I've done a fair bit of research into this. In my country we don't get buy back for feeding into the grid, so ROI is purely based on power saved.
Which means if you're opting for a high power system (3kw or above), it's generally worth the expense of adding a battery bank.
Also be aware most solar suppliers are running 100% mark-up. So if you're a qualified electrician or are friends with one, importing your own gear can be very lucrative. 5kw of panels inc battery bank, inverters, regulators etc is approx $20,000 USD. Sub $15,000 if you don't need the battery bank.
With solar direct charging $80,000 for 10kw system (assume $40,000 for 5kw), and no battery banks, they're making a killing (assuming they are installing enough systems).
In my situation our annual expenditure on power is around $1,500. It's not financially viable to add solar to our existing house, but if I was to build new, I'd be looking at a 3kw system (around $10,000), and constructing a home that could run completely off grid with that amount (5kw is generally the target for off grid on a average sized house).