Unfortunately for Plug, batteries remain the dominant alternative vehicle fuel, and with gasoline prices so low right now, the economic argument for switching to alternative-fuel delivery vans is likely to take a hit. As for Plug, it's tough to assess its valuation, because the company has never posted an annual profit in its more-than-20-year history, so price-to-earnings ratio can't be calculated. Today, let's compare pure-play hydrogen fuel cell specialist Plug Power (NASDAQ: PLUG) -- shares of which are up 33.8% so far this year -- with renewable energy generalist Brookfield Renewable Partners (NYSE: BEP), which is only up 3%.