The Spanish utility said the fall was due to "reduced wind availability" in Spain and the UK.
Earnings from renewables were €434 million in Q1, approximately 23% of the group's total earnings, which fell 8.2% to €1.86 billion.
Iberdrola said renewables accounted for 46% of its €1.02 billion investment total in Q1.
"As a result of its investment strength, the company plans to commission a total 2,011 megawatts (MW) in renewables and regulated generation in 2017," the company said.
It also confirmed a pipeline of 1,546MW of onshore wind, and 1,064MW of offshore wind.
Iberdrola posted net profit of €827.6 million in Q1, a fall of 4.7% year-on-year, but said it expects to reach its 2017 outlook.
The group also reported an income of €255 million from the Siemens-Gamesa merger, in which Iberdrola reduced its stake in the Spanish manufacturer from 20% to 8%.
The new Siemens Gamesa Renewable Energy manufacturer was formed at the start of April.