Comment by itsmek

The fundamental difference is that suspending something heavy over a waterway incurs significant cost - more structure needed to hold it up, harder to clean, etc. No idea how that cost balances out against benefits, but looking at the photos it's clearly a much more expensive structure than parking lots or rooftop due to the long span required and more specialized construction. Solar in a field plus a cheaper lighter shade structure is a pretty natural comparison to decide if this is economical isn't it?