Tesla has unveiled its solar roof and begun taking pre-orders for installations. The roof, in case you haven’t heard, is made of super-strong glass tiles, some of which have solar cells inside. It’s designed to be a permanent replacement for your roof (so permanent the tiles come with a warranty that extends to “infinity”), though the solar cells are only guaranteed to make electricity for 30 years.
Wait, 30 years is longer than the average solar warranty, and an infinite-life roof sounds nice. How much does this thing cost?
How much this thing costs
Well, Tesla says the average homeowner will end up with a cost of $21.85 per square foot of roof space. But each roof will require a unique mix of the solar tiles, which have a cost of $42/ft² and the non-solar tiles, which have a cost of about $11/ft². Your cost will depend on how many of each you need.
How does the cost of Tesla’s roof compare to other kinds of roofs?
Helpfully, Tesla provides a comparison chart on its website:
OK, that chart is maybe a little disingenuous.
That blue bar in the negative won’t be the same for everyone, because the value of energy is so different depending on where you live. Your mileage will vary—like with any kind of solar installation—by how much sun you get and how much you pay for electricity.
We reverse engineered (i.e., did some algebra) Tesla’s calculator, and discovered some interesting things the company hasn’t publicly let on about its solar roof. Specifically, we can estimate how big the solar cells are, how much energy they can make, and whether buying it is a good idea compared to your best alternative.
The Tesla tiles look like they’ll be rated to produce about 11 watts of electricity per square foot, and lasting 30 years means they’ll degrade by about 0.5% per year, ending their 30-year warrantied life producing about 85% of the electricity they did when new.
Tesla’s calculator is designed to produce a system that would produce all the energy your home needs. It also recommends at least one Tesla Powerwall battery for the system, which adds $7,000 to the cost of the system. That’s weird because people in states with net metering don’t need a Powerwall unless they want battery back-up when (if) the grid goes down.
When does the solar roof make sense?
To produce all the energy you home needs, you usually need a pretty big solar installation. For a 2,000-ft² single-story house with central heating and cooling, you’d need a system of about 10-kW in size (depending on where you live, which we’ll cover below).
The typical cost for a 10-kW solar system is about $30,000-$35,000 these days, and the roof that goes under it ain’t cheap either. Here’s a comparison of the costs to install a 10-kW Tesla solar roof on a 2,500-ft² roof vs. the cost of installing that much standalone solar along with a new roof made of traditional materials:
So you can see, if you want solar panels (and why wouldn’t you?), and you need a new roof, and you’re okay with asphalt shingles, you might be better off choosing that route. But if you’re already going to install solar and a fancy slate roof, the Tesla roof is cheaper.
One thing to remember, too, is that asphalt roof will have to be re-shingled again in 15-20 years, and the slates can break after a few decades, while the Tesla roof is warrantied forever.
Here are a few other scenarios to consider:
Tesla’s solar roof vs. doing nothing
Surprise! Doing nothing isn’t something you might think about, but it’s a valid option for our purposes. If you’ve got a newer roof, or if your house is in shade most of the day, Tesla’s shingles are an expensive way to make your house look expensive.
If that’s your bag, you do you; but you won’t be getting any of the benefits of the solar roof.
Differences between states
Some states get more sun that others. Some states have higher electricity prices than others. If you live in a state like California, which has both lots of sun and high electricity prices, the solar roof is better for you than it would be for someone who lives in Michigan, which is both less sunny and less expensive.
As daily sun increases, the number of solar tiles needed to produce the same amount of electricity decreases, and with it, the cost of the roof ($/ft²). Similarly, as energy price increases, the amount of money you save with the solar roof goes up, even with the same amount of sun as another person.
We mentioned this above, but if you live in a state without net metering, going solar at all can be a challenge, unless you get enough batteries to use all the solar energy you make for yourself.
This is where Tesla has a bit of an advantage. In a state like, say, Nevada, where the sun shines bright all day long but the utility company pays peanuts for energy you send onto the grid, a Tesla solar roof installation with Powerwall batteries added can save you a good deal of money over the 30-year term. A roof that pays for itself!
Another difference between states is solar incentives. Tesla’s calculator doesn’t account for state-by-state incentives, which cary widely depending on where you live. Every homeowner in the U.S. is eligible for the Federal solar tax credit of 30% of the installation costs, but people in New York, Oregon, Rhode Island, Maryland and other states can also get thousands more back on their state taxes.
Your best bet is to read about your state’s solar policies and incentives on our site.
The bottom line
As part of a 30-year mortgage, a Tesla solar roof can be a brilliant investment. Here’s a chart showing the example returns of a California home with a Tesla solar roof:
A roof that pays for itself with a tax credit and electricity bill savings. We call that a bargain!
Our numbers use a 30-year loan at 4% interest, and the NPV of nearly $6,000 is calculated using a discount rate of 7%, or the long-term average annual return of the S&P 500. That year 1 tax credit makes all the difference, as the loan payments and electricity bill savings basically cancel each other out over the life of the system
Look, the Tesla Solar roof is expensive, but if you’re building a new home out of premium materials, and if you live in a good state for solar it’s worth the cost.
If, instead, you have an existing home with a roof you love (especially a fancy tile one that should last for a few decades more), installing a standalone solar system on top of it still provides you with the best way to make electricity and save money.
No matter what you choose, you should get multiple solar quotes from installers in your area to compare the costs to what we’ve outlined above.