Consider the lower production cost of renewable electricity: in the long run, it offsets the investment. Bonus: no risk of accidents, no hazardous waste, no dependence on a fuel source, no weapons proliferation...
Decentralizing solar power reduces electricity transmission costs and improves reliability. This doesn't offset the additional cost, but it's not negligible.
If the grid gets heavily overloaded, the frequency and voltage drop. And home-based grid-tie solar will shut itself off when it's most needed. This is fragile and DEcreases reliability.
Decentralizing through subsidies at the homeowner level is maybe not the best use of money.