How windmills as wide as jumbo jets are making clean energy mainstream

OSTERILD, Denmark — At the northern end of Denmark’s Jutland peninsula, the wind blows so hard that rows of trees grow in one direction, like gnarled flags.

The relentless weather over this long strip of farmland, bogs and mud flats — and the real-world laboratory it provides — has given the country a leading role in transforming wind power into a viable source of clean energy.

After energy prices spiked during the 1973 oil crisis, entrepreneurs began building small turbines to sell here.

“It started out as an interest in providing power for my parents’ farm,” said Henrik Stiesdal, who designed and built early prototypes with a blacksmith partner.