Support for innovation should involve competitive selection processes, it should focus on performance rather than individual technologies, avoid favouring incumbents, ensure rigorous evaluation of policy impacts and contain costs. Governments should embrace a certain degree of trial and error to account for uncertainty when providing discretionary support, providing exit mechanisms when a technology proves unsuccessful, or successful enough to be driven by private actors {Egli, Menon and Johnstone, forthcoming). Firms engaged in green innovation can find it challenging to access finance, because of the greater commercial risk associated with immature markets, high capital-intensity of some technologies, and relatively long-term investment periods.