Here... if you produce more than you use, the power company will only pay you WHOLESALE prices for the power.. For instance you the customer pay 12cent a kilowatt, but you sale excess back at 3 cents a kilowatt. SO... there is no way you can make money on a 30k to 60k investment at 3 cents a kilowatt. Some areas, the power company will not buy back excess power. SO!!!!!!... only build your system to power your house so that you break even or pay the power company a little bit each month. Then you will break even at 14 to 16 years.. and then make a bit on money after that.. HOWEVER inflation makes a huge difference in this build as if power continues to go up and up and up,,, your pay back become shorter and shorter and look like a genius. If power is then 24 cents a kilowatt, your golden. If there is no or little inflation, you might make more money in the stock market over the 25 year period. Much more. Then come a hail storm, and you loose your system and your roof. And you pay twice as much on insurance. Or a lightning strike fries it all. Then if you sale the house, and move, you usually do not recoup the full price of you system same a pool or other add on. So, will you be in the same house for the next 25 years?. If your over 65 years old, you will probably not live long enough to get all your money back?.. So there can be many factors to consider. Also solar panels will degrade to about half or less output after 12 years, so the system output drops more and more, so now you install panels rated twice as high as your need to keep the output up at 16 years (as this is factor is now built into most panel ratings today). So a system will put out more than its rating new, but still meet it rating as it ages to a specified year point. And you must wash the panels periodically, change out defective inverters, decide you want to install batteries, which are a whole another box of uncertainty, risks and cost. Will you do snow removal when your 65 years old? Will you trim the trees so that they dont block or drop limbs on the panels. Will you have to remove the entire system to replace a defective roof every 20 years or so. How many sunny days in your area of the country? Do you have mountains that limit the amount of daylight by 2 hours a day. And solar claims to work for only 8 hours a day average pending on location and other factors, so you need batteries??
If your young and gonna stay put 25 years, then with inflation and abundant government, solar is a very good ideal. Just as my own water well would be a great investment that pays back... in this area, However there are many factors to consider.