China has started construction of the world’s biggest hydroelectric dam, a project that’s set to be far larger than the Three Gorges Dam — already the world’s biggest single source of green power — and more expensive than the International Space Station.

The megadam is set to become the world’s largest hydropower system and, costing an estimated $167 billion, by far the most expensive megadam of all time. It is anticipated to provide 300 billion kilowatt-hours of electricity annually, or around 4 percent of China’s energy needs.