LISBON (Reuters) -Portugal's largest utility EDP on Friday reported a stronger-than-expected 21% increase in first-quarter net profit, after heavy rainfall boosted hydroelectric output in Iberia, where power prices almost doubled.

Net profit rose to 428 million euros, beating the average forecast of 368 million euros in an LSEG poll of analysts, even though it did not make a capital gain in the quarter. A year ago it had booked 108 million euros worth of capital gains.

Excluding capital gains, recurring net profit rose 69%, it said.

Subsidiary EDP Renovaveis, the world's fourth-largest wind energy producer, on Thursday reported a 24% fall in net profit to 52 million euros.

EDP said in a statement that total electricity generation rose 5% to 18,300 gigawatt-hours (GWh), sustained by "significant rainfall" during the first three months of the year in Iberia, which filled reservoir volumes to 88% of their capacity.

In the Iberian market, first-quarter average electricity spot prices almost doubled year-on-year to 85 euros per megawatt per hour, it said.

"It was a good start to the year with solid and sustainable results," Chief Executive Miguel Stilwell de Andrade said. EDP would focus on business execution and efficiency, he added.

Earnings before interest, taxes, depreciation and amortisation (EBITDA) rose 6% to 1.42 billion euros, compared to 1.38 billion euros expected by analysts.

As of March, EDP's installed capacity reached 32 GW, 10% more than a year earlier.

EDP ​​​​will announce a new strategic plan in November to "reinforce its commitment to the energy transition and investment in networks and renewables", the CEO said.

(Reporting by Sergio Goncalves; editing by Inti Landauro, Kirsten Donovan)