CHAPTER ONE

INTRODUCTION

1.1 Background of the Study

A power inverter, also referred to as an inverter, is an electronic device or circuit designed to convert direct current (DC) into alternating current (AC) (The Authoritative, 2000). The input voltage, output voltage, operating frequency, and overall power capacity of an inverter depend on the design specifications of the particular device or circuit. An inverter does not generate electrical energy independently; rather, it converts the energy supplied by a DC source into a different electrical form. An inverter may be constructed entirely from electronic components or designed by combining mechanical systems, such as rotary equipment, with electronic circuitry. Static inverters, however, accomplish the conversion process without the use of moving mechanical parts (Power Inverter, 2014).

A solar inverter, also known as a photovoltaic (PV) inverter, is a device that converts the variable direct current produced by photovoltaic solar panels into alternating current at the required utility frequency. The resulting AC power can be supplied to the public electricity grid or used within a local electrical network that operates independently of the grid. The solar inverter is an essential balance-of-system (BOS) component of a photovoltaic installation because it enables conventional AC-powered appliances and equipment to operate using solar-generated electricity. Solar inverters also incorporate functions specifically designed for photovoltaic systems, including maximum power point tracking and anti-islanding protection (Solar Inverter, 2014).

The solar inverter is one of the most important components of a solar energy installation. Its primary function is to transform the variable DC output generated by photovoltaic modules into a suitable sinusoidal AC waveform at a frequency of 50 or 60 Hz. The converted electricity can then be supplied to the commercial electricity grid or used by an independent, off-grid electrical system.

A solar cell, also referred to as a photovoltaic cell, is a solid-state device that converts sunlight directly into electrical energy through the photovoltaic effect. A photovoltaic module consists of several interconnected solar cells arranged in series or parallel to obtain the required voltage and current. A solar panel is an arrangement of modules mounted on a supporting structure, while a solar array consists of several panels installed together at a particular location. Modern solar inverters may also include communication facilities that allow users to monitor operating conditions and energy output, receive performance reports, install firmware updates, and manage the inverter's connection to the electricity grid.

At the centre of an inverter's control system is a real-time microcontroller responsible for executing the precise algorithms needed to convert the DC voltage generated by the solar modules into AC power. The controller is programmed to manage the control loops required for power conversion and energy management, including DC-to-DC and DC-to-AC conversion. It also helps maximize the power obtained from the photovoltaic array through a technique known as maximum power point tracking (MPPT).

The maximum power available from a photovoltaic system changes continuously in response to environmental and operating conditions. Factors such as temperature, shading, dirt accumulation, cloud cover, and the time of day affect the amount of electrical power that the solar panels can deliver. Consequently, the controller must continuously adjust the operating conditions of the photovoltaic system to obtain the highest possible power output. In systems equipped with battery storage, the controller may also regulate battery charging and manage the transition to battery power when sunlight becomes unavailable or cloud cover reduces the output of the solar panels (Aditee P. Bapat et al., 2013).

Power electronic systems are widely applied in the conversion of electrical energy from one form to another through the use of electronic switching devices. The four fundamental functions of power electronics are AC-to-DC conversion, DC-to-AC conversion, DC-to-DC conversion, and AC-to-AC conversion. These functions form the basis of several electrical applications, including power supplies, direct-current transmission systems, and electric drives.

In recent years, the demand for electricity has increased significantly because of population growth, economic development, and the declining availability of conventional fossil-based energy resources. These challenges have strengthened the need to explore alternative energy sources, particularly renewable sources that can provide electricity with minimal environmental harm. Advances in power electronics technology, combined with increasing energy shortages, have accelerated the development of electricity generation systems based on renewable sources such as photovoltaic solar energy, wind energy, and fuel cells.

