Hydrogen is a huge bet for the most valuable power company in the United States.

Through early investments in wind and solar farms, NextEra Energy NEE 0.73%increase; green up pointing triangle has become a clean-energy powerhouse. Hydrogen is a much-touted energy source, but its economic viability remains unproven, so now the company is betting its expansion on it. The Florida-based company is taking a major risk with its new approach, but it may pay off: it has become the most valuable power company in the United States, ....