I heard this one when I was a small child, but it could probably work wonders. There are some enclosed seas with very few inlets, like the Mediterranean, and the gulf of Hormuz. The Mediterranean would be the biggest beneficiary of this. Also, we could dam it off entirely on Spanish territory to prevent nationalistic squabbles about power rights from this.
Anyway, we dam off the Mediterranean with a hydroelectric dam. Then we pump the water out, perhaps by a million people bailing buckets for years, or perhaps we use an electric pump with some spare capacity. Power is generated as the water flows back in through our dam. Occasionally we re-pump out the water.
This will mean extra land. All of south Europe and North Africa will have to divide this new turf by some reasonably logical means. Preferably without the traditional agonizing war.
Downsides: Any wildlife in the Mediterranean will have to be moved out to the Atlantic. It might not survive the journey.