What We Still Don’t Know About Tesla’s Solar Roof

On May 10, Tesla announced it's now taking orders for the company's highly anticipated Solar Roof systems. The Tesla website now provides more details about the cost and durability of the tiles and allows interested homeowners to place a $1,000 deposit for the system.

For those who understand solar, however, the announcement of the new solar roof has prompted more questions than answers. On Pick My Solar’s blog, we briefly discussed the economics of Tesla’s solar tiles and found them to be significantly overpriced. A number of questions have subsequently been raised that Tesla has left ambiguous or unanswered:

  • How can we accurately compare the cost of the Solar Roof to standard solar panel systems?
  • How will Solar Roofs work with the federal Investment Tax Credit?
  • What’s the efficiency of the Solar Roof tiles? How does this compare to conventional solar panels?
  • How much do the tiles weigh?
  • What about flat roofs?
  • How does the durability of the solar tiles compare to conventional solar panels?
  • Who should get a Solar Roof?

In this comprehensive review, we’ll investigate each of these important questions to reveal what’s known and still unknown about this new solar product. The Tesla Solar Roof follows a long line of largely unsuccessful Building Integrated Photovoltaic (BIPV) products. Despite all the excitement it has generated, the jury is still out on whether or not this product will have a similar fate.

How can we accurately compare the cost of the Solar Roof to standard solar panel systems?

The cost and lifetime value of the Solar Roof depends on the size of your roof and your electricity bill. A higher utility bill means greater electricity consumption, which means that you will need a greater composition of solar-generating tiles compared to non-solar tiles. Generally, the higher your utility bill, the more attractive the economics of Solar Roof become.

Tesla has stated that they “believe in transparency and putting the customer in control,” thus building a Solar Roof Calculator to show upfront estimates for the system. It’s a fun tool, but does lack certain key pieces of information that would enable someone to accurately compare the system cost to a standard solar PV system.

The calculator will display the total system cost and percent blend of solar tiles to non-solar tiles, but it doesn’t show you the power rating of the system. An easy workaround for this is to input the home address in our own solar calculator, which will provide upfront the needed system size for a given location and bill amount.

Once you know the system production size in kilowatts for the Solar Roof, you can determine the key metric for comparing solar system costs: price per watt. Multiply the roof square footage by the percentage of solar-tiles, multiply by $42 per square foot (what Tesla has disclosed as the solar tile cost), then divide the amount by the number of watts. With this methodology, we’ve determined that the solar-only portion of the Solar Roof costs $6.30 per watt, give or take $0.50 per watt because the solar coverage slider on the Tesla calculator only moves in 10 percent increments.

A cost of $6.30 per watt is essentially double some of the solar prices available today, and translates to a $25,000-$35,000 premium on standard solar panel systems for the solar-only aspect of Solar Roofs. Is that premium worth it for superior aesthetics? Do you need a new roof and are you in the market for something high-end? If you answered yes to both of those questions, you may want to consider putting down $1,000.

How will Solar Roofs work with the federal Investment Tax Credit?

On the Solar Roof calculator, Tesla says that the 30 percent federal Investment Tax Credit (ITC) applies to both the entire roof and the Powerwall energy storage product. But this isn’t as clear cut as the webpage would lead you to believe.

BIPV doesn’t fit into the mold of the ITC structure and would need a special appeal process in order to determine which components of the system apply for the credit on a case-by-case basis. For example, solar shingles will qualify for the ITC, while the non-solar ones may not. This will depend on if the IRS determines that the non-solar components of the Solar Roof are “so specifically engineered that it is in essence part of the machinery or equipment with which it functions.”

It will likely be a lengthy process until the IRS clarifies the ITC code. Hopefully Tesla will take care of this entire process for homeowners or educate them completely on the process of claiming the tax credit. Time is short, however — this incentive is phasing down January 2020 and ends in 2022. Considering the long timeline Tesla will need to fully scale Solar Roof production, many homeowners may not even be able to benefit from the entire credit.

Despite what’s shown on Tesla’s calculator, customers shouldn’t expect the full ITC benefits. This delay to receive a Solar Roof is likely to be even longer for customers outside of California. In the meantime, potential Solar Roof customers won't be buying solar products that are already on the market today.

“Taking pre-orders for this unproven technology will undeniably have a negative impact on the adoption of solar,” said Pick My Solar CEO Max Aram. “By leveraging Tesla’s sexy brand, Elon Musk can lure a few thousand homeowners off the solar market. Many of these homeowners may never get their system turned on before the expiration of the federal tax credit.”

“The difference between Solar Roof and Model 3 is that Tesla has already proven they can manufacture great cars and that the Model 3 is coming at an affordable price point,” he added. “With solar roofs, he hasn’t proven either.” 

What’s the efficiency of the Solar Roof tiles? How does this compare to conventional solar panels?

Tesla plans to make the entire product in Buffalo, New York, with cells made from its partner, Panasonic. Peter Rive, former CTO at SolarCity and now head of solar tech at Tesla, said the efficiency of the solar tile is equivalent to a standard solar module.

However, SolarCity’s website breaks down the anatomy of the solar tiles, including how the colored louver film “allows the cells to blend into the roof while minimizing solar efficiency loss.” This implies that some efficiency is sacrificed for the system’s aesthetics. 

To date, Panasonic’s most efficient solar cells in production are the N330 HIT modules, which have an efficiency of 19.7 percent. The highest efficiency cells they’ve developed in lab are 23.5 percent. The market average efficiency of solar modules is around 16 percent, while the average for modules installers use on the Pick My Solar marketplace is around 19.5 percent.

