Solar power is the energy generated by the radiation of the sun, more specifically the radiation that reaches the earth. The energy received the by the sun in form of radiation can be converted directly or indirectly into forms of energy, such as heat and electricity. The amount of energy from the sun that falls on earths is immeasurable. Solar power came into existence more than billion years ago, however the use of this renewable source of energy has been in practice from earlier period of century, still the technicians from all over the world are working and discussion how to progress this renewable source of energy which is completely free.
Ursula (2006) demonstrated a square metre of horizontal earth surface receives, under German climate conditions, between 925 KWh/m2 in the north to 1170 KWh/m2 in the south solar irradiance annually. The amount of energy received by radiation of sun a daily average of around 3 KWh/m2.
Get your grade
or your money back
using our Essay Writing Service!
From last few years people start installing solar panels on roof of house and are trapping solar energy for their electricity. By the help of advanced technology the use of solar energy is increasing day by day. The subsequently frequent use of the solar power water heating, solar cars, solar pump and solar electricity which can be used in any appliances used in house.
The term photovoltaic has been in used in English since 1849. It comes from the Greek word "phos", meaning "light" and "voltaic" meaning electrical. The "voltaic" derived from the name of the Italian physicist Volta, by whom the unit of electrical potential volt is named. However, until 1883 the solar cell wasn't built, but at the same time Charles Fritts coated the semiconductor selenium with an extremely thin layer of gold, to form the junctions. The efficiency of selenium semiconductor cell was not too much. So in later on in 1946 Russel Ohl invented modern type of cell. In 1954 Bell Laboratories accidently found that when semiconductor silicon doped with certain impurities can give 6% efficiency in energy conversion by sunlight. In 1958, US satellite Vanguard 1 launched the first spacecraft with solar panels. In 1970, Zhores Alfervo and team of USSR researches created the first highly effective Gallium arsenide (GaAs) heterostructure solar cells. In 1988, Applied Solar Energy Corporation (ASEC) manufactured the first 17% efficient air mass zero (AMO) single-junction GaAS solar cells. In 1993, ASEC developed the first dual junction cells for spacecraft which start giving efficiency of 20%. However, than Triple Junction solar cells developed which increase the efficiency approximately 24% in 2002, 28% in 2005 and in 2007 has reached 30%. In 2007, the two companies of US, Emcore Photovoltaic and Spectrolab produced 95% of Triple Junction solar cells with the efficiency of 38%.
16th of October 2008, 15:32 GMT | By Georgiana Bobolicu, http://gadgets.softpedia.com/news/History-of-the-Solar-Panel-039-01.html (07/11/2010)
1.1 The advantages and disadvantages of solar energy
The advantages of solar power are increasing day by day in daily uses and in industries uses, although it is a relatively new energy source. In future it's going to be the most important energy source. Solar power is a renewable resource. However, the solar panel does not work in night or on stormy, cloudy days. But the sun appears next day and it is ready to give more energy and light. Solar power is non-polluting. It the most important advantage because it does not emit any greenhouse gases. The solar power is one time investment method, once the solar panel is set up; there is no electrical expenses lifetime. The solar cells are totally silent. The solar cells required very little maintenance because there will be no moving parts they need to be fixed. However, the solar power has too many advantages but it got some disadvantages as well like it is too much expensive. The initial costs of the equipment used in solar panels are too costly, especially the solar cells which is made of silicon crystal which is grown very slowly. Silicon crystals growth from pure silicon and the process is too slow and expensive. The solar energy installations require large area to install; this is the disadvantage in areas where space is short like inner city. Pollution is also the one of the most disadvantages of the solar panels, as pollution can decrease the efficiency of photovoltaic cells. The solar energy work only when the sun is shining, but during night the expensive solar equipment will be useless. The different location has different affect performance, due to obstructions from the surrounding buildings or landscape.
