That's not the same meaning of reliable. What is usually meant is "can I trust this source to give me this amount of power at this time", or can I rely on it be

That's not the same meaning of reliable. What is usually meant is "can I trust this source to give me this amount of power at this time", or can I rely on it being available: fossil can, intermittent (by definition) can't. You need to look at the overall electricity generating system, not just the individual sources hoping they will seamlessly integrate in the grid with little changes.