sentences:  These are both true in the case of residential installs, where the roof defines the total size of the system that can be installed, and the cost of labor is the largest single cost of the system.Simply replacing conventional panels with SunPower panels will increase the total power of the system as much as 25% without having any effect on install times, in which case the total install cost in terms of price per watt can improve in spite of higher prices on the panels.The company's shares have been listed on the Photovoltaik Global 30 Index since the beginning of this stock index in 2009.