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With the rising focus on integrating high shares of renewable energy into energy supply systems, the need to meet the viability of these renewable sources becomes pressing. Apart from storing electricity in electrochemical storage units, the concept of sector coupling could promise to provide the needed flexibility and storage capacities. A strong metric is needed to determine the viability and economic feasibility of different sector-coupled energy systems. This conference study presents an empirical method to develop a list of key performance indicators (KPIs), as a direct adaption of the KPI of the energy system with a single energy vector is not always possible. The list was developed based on a stakeholder workshop within the H2020 research project E-Land. The authors proposed the introduction of three new indicators for the evaluation of sector-coupled energy systems, namely degree of autonomy, levelised cost of energy and degree of sector coupling. A sector-coupled case study is evaluated to validate the performance of such new indicators while proving their utility to better assist decision-making. Peer Reviewed Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.2 - Per a 2030, augmentar substancialment el percentatge d’energia renovable en el con­junt de fonts d’energia Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.a - Per a 2030, augmentar la cooperació internacional per tal de facilitar l’accés a la investigació i a les tecnolo­gies energètiques no contaminants, incloses les fonts d’energia renovables, l’eficiència energètica i les tecnologies de combustibles fòssils avançades i menys contaminants, i promoure la inversió en infraestructures energètiques i tecnologies d’energia no contaminant Objectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.1 - Per a 2030, garantir l’accés universal a serveis d’energia assequibles, confiables i moderns

While national grids are traditionally the predominant electrification projects of governments, recent multi-track plans also include the utilization of decentralized supply, such as off-grid micro grids. In their Energy for All Case aiming at full electrification by 2030, the IEA expects that 44 % of the households will gain electricity access by connecting to a micro grid. Uncertainty regarding national grid extension plans poses the main implementation barrier: Investors are especially cautious when the possibility of a future national grid extension to their project site implies the danger of rendering their whole investment to sunk costs. This can leave whole communities, otherwise feasible project sites, without electricity. However, there are successful examples of micro grid interconnection. But research into postinterconnection options, especially connected to often unreliable national grids, is rare. This study contributes to this gap. In order to evaluate possible post-interconnection options of previously off-grid micro grids with the arrival of both a reliable and an unreliable national grid, an open-source techno-economic optimization and simulation tool based on the Open Energy Modelling Framework (oemof) is developed. The energy system simulated can include grid connection, generator, wind power, PV panels and storage as well as inverters and rectifiers, supplying both DC and AC demand. The capacity and dispatch optimization can allow annual shortage or require a stability or minimal renewable share criterion to be fulfilled. From the optimization results, the simulation tool calculates the systems performance indicators: supply reliability, renewable share, autonomy, Net Present Value, Levelized Costs of Electricity and others. The tool is applied to and validated by a case study based on an electrification plan for the Nigeria’s Plateau State, analysing 544 potential project sites. The paradigm of micro grids becoming stranded assets after the arrival of a reliable grid is confirmed, if no appropriate policies are in place. If, however, the arriving grid has a low supply reliability, 17 % of the project locations could supply their communities at lower cost off-grid. The post-interconnection options of a micro grid, if the national grid was to arrive after five years of off-grid micro grid operation, are evaluated, considering: on-grid operation, capacity adaptation (refitting), transformation into a Small Power Producer (SPP) or Small Power Distributor (SPD) as well as reimbursement and abandonment. This reveals, that the micro grid operator would favour on-grid operation, if subsidies were provided, or reimbursement. In case of an arriving unreliable national grid however, the operator would choose reimbursement over continued operation. The micro grid operation would be terminated and communities left without reliable electricity supply. From an electrification planners perspective, continued on-grid operation of the micro grid would be preferable, as it is the least-cost option ensuring reliable supply. Therefore, governments should consider the value of reliable supply and, next to reimbursements, develop subsidy schemes that encourage operators to continue operation, especially if the national grid experiences blackouts.