Future Costs?

What about future costs for solar? Based on the graph below, what is going to be the scenario when the price of solar PV installed reaches a pay-back of 3 years? The demand for the retrofit market will be 30% which means for the United States that there will be approximately 100 million single family detached homes in the United States that would be suitably situated for solar (about 1 home in 5). So 30% would be 30,000,000 homes. With each home holding 5 kilowatts of panels, that would amount to a market demand of 200 panels per home (250 watts per panel) or a total demand of 6,000,000,000 panels (6 billion panels).

Expected demand for solar PV based on simplified years for payback

Today the yearly production of panels amount to 60 gigawatts of panels. Using the 250 watts per panel, means a total yearly production of 240 million panels. Based on the production rate, it would take 25 years of production to satisfy the market with a three year payback as the driving force.
Needless to say that the supply/demand ratio will be tipped to increase price to lower the demand. Let us label that as a future cost factor in any projections of solar pricing and payback period.
Right now for the residential market the payback is more than ten years based on today’s solar pricing assuming no subsidies.