It's already proven depending on how the sunlight is where you live. Currently payoff is less than 5 years in such places, much less with this cheaper technology. Solar installations are normally guaranteed for 20 years, so that means at least 15 years of profit.
Here in the Northeast we get the equivalent of 4 hours of peak sunlight, averaged throughout the year. This means a 1Kw panel, costing $2K installed, would produce about 1500 KwH per year, for a cost savings of $150/year. This makes payoff about 7 years, assuming no maintenance costs during those 7 years (a big assumption)
As I said before, I see these panels being most cost effective in the southwest, where there's more sunlight and higher electric prices. And we can expect that the price of panels will come down over time, increasing the areas over which they would be cost effective (without subsidy).