That would mean your solar batteries would sustain the GPUs for not more than an hour before they run out of juice if running in times when there is no sun like at night. Also during the day there will be fluctuations of light intensity from the sun due to weather changes so, you won't be able to run the equipment on that solar power constantly.

You would need a solar power system with capacity way more than 500w for it to handle the two running GPUs day and night.

Do you think it's worth it? Personally, I don't think so. IMO solar system is just good for backup.