2.1. Solar energy Previous studies mostly defined solar energy as a free and somewhat accessible in various part of the world. Compared with different energy sources, such as nuclear and fossil fuels, scientists claim that significantly energy can be provided for earth by sun radiations. The effectiveness of the solar energy application in various technologies can be exemplified as follows: • Photovoltaic (PV) technology which light can be directly changed into electricity. • Solar–thermal systems which solar collectors utilize.
It has been estimated that a yearly average of about 2,300KWh/m2 of solar energy tails on a horizontal surface in Nigeria, and that in Lagos the intensity of solar radiation is about 930W/m2 on a clear sunny day (FMST, 1987). At the international institute for tropical agriculture at Ibadan, incident solar energy varies from 5.1KWh/m2/day during the least favourable day in August to 5.8KWh/m2/day in March and April. What Nigeria requires is an affordable solar energy technology and cheap appliances. Nigeria has within a high sunshine belt and thus has enormous solar energy potentials. Solar radiation is fairly well distributed with average solar radiation of about 19.8MJ/m2/day and average sunshine hours of 6 hours per day.
Geothermal energy is a lot cheaper to produce than any other resources, it is even more efficient than the solar energy, and resulting less emission compared to fossil fuels, in other word, geothermal energy is environment-friendly. Some geothermal power plants use the steam from a reservoir to power a turbine/generator, while others use the hot water to boil a working fluid that vaporizes and then turns a turbine. Hot water near the surface of Earth can be used directly for heat. Direct-use applications include heating buildings, drying crops, heating the water at fish farms, growing plants in greenhouses, and several industrial processes such as pasteurizing
The key component of all solar system is the solar collector. This is a device which absorbs the solar radiation from sun converts into heat and transfers this heat to a fluid ( air, water, oil ) passes through the collector. The solar energy collected is carried from the circulating fluid either directly to the hot water or to a thermal energy storage tank from which can be utilized for use at night or cloudy days. There are basically two types of solar collectors: non-concentrating/stationary and concentrating. A non-concentrating collector has the flat surface for intercepting and for absorbing solar radiation, where a sun-tracking concentrating solar collector usually has concave reflecting surfaces to intercept and focus the sun’s radiation to a smaller receiving surface, by means of increasing the radiation flux.
The sun light strikes the upper surface of the cell; some photons are absorbed near the junction of two layers. This generates e.m.f and if the two electrodes are connected through the external circuit a current flow. Photo voltaic cell generates DC supply. However it can be converted to AC of required voltage by power conditioning unit (PCU). There are many companies are supplying solar panels but the institute installed Mono crystalline solar panels of “solar semi-Conductor
The above comparisons show that solar energy have impressive magnitude, it provides more energy than present day human technology can provide. The first solar cell were developed about 50 years ago by Bell Laboratories in 1954. These solar cells were used as power source in satellites. In the end of 1970 scientists were able to develop silicon solar cells (Photo voltaic cells) on industrial basis, since then these have become more and more attractive. The main steps involved in utilizing solar energy are Capture, Conversion and Storage.
When the solar cell was cooled the power output remained high to indicate that the colder temperature promoted the greatest output of power. The power output remained high and unchanged at 9.5 V and 70 mA from a cool 52° F to the mid temperature range of 77° F. However, when the solar cell was heated, the power output began to decline and eventually reached a power output of 13% less at 8.2 V and 63 mA. EXPERIMENTAL DESIGN AS A KEY
Essentially, passive solar power is designing homes in a way that effectively reduces the consumption of energy. Strategically placed windows which allow sunlight at certain times, proper insulation, brick and stone houses, fans, lighter colors, and blinds are all some elements of the passive solar power strategy. This strategy is the most affordable of all the mentioned solar power and energy conservation
However, for drying highly perishable products, it is extremely important to develop low cost systems . Most important advantage of the solar dryers is they work on renewable energy and are pollution free. Also, solar dryers can be easily constructed from local materials. It is successfully proved how solar dryer technology is key element to climatic and environmental protection as well as sustainable development