Among the various renewable energy technologies, solar photovoltaic electricity generation has experienced rapid growth worldwide. In a photovoltaic installation, the solar array converts sunlight into electrical energy, while an inverter converts the resulting DC power into AC electricity. In grid-connected systems, the converted electricity can be supplied to the public grid, subject to the system's design and applicable requirements. An inverter is therefore an electrical power conversion device that changes direct current into alternating current at the required voltage and frequency. According to the Authoritative Dictionary of IEEE Standards Terms (2000), an inverter is an electrical power converter that transforms DC into AC. Appropriate transformers, switching components, and control circuits can be incorporated to obtain the desired output voltage and frequency.

Against this background, this project focuses on the design and construction of a 1 kVA mobile solar power inverter system intended to provide an alternative source of electrical power for domestic applications.

1.2 Statement of the Problem

Uninterruptible power supply (UPS) systems are commonly installed in private residences, commercial establishments, and industrial buildings in Nigeria because of the irregular and unreliable nature of public electricity supply. However, these systems have not always provided the level of reliability, efficiency, and continuity expected by their users. One major challenge is that their internal batteries may not receive sufficient charging when public electricity is unavailable for extended periods. Consequently, the systems may be unable to provide backup power when it is needed most.

A power outage occurs when electricity from the public utility supply is interrupted completely. Such interruptions may result from circuit breaker tripping, failures within the electricity distribution network, excessive demand on the power grid, or objects interfering with transmission lines and causing protective equipment to disconnect the supply. To reduce dependence on an unreliable electricity source, alternative methods of generating electrical power must be considered. Solar energy provides one possible solution because it can be converted into electricity through photovoltaic panels. The electrical energy can then be stored in batteries and supplied to an inverter, which converts DC power into AC power for operating electrical appliances. A modified sine-wave inverter may be used for this purpose where its output waveform is appropriate for the intended loads.

Electricity supply has remained a major obstacle to Nigeria's social and economic development. Despite the substantial financial resources invested in the electricity sector, many households and businesses still cannot depend on the public grid for a continuous 24-hour supply. The country's electricity infrastructure has therefore struggled to provide sufficient and reliable energy to meet the needs of its population and growing economy.

As a result, many Nigerians depend on privately owned electricity generators to meet their power requirements. The cost of purchasing fuel places additional financial pressure on households and businesses, while the continuous operation of generators produces noise pollution and exhaust emissions. These conditions can affect people's comfort, the environment, and public health. The challenges associated with conventional backup power sources have created a need for alternative electricity systems that are quieter and less polluting. A solar-powered inverter system can complement electricity from the public grid by providing backup power without the noise and direct exhaust emissions associated with fuel-powered generators (Lookman Oshodi, 2014).

There is therefore a need to design and construct an inverter system capable of using solar energy to recharge its built-in battery. Solar energy is a renewable resource that is readily available in many locations, making it a potential source of electricity for reducing dependence on the public grid. A mobile solar power inverter system could help address the problems associated with unreliable electricity supply by providing stored electrical energy for use when the main supply is unavailable.

1.3 Aim and Objectives

Aim

The main aim of this project is to design and construct a 1 kVA mobile solar power inverter system.

Objectives

The specific objectives of the project are:

1. To improve the reliability and stability of the power supplied to electrical appliances by ensuring that electricity remains available when the public mains supply is interrupted.

2. To reduce the uncertainty and disruption caused by unexpected electricity outages, particularly during the completion of important and urgent tasks.

3. To develop a simple, durable, and practical technology suitable for powering appropriate household and locally available electrical appliances.

1.4 Significance of the Study

Human needs are extensive, whereas the resources available to meet them are limited and, in many cases, scarce. It is therefore necessary to use available resources efficiently and minimize unnecessary waste. Energy is one of the essential resources required to satisfy numerous human needs, including domestic, commercial, and industrial activities. The proposed 1 kVA mobile solar power inverter system seeks to provide a practical means of harnessing solar energy for electricity generation, particularly for domestic use.

The solar inverter is one of the major and relatively expensive components of a photovoltaic system. Its importance lies in its ability to convert the direct current generated by solar panels into alternating current suitable for use by conventional electrical appliances connected to standard AC outlets. Inverters may also incorporate control technologies that help optimize the amount of usable electrical power obtained from the DC energy generated by the solar panels.

