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This Article explores constitutional limits and regulatory openings for innovative state policies to mitigate climate change by promoting climate-friendly, renewable energy. In the absence of a comprehensive federal policy approach to climate change and clean energy, more and more states are stepping in to fill the policy void. Already, nearly thirty states have adopted renewable portfolio standards that create markets for solar, wind, and other clean electricity. To help populate these markets, a few pioneering states have recently started using feed-in tariffs that offer eligible generators above-market rates for their clean, renewable power.

But renewable portfolio standards, feed-in tariffs, and other state climate policies have increasingly come under attack for alleged violations of the Constitution. How much latitude do states have when they experiment with innovative climate and clean energy policies? And which policy best protects states from the risk of lengthy and costly litigation over its constitutionality?

To answer these crucial questions, this Article takes stock of recent litigation challenging the constitutionality of state renewable portfolio standards and feed-in tariffs. Qualitative analysis reveals markedly different constitutional risk profiles for both policies with portfolio standards more prone to Commerce Clause challenges and feed-in tariffs more likely to face Supremacy Clause challenges. These vulnerabilities have prompted widespread scholarly skepticism over both policies' constitutional viability when implemented at the state level, often accompanied by calls for sweeping legislative or judicial reform. Pushing back against the prevailing scholarly skepticism, this Article draws on recent precedent to make the case for joint implementation of both policies as a way to reduce, rather than exacerbate, a state's overall exposure to the risk of constitutional attacks on its climate and clean energy policy.