Many renewable energy sources are intermittent. What does this mean, and why does it pose a challenge to the use of these sources for electrical power generation

Many intermittent

Intermittent renewable energy sources which are intermittent are difficult and challenging which means that they have an disrupting effect on the conventional procedures used to plan the daily maintenance and operations of the electric grid. The power fluctuates over different and many time horizons which will force the operators to adjust it before time i. e an hour ahead to day ahead to adjust the operating procedures manually.