Hello Adesh,

 You can do M.Tech in Renewable Energy after a bachelors in Mechanical Engineering.

The best colleges that provide this course are :

Government Colleges

• Tezpur University
• University of Pune
• Indian Institute of Technology, New Delhi
• Indian Institute of Technology, Bombay
• National Institute of Technology, Trichy
• Devi Ahilya University, Indore

Private Colleges

• UPES, Deharadun
• PDPU,Gandhinagar
• SRM, Chennai
• Amity University, Noida
• TERI, New Delhi
• VIT University, Vellore
• Amrita University, TN

All the best!