The renewable energy industry continues to grow, replacing fossil fuel plants around the world. One challenge facing the industry long-term is how to store energy for more than just a few hours, or for use in applications like marine or long-haul trucking where batteries may not be feasible.

Hydrogen could answer some of those challenges, and there's potentially a multitrillion-dollar market for producing and consuming hydrogen. As an industry leader, Bloom Energy (NYSE:BE) is my favorite hydrogen pick and is my top renewable energy stock today. 

Bloom Energy fuel cell servers at a commercial building.

Image source: Bloom Energy.

A best-in-breed fuel cell stock

Bloom Energy isn't the hottest fuel cell stock on the market, a title that goes to Plug Power (NASDAQ:PLUG) and Ballard Power Systems (NASDAQ:BLDP), both of which have higher market valuations. But Bloom Energy generates more revenue and has higher margins, so it's arguably a better operator. 

BE Market Cap Chart

BE Market Cap data by YCharts

Bloom Energy isn't profitable, but it has a solid foundation and multiple untapped markets that could drive future, profitable growth

Untapped markets

Bloom Energy is currently used primarily for backup or auxiliary power with natural gas as its fuel, but a decade from now that may not be the case. The company is working on demonstrating and launching a number of new and potentially massive markets. 

Marine power is one that investors should get excited about. Bloom Energy has a joint development agreement with Samsung Heavy Industries, which will design and develop fuel cell-powered ships.

Bloom is building demonstration carbon capture units, which it says can "deliver carbon neutral or carbon negative generation on biogas during the energy transition." This product isn't expected to reach commercial operation until 2023, but could provide CO2 as a raw material to industry. 

Biogas could enable carbon-negative power by capturing biogas from landfills, livestock farms, and wastewater treatment plants. Commercial projects are already being built, with a ramp of production in California expected next year. 

Hydrogen fuel cells, ironically, are not Bloom Energy's core business, although that may be the impression today. But Bloom Energy is building demonstration projects to use hydrogen fuel in its fuel cells with an expected ramp in production beginning in 2023. 

Fuel cells can't run off hydrogen without it. To that end, Bloom Energy's fuel cells can actually be run backward and produce hydrogen from water and electricity. The company is building demo electrolyzer projects right now with a commercial launch expected in 2022. 

Growing into a multitrillion-dollar market

Bloom Energy is just getting started in building its energy business. The company has established itself as a leader in fuel cells for electricity backup, but the future could be defined by marine, biogas, and electrolysis and hydrogen. And management says these markets could be worth over $2 trillion. 

As the renewable energy industry grows, there's a big need for an energy storage medium for hydrogen. Bloom Energy could make that a reality and enable hydrogen for cost-effective energy storage. That would truly be disruptive, and it's why Bloom Energy stock is my top buy in renewable energy right now. 

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.