1.2 Rural electrification of India
Always on Time
Marked to Standard
Rural electrification means providing the electricity to the rural area. By providing the electricity to rural areas in developing countries enhances the quality of life. There are lots of villages in India have no electricity and are not expected to be connected. Panda (2007) demonstrate that rural electrification in India is one of the biggest challenges. Until now only 42-44% of Indian village are getting the facility of electricity still there are 77-88 million households still require the access to the electricity. However, the photovoltaic electricity is best source of electricity for rural part of India. Hansen and Bower (2003) demonstrate that the condition of Indian climate is highly suitable for the solar photovoltaic technology. In India there are approximately 250-300 sunny days in a year. Solar energy provides 4-7kwh/m2 in India whereas it provides only 2.7kwh/m2 in UK and Germany.
Figure 1.2 Increase in installed power capacity by solar system http://spacejournal.ohio.edu/issue16/images/gopal1.jpg (17/11/2010)
The overall objective of this report is to design a particular system which is capable of generation of power by means of solar concentration for use in emergency in situations of an existing off-grid situation. The aim of this project is towards the understanding as well as the development of a cost effective system which would be considered as reasonably affordable for the purpose of the newly developing regions of the India. This system should be capable of utilizing the available sources and it should contain a simple to promote the idea of repairing quite easily. However, in order to reach this goal it is imperative that a few key research objectives must be met. The key objectives include characterization of the solar PV panel and the charge controller so that it is possible to determine the overall efficiency of the system. This characterization of the different components of the constructed system will help in future work ideas on a similar project which is aimed towards increasing the efficiency as well as the overall output of power.
The main aim of the project is to design a system which is more efficiency and low in price for solar energy generation which supply power to the houses which are based in a village in certain areas of India.
To learn that radiant energy can be converted directly into electricity.
Understand the structure of a photovoltaic system, and its subsystems.
Progress on skills and know-how to model economical photovoltaic solar panel.
To learn how to increase the efficiency of photovoltaic solar panel.
Gathering information about solar energy, working and its history
How much it beneficial for the off-grid area and the working of solar panel system and subsystem
Comparing the price and efficiency of existing model and new model
Design of solar module
Parameter of solar subsystem
Of system and subsystem
Design of solar system and subsystem
Solar panel model
Checking the working of the model
ANALYSIS OF RESULT
Checking the voltage and current of the new model
Economical and efficient solar panel for the off-grid area for two bulbs
Checking how to increasing the efficiency of the model
Reading: - Gathering information about the solar panel and the photovoltaic system. Collecting information about solar panel history and background from different resources.
Research: - Rural electrification of India and off-grid area of India. Providing the graph for the rate of solar power installation increasing in India. The advantages and disadvantages of solar system and by the base of it the aim and objective of the project. The brief explanations of the working of solar system and the component of solar system (subsystem)
Patent: - selecting the cheap and efficient subsystem for the solar system and creating a economical and efficient solar module for the solar system.
This Essay is
a Student's Work
This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.Examples of our work
Draft design: - Sketch design of working of solar system and the solar panel and the parameter of all the subsystem. Comparing the selected subsystems from the other subsystems. Describing the component of the new model of solar system and explaining the series connection of solar cells.
Working of model: - Explaining the soldering of solar cells in series to obtain the require voltage to charge the 12V battery and the advantages of all the subsystem selected and their price and details. Explaining the each step of modelling of solar panel.
Engineering analysis: - Checking the working of the new model and their subsystem. If the system is working than go to analysis process if not go back to the working model and check the model again.
Analysis of result: - Checking the voltage of the whole system and charging the 12V battery to glow the CFL bulb. If the voltage is not obtained to charge the 12V battery again checks the model of solar module.
Validate: - Increasing the efficient of the model and explaining the advantages in efficiency and the future solar panels.
Conclusion: - Design of economical and efficient solar panel for the off-grid area for glow two CFL bulbs.
3. Solar power
The sun supply energy in the form of radiation, lacking of which existence on the earth is not possible. The sun radiates energy due to the fusion which generates which change hydrogen atoms into helium. In the other word we can say sun is the enormous nuclear fusion reactor. The energy supply from the sun is unlimited. Markvart (1994) states that the average energy received by the sun is nearly 1.2*1017W, in average in one hour the sun supply enough energy to the earth surface which can satisfy the entire energy requirement of the human population over the whole year. The intensity of solar radiation depends upon the distance between the sun and the earth outside of the earth's atmosphere. Deutsche (2008) demonstrate that the sun radiation reach earth nearly after travelling 1.47 x 108km and 1.52 x 108km, by which the irradiance Eo fluctuates between 1325W/m2 and 1412W/m2. The average value is called as the solar constant.
Solar constant: Eo = 1367W/m2
The whole irradiance never reach earth's surface, the earth's atmosphere reduces the insulation through reflection and absorption by ozone, water vapour, oxygen and carbon dioxide and scattering caused by air molecules, dust particles or pollution. The irradiance value depends on the region. Mostly the equator regions reach the maximum irradiance of 2300kWh/m2 per year. As shown in the figure 3.1 the different irradiance depending on the region.
Figure 3.1 Worldwide distribution of annual solar irradiance in kWh/m2
Krishnadas (2008) reported that the largest solar power project of the world is purportedly entity planned in western India at Gujarat at a cost of about $5 billion, which will generate power approximately 5 gig watts. State government of Gujarat, Ahmadabad said that the total cost of the enormous project will be less than pervious the power generation project. The official said that it will reduce the cost of power generation from 25 % to 10 %.
3.1 Photovoltaic cells
Photo means light and voltaic refers to volt, a unit of electrical force. Photovoltaic has two very important aims in its area of application. First provide professional devices and supply systems for off-grid area (solar home system, solar pump and telecommunication equipment) and secondly energy generation at the large scale. It is the technology in which photons illuminated by the semiconductor material in result generates direct current electrical power measured in watts or kilowatts.
3.2 Working of solar cells
The operation of solar cells is due to the ability of semiconductors to convert sunlight directly into electricity. Mostly the semiconductors use in solar cells is silicon crystal. The sun is composed of photon and this photon contains various amount of energy. This photon strike the solar cell and they reflected or absorbed, only the absorbed photons generates electricity. By the help of semiconductor the energy of photon is transferred to an electron in an atom of cells. The absorbed photons excite the bond electrons into a higher energy state, help them to move free. These free electrons start moving in all direction leaving the holes where it was bonded. The negative electrons will go to N-layer and the positive holes got to the P-layer. The P-N type junction created in solar cells and the working of the solar cells shown in the figure 3.2.
Figure 3.2 P-N junction of solar cells source http://www.wcubed.com/solar/What%20is%20a%20Solar%20Cell%20.htm (12/11/2010)
The P-N junction formed by placing P-type and N-type semiconductor next to each other, Although the materials are electrically neutral, the negative silicon has excess electrons and the positive silicon has excess holes, putting these together creates P-N junction at their interface and electric field generates.
SOLAR CHARGE CONTROLER
3.3 Characteristics of solar cells
The voltages of the solar cells depend upon the material selected in semiconductor. http://www.solarserver.com/knowledge/basic-knowledge/photovoltaics.html (12/11/2010)
In the silicon semiconductor there is only 0.5V voltage generated. Terminal voltage is usually depending on the light radiation. The current intensity increase with the higher luminosity, like if the sun radiate 1000 W/m2 on a 100 cm2 silicon cell the maximum current intensity will be 2 A. The product of electricity and the voltage of cells are depending on the temperature. The output will be low if the temperature is high. Markvart (1994) demonstrate that the voltage will decrease with the increase of the temperature as shown in the figure 3.3. In silicon the voltage decrease is approximately 2.3 mV per oC.
Figure 3.3 I-V characteristic of a solar cell depending on temperature
3.4 Different types of solar cells
There are basically three types of solar cells according to the type of crystal.
Single Crystal solar cells - first generation
Thin film cells - second generation
Multi crystal solar cells - third generation
Single crystal solar cells - first generation
These types of cells are made of slice of silicon crystal by purifying, melting and freezing silicon. These type of solar cells also known as the monocrystalline cells. These types of cells are most efficient as well as most expensive. Krebs (2010) demonstrates that the maximum photovoltaic production comes from the first generation cells nearly 90% of current. However the cost per produced 1 watt of power is much more than the cost of electricity formed by usual.
Thin film solar cells - second generation
These types of solar cells are made by putting the layer of amorphous silicon upon the plastic, glass or metal. The efficiency of thin film solar cells are too much as those made from individual solar cells, although it has been improved in recent year. These types of solar cells are not too much expensive but as their efficiency is too low require more panels to get require output therefore more space is taken up. These types of cells are also known as amorphous silicon cells.
