Lyndon Rive, the co-founder and former CEO of SolarCity, did not attend last week's call with reporters when Tesla unveiled new details about the Solar Roof. It was a sign of a coming change.

Today, Rive announced that he will be leaving Tesla to focus on building a new company. 

"I am an entrepreneur at heart; starting and growing companies is what I do best. I want to pursue a new venture, but I didn't want to do that until the time was right. With Tesla ready to implement the next stage of its vision, I think that time is now. That's why, after much consideration, I'll be departing Tesla in June," wrote Rive in a letter to employees.

Since Tesla acquired SolarCity last November, Rive has been acting as head of sales and services at Tesla Energy. 

In an interview with Reuters, Rive said he had been thinking about departing Tesla for months. 

Rive has always expressed a passion for starting companies. In a 2015 interview with the San Jose Mercury News, he talked about how his mother encouraged him to start a company as a teenager in South Africa. 

In the late '90s, he co-founded a software management company called Everdream, which was sold to Dell in 2007.

"We funded the company (Everdream), spent a year building out the business model, getting customers, proving out that a remote management of a PC on a subscription basis can be a real business. In ’99, we got our first funding from DFJ. Steve Jurvetson led that round. At 20 years old, I got my first $2 million check. I went, 'Wow. OK,'" said Rive in the interview.

Years later, his cousin, Elon Musk, convinced him to get into the solar industry while on a drive to Burning Man. In July 2006, Rive launched SolarCity with his brother Peter, who became the chief technology officer. Musk became chairman.

Here's a picture of Lyndon and Peter in their first office, courtesy of SolarCity.

SolarCity was an early pioneer in residential solar leases and PPAs -- eventually growing to 14,000 employees, 2 gigawatts of installations in 27 states, and a small manufacturing facility -- before getting scooped up by Tesla last fall. (The wisdom of Tesla's SolarCity acquisition is still hotly debated in the solar industry.)

In his letter to staff, Rive expressed his passion for the combined company and the new solar-storage products that Tesla is developing.

"The solar business is making a positive cash contribution to Tesla, and Solar Roof is creating a massive new market around the world for consumers that would never have considered using solar power otherwise. The market opportunity for standalone energy storage is expanding, and solar customers are increasingly looking to add storage. I have no doubt these trends will accelerate," he wrote.

A Tesla spokesperson issued a written statement to GTM: “Thanks in large part to the foundation Lyndon helped create, Tesla has now built the world’s first integrated sustainable energy company, from generation to storage to transportation. Because of his leadership and dedication to our mission, Lyndon has helped position Tesla for an amazing future. We know he’s an entrepreneur at heart, and we wish him the very best on his next venture."

Below is the full text of the letter from Rive.

Team,

This is a very exciting moment in Tesla's history, as it continues to execute on its mission to accelerate the world's transition to a more sustainable future. I believe Tesla will ultimately become the most important company in the world, because energy generation, storage, and transportation are the most powerful levers to slow the negative effects of climate change. With the launch of the Solar Roof last week, I think we're really demonstrating to the world why the integration of SolarCity and Tesla makes sense and is so important.

I am an entrepreneur at heart; starting and growing companies is what I do best. I want to pursue a new venture, but I didn't want to do that until the time was right. With Tesla ready to implement the next stage of its vision, I think that time is now. That's why, after much consideration, I'll be departing Tesla in June.

Following my departure, Cal Lankton will be taking on an expanded role as head of sales and operations for Tesla's energy products. Cal is one of the most talented managers I've ever worked with, and I think he is absolutely the perfect fit to help transform the energy delivery and installation infrastructure we've built to deliver Powerwall, Powerpack and solar installations at a steadily increasing scale.

The solar business is making a positive cash contribution to Tesla, and Solar Roof is creating a massive new market around the world for consumers that would never have considered using solar power otherwise. The market opportunity for standalone energy storage is expanding, and solar customers are increasingly looking to add storage. I have no doubt these trends will accelerate. 

I can't adequately express my appreciation to Elon, and to all the people at SolarCity and Tesla for the opportunity to work with you. You have already built the most important sustainable energy company in the world, and that is only the beginning of what you will ultimately accomplish.

- Lyndon