The Irish government has a long-term ambition to reduce energy related emissions by 80-95% by 2050 relative to 1990 levels. Biogas and biomethane generated from everyday materials and by-products can contribute to efforts to realise this – primarily by replacing fossil fuel use in the energy sector, but also by increasing the capture of emissions from the management of food and animal wastes. Renewable gas is most commonly produced from a process known as anaerobic digestion (AD), which turns material like food waste, grass silage and farm-animal waste into biogas. Biogas can be burnt directly to produce heat and electricity or can be upgraded to a standard suitable for injection into the natural gas grid. The upgraded gas is often referred to as biomethane and is a direct substitute for fossil fuel gas supply. Biogas and biomethane can also be used as a fuel compressed natural gas in trucks, buses and cars. Several of our European neighbours have polices in place to encourage the deployment of renewable gas technologies. The SEAI study was commissioned to fulfil a government commitment to examine the economic potential of biogas and biomethane in Ireland [1]. The results show that the equivalent of 28% of Ireland’s 2015 gas demand could be supplied from renewable sources by 2050 and save up to two million tonnes of CO2 e per year. This represents just over 3.5% of Irelands 1990 emissions, but support is required in order to overcome the challenges facing the sector.

What resources are available?

There are three main types of resource commonly available for use in AD in Ireland: food wastes, animal manure and the surplus grass silage available after animal feed requirements are met. Previous SEAI work [2] has estimated the potential quantities of these resources at various market prices for the resources. The use of food and animal wastes are available at the lowest cost and offer the largest potential carbon savings. Grass silage is required to increase the injection of biomethane at the most accessible and least cost-injection points on the gas grid. Developing the sector to maximise the use of all the available resources relies on improved management of the grass silage resource including better utilisation of the grass produced and increasing the yields from the current average of seven tonnes of dry matter per hectare (tDM/ha). The use of grass silage can help deal with farm size limitations in Ireland by supplementing other waste streams. Unlike these other resources, however, grass silage has a production cost that makes the energy produced more expensive. Efforts are under way to optimise production methods to raise yields and to reduce cost in the future through schemes such as Teagasc’s Grass 10 programme [3]. These schemes may also lead to a reduction in the fertiliser requirements for the growing of grass crops. The use of fertiliser, both man made and organic, causes the release of nitrous oxide (N2O) emissions. These are more damaging to the climate than CO2 and efforts to optimise the balance between grass yield, utilisation and fertiliser input can help improve the life cycle greenhouse gas emissions of using grass. In a paper published by Jerry Murphy’s research group in University College Cork [4], the life-cycle emissions for one hypothetical AD system in Ireland are compared to diesel fuel for transport. The paper found that the greenhouse gas savings, from grassland with a yield of 12 tDM/ha, can range between 21.5 % in a base case, to 54-75%. The higher savings are achieved through process improvements and the counting of estimates for carbon sequestered in the soil under grass. The EU legislation governing [5] the sustainability of biofuels currently requires a 50% saving and is set to rise to 60% for new installations from 2018. The SEAI report points to the need for further work in this area to determine the optimal conditions that can balance production cost and life-cycle emissions for grass and other resources.

What is required to increase deployment?

There are only a small number of AD plants in Ireland and an estimated 900 plants, of varying scales, would need to be built in order to fully utilise available resources. The cost difference between gas and renewable gas technologies means that uptake is likely to be limited without financial incentives. A recent government support for AD renewable electricity generation saw a very low uptake [6]. The tariff offered was the highest available to any renewable technology but was not sufficient to encourage investment. This was in part due to cost, but also due to the other non-financial challenges experienced by prospective projects. For example, AD projects can have a significant administrative overhead to bring to fruition and a project may have to engage with planning, waste licensing, agricultural regulations, government support schemes and grid connection processes. The relatively small scale of farms in Ireland can compound these difficulties, as waste streams from a number of different sources are required to provide enough fuel for typical AD units. Transporting, storing, mixing of separate waste streams and the spreading of the nutrient rich leftovers form the AD process, known as digestate, must meet animal health and waste-licensing rules. These and other non-financial issues can lead to difficulties in getting project finance, even in the many situations where the project economics stack up. It is clear from conversations with project developers that financing difficulties are seen as one of the key factors holding the sector back. Work is already under way across a number of government agencies and industry bodies to overcome some of these issues, including the development of a green gas certification [7] scheme and the ongoing development of a renewable-gas business process and connections policy by Gas Networks Ireland.

