DES MOINES, Iowa — 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, said Spencer Moore, MidAmerican Energy’s vice president of generation.

Each upgraded turbine will annually net between 19 and 28 percent more energy, the company said.

The Des Moines Register reports that the project is beginning with MidAmerican’s first three wind farms, built in 2004 in northern Iowa. The entire project will likely update seven wind farms.

The utility company’s turbines are designed so they can be upgraded as they age and technology advances, Moore said. The old equipment from the wind farms will likely get recycled by the manufacturer, General Electric.

Construction crews often work overnight, when winds die down. Work stops when the wind exceeds 20 mph.

The company also plans to add 1,000 more turbines around the state. That project is estimated to cost $3.9 billion. The company currently has more than 2,000 turbines in Iowa.

The company expects the upgrades and expansion will allow it to supply about 95 percent of its customer’s energy needs through wind. The utility said wind energy helps keep electricity costs low.

Both projects are scheduled to be completed by the end of 2020, before the United States’ production tax credits are phased out. A U.S. House tax bill released last month looks to roll back the credits.

Iowa got almost 37 percent of its energy last year from wind.