CHAPTER ONE

INTRODUCTION

1.1       Background of study

A power inverter, or inverter, is an electronic device or circuitry that changes direct current (DC) to alternating current (AC). (The Authoritative, 2000). The input voltage, output voltage and frequency, and overall power handling depend on the design of the specific device or circuitry. The inverter does not produce any power; the power is provided by the DC source. A power inverter can be entirely electronic or may be a combination of mechanical effects (such as a rotary apparatus) and electronic circuitry. Static inverters do not use moving parts in the conversion process. (Power Inverter, 2014)

A solar inverter, or PV inverter, converts the variable direct current (DC) output of a photovoltaic (PV) solar panel into a utility frequency alternating current (AC) that can be fed into a commercial electrical grid or used by a local, off-grid electrical network. It is a critical balance of system (BOS) –component in a photovoltaic system, allowing the use of ordinary AC-powered equipment. Solar inverters have special functions adapted for use with photovoltaic arrays, including maximum power point tracking and anti-islanding protection. (Solar Inverter, 2014).

The solar inverter is a critical component in a solar energy system. It performs the conversion of the variable DC output of the Photovoltaic (PV) module(s) into a clean sinusoidal 50 or 60 Hz AC current that is then applied directly to the commercial electrical grid or to a local, off-grid electrical network. A solar cell (also called photovoltaic cell) is the smallest solid-state device that converts the energy of sunlight directly into electricity through the photovoltaic effect. A Photovoltaic (PV) module is an assembly of cells in series or parallel to enlarge or increase voltage and/or current. A Panel is an assembly of modules on a structure. An Array is an assembly of panels at a site. Typically, communications capability is included so users can monitor the inverter and report on power and operating conditions, provide firmware updates and control the inverter grid connection.

At the heart of the inverter is a real-time microcontroller. The controller executes the very precise algorithms required to invert the DC voltage generated by the solar module into AC. This controller is programmed to perform the control loops necessary for all the power management functions necessary including DC/DC and DC/AC. The controller also maximizes the power output from the PV through complex algorithms called maximum power point tracking (MPPT). The PV maximum output power is dependent on the operating conditions and varies from moment to moment due to temperature, shading, soilage, cloud cover, and time of day so adjusting for this maximum power point is a continuous process. For systems with battery energy storage, the controller can control the charging as well as switch over to battery power once the sun sets or cloud cover reduces the PV output power. (Aditee P. Bapat et al 2013).

Power electronic systems are used widely to convert electric energy from one form to the other using electronic devices. Four basic power electronics functions are AC to DC conversion, DC to AC conversion, DC to DC conversion and AC to AC conversion. These basic functions are used to build power supplies, DC transmission systems, electric drives and others. In today’s scenario the demand of electricity has increased tremendously. The cause of it is increase in population day by day, economic development of a country and diminution of fossil based fuels. So alternative energy sources i.e. renewable energy sources are the best option without any harm to the nature. With the advancement in technology in the field of power electronics more than past few years and rising crises for energy have led to increase progress in generating power using renewable energy sources like Photovoltaic (PV), Wind, Fuel cell (FC) based renewable energy technologies. Among all renewable energy sources, solar photovoltaic (PV) electricity generation is the fastest growing source now are days throughout the world. In a PV system, a PV array converts solar power to electrical power and a grid connected inverter is required for inverting the electrical power to ac power then it is fed back to the grid. The power electronics device which converts DC power to AC power at required output voltage and frequency level is known as inverter. According to the Authoritative Dictionary of IEEE Standards Terms (2000), inverter is an electrical power converter that changes direct current (DC) to alternating current (AC). The converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits.

This project work involves the design and construction a 1kVA mobile solar power inverter system.

1.2       Statement of the problem

Uninterruptible power supply units are common electrical items found in most private and industrial buildings in Nigeria as a result of the never-stable and not-always-available power supply situation in the country. However, these units have not provided the much desired reliable, efficient and effective power supply delivery to their owners because these not-very-intelligent units do not, most of the time, get energy to recharge their built-in batteries.

Power failure is the total loss of utility power. It may be caused by the tripping of a circuit breaker, power distribution failure, excessive demand on the power grid, effect of object on the power transmission line can cause the circuit breaker in charge to trip. In order to avoid this inconsistence, supply of electric power another means of generating electric power from other sources of energy such as solar energy can be employed and this why a Modified sine wave inverter is needed for the conversion of chemical energy into electrical energy and solar panel is needed for the conversion of solar energy into electrical energy.

If there is one factor that has perpetually maintained the status of Nigeria as a less developed country, it is its electricity sector. Till date, many households and businesses cannot be guaranteed of 24 hours supply of electricity from the public grid. At this stage of Nigeria’s social and economic development, the country cannot deliver adequate energy to the citizens despite huge financial resources that have been expended in the sector.

