Originally published on CleanTechnica
When Tesla CEO Elon Musk unveiled the company’s Solar Roof tile system back in 2016, he boldly proclaimed that it would cost less than buying a roof and electricity. Since then, we have not seen any data to support his claim, until now.
I signed a contract with Tesla for the installation of a new Tesla Solar roof tile system and have unpacked the details, good and bad, from the contract in a series of articles. To kick things off, I will start by comparing the cost of the system against Elon’s claims to see if a Tesla Solar Roof tile system is actually cheaper than buying a roof and the power generated by the system over its life.
One Roof To Rule Them All
An accurate comparison requires an accurate baseline to be used for the cost of electricity and the cost of a new roof. Getting a new roof installed can range from $10,000 to $50,000, depending on the material used. Composite shingle roofs and tile roofs are more cost effective, but do not have the same durability as a Tesla Solar Roof with its tempered glass tiles. Tesla’s Solar Roof is comprised of, “Glass solar tiles are so durable they are warrantied for the lifetime of your house, or infinity, whichever comes first.”
The only roofing product on the market that comes close to this bold proclamation is a metal roof with an expected 50 year life. This is an important comparison to understand because just looking at the Tesla Solar Roof as simply the covering for the home already sets it apart from most common roofing products. It is a high-end roof, even without the solar aspect. This is not a justification for a higher price, but it is simply the reality of buying a roof that lasts.
The Tesla Solar Roof is not a typical roof, and that is highlighted in the fact that it comes with two different guarantees. The first is for the solar production from the roof. The solar production from the Solar Roof is guaranteed for 25 years. This protects the buyer from subpar solar cells, cells failing, or other factors that impact the electrical generation from the system. Such a guarantee is standard across the solar industry. The second warranty is for the physical roof structure. Because the Tesla Solar Roof is a building-integrated photovoltaic (BIPV) system, in addition to generating power, it also must serve as the physical roof for the house. As a roof, the Tesla Solar Roof is warrantied for infinity or the life of the home, whichever comes first.
To ensure accuracy, I went out and got bids for the job from 5 real local contractors in Southern California. This was not a hypothetical exercise, as we are in need of a new roof and were actively pursuing both options to determine which was a better fit for our family. Bids were made based on actual permitted architectural drawings of the roof, with all associated wrinkles and warts. After receiving all of the bids, I took the average price from all 5 contractors and used that as the baseline cost for a comparable roof installation. That came to $37,865.80 for a new metal roof.
Electricity By Any Other Name
Musk and his team of energy engineers at Tesla were not simply trying to build a better roof. They were ultimately trying to build a solar product that would help the masses to adopt solar because it was easier, cheaper, higher quality, and better looking. That is a tall order to fill, by any measure.
On the cost side of the equation, it is a simple matter of taking the cost of electricity from the U.S. Energy Information Administration (EIA) and extrapolating that price out over 25 years. I used the most recent cost of residential electricity in California of 19.3 cents/kWh (March 2019) and extrapolated that out using a conservative 2% annual increase. For parity, I priced the system out using the production of the solar system, following the maximum degradation noted by Tesla. Over the 25 year warrantied life of the solar production from the system, the Solar Roof system should generate $73,436.14 worth of electricity.
Sizing The Solar Roof
We do not have a gas line running to our home, so everything in the home runs on electricity. We also have two electric vehicles that pull the vast majority of their electricity from our home. To offset as much of this consumption as possible, we are installing the largest Tesla Solar Roof tile system that our roof can handle.
System sizing on a Tesla Solar Roof is done differently than traditional solar systems, where the number of solar panels used depends on the need and roof capability. Because a Tesla Solar Roof has to serve as a physical cover for the house as its primary function, tiles must cover the entire surface. To size the system, Tesla has developed tiles that have solar cells and tiles that do not — and they all look essentially the same. For smaller systems, Tesla simply uses fewer tiles containing the actual solar cells.
The Tesla Solar Roof for our home has solar cells in every location possible. There are some areas around the edges of the roof and near the hips and joints without cells, but every other surface is setup to produce power. The primary surface of our roof faces south, which is ideal for solar production, but the configuration we are using utilizes the north-, east-, and west-facing roof surfaces as well. That does indeed maximize our solar generation, but results in a lower yield from the system compared to a system with all active tiles facing south.
All told, Tesla was able to fit a 10.59kW system in our roof, which it expects will produce 13,126 kWh in its first year of operation. This is the equivalent size of a system of 32 x 330 watt solar panels! The system, which I’ll remind you also serves as the roof for our home, came out to $70,375.23 before rebates and $58,603.04 after rebates. Compared to the cost of a metal roof, the Tesla Solar Roof was $20,737.24 more.
Translating this data into nerd-speak, aka an Excel spreadsheet, we can see that the cost of installing a metal roof and simply buying the equivalent of the electricity produced by the Tesla Solar Roof system would equal $111,301.94, whereas the Tesla Solar Roof is only $58,603.04. These are not hypotheticals or mythical numbers, just a simple summary of expenses in two different scenarios over 25 years. Said another way, the Tesla Solar Roof is 52.7% of the cost of installing a comparable roof and just buying power from the utility.
What About A Composite Shingle Roof?
Costing out a Tesla Solar Roof versus a metal roof is interesting, but that’s still a really expensive roof. Musk said at the company’s annual shareholder meeting on June 11th, 2019, that the Solar Roof team was really pushing to beat even the ubiquitous composite shingle roof. Using the single estimate we received for a composite shingle roof for our house at a mere $12,000, the Solar Roof system still comes out on top.
We can use the same $73,436.14 for the value of the electricity produced and $12,000.00 for the composite shingle roof for a total of $85,436.14. That includes the cost of electricity over the life of the system from the utility and the physical composite shingle roof. Compared to the $58,603.04 for the Solar Roof, composite shingle is already more expensive here in Southern California.
In fact, even if I throw in the roof itself as free, the Solar Roof is cheaper than simply buying power from the utility here in California, for a savings of almost $15,000 over 25 years. It won’t make or break your retirement, but it is impressive to see that the Solar Roof is already holding its own against roofing materials of any type in California. In fact, that is conveniently close to the installed price of two Tesla Powerwalls, so throw those in for some extra resiliency and call it a day.
The payback time for the Solar Roof will vary state by state and utility by utility, so be sure to run your own numbers before pulling the trigger on your own system. We spent months looking into this topic. Check back at CleanTechnica for more analysis of the Tesla Solar Roof system as the installation of our system progresses.
If you are in the market for a Tesla, find someone locally who you know (like, someone you know in real life) and use their referral code. If you don’t know anyone with a Tesla, go find someone at your local Supercharger and try not to be a creep and ask them for their referral code (they won’t mind). If that doesn’t work, ask a co-worker or a distant relative, post on Facebook or Twitter, or just hit up Google. If all of that fails and it’s an odd-numbered day and not too sunny out, you can use my Tesla referral link to get 1,000 miles of free Supercharging, I guess. Here is my referral code: http://ts.la/kyle623