Growing global awareness of climate change has ushered in a new era demanding policy, financial and behavioral innovations to accelerate the transition to a clean energy economy. Dramatic price decreases in solar photovoltaics (PV) and public policy have underwritten the expansion of solar power, now accounting for the largest share of renewable energy in California and rising fast in other countries, such as Germany and Italy. Governments’ efforts to expand solar generation base and integrate it into municipal, regional, and national energy systems, have spawned several programs that require rigorous policy evaluations to assess their effectiveness, costs and contribution to Paris Agreement’s goals. In this study, we exploit a natural experiment in northern California to test the capacity of Property Assessed Clean Energy (PACE) to promote PV investment. PACE has been highly cost effective by more than doubling residential PV installations.