Energy modelling can assist national decision makers in determining strategies that achieve net-zero greenhouse gas (GHG) emissions. However, three key challenges for the modelling community are emerging under this radical climate target that needs to be recognized and addressed. A first challenge is the need to represent new mitigation options not currently represented in many energy models. We emphasize here the under representation of end-use sector demand-side options due to the traditional supply side focus of many energy models, along with issues surrounding robustness in deploying carbon dioxide removal (CDR) options. A second challenge concerns the types of models used. We highlight doubts about whether current models provide sufficient relevant insights on system feasibility, actor behaviour, and policy effectiveness. A third challenge concerns how models are applied for policy analyses. Priorities include the need for expanding scenario thinking to incorporate a wider range of uncertainty factors, providing insights on target setting, alignment with broader policy objectives, and improving engagement and transparency of approaches. There is a significant risk that without reconsidering energy modelling approaches, the role that the modelling community can play in providing effective decision support may be reduced. Such support is critical, as countries seek to develop new Nationally Determined Contributions and longer-term strategies over the next few years. Key policy insights. Energy systems that reach net-zero greenhouse gas emissions will be radically different to those of today, necessitating a modelling analysis rethink. . On modelled options for mitigation, a range of demand-side measures are often absent resulting in a risk of over-reliance on carbon dioxide removal (CDR) and leading to concerns over robustness of corresponding pathways.. Regarding models for policy, there is significant scope for improvements, including the use of scenarios that help imagine the radical change that will be required, techniques for improving the robustness of emerging strategies, and better alignment with broader policy goals.

Although energy for heating and cooling represents the largest proportion of demand, little progress towards meeting environmental targets has been achieved in these sectors. The recent rapid progress in integrating renewable energy into the electricity sector however, can help in decarbonising heat by electrification. This paper investigates the impacts and benefits of heat electrification in a wind dominated market by considering two options; with heat pumps, and with direct electric heating, both operated with energy storage. The Irish all-island electricity market is used as a case study. Modelling results reveal the significant potential of heat pump electrification, delivering at least two and three times less carbon emissions respectively, when compared with conventional options such as gas or oil for 20% of domestic sector of the All Ireland market. Heat electrification using direct, resistive heating systems is found to be the most carbon intensive method. Energy storage systems combined with heat pumps could deliver potentially significant benefits in terms of emissions reductions, efficient market operation and mitigating the impacts of variable renewable energy on baseload generation. The main barrier to heat electrification in the all island market is the absence of appropriate policy measures to support relevant technologies.

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The increasing number of elderly people (over 65 years of age), long-term home care policies and the generally higher energy demand of houses inhabited by elderly people will pose an energy challenge for the built environment. The paper analyses the benefits of poly-generation technologies, focusing on the case of hard to heat homes in Northern Ireland. The energy consumption of a test house that is representative of 28% of Northern Ireland housing stock and of a house with elderly inhabitants has been monitored without any intervention. An optimization procedure has been developed to identify the optimal mix of poly-generation technologies. The technologies considered are micro-combined heat and power, heat pump and photovoltaic systems with possible integration of thermal energy storage systems. Six scenarios based on different energy tariffs and technology incentives have been presented. In the best case scenario, the combination of photovoltaic, heat pump and thermal energy storage provides 26% reduction in carbon dioxide emissions and 80% savings in the energy bill compared to standard energy generation. The investment required would be in the order of £11,000. In Northern Ireland, 307,000 households (79.1% more than in 2012) will have elderly inhabitants Highlights • The built environment is facing an energy challenge due to an aging population. • Benefits of poly-generation for houses inhabited by elderly people were analysed. • Results show 26% reduction in CO 2 emissions and 80% savings in the energy bill.

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