Target Ambition and Realisation Across Phases of Renewable Technology Growth

Accelerating low-carbon technology growth often relies on progressively more ambitious policy targets. While this ‘ratchet-up mechanism’ is central to the Paris Agreement, we lack approaches to compare target ambition over time and robust evidence on whether ambitious targets are realised. More specifically, there is no systematic method to assess ambition, accounting for the non-linear nature of technology growth or the fact that countries, and the technologies within them, may be at different phases of the technology cycle. Consequently, evidence derived from one growth phase offers limited—and potentially misleading—guidance for others, where deployment mechanisms differ fundamentally. This paper addresses this gap by asking three questions. First, how does target ambition vary across identifiable phases of technology growth? Second, when do policymakers set ambitious targets far exceeding historical trajectories? Third, to what extent is such ambition realised, and how does this relationship differ across growth phases? To answer these questions, we advance a phase-contingent perspective by distinguishing four phases of technology growth—formative, accelerating, steady, and slowdown—using a phase-detection framework for policy-driven technologies. Focusing on the G20 countries with sustained renewable growth and regularly updated technology-specific targets, the analysis applies this framework to solar power, onshore wind, offshore wind, and bioenergy using a newly constructed dataset over the past three decades. Target ambition is assessed relative to recent growth performance and historically maximum growth rates observed at the time of target-setting, while realisation is evaluated against subsequent deployment outcomes. We specifically focus on the steady growth phase, which offers a unique analytical window on the political feasibility of accelerating transitions. In this phase, accumulated experience with technology growth—including historical growth dynamics and episodes of slowdown and re-acceleration—shapes policymakers’ perceptions of a feasible space for expansion under evolving conditions. Simultaneously, mounting climate pressure pushes them to set ambition beyond this feasibility space. Preliminary findings show that target ambition and realisation sharply differ across phases. In formative and accelerating phases, ambition is weakly anchored in historical growth, and deployment outcomes are highly volatile, with frequent over- and under-achievement. In steady growth phases, targets reflect historical experience more closely, and ambition set within this range is more consistently realised. However, when targets in this phase exceed historical maximum growth rates, they are often underachieved, suggesting that accumulating constraints limit the extent to which targets translate into acceleration beyond historical growth, even under heightened ambition. By situating targets within empirically identified growth phases, the paper enables systematic comparison of target ambition and realisation across technology cycles. In doing so, we aim to provide phase-specific guidance on when and how target-setting can function effectively as a policy instrument, and where its limits become visible. These findings advance both theoretical understanding of low-carbon transitions and practical climate policy design, offering empirical grounding for the ratchet-up mechanism under the Paris Agreement.