The opportunity in Ireland is to create a circular, rural economy whereby agri-feedstock of excess grass, rotation and catch crops and residues will be used to produce biomethane for heat, and transport.
The digestate by-product is an excellent bio-fertiliser organic soil improver and will reduce carbon footprint by displacing artificial fertilisers and associated increasing costs of chemical fertilisers.
Farmers may wish to invest in these plants, lease land for them, operate them, and, or, contract to supply feedstock.
Farmers can use the AD plant to improve slurry management, address N, P, K or ammonia issues and reduce the use of chemical fertilisers while also bringing currently unproductive land into profitable use.
The whole process reduces greenhouse gas emissions and captures carbon in the soil.
The AD biomethane technology is being promoted and designed to be a complementary discipline to existing farm operations and land management practices. The majority of individual farmers will not be able to build and supply feedstocks as a sole enterprise. This means an approach whereby farmers pool feedstock and resources to develop a plant in co-operation will be required. Alternatively, some projects can be developer led, where a plant is built and operated by one party with contracts for feedstock provision with farmers in the local area. Typically, an average AD plant will require a number of farmers’ inputs to provide feedstock and land, and to operate the plant.
All different sizes and types of farming enterprises are suitable for AD. The key ingredient is bringing together the right collective mix.
Currently, any pig farming operation in Ireland would produce enough slurry for a 20 GWh plant.
In many cases, a mixture of dairy beef and tillage farms would be encouraged to collaborate in setting up a cluster of 5 or 6 farms working co-operatively.
Most sucker, beef farmers and beef finishers that keep cattle under roof could provide slurry and could also utilise set-aside grassland to supply grass silage to the AD plant. This industry would provide livestock farmers with an outlet for excess grass, particularly in areas where beef farming is dominant.
Tillage farmers could plant rotation and catch crops of mixed grass swarths including red clover as part of their five-year rotation. They can also grow a second catch crop in the year as the crops do not have to be at full maturity when harvested for anaerobic digestion.
It is recommended that AD plants be within a range of 100km access to a central grid injection facility in order to be economically viable. There may be an option to supply large gas consumers directly who are off grid. Some developments will not meet the requirements for direct gas injection, currently distances of 14 km of low pressure gas pipeline is economically viable for large AD plants.
The best feedstocks are agri-food and drinks by-products, however, grass and slurry will be the most common feedstock in Ireland’s renewable gas industry. Teagasc figures show that the average grass yield could be increased by at least 50%. University College Cork research shows how underutilised land, particularly in the less intensively farmed areas in the west of Ireland and the midlands, could be brought into production.