1 Introduction

An Introduction to Photovoltaic Systems

PV systems are electrical power generation systems that produce energy. They vary greatly in size and their applications, and can be designed to meet very small loads from a few watts or less up to large utility-scale power plants producing tens of megawatts or more. PV systems can be designed to supply power to any type of electrical load at any service voltage.

The major component in all PV systems is an array of PV modules that produces dc electricity when exposed to sunlight. Other major components may include power conditioning equipment, energy storage devices, other power sources and the electrical loads. Power conditioning equipment includes inverters, chargers, charge and load controllers, and maximum power point trackers. Energy storage devices used in PV systems are mainly batteries, but may also include advanced technologies like flywheels or other forms of storing electrical energy or the product, such as storing water delivered by a PV water pumping system. Other energy sources coupled with PV systems may include electrical generators, wind turbines, fuel cells and the electric utility grid. See Fig. 1.

Balance-of-system (BOS) components include all mechanical or electrical equipment and hardware used to assemble and integrate the major components in a PV system together. Electrical BOS components are used to conduct, distribute and control the flow of power in the system.

Examples of BOS components include:

• Conductors and wiring methods • Raceways and conduits • Junction and combiner boxes • Disconnect switches • Fuses and circuit breakers • Terminals and connectors • Grounding equipment • Array mounting and other structural hardware

PV System Components

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2011 Jim Dunlop Solar Figure 1. - PV system components

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3 4 5

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7 1. PV modules and array 2. Combiner box

3. DC disconnect

4. Inverter (charger & controller) 5. AC disconnect

6. Utility service panel 7. Battery (optional)

Solar Radiation: 2 -2

Figure 2. Stand-alone PV systems operate autonomously and are designed to meet specific electrical loads.

PV Array

Charge Controller DC Load

Battery Inverter/ Charger

AC Load

AC Source (to Charger Only)

2011 Jim Dunlop Solar System Components and Configurations: 4 -2Figure 2. Stand-alone PV systems operate autonomously and are designed to meet specific electrical loads.

Types of PV systems are classified based on the loads they are designed to operate, and their connections with other electrical systems and sources. The specific components needed depend on the type of system and its functional and operational requirements.

Stand-alone PV systems operate independently of other electrical systems, and are commonly used for remote power or backup applications, including lighting, water pumping, transportation safety devices, communications, off-grid homes and many others. Stand-alone systems may be designed to power dc and/or ac electrical loads, and with a few exceptions, use batteries for energy storage. A stand-alone system may use a PV array as the only power source, or may additionally use wind turbines, an enginegenerator, or another auxiliary source. Stand-alone PV systems are not intended to produce output that operates in parallel with the electric utility system or other sources. See Fig. 2.

Interactive PV systems operate in parallel and are interconnected and synchronized with the electric utility grid. When connected to local distribution systems, interactive systems supplement utility-supplied energy to a building or facility. The ac power produced by interactive systems either supplies on-site electrical loads or is back-fed to the grid when the PV system output is greater than the site load demand. At night, during cloudy weather or any other periods when the electrical loads are greater than the PV system output, the additional power required is received from the electric utility. Interactive PV systems are required to disconnect from the grid during utility outages or disturbances for safety reasons. Only special battery-based interactive inverters can provide stand-alone power for critical loads independent from the grid during outages. See Fig. 3.

Figure 3. Utility-interactive PV systems operate in parallel with the electric utility grid and supplement site electrical loads.

AC Loads

PV Array Inverter Load Center

Electric Utility

2011 Jim Dunlop Solar

System Components and Configurations: 4 -3

Figure 3. Utility-interactive PV systems operate in parallel with the electric utility grid and supplement site electrical loads.

PV systems can be designed to supply power to any type of electrical load at any service voltage.