That's actually a trick question, because they all are.
Tesla's first ever solar product is stunning It's not a solar panel—instead it's a range of four solar roofing materials that look virtually indistinguishable from high-end terracotta, slate, or slick modern asphalt shingles.
Here's how it works: the top of the roof tiles is made of textured glass.
It looks like shingles from most angles, but it allows sunlight to pass through from above and into a standard solar cell with almost no loss in efficiency.
Tesla says the glass is as tough as steel, and can weather a lifetime of abuse from the elements.
It can also be fitted with heating elements to melt off snow in colder climates.
Active solar tiles will cost about about $42 per square foot -- cheaper than traditional shingles with solar panels on top.
But ultimately you'll probably need more tiles to do the same job so Tesla's total roof cost will be a bit higher.
You want to call your neighbors over and say check out the sweet roof--it's not a phrase you hear often.
This represents the grand unification of Tesla's plans to become a sun-to-vehicle energy company.
The idea is that you can run your home on solar power, store it in a slim battery that hangs on your wall, and use that electricity to power your home and car.
This combination is perhaps the closest we've ever come to affordable off-grid electricity.
the goal is to make solar roofs that look better than a normal roof, generate electricity, last longer, have better insulation and actually have an installed cost that is less than a normal roof plus the price of electricity.
Why would you have anything else?
The solar roof was Musk's closing argument to shareholders before their vote to approve Tesla's $2.2 billion bid to buy the biggest U.S. rooftop solar installer, SolarCity, to make it all possible.
There's plenty of reason for skepticism, but if Musk can pull it off, this trifecta of Tesla products: the solar roof, the Powerwall 2, and the Model 3 electric car will be available in Tesla stores across the U.S. by the end of 2017