Design And Construction Of A Stand Alone Solar System

INTRODUCTION
This section of the work discusses the following in details: solar energy, radian with the time of the day, application of solar energy, solar energy conversion.

1.1 SOLAR ENERGY
Solar energy is one of the renewable sources of energy well investigated to be capable of meeting the needs of the society when the fossil fuels are finally exhausted.
At its core, solar energy is actually a nuclear energy. In the inner 25% of the Sun, hydrogen is fusing into helium at a rate of about 7 x 10 kg of hydrogen every second but the sun has enough hydrogen in the core to continue at this rate for another five billion years [Babatunde E.B, 2012]. This is an indication that solar energy will always be available for the benefit of mankind even if fossil fuel is no more available for human consumption.
The sun radiates 3.85 X 1026 joules of energy every second, a value which is more than the total energy man has ever used since creation. Although some of this energy is lost in the atmosphere, the amount reaching the earth’s surface every second, if properly harnessed is still probably enough energy to meet the world’s energy demand. The only restrictions of solar energy are weather condition, time of the day which makes it not constantly available on earth. Thus some form of storage device is needed to sustain a solar power system through the night periods when local weather conditions obscure the sun [Babatunde E.B, 2012].
It was reported that about 80% of the world’s oil reserves have been consumed by 1980 at the rate of the world energy consumption in 1975. The remaining reserves of coal in the world is estimated to last for about 25 years, while the life expectancy of the oil and gas reserves in the world is not positively known [Babatunde E.B, 2012].
Of all the energy sources available, solar has perhaps the most promise. Numerically, it is capable of producing the raw power required to satisfy the entire planet’s energy needs. Environmentally, it is one of the least destructive of all the sources of energy. Practically, it can be adjusted to power nearly everything except transportation with very little adjustment, and even transportation with some modest modification to the current general system of travel [Eric W. B, 2010].
The current and power output of photovoltaic modules is approximately proportional to the sunlight intensity. This implies that the efficiency of solar panel depends on the weather condition, time of the day and the site of installation of the system. Consideration of the site of installation brings about installing a solar panel in a place where it will be able to capture enough sunlight [Eric W. B, 2010].
PV modules are very sensitive to shading. If a tree branch, roof vent, chimney or other item is shading from a distance, the shadow is diffused or dispersed. This significantly reduces the amount of light reaching the cells of a module. Other sources are those that stop light from reaching the solar cells, such as a blanket, tree branch, bird dropping etc. If one full cell is shaded, the voltage of that module will drop to half of its un-shaded value in other to protect itself. If enough cells are shaded, the module will not convert any energy and will in fact become a tiny drain of energy on the entire system [Eric W. B, 2010]. This connotes the importance of installing a solar panel in an open space where it will be free from any shadow or obstruction no matter how small it may be. It also implies that the surface of the panel must be free from any dirt for efficient capturing of sunlight by the solar panel.
According to Stefan-Boltzmann’s law, the amount of energy that is radiated per unit area of surface depends upon the temperature of the object to the fourth power. This implies that the amount of energy that is emitted by the sun is very much dependent upon the surface temperature.
Solar panel temperature is one of the important factors that affect how much electricity a solar panel will produce. It is ironic, but the more sunshine available get, the hotter the panels get and this in turn counteracts the benefit of the sun [Eric W. B, 2010]. High temperature reduces solar panel efficiency and hence, a solar panel system has to be designed in such a way that it will allow air circulation around the solar panel to cool it.

1.2 RADIAN WITH THE TIME OF THE DAY
At any given instant, solar panel will generate maximum output when pointed directly at the Sun. The maximum angle of inclination is perpendicular to the Sun’s rays at true solar noon [Wholesale Solar, 2012]. True solar noon is when the Sun is at its highest during its daily East-West path across the sky known as 00 Azimuth.
In order to capture the maximum amount of solar radiation, the angle of inclination should be adjusted seasonally at 150 more than the latitude angle [Wholesale Solar, 2012].

