LISBON, March 19 (Reuters) - Portuguese power grids operator REN posted a 8.1% drop in 2020 net profit on lower remuneration from its regulated activities and higher operating expenses. The owner of high-voltage electricity and high-pressure natural gas transmission grids in Portugal reported a net profit of 109.2 million euros ($130 million), REN said in a statement late on Thursday. Core earnings before interest, taxes, depreciation and amortisation (EBITDA) fell 3.3% to 470.2 million euros, it said. REN blamed the fall on lower remuneration of its Regulatory Asset Base (RAB) which fell by 23.8 million euros while operating expenses increased by 6.7% to 142.4 million euros. The lower RAB remuneration reflected a fall in the average yield of 10-year Portuguese sovereign bonds, to which it is indexed, to 0.4% in 2020 from 0.8% in 2019, as well as new gas sector regulations and a smaller asset base, REN said. An extraordinary tax on the energy sector also rose by 3.7 million euros to 28.1 million, it said. “We think it was a good year ... our activity is under great regulatory pressure, which is normal, and we must strive to maintain profitability, despite the difficulties,” CEO Rodrigo Costa told a news conference. The board proposed a gross dividend of 0.171 euro per share, “in line with previous years”. Costa said the pandemic caused delays in planned investments, with capex falling 8.1% to 173.3 million euros. This year, he said REN expects to launch its first green bonds with a maturity between seven and 10 years “in March or April”. “We usually issue between 300 and 500 million euros... but the amount is not yet decided,” he said. Green bonds are a growing category of fixed-income securities that raise capital for projects with environmental benefits, such as renewable energy or low-carbon transport.