Out of curiosity... for utility-scale solar, do they tend to dismount the old panels, or just leave them in place for whatever small fraction of their original generating capability they still provide?
I imagine that they'd eventually run out of land to put them on, but from what I've seen, utility-scale solar often sits in places with a fair bit of room for expansion.
Modules degrade in production really slowly (<1% per year) and are often used for 40 years. They're generally replaced quicly if they break due to manufacturing defects or impact damage (hail, tree branches etc.). A lot of the recycling of solar panels is for panels that are a decade or two old but in perfectly good condition. What's happening is that new modules have increased 30-40% in efficiency over the same time frame that the old modules have decreased by 10-15%.
So its cost effective to upgrade them in certain cases - generally where the utility will allow it.
The other factor here is that many agreements between a solar power and a utility that buys the power only have 20 year terms. Generally, there's a strong incentive to renegotiate at the end of the term, but frankly, that renegotiation is kind of a mess in practice. It depends on the policies of the state, the utility's interests, the ISO market, etc. as to how that ends up working. Every solar farm is working in at least five overlapping regulatory environments - local, state, utility/retailer domain, the ISO or regional grid, and the federal regulatory environment. Decentralization is nice in theory, but definitely makes it difficult to scale the widespread change that's required right now.
I imagine that they'd eventually run out of land to put them on, but from what I've seen, utility-scale solar often sits in places with a fair bit of room for expansion.