DES MOINES, Iowa (AP) — MidAmerican Energy says it plans to spend $1 billion updating more than 700 older wind turbines across Iowa. The turbines will be retrofitted with newer, more efficient components, including longer blades, to extend their lifespans an estimated 20 years. The company says each upgraded turbine will annually net between 19 and 28 percent more energy.

The project is beginning with MidAmerican’s first three wind farms, built in 2004 in northern Iowa. Construction crews often work overnight, when winds die down. Work stops when the wind exceeds 20 mph.