There are barriers to putting up your own solar panels. Maybe your house has too many trees around it or you rent your business space. Community solar can take advantage of land or large commercial rooftops. It can also bring down the cost of installation (in part because the inverter, which converts DC to AC, is a significant cost which you need no matter how large the array).
Rocky Mountain Institute's SHINE program has been working to bring down the cost of and support the creation of community solar projects. Learn more: