Victorian Premier Denis Napthine has officially opened the largest wind farm in southern hemisphere, at Macarthur, in south-western Victoria.

It has taken two-and-a-half years to build the $1 billion project with 140 wind turbines, which became fully operational at the end of January.

Dr Napthine opened the wind farm on Friday.

"This is a great investment in Victoria, 700 jobs during construction and 40 ongoing jobs," he said.

"It will generate enough electricity to power over a quarter of a million average households in Victoria."

But the wind farm has also been the source of complaints.

Protesters say the wind farm is upsetting their sleep and has cut land values.

A handful of protesters were at the site holding placards saying stop the wind farm.