Solar Panels on Your House: Do the Math Before You Sign Anything

Somebody knocked on your door and told you solar panels will make your electric bill disappear. They showed you a chart where the line goes down to zero and said the panels basically pay for themselves. It sounds great, and sometimes it is great. But the math is doing a lot more work than that chart lets on, and a solar contract is a 25-year commitment you sign in an afternoon. Before you sign anything, run the actual numbers.

Start with the real price. A typical residential system in the U.S. costs around $25,000 to $30,000 before incentives. That is the number the salesperson sometimes skips past, because they would rather talk about your monthly payment. The federal tax credit knocks 30% off, which sounds huge, and it is — but it is a credit against taxes you owe, not a check in the mail. If your federal tax bill for the year is $3,000, you can only use $3,000 of the credit that year (the rest carries forward, but it is not instant cash). After the credit, you are still looking at roughly $17,500 to $21,000 out of pocket, either upfront or financed.

Now the savings side. The average American household spends about $140 a month on electricity. A well-sized solar system can cut that by a lot — often 70 to 90 percent — but almost never to zero, because you still pay a monthly connection fee to your utility, usually $10 to $25. So call it roughly $100 to $120 a month in real savings, or about $1,200 to $1,400 a year. Divide the $18,000 net cost by $1,300 a year and you get a payback period of about 14 years. In a sunny state with high electricity rates, like California or Florida, the payback can be 7 to 9 years. In a cloudy state with cheap power, it can stretch past 15. Your payback depends entirely on your roof, your rates, and your sun — not on the national average in the brochure.

That brings up the roof. This is the detail that costs people thousands. Solar panels last 25 years. If your roof is 15 years old, it will need replacing while the panels are still up there. Removing the panels, replacing the roof, and reinstalling the panels runs $3,000 to $8,000, and that is on you. If your roof has less than 10 good years left, replace it first or do not install solar yet. The salesperson will not bring this up. Ask them directly: how old is my roof, and what happens when it needs work?

Then there is the lease versus own question, and this one matters more than anything else. A lot of door-to-door solar deals are leases or power purchase agreements, where you do not own the panels at all. You pay a monthly lease payment or buy the power the panels produce at a set rate, usually with an annual price increase of about 3 percent built in. The company owns the panels, keeps the tax credit, and you get a modest discount on your bill. The real problem comes when you sell the house. The buyer has to agree to take over your lease, and plenty of buyers refuse. A leased system can make your house harder to sell, not easier. Owning the panels outright is a different story — owned systems generally add value to a home. Leased systems often do the opposite.

Net metering is the other thing that can change under your feet. Net metering is the rule that lets you sell your extra daytime power back to the grid for credits. In some states, utilities pay you the full retail rate for that power. In others, they pay a wholesale rate that is a fraction of it, or they have started phasing the good rates out entirely. California already cut its net metering payout dramatically, which stretched payback periods by years for new systems. Before you sign, find out what your utility actually pays for exported power right now, and whether a change is already on the table. The salesperson's savings estimate is built on today's rules staying the same for 25 years. That is a bet, not a guarantee.

Finally, the moving question. If there is a real chance you move within seven years, solar is probably a bad deal for you. You will not have hit payback yet, and you will be selling a house with a system that buyers may or may not value. The exception is if you own the system outright and you are in a sunny market where buyers expect solar. But if you are renting, planning to relocate for work, or just not sure where you will be in five years, wait.

Solar can be a genuinely good investment. If you own your home, plan to stay at least ten years, have a young roof, live somewhere sunny with high electric rates, and buy the system outright — the math works, and it works well. But that is a lot of conditions, and the door-to-door pitch is built to make you skip every one of them. Get three quotes, check your roof's age, call your utility about net metering, and do the payback math with your own electric bill, not the salesperson's chart. If the numbers work after all that, sign with confidence. If they do not, walking away costs you nothing.

Disclosure: This article was drafted with AI assistance and reviewed by the author.