SUMMARY

The concept of thermoelectricity was employed in the investigation of thermoelectric potential of a multi-junction thermocouple embedded in an asphalt bonded solar panel. The system consists of asphalt embedded thermocouples; placed at a convenient angle and provided with transparent cover for applications requiring energy delivery at temperatures up to 100^oc, storage for electric potentials and load output.

INTRODUCTION

The development and use of new and renewable sources of energy has to be accelerated (Oladiran, 1999; Akarakiri 2003) as petroleum resources are being rapidly depleted, it is essential to diversify power production techniques so as to conserve these fuels for premium applications. In this era of energy shortages, the sun has become an unfailing source of energy because of its abundant and environmentally attractive potential with enormous economic promise. It is free, the only cost being to harness it.

APPLICATIONS

Solar energy has been limited mainly to low grade thermal applications in the Sub Saharan African region. For instance over 10,000 units of solar water heaters have been installed in Botswana, Zimbabwe, and South Africa Akarakiri (2003). A project funded by the Agency for International Development (AID) in Tangaye, Africa provides fresh water and runs a grain mill to make flour for sale (Maycock, 1981).

Specific areas of application of solar technology in Nigeria have been identified to include electricity supply during power outages and drying of agricultural and forestry products like cocoa, timber etc (Akarakiri and Ilori, 2003). In 1992, Nitel powered Ugonoba and the Gewadabawa repeater stations for electricity generating station in Nigeria. By 1997, more than 50 repeater stations in the Nigerian Network were powered by PV systems Coker (2004). Iheakpu-Awka village electrification project facilities were installed in 1998.

Several researches have been undertaken concerning the direct thermoelectric generation of electricity using the heat produced by nuclear reactors, kerosene lamps and firewood. Radioactive resources especially Strontium-90, have equally provided heat to activate small, rugged thermoelectric batteries for use in lighthouses, navigation buoys, isolated weather stations or oil platforms, in spaceships etc. Development of improved materials, use of multi-junction devices and novel cell designs to capture a higher proportion of the solar spectrum and use of concentration (Fresnel) lenses to focus the sunlight to high efficiency cells are areas of rapid development. For a given combination of materials (composite materials), the voltage difference varies in direct proportion to the temperature difference.

MECHANISM

Thermoelectric phenomenon can be utilized for the accurate measurement of temperature by means of a thermocouple in which a junction of two dissimilar wires is maintained at a known reference temperature (0^o, in an ice bath) and the other junction at the location where the temperature is to be measured. Thermocouples can be made very small, and also provide a means for the accurate measurement of local spot temperatures. The current can be increased by using semiconductors instead of metals, and a few watts of power can be produced at efficiencies of up to 6%.

The concept of thermoelectric power generator, a device that converts heat energy into electric by using the Seebeck effect was employed intended to generate power for poultry house lighting programme. Since natural light does not provide the desired day lengths for various poultry management systems, artificial lighting is used almost exclusively in modern poultry housing. Duration of light (photo period) is an important factor in poultry production and its variation is used to stimulate egg production in pullet flocks for both breeding and commercial layers (Winchell, 2001).

Therefore, the objective of this work is to investigate the use of solar thermal energy and thermoelectric potentials of asphalt-embedded thermocouple for electricity generation for poultry house lighting using asphalt as heat source.

RESULTS

The peak sun-hour value monitored at the site during raining season and dry season were found to be 4hrs and 5hrs respectively, a value agreeing with Onojo et al., (2004). According to measured temperature data, the average daily surface temperature increases with increase in sun-hour and reaching its peak between 1300hr and 1400hr (Figure 1) and then decline. There are on average, 10hrs of sunshine per day, but for useful solar harvest, 8hrs of sunshine is suggested because of difference in temperature between the collector surface and the ambient.

There appeared to be no significant difference in spot temperatures measured in each of the surfaces per hour, hence the surface temperature is independent of surface area. The Collector compaction test shows that a densely packed material retains more heat than a loosely packed material and hence increased surface temperature and higher electric potential.

The measured average daily current required within the mapped area is 5.14Ah. An average of 4 hrs of full sun hours per day round the years is taken for a non-critical system. When a peak sun-hour of 4.5 hours/day is required, the thermocouple array is capable of generating a measured 1.14A continuously to satisfy the load demand of 5.14Ah. At increased sun-hour period above 4 hours, more current generation is possible whereby the battery could be recharged. The daily load requirement determines the necessary battery bank capacity. The measured total useable capacity (TUC) of the battery in the system is 22.84Ah.

CONCLUSION

The research work showed the possibility of the utilization of asphalt bonded thermocouples to generate enough current for lighting programme in a small scale poultry house. The output voltage across the thermocouple generator can be increased to higher value enough to provide energy for other low thermal processes. Further work is on-going to develop a unit to supply light to a small poultry project.

REFERENCE

Akarakiri J.B. and Ilori M.O. (2003). Application of photovoltaic technology in developing countries. Nig. Jour. of Industrial & Systems Studies (NJISS) vol.2 No.2

Madueme T.C. (2002). Independent power producers and the power sector in Nigeria. Nig.J. Ind & Sys. Studies (NJISS) vol.1 no2. P.38-45.

Maycock D. Paul, Edward N. Stirewait (1981). A guide to the Photovoltaic revolution. Rodale Press, Emmans, Pa.

Oladiran M. T. (1999). New and renewable Energy Education in Sub. Saharan Africa. Proc. of renewable Energy Conf. Perth, Austria-energy 16.

Winchell W. (2001). Lighting For Poultry Housing. The Canada Plan Service 5602 2001:04