Photo/Illutration Roofs with solar panels in a residential area in Tokyo’s Hachioji on Dec. 3 (Harufumi Mori)

The Tokyo metropolitan assembly adopted an ordinance on Dec. 15 requiring new homes and buildings to be outfitted with solar panels with the aim of curbing rising carbon dioxide emissions from households.

This will make Tokyo the first place in Japan to require solar panels on new detached houses. The ordinance will come into force in April 2025.

“We have gone ahead with requiring businesses (to install solar panels),” Tokyo Governor Yuriko Koike said at a news conference held after the ordinance was approved. “We would like to move forward while gaining further understanding (from businesses).”

Under the new framework, the obligation to install solar panels for large structures, such as office or apartment buildings, falls on anyone who commissions their construction.

For other smaller structures with a total floor space under 2,000 square meters, such as detached houses, developers or housing providers are required to install solar panels.

However, the requirement in the second category is only applied to major corporations that offer a total floor space of at least 20,000 square meters per year in Tokyo.

Tokyo’s new framework is mostly targeted at the second category, meaning it will lead to a big boost in the number of homes owned by the general public outfitted with solar installations.

According to the Tokyo metropolitan government, around 50,000 buildings and houses are built in Tokyo each year, and around 20,800 of these will need to have solar panels under the new rules.

Around 20,000 of those qualify as other smaller structures in the second category.

Officials explained there are two reasons for setting the regulations like this.

The first is that CO2 emissions from households are not falling.

According to the metropolitan government, CO2 emissions from transportation, including those from vehicles, in the capital fell significantly over the past two decades. The level of emissions measured 8.7 million tons in fiscal 2020, 49.3 percent of the volume in fiscal 2000.

By contrast, CO2 emissions from Tokyo households have risen dramatically over that same time. There were 17.05 million tons of emissions in fiscal 2020, 132.9 percent of the level in fiscal 2000.

While more people are using low-emission and electric vehicles in Tokyo, the capital’s population rose by 17 percent over that period—a major factor behind the rise in emissions.

But the second reason is the dismal adoption rate of solar panels on rooftops, despite Tokyo’s massive concentration of houses and buildings.

The capital has around 2.67 million buildings and houses, but only 4 percent, or around 100,000, have solar panels.

Mega solar installations boasting gigantic panels with a capacity of 1,000 kilowatts or more are also rare in Tokyo, where there are not many open spaces.

The metropolitan government estimates the new solar regulations will lead to an additional 40,000 kW of power generated per year.

The capital currently produces 646,000 kW of solar power a year, which would increase by 6 percent under the new framework.

But some have raised concerns about the costs of installing and managing solar panels, which are estimated to be around 1 million yen ($7,280) per house.

Many houses in Tokyo have roofs that face north so that they do not block the sun from shining on neighboring houses. But solar panels should face south.

Houses in Tokyo are also typically very small, meaning they will each only have space for a small number of panels.

However, the metropolitan government argues that residents will still benefit from the solar panels because they will be able to save electricity or sell it back to the grid.

The metropolitan government will set targets for each developer or housing provider for how much power the solar panels should generate based on the number of houses they build and other criteria.

Housing providers and developers will be free to choose which properties they will equip with solar panels, so long as they meet their targets.

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