Elon Musk's vision is all about clean energy. The entrepreneur's electric-car maker, Tesla Motors, on Tuesday offered to buy Musk-backed solar-panel installer SolarCity for shares worth up to $2.8 billion. He may see possibilities others are missing. The two public companies, however, seem to share little beyond grand ambitions, big cash outflows and large Musk stakes. Similarities to fossilized corporate governance are more apparent.