The renewables division's recorded earnings before interest, taxes, depreciation, and amortization (EBITDA) of €836.5 million, down 3% year-on-year.
The fall was mainly due to a drop in production in the UK. Output fell 26.2%, Iberdrola said, causing EBITDA from its ScottishPower Renewables UK business to fall 34.4%.
The decrease is blamed on a particularly strong 2015, when output was 27% higher compared with 2014, a spokesperson for ScottishPower Renewables explained.
In Latin America and the rest of the world, Iberdrola said renewable EBITDA was down 2.2% and 4.4% respectively.
The company's other regional business performed well in renewables. In Spain, EBITDA grew 22.7% to €319.7 million, due to a 7% increase in output.
In the US, renewables EBITDA was up 3.9% thanks to a 10.3% rise in output.
Iberdrola maintained its outlook for 2016, with an expected 5% increase in EBITDA across the group. In the first half, the whole Iberdrola group recorded a €3.9 billion – up 1.4% year-on-year.
The firm said performance would not be affected by the UK's decision at the end of June to leave the European Union.