* Sees underlying profit growth of 15 percent in year ahead
* Targets 10-15 pct underlying profit growth in medium term
* Flags potential write-off in exploration expense (Adds details on outlook)
PERTH, Aug 19 (Reuters) - Origin Energy Ltd (ORG.AX), Australia's No. 2 power retailer, sees profit growth slowing next year after beating forecasts with a 20 percent rise in full-year underlying profit on Wednesday.
Origin, a partner with U.S. firm ConocoPhillips (COP.N) in a proposed liquefied natural gas project in Australia, said underlying profit for the current financial year is expected to rise around 15 percent, and average between 10-15 percent in the years ahead.
The company said earnings will be driven by the completion of more new power generators, a wind development, regulated electricity price increases in Queensland state and a better performance from its 50-percent owned Contact Energy (CEN.NZ) unit in New Zealand.
Underlying net profit in the year ended June 30 was A$530 million ($438 million), compared with A$443 million a year ago. Analysts on average had expected A$523.7 million.
Origin said it is beginning a sizeable offshore exploration programme in south Australia to boost its reserves for the domestic market, with the initial five-well campaign expected to cost around A$100 million.
But it said some parts of the programme may be unsuccessful and could lead to a substantial write-off of exploration expenses in the current financial year.
Origin declared a final dividend of 25 cents per share, double the amount paid last year.
Origin's shares inched up by 0.6 percent to A$15.10. They have fallen 7 percent so far this year against a 17.7 percent rise in the broader market .AXJO. ($1=1.210 Australian Dollar) (Reporting by Fayen Wong)