I don't think these sunken cylinders are going to be either cost-effective or eco-friendly.

Mechanical seal problems with water leaking into the electrics or hydraulics will be of major concern.

Likewise the corrosion problems associated with fresh/seawater.

Annoying they will be to bottom dwellers, fish, seals, and other marine life.

Before long the installation would be colonised by barnacles.

I shall not be investing in such a madcap scheme.

Kind Regards....