Mercury NZ and infrastructure investor Powering Australian Renewables (PowAR) have lifted their offer for Tilt Renewables to $8.10 a share from $7.80 in response to a reported Canadian bid.
Separately, Tilt's majority shareholder Infratil said it supported the offer, which values its stake at $2 billion.
Tilt's shares last traded on the NZX at $7.60.
The revised bit comes after Australian media speculated that Canadian pension fund CDPQ may have launched a competing bid for the wind power specialist, which has extensive assets in New Zealand and Australia.
AusralianSuper was also understood to be on the sidelines.
Under the revised agreement, PowAR will acquire all the shares of Tilt - including Mercury's shares - at $8.10 for a total of $3.07 billion.
Mercury will acquire all of Tilt's New Zealand operations, including its future development options, for an enterprise valuation of $797m (previously $770m).
The acquisition of the New Zealand operations by Mercury will be funded from the sale of Mercury's 19.9 per cent Tilt shareholding, worth $608m (previously $585m) and net debt of $189m (previously $185m).
In addition to the increased price, the deal has been amended to remove provisions allowing Tilt to evaluate any "competing proposal" "giving greater certainty to all parties and Tilt shareholders that the transaction will complete by August".
Mercury chief executive Vince Hawksworth said it was import to keep Tilt's New Zealand renewable generation and development assets in New Zealand ownership.
"As New Zealand addresses the continuing need for decarbonisation and recognising the vital role that electrification plays, we believe ownership of these strategic assets by Mercury, a New Zealand owned generator with an outstanding track record of generation development, is in New Zealand's best interest,"he said in a statement.
The Scheme requires Tilt shareholder approval and is conditional on High Court approval, and regulatory approvals. The scheme is expected to be finalised in August.