Aerators and water quality are the focus of energy savings for a Central Coast yabby farmer

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With several hundred tonnes of crays destined for high-end restaurants in Sydney, and to service shops throughout NSW and Victoria, achieving good water quality in ponds is essential to ensuring the highest-quality product. Energy savings can be made nevertheless, by minimising or limiting the run time of aerators to peak and shoulder supply periods. “ We knew we had to focus on the quality of the water and feed for our yabbies but we didn’t factor into our business plans the doubling of our energy costs in the past five years. Yes, it’s certainly time to take action,” says David Flanagan, owner and manager of Reedy Creek Crays.

David Flanagan isn’t your typical farmer. He spends most of his weekdays working in an office and drives up to the farm for weekends. You could call David a hobby farmer, but many others who know him would say he’s much more than that.

No paddocks, just ponds

The Flanagans have a yabby farm, growing their yabbies in ponds on the property. While yabby farming is something of a boutique business, other types of large-scale commercial aquaculture operations (fish, prawns, oysters) employ similar methods. Yabbies are raised in small ponds on the property, which are fed with aerators to ensure there is sufficient oxygen in the water.

The market for yabbies is pretty consistent, with peaks in summer and troughs in winter. Smaller yabbies are used as bait by local fisherman, and David supplies bait and tackle shops around the country. The larger yabbies are sold to restaurants. As the business continues to grow, David will consider expansion options, such as adding additional ponds or increasing the yabby population capacity of each pond. Importantly, however, energy productivity will continue to be a key consideration in his business plans.

Reedy Creek energy profile

Table 1: Reedy Creek energy breakdown

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The farm’s largest energy expense is the operation of the aeration blowers, closely followed by the use of electricity in the house and for pumping water for the various transfers and pond top-ups required.

Table 2: Reedy Creek's energy breakdown by end-use purpose

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Figure 1: Reedy Creek energy use by type and purpose. With 51 percent of the energy used for aeration in the ponds, it’s easily the greatest focus for savings.

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Cost reduction opportunities

How energy fits into the equation

Electricity dominates energy usage on the Flanagan farm: it is used to drive pumps, aerators in the ponds, and storage for the yabbies post-harvest. David has looked at various set-ups in a bid to maximise the efficiency of his pumps and motors.

Solar is attractive for aquaculture farming

Typically, aquaculture operations use a relatively consistent amount of power over extended periods of time. This makes them good candidates for solar PV systems. Additional opportunities identified for Reedy Creek include ensuring that the farm is on the least expensive electricity tariff, experimenting with using blowers for only half the time they would normally run (subject to water quality), and optimising the aerator set-up (individual equipment versus one large air compressor to service the aerators in each pond).

Reducing the operating hours for blowers

Blowers and aeration are the largest energy users on site and therefore these areas hold the greatest potential for savings. David will investigate whether he can reduce the operating time of the blowers without jeopardising required yabby growth rates and quality or negatively impacting water quality. (Refer also to this Quick guide .)

Currently, Reedy Creek’s blower operates for about half the day (depending on the time of year) and pond water quality is tested daily. Dissolved oxygen (DO) and temperature are routinely measured for each pond. The Department of Primary Industries (DPI) recommends minimum DO levels of 4ppm or more.

David reduced the blower run time at Reedy Creek by an hour per day over a fortnight until a measurable impact on DO was achieved. Once a new run time had been established, the solar PV supply potential of the operation could be re-assessed. If the run time is sufficiently small, blower time could also be limited to off-peak periods during the day. The time of use schedule for the region is:

• Peak : 2pm-8pm weekdays
• Shoulder : 7am-2pm and 8-10pm weekdays
• Off-peak :10pm-7am weekdays, all weekends, and public holidays

After run times were cut in half, Reedy Creek’s DO levels were still more than 4ppm,resulting in $3,000 in savings . A six-hour (50%) aerator time buffer will remain for now, and further reductions may be on the cards.

Pursuing energy savings begins with a strategy

First, eliminate consumption before buying a new kit (efficiency upgrades). For Reedy Creek, this was necessary before they could install any solar PV or invest in jet aerators for each pond. A long-term investment is best sized to match the farm’s future needs, not its past requirements.

Of course the other consideration for David is expansion which, along with energy efficiency, is now in the Reedy Creek business plan and can be referenced the next time he and the team make decisions about energy savings opportunities.