Multi crystal solar cells - third generation
Multi crystal solar cells also known as the polycrystalline cells. It is made from the cast block of silicon which contains many small crystals. These types of solar cells are being used in large scale in recent days. The polycrystalline cells introduce the idea of multijunction solar cells which help to increase the efficiency and in economically way.
3.5 The structure of a photovoltaic system, and its subsystems
Photovoltaic system assembled by many components not only from solar cells. Many other parts required to complete the design to obtain electricity. All the components have to be interconnected, seized and specified for photovoltaic operation. The size of the system or photovoltaic generator and storage sub system depend on the geographical location and it the application for which the system is design.
The photovoltaic system consists of many parts or subsystems.
The photovoltaic generator
Mechanical support for photovoltaic generator
Batteries (storage sub system)
Wiring for electrical connections
3.5.1 Photovoltaic Generator
The main part of the system is photovoltaic generator. It is made of photovoltaic modules which are interconnected to form a photovoltaic generator which generate electricity. When the modules assembled with the mechanical support is usually called as array. These types of modules shown in figure 3.5
Figure 3.5 Different type of solar module
Module is the basic construction unit of a photovoltaic generator. Module is constructed by the crystalline or semi-crystalline silicon cells. These types of modules are commonly used in solar electrification. Markvart (1994) states that the cells in the module are connected in series due to electrical characteristics of individual solar cell, usually 4-inch diameter crystalline silicon solar cell produced 1 and 1.5 watts on the standard condition depending upon the cell efficiency equal to the voltage of 0.5 to 0.6 V. The number of cells in a module is depending upon the requirement of voltage in module. The voltage should be match between the system and sub system. There are some standard storage conditions by which module parameters are specified
Spectral distribution AM 1.5
Cell temperature 25 oC
3.5.2 Mechanical support for photovoltaic generator
Mechanical support for the photovoltaic generator can be design by the two way first the modules can be moulted to the fixed positions and the orientations will follow the motion of the sun. The modules are supported at the fixed position facing the inclination of the equator in maximum arrays. Due to which the cost of solar system get reduce because there will no moving parts. However the support which move along with the sun gives more efficiency because captures more radiation. Mechanical support for photovoltaic generator is shown in figure 3.6
Figure 3.6 Support for solar generator
3.5.3 Batteries (storage sub system)
A battery is an enclosed and protected material which can be charged by electricity and provides electricity when needed. It is consist of an anode, a cathode and an electrolyte.
Without batteries to store electrical energy in photovoltaic system is very difficult, however the photovoltaic system will provide electricity only when the sun is shining or the generator is running. Batteries in photovoltaic systems operate under specific conditions which must be suitable for the system design. There are several types of storage batteries use in solar system.
RV/ Marine / Golf cart: RV or Marine type of batteries are deep cycle batteries and mostly for boat and camper. It is suitable for only very small systems. They do not have capacity for the continuous services for charge and discharge for many years. Golf cart batteries are very good for small system and fairly they are more costly than deep cycle batteries.
Flooded types: These types of batteries are also known as lead acid batteries as they have caps to add water. These types of batteries mostly use in solar system for store electricity. They are not too much expensive and work for many years, however they release gas during the charging so usually it is not used in indoors otherwise there must have ventilation system for releasing the explosive gas outside.
Gel: These types of batteries are mostly used in indoors because it does not release gas during charging process like flooded batteries. It allows batteries to preserve a most stable temperature and carry out superior.
AGM: AGM means Absorbed Glass Mat. These types of batteries are best for the solar power system as there a woven glass mat is used sandwiched between the plates to grip the electrolyte. They do not release gas when charging and they have superior performance. It has all characteristics superior quality, preserve voltage better, self discharge slower and very last longer. They are more expensive and used in airplanes, hospitals, remote telephone tower installations.
3.5.4 Wiring for electrical connections
Wiring in solar panel is not too much difficult as installation, when the photovoltaic generator mounted successfully with the mechanical support than the simple phase wiring only left. Firstly connect all panels with inverter with the required wire, than the power inverter connected to batteries in where the energy will store for the use in night time and these batteries further connected to the home grid. There are different types of wires are there to use in solar system.
