MidAmerican Energy Co. officials said Monday that work has been completed on four of the five wind farms that make up its 1,050-megawatt Wind VIII expansion. The last turbines of the project will be in place by the end of this year. Billed as the largest economic development project in the state’s history when it was announced in May 2013, the project represents an investment of up to $1.9 billion by MidAmerican Energy. With the addition of Wind VIII’s 448 turbines at the five wind farm sites, the company will have 1,715 turbines that can produce enough energy to power the equivalent of more than 1 million average Iowa homes. The final piece of the Wind VIII project – the 495-megawatt Highland wind farm in O’Brien County – will be finished by the end of 2015.  By 2016, the Des Moines-based utility company said it will have spent nearly $6 billion on wind generation projects and estimates that next year it will produce about enough energy from wind to meet approximately half the electricity demand of its retail customers.