How do you keep the battery from degrading after a few decades? Are there specific battery types that are long-term (hundreds of years?). Such as capacitors?
And the solar panels themselves would need maintenance, even if it is simply cleaning.
Where/how is the book being printed? Locally? What's powering the printer? How do you ensure that the materials (paper, ink, lubricant, etc.) last all those years? What about binding/collating those pages?
Or is the printing occurring once (since the site is static)?
Ideally the printer would only run a few times, I imagine when the internet finally goes down there's no reason to keep printing new copies of the book.
And the solar panels themselves would need maintenance, even if it is simply cleaning.