3.5.5 Junctions boxes
It is an electrical box which is used to connect wire in different connection or in more direction which will bring power to different electrical devices. Basically it is the unit where different wires connected together. By the help of junction box it easy to connect the photovoltaic generator and the batteries wire to the house grid. The junction box used in solar system shown in figure below.
It is electronic equipment which is used to change direct current (DC) to alternating current (AC). The output of the photovoltaic generator is DC and the inverter changes it into AC current which can be used directly to the house grid or home appliances. The efficiency of inverter depends on the load of current being a maximum at insignificant output power. The inverter can be classified into three categories depending upon the photovoltaic application.
Variable frequency inverters
Self-commutating fixed-frequency inverters
Line-commutating fixed-frequency inverters
Variable frequency inverters are mostly used in photovoltaic pumping system whereas other two inverters used for grid connection. The inverter is shown in the figure.
3.6 Economics of photovoltaic installations
The economical value of a photovoltaic system is low as compared to other method of power generation. Photovoltaic is mostly very economical and useful where small amount of electricity required like off-grid area. There is some of the reason why the photovoltaic system is different and more economical than other type of power system.
The only initial price of the system is high.
In this system there is no fuel cost.
Maintenance costs are too low.
Replacement costs are low due to high reliability.
Output of system depend upon the different location
The economical benefits can be discussed by two ways firstly the money which is been saved or that has been collected at the time of operating the systems. And secondly the social and environmental benefits which one should consider as well when we compare between another systems.
3.6.1 Life-cycle costing
Life-cycle costing is the total amount of money expend for the system for its life time which expressed in today's money. In this type of parameters not only the initial costs but all the future costs for the life time of the photovoltaic system consider. The time for analysis should be for the lifetime as the system lived. Markvart (1994) demonstrates that the initial cost for the photovoltaic generators are more to buy than a diesel generators, however the lifetime of PV generators are 20 years whereas the diesel generators lifetime is only 10 years and use certain amount of fuel every time. To do the meaningful comparison all the costs like future costs and benefits have to be low-priced to their equivalent value in today's economy which is known as 'present worth' (PW).
3.6.2 Parameters of life-cycle costing
There are some values which should be known as to calculate the life-cycle costs
Period of analysis: - longest lived system as compare to the other system for the life-time.
Excess inflation: - The rate of price increases for the component up and down from general inflation which is usually assumed as zero.
Discount rate: - The rate relative to the general inflation at which funds would rise in value if invest.
Capital cost: - The total cost of initial cost of installing or buying the system.
Operation and maintenance: - The amount of cost which is invested to keep operating the system through whole year.
Fuel costs: - The amount of money spend to fuel in year (Annual fuel bill)
Replacement costs: - The amount of money spends to replace each component at the end of its lifetime.
3.6.3 Calculation of present worth
There are two types of calculation of present worth which can be used in life-cycle valuation when express a future price or benefits. Single payment and annual payment are the two types of calculation of present worth. Single payment calculation is use for like battery replacement after five years and annual payment calculation is use for as annual fuel cost and maintenance cost for a year. Markvart (1994) demonstrates that the formula for the present worth for single payment calculation is
PW = Cr X Pr
Where, PW is present worth
Cr is single future cost
Pr is values of present worth factor in N year's time
For calculating the present worth factor there is another formula which is
Where, i is excess inflation, d is discount rate, N is year time
The formula for the present worth for annual payment calculation is
PW = Ca X Pa
Where Ca is payment occurring annual
Pa is present worth factor in an annual requirement cost
However there is a formula to calculate present worth factor for annual requirement cost
4. Major components of the off-grid PV system
Balanced of system
PV modules cable, combiner box, lighting arrestors, over current protection, fuses and circuit breakers, AC & DC disconnects, circuit breakers, dedicated disconnect switches, meters and monitors, various enclosures boxes and battery cables.
As for the required project the aim is to provide the electricity for off-grid selection area (At least for two bulbs), before we select the solar panel for the project, we should calculate the total load required for the two bulbs.
