BIODECKATSINA

1.0 INTRODUCTION

For centuries, energy has always been as essential input to all aspect of modern age. It is indeed the life wire for industrial producing the fuel for transportation as well as for other conventional power generations. Presently, fossil fuels provide the bulk of the world’s primary energy with hydro-electricity providing about 2% while nuclear fission, wood and other sources account for less than 1% of the primary industrial energy used in the world (1). Since fossil fuels are un-renewable natural resources, their resources, especially oil and natural gas, may soon be completely depleted. This is because the rate of formation, which is if the order of billions of years is by far out-stripped by their consumption rate. The global consumption of oil was about 3 billion tones (2) per year.  This indicates that the present recovery rate of oil from wells is well increased from 25% to 40%, the ultimate recoverable resources would be about 260 billion tones. With the oil consumption rate, this amount would be exhausted in about 86 years. A similar situation exists for natural gas.

Over the past few years, energy forecasts (Habib 1996) have predicted large increase in the consumption of oil and rapid escalation of the product. Several studies have predicted that there will not be too long a considerable gap between OPEC production levels and the demand for oil by the oil importing countries. The extend to which this shortfall would appear depends on so many factors, such as the economic growth of the oil importing countries, oil production level, oil price and rate of substitution of oil. Also, oil supply could be upset easily by political disturbances.

As a result of the energy crises in the 1970’s and the era of population explosion with growing public awareness on the cost of conventional energy, this led to the search for various renewable energy sources. Renewable energy resources which include solar radiation, hydropower, wind geothermal and biomass are available in both the developed and the developing countries in significant quantities. Among these renewable energy resources solar energy is the most important, because of its availability almost everywhere, also being it in exhaustible and more so it cannot be contaminated. There’s also maintenance free culture of the photovoltaic cells, because they contain no moving parts.

PHOTOVOLTAIC

Photovoltaic power system involves the conversion of sunlight into electricity and is achieved using materials known as semi-conductors, which are formed mostly from silicon material when properly doped, solar cells are obtained whereby incident sunlight (photos) upon strike their surface with the sufficient energy will cause the release of electrons. Movement of the electrons from cells to the external circuit results on the production of electricity. The form of electric current generated is direct-current (dc) which could be used to charge batteries for storage and subsequent usage when there is no sunlight available. However, alternating current appliances could be powered with photovoltaic. An inverter in this case is necessary to change the dc voltage into an alternating current (ac) type suitable for most commonly available appliances such as fluorescent lamp, fans and fridges. In most cases, charge regulators and other controls can be included to protect and ensure proper charging of the storage batteries.

The aim of solar photovoltaic is to see that electrification has been substituted from hydropower and other sources to solar PV. Solar photovoltaic is currently being utilized in many places including Nigeria for a variety of applications such as village electrification, water pumping for both community water supply and irrigation, powering of microwave repeater stations and for powering of vaccine storage refrigeration’s in rural clinics. A practical example of the use photovoltaic had been demonstrated at kwalkwalawa village in Sokoto state in which about 50 households are served from a 7.2 KWp photovoltaic generator also a solar power project is underway in Katsina to produce 65MW of electricity.

The efficiency of a cell can be decreased by creating different short circuit current by shadowing one of the cells or by mismatch either through shadowing of crack of the module. The crack of the module do really affects in such a way that the maximum power output cannot be met because of the crack. The main cause of mismatching between cells is partial shadowing which often occurs during module operation. Fortunately, practical cells do have larger leakage currents. The leakage current represented by the shunt resistor in the equivalent model of a solar cell, decreases the individual cell efficiency but makes the module performance much less sensitive to cell mismatching and shadowing effects.

The effect mismatch may not result to the power losses but may also cause serious damage in the modules if precautions are not taken.

OPERATION OF A PV CELL

When Albert Einstein published his 1905 paper on the photovoltaic effect, he postulated that photons are able to penetrate not only the surface of matter but also into atoms. These photons/atoms collision, he stated, could cause an electron to be knocked loose from an atom’s valence shell.

When a photon of sufficient energy strikes an atom of silicon, it pushes an electron from the valence shell into the conduction band, where it is free to become part of an electric current. Suppose a piece of silicon is exposed to light, what happens is that, the atoms are absorbing photons, and electrons are being displaced. (Photon energy not converted into electricity is given off as heat). The empty   places in the valence shells, where electrons use to be, are called holes. These are appearing as rapidly as the electrons can vacate them, but they are filled by dislocated electrons from neighboring atoms.

COMBINATION OF SOLAR CELLS

A solar cell is the individual part of a solar module that converts sunlight into electricity.

When a group of photovoltaic cells that are joined in a series of parallel configuration or both are combined into one sealed unit, what results is the PV module, the basic power-producing unit in all PV energy system. All of the PV modules that deliver electrical energy of the same load are collectively referred to as the PV arrays. A group of module within the array connected and mounted together to form a single structural component is sometimes called a panel. The PV modules wired together to form one series circuit within a PV are often called a series string or array string, and are sometimes referred to as a source circuit.

Photovoltaic array can be assembled across a very broad range of power arrays elements to closely match the needs of any specific application. Sometimes power spectrum is arrays that pump megawatts of power into the central distribution grids of some electric utilities. This is one of the important of photovoltaic that distinguishes it from all other sources of electricity and makes it so very appealing (7)

COMPARISM TABLE

Table 1(a): SERIES COMBINATION

Table 1(b): PARALLEL COMBINATION

REFERENCES

1.      Sambo G. and B.G. Danshehu (DR.), Energy Situation in 21^st Century, “Journal” 1990. 2. J. W. Iwu, Energy Crisis. A Seminar Paper. 1990.

2.      Habib M. A., A Text on Energy Forecast.”Journal” 1996.

3.      H.S. Ranshenbech, “Solar Cell Array Design” . Hand Book, Von Nostrand Reinhold company, New York, 1980.

4.      John T. and Tony W., Renewable Energy Resources, 7, 143 – 179 (1986).