Understanding the Generation of Solar Photovoltaic (PV) Systems

The process of converting solar energy into electricity using solar panels is known as solar photovoltaic (PV) power generation. A PV system is made up of arrays of solar panels, also known as PV panels. PV systems can be grid-connected or off-grid (stand-alone).

Solar panels, combiner boxes, power inverters, optimizers, and disconnects are the fundamental components of these two PV system configurations. Meters, batteries, charge controllers, and battery disconnects may be included in grid-connected PV systems. Solar PV power generation has several benefits and drawbacks (see Table 1).

Advantages	Disadvantages
In many parts of the country, sunlight is free and easily accessible.	The initial cost of PV systems is high.
PV systems emit no harmful gases, greenhouse gases, or noise.	For electricity generation, PV systems require a large surface area.
There are no moving parts in PV systems.	The amount of sunlight that falls on the ground can vary.
PV systems help to reduce reliance on petroleum.	When PV systems cannot provide full capacity, they require additional energy storage or access to other sources, such as the utility grid.
PV systems can generate electricity in remote areas that aren’t connected to the grid.
Electric bills can be reduced by grid-connected PV systems.

Grid-Connected PV Systems

Grid-connected PV systems are more common because they are easier to design and typically less expensive than off-grid PV systems that rely on batteries. Grid-connected PV systems enable homeowners to consume less power from the grid while supplying unused or excess power back to the utility grid (see Figure 2).

The system configuration and size are determined by the system’s application. Residential grid-connected PV systems, for example, are rated less than 20 kW, commercial systems are rated from 20 kW to 1MW, and utility energy-storage systems are rated greater than 1MW.

Figure 2. A grid-connected PV system with no battery backup is a common PV system configuration.

Off-Grid (Stand-Alone) PV Systems

Off-grid (stand-alone) PV systems use solar panel arrays to charge banks of rechargeable batteries during the day for use at night when solar energy is unavailable.

Reduced energy costs and power outages, production of clean energy, and energy independence are all reasons to use an off-grid PV system. Battery banks, power inverters, charge controllers, battery disconnects, and optional generators are all components of off-grid PV systems.

Solar Panels

Solar panels, which are commonly used in PV systems, are assemblies of solar cells that are typically made of silicon and mounted in a rigid flat frame. Strings are formed by connecting solar panels in series, and arrays are formed by connecting solar panels in parallel. The amount of direct current (DC) produced by solar panels is rated. Solar panels should be inspected on a regular basis to remove dirt, debris, or snow and to ensure that electrical connections are in good working order.

Since photovoltaics are harmed by shade, any shadow can significantly reduce a solar panel’s power output. A solar panel’s performance varies, but in most cases, the guaranteed power output life expectancy ranges between 10 and 25 years. Watts are units of measurement for solar panel power output. In ideal sunlight and temperature conditions, power output ratings range from 200 W to 350 W.

Solar Arrays Construction and Mounting

Solar arrays must be installed at an angle to receive the most sunlight when they are installed on a property. Roof, freestanding, and directional tracking mounts are common types of solar array mounts. Roof-mounted solar arrays can blend in with a home’s architecture and save yard space.

Figure 4: Roof, freestanding, and directional tracking mounts on the roof or on the ground are common solar array mounts. Greensarawak provided the image.

Roof-mounted solar arrays are attached to the roof rafters and are designed to withstand the same forces and weather conditions as the roof. Composition shingles are widely regarded as the easiest roofing materials to install solar arrays on, whereas slate and tile roofing materials are widely regarded as the most difficult. The main disadvantage of roof-mounted solar arrays is that they require maintenance access.

Freestanding solar arrays can be placed at convenient heights for maintenance. Freestanding solar arrays, on the other hand, typically require a lot of space. Furthermore, freestanding solar arrays should not be installed on the ground in snowy areas.

Fixed and tracking solar array mounts are also available. Fixed solar arrays, which are frequently roof-mounted or freestanding, are fixed in height and angle and do not move with the sun. Solar arrays that track the sun from east to west adjust their angle to maintain maximum exposure as the sun moves.

Solar arrays with directional tracking can boost a PV system’s daily energy output by 25% to 40%. However, despite the increased power output, the complexity of the mounting system may not justify the higher cost of directional tracking arrays.

PV Combiner Boxes

A PV combiner box collects the output of multiple solar panel strings and consolidates it into a single main power feed that connects to an inverter. PV combiner boxes are typically placed near solar panels and before inverters. PV combiner boxes can include overcurrent and surge protection, as well as pre-wired fuse holders and pre-configured connectors for easy installation to the inverter. Pre-wired connectors eliminate the need to run wires to the inverter. PV combiner boxes should be checked for leaks and loose connections on a regular basis.

PV combiner boxes are not always required for PV system installations. A combiner box, for example, may not be necessary if there are only two or three strings of solar panels. Solar panel strings are directly connected to the inverter in these cases.

PV Inverters

An inverter is a device that converts direct current (DC) to alternating current (AC). PV inverters perform three basic functions: they convert DC power from PV panels to alternating current power, they ensure that the alternating current frequency produced remains constant at 60 cycles per second, and they minimize voltage fluctuations. Micro-inverters, string inverters, and power optimizers are the most popular ac inverters.

Figure 5. Microinverters are connected to each solar panel in parallel and convert DC to AC directly. String inverters are used in conjunction with a series of solar panels. Each solar panel, which is connected in parallel, has a power optimizer installed. LetsGoSolar provided the image.

A microinverter is a device that converts direct current (DC) power to alternating current (AC) power and is directly mounted to individual solar panels. Microinverters maximize a system’s potential output because DC to AC conversion occurs at each solar panel. For example, if one solar panel is shaded by a tree, the output of the remaining solar panels will not be affected. Microinverters also eliminate the need for high-voltage DC wiring, which can be dangerous.

A string inverter is a device that converts DC power from a series of solar panels to AC power. In a series configuration, however, if one of the solar panels stops producing electricity, even if only temporarily due to shading, the overall system performance suffers. String inverters operate at high voltages (600V to 1000V) and are used in large PV systems with no shading concerns. In most cases, only one string inverter is required for a residential application.

Instead of converting the DC power from the solar panels directly into AC power, a power optimizer (maximizer) is a hybrid microinverter system that conditions the DC power before sending it to a centralized inverter. When one or more panels are shaded or when panels are installed facing different directions, power optimizers, such as microinverters, continue to perform well. Power optimizer systems are more expensive than string inverter systems but less expensive than microinverter systems.

PV Disconnects

Safety disconnects, both automatic and manual, protect the wiring and components of PV systems from power surges and other equipment malfunctions. Disconnects allow the PV system to be safely turned off and system components to be removed for maintenance or repair. Safety disconnects in grid-connected PV systems ensure that the generating equipment is isolated from the grid for the safety of utility personnel.

Each power source or energy storage device in the PV system requires a disconnect. Typically, an AC disconnect is installed inside the home before the main electrical panel. Utilities frequently require an exterior AC disconnect that is lockable and mounted next to the utility meter so that utility personnel can access it.