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 WITH BATTERY STORAGE
Grid connected systems can be designed with optional battery back-up. However, battery back-up for utility interactive systems requires a listed utility interactive inverter and anti-islanding safety features. It is usually not feasible or economically viable to design the battery back-up feature to carry the entire consumption load. Battery back-up on a grid interactive system is typically reserved for backing up power for essential AC loads such as electric water heater, clothes dryers, and other large appliances. The Figure below displays a typical flow chart for the operation of a grid connected PV system with battery back-up.
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anti-islanding requirements, the PCU is equipped to automatically stop supplying power to the grid when the grid is no longer active.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.
