What happened

Shares of fuel cell pioneer Plug Power (NASDAQ:PLUG) popped nearly 9% higher after reporting fiscal Q4 2018 earnings last Thursday and haven't looked back since. This morning, Plug stock opened the week with another strong performance, up 9.5% as of 12:30 p.m. EDT.

So what

There hasn't been any major news regarding Plug Power since the earnings came out, so chances are today's move is just a continuation of the enthusiasm investors showed last week.

But what explains that enthusiasm? On Thursday, Plug reported an adjusted loss of $0.07 per share on sales of a little less than $60 million. Analysts, however, had predicted Plug would lose only $0.06 pro forma, on sales of a little more than $60 million -- and Plug's actual GAAP loss for the quarter was even bigger at $0.08 per share.

Check out the latest earnings call transcript for Plug Power.

Cartoon teacher explaining why a red arrow is pointing up

Plug Power's sales estimates are pointing up. Image source: Getty Images.

Now what

On the plus side, Plug's per-share loss one year ago, in Q4 2017, was $0.09 GAAP -- so even the $0.08 loss was an improvement. What's more, Plug's guidance for 2019 was something of a happy surprise. Instead of the $232.8 million in sales that Wall Street is expecting, Plug promised to deliver gross billings between $235 million and $245 million, more than making up for Q4's revenue shortfall, and about 3% ahead of estimates at the midpoint.

I'm not convinced that a promise of 3% better revenue and no profit is reason enough to value Plug Power stock 18% above what it cost pre-earnings. But it appears I'm in the minority today.