Decreases in panel costs result in only modest decreases in residential solar costs, because the panels aren't the bulk of the cost of install. There's all the labor of installing them, the other equipment like inverters and electric panel upgrades, the engineering time to evaluate the site and design an optimized system size and placement, and then just the general overhead that comes with the business (sales, marketing, admin, billing, etc.). The panels themselves might only be 30% of that.
Looks like even less than 30% - the chart in this article shows panels are only around 10% of total cost for residential, meaning further panel price declines now have very little effect:
