Image source: Vivint Solar.

What: Shares of residential solar installer Vivint Solar Inc. (NYSE:VSLR) jumped an incredible 39% on Friday after an analyst upgrade.

So what: Analysts at Deutsche Bank upgraded the stock from hold to a buy rating and increased its price target from $3.50 to $7.50 per share. The analysts argued that Vivint Solar's tax equity funding is improving and with shares depressed there's value for investors at today's price.  

This follows shortly after Vivint Solar closed a new $75 million tax equity fund with a new unnamed investor.  

Now what: The rooftop solar market has struggled in 2016, in part because consumers have preferred buying instead of leasing and in part because there's little urgency to go solar after the solar investment tax credit extension. And Vivint Solar, like its competitors, struggled in the first quarter with both installation levels and costs. Until those factors improve and Vivint Solar shows it can shift away from the door-to-door sales model and a reliance on leases, this isn't a stock I will own. The market is just moving away from Vivint Solar's core product and that's a bigger worry than any positive from an upgrade.