1.3 APPLICATION OF SOLAR ENERGY
Concentrating Solar Power (CSP): Concentrating solar power (CSP) plants are utility-scale generators that produce electricity using mirrors or lenses to efficiently concentrate the sun’s energy. The four principal CSP technologies are parabolic troughs, dish-Stirling engine systems, central receivers, and concentrating photovoltaic systems (CPV).
Solar Thermal Electric Power Plants: Solar thermal energy involves harnessing solar power for practical applications from solar heating to electrical power generation. Solar thermal collectors, such as solar hot water panels, are commonly used to generate solar hot water for domestic and light industrial applications. This energy system is also used in architecture and building design to control heating and ventilation in both active solar and passive solar designs.
Photovoltaics: Photovoltaic or PV technology employs solar cells or solar photovoltaic arrays to convert energy from the sun into electricity. Solar cells produce direct current electricity from the sun’s rays, which can be used to power equipment or to recharge batteries. Many pocket calculators incorporate a single solar cell, but for larger applications, cells are generally grouped together to form PV modules that are in turn arranged in solar arrays. Solar arrays can be used to power orbiting satellites and other spacecraft, and in remote areas as a source of power for roadside emergency telephones, remote sensing, and cathodic protection of pipelines.
Solar Heating Systems: Solar hot water systems use sunlight to heat water. The systems are composed of solar thermal collectors and a storage tank, and they may be active, passive or batch systems.
Passive Solar Energy: It concerns building design to maintain its environment at a comfortable temperature through the sun’s daily and annual cycles. It can be done by (1) Direct gain or the positioning of windows, skylights, and shutters to control the amount of direct solar radiation reaching the interior and warming the air and surfaces within a building; (2) Indirect gain in which solar radiation is captured by a part of the building envelope and then transmitted indirectly to the building through conduction and convection; and (3) Isolated gain which involves passively capturing solar heat and then moving it passively into or out of the building via a liquid or air directly or using a thermal store. Sunspaces, greenhouses, and solar closets are alternative ways of capturing isolated heat gain from which warmed air can be taken.
Solar Lighting: Also known as daylighting, this is the use of natural light to provide illumination to offset energy use in electric lighting systems and reduce the cooling load on HVAC systems. Daylighting features include building orientation, window orientation, exterior shading, saw tooth roofs, clerestory windows, light shelves, skylights, and light tubes. Architectural trends increasingly recognize daylighting as a cornerstone of sustainable design.
Solar Cars: A solar car is an electric vehicle powered by energy obtained from solar panels on the surface of the car which convert the sun’s energy directly into electrical energy. Solar cars are not currently a practical form of transportation. Although they can operate for limited distances without sun, the solar cells are generally very fragile. Development teams have focused their efforts on optimizing the efficiency of the vehicle, but many have only enough room for one or two people.
Solar Power Satellite: A solar power satellite (SPS) is a proposed satellite built in high Earth orbit that uses microwave power transmission to beam solar power to a very large antenna on Earth where it can be used in place of conventional power sources. The advantage of placing the solar collectors in space is the unobstructed view of the sun, unaffected by the day/night cycle, weather, or seasons. However, the costs of construction are very high, and SPSs will not be able to compete with conventional sources unless low launch costs can be achieved or unless a space-based manufacturing industry develops and they can be built in orbit from off-earth materials.
Solar Updraft Tower: A solar updraft tower is a proposed type of renewable-energy power plant. Air is heated in a very large circular greenhouse-like structure, and the resulting convection causes the air to rise and escape through a tall tower. The moving air drives turbines, which produce electricity. There are no solar updraft towers in operation at present.

1.4 SOLAR ENERGY CONVERSION
Photovoltaics (PV) use silicon solar cells to convert the energy of sunlight into electricity. Operates under the photoelectric effect which results in the emission of electrons. Concentrated solar power (CSP) Uses lenses or mirrors and tracking devices to focus a large area of sunlight into a small beam.