NTPC Green Energy shares tumbled after anchor investors sold off their stake following the first lock-in period expiry.NTPC Green allotted 4.35% of equity to anchor investors, with half of them coming out of the lock-in period.The renewable energy arm of NTPC Ltd. raised Rs 3,960 crore from 107 anchor investors a day before its IPO opened for bidding.NTPC Green plans to utilize 75% of the IPO proceeds for debt repayment.