Types of Systems: Utility Intertie (UI) Systems
Utility intertie systems, otherwise known as net metering systems, sell power back to the local utility.  UI is becoming increasingly popular as the cost of public power increases and supply & distribution channels suffer in reliability. At the present time, roughly  two-thirds of all U.S. states mandate by law the right to sell power to the utility. 

Net metering systems convert DC power generated by the solar array or other renewable source into grid-quality AC power. The power is fed back into the grid through the home’s existing power panel and utility meter. As the power sent to the grid passes through the meter, it will count slower, or even run in reverse (if the power generated is greater than household demand at any instant in time). Utility power is being displaced at a retail rate in this manner. 

Net metering systems can be designed both with and without battery storage. A battery-less UI system is significantly less expensive, more efficient, and easier to design and install.   < See diagram below. >   A battery-less inverter has a conversion efficiency of 90% or greater, so more usable power is delivered to the grid from the solar array. In addition, battery-based inverters require a power draw from the grid in order to keep the batteries charged, effectively increasing the household load and thus decreasing the amount of power available to the grid from the array. Battery-based UI systems also incur additional costs due to more sophisticated control and overcurrent protection, and for the batteries themselves. A battery-based system will cost 30-50% more than its battery-less counterpart. 

All this said, battery UI still has a place- if your home experiences frequent power outages and there are critical loads that must be kept running. A battery-less system cannot power your home independently of the grid. Choosing the right system must take into account the reliability of your local utility, possible critical loads, and your budget.