AGL Energy's acquisition of a major Victorian power plant has contributed to a significant rise in first half profit to $365 million.

AGL acquired Loy Yang A, Australia's third largest coal fired power station, in June 2012.

The contribution of earnings from Loy Yang helped AGL's net profit in the six months to December 31 rise from $117 million in the previous corresponding period.

But the company said profit growth in the second half of the 2012/13 financial year would be constrained by volatile wholesale electricity prices, deregulation of prices in South Australia and low demand for electricity.