Tesla and Panasonic build batteries together at the Gigafactory in Nevada, but haven't directly collaborated on solar panels before. "We are excited to expand our partnership with Panasonic as we move towards a combined Tesla and SolarCity," says Tesla CTO JB Straubel. "By working together on solar, we will be able to accelerate production of high-efficiency, extremely reliable solar cells and modules at the best cost."

A proposed Tesla solar charging station.

On October 28th, Musk will show off new rooftop SolarCity panels and how they integrate with his Powerwall 2.0 battery storage systems and Tesla EVs. A year ago, SolarCity revealed the "world's most efficient" solar panels, which hum along with 22 percent efficiency. Those can reduce the size of a rooftop solar installation or generate more power for businesses and commercial operations. Musk said at the time that SolarCity was shooting for a 55 cent per watt photovoltaic panel price.

Tesla recently announced that it would acquire SolarCity, bringing both of the Musk-led companies under one roof. However, the deal is controversial -- many analysts and shareholders think Tesla isn't liquid enough to absorb the $2.6 billion purchase price. A vote on the deal will be held on November 17th, so the upcoming event is no doubt intended to show investors and the public that Tesla and SolarCity's products are made to be together.