Thousands of megawatts of cheap, clean hydroelectricity from Canada are continuously rushing into the New York Power Authority's sprawling substation in Marcy, NY-enough juice to light up 40 World Trade Centers. For almost a half-century, the Marcy facility, located just a few miles from the remote Adirondack National Park in upstate New York, has transformed this torrent of electricity from a blistering 765,000 volts to the slightly more manageable 345,000 volts used by the overhead transmission cables that feed power-hungry Manhattan 300 kilometers to the southeast.

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