Here’s another glimpse of the challenges involved in attempts to run countries on renewable energy.

In theory, Japan has a huge offshore wind resource—there’s enough to power Japan eight times over, according to an article in the New York Times. But in practice, that’s going to be hard to take advantage of. Since the disaster at Fukushima, Japan’s 50 nuclear reactors have been largely out of commission. To replace just one of them, it needs to  build 140 offshore wind turbines.

And these are no ordinary wind turbines. Because Japan doesn’t have a lot of shallow coastal waters where wind turbines could be secured to the sea floor, as it done in all big offshore wind farms now, the wind turbines have to float, like deep sea oil platforms. The idea of floating turbines isn’t new (see “Wind Power That Floats”) but they’re expensive. The wind turbines are expected to cost eight times as much as wind turbines built on land.

According to the Times, these other challenges might reduce the practical wind resource to just one-third of the country’s electricity needs.