A MAXIMUM POWERPOINT TRACKING SCHEME FOR STAND-ALONE SOLAR ENERGY BASED POWER SUPPLY

This work is concerned with the features, analysis and design of a stand-alone solar energy based power supply with maximum power point tracking (MPPT) scheme. The features and operations of various types of solar cells and panels and the performance characteristics under varying temperature and irradiance conditions are studied. Subsequently, various methods of maximum solar power point tracking methods are reviewed. From the results of the review of similar works in literature, two most popular maximum power point tracking methods were selected and their detailed operational features were analyzed, designed and the performance characteristics presented. Those methods are the perturbation and observation (P&O) method and the incremental conductance (InCond) method using the Cuks or SEPIC dc to dc converter operating in the discontinuous capacitor voltage mode (DCVM) and/ or discontinuous inductor current mode (DICM). The results of the analysis show that incremental conductance method has superior performance characteristics when compared to the perturbation and observation method. With the incremental conductance method, the problem of sustained oscillation around the maximum power point of the solar panel which is the usual characteristic of the perturbation and observation method is essentially absent. Furthermore, the power available for the load when MPPT is applied is 1.1 kW which gives a tolerance of 0.1% to the load it powers. But without MPPT, the available power is 0.9 kW using the same number of PV panels and batteries. MPPT has 17.65% edge in power delivery over non-MPPT PV powered energy supply. An experimental prototype of a 1kW, 230V, 50Hz stand-alone solar based power supply with the incremental conductance scheme was successfully built and tested. The experimental results agreed with the predicted results.

In this work,a maximum power point tracking Scheme for stand-alone solar energy based power supply is explained, analyzed and implemented. Global climatic change, world-wide increase in energy demand, uncertainty in price and availability of non-renewable energy and world energy policies on using environmental friendly source of energy have made Photovoltaic (PV) systems suitable for energy generation in recent times.

Energy is one of the most basic and essential of all the natural resources given to mankind. Sun is the bedrock of all the energy used in this planet earth due to fission or fusion of atomic nuclei in the sun. Energy released from the sun if properly harnessed will go a long way in ameliorating the world energy problems. Nigeria for instance, receives 5.08 x 1012 kWh of energy per day from the sun and if solar energy appliances with just 5% efficiency are used to cover only 1% of the country's surface area then 2.54 x 106 MWh per day of electrical energy can be obtained from solar energy [1]; this is the basis of this research investigations. Stand-alone photovoltaic power supply system is established as a reliable and economic source of electricity in rural areas, especially in developing countries where the population is dispersed.This is because rural areas have low incomes and the grid power supply is not fully extended to these areas due to viability and financial constraints; or even due to intermittent power supply in areas where grid system is available. It is defined as autonomous systems that supply electricity without being connected to the electric grid.

It is worthy to note that for ages the world energy sources depend on conventional sources such as fossil fuel, hydro, coal, radioactive decay etc. But all these have their peculiar problems of scarcity, rapidly depleting, causes pollution and harmful to both man and other living organisms.

It is in an attempt to solve the above problems, that necessitated this research work, since renewable energy sources are clean, pollution-free, harmless, recyclable, distributed throughout the earth and inexhaustible that makes it a better substitute. Moreover, global climatic change world-wide increase in energy demand, uncertainty in price and availability of non-renewable energy and world energy policies on using environmental friendly source of energy have made PV systems suitable for energy generation in recent time. Similarly, with the cost ofsolarcells decreasing [2-4],the conversion ofsolarenergy toelectrical energy isincreasingly becomingeconomicallyviable. This isparticularly true in aCountry like Nigeriawhere there isabundant solarenergy available throughout the yearwith reserve estimate of 3.5 – 7.0 kW/m 2/day [5].