Ok, I understand where you're coming from, and its a logical argument. However, a lot of fossil generators (esp coal) are baseload plants that stay running for

Ok, I understand where you're coming from, and its a logical argument. However, a lot of fossil generators (esp coal) are baseload plants that stay running for system reliability. They might stay running during off-peak hours when the output is barely needed, just to ensure availability during on-peak hours. In those cases, you can't tweak output to match variable renewable energy output.