Hawaiian Electric Industries Inc. today reported a 39 percent increase in fourth-quarter earnings, driven largely by gains at its electric utility subsidiary.

HEI, which operates Hawaiian Electric Co. and American Savings Bank, reported net income of $34.2 million, or 36 cents a share, in the October-to-December period, up from $24.7 million, or 26  cents a share in the same period a year earlier.

For the full year, HEI’s earnings rose to $138.2 million, or $1.44 a share, up from $113.5 million, or $1.21 a share in 2010.

Constance Lau, HEI president and chief executive officer, said the solid earnings allowed the company to invest $200 million in modernizing its grid to accept larger amounts of renewable energy.