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What: Shares of solar installer Vivint Solar Inc (NYSE:VSLR) dropped 14.5% in June as the residential solar market began to look dimmer than it had earlier in the year.

So what: One big negative during June was net metering negotiations in Arizona falling apart. But negotiations between SolarCity and Arizona Public Service didn't go anywhere and net metering could be cut in July 2017 if an agreement can't be reached.  

Solar stocks in general fell during the month as investors worried about the value solar companies like Vivint Solar generate each year and whether the preferred leasing model will last. Loans and cash sales are growing in popularity, which could require a business model change for Vivint Solar.

Now what: Since its acquisition by SunEdison fell through, Vivint Solar has struggled to regain momentum in the residential solar market. And the residential solar market has been in turmoil, which has hurt all of the major players.

The biggest question is whether Vivint Solar can adapt to a quickly changing solar market. Residential customers' demands are changing and local installers are gaining market share. And if those trends continue it'll be bad news for Vivint Solar, which was a big concern in June.

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