Tesla's hot Model S has no green-friendly rivals yet, but it's a safe bet that they're coming. Photo credit: Tesla Motors.

Plenty of investors feel that Tesla Motors' (NASDAQ:TSLA) battery-electric Model S sedan represents the future of automobiles. They may yet be proven right, but the truth is that battery-powered cars represent just one of several ways forward.

This week, giants General Motors (NYSE:GM) and Honda (NYSE:HMC) announced a big bet on another path: hydrogen fuel cells. In this video, Motley Fool contributor John Rosevear looks at the new alliance and at the challenges facing fuel-cell technology – and at whether it's time for Tesla to start worrying.