It's already cost effective but people don't want to believe it.
"The data show that utility-scale solar and wind installations are now competitive with conventional coal- and gas-fired power plants. Moreover, wind and solar costs are projected to steeply decline in the years ahead."
"Onshore wind has the lowest average levelized cost in this analysis at $59 per megawatt-hour, and utility-scale photovoltaic plants weren’t far behind at $79. By comparison, the lowest cost conventional technologies were gas combined cycle technologies, averaging $74 per megawatt-hour, and coal plants, averaging $109. These numbers are the average of Lazard’s low- and high-end estimates (see their study for more about their cost calculations)."
