Grid-Tie PV System
A grid-tie PV system is designed to supplement the electric grid. It is basically like using the grid as a "battery" for your system. (Note that another type of grid-tie system will be explained soon where you will have energy even when the grid is not available, e.g. Tesla PowerWall.) When your PV panels are producing more energy than you are using, the excess energy is pumped into the grid. When you are producing less than you are using, you draw energy from the grid.
The components of a grid-tie system consist of:
- PV panels to convert sunlight into direct current electricity
- Grid-tie inverter to control and route PV panel energy either for local use or to the grid
- Safety equipment to protect the panels, charge controller, batteries and you
PV Panels
These are flat panels of typically silicon-based cells. Typical panels of today will generate 400-500 watts per two square meter panel. They are totally passive (no moving parts) and tend to have a guaranteed life of from 20 to 30 years.
Grid-tie Inverter
This is a controller that converts DC from your PV panels to AC synchronized with the electric grid and sends any excess power you are generating into the grid. It also has a "grid fault" circuit which shuts down the system if your grid connection. While this may seem counter-productive (that is, you would like to use the energy you are producing when the grid isn't available) it is necessary for the safety of those who might be working on the grid.)
Safety Equipment
Fuses or circuit breakers between the panels and charge controller and between the charge controller and battery should be installed to protect the equipment. You also should put a circuit breaker between the battery and the load.
A second important piece of safety equipment is lightning arrestor. This will protect the grid-tie inverter if a panel gets struck by lightning. Note that the metal frame of the panels needs to be connected to a good electrical ground.
Unlike with an off-grid system, PV panels are always connected in series (with possibly multiple strings) to get a higher voltage suitable for inverting -- converting to the grid voltage.
