The decline in the cost of solar, wind, and batteries all follow the learning curve, or what is sometimes called Wright’s law. Theodore “T.P.” Wright was a World War II economist who studied the production of aeroplanes and found that every doubling of manufacturing of the same model aeroplane brought down the price by a fixed percentage of 16%.
Every doubling of scale of the manufacture of solar has brought down the price by an average of 30%. A small part of this is the improvement of panels, but this steady decrease in costs is mostly because the manufacturing process gets better. Despite criticisms of the solar industry’s small 1% reinvestment of revenue in R&D, it isn’t the R&D budget that’s bringing the price down, it’s actually factory efficiencies.