The legislation, introduced by Supervisor Scott Wiener, just got approval from San Francisco’s Board of Supervisors. The mandate calls for all new buildings up to 10 stories tall, both residential and commercial, to use either solar panels for electricity or a solar system to heat water.

The mandate is the latest example of cities taking the lead when it comes to enacting laws around installing new clean energy and energy efficiency technology.

While the U.S. federal government and state governments have various ways to push clean energy, in some cases aggressive cities have moved much faster than state and federal governments and have implemented their own methods for meeting clean energy goals. In California, the cities of Lancaster and Sebastopol have similar solar laws.

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San Francisco has a goal of meeting 100% of its electricity needs with clean energy by 2025. The state of California is requiring 50% of electricity from utilities to come from clean energy by 2030. It’s one of the strongest such state mandates in the nation.

San Francisco’s new mandate builds on a prior city law that says 15% of the rooftop space on all new small and medium-sized buildings needs to be “solar-ready” (unshaded and unobstructed). The new rule now says those solar-ready spaces will need to have solar installed.

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While many will cheer San Francisco’s new clean energy rule, it’s also the latest rule that developers in the city will face when constructing new buildings. San Francisco is a notoriously difficult place to develop in, leading to a shortage of housing and real estate for its expanding population.

California has the most solar energy in the U.S., but a few other countries in the world have passed laws to push clean energy faster. Most of Israel’s buildings buildings use solar hot water heaters, thanks to a mandate.