4.1 CFL Bulb
CFL stands for the compact fluorescent lights. Compact fluorescent light is argon and mercury based bulb which are used as energy sever which save money on electricity cost. It work by the mercury which is inside the bulb give ultra violet light which is changed to colour and there is coating of phosphors on tube that will visible to human eye. CFL bulbs are four times more efficient as the incandescent bulbs and 10 times long last. The 24 watts CFL bulb produced the same amount of light as the 100 watts incandescent bulb. The 18 watts and 13 watts produced the same amount of light as the 75 watts and 60 watts respectively. CFL bulbs are not only made for energy saver but they are last long as well, normally the CFL last long for 8,000 hours which is equivalent to 7 years. These types of bulb are ideal for main electricity supply and they are suitable for 12 volt battery as well, so the benefits of choosing this type of bulb is the PV system will not required any inverter. Actually inverter change the AC current to DC current because all the appliances in house operate on AC current. But the PV generator produced DC current and CFL bulb can operate on DC current so in that case there will be no need of inverter. There is some parameter of the CFL bulb which is going to be used in this project.
Figure4.1 White Compact Fluorescent Bulb
Working Voltage: 12 Volts DC nominal, input range 11 -15 volts DC.Â Â Â
Life: 8000 hoursÂ
Base connector: B22D Bayonet Connector (BC)
Light output: 18 watts +/- 5% 6400K 50Lum/W Daylight typeÂ
Conforms to ISO 9001 2000
Ideal for use with solar panel charger (see my other auctions)
Electronic ballast and preheat for quick start and no flicker
Size:Â Â Â Â Â Â Â Total lengthÂ = 155mmÂ
Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Length of tube = 70mm
Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Diameter of body = 58mm
Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Diameter of tubeÂ =Â 55mmÂ
4.2 Photovoltaic Module
The number of solar panels needed depends on the amount of electricity required. Usually the solar panel comes with the various wattages. Watts and voltages are the main measure of the PV module. As it is discussed in section 3.4 and 3.5.1 the solar modules can be classified as monocrystalline, polycrystalline or amorphous. It is quite complicated but the output of the monocrystalline solar panel is the same as the other panel. However the difference is in the amount of area the solar panel going to require. And the structures of monocrystalline solar panels are more efficient than the other solar panels in producing electricity from sunlight. As in this project we have selected two CFL bulbs each working at 12 volts and need 20 watts. The monocrystalline modules take less space and give the same output so we will use this type of module for this project. To design 20 watt monocrystalline solar panel we need solar cells which should be square shape. The number of cells required are depends on the voltage required to charge the battery or the voltage require to light the bulb.
Monocrystaline Cell Specifications
Open circuit voltage
Close circuit current
Maximum power voltage
Maximum power current
75 mm X 64 mm
Figure 4.2 Monocrystalline photovoltaic cell
For the 12V solar panel we need to tab cells in series to get the 20 watts for 12V battery. The components require for the DIY the solar panels are
Aluminium, bolts and nuts etc
4.3 Charge Controller
The charge controllers regulate the voltage and current coming from your PV panel to the battery. It is a device which protects the battery to being overcharged and being over discharged. Overcharged battery has a very short life time and overly discharged battery turn into permanently damaged. For this project PWM Solar Charger Controller 10A is used as shown in figure 4.3
Figure 4.3 PWM Solar Charger Controller 10A
Benefits of choosing this solar charge controller is
It has fully automatic operation
It has electronic operation
It is suitable for 12 volts lights
It has microcontroller for digital accuracy
It has temperature compensation
Specification of PWM Solar Charger Controller
25% current overload
Equalization voltage (10 min)
Boost voltage (10 min)
Temperature compensation (mV/C)
Terminals for wires
-35 to 55oC
133 X 70 X 24 mm
Battery is one the most important parts of the solar system for off-grid because it will store the electrical energy in the form of chemical energy which will come to use in night or when the sun is not shining. In this particular project the batter should be of 12 volts or the battery should be charged at 12 volts. In all type of battery gel or acid type of battery is the best battery to use in solar system as they are not that much expensive and easily can be use in house. As for the small solar plant it is enough to provide electricity, so 12 Volt 18 Ah Sealed Lead Acid Battery is used in this project as in figure 4.4 shown.
Figure 4.4 12 Volt 18 Ah Sealed Lead Acid Battery http://www.batterymart.com/images/products/full/SLA-12V18.jpg
Sealed Lead Acid Battery