When Tesla unveiled pricing for its Solar Roof earlier this year, Consumer Reports ran a cost-benefit analysis on three real-world houses. Two of them more than recouped the high up-front costs of the Solar Roof over 30 years, and one came out a net loss.

After publishing our analysis, we received some smart questions from CR readers about the assumptions built into Tesla's Solar Roof cost calculator. So here you go, Jerry in Florida, Kurt in Ohio, and all the other readers who joined the conversation. Keep the comments and questions coming, and we'll update this story as we find out more.

Q: Does Tesla’s Calculator Overestimate Tax Incentives?

A: No

Like any solar installation, Tesla's Solar Roof qualifies for a 30 percent federal tax credit. But it's unlikely that 100 percent of the roof would qualify. That's because it's made up of a mix of functional solar tiles (energy-producing photovoltaic film and glass) and nonsolar tiles (just glass).

The tax credit applies only to energy-producing tiles and Tesla's Powerwall battery—assuming it’s installed at the same time as the tiles. For instance, if your roof has a 60/40 split between solar and nonsolar tiles, the tax break wouldn't apply to the 40 percent of tiles that don't produce electricity. Likewise, the cost of removing your old roof wouldn't be eligible.

You should also know that the tax credit is being phased out: The 30 percent is good through 2019, then it drops to 26 percent in 2020 and 22 percent in 2021 before expiring in 2022.

Consumer Reports’ statisticians ran six hypothetical projects through Tesla’s Solar Roof calculator and found that the calculator does accurately apply the 30 percent tax credit only to energy-producing tiles plus any Powerwalls—meaning it doesn’t include the cost of nonsolar tiles.

Q: Do Energy Prices Affect Potential Long-Term Savings?

A: Yes

Projecting future electricity costs is a difficult task because they’re affected by everything from consumer demand to government policy. The Solar Roof calculator assumes your electric bill will increase by 2 percent each year for the next 30 years, meaning that 30 years from now you’ll be paying about 78 percent more for electricity than you are today. But the U.S. is in the midst of an energy boom, and if that keeps electricity costs down—or causes them to drop—it could dramatically alter the cost-benefit analysis of installing the Solar Roof.

Cost Analysis
The automaker/solar company released pricing for its energy-producing roof tiles. CR checks the costs for real-world homes.

When we ran the numbers on real-world houses, we found that a CR staffer with a 2,700-square-foot house near our Yonkers, N.Y., headquarters would save $46,800 over 30 years—enough to recoup the costs of installing Solar Roof and pocket a net savings of $13,900.

But that example relies on Tesla’s baked-in prediction of a 2 percent annual increase in electricity costs. If rates stay flat for the next 30 years, that same staffer would save about $34,600 in energy costs over the same time frame, pocketing a more modest $1,700 net savings. If rates dropped by 5 percent next year and stayed there, installing the system would result in a net loss.

Of course, energy costs could always rise faster than Tesla is predicting, in which case your potential savings would grow proportionally. Like the energy economy itself, your potential savings with the Solar Roof are highly variable—a fact you’ll want to keep in mind when you crunch the numbers for yourself.

Q: Will My Real Electricity Use Affect Potential Savings?

A: Yes

Tesla’s cost calculator pulls data from the Energy Information Administration to determine your local rate for electricity and relies on some assumptions about how much energy a typical home uses to provide your potential savings over the life of the Solar Roof. What it can’t account for are your particular energy-use habits. And how much electricity your household actually uses will directly affect what you'll save with Solar Roof.

If you’re the kind of person who doesn’t leave the lights on, and springs for energy-saving LED lightbulbs or an Energy Star certified refrigerator or washing machine, the amount you can save with the Solar Roof will be reduced.

Tesla accounts for this variability by letting you override the default assumption with your actual average energy usage. Click “edit assumptions” on the calculator and enter your own average monthly electric bill to get a more accurate picture of how you’d fare. Tip: You can get at least a year’s worth of recent billing statements from your utility company.

Q: Should I Think About How Long I’ll Stay in My Current House?

A: Yes

According to Tesla, the solar tiles are warrantied to produce electricity for 30 years. And the company’s calculator bases potential savings on a 30-year time frame. But your savings could diminish dramatically if you move or sell before then.

And in fact, most people do. According to an American Housing Survey (a joint effort by the Department of Housing and Urban Development and the Census Bureau), about half of Americans move after 13 years of home ownership. If you move out 13 years after installing a Solar Roof, you’d miss out on potentially the most profitable years of owning it. No scenario we’ve run through the calculator would allow you to recoup the roof’s cost in that amount of time.

“According to Tesla’s calculator, the CR staffer in New York would stand to save $1,153 in electricity in the Solar Roof’s first year,” explains Michael Saccucci, CR’s director of statistics. “But that 2 percent annual climb means that they’d save $2,048 per year by year 30. The potential savings would shrink significantly if that person moved out sooner.”

If there’s a good chance you’ll relocate before recouping the costs, but you still like the idea of solar power, consider traditional panels. For an average American house, these systems start around $12,000 to install over an existing roof.

“And if you own the system, traditional solar panels offer 100 percent payback in an average of seven years, depending on your state and utility,” explains Vikram Aggarwal, founder and CEO of EnergySage, an online marketplace for comparison shopping solar quotes. That way, if you move or sell after a decade or so, you’ll probably have recovered the cost of the system.

Q: Will Installing a Solar Roof Improve the Resale Value of My Home?

A: Maybe

“Residential solar installations are on the rise, and Solar Roof may be the latest evolution,” says Amanda Stinton, director of sustainability and green designation at the National Association of Realtors. “But as for resale values, it’s early. We’ll just have to wait and see.”

In the 2017 National Association of Realtors Sustainability Report, the organization polled its members and found that 42 percent believed that traditional solar panels improve the resale value of a property and 9 percent believed that the panels might bring a house’s value down.

Any boost to resale value may depend largely on how you pay for the system in the first place. If you pay cash for the high cost of a Solar Roof, you could see a nice bump to your home’s resale value. But some homeowners might consider financing the roof with a loan through a bank, credit union, or other lender. Tesla offers financing options for the Solar Roof, too.

Certain traditional solar-panel companies offer financing as well, and if you decide to sell the home before you’ve paid off the roof, your contract might allow you to transfer the financing terms to the next owner. Depending on how that person or family feels about solar power (and how your year-over-year electricity savings measure up against the added expense of paying down the loan), it could become a liability—or a boon—for a potential buyer.