Design Of A PV-Diesel Hybrid System
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Design Of A PV-Diesel Hybrid System And Its Comparison With Grid Connected System In Pakistan
1. Project Background And Introduction
The project with respect to this thesis is to design a PV Diesel hybrid system and to compare it with already existed grid connected system. This system is designed for a Jamia Masjid (Islamic center) in Pakpattan, Pakistan. The exact site of the project is a colony of Pakpattan which is in the south-west of the city Pakpattan. The Pakpattan city is situated around 161 Km south west to Lahore. The climate and weather data is almost same for Lahore and Pakpattan. Furthermore it will be first project of its own nature in this area and it will help to design the systems for the residential areas by which a common person can get benefits and get rid of power failures.
Pakistan is located between latitude 24 and 37 degrees North and longitude 62 and 75 degrees East. Pakistan has Afghanistan in the north-west, Iran on west boarder, India is on the east, China in the north and the Arabian Sea is on the south. Pakistan is ageographical centre of the Asian Continent because it builds a type of bridge between Far East and Middle East; also it has a continental type of climate which can be characterized by extreme variations of temperature. Generally the climate of Pakistan is arid, means very high temperature in summer and low temperatures in winter. High altitudes change the climate in the freezing northern mountains which are covered with snow.
There is little rainfall. There are some differences exist distinctly in various locations, e.g. the coastal line along Arabian Sea is usually under warm conditions, whereas the Karakoram mountain range and some other mountains of far north are so cold, completely frozen and covered with snow that these are only visible and accessible by some international world-class climbers for a couple of months of May and June of each year. The variation of daily temperature could be 11 0C to 17 0C but in winters the minimum mean temperature is about 4 0C in January.
Pakistan has tremendous recourses of energy but unfortunately due to mismanagement out of 170 million population just 65-70% has access to electricity. Demand is more than supply of energy to residential and industrial sector. Currently Pakistan is facing 3000 MW of power storage and it is expected that in year 2010 the demand will exceed supply by 5500 MW. The current power and electricity demand and supply gap shows that there is a big need to increases the current power generation capacity in Pakistan.
Aim Of The Thesis
The main aim of the project is to explain the design phase of a single home PV system. The procedures and details of the design are presented with step by step. There are main following aims which are supposed to be fulfilled by this thesis.
a) To go through and grab the core knowledge of the designing process.
b) To get familiar with different tools used for designing and make selection between them.
c) Beyond from bookish knowledge, get to know some real and practical aspects of different PV systems and projects.
The body and structure of the thesis is mainly divided into four phases.
a) Calculation of the primary load for this specific project with the help of PVSYST version 4
b) Division of the load to PV and Diesel Generator according to boundary conditions and design parameters.
c) Economical and technical look on already existed grid connected system.
d) Comparative study between this newly design system and already existed grid connected system in terms of economics, availability and life time
World Energy Situation
There are different factors which effect and play an important role in the consumption, demand and availability of energy, for example the consumption by individual user and business is being increased, everyday growing population and new government policies are some of these factors. But the fossil fuels are exhaustible. There are two aspects of the fossil fuels, 1st is their availability and 2nd is those harmful environmental impacts which appear after using and burning of these fossil fuels. It is equally harmful for the present generations as well as for future generations. But with the passage of time more and more people and governments are getting awareness about these impacts.
The current energy demand projections can be seen from the facts and figures provided by World Energy Administration (EIA)
“The total world energy consumption increases from 472 quadrillion Btu in 2006 to 552 quadrillion Btu in 2015 and 678 quadrillion Btu in 2030—a total increase of 44 percent over the projection period”
Renewable Energy Situation Of The World
When the first Renewable Global Status Report was published in 2004, many indicators have shown dramatic gains. In the last four years from the end of 2004 to the end of 2008, solar photovoltaic capacity increased six times which is more than 16 gigawatts (GW). Wind power capacity has been increased 250 percent to 121 GW; the total power capacity from new renewable recourses has been increased 75 percent to 280 GW which includes significant gains in small geothermal, hydro, and biomass power generation. During the same period of time, solar heating capacity become double to 145 gigawatts-thermal, while the biodiesel production has been also increased six times to 12 billion liters per year and ethanol production doubled to 67 billion liters per year.
