More generally you need to look at wholesale prices and more specifically inflation adjusted wholesale prices to see large drops from the recent solar price drops.

https://www.bls.gov/opub/btn/volume-10/mobile/trends-in-elec...

Of particular note is the graph showing prices in areas heavily reliant on coal, vs those with a high renewable usage.

Conclusion:

> Regions with higher use of natural gas and renewable fuel for electric power generation, in particular hydroelectric power, have seen prices rise more slowly than prices in regions that have predominantly used coal. Although it is not possible to attribute the differences in the retail price development solely to fuel mix, the significant role that capacity investment and fuel costs play in determining distribution rates suggests that at least part of the variation between these regions is explained by capacity shifts in the industry.