SOLAR POWER INVERTERS, ANALYSIS AND TEST EVALUATION

CHAPTER ONE

1. INTRODUCTION

The quest to satisfy our need for stable power supply in Nigeria has driven most Nigerians into an ardent search for alternative renewable power sources. One of such major renewable power source in use is solar energy, which is energy obtained from the radiation of the sun.

To obtain electrical power from the sun, four key components are required to effectively and efficiently convert the sun’s radiation energy. These four key components include:

• A solar energy-conversion system  (Solar PV modules or array)
• A regulation system (Charge controllers)
• Electrical energy storage media (Batteries)
• DC-AC conversion system (Inverters)

 Fig 1.1: Simple diagram of a house hold Solar Power System[85]

Fig. 1.1 above gives the diagrammatic description of a solar power system. As can be seen from the diagram, radiant energy from the sun striking the solar panels is converted into DC voltage which is fed into a battery through a charge controller. The electrical energy stored in the battery is then converted from DC to AC, and stepped up to the voltage level required for the operation of house hold electrical equipment.

It is important to note that to efficiently and effectively convert the DC electrical energy from solar PV modules into AC quantity, an inverter must be incorporated into the system. The area of contention, as regards to this project report is in the area of selection of the most efficient and cheap solar inverter.  Knowing how efficient an inverter will be can only be determined through usage and/or testing of the inverter in question, and further analyzing the results obtained, in order to compare them with that of an ideal inverter. This whole idea gave birth to the topic of this project “Solar power inverters, analysis and test Evaluation”

It is our belief that an inverter whose characteristics is close to that of an ideal inverter can be regarded as a good inverter, while that whose characteristics is far from an ideal inverter can be regarded as inefficient.

As mentioned before electricity crises is a major problem in the present era. This problem is even more critical for a densely populated poverty corrupted developing third world country like Nigeria. A lot of people live here without the basic facility of electricity. Daily, electricity crises and price is increasing whereas no other solution is left for us without using the solar power or diesel turbine to generate electricity in remote areas which seems to be very expensive to run. Again, not only do we face electricity crisis but also, the cost of gas and other natural resources like fuel, diesel , petroleum etc. is on the increase, beyond the reach of the general populace. To this effect, a system capable of not only reducing the electricity crisis but also the need for petroleum or other natural resources used in energy generation is therefore the desired choice in Nigeria today.

Presently, the demand for solar power generating system is on the increase, as the world today is seeking better sources of electricity lees capable of causing damage to the environment.  

1.1 Statement of problem

            This report will have no understandable meaning or importance without it being able to present solutions to some of the problems posed while embarking in a solar power installation project, as well as provide answers to some of the questions commonly asked by electrical engineering students when faced with solar power system installation. To this effect, the problems/questions listed below follows. 

• How do we determine the best type of inverters from a selection provided in today’s market?
• How do we determine the best type of batteries required for a particular solar power system installation?
• What process(es) is/are required for the determination of the actual operating characteristics/properties of an inverter, when given an inverter whose operating characteristics are not given?
• How do we carry out a troubleshooting operation for a faulty inverter?
• How do we know the amount of distortion introduced into the output of an inverter by the presence of harmonics?
  1. Aims and objectives of this study

The aim of this study is to provide a platform for carrying out standard basic tests and analysis on solar inverters for electrical/electronic engineering students/instructors, as well as provide a foundation for carrying out standard comparison between inverter brands.

The objectives of this study thus follow:

• To provide a platform for the selection of the best type of inverters from an available market selection.
• To provide a means for the determination of the best type of batteries required for a particular solar power system installation
• To provide a standard list(s) of tests required for determination of the basic operating characteristics of solar inverters.
• To provide an encyclopedia of information on solar power system for students who wish to major in the field of solar power system installation
• To familiarize electrical/electronics engineering students with the solar power installation and harvesting process.
  1. Study methodology

Within a four week period, various tests were carried out on two inverter brands. The results obtained from these tests were recorded on a record sheet in a tabular form, graphs were plotted with the information recorded, and comparisons were made based on the graphs obtained.

            The brands of inverters tested were the famous blue gate inverters and luminous inverter technologies.  The tests carried out were repeated severally to obtain correct values. Basic tests carried out include:

• Variable load test
• Constant load over time
• Idle test
• Night time power consumption

Generally, all tests were grouped into:

• Test for input characteristics
• Test for output characteristics
• Protection test and other special tests.

The wave form of both inverters were also observed on an oscilloscope, and comparisons were made and recorded in chapter five (5) of this report. The harmonic distortions were observed but not measured.

1. Limitations of the study

Within the course of this project, certain problems/constraints were encountered. Some of these problems/constraints encountered marginalized the area under study while others prevented the complete carrying out of certain tests/test procedures. Some of these problems include:

• Poor state of equipment; some analogue measuring equipment like the high range ammeter available was improperly damped, making it almost impossible to read instantaneous values of current.
• There was a shortage in the availability of high range measuring equipment at the school lab. This restricted tests carried out to lower values. Certain tests had to be attenuated or completely stopped when the values obtained exceeded the deflection of analogue meters, or the range of digital meters.
• Unavailability of certain measuring equipment like the THD analyzer used in the measurement of harmonic distortion. Computer programs like the PV array simulator, required to carry out MPPT performance test was also not available.

• As a result of shortage in certain measuring equipment, the data collected were from various measuring instrument ( analogue, digital), leading to a non-uniform measurement
• Unavailability of standard connecting cables
• The duration for the study, when compared to the volume of work required for completely carrying out the project was limited.
• We also had inadequate financing as at the instant it was required.