What happened

Shares of solar power company SunPower (SPWR 5.85%) exploded higher on Wednesday, rising 10.1% through 2:30 p.m. ET.

You can thank Raymond James for that.

So what

Bright and early Wednesday morning, Raymond James upgraded SunPower stock from outperform (i.e., buy) to strong buy (i.e., buy it now), and maintained its $21 price target to the $10.50 stock, implying this stock could literally double off of its current share price.  

Raymond James, of course, already had SunPower stock pegged for a $21 target price before its extra emphatic upgrade. However, the analyst said SunPower shares have "excessively underperformed" in the first half of this year as its stock fell 46%, even as rivals SunRun lost only 26%, and Sunnova gained 2%. As the disparity in performance among the solar companies grows, therefore, so does RJ's enthusiasm for buying the relative bargain that is SunPower.  

Now what

As Raymond James points out, only about 4% of homes in the U.S. presently have solar panels installed, versus 15% in Germany for example, and 25% in Australia. This disparity, too, says Raymond James, implies that companies like SunPower, SunRun, and Sunnova will enjoy "ever-rising penetration" over time, growing their sales, and their profits. And if that's the case, it makes sense to buy the cheapest stock of the three.

The key to when this expected penetration will happen -- when slow growth turns into hypergrowth -- is utility rates. As the analyst observes, U.S. electricity prices are relatively low compared to rates in other countries. But as electricity grows in price, so will solar panel adoption as consumers seek ways to avoid price increases, making this really just a question of time.

How fast will SunPower grow, however? Curiously, management is forecasting 20% growth in customers this year, a forecast that analysts largely agree with (according to S&P Global Market Intelligence estimates). But longer term, most analysts are only forecasting about a 10% growth rate over the following four years -- a trend that appears to contradict Raymond James' prediction of electricity prices rising, and growth accelerating.

Meanwhile, SunPower stock at 31 times trailing earnings looks a bit pricey if 10% sales growth is all the company will be able to manage, long term. At this valuation, and at this expected growth rate, Raymond James may turn out to be not only early in recommending SunPower stock, but wrong, too.