Construction at the 140MW Khobab, the 140MW Loeriesfontain 2 and the 80MW Noupoort projects can now start.
Mainstream said building activities could begin this month. The company was awarded the license to build these projects in October 2013.
Siemens has been handed the contracts to supply and install the turbines at all three sites, located in the Northern Cape.
Siemens provided turbines to Mainstream's other South African project, the 138MW Jeffreys Bay, which came online with Siemens 2.3MW turbines last year.
Mainstream is being partnered by South African investment firm Thebe Investment Corporation, Old Mutual's Ideas Managed Fund, development investor Futuregrowth Asset Management, and South African renewable energy firm Genesis Eco-Energy for the current projects.