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s National-scale energy systems optimisation models (ESOMs) have been limited in the past by the lack of sub-national data availability leading to aggregated treatment of spatial dynamics. This review paper first determines how a combination of supply and demand data requirements and socio-economic, environmental and political issues, can challenge the results of a low-spatial resolution model. It also demonstrates the incompleteness of single region ESOMs that do not capture sufficient spatial detail. Specifically, 36 multi-regional ESOMs from 22 countries with varying levels of spatiotemporal resolution, sectoral focus and planning horizon are systematically identified and comprehensively analysed. The review reveals that existing temporally explicit ESOMs with a single sector coverage can permit regional disaggregation up to the first-level administrative divisions within a country (such as state and province) while maintaining computationally tractable. Findings from the literature review also show when, how, and to what extent higher spatial resolution impact on the results of energy system analysis. (1) Finer spatial resolution in ESOMs offers significant added value for regions with heterogeneous renewable potential or across regions with higher variability in energy service demands. However, in homogeneous areas, aggregated single-region modelling is more efficient. (2) Spatially resolved models can significantly change the results of the scenarios with very high shares of variable renewable energies. But it is not straightforward to find a direct relationship between the level of geographic disaggregation and penetration of renewable energies. This trade-off should be explored case-by-case. (3) Total system costs can be under- or over-estimated in various levels of spatial resolutions. Disaggregation of renewable resources leads to lower costs, and disaggregation of transmission grids leads to higher costs.

The role of different technologies in a future low carbon energy system is determined by numerous factors, many of which are highly uncertain. Their deployment may be a function of dependency on other technologies, or competition, or wider system effects. In this paper, using a UK example, we explore patterns of interdependency between technologies using a hierarchical clustering approach across multiple scenarios. We find that technologies compete in some instances, often on costs, cluster because they co-depend on each other, or emerge under all conditions, as robust options. Crucially, the broader scenario framing around carbon capture and storage (CCS) availability and climate policy stringency strongly influences these interdependencies. Keywords: Energy system models, Scenario clustering, Technology interdependency, Low carbon pathways

To attain emissions reduction targets within lagging transportation areas, several alternative fuel technologies such as methanol, natural gas, electric, hydrogen and biofuels have been suggested to replace conventional gasoline-powered vehicles at different points. In the process, several policies have been implemented and assessed in attempts to stimulate the diffusion of cleaner alternative vehicle technologies. This study seeks to explore the effect of some of these policies on driving vehicle switching within the Irish road freight. An agent-based model (ABM) is developed to evaluate the relative policy effect on natural gas vehicle (NGV) switching. More specifically, the model focuses on vehicle features and payback decision as conditions with the potential to impact natural gas vehicle switching. A simulation was performed over 13 years with the base year of 2017 running towards the 2030 vision. Initial findings indicate opportunities for NGVs with regards to a few determinants, which include vehicle switching population, gas demand, carbon (CO2) savings and incentive costs. In a ‘business as usual payback’ scenario with a carbon tax levy of €20/CO2 tonne(t), these opportunities decline with a reduction in vehicle weight category and kilometres travelled, requiring the intervention of supporting policies such as subsidy provision and improved fuel price gaps through increasing CO2 tax rates per tonne (€20-€100/CO2 tonne). Based on the observed emissions savings, natural gas is recommended as a bridging path towards renewable fuels integration in road freight, if significant emissions reduction is to be achieved.

Studies focusing on 100% renewable energy systems have emerged in recent years; however, existing studies tend to focus only on the power sector using exploratory approaches. This paper therefore undertakes a whole-system approach and explores optimal pathways towards 100% renewable energy by 2050. The analysis is carried out for Ireland, which currently has the highest share of variable renewable electricity on a synchronous power system. Large numbers of scenarios are developed using the Irish TIMES model to address uncertainties. Results show that compared to decarbonization targets, focusing on renewable penetration without considering carbon capture options is significantly less cost effective in carbon mitigation. Alternative assumptions on bioenergy imports and maximum variability in power generation lead to very different energy mixes in bioenergy and electrification levels. All pathways suggest that indigenous bioenergy needs to be fully exploited and the current annual deployment rate of renewable electricity needs a boost. Pathways relying on international bioenergy imports are slightly cheaper and faces less economic and technical challenges. However, given the large future uncertainties, it is recommended that further policy considerations be given to pathways with high electrification levels as they are more robust towards uncertainties., Highlights • 100% renewable energy can be achieved by multiple pathways with similar cost levels. • Focusing only on renewables is not the most cost-effective path to decarbonization. • Pathways relying on bioenergy import are more susceptible to uncertainties. • Indigenous bioenergy needs to be exploited to its full potential. • Much greater efforts than current national action plans are required.

