INTRODUCTION AND BACKGROUND
OVERVIEW OF CHAPTER 1
Design of and an economic analysis of a stand-alone solar system for an off-grid village shop.
More than a billion people live without access to electricity in developing countries. Energy has long been considered as one of the key fundamentals of modern life and if one does not have energy, then they are poor. Absence of energy influences individuals from numerous points of view, kids have less hours to study, medical clinics and facilities have no light to see patients and independent small business cannot power electronic gadgetry (01).
Electricity is necessary for the daily survival and further development of communities . In Botswana, there are many villages in the rural areas that are without electricity as they are located far from the national electricity grid. These remote areas are small and dispersed from each other which makes it difficult for the government to install national electricity .grid. Therefore, with that difficulty to access electricity in remote areas.
This pushes the residents to thrive for survival by the use of fosiel fuels like oil and natural gas to generate electricity. The use of energy is essential in everyday activities. Energy can be used in electrical appliances e.g. stoves, laptops, fridges etc. and lighting. Fossil fuels like coal, oil and natural gas can be used to generate electricity. As such fuel transportation to produce electricity via generators is expensive due to rough roads and long distances from developed areas. Furthermore, Botswana generates its own electricity using coal at Morupule power station. The use of coal to generate electricity causes air pollution, this air when inhaled by human beings causes respiratory diseases. However, the generated power is not enough to sustain the whole country. This forces the Botswana government to import electricity from its neighboring countries (10). Clearly not all villages will be connected to the grid in the short term as such the use ofs alternative energy sources such as solar energy emerges as the solution.. This alternative is well supported by the fact that Botswana is one of the areas that experience a high solar radiation and has high potential of solar energy. (repetition) This alternative source of energy is well supported by the fact that Botswana has a gigantic potential to wander into the utilization of sun based energy. As it encounters yearly an immediate ordinary light equivalent to 3000 kWh/m2/a.
As pointed out earlier, access to electricity in remote villages is a challenge. Mr. Ontireletse Rebagamang is a sole trader operating a village shop in Majwanaadipitse village, some 105 km from the BIUST campus. He is currently using a generator and LPG gas as sources of energy for his requirements. He has to procure these sources of energy from the nearest town of Serowe and in the process incurs further transport costs. He is not happy with his energy expenditure and complains that his income is being eroded as a result. As such Mr. Ontireletse Rebagang is keen to switch to a stand-alone solar PV system as an alternative. A need has therefore arisen to design and cost an appropriate solar PV system for Mr. Rebagamang and carry out an economic analysis that convinces him that he is indeed better off switching to solar energy.
1.2 STATEMENT OF THE PROBLEM
Mr. Rebagamang a sole trader operating his essential business in a remote area Majwanaadipitse which is located away from the national power grid. The fossil fuels he uses in the form of petrol and gas for his energy requirement poses a big threat to health and environment and also are too expensive for his business. Therefore, there is a need for an alternative source of power which must replace them and prove to be economically viable for the business. Mr. Rebagamang a sole dealer working his basic business in a remote territory Majwanaadipitse which is found far from the national power matrix. The petroleum products he utilizes as oil and gas for his vitality necessity represents a major danger to well-being and condition and furthermore are unreasonably costly for his business. Along these lines, there is a requirement for an elective wellspring of intensity which must supplant them and demonstrate to be financially suitable for the business.
Design of and an economic analysis of a stand-alone solar system for an off-grid village shop.
PV system if designed well will minimize the cost compared to the use of fuel and lpg gasgas. Also, PV system.
PV system if installed well will provide energy requirement for Mr. Ontireletse Rebagamangs shop at a lower cost as opposed to fuel and Lpg gas.
The objective of this study will be:
To fFind out the energy requirements of the shop
To cCost the energy currently being used at the shop
To eEstimate the contribution to pollution by the fossil fuels
To dDesign, size and cost a PV system to replace the fossil fuels
To cCarry out an economic analysis and find the payback period of the solar PV system and
To dDiscuss and conclude on the implementation of the solar PV system.
