This very recent paper focuses in costs studies of a fully renewable electricity supply system based in part of EEUU states grid. It is very interesting and deserves a more profound reading but the main conclusion is that for 2030 (less than 20 years ahead) it is not only possible to supply 100% electricity in this part of the USA by renewables, it would even be profitable!.
The good news do not end there, another study says that new wind and solar are competitive in the long-term with new natural gas in Texas. And another study, based on Australian data shows wind is cheaper than fossil fuels in Australia, even without carbon tax.
OK, maybe some of those data have been analysed with a positive bias towards renewables (in the first one for example), and it is true that renewables always compete to already paid systems of energy production, so it is a difficult-to-win battle; (it is interesting the debate in England about the feed-in-tarif or similar to new nuclear, newborns have a hard time even with Uranium). Nevertheless, the good news are that renewables are reducing costs clearly, and have been for a long time, while fossil fuels are more fluctuating and nobody is really confident they will not increase in the near future, so the maths continue to be confusing but they are changing.
Of course, all this without considering the enormous costs of climate change effects, sooner or later they will be evident in the balance and then the doubts will simply disappear, the problem is that by then it may be too late for some and will be more expensive for sure.