Governments must increase bioenergy use to realise the Paris agreement ambition. Most countries have limited biomass resources and policy goals beyond carbon reduction. This can lead to policy incoherence. Previous studies tended to focus on one end-use sector or on optimising CO2 reduction. This study goes beyond optimisation approaches and investigates cross sector impacts of bioenergy policy proposals via simulation methods for policy proposals in Ireland. As an EU member with ambition for increased bioenergy use, Ireland is a useful case to examine trade-offs. Using the BioHEAT policy decision support tool (Durusut et al., 2018) we find policy in the heat and transport sector close the gap to Ireland's 2030 climate targets by 3%. Policy supporting co-firing of biomass with fossil-fuel to produce electricity increases emissions by 8.3 MtCO2 overall and reduces the policy impact on national climate targets by 63%. Co-firing uses more of the available biomass resources and this limits renewable uptake in the heat sector. Coal conversions and the use of advanced biofuels are found to rely on high availability of imports. Policy supporting biomass use in the power sector may make national climate targets less achievable for EU countries.

For many countries, the leading energy system decarbonisation strategy is to decrease reliance on imported fossil-fuel by developing renewable electricity. This paper offers insights on the net effects of transition to low fossil-based electricity by adapting an input-output (I-O) substitution model. Firstly, it addresses a common challenge with national I-O tables, namely how to isolate figures for inhomogeneous products like ‘electricity’ and ‘gas’ aggregated into one sector for a case study of Ireland. Secondly, it applies an extended I-O model to compare the net impacts on energy and non-energy sectors when substituting imported fossil fuels for electricity with renewable resources. Within the framework of the I-O model, for each 1% GHG reduction of the gas substitution scenario, there are increases of 26.2 net jobs and €5.1 m net value-added. These impacts are lower by 73–78% for coal substitution scenarios. Without taking account of the lost jobs and value-added from the economy, the job creations and value-added of renewable electricity would be overestimated by 17%–35% and 25%–50%, respectively. As well as giving insights into the net benefits of renewable electricity, the study provides techniques that could be applied to I-O tables for other jurisdictions to enable improved analysis of energy scenarios.

Iron and steel production in China contributes to 14% of China’s total energy-related CO2 emissions. Decarbonizing the iron and steel sector will therefore play an important role in achieving the goal of carbon neutrality. This study explored possible low-carbon transition pathways for China’s iron and steel industry to achieve carbon neutrality by 2050. An integrated approach was developed that combined a computable general equilibrium model and a bottom-up technology-selection module. The results indicated that although energy-saving technologies can reduce CO2 emissions in the short term, in the long term, adopting breakthrough technologies (e.g., carbon capture and storage (CCS) and hydrogen-based direct reduction (DR)), increasing the share of scrap-based electric arc furnace (EAF) steel production, and decarbonizing upstream energy-supply sectors will be crucial for climate change mitigation. Hydrogen-based DR could be an effective option for CO2 emission reduction in scenarios where CCS is not available, with its share increasing to 23%–25% by 2050. System-wide cross-sector decarbonization can help achieve climate targets at lower costs through flexible technology combinations and avoid carbon leakage into upstream energy-supply sectors.

