Solar has hit grid parity...

[Bob Wallace]

From the article:

Solar materials prices are down, financing is more accessible and technology has extended solar system life. The result: The price of solar energy-generated electricity, calculated by a legitimate levelized cost of energy (LCOE) method, is now competitive in many regions with the price of electricity generated by conventional sources.

To be clear, this review of solar photovoltaic LCOE is not one of those “if coal and nuclear paid for the real harm they do” analyses. It is a hard look at the actual numbers.

“We have reached a tipping point,” he said. “Solar has gone past grid parity.”

Parity, according to the study, is “the lifetime generation cost of the electricity from PV being comparable with the electricity prices for conventional sources on the grid.”

That's parity based on a 30 year lifetime of panels. We can't yet prove that solar panels continue to work well past 30 years, to 40, 50 or more years, but there's no known "solar panel cliff" over which they will fall after reaching a 'certain age'.

A panel “has no moving parts; it’s all electronic and a solid-state device,” meaning that should last “a long, long time,” Pearce said. This means “we should be doing our economic analysis at least on a 30-year lifetime,” but there is not yet adequate data, he explained.

http://www.greentechmedia.com/articles/read/New-Study-Solar-Grid-Parity-Is-Here-Today/