How is the high energy cost of mining Bitcoin solved by exchanges? Also if I want to use crypto for anything except speculation within an exchange, the transact

How is the high energy cost of mining Bitcoin solved by exchanges? Also if I want to use crypto for anything except speculation within an exchange, the transaction speed is still an issue, even with apps like Coinbase. (Or at least it was last time I used it). I know Lightning Network helps but that's like a layer on top of Bitcoin because the Bitcoin tech itself doesn't scale well