SolarCity announced on its company blog: "We are excited to announce that SpaceX has invested $90 million in solar bonds.  Solar bonds are issued - and backed - by SolarCity and powered by monthly solar payments from thousands of solar customers across the country. SpaceX is effectively getting paid by the sun."

SolarCity is a company that provides rooftop solar energy systems to residential clients or commercial clients. According to the company's website, SolarCity was founded in 2006 and "has since grown to become America's largest solar provider with more than 6,000 employees."

SpaceX purchased the shares online, just as anyone can - provided they are willing to invest a minimum of $1,000.

"That's almost all of the $93 million in one-year bonds that SolarCity is offering at a 2 percent interest rate, the San Mateo, California-based solar developer said today in a regulatory filing," according to Bloomberg.