THe solar resource is high there so the plant will run more predictably and closer to it’s nameplate specifications. Therefore the bidder is willing to sharpen his pencil on the upfront costs.
according to this article Mexico last year caught a bid of US¢2.699/kWh for the solar power project.
http://cleantechies.com/2016/10/31/fotowatio-wins-300-mw-solar-in-mexico-auction-at-us%C2%A22-69kwh/
so there are three bids recorded in 2016 in three different countries in three different deserts on three different continents by three different companies that are sub 3 cents @ kwh. The diversity of circumstances increases the probability that the numbers work.
Its worth noting too that the costs of these types of solar projects—ie utility scale solar—have been coming down pretty dramatically in the last couple years.