A new training video released in partnership with Cal Fire details the best practices for rooftop firefighting on houses with a Tesla Solar Roof Tile roof. The video includes footage of firefighters tearing into the panels using a few different techniques and reveals a bit about how the panels are wired.
Notably, the video highlights the low risk of shock or electrocution when interacting with the lower voltage wiring connecting the panels to the residential AC circuit, as the rooftop DC system is not earth grounded anywhere on the roof and, thus, presents a minimal risk to safety. This was confirmed by their own testing as well, not just taken from a statement from Tesla.
The video highlighted that the Tesla Solar Roof Tiles come in blocks of what looks like 3 shingles on the roof and are wired as such, with each tile of solar roof shingles being wired together into branches as they are installed. Each branch will typically consist of 1–4 of these tiles. As on a tree, the branches are wired back to a trunk — which Tesla calls the diode trunk harness. This is where the ~16 volts present on each branch is pumped up to a higher voltage.
The diode trunk harness is sent down toward the main power panel of the home, with its own Rapid Shutdown Device which is essentially a dedicated breaker switch for the entire Solar Roof Tile system. This device exists to cut the flow of power to and from the rooftop solar roof tiles to the inverter for the system.
The experts note in the video how even when cutting through a trunk cable, the likelihood of being shocked by the system is very low because none of it is earth grounded. It even goes so far as to note that interacting with a typical AC circuit in a home is far more dangerous because it is earth grounded, thus allowing power to flow through a firefighter to the ground, resulting in electrocution.
Okay, I know this next part is serious, but something can be serious and humorous. The video highlights how the roof can be slippery when wet. This is a very real concern for firefighters using water to fight a fire and is something they watch out for on many other roof types including metal roofing and slate. It still made me laugh to watch a firefighter demonstrate how slippery the roof can be when wet. I can imagine the dialog that went on behind the scenes for that shot. “Okay, who wants to be the guy sliding down the roof?” Pick me! Oh well…
They are able to mitigate this by either chopping a path through the panels from the eaves or by hooking a ladder over the crown of the roof and walking on the ladder to the area where access is needed.
Overall, it’s a very informative video for those who are curious about how the Tesla Solar Roof Tiles are installed, removed, and remediated in the event of a fire.