It happened quietly nearly nine months ago, but the event could be the sign of things to come in the U.S. power generation mix.
In April, renewable sources provided a higher portion of electricity than coal for the first time, according to the U.S. Energy Information Administration. The EIA reported that renewables totaled 23 percent of the mix, while coal was only 20.
The renewables front includes many parts: utility-scale hydropower, wind, solar, geothermal and biomass.
What happened in April was likely due to the fact temperatures were moderating and electricity demand was falling. Typically, generation output from large coal, gas and nuclear plants is lower during those demand lulls, according to the EIA.
Nonetheless, renewable capacity has been growing and coal-fired power falling in recent years. Last year, about 15 GW of wind and solar generating capacity came online.
Each renewable resource set record high generation outputs sometime during 2018. Wind power generated 30.2 million MWh in April, a new monthly high, while a combination of utility-scale solar photovoltaics and solar thermal made history in June with 7.8 million MWh, the EIA report shows.
U.S. coal generation has declined from its peak a decade ago. Since the beginning of 2015, about 47 GW of U.S. coal-fired capacity has retired, and virtually no new coal capacity has come online. Based on reported plans for retirements, EIA expects another 4.1 GW of coal capacity will retire in 2019, accounting for more than half of all anticipated power plant retirements for the year.
Overall, though, thermal generation still accounts for more than 80 percent of the U.S. generation mix. Ga-fired power holds the lead at 35 percent, while coal is close to 27 percent and nuclear 19 percent.
Hydropower generates seven percent of the electricity mix, while wind and solar total 8 percent and growing, according to an EIA estimate in October.