Depends on your house and how much direct sunlight. I had found a website a while ago that lets you use the online satellite photos of your house, and add panels where you want to show what size system you would need. I'll try to find the site and post here.
I pd $30k after incentives. With mini-splits for heat/AC, and an electric water heater/dehumidifier thanks to mass save, I've had no electric bills since the solar went online. Also no oil bills.
Bottom line: No more bills for heat, AC, electricity, and hot water. The money I had been paying for each more than pays for the loan used to pay for solar. Loan will be pd off in seven years.
I made two mistakes:
1) I ended up using a home equity line to pay for the solar. At the time the rate was 3%. It is now 3.75%, and likely to climb, at least in the short term.
2) If anything, I pd for too large of a solar system. After three months my system has generated a surplus of $817. At one time the electric company issued a refund check. Now it's a running credit. My guess is I'll only dip into the credit in Dec and January. May be time to start mining Bitcoin
There is also a Mass SREC program that will be cutting me a check for several hundred dollars yearly.
There are no guarantees the running credits and SREC payments will be renewed yearly, but my guess is they're not going anywhere anytime soon. Check to see what type of programs are available in your state.
Battery back up is a waste of money at this point, from what I'm told. Way over priced. I bought an inverter generator and have a box connecting it to my panel directly. About $1,500 total.
Make sure to get several quotes. Also check out the Reddit sub for solar. Lots of good info, and a good way to ask questions.