SAN FRANCISCO Ryan Hanley built his career at some of the worlds biggest clean energy startups. The civil engineer became fascinated with the potential for small-scale, clean energy devices on the electrical grid, which led him from utility Pacific Gas & Electric to SolarCity, the largest rooftop solar company in the U.S. at the time.

There, he focused on creating a crowdsourced power plant that could deliver clean energy to the grid at scale by combining the power of solar systems and other devices in individual homes. Hanley stayed on when electric car company Tesla acquired SolarCity in 2016. Tesla later built the biggest grid battery in the world in southern Australia; it was Hanley who figured out the business model for that unprecedented project.

It may be surprising, then, that Hanley now works for one of the worlds largest oil companies, Royal Dutch Shell. When the job offer came, he asked himself if he could continue the clean energy mission there.

I had to do my best to assess Shell from the outside, he said. There were enough data points that I walked away and said, I think its authentic and I think its credible.

Shell tapped Hanley to build a virtual platform to unite its clean energy assets. Based in The Hague, Netherlands, a coastal city that sits just a few meters above sea level, Shell has taken considerably more interest in clean energy than many of its peers, and has allocated up to $2 billion annually to this effort through 2020. The strategy, as described in a June shareholder presentation , is to prove investment case in the first few years; if the clean energy business hits financial milestones, Shell will scale up investment and business activities considerably by 2025.

Since 2016, Shell has absorbed electric vehicle charging companies, retail electricity providers, and solar battery vendors across Europe and the United States. It has begun work on massive offshore wind farms and solar power plants, and plans to roughly quintuple its installed renewable capacity by 2025.

Hanleys job, as a general manager in Shells New Energies division, is to transform this global array of clean energy assets into a cohesive, economically beneficial whole.

Im at a big oil and gas company because the problem requires scaled resources and scaled ambitions, Hanley said. The potential for impact that I feel in my small contribution at Shell is an order of magnitude higher than Ive felt so far in my career.

The limits of startups

Hanleys view clashes with a sentiment common among activists: that oil companies wont solve the climate crisis and should be punished for their role in supplying planet-warming fuels. But for him, the role seemed like the opportunity of a lifetime to convert the world to clean energy.

Over the last decade, Silicon Valley startups made electric cars sexy, put solar panels on hundreds of thousands of roofs, and built batteries to store solar-powered electricity.

These startups have had an incredible impact on the power sector, Hanley noted, but even the best-funded companies face a structural challenge. They have to pick a specific problem to obsess over and tackle better than incumbents. The jump between doing one thing really well and eliminating fossil fuels from the entire global energy system is basically impossible.