I played through a few times, could only find one of the solar panels? It's a pretty unique game, haven't seen one like this so far, although I'm not sure the reasons that is unique (the beam of light as damage) is particularly tied to the "only one" theme.
Did you ever play Nintendoland? There was a minigame where you had to hunt a ghost using a beam of light, and had to balance not using up your battery with not getting caught by the ghost. They did a really good job of making it feel like the beam of light was hurting the ghost. I think a bit more visual feedback that the beam of light is hurting the monsters would be really satisfying!
Great job on such a unique game!