Just when it looked like smooth sailing for wind power generation in Japan, electric power companies, its main buyers, have placed limits on their purchases, citing the unreliability of the clean energy. The wind power industry, in more ways than one, has become a victim of its own success. A surge in wind power supply has raised concerns among regional utilities that a greater dependence on natural forces may destabilize their power grids. Wind power has been tipped as a key alternative energy source to greenhouse-gas emitting fossil fuel, and initiatives by local governments have led to its introduction around the country. But with little demand left to fill at electric utilities and little chance of finding other buyers, many projects are likely to be stalled.