Solar energy offers several advantages. First, sunlight is a renewable energy resource that is freely available in many parts of the world. Unlike fossil fuels, solar energy does not require the continuous purchase and combustion of fuel to generate electricity. The sun will continue to provide energy over an extremely long period, making solar power a valuable resource for sustainable electricity generation.

Furthermore, silicon, which is used in the manufacture of many photovoltaic cells, is an abundant and relatively nontoxic material. Silicon is the second most abundant element in the Earth's crust, making it an important material in the development of solar technologies.

Another major advantage of solar power is its relatively low environmental impact during electricity generation. Solar panels generate electricity without producing combustion-related noise, smoke, or exhaust gases during normal operation. In contrast, burning fossil fuels can release pollutants that contaminate the air and contribute to acid rain and other environmental problems. Fuel combustion also produces carbon dioxide, a major greenhouse gas associated with global warming. By using sunlight as its primary energy source, a solar power system can reduce dependence on fossil fuels and help limit the environmental effects associated with conventional electricity generation.

Consequently, the design and construction of a 1 kVA mobile solar power inverter system are significant because the system can provide an alternative source of electrical energy, reduce dependence on the public electricity grid, and offer a quieter and cleaner option for supplying power to suitable household appliances.

1.5 Scope of the Study

The project involves the development of a mobile solar power inverter system built around a 1 kVA inverter. The inverter's operation will be controlled by an embedded microcontroller in response to the battery voltage level. A PIC16F876A microcontroller, together with its associated electronic circuitry, will form the central control unit of the proposed system.

The control arrangement is intended to manage solar energy harvesting through maximum power point tracking (MPPT) and regulate the charging of the battery. The system is designed to use solar energy as its sole intended charging source for the inverter's built-in battery. The scope of the project therefore covers the design and construction of the inverter system, its solar charging arrangement, the microcontroller-based control system, and the provision of AC power from the stored battery energy.

1.6 Inverters

An inverter draws direct-current electricity from a charged battery bank and converts it into alternating-current electricity for operating household lighting and other compatible electrical appliances. Before selecting an inverter, it is necessary to determine the total energy required over a typical day and identify the highest combined power demand of the appliances expected to operate simultaneously. This highest demand is known as the peak load.

For example, electrical appliances containing motors, such as water pumps and washing machines, may have substantial power requirements, particularly during startup. If the combined peak load of the appliances is estimated to be 1,875 watts, the inverter must be capable of supplying that demand continuously and handling any additional startup surge required by the connected equipment. An inverter rated at 1,000 watts would not be adequate for a continuous load of 1,875 watts. Therefore, the inverter rating must be selected based on the actual load requirements, including suitable allowances for starting currents and conversion losses.

It is also useful to consider possible future increases in electricity demand when selecting an inverter. Choosing an appropriately sized system at the planning stage may help avoid the additional expense of replacing an undersized inverter later (Pure Energies, 2014).

There are two basic types of solar inverters commonly discussed in relation to photovoltaic installations: central inverters and microinverters.

1.6.1 Central Inverters

Central inverters are established and widely used systems with a long history of application in solar power installations. They are among the most common inverter types. In a central inverter arrangement, multiple solar panels are connected in a series configuration known as a string, and the string is connected to a central inverter. The conversion of DC electricity into AC electricity takes place at a single location, which may be situated in a garage or another suitable area.

Because the panels in a string are connected in series, the performance of the overall string can be affected when one or more panels experience reduced output. For instance, if a tree casts a shadow over one panel, the power produced by the string may decrease, depending on the system configuration and the availability of bypass diodes and other protective features. This situation resembles a string of Christmas lights in which a faulty bulb may affect the operation of the entire string. Consequently, assessing the amount and movement of shade at a proposed installation site is important when designing a photovoltaic system. Accurate shade analysis helps determine the best panel placement and reduces avoidable losses in electricity generation (Pure Energies, 2014).

