Modelling the ice bank and hot water as deferrable components in HOMER Pro did not show significant differences from when these elements were modelled as part of the fixed load profile. Doubling the deferrable storage volume did reduce the system NPC in all cases.
For the SF the lowest cost option was IN+VSD. For the MF the lowest NPC option was IN+VSD+HP+IB. However, the difference between IN+VSD+HP+IB and IN+VSD with two days of hot water storage was only $300. This price difference does not include the cost of the additional hot water storage (Table 24). For SF; the IN+VSD was the only technology scenario option which had lower cost systems than the IN+VSD+HP from Table 22. In the case of the LF the IN+VSD+HP+IB with deferable hot water and IB scenario had the lowest NPC (Table 24).
Modelling hot water (HP) and ice bank (IB) individually as a deferrable load reduced the NPC when compared to the fixed daily load profile from Table 23 by between 0.4% and 2.8% when compared to their respective non deferrable load option (Table 25). The effect of deferrable storage was larger when deferrable hot water and ice banks were modelled together. The difference between the fixed load and deferrable load ranged between 2.3% for a SF and 8.2% for a LF (Table 25). These
differences arose because of the reduced need for battery storage and generator operation and increased solar utilisation (Appendix 24).
Table 24 Hot water and ice bank electrical loads models using the deferrable load model in HOMER
Pro
Days of storage 1 2 1 2 1 2
Farm size Small Medium Large
Base Hot water* $276,000 $273,000 $525,000 $518,000 $1,000,00 $994,000 IN+VSD $265,000 $264,000 $491,000 $484,000 $945,000 $931,000 IN+VSD+HP+IB Ice bank** $280,000 $279,000 $497,000 $493,000 $870,000 $861,000 IN+VSD+HP+IB Hot water and ice bank*** # $275,000 $273,000 $483,000 $481,000 $819,000 $810,000 IN+VSD+HP+IB ## $276,000 $274,000 $484,000 $480,000 $834,000 $826,000
Each of the abbreviations stand for a change to the base scenario with all other parameters remaining the same. IN = insulation of the vat. IB = ice bank milk cooling. HP = hot water superheat heat pump. VSD = variable speed drive milk pump. HOMER Pro only allowed a single deferrable load but that dairy farm model included multiple deferrable loads. *Hot water component modelled as a deferrable load,**Ice bank component modelled as a deferrable load and ***Hot water and ice bank modelled together as a combined load. #Hot water is dispatched first in the deferrable load. ##The ice bank is dispatched first in the deferrable load
For the SF and MF options the models using deferrable loads in HOMER Pro had the same system configuration as the standard fixed load models. Large farms differed in the IN+VSD+HP+IB with deferrable hot water and ice bank options, one and two-day storage and the IN+VSD+HP+IB. With ice bank with two-day storage where the battery storage was reduced from two units to one unit, the minimum peak load in the IN+VSD+HP+IB with deferrable hot water and ice bank options had only a small effect on the SF and MF. The effect was greater on the LF (Table 24).
LF differed in the IN+VSD+HP+IB scenario with deferrable hot water and ice bank option where peak load was set to 66.7% and two days of storage. The solar array size increased from 100 to 120 kW (Appendix 24).
Table 25: Comparison of hot water and ice bank options in the storage sensitivity scenario with one
day's worth of storage with their fixed storage equivalent.
Small Medium Large
Base Hot water* 1.0% 1.6% 2.9%
IN+VSD Hot water* 1.8% 2.3% 2.7%
IN+VSD+HP+IB Ice bank Hot
water ***
# 2.3% 4.0% 8.2%
IN+VSD+HP+IB ## 2.3% 4.0% 8.2%
Each of the abbreviations stand for a change to the base scenario with all other parameters remaining the same. IN = insulation of the vat. IB = ice bank milk cooling. HP = Hot water superheat heat pump. VSD = variable speed drive milk pump. HOMER Pro only allowed a single deferrable load but the dairy farm model included multiple deferrable loads *Hot Water Component modelled as a deferrable load and ***Hot water and ice bank modelled together as a combined load. #Hot water is dispatched first in the deferrable load. ##The ice bank is dispatched first in the deferrable load.
