Energy cost can be very low when using Proof of Stake. For example a 7000 transactions per second network could run on the energy of a single windmill: https://www.reddit.com/r/nanocurrency/comments/7ucw1a/the_en...
And for use cases, the second hand car industry is ready for disruption. You could say all blockchain use cases can be also handled by a central database. But this has failed miserably in the car industry. There are plenty of companies trying to log metadata, and as a result none of them have the complete picture. Even data aggregator companies are not able to properly bundle it.
Blockchain could offer a very good trustless solution, where you could log a cars history, and a second hand buyer could consult it.
Therefore, big names are entering this space, and I'm confident we will see blockchain solutions in that market soon.
This is only 1 example: https://www.ledgerinsights.com/mercedes-benz-blockchain-used...
The DHL website also has a nice explanation on their use cases https://www.dhl.com/global-en/home/insights-and-innovation/i...