The 215 wind turbines at Whitelee wind farm on Eaglesham Moor, East Renfrewshire, can generate 539MW of electricity.
Iberdrola is seeking permission from the Scottish government to build five more wind turbines on land in East Ayrshire, to the west of the existing site. It believes the project could involve up to 60 construction jobs.
Scottish Power Renewables managing director Simon Christian said: “Whitelee has proved to be an excellent location for a wind farm development.
“There has always been potential to extend Whitelee – it is well located near to major roads, it has access to a strong grid network and there is high demand for the electricity generated from the heavily populated nearby areas of Glasgow and East Kilbride and rural Ayrshire.
“Although our proposals for the third extension are relatively small, we think it is important to make the most of this excellent site and this development would make an important contribution towards Scotland’s renewable energy targets.”
The expansion plan would add another 12MW of capacity, allowing the wind farm to power more than 300,000 homes.