space able to support the system is limited and only allows a 20kW array to be installed.

Table 1. Costs and savings from audit recommendations.

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


Capital Cost ($) Payback Period (Years)
Refrigerator upgrade 1,560 395 1.3 977 2.5
(1) Heating insulation 2,094 479 1.7 614 1.3
(2) Heating insulation and hot water system 8,386 1,855 6.8 2,549 1.4
(3) Solar hot water 11,041 2,173 8.9 9,465 4.4
20 kW Solar PV 18,940 7,000 15.3 32,100 4
Total 42,021 11,902 34 45,705 2.7


During 2020 a new greenhouse and staff room have been installed, increasing the plant production by approximately 24%, which has increased energy usage. For that reason, 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, as suggested in the audit report, with a capital cost of $40,590.

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) 62,634 52,089 -17
Cost Savings including exports revenue ($) 17,017 10,916 -36

* Adjusted to the 39kW solar PV system implemented.

The lower energy and cost savings compared to the adjusted recommendation, have been influenced by a decrease in the average solar radiation received at this location during 2020. The lower feed-in tariff offered in 2020 compared to the evaluated in 2019 has also reduced the estimated cost savings of the system.

From the solar energy generated, 68% or 35,613 kWh is being used onsite valued at $9,927, and around 16,476 kWh are being exported to the grid with a revenue of $989. Considering that 42,015 kWh – 54% of total energy use onsite – are being imported from the grid at a cost of $10,962, 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 ES155

Cost ES155

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 16,476kWh of energy consumption per year to coincide with solar generation times, they would save an extra $3,310 per year.

Solar optimisation ES155

From the implementation of recommendations in the audit, the farm has reduced energy consumption by 67% and costs by 52%, including feed-in revenue, with Carbon emission savings of 42.2 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) 77,628 25,539 67
Cost ($) 20,889 9,973 52
Energy productivity (kWh/ha) 97,035 31,294 67


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 onsite.  

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  

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.