In November 2024 the Japanese government set a target of installing about 20 GW of perovskite solar cells in Japan by 2040. Two years on, manufacturing subsidies awarded to companies exceed 200 billion yen in approved ceilings, the deployment subsidy has grown to 7 billion yen a year, and government buildings have started to install the cells ahead of the market.
This series checks that policy against the primary record. We read the handouts and minutes of the public–private council, the government-commissioned demand study, the subsidy award lists, the Ministry of the Environment's implementation materials and the Diet record side by side, and we separate what the documents confirm from what remains inference.
This is the English edition. The Japanese pages are the original text; where a chapter has not yet been translated, the link below goes to the Japanese page, which offers machine translation through the language menu. The evidence register, claims register and primary-source list are published as CSV files with Japanese column headings; the evidence IDs (EV, CL, COI, PS) are the same in both languages.
How to read the grades
Each statement carries a grade showing how well it is supported. The EV number after the grade is the row in the evidence register.
| Grade | Meaning |
|---|---|
| A | Confirmed in a primary source |
| B | Corroborated by two or more independent sources, or a company's own published figure |
| C | A reasonable inference from the sources, including our own calculations |
| D | Hypothesis, still being checked |
| E | Insufficient evidence, or refuted |
Where people are named, we record only their public roles and publicly disclosed economic interests. That a person or organisation holds more than one role is a different matter from improper influence; the latter is stated only where we could confirm it, together with the evidence.
Chapters
| Chapter | Content | Status |
|---|---|---|
| Chapter 1 Where did 20 GW come from? | How the commissioned study estimated demand; a 10-year lifetime versus a 20-year lifetime; a cost estimate that misses the self-sustaining level | English available |
| Chapter 2 What the council discussed | Ten council meetings, 40 unpublished handouts, minutes without speaker names, and the eighth meeting that delegated the final text to the chair after one hour | Japanese |
| Chapter 3 Who decided, who received | Council membership and turnover, subsidy recipients, overlaps with award review, industry associations | Japanese |
| Chapter 4 Comparing generation costs | 15.3–16.4 yen/kWh in 2040 against 7.9–8.4 yen for silicon; what a 10-year lifetime does to the number; what the 10–14 yen "self-sustaining level" is compared with | English available |
| Chapter 5 Demand created by subsidies | Deployment subsidies at 6.05–7.86 million yen per kW, 100 MW on government buildings, 5–7 GW of public-sector demand, municipal targets | Japanese |
| Chapter 6 How the press reported it | Five major outlets on launch day; "20 nuclear reactors' worth", a phrase absent from the strategy; 3.5 reactors in energy terms; changes in ministry communication | Japanese |
| Chapter 7 What is happening abroad | Seven overseas companies the strategy listed as "under construction or planned", two years later; Saule's shutdown; Hanwha's delay; IEEFA's recommendation | English available |
| Chapter 8 What the same money could have bought | About 288 billion yen of published support ceilings; what it buys at 2023 unit costs; a 150–180 billion yen annual cost gap in 2040 | English available |
| Chapter 9 Open questions to the government | Full text of ten questions and the status of replies | Japanese; sent, reply deadline 28 November 2026 |
| Chapter 10 Documents obtained by disclosure request | Content and results of the administrative document disclosure requests | In preparation |
Data
- Policy timeline 2023–2026 (Japanese) — the ten council meetings and liaison meetings, the path of the 20 GW figure, budgets and awards, the Diet
- Public support register (Japanese) — budgets, awards, grant decisions and actual outlays kept separate
- Evidence register and primary sources (Japanese; CSV) — the source behind each statement, the grade of each claim, the URL of each document
About the company writing this series
I-S3 Co., Ltd. sells and installs crystalline-silicon solar, battery storage and EV charging equipment in Annaka, Gunma Prefecture, Japan. A policy to promote perovskite solar cells affects our business. We state that position first. The series relies only on primary sources and published figures, separates inference from fact, accepts corrections at s_masuda@i-s3.com, and records every correction in the change log on this page. Anyone named in the series may rebut at equal length.
Change log
- 2026-10-29: English edition opened with the series home and Chapters 1, 4, 7 and 8. The Japanese edition published Chapters 1–8, the open questions (ten questions), the policy timeline, the public support register and the evidence register on the same day
Deciding whether to put solar on your roof in Japan? We help you weigh waiting for perovskite against installing crystalline silicon now, based on your roof and how you use electricity.
Ask about your own roofPages in this series
Citation and reuse
The CSV and Markdown source files (index) are released under CC BY 4.0. You may copy, adapt and use them commercially if you credit I-S3 Co., Ltd. and link to this page. Quotations from the text with attribution are welcome.
Anyone named in this series who wishes to rebut or correct a statement may write to our contact form or s_masuda@i-s3.com; we publish rebuttals at equal length.
Suggested citation
Masuda, S. (2026). "Scrutinising Japan's Perovskite Solar Policy". I-S3 Co., Ltd., published 2026-10-29, https://www.i-s3.com/perovskite-policy-investigation-en.html