Can you really install a solar roof on your home that would cost about as much—or even less—than a regular roof? That’s the claim Tesla CEO Elon Musk made Friday when he announced plans to create Solar Roof tiles that will "look better than a normal roof, generate electricity, last longer, have better insulation, and actually have an installed cost that is less than a normal roof plus the cost of electricity."

Tesla's Solar Roof tiles would be made of glass over a photovoltaic substrate. Unlike aftermarket solar panels, they stand in for traditional roofing materials and look like the real thing from the ground.

That’s an important distinction, aimed squarely at one of the hurdles to the wider adoption of solar: the questionable aesthetics of those black silicon panels. Tesla unveiled four styles: smooth glass tile, textured glass tile, Tuscan glass tile, and slate glass tile.

The Numbers Are In
The automaker/solar company released pricing for its energy-producing roof tiles.

"People like the idea of being energy efficient, but solar panels can be an eyesore," says Giovanni Bozzolo, a partner at Roof4Less roofing in Seattle, Wash. “To be able to combine the energy savings with aesthetics would be a very big thing in the industry. But the pricing has to be right.”    

Musk didn’t provide specifics on how much the tiles will cost, and a company spokeswoman told Consumer Reports, “we haven’t released details on pricing” when we followed up.

That begs the question: What will the Tesla Solar Roof have to cost in order to be the no-brainer proposition Musk describes?

We've run some numbers and determined that a textured glass tile Solar Roof should cost no more than $73,500, installed, to be competitive with an asphalt roof.

How We Did the Math

To get there, we pulled together ballpark pricing for the various roofing materials Tesla’s solar shingles mimic, from sources like the Slate Roofing Contractors Association, the Tile Roofing Institute, and the Remodeling 2016 Cost vs. Value Report.      

There are plenty of variables, of course, including the location of the home and shape and height of the roof. (And we’re leaving out any consideration of solar rebates and incentives.) But here’s what the installed costs look like for the roughly 3,000 square feet of roofing needed to cover an average size home in the U.S. 

Clay Tile: $16,000
Asphalt: $20,000
Slate: $45,000

So how could a $73,500 roof be considered cost-competitive with a $20,000 asphalt roof? To compensate for the proposed added value of the “free” electricity from Tesla’s roof, we added in $2,000 a year, over the lifespan of the roof. That’s a typical electric bill in states where solar is big, like California, Texas, and North Carolina. 

Tesla says the life expectancy of its tiles will be 30 years. So that adds $60,000 to the value of the roof. (Our rough estimate assumes our hypothetical Solar Roof homes generate exactly as much electricity as they use.)

One final factor: the Tesla Solar Roof will work like any rooftop solar system, connecting to your home’s electric panel through an inverter. You could stop there, but the system is being packaged alongside Tesla’s forthcoming Powerwall 2.0, a battery storage device with a built-in inverter and an installed cost of $6,500. Combining Solar Roof and Powerwall 2.0, Musk promises, will power an entire home with 100 percent renewable energy.

The easy way to factor in the cost of a Powerwall to our roofing calculation is to subtract it from the value of the electricity over the life of the roof. So $60,000 worth of electricity becomes $53,500. (Though we should note that the warranty of the Powerwall 2.0 is 10 years, so you would most likely need to replace it more than once over the life of the shingles).

So put all that together, and here's how Tesla would need to price its tiles to meet Musk's claims.

Tuscan Tile (Tesla's equivalant of clay tile) would need to cost less than $69,500, installed (or about $2,300 per 100 square feet), to beat its traditional counterpart;
Smooth and Textured Tile (Tesla's equivalent to asphalt tile) would need to cost less than $73,500, installed (or about $2,450 per 100 square feet);
Slate Tile would need to cost less than $98,500 (or about $3,300 per 100 square feet).

Bottom line: For sure, $70,000 to $100,000 is a lot to spend on a roof. If Tesla's roofing tiles end up priced that high, it will be because consumers will essentially be paying for long-term electricity costs up front, according to Musk’s formula. And even if Solar Roof products cost less than our estimates, it will most certainly be initially aimed at the luxury home market.    

Natural slate may be the easiest alternative for Tesla to beat from a pricing perspective, since its expense is largely due to the fact that the material is very heavy and hard to work with. If the Tesla slate is lightweight and easy to install, it could be a cost-effective option.

But that’s a big if. “Roofers aren't electricians and vice versa, so I'm most interested in seeing how the costs of labor affect the end price to consumers,” says Vikram Aggarwal, CEO of EnergySage, an online marketplace of solar installers. 

No word from Tesla on whether it will back its Solar Roof like some installers do slate—with a 100-year warranty. Or stick with a more typical 25-year warranty.  

Musk ended his announcement at Universal Studios in Los Angeles by asking: “So, why would you buy anything else?" The question was rhetorical, obviously, but the answer will have a lot to do with price.