1.6.2 Microinverters

Microinverters are an alternative to conventional central inverter systems. Rather than converting DC electricity from several panels at one central location, microinverters are typically installed beneath or near individual solar panels. Each microinverter converts the DC output of its associated panel into AC electricity.

One of the main advantages of microinverters is that each panel can operate more independently of the others. If one panel experiences shading or a reduction in output, the remaining panels can continue producing electricity according to their own operating conditions. This arrangement can improve the overall energy yield of a solar installation where shading affects panels differently.

However, microinverters may increase the initial cost of an installation because a separate inverter is required for each panel. Their replacement and maintenance may also involve additional labour, particularly when the units are installed in difficult-to-access locations. Their reliability depends on the quality of the equipment, installation practices, environmental conditions, and operating history. The selection between central inverters and microinverters should therefore consider cost, installation requirements, expected performance, maintenance, and the conditions at the installation site (Pure Energies, 2014).

1.7 The BOS (Balance of System)

A solar power installation contains several components apart from the solar panels and the main inverter. These supporting components are collectively described as the balance of system (BOS). Although many of these components are less prominent and individually less expensive than the inverter or solar panels, they are essential to the safe and effective operation of the installation.

The balance of system includes electrical wiring, DC disconnect switches, monitoring equipment, mounting frames or racking systems, fasteners such as nuts and bolts, and roof-flashing materials used to prevent water leakage where panels are installed on rooftops. Depending on the system design, the BOS may also include protective devices, connectors, and other equipment required for installation, monitoring, maintenance, and safe operation.

These components provide the necessary electrical connections, mechanical support, protection, and monitoring functions that enable the solar installation to operate effectively. Proper selection and installation of BOS components are therefore important for system safety, reliability, and performance (Pure Energies, 2014).

1.8 Solar Panels

Solar panels can be used to charge batteries in solar power systems. They provide a useful solution for individuals who want to reduce dependence on conventional electricity sources, including those undertaking extended camping trips or travelling through remote locations where public electricity is unavailable. Solar panels are manufactured in different voltage and power ratings to meet various energy requirements.

More than one solar panel can be connected in parallel to increase the total current available from the arrangement while maintaining approximately the same voltage. When combining panels, it is generally advisable to use panels with compatible electrical characteristics. Where identical panels are connected under similar environmental conditions, they can be arranged to operate efficiently within the system's intended operating range. Combining panels with different electrical characteristics may create mismatches that reduce overall system efficiency or make it more difficult to obtain the best operating point for every panel. Although mixed-panel arrangements can operate, their configuration must be considered carefully to avoid unnecessary power losses.

1.8.1 Polycrystalline and Monocrystalline Solar Panels

Silicon-based solar panels are commonly manufactured using two principal cell technologies: polycrystalline silicon and monocrystalline silicon. Although both technologies convert sunlight into electricity, they differ in their manufacturing processes, cost, efficiency, and temperature-related performance.

Monocrystalline solar cells are manufactured from single-crystal silicon. They have traditionally been associated with higher conversion efficiencies and may cost more to manufacture because of the processes involved in producing the silicon material. Polycrystalline solar cells are produced from silicon containing multiple crystal structures and have traditionally offered a lower-cost alternative, although their efficiency has generally been somewhat lower.

The manufacturing energy requirements and environmental implications of these technologies can vary depending on the production methods and materials used. Their performance under elevated temperatures also differs according to the specific panel design and its temperature coefficient. A panel with a more favourable temperature coefficient experiences a smaller reduction in output as its temperature rises.

The differences between monocrystalline and polycrystalline panels depend on the particular products being compared. Therefore, the selection of a solar panel should not be based exclusively on whether it is monocrystalline or polycrystalline. Other important considerations include conversion efficiency, temperature coefficient, rated power output, available installation space, cost, durability, and compatibility with the charge controller and battery system. Selecting a panel with suitable electrical characteristics and reliable performance is more important than relying solely on the cell technology.