Rather, Nigerians have continued to rely on electricity generators for their power supply, fuel marketers are taking significant portion of households’ and businesses’ incomes to supply power, noise pollution from regular humming generators have become integral part of living for many Nigerians with imaginable consequences on their health. Because of these problems, there is a need to design and construct the solar panel inverter which will complement the electricity supply from the public grid. It is less noisy and does not have any consequence(s) on human health. (Lookman Oshodi 2014)

Hence, there is a need to design and implement a power inverter system that gets energy to recharge its built-in battery from solar energy that is relative cheap and available.

1.3      Aim and Objectives

Aim

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

Objectives

The objectives of this project are;

1.      To provide efficiency, steadiness in the use of power appliances, by ensuring continuous availability of power supply even in the absence of mains.

2.      To eliminate all suspense from mains outage during the execution of an important and urgent assignment as may be required.

3.      To design a simple and rugged technology; this will utilize the appropriate use of home or local electrical appliances.

1.4       Significance of Study

Human needs are numerous and the resources to satisfy these needs are limited and in most cases scarce. Hence, there is a need to maximize these limited resources and to minimize waste of these resources to the barest minimum. Energy (power) is one of those limited resources that man needs to satisfy his numerous needs. The 1kVA mobile solar power inverter system seeks to provide a means to adequately, harness the potentials of solar energy for power (energy) generation for domestic usage.

The solar inverter is the second most important (and second most expensive) component of a solar

PV system. It’s important because it converts the raw Direct Current (DC) solar power that is produced by your solar panels into Alternating Current (AC) power that comes out of the wall sockets. Inverters also have technology that maximizes the power output of that DC energy.

The use of solar power has many advantages. First, the energy from the sun is free and readily accessible in most parts of the world. Moreover, the sun will keep shining until the world's end.

Also, silicon from which most photovoltaic cells are made is an abundant and nontoxic element

(the second most abundant material in the earth's crust).

Second, the whole energy conversion process is environmentally friendly. It produces no noise, harmful emissions or polluting gases. The burning of natural resources for energy can create smoke, cause acid rain and pollute water and air. Carbon dioxide, CO2, a leading greenhouse gas, is also produced in the case of burning fuels. Solar power uses only the power of the sun as its fuel. It creates no harmful by-product and contributes actively to the reduction of global warming.

1.5       Scope of Study

The mobile solar power inverter system would be built around a 1kVA power inverter whose output is controlled by an embedded microcontroller in relation to the battery voltage level. At the heart of this design, the microcontroller, PIC16F876A, with associated circuitry would be used for the control of the harvesting of solar energy (MPPT) and charging of the battery. The design of the mobile solar power inverter system would be implemented to have one sole source of energy, solar energy, available to charge the built-in battery of the inverter system.

1.6    Inverters

The inverter takes DC power from the charged battery bank and converts it to AC power for the typical household lights and appliances.  Once the number of watt-hours required for a day is determined, the peak loads need to be ascertained to properly size the inverter.  This is the amount of watts used based on all appliances and loads that will be running at one time.  A water pump and washing machine motor is an example of what may be the peak load requirements.  A 1/2 HP (horse power) pump and washing machine will use about 1875 (adjusted) watts per hour.  If this represents the total peak loads, an inverter that will be able to supply at least 1875 watts of continuous power from the battery bank; say one in the 1000 watt range will be needed.  It's a good idea to start out the system with the size of inverter you plan to grow into, as upgrading to newer, larger models is costly. (Pure Energies 2014) There are two basic types of inverters.

1.6.1 Central Inverters

Central inverters are well-tested and reliable systems that have been around for decades. These are the most common types of inverters. With central inverters, every solar panel is wired in a “string” to the inverter box. The conversion from DC to AC occurs at one central location, such as a garage.

Because the solar panels are wired in “series,” each panel’s power output depends on all of the panels working. For example, In a string of Christmas tree lights. If one bulb goes out, the whole string of lights go out until the bad bulb is replaced. So, if shade from a tree covers one panel, it can seriously diminish the power produced by the whole solar system until the shade clears. This is why an accurate shade analysis is so important.

1.6.2 Micro Inverters

Micro inverters are relatively new to solar. Instead of converting the DC to AC power at a central location, micro inverters are installed right under each solar panel. The main advantage to micro inverters is the ability for each solar panel to transmit power into the house. In other words, each panel produces its own solar power and keeps producing out solar watts regardless of what happening to the panel beside it. The down side of micro inverters is that they can be more expensive and take more labour cost to replace each inverter. Also, because they are so new, micro inverter reliability is unproven outside of lab testing. (Pure Energies 2014)

1.7 The BOS (Balance of System)

There are many other less well known and less expensive parts to a solar system. Installers typically wrap these up into “The BOS” or “Balance of System.”

The balance of system includes components such as wiring, emergency DC disconnects, system monitoring hardware, the frames or “racking” that holds your panels to the roof and at the right angle, nuts, bolts, roof “flashing” to prevent leaks, and more. (Pure Energies 2014)

1.8    Solar Panels

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