The annual percentage gain for the year 2008 was also very amazing and more dramatic. The growth in Wind energy was 29% and grid connected solar PV by 70%. The capacity of utility scale PV plants also increased during this period. Solar hot water systems also grew by 15%. All around the world the governments are changing the policies about the future energy crises and energy markets and policy. In this race the United States of America became the leader and invested $24 billion for new capacity which is 20% of the total global investment. The United States is also leading in adding the total wind energy capacity and also surpassed Germany who was a wind power leader for a long time. Spain has added around 2.6 GW of solar PV, which is a full half of grid connected installations all around the global and five times increase over Spain's 2007 additions.
China has doubled its capacity to produce wind energy and now ranked at fourth place all around the world. Another significant and important milestone was that the European Union and the USA added more capacity to produce power from renewable recourses than from conventional energy sources (as gas, oil, coal and nuclear) and it happened for the first time. The industries of Renewable energy boomed mostly during 2008. Global solar PV production was increased by 90% to 6.9 GW in 2008.
Energy Profile Of Pakistan
The energy profile of Pakistan is inadequate and there are always short falls of energy (electricity) especially during summer. Pakistan needs around 14,000 to 15,000 MW electricity everyday to meet all residential and industrial demands. But Pakistan can produce around 11,500 MW, so it means there is around 3000 MW to 4000 MW short fall. This shortfall was experienced extensively and on its peak this year and affecting industry, commerce and daily life. During this year the shortfall for electricity in rural areas was around 12 to 16 hours and in urban areas it was about 8 to 12 hours. The reasons for this deficiency are limited fossil fuel resources, weak economy and mismanagement of the available energy sources. There are some commercial sources of energy available in Pakistan, they are:
- Hydro energy;
- Nuclear energy;
- Oil and gas;
- Conventional fuels like agricultural wastes, animal dung and wood fuel.
Here, it is an overview of primary energy supplies in Pakistan in MTOE (TOE: ton of oil equivalent. It is an energy unit which is equal to the energy of burning of 1 ton of crude oil which is about 42 GJ)
From fig 1.3 it is clear that energy supply of Pakistan is highly dependent on Oil and Gas. Both Oil and Gas contribute more than 79% of total primary energy supplied. The other sources of energy like hydro- electricity, coal, nuclear electricity and imported electricity contribute about 21% of the total share. As energy is essential for all types of production processes. Pakistan has been growing in agricultural and industrial sector during last decade and that's why energy demand is being increased. As population and industry is growing, the daily demand will increase up to 20,000 MW in 2010.
Pakistan meets around 75% of its energy needs by oil, gas and hydro electricity production. Natural gas has played an important role to meet the energy needs in recent years. But Pakistan needs to expand its energy resource on permanent bases. In order to overcome this energy shortage, Pakistan needs to expand and develop its indigenous energy resources such as hydropower, wind and solar energy. Pakistan is one of the highest solar insulation areas of the world.
Now we will briefly discuss the main energy sources in Pakistan.
After the independence of Pakistan in 1952 Sui natural gas field resources in Baluchistan were discovered first time. The production at Sui started in 1955 and was on its peak in 1985. It was the most productive gas field of Pakistan in early 1990s. In FY 1993 it was accounting 46% of production. After that the second largest gas field was discovered which is also located in Baluchistan at Mari, which was contributing 20% of all production. Total 25 gas fields were fully operational in FY 1993. The estimation of recoverable natural gas reserves were estimated around 662.0 billion cubic meters, with an extraction rate around 14.0 billion cubic meters.
In order to meet the increasing demand of energy and for future planning, efforts from government are being made to increase the production of gas in the country. To do this exploration activities are the first step. The estimation of recoverable reserves of natural gas was 29.671 trillion cubic feet in January 2009. During July-March 2008-2009 the average production of natural gas was 3986.5 mmcfd (million cubic feet per day) but during the corresponding period of last year it was around 3965.9 mmcfd which shows an increase of around 0.52%. At the moment 26 public and private sector companies are engaged in exploration and production activities of oil and gas in Pakistan.
