Berlin’s senate, the executive body governing the city-state, has approved a new solar law that includes an obligation from 2023 on for most new buildings to install a PV or solar thermal installation on their roofs, as part of a strategy to source a quarter of the German capital’s power from solar by mid-century.

The legislation still needs to be passed in the city parliament, but approval is a formality given the left-green coalition majority in the state.

The solar mandate – Solarpflicht in German – also will be valid for already existing buildings in which the roof is substantially renovated.

“With our solar law, a Solarpflicht for all new buildings and for existing buildings with fundamental roof renovation comes from 2023 on,” energy senator (minister) Ramona Pop said.

“Berlin has many roofs and therefore a lot of potential for solar energy. We want to use that, because Berlin needs more photovoltaic systems to become climate neutral.”

Berlin with its solar obligation follows a growing trend among cities and regions across the world that mandate certain parts of new private or public buildings to be equipped with solar installations in order to tap into the vast solar potential of cities.

The US state of California last year probably became the largest region to adopt a solar mandate for most new homes. In Germany, the states of Baden-Württemberg, Schleswig-Holstein and Hamburg also plan or consider solar mandates from next year or 2023 on.

All of them, like Berlin, have governments including the Green Party.

Berlin’s Solarpflicht will require new buildings to cover at least 30% of its roof with solar installations, as long as their capacity doesn’t exceed 6 kilowatts. Exemptions will be made for roofs facing north. PV installations integrated in facades can replace rooftop plants, according to the legislation.

The new law comes after Berlin early last year had passed its ‘Solarcity’ plan to speed up the deployment of PV on its territory, and meet a quarter of its power needs by solar energy by 2050.

Despite its often cloudy climate and northern European location, Germany as whole already today meets some 10% of its power demand with solar energy, one of the highest solar penetration levels in the world.