https://www.lexology.com/library/detail.aspx?g=134d14be-0937-43c2-949d-27b9fb6118da  - "A Non-Fossil Fuel Certificate was introduced in 2018. The Certificate, which embodies the zero-emission value created by a renewable project under the FIT programme, is issued by a governmental agency and sold to electricity retailers at auction. The scope of electricity generators eligible to receive the Non-Fossil Fuel Certificate has been expanded since November 2019 to cover the 'post-FIT' non-fossil fuel power generation, and was also expanded in April 2020 to cover non-fossil fuel power generation outside of the FIT programme. As such, the industry landscape surrounding the Non-Fossil Fuel Certificate may change in the future."

Probably worth having.

@@ -12 +12 @@
-<gloss>Non-Fossil Certificate</gloss>
+<gloss>Non-Fossil Fuel Certificate</gloss>

https://hachidori-denryoku.jp/qanda/
https://tr-ex.me/翻訳/日本人-英語/非化石証書