Powering our art from the sun frees it from ugly cords and the need to replace batteries. With solar power, we can place the art in a window, or out in the garden, and it will function unattended, getting its power from the sun, like plants do.
The obvious problem is that the sun isn't always there. For some art pieces, that is just fine. We don't expect a sundial to give us the time of day at night. It is telling us we should be asleep, and not worrying about what time it is. An artificial flower that always faces the sun is an interesting piece in the daytime, and at night we don't expect it to entertain us. A solar powered water fountain simply goes to sleep at night, and that may be a nice feature, as otherwise the sound might keep us awake. Likewise a piece of sculpture that sings or quotes poetry would give our ears a rest at night. There is a reason we don't hang wind chimes outside the bedroom window.
We can group solar powered devices into categories according to how they deal with the potential lack of power. Some only work in the sunshine. Some produce more power than they need during the day, and store the excess for use at night (plants do this). Some work only at night, simply storing energy during the day. Solar garden lights are like this. It hardly makes sense for the lights to be on during the day. Some store energy during the day and only use it when called upon, like solar powered flashlights. Lastly, some devices only turn themselves on for a bit on a timer, making careful use of their energy budget.