Buildings as Power Plants: Japan's New Policies and Smart Energy Week Highlight Emerging Trends in BIPV Technology

Japan is advancing the adoption of Building-Integrated Photovoltaics (BIPV) through a dual-track approach of policy and industry initiatives. The Ministry of Land, Infrastructure, Transport and Tourism (MLIT) has recently expanded its energy-efficient housing incentives under the “Flat 35” long-term fixed-rate mortgage program to encourage the construction of green homes. Meanwhile, the Tokyo Metropolitan Assembly made history by passing Japan’s first ordinance mandating the installation of solar panels on new houses beginning April 2025. On the industry side, the 2025 Smart Energy Week in Tokyo will introduce a dedicated “BIPV World” pavilion, showcasing the integration of solar power generation directly into building materials. Key innovations on display include the perovskite solar window “Windows ZERO,” which offers both power generation and energy-saving functions, and Taiwan’s first P-BIPV perovskite solar house, which demonstrates high levels of energy self-sufficiency—both drawing significant attention.

Policy Driver 1: Green Finance and Mortgage Incentives

The Japanese government has actively promoted energy-saving and carbon reduction policies in the residential sector. The “Flat 35” mortgage program, provided by the Housing Finance Support Organization under MLIT, offers long-term fixed-rate loans (around 1.5% interest) for up to 35 years. Since April 2023, newly built homes applying for Flat 35 loans must meet national energy efficiency standards to qualify. In addition, homes that meet higher efficiency criteria can receive preferential rates: for example, a base mortgage rate of 1.5% can be reduced to 1.25% for homes rated at energy level B, and further down to 1.0% for level A certified homes. These financial incentives aim to reduce homeowners' loan burdens and encourage the development of green housing.

This policy aligns with Japan’s broader timeline to mandate all new homes meet energy efficiency standards by 2025. It is a key strategy to improve household energy performance and reduce greenhouse gas emissions.

“Flat 35” is a long-term fixed-rate home loan jointly promoted by the Japanese government and the Housing Finance Support Organization.

Policy Driver 2: Tokyo’s Mandatory Green Rooftops

At the same time, the Tokyo Metropolitan Government has adopted more aggressive renewable energy mandates. Under an ordinance passed at the end of 2022, all new detached homes built in Tokyo from April 2025 onwards must install solar panels on their rooftops. Tokyo thus becomes the first city in Japan to mandate photovoltaic equipment on residential buildings.

The rule applies primarily to large developers building over 50 homes annually, requiring solar panel installation on each home within housing projects with a total floor area under 2,000 m². Notably, the obligation is on developers, not homebuyers, and exceptions are allowed for rooftops with limited sunlight or insufficient space.

Governor Yuriko Koike emphasized that the move aims to fundamentally reshape Tokyo’s use of renewable energy. While only about 4% of suitable buildings in Tokyo currently have solar panels, the new mandate is expected to significantly boost this figure. The Tokyo government estimates that a single household with solar panels can self-supply about 80% of its electricity needs, with savings and energy sales recouping installation costs within 10 years.

Driven by such policies, Japan’s residential solar market is poised for significant growth, creating new opportunities for the adoption of BIPV technologies.

Exhibition Focus: BIPV Trends at Smart Energy Week 2025

Beyond policy, the industry is actively responding to the BIPV trend. At the 2025 Smart Energy Week in Tokyo, organizers have partnered with the Japan Photovoltaic Energy Association (JPEA) to launch a new pavilion called “BIPV World.” As part of the PV Expo, this zone spotlights the latest innovations in building-integrated photovoltaics.

BIPV involves embedding solar power components directly into building materials, allowing them to serve both structural and power-generating functions. Compared to traditional rooftop-mounted solar panels, BIPV systems offer enhanced aesthetics and multifunctionality. Applications include solar tiles, exterior walls, and photovoltaic windows that generate electricity while providing insulation and weather protection.

