Types of PV Systems
PV solar systems provide both alternating current (AC) and direct current (DC) power, and fall into two primary classifications, Grid Connected systems, or utility interactive, and Stand Alone. The two systems are based on the system’s ability to run dependently or independently off the public utility grid. These two systems are defined by their connection and interaction with various power sources, types, component configuration, and method of electrical transference to appliance. A stand-alone system with the added ability to interface with alternate power sources, including utility back-up is known as a Hybrid system.
GRID CONNECTED RESIDENTIAL SOLAR SYSTEMS
The fundamental defining characteristic of a grid-connected PV system is that it provides power in tandem with the utility grid and utilizes the same distribution system as the utility grid. Due to the component configuration and operational interface with the utility grid to back-feed reserve energy for consumer credit, this type of system typically presents a greater return on investment.
Since the grid-connected system runs parallel to the utility grid, it is dependent upon utility grid operation to function. In the event of a power outage, the PV system will automatically shut down by utilizing a safety mechanism called an anti-islanding device which is a mandatory requirement for all utility interactive systems. The Figure below displays a flow chart of a typical grid connected PV system.
Power Conditioning Unit
The PV modules located in the collector array convert sun energy into DC power. The Power Conditioning Unit (PCU), also known as an Inverter, coverts the DC power produced by the PV modules into AC power, in order to be compatible with the utility grid voltage requirements. As part of the mandatory anti-islanding requirements, the PCU is equipped to automatically stop supplying power to the grid when the grid is no longer active. NOTE: The PCU for a grid-connected PV system must be listed as a “utility interactive Inverter” in order to properly function in a utility interactive system.
Distribution Panel
The distribution panel in a utility interactive system receives AC power from the PCU and distributes power bi-directionally to either the electrical loads (total appliance consumption) it or is back-fed to the utility grid.
Explanation
During peak times, power is distributed to the electrical load service panel for distribution to various branch circuits. If at any time the PV output is insufficient to meet the total load demand, the utility grid will supply the difference. Conversely, when the PV output is greater than the consumption load demand, the residual power is back-fed into the grid and accredited to the consumer. NOTE: The “automatic” bi-directional distribution panel is a mandatory feature required on all utility interactive PV systems. Figure 1 displays a flow chart of a typical grid connected PV system.
