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Output from the facility on the Brazil-Paraguay border reached 87.8TWh, down from 98.6TWh in 2013.
"This was above expectations given the atypical conditions," the plant's operator Itaipu Binacional said in a statement.
Last week China's 22.5GW Three Gorges Dam announced it had broken Itaipu's yearly generation record with 2014 output of 98.8TWh.
Itaipu Binacional said it aimed to eclipse the 100TWh mark in 2015, adding it would need "favorable" weather.
More than 75% of Paraguay's electricity comes from Itaipu, which also supplies 17% of Brazil's needs.