In November, Elon Musk spoke about Solar City’s plans to install solar roof tiles manufactured by Tesla.  Many people have asked us about the potential of installing solar roof tiles.  We look forward to seeing what becomes available and understanding the details of pricing and performance of this product.  In the absence of any details from the manufacturer, you can look at pictures and sign up for updates here

This concept has previously been referred to by the nickname BIPV, denoting Building Integrated Photovoltaics, although we see that term used less these days.  The concept of having one product that serves as roofing and also generates electricity is very attractive.  It would be helpful to the product’s feasibility if the solar roof tiles cost less than the combination of a standard asphalt shingle roof with standard framed modules installed on top of it, but no solar roofing product that currently exists comes close to this price point.  So in order to have a solar roofing product, customers will pay a premium.  We have never installed one, though there have been many options available for over a decade, from Sharp Electronics, Open Energy, CertainTeed, and Dow, to name a few manufacturers.  Musk claims that the Tesla solar roof tiles will cost less than a “dumb” roof.  I look forward to seeing that, but I am not holding my breath while waiting.

The other solar roofing products on the market have a relatively low efficiency in terms of watts per square foot compared to standard mono-crystalline silicon modules.  So even though there is the supposed convenience of a single product to install, the amount of energy that could be produced is actually lower than from a standard pv module array.  In most residential installations, our design imperative is to produce as much energy as possible on the limited roof space available, so unless the Tesla product has a higher efficiency than the most efficient product currently available, it will involve making a sacrifice in performance.  We are looking forward to the technical details to be able to make a true evaluation.

Only a portion of a home’s roof is practical for the installation of solar pv, eg, we would install solar on the south-facing roof, but not the north-facing roof of a simple house that is a single gabled rectangle.  Most homes of course don’t have such simple roof shapes nor orientation.  There are usually hips, dormers, clerestories and other roofs with different pitches and compass azimuths, and a big part of our design process is identifying and prioritizing the suitable roofs upon which to install pv.  With the solar roof tiles, the question comes up as to what to do on the roofs not suitable for solar pv.  Will Tesla provide a visually identical product minus the photovoltaic cells?  I imagine this will be the intention, though this will surely raise the price further even for the roof planes not making energy.

Another aspect of this product that gives us pause is the need for a specialized tradesperson to perform the installation.  In a solar installation on a standard home, the roof has been installed by roofing contractors who specify the products and warrant their roof installation for many years.  The solar installers then install their product over the top of that and warrant our penetrations and product performance for many years.  The roofers we work with are great, but it is a fair generalization to state that roofers are generally conservative and slow to adopt new products, which is exactly what you want in a roofer.  As far as solar installers, they generally spend a lot of time surveying this rapidly changing market and keeping abreast of new products and dynamic pricing, updating their offerings for their clients as the options change and better products become feasible.  There is an inherent tension in these two cultures, and the concept of combining those two trades into a single new trade is interesting.  At Power Trip Energy, we have roofing skills related to penetrating, sealing, and flashing many different roof types in order to install our product on any roof, but we have no interest in becoming roofers at this time.  In some situations with certain less common roofs or proprietary roofing membranes, we coordinate our installation with the roofers who follow us on the roof and come in right after us to flash our work and maintain responsibility for the entire roofs warranty.  Perhaps other larger markets will lead in the creation of a new trade specialist, the solar electrician roofer, but we have yet to see evidence of that in the trade literature.  If the installation will require coordination roofers and solar electricians, that coordination will inherently increase the cost of installation and inevitably slow us down.

There are unanswered design questions.  Currently, if we are designing a system using string inverters that accept strings of DC electricity from the solar pv on the roof, we need to make certain we are bringing the DC power to the inverter with the proper voltage and amperage, sometimes a challenge to fully and exactly utilize available roof space.  What will be the design constraints of these solar roof tiles?  More often now instead of string inverters, we are using AC modules each with integrated micro-inverters in the 320 watt range, on a module that is roughly 15 square feet in area.  If each solar roofing tile were to have its own integrated micro-inverter on a much smaller scale, that would increase costs and dramatically multiply the potential points of failure, and increase the complexity and expense of any warranty work.  I doubt whether we will see solar roof tiles with integrated micro-inverters any time soon, but this is exactly where the leading edge of the market is right now for the standard framed modules.

Unless the solar roof tiles can provide some benefits that surprise me in relation to the issues I raised above, the only benefit is the aesthetics some people will find in the look of those roofs.  We have been able to design systems to satisfy even the most aesthetic conscious clients using SunPower’s black-framed modules.  Of course most of our clients find the creation of clean energy a thing of beauty in itself, and are happy to be reminded of their arrays when they come home.

Please pardon our slightly jaded response to some of the industry’s more hopeful forward-looking announcements, we have seen a lot of those in the last 14 years, and it is a rare jewel that makes it from announced intention to actually becoming the best product for your roof.  We’ll be keeping a close eye on these developments and let you know when they are ready for you.  In the meanwhile, what we have right now is a selection of the best solar products made to date, at the lowest prices ever seen, and a relatively friendly regulatory environment, facts which may combine to encourage you to act now rather than following Tesla’s implied advice to continue waiting for something better.