It measured volts before I attached it, and after attaching the voltage regulator device, the voltage dropped down to 3 volts, even when just measuring the difference in the solar panels nodes themselves, suggesting that the entire panels voltage dropped and not just the voltage in the regulator. I tried testing it with a power supply of 7 V 0. A and it works fine, but I don't know why it won't work for the solar panel.
you cannot treat the open circuit voltage of a solar panel like a voltage source (like a battery.) the load response of the panel doesn't behave that way. small panels and panels that are producing less than about .5A are very happy to have their output voltage pulled down to whatever they're connected to (typically zero.) I observed the same phenomenon when i connected a 2V 725mA panel to a 2V 325mA fan -- the open circuit voltage of 5V dropped to 3V when connected to the fan, and returned to 5V when disconnected. The easiest workaround is to use 2V of rechargable batteries in parallel with the panel so that the battery holds the 2V potential difference and the panel just supplies the current. any excess current charges the batteries, so you might consider whether or not you need some type of charge controller to prevent burning the batteries via overcharging. there are actually very few applications of solar panels connected directly to circuits that i have seen that have any kind of robust performance -- if they work at all, they eventually die/burn themselves out in a couple of months. the best robust designs always have a rechargable battery and charge controller somewhere in the power circuitry to buffer the load circuit from the panel. .
