CIRCLEVILLE, Ohio  With surprising speed, and with the help of ample public incentives, a solar energy manufacturing center has emerged in the upper Midwest that is helping to supply the world’s growing demand for clean power.

Here in this central Ohio city of 13,400 residents, DuPont is building a $175 million, 162,000-square-foot solar materials plant that will employ 70 people.

About 320 miles north, near Midland, Mich., Hemlock Semiconductor is completing a $1 billion polycrystalline silicon plant to supply a basic raw material in the manufacture of solar photovoltaic cells, which convert sunlight to electricity. The Hemlock plant will add 300 new jobs by the end of the year.

In between the two plants are six more new solar facilities in Michigan and three others in Ohio.

A number of conditions in the Midwest have allowed the sector to flourish. The upper Midwest has a history of advanced manufacturing, and machined parts and many of the basic materials of photovoltaic panels  polycrystalline in central Michigan, glass in the Toledo region, plastic films in Ohio  were already being made in the region.