Contact Energy, the country's second-largest electricity retailer, increased first-half profit five-fold on the sale of its Ahuroa gas storage and LPG business last year.
Net profit rose to $276 million for the six months ended December 31, from $58 million a year earlier, boosted by a $172 million gain from the asset sales.
Earnings before interest, tax, depreciation, amortisation and changes in financial instruments from Contact's remaining businesses rose to $278 million, from $217 million a year earlier.
The company, which has simplified its business to improve its retail and generation margins, generated 4,532 GWh of electricity in the six months, almost 5 per cent more than a year earlier.
A 25 per cent jump in hydro output from its Clyde and Roxburgh dams enabled the firm to benefit from record wholesale prices in October and November when gas supplies were tight and storage was low in the Waitaki hydro catchment of rival Meridian Energy. That saw generation ebitdaf increase by $58 million to $243 million.