In its first-quarter results, SolarCity (NASDAQ:SCTY.DL) increased 2014 guidance to 500-550 MW and gave 2015 guidance of 900 MW to 1 GW, more than the entire country installed in 2013. Growing installations is one of the value levers SolarCity has at its disposal, and it's growing faster than competitors like SunPower (NASDAQ:SPWR) and NRG Energy (NYSE:NRG)

It's also important to keep an eye on retained value per watt, which was down slightly in the first quarter. As competitors enter the market SolarCity may have to compete more on cost than it did in the past. Keep an eye on this figure in the future because it's just as important as installation growth. 

In the video below, solar specialist Travis Hoium covers SolarCity's incredible growth trajectory and how investors should be looking at the company now. 

Travis Hoium manages an account that owns shares of SunPower and is personally long SunPower shares and options. The Motley Fool recommends and owns shares of SolarCity. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.