"We're looking at potentially 400 on-farm anaerobic digesters by 2030," Gas Networks Ireland (GNI)'s Ian Kilgallon told a meeting of the Guild of Agricultural Journalists on Friday. He sees a market for another 50 larger industrial plants as well.

GNI operates the gas transportation network throughout the country and is planning to distribute 20% of renewable gas in 2030. The utility is beginning construction of a network of 14 injection points where collection trucks will deliver gas derived from the fermentation of organic material – much of it from farms. "Collecting biomethane from farms is much like your creamery operation," said Kilgallon, who is in charge of developing renewable gas for GNI.

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According to GNI's plans, the industry would be fuelled by slurry and crop residue in intensive dairying and tillage areas of the south and east, and increased grass production in the north and west. While building an anaerobic digester will be out of the reach of most individual farmers – typical costs range from €1m to €2m – co-ops or larger operators could invest in the installations, buy grass or catch crops from neighbouring farmers. They would also process their slurry, giving back a digestate shown in early research to have higher nitrogen availability and lower emissions than raw slurry. "The biggest opportunity for smaller farmers will be to become feedstock suppliers," said GNI's head of commercial Denis O'Sullivan.

One of the proposed locations for the early gas network injection points in Mitchelstown, Co Cork, where Dairygold already produces gas from the anaerobic digestion of dairy processing wastewater. "It produces 6% of our demand for heat," said Dairygold's head of sustainability Dave Fitzgerald. The gas is used both for drying milk and to generate electricity for the co-op's plant. The location could become a hub for gas collections stretching to Cork and Limerick cities, and Thurles in Co Tipperary.

But the first collection point is planned for next spring in Cush, Co Kildare. Its first supplier will be Green Generation, the company of pig farmer and energy entrepreneur Billy Costello in nearby Nurney.

Every hour, a €6m double digester takes in 3t of food waste (pictured) and pig slurry from the 2,500-sow farm. The plant upgrades the gas to fuel-grade quality and burns it in a combined heat and power (CHP) plant. The electricity is sold to the ESB at a subsidised tariff obtained before those schemes closed in 2015 and the hot water is shared between the digester's own heat needs, those of the pigs and a new plastic washing business for the recycling industry.

However, much of the heat is lost and this will exclude this type of setup from upcoming Government support schemes. Instead, the GNI injection point will allow Green Generation to sell its gas to Diageo through the national network. The St James's Gate brewery in Dublin will use it to power its own CHP plant and cover its industrial heat and electricity needs.

Diageo targets

Simon Shannon, who manages utilities for Diageo Ireland, said this was the best way for the Guinness brewery to reach the company's 50% greenhouse gas emissions reduction target between 2007 and 2020.

Kilgallon argued that biogas was a more promising source of renewable energy in Ireland than wood and other types of biomass because it is cheaper to transport and more energy-efficient. According to his estimates, the sector could buy silage from farmers for €25/t, generating a gross margin of €376 to €450/ha. He compared this with the average gross margin of €310/ha for willow and an average income of €282/ha to lease out the land.

You're still a farmer

At a workshop on biogas organised by the Agriforvalor group on Tuesday, KPMG's Russel Smyth, who specialises in raising finance for the sector, said Northern Ireland farmers were now selling silage to anaerobic digesters for €30/t – admittedly at a higher level of subsidy to the industry than is expected in the Republic. The much-awaited Renewable Heat Incentive scheme from the Government will set the scene for the industry's profitability.

Another advantage to biogas over biomass, according to Costello, was that suppliers of slurry and grass could generate this as part of their usual livestock enterprise instead of planting their land with forestry or energy crops.

"You're still a farmer," he said.

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