A grid-tie inverter interfaces the varying DC output from solar panels, converting their power into standard AC power that is useful for home and industry.
Primarily for reducing your electric bill, a grid-tie inverter simply sends as much power as it can - as much as is available from the solar array - into the grid. When you're using more than it's generating, you're buying power. When it's generating more, your meter's going backwards and you're getting credit for the surplus. Most utilities allow you to bank this surplus power and use it later. You can use it at night or in the winter (since it's likely you'll generate a surplus in the day and in the summer). The energy isn't actually stored, but from your point of view it is because you can use it later (and the electrical grid is far more effective and efficient than batteries). For this reason, you always want to utilize the grid when it's available to avoid the need for expensive batteries (with a finite lifespan). If you think you want to get off-grid, check out our off-grid inverter/chargers.