What is a solar PV system

Simply put, PV systems are like any other electrical power generating systems; just the equipment used is different than that used for conventional electromechanical generating systems. However, the principles of operation and interfacing with other electrical systems remain the same, and are guided by a well-established body of electrical codes and standards. 

Although a PV array produces power when exposed to sunlight, a number of other components are required to properly convert, control, distribute, and store the energy produced by the array. Depending on the functional and operational requirements of the system, the specific components required may include major components such as inverter, battery bank, charge controller and an assortment of balance of system (BOS) hardware, including wiring, overcurrent, surge protection, arc fault protection, disconnect devices and other power processing equipment.

Back bone of a solar PV system is solar panels which convert sun’s energy into DC electricity. A solar panel is made of number of solar cells, these cells are connected series and parallel within a panel to create desired voltage, current and power out puts. These connected PV cell circuits are then sealed in an environmentally protective laminate, to make a solar PV panels which are the fundamental building blocks of PV systems. 

Similar to cell connections within a solar PV panels number of solar panels are connected in series and parallel to obtain desires power outputs. A group of such connected solar panels are called solar array. The performance of PV modules and arrays are generally rated according to their maximum DC power.

Today’s photovoltaic modules are extremely safe and reliable products, with minimal failure rates and projected service lifetimes of 25 to 40 years. Most major manufacturers offer warranties of 20 or more years for maintaining a high percentage of initial rated power output. 

Type of PV system

Photovoltaic systems can be designed to provide DC and/or AC power service, can operate interconnected with or independent of the utility grid, and can be connected with other energy sources and energy storage systems. Solar PV power systems are generally classified according to their functional and operational requirements. The two principal classifications are grid-connected systems and off-grid systems.

Grid-connected solar PV system

Grid-connected solar PV systems are designed to operate in parallel with and interconnected with the electric utility grid and commonly used in urban setting where a utility electric grid exists.  This allows the AC power produced by the solar 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. At night and during other periods when the electrical loads are greater than the PV system output, the balance of power required by the loads is received from the electric utility. Due to utility’s safety requirement all grid-connected PV systems are designed to shut down when the utility grid is down. 

Stand-Alone / off-grid Photovoltaic Systems

Stand-alone PV systems are designed to operate independent of the electric utility grid, and are generally used in remote areas where a utility grid is non-existence. These types of systems may be powered by a PV array alone, or may use wind, gas or a diesel generator 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. When these type of solar PV systems need to provide power in the night some kind of energy storage is used. Energy storage store the energy produced by the solar PV system during day time and deliver the stored energy to the load in the night. Depending on the amount energy need to be stored batteries, flywheels, compressed air, pumped hydro are used to store the energy. Currently batteries are the most commonly used storage technology. 

Grid-interactive solar PV system

This type of system is becoming extremely popular for homeowners and small businesses where a critical backup power supply is required for critical loads such as refrigeration, water pumps, lighting and other necessities. Under normal circumstances, the system operates in grid-connected mode, serving the on-site loads or sending excess power back onto the grid while keeping the battery fully charged. In the event the grid becomes de-energized, control circuitry disconnects the solar PV system from the utility grid, and solar PV system continue to operates to provide electricity to the selected dedicated loads. During night stored energy in the batteries provides electricity to the selected dedicated loads. Wind, gas and diesel generators can also be connected to this type of solar PV system and making every property with grid interactive solar PV system a Nano grid.