Here is the EIA Levelized Cost estimates: https://www.eia.gov/outlooks/aeo/pdf/electricity_generation.pdf

Capital cost may be higher, but overall cost is in fact competitive.

And it would be very out-dated of say it needs to be backed up.  There are different solutions for different levels of integration.  You can often shift to areas of higher demand and balance it out that way, especially with low levels of integration.   You can use gas, coal, or storage, yes.  But you can also use hydro-power, nuclear, or geo-thermal.  There are many other solutions other than just store it or use coal/natural gas.  And solar only producing during the day is a good thing for the most part, that's when demand is higher.