The contribution of LPG (Liquefied Petroleum Gas) is about 0.7% to the total energy supply of Pakistan. LPG is being supplied to many remote areas where the supply of natural gas is not technically suitable. To do this government has changed policies for energy supply and management and as a result of this modification the supply of LPG in 2007-2008 was 601,592 Metric Ton and in last few years the annual cumulative growth rate was 18.2%.years. Around 32,621 MT of LPG was imported during July-March, 2009.
The main reason of encouragement of Compressed Natural Gas (CNG) use is to improve environment and to decrease the dependency on other fuels. The price difference between petrol and CNG is about 60.0 percent, that's why vehicles are being converted to CNG day by day and around 2.0 Million vehicles are using CNG. The numbers of CNG stations are also increasing day by day and there are around 2,700 established CNG stations in Pakistan which covers an investment of Rs.70 billion. At present Pakistan is the largest CNG user country.
The estimation of recoverable reserves of crude oil in total in Pakistan were around 313 million barrels in January 2009. The average production of crude oil during July-March 2008-09 was 66532 barrels per day. The average production of crude oil during last year was 70166 barrels per day which shows a negative growth of 5.2 percent.
The average production of oil in Pakistan remained 67,438 BOPD in 2006-2007. Oil and gas development company and limited (OGDCL) was the biggest oil producing company in Pakistan with a production of around 13.261 million barrels which contribute around 54% of the total oil production per year of Pakistan with an average rate of 36,332 BOPD. After that British Petroleum (BP) is the second largest oil producing company with total contribution of 16% of total oil production in Pakistan. BP produces around 4.025 million barrels averagely with 11,029 BOPD. Pakistan oil fields limited (POL) produced around 3.231 million barrels. There are other small oil production companies as well in Pakistan.
The total estimation of coal recourses of Pakistan is more than 185 billion tones. Thar coalfield (Sindh province) is the biggest coal source which worth more than 175 billion tones. Pakistan's coal is generally ranked from lignite to sub bituminous. The production of coal was decreased in during July-March 2008-09 by 28.8%. About 60.4% of the total coal production is being consumed by the brick kilns industry. Cement industry is also using a large fraction of coal which is around 37.4% and almost all cement industry is being switched on coal from furnace oil. As energy demand is increasing day by day and government is reshaping the energy policies. Due to high prices of imported energy government of Pakistan has decided to increase the share of coal from 05 to 19% in the overall energy mix up to 2030. In view of expected shortfall of energy resources and electricity during the next 10 years the maximum utilization of coal would be needed for power generation and gasification. According to government energy security plan, a target has been set which is to generate about 20,000 MW power from coal by 2030 and 50% by 2050.
Pakistan is the 7th nuclear power of the world. In 2009, the nuclear power plants contribute up to 2.4% share to the total electricity production in Pakistan. Pakistan has two working nuclear reactors which produce about 425 MW power for the generation of electricity. The third nuclear reactor will be operational in spring of 2010. In Pakistan nuclear power contributes very small to the electricity production. The total generating capacity is around 20 GWe while in 2006; 98 billion kWh gross was generated. First nuclear power reactor was started in 1971 in KANUPP near Karachi and it has small capacity of 125 MWe and it is pressurized heavy water reactor (PHWR). The second unit was started in May 2000 and is known as Chashma-1 in Punjab. It has capacity of 325 MWe. It is pressurized water reactor (PWR) and was supplied by China's CNNC under safeguards. It is also known as CHASNUPP-1. In December 2005 construction of its twin Chashma-2 was started. It is reported that it cost PKR 51.46 billion (US$ 860 million, $350 million were financed by China).
But these sources are not sufficient to overcome this energy crises and Pakistan needs to develop renewable energy sources.
Renewable Energy Sources In Pakistan
Pakistan is situated in such a special geographic location that it is blessed with abundant and inexhaustible Renewable Energy (RE) resources. These resources can play an effective and considerable role for the contribution towards energy security of Pakistan. When we look into current world energy scenario in general and energy scenario of Pakistan in particular, the development and adoption of RE technologies makes better sense. Government policies and objectives to develop RE technology are also matching with this sense so that the share of RE in overall energy mix should be at least 5% by the year 2030.
