A 73 percent increase in earnings at its utility subsidiary drove Hawaiian Electric Industries’ profitability sharply higher in the third quarter compared with the same period a year earlier, the company reported today.

HEI, which is the parent of Hawaiian Electric Co. and American Savings Bank, reported net income of $48.4 million, or 50 cents a share for the July-through-September period, up from $32.4 million, or 35 cents a share a year earlier.

The biggest factor was a $16 million jump in net income at HECO, fueled largely by $6 million in rate increases across three counties and $5 million in revenue from the implementation of a “decoupling”  mechanism on Oahu designed to encourage the development of renewable energy by eliminating the economic incentive for HECO to sell more electricity.

Net income from American Savings Bank was $15.5 million in the third quarter compared with $15.2 million for the same period in 2010.

“While utility earnings are recovering from the depressed levels of 2010, returns will continue to fall short of those allowed by the Hawaii Public Utilities Commission,” said Constance Lau, HEI president and chief executive officer.

“Continued regulatory support to recover our investments in a timely manner is essential to our success in attracting the significant capital needed to fund our utilities’ reliability and clean energy plans,” Lau said in a news release.

HEI shares were up 80 cents at $26.18 in afternoon trading on the New York Stock Exchange.