This is untrue. Solar panels don't have to be replaced after 20 years. If you buy a quality panel, (like SilFab, which are made in Bellingham) it will come with a warranty guaranteeing the the conversion efficiency after 30 years will still be at 97% of what it was when new. The typical conversion efficiency for a new panel is 21-22% these days. So, after 30 years, your panels will still be cranking out plenty of power. In fact, they'll still be cranking out plenty of power after 40 years.