Wind potential: 0. 346 Million MW
Solar potential: 2.9 Million MW
Mini & Small Hydel: 2,000 MW 
There is a significant potential of wind energy in Pakistan especially in the coastal belt of Baluchistan and Sindh, and also in the desert areas of Punjab and Sindh. However this renewable energy source has not been utilized. AEDB collected the wind data of all Pakistan from Pakistan Metrological Department and was analyzed. On the basis of this collected data and analysis, it was stated that the coastal belt of Pakistan has a God gifted 60 km wide (Gharo-Keti Bandar) and 180 km long (up to Hyderabad) wind corridor. This wind corridor has the potential to generate 50,000 MW of electricity. AEDB has done other different surveys in Gharo and Jhimpir regions and some coastal area of Baluchistan. After these surveys it is concluded that in the south region most of the remote villages can be easily electrified through micro wind turbines. Furthermore it is estimated that in Baluchistan Sindh and Northern areas more than 5000 villages can be electrified through wind energy.
Sincere efforts and aggressive lobbying has been done by AEDB with national and international investors to invest and to make them realize the tremendous potentials of RE. AEBD is in negotiations with international companies to set up their business in Pakistan. However large wind mills have not been installed yet but 30 wind mills for water pumping have been installed on experimental basis in different parts of Baluchistan and Sindh. In southern coastal areas of Pakistan remote villages are currently electrified with energy and so far more than 17 villages have been electrified using micro wind turbines.
Around 95% of total electricity generation is from hydropower in Pakistan. But during summer in hottest and driest months of the year it becomes less productive and cannot meet the energy demands. Also, around 70% of the population lives in 50,000 villages. Many of these villages are very far from the main transmission lines and also it is not economically viable to connect these small villages to the main grid due to their small population. On the other hand solar energy has excellent and significant potential. Pakistan is one of those countries which receive solar radiations at high level throughout the year. Every day it receives an average of about 19 MJ/m2 of solar energy. Studies have been already done and solar systems have been developed and tested.
There is a list of different projects which are completed by Pakistan council of Renewable energy technology.
Potential Of PV In Pakistan
The location of Pakistan is very ideal to take advantage of solar energy as a source of energy because Pakistan is in the Sun Belt region. Solar energy is available abundantly and widely distributed all around the country. Following figure shows solar insolation map for Pakistan. The map shows around 200-250 W/m2 per day. The Baluchistan province is very rich in solar energy. It receives around 19-20 MJ/m2 per day averagely which is equal to 1.93-2.03 MWh/ m2 per day with annual 8-8.5 mean annual sunshine hours. These conditions are ideal for PV and solar energy applications.
Solar energy is very good option for off-grid villages. There are around 75,000 off-grid villages which contains 4 million homes and every home accommodates around 4-5 people. These off-grid villages are situated in the Baluchistan and Frontier Province. AEDB has set a target to electrify a thousand villages via solar technology by the year 2010. In this respect the first contract has been given to the Sehgal electronics group (Pakistan). Each home which is electrified with PV will have around 400 W power supply and lead acid batteries for overnight storage. There are also other plans to have local production using PV modules with and estimation of this production is around 3MW/year.
Possible Routes For Solar PV In Pakistan
The global demand of PV equipment is increasing day by day and due to this fact the prices for PV systems, equipment and electricity has gone down remarkably. PV could be exploited in Pakistan through following two routes.
Off-grid Or Stand-Alone Sector
Stand-alone systems generate electricity independently of the utility grid. Stand alone systems can be a very good option for the remote areas and very deep located villages, where the extension of power transmission lines would be more costly. Also it could be implemented in environmentally sensitive areas as parks, remote homes and cabins. In rural areas, it could be used for solar water pumps and farm lighting. 
Grid-connected PV systems supply extra power when the home system's power supply is not sufficient to fulfill the load. These systems remove the need of battery bank. In some situation, utilities allow net metering, by which the owner can sell extra power back to the utility.
Current Solar Energy Applications In Pakistan
Both PV and solar thermal have a wide range of applications in Pakistan. Although the scale of utilization and adoption has been very small but it has been utilized for last 25 years in Pakistan. Different applications mainly PV and solar thermal applications are summarized as.
