ValueAct Capital founder and CEO Jeff Ubben is betting on electricity with his private investment in hydrogen-fueled truck company Nikola Motor.

"The electricity grid is the crown jewel in the clean economy," Ubben said on Tuesday in an interview with CNBC's David Faber at 13D Monitor's Active-Passive Investor Summit in New York.

The companies that can best address environmental and social goals are "where the breakout returns are over the next 20 years," Ubben added.

Ubben told Faber ValueAct had built a stake in Nikola without disclosing the amount of investment. Bloomberg first reported the investment Monday.

Nikola's technology uses solar power and grid power to produce hydrogen that can be used for trucking fuel, which is significantly cheaper than diesel, Ubben said. He said the technology could help Nikola grow into a $300 billion giant.

"Because the energy is so cheap, they are beating diesel handily today on a per hour basis," Ubben said.

Ubben also has a stake in renewable utility company Hawaiian Electric, CNBC previously reported.