Tesla Solar Roofs
We’ve been hearing a lot of buzz in the industry surrounding Tesla’s recent announcement of the “Tesla Solar Roof” product. Being designers and installers of solar technologies we wanted to share some of our thoughts on this product announcement and hopefully clear up some of the questions and confusion left by the announcement event.
Firstly, the concept of a solar integrated roofing shingle is not entirely new. It has been attempted previously by several manufacturers in the residential market including some big industry players like Dow with their Powerhouse shingle, and Sunpower with their SunTile product. Both products underwent signifanct marketing efforts and the building out of dealer channel networks, but ultimately were met with limited success in the market and discontinued.
For those with a negative view of the aesthetics of solar panels, there is a clear advantage to using an integrated roofing shingle product. Others, however, find the look of roof mounted solar panels quite beautiful and see their addition as an upgrade to the home’s overall aesthetic.
Placing that discrepancy aside there are several additional points that should be considered in this discussion.
Power output: Tesla has not yet said much about the technology behind the “Solar Roof” product, but historically PV roofing shingles have utilitized less efficient “thin film” solar technologies which would require far more roof space to achieve the same system power when compared with standard, framed PV modules. Even if the end product uses a higher-efficiency PV cell, the fact that the cells will be spread across individual shingles will again cause a decrease in array efficiency since they cannot be packed as tightly onto the roof. Furthermore, these cells and shingles will be installed directly on the roof’s surface which will cause them to operate at a higher temperature. Standard PV panels utilize racking systems which allow for air to flow below the array, thereby cooling the cells. The power output of PV cells is reduced as cell temperature increases, so this cooling effect is very beneficial.
Maintenance: For a PV array to operate efficiently it needs to be capable of moving electrons from all of the PV cells making up the array into the home’s electrical system where they are utilized. This requires thousands of electrical connections. In a standard system most of these connections exist within the solar panels themselves and are protected by the glass face, aluminum edges, and insulating backsheet of the panel. The panel-to-panel connections and those into the house are made with highly durable locking components and wire tested to stand up to harsh, outdoor conditions. In PV shingle products each shingle needs to be electrically connected to the shingle next to it, and for this to remain relatively flat will require those connections to be more fragile than those utilized to interconnect standard PV panels. Also, when one of these fragile connections breaks between two shingles, imagine the task of standing on a roof covered with thousands of shingles and trying to troubleshoot and isolate where that problem is located! The modular nature of a PV system built with standard modules makes it relatively easy to determine where a problem has occurred and, if need be, replace a panel or a section of wiring. Lastly, once this solar shingle roof is installed and functioning the smallest change to the roof to add a vent, chimney, or change the roofline for any reason becomes extremely complex and costly.
Cost: If one were to ignore the maintenance issues with this type of product, it could be argued that cost-competitiveness could be achieved in a new home construction scenario or possibly a re-roof. Many homebuilders, however, will not want to risk the reliability of a new roofing product nor the need establish relationships with new sub-contractors in the conservative roofing installation market. Regardless the solar shingle will most likely cost more than standard roofing plus solar panels combined, will require a more expensive installation procedure, and as noted above, will incur a higher cost of maintenance across the system’s lifetime due to lower overall reliability. When working with roofing companies on Dow solar shingle projects we saw turnkey system costs that were over 400% higher than standard solar PV system costs.
Elon Musk has great vision, is a clever marketer, and certainly has done well to produce a high-quality electric car. With that being said, we will withhold final judgement on the Tesla Solar Roof until technical specifications and pricing are released, but certainly have concerns about Tesla’s ability to get this product to market and find a place for it to be competitive against the increasingly efficient, reliable, and cost-effective mainstream PV market.