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 surpassed Sharp last year to become the world’s largest maker of photovoltaic solar cells. Q-Cells is the main tenant among a flowering cluster of solar start-ups here in an area known as Solar Valley.

Thanks to its aggressive push into renewable energies, cloud-wreathed Germany has become an unlikely 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 installations. 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 in a time of record oil prices. Conservative lawmakers, in particular, want to pare back generous government incentives that support solar development. They say solar generation is growing so fast that it threatens to overburden consumers with high electricity bills.