1.5 SIGNIFICANCE OF THE STUDY
The significance of the study will be:
To reduce cost of electricity by replacing the use of non-renewable energy sources with renewable energy sources.
To reduce air pollution caused by non-renewable energy sources
2.0 INTRODUCTION OF CHAPTER 2
2.0 OVERVIEW OF ELECTRICITY AND SOLAR ENERGY IN BOTSWANA
Botswana is a land-locked nation found in Southern Africa. It lies between scopes 17 ?S and 27 ?S and longitudes 20 ?E and 30 ?E. It shares borders with South Africa, Zimbabwe, Namibia and Zambia. Morupule Power Station through Botswana power corporation(BPC), is the main power plant in Botswana situated close to Palapye. It is in charge of generation, transmission and conveyance of power. Morupule power station is separated into two operational coal terminated units being Morupule A and Morupule B. Morupule A is comprised of four units every give out 33 MW along these lines it gives an introduced limit of 132 MW. Morupule B is likewise made of four units each offering 150 MW which currently gives an introduced limit of 600MW (09). Both operational units fail to fulfill the normal national need of 400MW, while 71 percent of power is imported from South Africa (20).
Due to lack of power in Botswana. The remote territories depend on chiefly in the utilization of petroleum products as oil and gas, as their wellspring of vitality. These wellsprings of energy present well-being and ecological dangers, likewise are excessively costly. In that capacity Botswana has a gigantic potential to wander into the utilization of sun based energy. It encounters yearly an immediate ordinary light equivalent to 3000 kWh/mm2/a .It likewise encounters a normal protection on an even surface of 21 MJ per m2/day in most part of the country (08).
2.1 SOLAR ENERGY
Sun based vitality is a light and warmth from the sun that can be put to use by the utilization of various innovations, for example, sun powered warming, photovoltaic, solar thermal energy. Sun powered vitality can be utilized to give warm energy(heat) or to produce power without making harm to the environment (07). The sun is the principle wellspring of energy. The sun is fundamentally made of helium and hydrogen gas which produce sun oriented radiation. Sunlight based radiation is delivered by atomic combination response where four hydrogen consolidate to frame helium core in the sun’s centre. The radiation has a successful black body temperature of 5777 kelvins. The atomic combination response makes the sun release huge measure of electromagnetic radiation in a type of UV light. This radiation is the vitality that warms the earth as it warms up the earth it ricochets off the climate and mists once again into space (06). Solar panels which are made of many solar cells can be used to turn solar energy into electricity. The efficiency of solar energy system is rated according to their performance under a standard test irradiance of 1000 w/m2. The power per unit area, received from the sun in form of electromagnetic radiation will depend on latitude and local climate conditions. But the yearly average solar energy density lies in a range from 100-250 w/m2 for most locations. Sun powered boards which are made of numerous sun powered cells can be utilized to transform sunlight based energy into power. The efficiency of sunlight based energy framework is evaluated by their presentation under a standard test irradiance of 1000 w/m2. The power per unit territory, got from the sun in type of electromagnetic radiation will rely upon scope and nearby atmosphere conditions. In any case, the yearly normal sun powered energy thickness lies in a range from 100-250 w/m2 for generally areas (05)Individuals utilize sunlight based vitality for various things for example sustenance, warming, power and so forth. Human beings use solar energy for different things e.g. food, heating, electricity etc.
Figure 1: Solar Irradiation in Botswana (kWh/m2) (29)
2.1 SOLAR PHOTOVOLTAICS
WHAT IS A SOLAR CELL AND HOW IS IT MADE
Sunlight based photovoltaic is an innovation that changes over sun’s radiation into usable direct current(DC) power by utilizing semi-conductors. Approaching photons from the sun interface with semi-conductors so as to create an electric flow. Semi-conductors are additionally used to develop the sun powered PV cell. A section of unadulterated silicon is utilized. The highest point of the chunk is made with ‘n’dopent, for example, phosphorus. The base part is diffused with little piece of boron.
