A “Grid-Tied” solar power system is the most common type of solar installation. Starting with an existing grid power connection, a solar power system is “tied” in or added to a breaker panel to power the building and reduce grid power use. In other words, the breaker panel is powered simultaneously by solar power and grid power.
A basic grid-tie system has one function: to offset use of power from the grid during the daytime. A power supply (other than solar) is required for solar power to generate, so a solar power system on its own does not provide backup power when grid power is out. Solar power systems must be connected to the grid or a battery system in order to operate.
Grid-tied solar systems can be coupled with a battery (see Backup Power Systems), but getting solar panels without backup power offers a lower-cost introduction to becoming self-powered. Since solar power is generated only during the daytime, and sized to meet the average daytime power usage, most grid-tie only systems will reduce grid use by up to half, sometimes more, but not completely.
Power generation and usage are almost never equal, as both change and fluctuate throughout the day. Sometimes solar offsets only part of the demand from the grid. Other times, there will be more solar power available than needed at any moment. When there is excess power it flows to the grid. However, using solar power is much more beneficial than selling it to the grid.
How it works
As solar power is generated it flows directly through the breaker panel and to any concurrent electrical loads on the property, reducing grid power use. Excess solar power flows to the grid, and insufficient power is compensated by the grid. The percentage of solar power used compared to solar power exported to the grid is known as your solar “self-consumption”. Higher self-consumption of solar results in greater bill reduction. Power that goes to the grid offers a small credit on each bill.
Power use and sunshine fluctuate constantly, varying by the season, the home, and the occupants. But to fully optimize self-consumption, try to align your power use with sunshine as much as possible, such as for vehicle charging, clothes drying, or kitchen use.
Though backup power is the main function of a battery system, the battery does more than provide backup. When excess solar power can be stored in a battery instead of the grid, grid usage is reduced further and a larger solar power system can be justified. However, battery systems have about the same price as solar power systems, making the functionality of a battery system more relevant than the additional savings it offers with solar power.
Fortunately, many options for battery systems now exist that make it easier to start with just solar and add a battery system later.