I need a comma there, as you have stated, the output would be zero.Where did I state that the output of solar panels would be zero. The only way the output could be zero is if they were in the dark and as cold as it is possible for humans to make it. And even then it probably wouldn't be completely zero. Because any amount of infrared radiation would probably produce some electrons.
Meaning, if you took a panel to test, and hooked up a voltmeter, the output would be zero.
You did not mention anything about a load. Without a load no power will be drawn. Solar panels are load dependent. Just saying, your simpleton scenario lacks technical details.
Further, would you not be interested in the amount of amperage they can provide vs voltage? Of course, all that will be known before they are taken out in the sun? The people who make solar panels will know the power output based on how they designed the panel.
Voltmeter? No way, if they conducted any sort of test they will need a dummy load and the ability to measure watts. Maybe they would use a multimeter, I doubt you can find many meters that only measure voltage these days.