The number of generator starts increased when a deferrable load was used from 826 to 1200 per year and the lifetime of the generator decreased slightly from 10 to 9.5 years. Intermittent operation at night-time increased under the deferrable load sensitivity scenario (Fig 35). The generator
produced 5185 kWh/year to meet the deferrable load during night-time. During these operations, the generator would be under minimal load between 20 and 30 kW which would bring the overall efficiency of the generator down.
5.7.6.1Deferrable effluent
Modelling the effluent pump as a deferrable load in HOMER Pro did not substantially change the net present cost when compared with static load modelling. The variation was less than 2.2% for the SF 3.6% for the MF and 5.8% for the LF (Table 26).
Day of the year
Figure 35: Generator power output on a large farm with insulation, variable speed drive,
superheat heat pump and ice bank. A) modelled with deferrable hot water and ice bank; B) modelled with fixed load hot water and ice bank
Increasing the volume of storage in the deferrable load model had little effect on the net present cost. The largest reduction from increasing storage volume from 7 to 14 days occurred in the VSD+HP+IN option. This option was the most dependent on fossil fuel resources with lowest
renewable fraction. Storage volume did affect solar PV sizing in two instances but did not substantially affect fuel consumption.
Biogas
In conditions where agriculture remains outside the ETS, the biogas scenario had a higher NPC than the standard scenario. The difference is greatest for SF and decreases as farm size increases (Table 27). These decreases occur at the same rate as the decreases for farms without a biogas system. As farm size increases biogas will remain more expensive than the conventional system (Appendix 25). In comparison with a conventional scenario the biogas scenario was less sensitive to changes in the oil price. To reach cost parity with the conventional scenario, the levelised cost of diesel would have to be more than $2.25. This is well outside the range considered in the study.
Table 26: NPC of Base, IN+VSD+HP, IN+VSD+HP+IB technology scenarios with deferrable effluent
pumping
Small Medium Large
Days of storage 7 14 7 14 7 14
Base $274,000 $274,000 $520,000 $520,000 $1,000,000 $1,000,000 VSD+HP+IN $265,000 $264,000 $461,000 $459,000 $860,000 $854,000 VSD+HP+IN+IB $275,000 $275,000 $487,000 $487,000 $844,000 $843,000
Each of the abbreviations stand for a change to the base scenario with all other parameters remaining the same. IN = insulation of the vat. IB = ice bank milk cooling. HP = Hot water superheat heat pump. VSD = variable speed drive milk pump
There is no change in the system configurations from base scenario without biogas (Appendix 25).If agriculture participates fully in the ETS in the future, then it is only under the 450 option (the highest carbon price option) that biogas has a cost advantage and this is only for large farms (Table 28).
Table 27: NPC of biogas scenarios under the three oil price sensitivity cases
Small Medium Large
Low oil policies
Base $ 339,000 $ 620,000 $ 1,087,000 IN+VSD+HP $ 321,000 $ 560,000 $ 959,000 IN+VSD+HP+IB $ 338,000 $ 599,000 $ 927,000 New policies BASE $ 348,000 $ 638,000 $ 1,134,000 IN+VSD+HP $ 328,000 $ 583,000 $ 1,010,000 IN+IB+HP+VSD $ 341,000 $ 608,000 $ 968,000 Current policies BASE $ 350,000 $ 642,000 $ 1,147,000 IN+VSD+HP $ 330,000 $ 589,000 $ 1,023,000 IN+IB+HP+VSD $ 342,000 $ 611,000 $ 994,000
Each of the abbreviations stand for a change to the base scenario with all other parameters remaining the same. IN = insulation of the vat. IB = ice bank milk cooling. HP = hot water superheat heat pump. VSD = variable speed drive milk pump.
The largest additional cost component of the biogas scenario is the maintenance cost of the biogas system. A 50% reduction in the maintenance cost is required for the biogas scenario to reach parity with the standard scenario.