I have solar at home and it's extremely reliable. For the last 11 years, it has generated electricity 100% of the time the sun was shining. Oh, maybe you meant something other than reliable?
The fact that your solar installation is in good working condition means it works reliably but that doesn't make it a reliable source of electricity.
Whether or not something is a reliable source of electricity or works reliably are two separate things and OP is talking about the latter. Can I flip a light switch at any time and reasonably expect solar to provide me electricity? No. Then it's not reliable source of electricity.
Gas, coal, and nuke generation goes down for maintenance all the time. But if it can be scheduled so energy demand is met all is good.
What about the other times?
Not really a great place to use solar when you need most electricity, although on the average we get more sunlight hours than Central Europe. We just get them when there is less need for electricity.
They've done studies, you know. 60% of the time, it works every time.