There's a few factors to consider:
1) Location is big. If you are in the southwest area (from southern California over to Texas) then it is absolutely worth it. ROI value will likely be in the 7 to 10 year range. If you are in Maine, it's not even worth quoting (30 year return). Indiana would be middle ground (20-ish years). You will still have power connected to your house from the utilities, but it is more of a demand-based system. Your system will pull from the solar first, and then pull the rest from the grid. If you actually produce more power than you use, some states will give you an energy bill credit / pay out.
2) How big of a system. Are you wanting to supplement or full load? You can set things up so that the system is only providing enough watts so that if there is a power outage, there will be enough power to run the refrigerator and the lights, but not other appliances. Or you can go full load where your full power requirements are being met by the solar. The difference will obviously be the number of panels that are required to meet that load and the associated costs.
3) How much area do you have to work with. Generally, only the southern facing parts of your roof can get panels (unless you have enough free area on the ground and you can pull off a ground-based system). That may limit what you can install. Technically, the best system is a ground based one that has a dual pivoting system that will track the sun during the day so that it is always directly perpendicular to the sun for maximum absorption, but that takes up a lot of real estate.
All three of those will have a big impact on the cost. If you are in San Diego and are only looking at a supplemental system, it may only be $5000-ish. If you are looking for a full load system in Indiana, it's probably closer to $20,000 / $25,000-ish. Different states will have incentive / tax benefits though that may cover portions of that cost.
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