This is a classic learning curve chart. Note double log scale. If cumulative solar shipments go up 20 fold from now (easily achieved), costs will more than halve from here. Actually the slope of the line since 2008 suggests an even bigger decline than that.
This was the curve for the model T-Ford.
Disclaimer. After nearly 40 years managing money for some of the largest life offices and investment managers in the world, I think I have something to offer. But I can't by law give you advice, and I do make mistakes. Remember: the unexpected sometimes happens. Oddly enough, the expected does too, but all too often it takes longer than you thought it would, or on the other hand happens more quickly than you expected. The Goddess of Markets punishes (eventually) greed, folly, laziness and arrogance. No matter how many years you've served Her. Take care. Be humble. And don't blame me.
BTW, clicking on most charts will produce the original-sized, i.e., bigger version.