Siemens will supply 157 2.3MW turbines to the 140MW Khobab, 140MW Loeriesfontein 2 and 80MW Noupoort sites. The deal includes ten years of servicing.
Mainstream reached financial close on the projects last week. Construction is expected to begin this month, with turbine installation due in August 2015.
Siemens previously supplied its 2.3MW turbine to Mainstream's 138MW Jeffrey's Bay project, commissioned last year.
This week, Mainstream announced a $1.9 billion partnership deal with UK investment firm Actis to develop projects across Africa. The three projects in South Africa will be the first included in the joint venture.