Something that works only during certain times of day and weather is not reliable from the perspective of generating electricity.

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.

From a grid scale perspective, reliability means it can be scheduled for a certain amount of energy. In some areas solar is very reliable.

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.

Maybe not reliable, but very predictable.

You can rely on solar to generate electricity when the sun is shining, but you cannot rely on the sun to always be shining, hence not reliable.

But if solar panels were located at both the north and south poles and connected to the grid, would that work?

"100% of the time the sun was shining"

What about the other times?

Yeah like Night. Where I live in winter the days are about 8 hours long, when I'm at work, so no electricity when I'm home at all.

Where I live, the number of sunshine hours in December varies between 6 and 49 (years 1981-2010), average is 26 hours. That means a bit under one hour per day on average, but sometimes there's a week when the sun doesn't show up at all.

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.

Probably reactive or controllable. Wind, solar, gas, nuclear etc. cannot be controlled to the degree that opening the gates can. So it can respond better to the energy demands based on time of day.

Gas and nuclear can both be adjusted to match grid demand.

Pulling out control rods or cranking up the gas turbine are presumably pretty quick. Helping this is the fact that humans aren't all that difficult to predict in terms of energy usage.

> it has generated electricity 100% of the time the sun was shining

They've done studies, you know. 60% of the time, it works every time.