As we await publication of the government’s National Biomethane Strategy, Ireland is playing catch-up with other countries when it comes to the large scale rollout of anaerobic digestion (AD) technology.
Under the Climate Action Plan, there is a target to expand the production of agri-centric biomethane to 5.7TWh/annum by 2030, which is around 10% of Ireland’s total natural gas demand.
This will require the construction of an estimated 150 to 200 AD plants around the country, a significant increase on the 15 facilities currently in operation.
If the target is achieved, the emission savings would amount to almost two million tonnes of carbon dioxide (CO2) equivalent annually.
The production of indigenous biomethane is seen as playing a key role in reducing emissions from the agriculture sector.
Anaerobic digestion
Anaerobic digestion (AD) takes place when organic material decays or is broken down by bacteria and enzymes in the absence of oxygen.
When this is carried out in a controlled environment of airtight tanks, covered lagoons or covered ponds, this is known as a biogas plant or AD plant.
The organic matter is released as biogas; this is a mixture of the combustible gas methane (50-75%), carbon dioxide (25-45%), small amounts of water (2-7%) and trace gases.
The type of feedstock used by anaerobic digesters can include pig or cattle slurry; food waste; energy crops (grass silage, maize-silage, grain); municipal solid waste from households and organic solid waste from industry.
The biogas produced can be “upgraded” to biomethane and injected into the gas network or used as a vehicle fuel.
Across Europe, where AD technology has been used since the 1970s, the gas is normally used on site to generate heat and electricity in a combined heat and power–unit (CHP).
Renewable technology
Although Ireland has developed other renewable technologies such as wind, solar and ordinary biomass, there has been no support mechanism introduced yet to make anaerobic digestion a reality in this country.
“For any renewable technology to evolve or to emerge, it needs some level of support to get it off the ground and this would be evident right across Europe,” Barry Caslin, energy and rural development specialist with Teagasc, told Agriland.
“It’s not for the faint hearted to be getting involved in the AD process, it can be quite expensive going down the whole planning route, there’s different interpretations in different local authorities.
“There can be a lot of local opposition that you may have to deal with in some areas as well. So getting a project off the ground, there’s a long lead-in process,” he added.
Caslin has a level of trepidation when it comes to Ireland meeting its biomethane targets as “there is a consideration amount of ground to cover” between now and the end of the decade.
“When I think about all of these projects that are in incubation at the moment and realising all the challenges that these people have in getting the projects off the ground, it does seem a bit unrealistic achieving the 5.7TWh/annum target by 2030,” he said.
One of the major hurdles in developing an AD plant will be financing, adjusted for inflation and supply chain issues, the capital expenditure of a modern 20GWh AD plant is around €10 million.
“If we are being conservative and say it’ll take 200 plants to meet the 2030 target of 5.7TWh. This will require a capital investment of €2 billion.
“Based on support schemes across Europe, State supports come in the form of capital grants, ongoing tariff support or both.
“If we take capital grants alone, and assume that a grant of 50% is needed to match our EU counterparts, that’s a state support of €1 billion by 2030,” Caslin said.
He added that in order for people to invest in AD as a technology, they need to see that there’s policy and government commitment around this whole area.
Many investors are awaiting the details of the National Biomethane Strategy which is due to be published “fairly soon” after being worked on over the past number of years.
However, Caslin stressed that the document is a strategy and not a support scheme for the AD sector.
Opportunities and challenges
Along with helping in the transition away from fossil fuels and promoting a circular economy, AD technology offers opportunities for Irish farmers.
The income generated from selling biomass, mainly grass silage, to an AD biogas plant will provide additional income streams for farm families in rural Ireland and provide a land use alternative.
“We’ve got over 80,000 beef and sheep farmers in this country who make a very low gross margin per hectare who would look at this area as a potential area to give them a diversification opportunity,” Caslin said.
The residue or digestate of the AD process can be separated into a liquid and fibrous fraction. The liquid can be returned to the land as a high-value fertiliser and the solid fibre used as a soil conditioner.
The fermentation improves the quality of manure as nutrients are more available for plants and pathogens and weed seeds are killed through the AD process.
Teagasc estimates that a total land area of 120,000ha, which is less than 3% of available land, will be needed to produce the silage to feed the AD biomethane plants.
In addition, winter slurry from 1.3 million cattle will be required which represents approximately one fifth of all winter cattle slurry produced in Ireland.
The land requirements could result in displacement of livestock or existing tillage production.
Caslin said that livestock displacement could be mitigated against by improving grass management and utilisation on farms.
“There will be challenges in mobilising the slurry together with possible resentment towards the technology in areas where grass availability for lease or conacre is in limited supply,” he said.
Ireland currently imports over 70% of our energy requirements, which can be impacted by geopolitical events, as has been particularly evident in recent times.
“As a nation we need to look at what is the best use of our land. Should we be using it all for food production or should we be also insulating ourselves on the side of our energy requirements going forward, which makes us more attractive in terms of foreign direct investment as well,” Caslin said.