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. These days I'm retired, and I can't by law give you advice. While I do make mistakes, I try hard to do my analysis thoroughly, and to make sure my data are correct (old habits die hard!) Also, don't ask me why I called it "Volewica". It's too late, now.
BTW, clicking on most charts will produce the original-sized, i.e., bigger version.