All new houses in Tokyo built by large-scale homebuilders after April 2025 must install solar power panels to cut household carbon emissions, according to a new regulation passed by the Japanese capital’s local assembly Thursday. The mandate, the first of its kind for a Japanese municipality, requires about 50 major builders to equip homes of up to 2,000 square meters (21,500 square feet) with renewable energy power sources, mainly solar panels. Tokyo Governor Yuriko Koike noted last week that just 4% of buildings where solar panels could be installed in the city have them now. The Tokyo Metropolitan Government aims to halve greenhouse gas emissions by 2030 compared with 2000 levels. Japan, the world’s fifth largest carbon emitter, has committed to achieving carbon neutrality by 2050 but faces difficulty as it has relied heavily on coal-burning thermal power after most of its nuclear reactors were closed in the wake of the 2011 Fukushima disaster. “In addition to the existing global climate crisis, we face an energy crisis with a prolonged Russia-Ukraine war,” Risako Narikiyo, a member of Koike’s regional party Tomin First no Kai, said at the assembly Thursday. “There is no time to waste.”