Eighteen PV stations were built by the government in the early 1980s to electrify different villages the country. The installed capacity was nearly 440 kW but due to the lack of technical knowledge and follow up, these systems could not perform as required. Currently in Pakistan solar energy is being used for telephone exchanges stand alone rural electrification, cathodic protection, highway emergency telephones and vaccine refrigeration in hospitals. In different parts of Baluchistan, about 20 solar water pumps have been installed for drinking purposes by The Public Health Department. The northern and western area of Pakistan are mostly hilly and mountain areas (Hindu Kush-Himalayas, HKH region), which are blessed with a lot of sunshine with 4-6 kWh/m2 daily average solar radiation. Seven solar stations were installed in this region in the late 1980s for lighting by different companies. The total capacity of these systems was 234 kW. They are not in operation now due maintenance problems.
SIEMENS Pakistan has installed many stand alone solar systems in Pakistan. On the Lahore-Islamabad Motorway, it has installed power supply systems for many microwave-link repeater stations and more than 350 emergency call boxes.
Solar Thermal Applications
There are many applications which utilize solar energy directly by utilizing its heat characteristics. Such applications are much simple, low cost and easy to adopt. The applications include heating and cooling of homes and buildings, cooking, water heating for domestic and industrial use and drying agricultural products. A brief description of such applications in Pakistan is given here.
Solar Water Heaters
This technology is quite mature in Pakistan but very limited because of its higher capital cost as compared to conventional water heaters which operate on natural gas. But in last couple of years it has started to gain popularity because a number of public sector organizations are working to develop low cost solar water heaters. The prices of natural gas and electricity are increasing day by day, so people are adopting solar water heaters and also private sector has already started the production of such heaters.
Different public sector organizations have been working to develop low cost and efficient design solar cookers. In HKH region of Pakistan, more than 2000 solar cookers are in use. This number is very small. It needs to be more popularized. Pakistan needs to reduce the use of precious forest resources as fuel wood and to replace it with solar cookers.
Solar energy can be very good option for drying agriculture products. By this, we can get very good quality products at much less cost. Northern mountainous areas like Gilgit and Sakardu are very rich in fruit production like apricots which used to be wasted by tons every year. But now solar dryers are being used to dry large quantities of fruit, which is leaving a positive effect on the economy of this area. Different NGOs are working for the popularizing and the use of such dryers.
Drinkable water is unavailable in many parts of Sindh, Baluchistan and southern Punjab and it is very critical issue. Underground water is available but it is highly saline. This saline water is not fit for drinking at all and causes many dangerous diseases such as hypertension. Solar energy can be utilized to convert this available saline water into drinkable water. Solar desalination is very simple, low cost and easy to use. Also it is very easy to adopt. A successful solar desalination project is in operation and it is working very fine and helping to change the life style of the population of Gawader in the Baluchistan province. It consists of 240 stills and each can clean 6000 gallons of seawater per day.
2. Basics And Components Of A PV System
Basics Of A PV System
Photovoltaic is the technology which converts solar energy directly into electricity and this process is carried out though solar cells. Solar cell is a device which converts sun energy into electricity. We can say solar cell as photovoltaic cell as well but solar cell term will be used when the source of light is defined as “sun” but if it is not defined than we can say it as photovoltaic cell.
Now days when entire world is looking for a neat and clean environment and want to meet huge energy requirements without disturbing and populating the environment, sustainable energy sources seems to play their important role. Researchers and scientists from all around the world are looking for these types of renewable sources. They are trying to get the energy needs from these renewable energy sources. The main advantages of using renewable energy sources are
1. Neat and clean environment
2. Yield of energy is higher
3. Safer for electricity production as compared to convention methods (low voltage)
4. Long life times
5. Low maintenance cost
6. Use of natural sources which are being wasted with time.
These are the reason, why people prefer renewable energy sources. There are different types of renewable energy sources as
1. Solar energy
2. Wind energy
3. Tidal energy
4. Geothermal energy
5. Wave power
7. Bio energy
We will discuss solar energy in detail and its related topics in this report. There are different units in a PV system and all these units combine to make a full working PV system. These are
PV System Components
1. PV Panels
2. Trackers and tracking system
3. Array DC Disconnect
4. Blocking diodes
5. Charge Controller
6. Battery Bank
7. System Meter
8. Main DC Disconnect
10. Kilowatt-Hour Meter
11. Backup Generator
PV panels are the defining components of a PV system, which uses sunlight to make direct current (DC) electricity. Wafers of semiconductor material are used for this purpose. They use light (photons) to produce electricity (photovoltaic effect). When the electricity is generated than it powers our electric loads such as lights, computers, and refrigerators. PV panels differ from each other on the basis of power rating in watts which is based on their maximum power generation capacity.
