Grid-tied solar systems have safe interconnection with a utility grid. Under net-metering (or net-billing) grid-tied solar systems allow to:
- consume on site the generated solar power when it is available and the utility grid is working;
- import electricity from the grid when site consumption exceeds solar generation;
- export excess of solar power to the grid and receive a credit for exporting power.
Grid-tied solar systems under net-metering regulations are the easiest way to produce and consume solar electricity generated at the site. A bi-directional meter records cumulative energy sold to the grid and purchased from the grid. The utility bi-directional meter only defines the cumulative energy that passes through the meter, however, it does not record total generation or total power consumption at the site. In order to have a full picture of generation and consumption, we recommend installing separate energy meters.
Larger scale grid-tied solar systems and solar farms connect to the distribution grid though a revenue meter. Unlike bi-directional meters, revenue meters record total solar generation in the absence of the electric load.
Simple grid-tied solar systems do not provide outage protection. When the utility grid falls, these systems must turn off for safety reasons.
Grid-tied systems with Secure Power Supply (SMA term) are developed to provide up to 20amps of solar generation during utility power outages. When the grid fails, a system owner turns the switch on to enable the Secure Power Supply. An inverter isolates the grid-tied solar system from the grid and generates up to 20 amps of energy for as long as it is sunny.
Adding a battery back-up to the system and rewring loads to a critical panel adds to the costs but ensures your lights are on during the grid outage. Batteries can be integrated to the system by one of the following three methods:
- Installing a hybrid inverter ( e.g. Tesla PowerWall2; SolarEdge StorEdge, Fronius Symo Hybrid, etc).
- Building AC-Coupled system by adding battery-based inverters (e.g. Magnum MS4448PAE, SMA Sunny Island, Outback Radian) to the existing grid-tie inverter.
- Building DC-Coupled system using charge controllers and battery-based hybrid inverters (e.g. Outback Radian)