Figure 2: A labelled diagram showing the photovoltaic cell (31)
The ‘n’ dopent gives the silicon wafer an extra free electrons and it is called n-type (negative charge). It has equivalent number of protons and electrons (some not held firmly to the molecule). Electrons are allowed to move inside the layers. The boron has the propensity to draw in electrons giving the base of silicon positive charge The p-type silicon has equivalent number of protons and electrons. The p-type and n-type both form a p-n intersection. The p-n intersection makes an electric field; this permit the progression of electrons when photon goes through the PV cell (19htt).
2.2 HOW ELECTRICITY IS PRODUCED IN A SOLAR CELL
In order to produce power, a voltage must be prompted just as current. The voltage can be created in a sun oriented cell by the procedure of Photovoltaic effect. Impurities are added to the semi-conducting materials in the sun powered cell to shape the P-N intersection as interior electric field. At the point when photon’s hit the sun oriented cell, some electrons are eager to progress toward becoming electron-hole(negative-positive) sets. In this way, because of the interior electric field electron-gap pair are prompt to split up. As pursues the electrons connect to the negative cathode, while the openings move to the positive anode. Accordingly, the movement of electrons in the sun based cell produce electric flow. A directing wire is then used to associate the p-type silicon to an electrical load and afterwards back to the n-type silicon to frame a total circuit. Electric flow is hence created to supply the electric load (17).
Figure 3: A diagram showing the photovoltaic effect in the solar cell (27)
2.3 SOLAR CELL OPERATION
2.3.1 SOLAR CELL ELECTRICAL PARAMETERS
I-V CHARACTERISTIC CURVE
These curves demonstrates the current and voltage (I-V) characteristic of a particular PV cell.It also summarize the relationship between the current and voltage at the existing conditions of irradiance and temperature (14).
Figure 4: The above graph shows the (I-V) characteristic of a typical silicon PV cell (htts)
The light shifts the I-V curve down, where the power can be taken from the diode. The diode law becomes
I= I_0 [exp?(qV?nkT)-1]-I_L [12.01]
The power curve has a maximum denoted as P_mp where the solar cell should be operated to give the maximum power output. Writing voltage in terms of current gives us:
V= nkT?q ? ln??((I_L-I)?I_0 ) [12.12]
2.3.2 SHORT-CURRENT CURRENT ( I_sc)
It is the maximum current from a solar cell and occurs when the voltage across the device is zero. The short-circuit is directly caused by the production and gathering of light-generated carriers.The short-circuit current mainly depend on the area of the solar cell, the number of photons, the spectrum of the incident light,the optical properties and the collection probability.
The equation of a short-circuit current can be approximated as
? J?_(sc = qG(L_n-L_(p ) ) ) . [12.23]
2.3.2 OPEN-CIRCUIT VOLTAGE(V_oc)
It is the maximum voltage from a solar cell and occurs when the net current through the device is zero. It is given by:
V_oc= nkT?q ln?(I_L?I_0 +1) . [12.34]
The above equation shows that the voltage depends on the saturated current of the solar cells and light generated current. The V_oc can also be generated from a carrier concentration :
V_oc= kT?q ln?? [ (?(N?_A+ ?n)?n)?(n_i^2 )? ] [12.45]
It is basically the product of current at maximum power times the voltage at maximum power.It is given by the following equation:
P_MP= I_MP?V_MP .[1.5]
Current at maximum power Imp is given by:
The exact maximum power point V_MP is given by:
V_(MP= ) V_t W (I_L?I_0 ) [12.76]
It is a constant which, in coexistence with voc and isc, deduce the maximum power from the solar cell.It is basically given by:
FF= P_MP/(V_(OC?) I_SC ) [1.8]
FF= (V_(MP?) I_MP)/(V_(OC?) I_OC ) …..[1.9]
Graphically, the FF is a measure of the squareness of the solar cell and is also the area of the largest rectangle which fit in the I-V curve
2.3.3 SOLAR EFFICIENCY
The efficiency of a solar cell is defined as the ratio of energy output from the solar cell to input energy from the sun.The efficiency depends on spectrum and intensity of the incident sunlight and temperature of the solar cell. It can be calculated as fraction of incident power which can be converted to electricity and is given by:
?=( (V_oc ? I?_sc FF)?P_in ) [2.09]