[neltnerb]

You need fewer mounting systems if the production per panel is higher. It's one of the major things you can do to reduce costs, panel efficiency gains mean you need to mount fewer panels.

If 20% more power is produced per panel, you need 5/6 as many panels your project is straight up 16% cheaper.

If anything, your statement about the panels being free and the balance of system and installation cost being expensive make efficiency improvements even more impactful.

The main historical issue with perovskite cells is damage and lifetime, which again directly relate to how many times you need to do these big capital investments. If they last twice as long you need to deal with half as much installation and mounting work over the lifetime.