Types of PV Systems
Photovoltaic-based systems are generally classified according to their functional and operational requirements,
their component configuration, and how the equipment is connected to the other power sources and electrical
loads (appliances). The two principle classifications are Grid-Connected and Stand Alone Systems.
Grid-connected or utility-intertie PV systems are designed to operate in parallel with and interconnected with the electric utility grid.
The primary component is the inverter, or power conditioning unit (PCU). The inverter converts the DC power produced by the PV
array into AC power consistent with the voltage and
power quality required by the utility grid. The inverter automatically stops
supplying power to the grid when the utility grid is not energized. A bi-directional
utility network, typically at an on-site distribution panel or service entrance. This
allows the power produced by the PV system to either supply on-site electrical
loads, or to back feed the grid when the PV system output is greater than the
on-site load demand. During periods when the electrical demand is greater than
the PV system output (night-time), the balance of power required is received
from the electric utility This safety feature is required in all grid-connected PV
systems, it also ensures that the PV system will not continue to
operate and feed back onto the utility grid when the grid is down for service or repair.
Stand Alone System
supply certain DC and/or AC electrical loads. Stand-alone systems may be powered by a PV array only, or may use wind, an
engine-generator or utility power as a backup power source in what is called a PV-hybrid system. The simplest type of stand-alone
PV system is a direct-coupled system, where the DC output of a PV module or array is directly connected to a DC load.
Since there is no electrical energy storage (batteries) in direct-coupled systems, the load only operates during sunlight hours,
making these designs suitable for common applications such as ventilation fans, water pumps, and small circulation pumps for solar
thermal water heating systems. Matching the impedance of the electrical load to the maximum power output of the PV array is a
critical part of designing well-performing direct-coupled system. For certain loads such as positive-displacement water pumps, a type
of electronic DC-DC converter, called a maximum power point tracker (MPPT) is used between the array and load to help better
utilize the available array maximum power output.
In many stand-alone PV systems, batteries are used for energy storage. Below is a diagram of a typical stand-alone PV system
with battery storage powering DC and AC loads.
power source (wind, engine-generator or utility power)
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