Nearly all houses in Tokyo will have to install solar panels after April 2025.
The regulation - passed by the Japanese capital’s local assembly on Thursday - requires 50 major construction firms to equip homes of up to 2,000 square metres with renewable energy power sources.
The rule will help the city transition to green energy, city counsellors declared.
"In addition to the existing global climate crisis, we face an energy crisis with a prolonged Russia-Ukraine war," said Risako Narikiyo, a member of the local assembly.
"There is no time to waste."
Why is Tokyo making solar panels mandatory?
Tokyo is the world’s largest city, with a population of nearly 14 million people in its central metropolitan area. Per year, its residents emit an average of 8.6 tonnes of CO2 each.
The IPCC recommends that to meet our decarbonisation goals we should exceed no more than 2.3 tonnes of carbon each, per year.
Tokyo hopes to bring down its emissions footprint significantly in the coming decades. The city’s Metropolitan Government aims to halve greenhouse gas emissions by 2030 compared with 2000 levels, and to be emission-free by 2050.
But Tokyo lags in its uptake of renewable energy. Just four per cent of buildings with the capacity for solar panels currently have them.
The new rule will help change this.
Overall, the measure will save residents money, the metropolitan government says.
The 4 kilowatt panels will cost around 980,000 yen (€6,725) to install, but the government estimates that this will be covered by electricity sales revenue within 10 years. Subsidies will reduce this pay off time to around six years.