California legislators are lobbying for a $300 million plan to help hydrogen fuel play a larger role in the state’s economy. The news comes to light after a bipartisan group of lawmakers wrote a letter to assembly leaders asking that $300 million of a $500 million executive order on emission reductions be set aside for hydrogen fueling infrastructure.

Hydrogen-powered fuel cells (HFCs) have recently gained popularity among advocates as a potential source of emissions-free energy. The only known byproducts, as Forbes reported, would be water and heat. In theory, the improvements from gasoline to hydrogen could improve energy efficiency by 25% to 80%.

Getting there, however, is another matter. Today’s hydrogen energy is not so clean. Even though the United States produces 10 million metric tons of hydrogen, 95% of it comes from an emission-intensive process known as natural gas reforming. Although there is a process that could produce “green” hydrogen, the process is expensive.