Renewable generation increased between 2017 and 2018. One consequence was that fossil fuel plants were fired up less often.
In the first quarter of the year, fossil-fired thermal plants were relied upon heavily to cover peak demand during winter cold spells. Wind power generation was also strong in the first quarter as the winter months were windy. Temperatures were milder than usual in January, as a result of which production decreased across all technologies.
In the third quarter, different factors came together to tighten the supply-demand balance. One was a decrease in wind power output relative to the first part of the year. At the same time, an exceptionally hot month of July drove energy demand up sharply, notably due to the use of air conditioning. Lastly, nuclear generation declined in August, as environmental regulations prevent plants from discharging water hot enough to potentially disturb the ecological balance.
These factors combined to drive up electricity production at fossil-fired thermal plants relative to the previous quarter. It should also be noted that solar radiation was strong in the latter part of the second quarter and the third quarter, resulting in particularly high solar power generation.
Production started trending upward again in the fourth quarter, as energy demand naturally increases in winter.