What: Shares of power generation company Generac Holdings (GNRC -3.17%) jumped as much as 15% in Tuesday trading after reporting earnings.

So what: Fourth-quarter net sales were down 11% to $357.8 million and net income fell 81% to $9.2 million, or $0.14 per share. After adjusting for one-time expenses from acquisitions and impairments, earnings were down just 5% to $65.3 million, or $0.97 per share. Analysts were only expecting earnings of $0.88 per share, so that outperformance is what investors are looking at today.

Now what: The big downside in 2015 came from commercial and industrial customers, where oil and gas customers are a key to demand. In the fourth quarter alone, revenue from commercial and industrial fell from $185.0 million a year ago to $131.9 million. Management could see the drop in demand coming and cut costs accordingly, but it's demand we won't likely see return in 2016.

To that end, management said that organic constant currency sales are expected to fall 5%-7% in 2016. Some of that will be offset by the acquisition of a majority ownership stake in PR Industrial S.r.l in Italy.

For today, earnings being "less bad" than expected was enough to rile up investors. But the key going forward will be finding organic growth and that may not be coming until energy markets improve significantly.