こんにちは!
ご質問ありがとうございます。
ご質問について、いくつか言い方が考えられますが、例えば、
Previously, I worked in a department related to thermal power. However, I felt that thermal power lacked prospects for new development due to its high environmental impact. At that time, I made the decision to transfer to a department where I could be involved in the development of renewable energy, which holds greater potential.
というように訳すことができます。
役に立ちそうな単語とフレーズ
thermal power [火力発電](https://eikaiwa.dmm.com/uknow/questions/61660/)
environmental impact 環境への影響
lack prospects for the future 将来への見通しを欠いている
hold greater potential さらに大きな可能性を持つ
involved in 関わる・関与する
参考になれば幸いです。