Key technologies on display at BIPV World include:

Perovskite Solar Cells: Showcasing the latest in high-efficiency solar technology.
Solar-Integrated Building Materials: Photovoltaic glass, walls, and roofs that offer power generation, insulation, and shading.
Decorative Films and Colored Coatings: Aesthetic options in various colors and patterns.
Energy Management Systems: Smart systems integrating solar power, energy storage, and EV charging.
Waterproofing and Insulation Solutions: Specialized systems for BIPV durability and thermal performance.
Power Conversion Equipment: High-efficiency inverters and converters.
Simplified Installation Technologies: Modular systems for fast and efficient deployment.

These innovations transform idle building surfaces into power-generating assets, blending function with form. Experts at the exhibition highlighted BIPV as a key solution for reducing the carbon footprint of buildings in the face of climate change and energy transition. Many companies engaged in live consultations, exploring how to integrate these materials into real-world projects—showcasing the industry’s growing interest in the BIPV business.

By gathering policymakers, energy firms, and investors, Smart Energy Week has created a collaborative platform that offers a glimpse into a future where buildings themselves become power plants.

Technical Innovation: Perovskite Power Windows and Energy-Self-Sufficient Buildings

Among the various BIPV technologies presented, Taiwan’s perovskite solar innovations were a major highlight. TPSC (Taiwan Perovskite Solar Corporation), in collaboration with AIZ Zero Carbon, unveiled the "Windows ZERO" perovskite solar window at the Smart Energy Week in late February. The launch attracted more than 1,000 visitors and industry professionals.

Taiwan Perovskite Solar Corporation (TPSC) presented the Windows ZERO perovskite power-generating window at the Tokyo Smart Energy Week, drawing a full-house audience.

The transparent power-generating window embeds perovskite solar cells into the glass, transforming standard building façades into energy-producing systems. According to the developers, the AIZ Zero Carbon Window has passed the highest levels of domestic waterproof and windproof testing, suitable for harsh weather conditions. Its laminated structure provides superior insulation, reduces HVAC load, lowers indoor noise, and enhances indoor comfort.

In essence, the window not only generates electricity but also offers energy-saving benefits. It serves multiple functions and can significantly reduce the building’s carbon footprint during construction and operation. The team also showcased A4-sized perovskite window and door module prototypes.

Windows ZERO combines eight functions: transparent solar power generation, waterproofing, air sealing, insulation, carbon reduction, noise reduction, anti-smog, and multi-purpose use.

Beyond windows, TPSC and AIZ have expanded perovskite applications to full-scale energy systems in buildings. Taiwan has recently completed its first P-BIPV (Perovskite-Building Integrated Photovoltaic) demonstration house, where lightweight perovskite modules are integrated into both the roof and exterior walls. The structure also includes energy storage and intelligent energy management systems, aiming to achieve high self-consumption ratios.

According to the R&D team, the building is expected to operate in a nearly zero-energy mode under ideal conditions—generating most of its electricity on-site. It can power essential lighting and partial HVAC needs. As perovskite efficiency and durability continue to improve, such self-sufficient green buildings may soon become more widespread.

Taiwan has also established the "Taiwan Perovskite Research and Industry Alliance," uniting government, academia, and industry to accelerate commercialization and global expansion of this emerging technology.

The perovskite energy house located in Taiwan’s Central Taiwan Science Park is the nation’s first zero-carbon building that integrates green energy generation, energy storage, energy saving, and smat energy (“4-in-1” capabilities), equipped with Windows ZERO.

Conclusion: The Rise of Buildings as Power Plants

From Japan’s green mortgage incentives and mandatory solar ordinances to cutting-edge BIPV innovations unveiled at industry exhibitions, a revolution in building energy systems is underway. Traditional buildings are being reimagined as decentralized power units: rooftops become mini power stations, and windows generate electricity while letting in natural light.

Japan’s national vision for net-zero carbon emissions by 2050 is steadily advancing through these combined policy and technological efforts. As market demand grows under policy support, and with increased investment in R&D and manufacturing, the cost of BIPV systems is expected to fall, paving the way for widespread global adoption.

Soon, we may see Tokyo’s skyline and Taiwan’s tech parks dotted with more and more “invisible” solar power installations across rooftops and façades. The deep integration of energy systems and architecture is no longer a futuristic dream—BIPV is fast becoming a cornerstone of sustainable urban development.

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