Between 2013 and 2018, the number of anaerobic digestion plants in Northern Ireland (NI) increased from 10 to 77.
This was achieved through the support of a Government-backed Northern Ireland Renewables Obligation scheme which provided 20 years of guaranteed support to developers.
Northern Ireland’s anaerobic digestion (AD) industry, while not without its challenges and opposition, has undoubtedly been a success story.
In 2019, the UK became the first major economy to commit to a 100% reduction in greenhouse gas emissions by 2050
However, this level of development is arguably only the tip of the iceberg for the potential of AD in NI. In 2019, the UK became the first major economy to commit to a 100% reduction in greenhouse gas emissions by 2050. This target could be even sooner for NI.
This will require both a reduction in greenhouse gas emissions and a rapid scale-up of renewable energy generation. AD technology can help achieve both and will play a significant role in NI’s carbon neutrality targets.
However, with opportunities come challenges and these featured heavily at the recent Anaerobic Digestion and Bioresources Association (ADBA) NI conference. This article will delve into the key numbers behind NI’s AD industry and discuss the key challenges facing developers and operators.
The lay of the land
The NIRO was a game changer for the industry and has been the envy of many prospective developers south of the border since its launch.
According to ADBA’s figures, there are 77 AD plants in operation in NI, 75 of which generate biogas to feed into onsite combined heat and power engines, producing electricity. Two plants upgrade the biogas to biomethane.
A further 164,000t of food waste is processed through AD plants
The majority of these plants are farm-based, with electricity output capacity of around 500 kilowatt (kW). These farm-based plants use over 1m tonnes agricultural feedstock annually including slurry, poultry litter, energy crops and silage. A further 164,000t of food waste is processed through AD plants.
Output and carbon savings
In total, NI’s AD industry has a combined annual output capacity of 135 megawatts (MW). This is enough to power 110,000 homes each year as well as heat around 40,000 homes.
However the majority of what is fed to an AD plant comes out the other end as digestate.
According to ADBA’s figures, the 1.2m tonnes of digestate produced annually in Northern Ireland contains approximately 3,670t of nitrogen.
To put this in context, the group says this nitrogen is enough to fertilise over 44,000ha (averaged between crops and grassland) per year or 4% of all agricultural land in NI. The digestate also contains an estimated 1,730t of phosphorus and 4,490t of potassium.
A further 22,000t CO2e is saved by replacing artificial fertiliser with digestate
In terms of carbon savings, the NI AD industry saves around 153,000t CO2e (carbon dioxide equivalent) per year by displacing fossil fuels. A further 22,000t CO2e is saved by replacing artificial fertiliser with digestate.
This figure doesn’t take into account the carbon sequestered in soils from using digestate. A further 173,000t CO2e are saved from avoided methane emissions from slurry and manure.
This totals a reduction of 348,000t CO2e or 1.6% of NI’s total GHG emissions. This figure doesn’t factor in the 105,000t of bio-CO2 which could be captured and used/stored from the biogas.
However, as mentioned earlier, the potential for further expansion of NI’s AD industry is great. AD can provide solutions across multiple sectors.
Analysis by ADBA shows that between food waste, livestock waste, crop residue and sewage, there is over 13,245,000t feedstock available for AD
This includes capturing methane or displacing chemical fertilisers in the agricultural sector (which accounts for around 27% of national emissions) or providing vehicle fuel for the transport sector (which accounts for 23% of emissions) or providing renewable gas for the energy sector (which accounts for 17% of emissions).
In terms of future feedstock, NI has it in an abundance.
Analysis by ADBA shows that between food waste, livestock waste, crop residue and sewage, there is over 13,245,000t feedstock available for AD, which could produce over 2.7 terawatt (TW) of energy. This level of output could cut NI emissions by 8.1%, saving 1,751,000t CO2e.
It’s widely accepted that the future development of AD in NI isn’t in the production of electricity, but rather in the production of biomethane for transport fuel or heat generation.
This will mostly be facilitated through injecting the renewable gas into the gas grid, similar to the proposed model in ROI.
Much of NI’s gas network is under 10 years old and is ready for biomethane.
Significant questions still surround the grid connection process
However, as outlined by Granville Ecopark’s David McKee, there currently isn’t any grid injection policy or support for producers of biomethane in NI. However, he says the Utility Regulator is working with grid operators and biomethane suppliers to develop rules for grid injection, which is a good start. Significant questions still surround the grid connection process, particularly its cost. Currently, the indication is that the gas producer will have to cover the cost of grid connection and gas pipeline extension, which could cost hundreds of thousands.
NI has three gas grid distribution operators – Firmus Energy, Phoenix and SGN. This is unique considering the relatively small size of the country.
Eric Cosgrove of Firmus Energy said that the company is currently investigating ways of reducing carbon in their networks and this includes using biomethane and hydrogen blends. They may eventually see full towns supplied by 100% biomethane or hydrogen.
He estimates that with co-ordinated development there could be sufficient biomethane to meet around 50% of the gas demand on the Firmus Energy network and he is already receiving enquiries from developers.
In terms of models, he says he sees AD plants either injecting directly to the gas network or the development of a hub-type model where a central injection facility will take biomethane from a number of local sites by truck before injecting into the gas network. Based on current timelines, grid injection could be possible by April 2022.