Assuming that the colored louver film only reduces a few percent efficiency and that they would be including the highest efficiency Panasonic technology in the tiles, that would validate Peter Rive’s claim that the solar tiles have more or less equal efficiency to standard PV panels.

At the end of the day, efficiency is not a deal breaker unless a home has limited roof space, in which case high-efficiency standard modules would be the better option. For homes with constrained roof space, it’s helpful to compare efficiency in terms of kilowatt per square foot. We’ve determined that Tesla Solar Roofs produce about 6 watts per square foot, whereas a high-efficiency module would produce 19 watts per square foot.

Simply put, if you do not have a lot of roof space in an area with the appropriate conditions for solar, a high-efficiency module system is a much better option.

How much do the tiles weigh?

According to Tesla, Solar Roof tiles are half the weight of a standard tile. However, they’ve never defined what tile material they consider to be “standard.” Concrete tiles weigh between 9.5 and 12 pounds per square foot, while asphalt shingles only weigh 2.5 to 4 pounds per square foot. Spanish tile can weigh up to 19 pounds per square foot, but lightweight versions are only 6 pounds. Slate tiles weigh between 7 and 10 pounds per square foot.

We would guess that, when factoring in all of the solar tile electronic components, the tiles will weigh between 15 and 20 pounds per square foot, but it’s hard to say considering how vague Tesla was in its statement.

It’s unclear whether or not more supporting components in the sheathing of the roof will be needed to support the solar tiles. If so, that would significantly drive up the net cost of the system. Regardless, it’s obvious that installing the shingles will be an extremely complicated process.

“Aesthetically the Solar Roof is beautiful, but we’ll need to wait and see how Tesla will resolve taking it to market,” said Trevor Leeds, president of Chandler’s Roofing, one of our close roofing partners. “Roofing is a different animal than solar. There are different variables that have to be considered like waterproofing and the roof-attachment method. Compliance codes for roofing are also much different than solar. Will Tesla figure out how to be a national roofing contractor? Is Tesla looking to assume this liability and overhead? All of these unknowns will need to be worked out.”

What about flat roofs?

In sales training seminars, Tesla revealed that homes with flat roofs are not eligible for the Solar Roof. Solar Roofs can only be installed on roofs with a pitch of 3:12 (14 degrees) and more. This is a clear disadvantage versus standard solar systems, which can utilize a tilted racking system for flat surfaces.

Tiled roofing in general isn’t typically recommended for flat roofs due to waterproofing constraints, which is an understandably greater risk considering the intricate electrical wiring in the Solar Roof. Another restriction for flat Solar Roofs may also be that the colored louvers from the solar tiles significantly inhibit production from a flat angle.

How does the durability of the solar tiles compare to conventional solar panels?

The Solar Roof has a warranty of “infinity, or the lifetime of your house, whichever come first.” Tesla clearly is confident in the durability of the tempered glass tiles. These claims, obviously unproven at this time, are supported by their entertaining videos of the tiles being pummeled by hail cannons in slow motion.

How does this compare to conventional solar panels? Standard solar modules are usually warranted by the manufacturer for 25 years, and will typically last much longer. Panels consist of a glass layer on top, a protective backsheet on the bottom, and an aluminum frame to protect the individual solar cells inside.

Tempered glass is up to six times stronger than regular plate glass. In fact, the material is already used in most, but not all, solar panel brands. Some cheaper panel manufacturers will use regular plate glass instead to cut costs. However, LG, Sunpower, Canadian Solar, Hyundai and other large manufacturers all use tempered glass.

A comparison video of a Solar Roof tile and a tempered-glass solar panel being shot at by hail cannons and other heavy objects would quickly reveal the winner in this category. Until then, we’ll never know which one is actually more durable because they are made of the exact same material and there aren’t any more details available at this time.

One factor that has not been discussed enough is how the solar components of the Solar Roofs will be replaced after the production degrades too much. Useful solar production is guaranteed by Tesla to last 30 years. Whereas regular panels could be easily replaced after this time, it’s likely going to be an expensive and labor-intensive process to retrofit Solar Roofs.

Who should get a​ Solar Roof?

By and large, Tesla’s Solar Roof will appeal to wealthy, tech-savvy homeowners with a passion for the environment but a disdain for the aesthetics of standard solar panel systems. These homeowners will also understand the relative risk of being an early adopter of these systems, but are excited to be the first to experience the technology. Details like the ITC and final system cost are still unknown, so these homeowners will need a significant surplus of spending money. They’ll also, most importantly, need a healthy level of patience, as it could be years before the system will be installed.

Overall, Tesla’s Solar Roof has and will continue to inject excitement into the solar industry, which has had it’s fair share of bad news these past couple months (American module manufacturing, for one). The fact that so many media outlets and individuals are talking about Building Integrated Photovoltaics (BIPV) again means that this technology is moving in the right direction.

Elon Musk himself has admitted that the Solar Roof will have significant challenges in the coming years, particularly in ramping up production to bring prices down and service more territory. Building a vertically-integrated national roofing company is a huge challenge by itself and he recognizes the Solar Roofs won’t be widely available for five or maybe even ten years to come.

If you’re one of the lucky first few to have a Solar Roof installed on your home, invite us over!


Max Aram is the co-founder and CEO of Pick My Solar, an online platform for comparing solar companies.

from GTM Solar https://www.greentechmedia.com/articles/read/what-we-still-dont-know-about-teslas-solar-roof


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