Despite a substantial potential of renewable energy sources, the current energy supply system in Iran relies almost entirely on fossil fuel resources. It has imposed significant financial burden on the country and has led to considerable GHG emissions. Moreover, the country is confronting several challenges for harnessing alternative clean energy sources and promoting rational energy policies over the recent decades. To probe the root cause of these problems, this paper first provides an overview on the previous energy planning attempts in Iran. It shows that adequate commitment to a long-term energy planning could have meaningfully prevented these serious challenges. However, the previous studies have had some limitations in terms of employing appropriate planning tools, comprehensive evaluations, and scenarios definition and ranking. This paper thus proposes a power planning framework to assess the sustainability of future electricity scenarios for the period 2015-2050. MESSAGE, a systems engineering optimization model, is employed to evaluate the potential impacts of transitioning to a low-carbon electricity supply system. Using a combined AHP-TOPSIS method, the scenarios are then ranked based on 18 different techno-economic, environmental, and social dimensions of sustainability. The results indicate that scenario Cl_32, in which the share of non-hydro clean energy for electricity generation reaches 32%, is ranked best.

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Abstract. Ireland has significantly increased its climate mitigation ambition, with a recent government commitment to reduce greenhouse gases by an average of 7 % yr−1 in the period to 2030 and a net-zero target for 2050, underpinned by a series of 5-year carbon budgets. Energy systems optimisation modelling (ESOM) is a widely used tool to inform pathways to address long-term energy challenges. This article describes a new ESOM developed to inform Ireland's energy system decarbonisation challenge. The TIMES-Ireland Model (TIM) is an optimisation model of the Irish energy system, which calculates the cost-optimal fuel and technology mix to meet future energy service demands in the transport, buildings, industry, and agriculture sectors, while respecting constraints in greenhouse gas emissions, primary energy resources, and feasible deployment rates. TIM is developed to take into account Ireland's unique energy system context, including a very high potential for offshore wind energy and the challenge of integrating this on a relatively isolated grid, a very ambitious decarbonisation target in the period to 2030, the policy need to inform 5-year carbon budgets to meet policy targets, and the challenge of decarbonising heat in the context of low building stock thermal efficiency and high reliance on fossil fuels. To that end, model features of note include future-proofing with flexible temporal and spatial definitions, with a possible hourly time resolution, unit commitment and capacity expansion features in the power sector, residential and passenger transport underpinned by detailed bottom-up sectoral models, cross-model harmonisation, and soft-linking with demand and macro models. The paper also outlines a priority list of future model developments to better meet the challenge of deeply decarbonising energy supply and demand, taking into account the equity, cost-effectiveness, and technical feasibility. To support transparency and openness in decision-making, TIM is available to download under a Creative Commons licence.