It depends on whether. We try to do the math. Maybe it doesn’t matter.
February 10, 2020
As we followed the progress of the Tesla solar roof installations in the San Francisco Bay Area, we found that some of the shingles were made in China.
We also received this product label which lists the electrical specifications of the Tesla solar roof tile model SR 60T-1, which has enough detail to calculate the efficiency of the tile. (This product is marked as made in the USA.)
To find out the efficiency of a solar module, you have to do a little math. First, you multiply the length and width of the complete solar panels including the non-generating frame to get the area of the product. Second, divide the area of the module by 1,000 because solar panels are rated based on standard test conditions of 1,000 W / m2. Finally, divide the nominal power of the module (in this case 24 W) by the area of the module that should provide the efficiency.
With the Tesla solar module specifications, we get dimensions of 1140mm x 430mm. Based on these values on the label (which do not represent the exposed area of the final installed product) the efficiency of the product is 4.9%. The first modern solar cell, invented by Bell Labs in 1954, had an efficiency of 4%.
Here we are speculating a bit based on limited data and trying to use common sense. Feel free to check out our math.
If we assume that the plastic parts protruding from the edges of the module are included in the dimensioning, we can cut off about 10% of the width and 33% of the height – which results in an efficiency of 8.1%. Better but still at the efficiency levels of the late 1950s.
Taking into account the overlap when laying the tiles on the roof, we can make another speculative sizing adjustment. All installations show that the solar modules are superimposed on other modules on one side and below.
If we assume another 20% of the height and 10% of the width, our efficiency reaches 10%. Still a low value compared to the average efficiency of solar modules in residential areas of around 18%.
However, according to reports, the solar tile installations cover 100% of customers’ electricity consumption. So is efficiency really important?
It is important to the point where it meets the needs of electricity consumers.
When Tesla’s solar roof is able to meet electricity needs because customers can install the tiles on a larger portion of the homeowner’s roof, the importance of efficiency falls off compared to the effectiveness of the product.
The Tesla roof installations that we monitor take ten days to two weeks. Whether this product can be profitable for Tesla or roofers, or provide homeowners with a return on investment is a different story.
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