I would have said "and SolarCity" but of course Tesla owns SolarCity now.

It's really quite genius to build a really expensive solar roof tile when the tax breaks are for solar installations. Find a way to charge a premium price for a premium product (eg, a tile, not just a simple panel), get tax breaks for it all!

Half of what Tesla does is product engineering, the other half is financial engineering. Both are critical to their success on an accelerated time table.