As anyone who has been to Japan knows, there are strict rules about bathing in onsen, or hot springs. Bodies must be scrubbed beforehand, swimming trunks are banned and tattoos are taboo. The industry's jurisdiction extends far beyond the tub, however. For decades, onsen owners have stifled development of a huge potential source of clean energy: geothermal power. They argue that the tapping of heated aquifers in volcanic Japan will drain the onsen dry, increase pollution and ruin a cherished form of relaxation. With Japan on the verge of running out of nuclear power, however, the demand for new sources of energy is becoming harder to resist.

Three Japanese companies-Toshiba, Mitsubishi Heavy Industries and Fuji Electric-control more than half of the global market for geothermal turbines, yet Japan itself gets a mere 0.3% of its energy, or 537 megawatts, from its own steam. The industry's promoters say that Japan sits on about 20,000 MW of geothermal energy, or the equivalent of 20 nuclear reactors, though not all of this could be developed. Since the disaster at Fukushima last year, all but one of the nation's 54 nuclear reactors are now temporarily suspended, reducing Japan's power-generating capacity by about a third. That has accelerated the search for alternatives.

In July the government is set to introduce a feed-in tariff that will force the ten regional electricity monopolies to buy renewable energy at above-market rates-though a price has not yet been set. At the end of March the environment ministry said it would abolish guidelines that restrict geothermal development in some national parks. Companies including Idemitsu, a refiner, have quickly announced plans to build a geothermal plant in the mountains of Fukushima prefecture, which is famous for its hot springs. But they expect it will take ten years before they start generating electricity.

Experts say the long time lag reflects some of the difficulties of developing new business in Japan.