Solar PV Systems, Types, Components and Functions for SS 1

Solar PV System

Performance Objectives

By the end of the lesson, students should be able to:

1. explain the meaning and principles of solar PV systems;
2. discuss the types of solar PV systems;
3. identify components in solar PV systems and discuss their function.

Meaning and Principles of Solar PV Systems

A solar photovoltaic (PV) system is an electrical power system designed to capture sunlight and convert it directly into usable electricity using semiconductor materials.

The term “photovoltaic” comes from two words: “photo,” which means light, and “voltaic,” which refers to electricity. Solar PV systems provide a clean, renewable, and sustainable source of energy, making them highly valuable in Nigeria for reducing reliance on fossil fuels and addressing electricity supply challenges.

The operation of a solar PV system is based on the photovoltaic effect. This physical and chemical phenomenon occurs when certain materials produce an electric current when exposed to sunlight. Solar panels are constructed using semiconductor materials, most commonly silicon.

The principle of operation involves the following steps:

1. Sunlight, which is composed of tiny packets of energy called photons, strikes the surface of the solar cells on a solar panel.
2. The semiconductor material absorbs the photons, transferring energy to the electrons within the material.
3. This energy excites the electrons, causing them to break free from their atomic bonds and move freely.
4. The internal structure of the solar cell forces these free electrons to flow in a specific direction, creating an electric current.
5. This flow of electrons produces direct current (DC) electricity, which can then be used immediately, stored in batteries, or converted for household use.

Types of Solar PV Systems

Solar PV systems are configured in different ways depending on how they interact with the public utility grid and whether they store energy for later use. The three main types of solar PV systems are:

1. Grid-tied solar PV systems
2. Off-grid solar PV systems
3. Hybrid solar PV systems

Grid-Tied Solar PV Systems

A grid-tied solar PV system is an electricity generating system that is connected directly to the public utility grid.

This system does not use batteries for energy storage. During the day, the solar panels generate electricity to power household appliances. If the panels produce more electricity than the home requires, the excess power is fed back into the public utility grid. At night or during cloudy periods when the panels cannot generate enough electricity, power is drawn automatically from the utility grid. While cost-effective, a major limitation of this system in areas with unstable power supply is that it shuts down during grid outages to prevent electricity from feeding back into the grid and endangering utility workers.

Off-Grid Solar PV Systems

An off-grid solar PV system is a standalone electricity generating system that operates completely independently of the public utility grid.

Because there is no connection to the utility grid, off-grid systems must rely on battery banks to store excess electricity generated during the day. This stored energy is used to power appliances at night or during periods of low sunlight. Off-grid systems are highly useful in remote, rural, or underserved communities in Nigeria where grid electricity is completely unavailable. These systems must be carefully sized to ensure the solar panels and batteries can meet the daily energy demands of the user.

Hybrid Solar PV Systems

A hybrid solar PV system is an electricity generating system that combines the features of both grid-tied and off-grid systems by connecting to the utility grid and incorporating battery storage.

This system offers the highest level of flexibility and reliability. During normal operation, the system uses solar energy to power loads and charge the batteries. If the batteries are fully charged and the household loads are met, excess electricity can be sent to the grid. In the event of a power outage or load shedding on the utility grid, the hybrid system automatically switches to battery power, ensuring an uninterrupted supply of electricity. This type of system is increasingly popular in Nigerian urban areas due to frequent grid power interruptions.

Components in Solar PV Systems and Their Functions

A functional solar PV system relies on several key components working together to generate, regulate, store, and convert electrical energy. The primary components of a solar PV system are:

1. Solar panels
2. Charge controllers
3. Batteries
4. Inverters

Solar Panels

Solar panels, also known as photovoltaic modules, are devices that capture sunlight and convert it into direct current (DC) electricity.

They are the primary power generation source of the system. A solar panel consists of multiple individual solar cells connected together and protected by a durable glass cover and an aluminium frame. Solar panels are installed on roofs or ground mounts where they can receive maximum sunlight throughout the day.

Charge Controllers

A charge controller is an electronic device that regulates the voltage and current flowing from the solar panels to the battery bank.

Its primary function is to protect the batteries from damage. It prevents overcharging by reducing or stopping the flow of electricity from the panels when the batteries are fully charged. It also prevents deep discharging by disconnecting loads when battery levels are critically low, and it stops reverse current from flowing from the batteries back to the solar panels at night.

Batteries

A solar battery is an energy storage device that stores the DC electricity generated by solar panels in the form of chemical energy.

Batteries are essential for providing power when there is no sunlight, such as at night or during heavy rainfall. Deep-cycle batteries, such as lead-acid or lithium-ion batteries, are specifically designed for solar systems because they can be repeatedly discharged and recharged over a long period without sustaining rapid damage.

Inverters

An inverter is an electrical device that converts direct current (DC) electricity into alternating current (AC) electricity.

Solar panels and batteries operate on DC electricity, but most household appliances in Nigeria—such as televisions, refrigerators, fans, and lighting systems—run on AC electricity. The inverter makes the generated solar power compatible with standard household appliances. In hybrid systems, the inverter also manages the charging of batteries from the grid and controls the flow of power between different sources.

Distinguishing System Components

To ensure proper installation and maintenance, it is important to distinguish between the different components based on their physical characteristics, inputs, outputs, and primary roles within the system.

The table below summarizes the key differences between the major components:

Summary of Component Identification

Identifying these components on an installation site involves observing their physical features and connections:

1. Solar panels are always located outdoors, positioned on roofs or ground racks to face the sun.
2. Charge controllers are usually small wall-mounted boxes with digital screens showing battery voltage and charging status, located indoors near the batteries.
3. Batteries are heavy, block-like units placed in well-ventilated battery racks or boxes.
4. Inverters are larger wall-mounted or floor-standing metal boxes, often featuring cooling fans, status indicator lights, and heavy cable connections.