I've posted before about 
I’ve posted before about Stirling Energy Systems, which sells solar electricity from concentrating mirrors and heat engines for around 11 cents per kWh.
But at least one technical advocacy group — Trans-Mediterranean Renewable Energy Cooperation (TREC) — suggests that mass production could bring prices down to 5 cents per kWh or less (PDF), even without technical breakthroughs.
The PDF linked is a summary, so I don’t know how good the case is.
I will also note that this price includes enough storage to ensure 70% reliability — which provides different economics than the 95% reliable wind grid component I mentioned previously, and different economics than wind without storage. Obviously sun and wind as grid components mix well together. The troughs — sunless weather and windless weather — tend to occur at different times. So do the peaks — strong winds and blazing sun. (Yes, there are exceptions, Santa Ana winds and so on.)