“We will always consider reducing consumption first, then size any potential upgrades. That’s one of our biggest lessons from this project and in this case we can deliver savings at no cost. What a bonus! ” says David.

Figure 2: The main blower comprises of a 10 kW electric motor and a 25 inch 4 blade blower

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Optimise blowers by maintaining pressure

With any air compressor or air-blowing system, leaks are a common source of energy waste.

A single one-centimetre hole in an air line can account for as much as 2% of the energy used by a blower. Fortunately for Reedy Creek, its system was well built and maintained, and leaks have been repaired in a timely manner.

Solar PV to power ponds if aerators’ time of use can’t be limited to off-peak periods

As David and his team reduce the blowers’ time of use and continue to monitor impacts on water quality, the option of solar PV power becomes plan B.

Once the cost of electricity drops below 20c/kWh, as is often the case for off-peak supply, installing solar panels to offset power consumption from aerators or other energy-using equipment on site may no longer be financially attractive. Should the need to pump at peak and shoulder periods continue, however, understanding the financial impacts of this and knowing what size solar PV unit would be optimal for the operation is useful, if and when it’s time to act.

Sizing a solar system: a rule-of-thumb approach

1. Most energy bills will give you an average energy use per day for the bill period in kWh/day.
2. If aerating through the day, expect that 60-80% of your operation’s total energy use will occur through the day. Alternatively, add up the motor ratings of major loads running during the middle of the day to derive an initial estimate.
3. Using a daylight generation default for the NSW Central Coast region, the number of sunlight hours is 6-8 hours per day and 1,300kWh/kW of installed PV.
4. With a peak load of 15-20kW and a peak time of use, the optimum-size solar PV unit is 15kW.
5. A unit of that size would provide savings of $3,900 p.a. based on current energy use, with a payback period of about six years.

Now blower energy use has been reduced by half and the farm’s energy profile has changed, the ideal size may only be 5-10kW. This should be re-assessed once the new electricity bill has been received.

If running aerators overnight, solar PV power can still be a possibility if on-site batteries are employed. The current high capital costs of buying batteries and the relatively low cost of off-peak power suggest that this is not the most cost-effective option but it is definitely one worth monitoring, as battery costs are expected to drop significantly in coming years, much as the cost of solar PV has fallen over the past five years.

Table 3: Full list of opportunities with priority opportunities highlighted. Note:’UI’ denotes ‘Under Investigation’

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Figure 3: Reedy Creek Crays’ focus is on the main aerator motor and blower run time, which need to be reduced before David can consider alternative sources of power generation, such as solar or wind. The shed is the ideal site for solar PV panel installation, although a couple of trees to the north may need lopping to maximise the panels’ exposure to sunlight.

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Outcomes

David has begun his investigation into reducing the aeration time of his ponds and, so far, results have been encouraging. Reductions in blower operating times have not resulted in appreciably lower yields or growth rates.

He has also made a small investment (~$1,300) to move from an electric heater system to a gas-powered instant hot- water system. This should provide some energy savings as well as improving the reliability of the farmhouse hot-water supply.

David has also renegotiated Reedy Creek Crays’ electricity contract, securing a discount of 18% off the farm’s energy bills.

Other improvements still to be undertaken at Reedy Creek include further optimising aerator run times, adopting the right-sized solar PV unit, and adding a timer to the pumps filling the farm’s water supply so that they operate only during off-peak times. Together, these improvements could halve the cost of energy for Reedy Creek, helping David to secure a more competitive position in the market for his yabby business.

Figure 4: Expected energy savings from continued implementation of projects (including solar PV).

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Planning for a long-term future in family farming

With the assistance of NSW Farmers’ Energy Innovation Program, David will continue to explore optimal aeration times and subsequent potential energy savings, helping to secure the financial viability of a small family farm serving a niche market.

In the short term , in addition to optimising his aeration system, David will seek quotes on a solar PV system but will wait to see what happens with demand, which will impact the need for additional ponds and aeration loads, et cetera.

Over the medium term , David will investigate the possibility of controlling aeration between ponds so that differences in DO levels can be accommodated without supplying air to every pond. Savings will be determined after DO records have been analysed over a whole season.

Long-term opportunities involve being mindful of energy use and its associated costs when making or evaluating any expansion plans. The Flanagans are aware of the value of considering energy conservation measures before spending money on kit for energy efficiency or renewable energy.