Concentrated solar power getting dirt cheap

Concentrated solar power (CSP) can produce power 24/7, just like a coal or nuclear power station.  It does this by heating molten salt to 1000 deg F (538 deg C) during the day when the sun is shining then using the molten salt to drive a turbine overnight when it's dark.  Its costs have fallen by 2/3rds over the last 4 years. CSP in sunny places is now cheaper than coal, produces no emissions or pollution, yet nevertheless provides base-load electricity. 

Source: Big Think

It's not 100% "firm", because prolonged cloudy weather will impact production, but then again, coal power stations often "trip" without warning.  The way the grid has always coped with this in the past is to have excess capacity, so that the loss of one generator can be offset by turning on another.  And the risk is reduced by having diversified supply sources.  For example, the wind often blows when the sun isn't shining, and it blows more in winter when sunlight is less.