China's west has long been framed as an undeveloped frontier, set apart by poverty and a resource-based economy. Since the 2000s, however, utility-scale renewable energy infrastructure has expanded rapidly in western China, promising local economic benefits tied to national low-carbon transition. This paper contends that these benefits have been precarious and unevenly distributed. I argue that utility-scale renewable energy has remade western China as a “low-carbon frontier,” a resource-rich region that generates low-carbon value for the national green economy. I highlight three features of low-carbon frontiers: they are constructed as spaces of exploitable low-carbon resources, creating an investment boom; they are enclosed through new land arrangements and infrastructure construction, rapidly and with little coordination; and they are reliant on external markets and policy decisions, entrenching dependency. These conditions make it difficult for frontier regions to capture sustained economic development benefits from the boom in the absence of persistent central state supports. I analyse these features by comparing two sets of technologies with similar, but ultimately diverging, trajectories: small and large hydropower in China's south-west, and solar and wind in the north-west.