Page 14 - APN March 2017

Is biogas a viable option for smaller piggeries?
It,s a gas
by ALAN SKERMAN Leader, Pork CRC Bioenergy Support Program
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WHILE the economic viability of installing biogas collection and use systems at large pigger- ies has been well docu- mented, the viability of installing biogas systems at smaller piggeries (less than 500 sows farrow to finish or 5000 SPU) has not yet been confirmed or documented.
A reported payback period of less than three years for a 2000-sow far- row-to-finish piggery in NSW was an impressive outcome and one which encouraged several larger piggery operators to in- stall on-farm biogas sys- tems in recent years.
This month’s column is devoted to examining the feasibility of installing a biogas system at a typical 500-sow farrow-to-finish piggery.
On-farm costs
On-farm energy costs are influenced by the mix of energy sources (grid electricity, natural gas, LPG, diesel generator, solar), climate, building design, shed heating and cooling systems, light- ing, water supply, efflu- ent management and the presence of on-site feed milling.
The proximity of the piggery to reliable grid electricity and supply tar- iffs is also important.
Because no two farms are alike in terms of en- ergy use and costs, the economic feasibility of biogas systems should be assessed on a site-specific basis and the examples outlined in this column can only provide general guidance.
For a typical 500-sow farrow-to-finish piggery, on-farm electricity con- sumption has been esti- mated to be from 90MWh/ year (gas heated sheds) to 280MWh/year (fully elec-
trically heated sheds plus feed mill), resulting in an- nual electricity costs of $23,000 to $70,000 a year, respectively.
If LPG is used for shed heating, consumption may be 41,000 litres/year at a cost in the order of $33,000/year.
Consequently, total on-farm energy costs are likely to range from $45,000 to $80,000/year. System costs
PigBal modelling sug- gests the 500-sow farrow- to-finish or 5000 SPU piggery would require construction of a covered 4.4ML-capacity anaero- bic pond at a construction cost of $121,000, includ- ing earthworks.
This CAP could produce an estimated 442 cubic metres of biogas on an average daily basis.
Assuming a methane content of 65 percent, it could provide 10GJ/day of total primary energy.
This biogas could be used to run an engine- driven generator, to pro- duce electricity, or a com- bined heat and power sys- tem, producing electricity and hot water from the engine cooling and ex- haust system.
The cost of a 50kWe CHP system, which could operate for about 20 hours a day, on average, is esti- mated at $150,000, while a generator system (with-
out heat recovery) may cost about $125,000.
Other biogas system components include a flare to burn excess bio- gas, a biogas cleaning sys- tem and safety and control systems.
The resulting total cost for installing a typi- cal biogas system at the piggery is estimated at $314,000 to $344,000.
Ongoing operation and maintenance costs are es- timated at $10,000/year.
Rather than using biogas to generate electricity, an- other alternative would be to install a biogas-fired hot water boiler, which may be feasible at pig- geries that currently use hot water boilers burning LPG for heating farrow- ing and/or weaner sheds.
The total system cost (including the CAP) would be about $166,000, which is less than half the cost of a CHP system.
The ongoing operation and maintenance costs would also be substan- tially less.
System returns
Depending on the pat- tern of on-farm energy use, the electricity and heat generated by the biogas system could po- tentially offset the entire grid-electricity and LPG consumption at the pig- gery, resulting in annual energy cost savings from $44,000 to $80,000 and simple payback periods of five to nine years.
However, it should be noted that biogas engine generators don’t operate efficiently at less than about half their full oper- ating capacity.
Consequently, close ex- amination of hourly power consumption records may indicate it is preferable to install two 25kWe genera- tors rather than the pro- posed 50kWe unit to more effectively meet base and peak loads.
However, there may be relatively few small-ca- pacity units available on the market and the cost per kilowatt generally in- creases for smaller units.
The payback period for the alternative biogas boiler system was estimat- ed at six years. Exporting electricity
The value and complex- ity of exporting surplus electricity to the supply grid is often difficult to justify, given the relatively low typical sale price of $0.03/kWh and the signif- icant capital investment often required to upgrade the supply grid to receive the exported electricity.
export electricity to the grid may improve the economic viability of run- ning the generator at full capacity during periods of low on-site electricity demand.
Carbon credits
Assuming that all bio- gas is burnt in an en- gine, hot water boiler or flare (rather than being vented to the atmos- phere), it is estimated that carbon emissions of 1495 tonnes CO2-e can be prevented annually for the 500-sow farrow- to-finish piggery exam- ple.
Under the Australian Government’s Emissions Reduction Fund, this rep- resents 1495 Australian Carbon Credit Units.
The average ACCU price at a recent ERF auction was about $10/ ACCU, resulting in a po- tential further income of $14,950/year for the sale of ACCUs earned by the proposed biogas system.
However, it should be noted that mandatory monitoring and auditing costs are likely to sub- stantially reduce the net income from the ERF.
Piggeries that generate electricity, offsetting the use of grid supplies, may be eligible to trade Re- newable Energy Certifi- cates.
One REC is equivalent to one megawatt-hour of electricity generation.
RECs can be traded for cash and their value fluc- tuates according to mar- ket conditions.
Historically, RECs have roughly paid for the gen- erator maintenance costs for some existing piggery installations.
Careful considerations
The examples provided in this column suggest that biogas systems may be viable at relatively small piggeries, giving simple payback periods of five to nine years.
These estimates do not include any income from the sale of RECs and AC- CUs.
In general, comprehen- sive, site-specific assess- ments that consider the mix of existing on-farm energy sources and use patterns are recommend- ed before proceeding with biogas system develop- ments.
If you require further information regarding the feasibility of biogas systems at smaller pig- geries, contact me on 07 4529 4247 or email alan.skerman@daf.qld. gov.au
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