For me, I had to find $350-$400/month for electricity, every month. I was lucky and got $10k inheritance. Various subsidies allowed me to install a $20k 3kw system (practical input about 2.3 kwh about 5 years ago. Legislature subsidy gave me 64c/kwh, dropping to 60c/kwh presently. As soon as my contract expires (any time now), I'll be paid 20c/kwh which is almost retail where I am (Australia). For the first few years it knocked 65% off my usage. Then when I got rid of the kids (sold for scientific experiments), I started to achieve credit in the summer months, almost evening out my winter usage, so I can say that I almost get a net 0 cost/year. It won't last though. When I get forced onto the reduced rate of 20c, my power bills will increase, but nowhere near what it was originally.
Now I didn't care too much *wasting* the $10k on the system because I didn't have to find $400/month, every month. That means that I had money for other things and much reduced stress on the family. After 5 years I worked out that I have almost paid the $10k back (there were 4 failures* in that time).
Doesn't matter about the capital expense! The long term savings in money and more importantly stress has paid for the system.
Failures:
The street voltage was too high for the inverter, so the inverter couldn't pump the power to the grid (2x). This was fixed by choking the street's line transformer.
The Inverter (cheap chinese shit) broke.
Birds ripped off the cover of a buss box on the roof and it filled with water.
Total cost to repair after insurance was about $500.
Loss of income from downtimes: $500 estimated.