Solar is getting cheaper and more efficient very quickly.
In order for solar to "compete" without subsidy, it needs to be cheaper, and alternatives need to be more costly.
But if the subsidy does make it financially advantageous to individual consumers, they buy it and help drive down the cost, making it cheaper as you say.
Also big jumps in technology could help.
In SoCal, residential installed solar reduces electric bills to almost nothing, for homes without pools.