Calliope Africa: Modeling the role of storage and transmission for renewable energy integration

This study introduces Calliope Africa, a country-resolution energy system optimization model designed to assess tailored energy policies in the African continent to support and guide a just energy transition. The model is built with manually gathered country-specific data, made available in open-source, and validated against official national statistics. The model is then applied to Nigeria and South Africa to evaluate the impact of national transmission expansion and pumped hydro energy storage (PHES) on variable renewable energy (VRE) penetration. Our results highlight that strategic combinations of storage and grid enhancements can significantly increase renewable utilization, reduce curtailment, and lower emissions. While PHES is particularly effective in solar-dominated contexts, transmission expansion plays a crucial role in overcoming regional grid constraints, as observed in South Africa. The findings emphasize the importance of country-specific strategies for VRE integration and reinforce the role of infrastructure planning in achieving Sustainable Development Goal 7 (SDG7), particularly Target 7.2 on increasing the share of renewables, and how this can potentially have beneficial indirect effects on Target 7.1, universal access, and 7.3, increased efficiency. This work introduces a novel application of the Calliope framework tailored to African countries, combining high-resolution national models with a flexible scenario-based methodology to quantify the role of PHES and grid expansion. Unlike existing studies, it leverages open-access, validated data and focuses on less-explored storage options such as PHES rather than BESS, thus filling a methodological and thematic gap in the current literature. By demonstrating how different approaches shape renewable integration outcomes, this study provides a replicable methodology for policymakers and energy planners seeking cost-effective, resilient pathways towards decarbonization.