Solar cell is the fundamental and basic building block in a PV system which acts as power conversion unit of this system. There are different types of solar cells now days available having different power about 1 or 2 watts. Usually solar cells are made of single crystal silicon and they are limited to about 25% efficiency. The reason is that they are most sensitive to IRL (infrared light), and the radiations in this region of electromagnetic spectrum are relatively low in energy.
Another type of solar cells is Polycrystalline solar cells. They are made by a special casting process. In this process molten silicon is being poured into a mould, allowed to cool down and then it is sliced into wafers. By this process we can make relatively cheaper cells as compared to single crystal cells, but their efficiency is less than 20%. The reason is that there is internal resistance on the boundaries of silicon crystals which affects the efficiency.
The third type of solar cells is amorphous cells and they are made by a special process in which silicon is deposited onto a glass substrate from a reactive gas such as silane (SiH4). These types of solar cells are used in solar powered watches and calculators, but now day's bigger modules are also manufactured. They are also rather cheap and their efficiency is only up to 10%. The reason is, since amorphous silicon cell has no crystal structure and there are much internal energy losses.
Solar cells are not just restricted to semiconductor materials; solar cells are available now days which convert sun light into electricity by organic molecules. Their efficiency is up to 10%. Apart from various types of silicon, other materials can also be used to make solar cells like cadmium telluride and gallium arsenide. There are different types of cell packing's. The most common are "raw cells," and they are often with cover sheet. Now we have discussed solar cells. These solar are combined together to make a module to get boosted power for practical purposes. Than these modules are combined together to make a panel, these panels are joined together to form a big array.
Trackers And Tracking System
Solar tracker is a device on which solar panels are fitted and the motion of the sun is tracked through this device. It ensures that the maximum amount of sunlight will strike to the panel throughout the whole day. Actually it is a mounting rack which follows the sun constantly. By using trackers, we can utilize maximum sunlight and thus can produce more electricity. In the morning time, it is low on eastern horizon while at the sunset it is low at western horizon. But at noon the position of sun is very high in the sky. This motion is due to the rotation of earth. Trackers keep PV modules perpendicular to incoming sun radiations and maximize the energy production. The increment in the energy production using trackers depends on the site and the type of tracker. Usually energy production increases 25 to 40% annually, which is shown in more detail in the following figure.
To get maximum efficiency tracker must be placed in a suitable location. A good tracker site is that on which sun can be seen very early in the morning time and receive sunlight until sunset. There should be no solar obstructions like trees and buildings on the site or near the site in order to work perfectly. Before considering the tracker into system design, an evaluation of the site is done using Solar Pathfinder. Trackers are usually mounted on ground and use a heavy steel pole which is sunk into a concrete foundation. There are some systems where the trackers are mounted on the roofs, but it can create structural problems. There are two basic types of trackers.
1. Electrically operated
2. Thermally operated
Thermally Operated Trackers
These trackers are based on mass transfer from one side to the other side of the tracker to track the sun. This transfer of mass causes the tracker to turn from east to west by following the sun. Actually two tubes filled with Freon (which vaporizes and become gas) are mounted on east and west sides of the tracker. With the sunlight, the temperature of Freon becomes higher on one side of tracker, it starts to become vapors. These vapors take more space than as compared to the liquid Freon, which pushes Freon (liquid) to the other side. This transfer of mass from the one side to the other side of the tracker causes the change in the balance of tracker which eventually rotates it to the west. Usually they are slow in their reaction as they are powered by solar heat. They can only track the east-west motion of sun but they do not track the seasonal north-south motion of the sun.
Electrically Operated Trackers
Photoelectric sensors are used to determine the exact location of the sun in these trackers. Electric motor is used to position the tracker which is activated by the sensor and an electronic control box. They keep the PV array perpendicular to the sun. The advantage of electrically operated trackers is that they are very precise. These trackers can be dual-axis as well which track seasonal north south motion as well. Since they are operated electricity and ignore the heat of sun, this makes them more accurate in cold and winter climates.
