When Tesla unveiled pricing for its Solar Roof last week, 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 coming.

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 not all of the company's Solar Roof may qualify. That's because it's made up of functional photovoltaic tiles and pure glass nonsolar tiles.

The tax credit applies only to solar-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 solar-producing tiles plus any Powerwalls—meaning it doesn’t include the cost of nonsolar tiles.

What’s not clear is how Tesla factors in the costs associated with removing your current roof, which wouldn’t be eligible for any portion of the tax credit. We asked Tesla whether the calculator accurately reflects that distinction and did not hear back.

Worst case, if the calculator does include the non-eligible costs of roof removal, the tax credit won’t be off by much. We determined, for example, that for a 1,000-square-foot ranch you’d receive about $300 less than promised.

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. Consumer Reports 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 relied on Tesla’s baked-in prediction of a 2 percent annual increase in electricity costs. If electricity rates stay flat for the next 30 years, that same staffer would save about $34,600 in energy costs over the same time frame and pocket a more modest $1,700 net savings after 30 years. 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. The good news is you can override the default assumption with your actual average energy usage by clicking “edit assumptions” on the calculator. Enter your own average monthly electric bill—you can get at least a year’s worth of recent billing statements from your utility company—and use that figure to get a more accurate picture of how you’d fare.