THALHEIM, Germany: This sad stretch of eastern Germany, with its deserted coal mines and corroded factories, epitomizes post-industrial gloom. It is a place where even the clouds rarely seem to part.

Yet the sun was shining here the other day - and nowhere more brightly than at Q-Cells, a German company that last year overtook Sharp, a Japanese company, to become the world's largest maker of photovoltaic solar cells. Q-Cells is the anchor tenant in a flowering cluster of solar start-ups here, known as Solar Valley.

Thanks to its aggressive push into renewable energies, a cloud-wreathed Germany has become an unlikely world leader in the race to harness the sun's energy. It has by far the largest market for photovoltaic systems, which convert sunlight into electricity, with roughly half of the world's total installed capacity. And it is the third-largest producer of solar cells and modules, after China and Japan.

Now, though, with so many solar panels on so many rooftops, critics say Germany has too much of a good thing. Even at a time of record oil prices, solar is encountering resistance from conservative lawmakers who want to pare back its generous state incentives. They say it is growing at an unhealthy pace, threatening to burden consumers with too many costs in the form of higher electricity bills.

Solar-energy entrepreneurs warn that reducing these incentives would deprive Germany of its pole position in an industry of tomorrow. They liken Germany to the United States and Japan, which were both once solar stars but faded as their subsidies became less attractive.