Costs and benefits to society of AD deployment

The chart below shows the high-level findings from the cost-benefit analysis carried for four deployment scenarios. The costs of deployment and the benefits from carbon savings are compared to a scenario where the same quantity of energy is delivered from fossil fuel. The sensitivity of the results to more and less favourable conditions for renewable gas production where examined to account for the inherent uncertainty in the future values of key variables like fossil fuel costs and carbon prices. The waste-based deployment scenario delivers a net benefit to society under all sensitivities examined, partly due to the gate fees received by AD units for the use of food waste and partly due to the large greenhouse gas savings achieved. Increasing biomethane injection to the grid requires the use of some of the grass silage resource and results in a net benefit to society in all the sensitivities examined. The net benefit is not quite as high as in the waste scenario due, to cost of producing grass and the lower carbon savings per unit of biogas produced from grass. Maximising the use of grass silage delivers a net benefit under favourable conditions such as lower silage production costs, higher carbon prices and higher fossil fuel prices. Gasification technologies are still at an early stage of commercialisation and have high capital costs. The scenario that includes gasification units does not deliver a net benefit to society at current cost levels.

Future technology development

The electricity grid is currently undergoing a transition from fossil fuel to renewable sources. Renewable gas produced from AD and not yet commercially mature technologies like gasification, can help to transition the gas grid to renewable fuels. The development of power to gas (P2G) technologies offers exciting potential to multiply the benefits of a renewable gas and renewable electricity grid. P2G technology can help to balance a high renewable grid and increase the renewable gas output form AD technologies. P2G combines the carbon dioxide from the AD process with hydrogen in a methanation process that produces methane suitable for injection into the gas grid. High variable renewable electricity systems can have times of very low wholesale market prices and researchers hope that P2G can utilise these periods to run the hydrogen producing electrolysis process more economically. Both gasification and P2G technologies have the potential to increase the production of renewable gas substantially. SEAI has funded a number of projects that seek to reduce the costs and scale requirements of AD technologies through our research programme. Our involvement with the International Energy Agency’s research collaboration on bioenergy is also linking to research in other countries on P2G, gasification and other important and policy relevant research areas. A number of government bodies and departments in the areas of agriculture, transport, and environment and energy have a role to play in helping to lower the cost of renewable gas and to maximise the carbon savings available. Actions could include developing incentives to maximise the use of our food and animal waste and increase biomethane production to inject renewable gas at accessible points on the gas grid. Significant potential exists to utilise surplus grass silage produced on farms. Farming practices that balance cost and emissions will help to improve the overall benefits. Renewable gas has an important role to play in Ireland’s energy future. It can help with the decarbonisation of the gas network and can make a contribution towards Ireland’s overall targets in the short and long term. To access the full report, please click here. Author:  Matthew Clancy, programme manager, Sustainable Energy Authority of Ireland References: [1] DCCAE(DCENR) (2014) Draft Bioenergy Action Plan, Available at: http://www.dccae.gov.ie/documents/Draft%20Bioenergy%20Plan.compressed.pdf [2] SEAI(2016), Bioenergy supply curves for Ireland 2015-2035, available at http://www.seai.ie/Renewables/Bioenergy/Sources/Bioenegy-Supply-Curves-2015-2035/ [3] Teagasc (2017), Grass 10 . Available at: https://www.teagasc.ie/publications/2017/teagasc-grass10.php [4] Korres, N.E., Singh, A., Nizami, A.S. and Murphy, J.D., 2010. Is grass biomethane a sustainable transport biofuel?. Biofuels, Bioproducts and Biorefining, 4(3), pp.310-325. [5] Directive 2009/28/EC on the promotion of the use of renewable sources. Available at: http://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32009L0028&from=en [6] DCCAE, Renewable Energy Feed In Tariff (REFIT) Scheme. Details available at: http://www.dccae.gov.ie/en-ie/energy/topics/Renewable-Energy/electricity/renewable-electricity-supports/Pages/REFIT-Schemes-and-Supports.aspx [7] More detail on the Green Gas Scheme development available at: http://www.ierc.ie/news/irelands-first-green-gas-certificate-scheme-step-closer-launch-greengascert-research-project/