Generally, Solar Power System, also named photovoltaic system, works when sunlight carries energy down to Earth. In off grid system, solar panels are mounted on the roof or exposed in the sunlight outside on ground. They convert sunlight into DC electricity and flows into PWM or MPPT solar charge controller, and then it charges different types of batteries (Deep cycle, Gel battery or Lithium-type battery), then inverters convert DC power to AC electricity for AC home appliances use. But in Grid-tie system, DC electricity flows to inverters directly, then it creates AC electricity. Your houses can use it,and it can be faded into Grid for a credit or selling by Net-meter. There are also other types, such as solar hybrid system, solar dc home kit or solar lighting system, etc.