Is Tesla’s solar roof a game changer or just an expensive / aesthetically pleasing roof with built in solar? Let’s do the math to see what it looks like.
About a year ago Solar City announced a goal to produce panels at $0.55 per watt with their new plant that would be online soon. Tesla and Panasonic have recently come to an agreement for Panasonic to manufacture panels for Tesla. Let’s assume Tesla / Panasonic can produce the new solar roof shingle at $0.55 per watt target. If the cell is a 6×6 (156 mm) cell the cost per square foot of the cell portion of the roof would be about $8.84 per square foot. Some of the shingle would not have solar on it so you can have overlap and shading. If part of the shingle is used for overlap and shading, then we can give a conservative cost of $7.07 per square foot.
Elon Musk said at his press announcement that the Solar Roof should last longer than the house. Let’s assume a 50 years’ life expectancy in this example although solar panels themselves are usually expected to last 25 to 30 years.
For some common roof materials as a sample we can compare Slate, Tile and Composition Shingle. Slate and Tile are examples installed on the Tesla sample projects.
Typical Slate materials sell for $5 per square foot and have a life expectancy of 50 plus years. The cost to install Slate Tiles would be similar to Tesla Solar Roof since they are individual tiles.
Typical Spanish S Tile materials sell for $1.70 per square foot and can have a life expectancy of 50 years. The cost to install Spanish S Tiles would be similar to Tesla Solar Roof since they are individual tiles.
50 Year Dimensional Composition Shingles sell for $1.70 per square foot and have a life expectancy of 50 years. The cost to install Compositional Shingles is less expensive to install than Tesla Solar Roof as they cover a larger area per bundle.
Materials Cost Per Square Foot
Tesla Solar Roof $7.07 Estimated
Slate Tiles $5.00
Spanish S Tiles $1.70
50 Year Composition $1.70
All three types of roof systems as well as Tesla Solar Roof would require similar roof underlayments and roof components for long term waterproofing so there should be no cost differential there.
One thing to consider on the energy side is how much heat is absorbed from UV due to the Tesla Solar Roof. In most climates in the US typical solar panels require a certain amount of air space around them to run at an efficient temperature. Solar panels can lose significant amounts of power production as temperatures rise. Some tests show losses of 45% or more above 90 degrees Fahrenheit depending on the type of cell used. This means the Tesla Solar Roof could be less efficient than a standard panel when at normal operating temperatures.
Another consideration is how much heat is reflected or emitted by the roof material itself. All roofing materials have a certain reflectivity and emissivity that in turn translates to heat being absorbed by the roof structure they are installed on. The more reflective and emissive a roofing material the less heat transferred into the building. More heat transferred into the building means higher air conditioner or energy costs. Higher roof top temperatures also mean shorter lasting roof systems and waterproofing underlayment. Since the Tesla Solar Roof is putting the panel directly into the roof system it is likely that there could be increase thermal load into the building from increased roof temperature and increased air conditioning costs. Slate, Spanish Tile and Composition Shingles have a higher reflectivity and emissivity than a typical solar panel cell.
There is the benefit of installing the roof and solar panel portion at the same time. The cost of just installing the panels on a residential house should be no more than $1,500 on an average solar install.
A standard residential solar install is currently running between $2.50 to $3.00 per watt. Assuming a system size of 5kw this translates to $15,000.
Roofing manufacturers understand a roof system is installed to provide long term protection against the elements. Roofing manufacturers design entire roof systems (Fasteners, Underlayments, Flashings and Tiles, Shingles or Slate) to last the entire warranty period. A roof system is more than what goes on the top of the roof it is what the entire roof system is made of. The potential liability of a poorly designed roof system can be in the millions depending on the damages caused by a faulty roof system.
For Tesla to install the Solar Roof they will need to create roof systems to back the performance of the Solar Roof Tile itself. Tesla will need to implement a manufacturer inspection on the entire roof and solar system installed. They will need to back the roof warranty with a policy or fund in addition to the warranty of the solar panel or generation. Tesla will also need to train / hire / buy or create a roofing division to install the roof tiles correctly.
Let’s compile the data above assuming we are installing a 2,000 square foot roof and 5kw of solar.
|2,000 square feet||Tesla Solar||Slate Tiles||Spanish S Tile||50 Year Comp|
The above does not include other materials required, markup, overhead or other items required to install a roof system and are for example only.
To recap the Tesla Solar Roof could potentially compete with traditional roof materials and solar install combination but they will be required to be able to sell at $0.55 per watt retail and the assumed competition must keep their prices at $3.00 per watt installed to be competitive. Many residential projects currently are installed at $2.50 per watt or lower on large tract homes or larger scale projects.
The Tesla Solar Roof would save money on the cost to install the panels assuming the other Balance of System costs are the same. There could be increased air conditioning costs due to increased heat load due to cells being installed into the roof system.
Tesla would create a larger liability for themselves by installing the roof system along with solar. Tesla may want to consider partnering with a large roofing manufacturer to create roof systems to go along with the Solar Shingle. This would lower their potential liability and open a broader market of potential installers.
About Platinum Roofing
Platinum Roofing installs millions of square feet of commercial and industrial roofing every year. Platinum Roofing also install 10 plus MW of roof top solar per year. Contact us today 800-284-5887 or firstname.lastname@example.org for more information about Roofing and Solar.