To implement an energy saving measure, companies must first decide to investigate the options available. Representative survey data shows that almost half of companies in the Irish commercial sector do not take this step. This paper explores the barriers and drivers of this. Two logit models are fit to data to estimate the influence of variables, representing company and building characteristics, on the likelihoods of a company investigating either a fabric upgrade or a behaviour change measure. Companies are more likely to investigate a fabric upgrade that: own the building they operate from, make energy related decisions locally, have more than 10 employees, have had a recent renovation, accept longer paybacks, and apply a case by case approach to budget decisions. Hotels and offices were found to have a higher likelihood of investigating fabric options. Lack of knowledge of building floor area reduced the likelihood of investigation of both fabric upgrade and behavioural options. Much of the previous research is concerned with the final adoption of measures; this analysis adds additional insights by identifying the factors that determine if a company is likely to investigate the options available.

The levelized cost of energy of biomethane from food waste was assessed at 87 €/MWh, (87 c/L dieselequiv). Allowing for gate fees the incentive required for financial viability was 0.13 €/m3 (13 €/MWh). For context, various successful renewable energy policies were analysed across the EU including photovoltaics and biogas in Germany and electric vehicles in Norway. The schemes were compared with an incentive applied (or required) per tCO2 avoided. For Ireland, this study predicts that biomethane needs a financial subsidy of less than 180 €/tCO2 avoided, while most successful EU systems offer incentivisation levels less than 260 €/tCO2 avoided. In terms of incentives per tCO2 avoided Electric Vehicles (EV) stand out. When including all incentives such as grants and avoided parking costs, EVs can receive a sixteen-fold higher incentive as compared to biomethane based on tCO2 emissions avoided. The rationale for this high incentive and supporting policy is based on the requirement to initiate a new infrastructure that would not otherwise happen without intervention of a government incentivising decarbonised transport and clean air. Biomethane as a transport fuel requires a very significant change in infrastructure, including the provision of compressed natural gas service stations and natural gas vehicles. Initially (as for other successful renewable energy systems) larger incentives would be required to allow initiation of the industry, but these subsidies can be reduced over time. Biomethane as a transport fuel offers similar rewards as for electric vehicles, decarbonised transport and clean air along with energy security, renewable energy, indigenous jobs and supporting greening of agriculture.

The European Union has a target to reduce greenhouse gas emissions to 80% below 1990 levels by 2050 to keep global warming within 2 °C relative to pre-industrial levels. The more recent Paris climate agreement has a more ambitious target of limiting the temperature rise to well below 2 °C and the EU ambition is growing to become climate-neutral by 2050. This research explores decarbonization options using an innovative analytical approach that combines energy systems analysis and marginal abatement cost curves (MACCs). System-wide MACCs are derived using scenario ensembles from Irish TIMES energy systems model. Decomposition analysis is then used to associate decarbonization options with carbon abatement costs. In addition, energy systems analysis is carried out on the underlying scenario ensembles that are used to generate the MACCs to capture more technological details and to reflect interactions among technologies. The results show that MACCs are highly dependent on model assumptions and the availabilities of bioenergy and carbon capture and storage (CCS) technologies play critical roles. The paper also shows how key mitigation measures can be ranked and classified into categories of resilient (wind energy, CCS, electric vehicles, biofuels), tipping-point (electrifying building heating, biomass plants), and niche (ocean energy) technologies.

Generation from synchronous machines in European power systems is decreasing as variable renewable energy penetration increases. Appropriate levels of system rotational inertia to ensure system stability, previously inherent in synchronous areas across Europe, can no longer be assumed. This work investigated the impact different levels of minimum inertia constraint have in Europe and in each synchronous area. Two scenarios with divergent decarbonisation ambitions were simulated for the year 2030 using a unit commitment and economic dispatch model. The key findings show that an increasing inertia constraint elevates total generation costs, variable renewable energy curtailment and carbon dioxide emissions across Europe for an ambitious decarbonisation scenario. When inertia constraints were applied to the contrasting scenario with a low decarbonisation ambition, decreases in carbon dioxide emissions of up to 49% were observed in some synchronous areas where the constraint was frequently active. The work also scrutinised the spread of inertia in the large synchronous area of Continental Europe. It emerged that some countries are likely to experience periods of low inertia even if an inertia constraint is applied at synchronous area level.