Yes, it is a second home for most tax purposes. You can treat it as a personal residence and letting family live there is personal use.
However, to claim the solar credit, you must live there as your home at least part of the year. It doesn't have to be your main home, but it must be a home you use as a home.
On the other hand, your daughter could claim the credit if she pays for the solar system. To claim the solar credit, you must install the system on a home you live in, but you don't actually have to own it.
