* Underlying annual profit drops 22%

* FY21 profit outlook around 20% below analysts' forecasts

* Co plans to pay special dividends in FY21, FY22

* Targets big boost in renewable energy share of generation

Aug 13 (Reuters) - Australia's AGL Energy on Thursday forecast a bigger-than-expected 30% drop in fiscal 2021 profit, pressured by rising costs, falling electricity prices and customer hardship due to the COVID-19 pandemic, sending its shares down over 10%.

The country's top power producer expects underlying profit between A$560 million and A$660 million ($401.46 million-$473.15 million) for the year to June 2021. The midpoint of the forecast range is 20% below analysts' estimates, according to Refinitiv data.

"FY21 will be a year of considerable uncertainty as we navigate the COVID-19 pandemic and its economic impact," Chief Executive Officer Brett Redman said.

The dire forecast came as the company reported a 22% drop in 2020 profit mainly due to weaker gas sales volumes, lower electricity and renewable energy certificate prices and an outage at its Loy Yang A coal-fired plant.

Underlying profit, which omits one-off items, for the year ended June 30 dropped to A$816 million from A$1.04 billion last year, above analysts' estimates of A$807 million, according to Refinitiv data.

AGL cut its final dividend to 51 cents per share from 64 cents last year, and said it intended to pay special dividends during FY2021 and FY2022.

The country's biggest carbon emitter set out a four-year target for increasing the share of renewable energy and clean storage to 34% of its generation capacity from 22% now, including boosting its grid-scale batteries installed to 850 MW from 30 MW.

It also said it aimed to provide 4.5 million broadband and phone connections by fiscal 2024, as it looks to add new offerings to its power and gas products.

The company's shares plunged 10.8% to A$15.15, posting their biggest intraday percentage drop since October 2007.

"While the earnings outlook today is lower than expected, rallying electricity futures may present some future upside over the next 6-12 months," Citi analyst James Byrne said in a note. ($1 = 1.3949 Australian dollars) (Reporting by A K Pranav and Arpit Nayak in Bengaluru; Writing by Sonali Paul; Editing by Devika Syamnath and Subhranshu Sahu)