CHARACTERIZATION OF SOLAR THERMAL ENERGY RADIATION POTENTIAL OF LAKE VICTORIA REGION : A CASE STUDY OF HOMABAY COUNTY , KENYA

The study sought to determine solar irradiation in Homa Bay County which can be tapped and utilized in improving lives of residents of the region by converting the solar thermal energy in Home Bay to other forms of energy such as electric form, mechanical form and light. The study was done by assessing the local atmospheric conditions which included sunshine duration data and air temperature records for the period of two years and the data obtained subjected to statistical analysis to determine the localized characteristics of the resource. The characteristics that were examined include; seasonal and annual power expectations as well as resource reliability. The solar irradiance of Home County was found to be 768.0W/m2. Key words; characterization, thermal radiation Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 21 November 2018 © 2018 by the author(s). Distributed under a Creative Commons CC BY license. doi:10.20944/preprints201811.0524.v1


Introduction
The key factor considered by investors before establishing any development project in a region is the availability and reliability of power.According to Abhishek Saxena, Nitin A garwal and Ghasyham sirivestava (2013), energy consumption for cooking, water heating, drying, heating and cooling of buildings, and water distillation in the developing world is a major component of total energy consumption in various households and commercial sectors.A major source of this energy is fossil fuels creating upward demand thus increasing the prices.As an alternative fuel, solar energy is a good option to utilize for various heating and cooling applications.Kenya is using solar energy devices for the above mentioned activities through solar cooking, water heating, solar drying, air heater, and solar still.To reduce the dependency on imported fuel and the pressure on natural gas, the present energy application system must be diversified and at the same time indigenous energy resources have to be explored and developed.Concern for environment is now a universal issue and conventional energy gives rise to greenhouse gases with adverse consequences for health and climate [12] In these perspectives, harnessing of renewable energies and development of relative technologies is a highly important strategic option.In Kenya, communities in rural and remote areas such as Homa Bay County have limited accessibility to the Kenya National grid electricity supply system.Only about 3.3 % of Homa bay populations has access to the National grid electricity supply system [13].Therefore this study sought to determine solar irradiation in Homa Bay so that the irradiation obtained can be utilized in upgrading the life standards of Homabay residence by improving industrialization and agro economic activities essential for sustainable development of the region.

Background
The location for the project was Homa bay County; Homa Bay County, Kenya.It is located in About 14.3% of its area is urbanized.About 3.3% of their population has access to electricity

Radiation
Radiation is the mode of transfer of heat energy from the sun to the earth does not require maternal media.It is therefore called radiation.The radiation from the sun falling on the earth outside the atmosphere is 1367 W/m 2 [3] The annual global solar irradiation on the earth depends on the latitude, as the angle of incidence of the solar irradiance results in a lower radiation at higher latitudes.There are two reasons for this occurrence.One is that the distance through which the solar radiation has to travel in the atmosphere is longer at higher latitudes, resulting in increased absorption and reflection before reaching the earth.The other reason is that the higher angle of incidence results in a lower irradiance on the horizontal ground.However, this may be compensated by a tilted surface towards the sun.
When using solar energy integrated in buildings, the optimal conditions for the irradiation on the solar collectors is not always possible to achieve, as the design of the building depends on a large variety of factors.In single family building the most common roof tiles are normally suitable as supporting structures for solar collectors.According to Elisabeth (2009), solar power generating systems converts solar energy to electricity.Every second sun sends about 42 trillion calories of energy to earth surface.[11]

Solar power
The rate at which an object radiates energy is proportional to the fourth power of its absolute temperature.This is known as Stefan's law, expressed in equation form as; Where, P is energy,ε is emissivity,σ is Stefans − Boltzman constant, Ais the surface area of the body and T is the temperature of the surface of the body [5] Therefore rate,  at which thermal (heat energy) is radiated from the sun to the earth per unit time in watts, ε is a constant called emisivity of surface of the sun from which the radiant heat origin is temperature of the sun,σ is boltz man's constant (σ = 5.67 × 10 W/  ).Bodies that can absorb all the heat reaching it and emit it all are called the black bodies.Such bodies have their values of  tending to 1.
The amount of heat radiated per second by a body over entire surface is called luminosity.Since the sun radiates about 42 trillion calories per second from its entire surface, this is sun's luminosity; Where Ts is temperature of the sun, is the temperature of the surface onto which heat flow.[5] When a surface absorbs all of heat energy, reaching it from the sun, then that material is said to be having reflectivity of zero.Reflectivity of a body is called albedo.Albedo of a surface refers to the ratio of the amount of reflected energy to the amount of the heat incited on to the surface.second .The sun is said to be black body and its emissivity is almost equal to 1.Sun emits different spectra of different wave lengths.This relationship between intensity and wavelength is given by Wein's law illustrated graphically as shown below.
Fig 1.A map of Homa Bay county showing the region of interest in orange [13]

Figure 2 .
Figure 2. A graph of Intensity of sun's radiation

Figure 3 .
Figure 3.A graph of Radiation for different sites in the for aperiod of sepember 2015 to 2016.

Figure 4 .
Figure 4.A graph of Radiation for different months in the for the year September 2016 to September 2017.

Table 1
Average monthly radiation for the region for the period of September 2015 to September 2016 in watts per square meters.

Table 1 : Average monthly radiation for the region for the period of September 2016 to September 2017.
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Table 3 below shows the overall daily average radiations for Homa Bay in watts per square metres.
It shows that the overall daily average radiations for Homa Bay in watts per square metres.we therefore deduce that Solar radiation in Homabay county is at it's maximum in the month of march thereafter it deteriorate to its minimum at the month of july.It again gradually rises to it's second maximum in the months of September October periods.

Table 3 : overall daily average radiations for Homa Bay in watts per square meters.
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) 650 700 750 800 850 Months of the year Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 21 November 2018 Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 21 November 2018 doi:10.20944/preprints201811.0524.v1 Conclusion From
the two sets of 12 months data obtain we can conclude that Homa Bay central region within a radius of 15KM around Homa Bay High Schools has the highest radiation This implies that in Homa Bay County, sunshine radiation is at its maximum in the month of March and minimum in the month of July.And following the analysis per station, Homa Bay central region experience the highest radiation and therefore highest solar potential site within the county.Results of the study proves that Homa Bay is substantially high solar energy of values ranging from a minimum of 679.8w/m 2 to a maximum value of 850.1 w/m 2 and an average solar Irradiance of 768.10Wm