Array DC Disconnect
It is used to interrupt the electricity flow in a safe way. It is very essential part of the PV system during maintenance and troubleshooting. It may also be integrated with either fuses or circuit breakers, if needed.
The Blocking Diodes
These blocking Diodes are used to prevent the reverse leakage of current from the battery through module. These are placed in series with cells or modules. We can use them to prevent this phenomenon on two situations.
A: At night: In the battery charging systems, module potential usually drops to zero at night, as a result of this, the battery can discharge in reverse direction through the module. This would result in the loss of precious energy which was stored at day time but this would not give any harm to the modules. To avoid this loss we place diodes between the cells (or modules) and the battery so that it can block this nighttime leakage.
B: During the day: Blocking diodes which are placed at the head of wired strings can stop Blocking reverse flow down damaged modules from parallel modules during the day. If there is some shading on one string, or if there is some short circuit in any of the modules, these blocking diodes prevent the loose of current backwards down from the shaded or damaged string. In this case the string which is shaded or damaged is “isolated” from the other strings, and more current is sent to the required load. In this type of configuration, these blocking diodes are called “isolation diodes”.
The function of charge controller in PV system is to protect battery bank from overcharging. It monitors the battery bank and when the battery bank is fully charged, it interrupts the electricity flow from the PV panels. Batteries are important, expensive and particular how they are treated. In order to maximize the life span of battery bank, one will definitely avoid their overcharging or undercharging. Modern charge controllers now a day's incorporate the maximum power point tracking (MPPT), which first optimizes the PV array's output and then increases the energy it produces. Some charge controllers are battery based which include a low-voltage disconnection. It prevents over discharging.
As solar energy supply varies with time, means at day time when sun will be at its peak the supply of solar energy will be higher and in the morning and evening timings the supply will be less but at night in the absence of sun the supply will be zero. So at night the energy needs could be fulfilled with the stored energy. This is the reason why energy storage is also important. Sometimes we don't need to store energy as if the energy is just required at day's timings. But for a home or commercial application where we need energy supply at night as well, than we need to store energy at day and to use it at night. There could be another option that we can use some backup system. There are many methods of energy storage like mechanical storage (in the form of compressed air or fly wheel) which is demonstrated for large scale storage, electromagnetic storage (in the form of electric current in superconducting ring) and chemical storage (in the form of batteries and hydrogen production). But all of these methods most commonly batteries are used because of their
1. good availability
2. cost effectiveness
Battery lifetime depends on the number of cycle rates numbers of charge/discharge. If we will discharge the battery deeper, the lifetime would be shorter. Capacity is the most important parameter of battery and it is measured in Ah. The battery capacity depends on the amount of discharging current, higher the discharging current, lower would be its capacity, and vice versa. There are many different ways to charge batteries, e.g. Constant voltage with constant current, which basically depends on the type of battery used. These charging characteristics are prescribed and recommended by different standards. That's why the solar batteries costs are much higher than the costs of classic car batteries, because they have longer lifetime, lower discharging rates and the maintenance costs are lower. 
Operation Of Batteries In PV System
Batteries operate under specific conditions in a PV system and these conditions must be kept in mind while designing the system. These are special conditions which affect the battery life and their efficiency. The most important is the cycling with various cycles of different regularity. In daily cycle, the batteries are charged in day time and discharged during night time. When there are variable climate conditions, there is some superimposition on daily cycle and it is called climatic cycle 
Discharge: During the discharging process, PbO2 (positive plate) and Pb (negative plate) react with the help of electrolyte of h3SO4 (sulfuric acid) to create PbSO4, h3O and energy.
Charge: During charging process, this cycle is being reversed. It means lead sulfate and water are electro-chemically combine and convert to Pb, PbO2 and h3SO4 by the help of an external electrical charging source.
The most commonly used batteries in PV systems are lead acid batteries and they are discussed below.
Lead Acid battery is basically made of two electrode plates, lead, and lead oxide (some other elements are also used to change hardness, porosity and density etc.) with a special electrolyte 35% h3SO4 and 65% h3O solution. This electrolyte causes reaction and in the result of reaction electrons are produced. When we test batteries for measuring the quantity of sulfuric acid in electrolyte and if this reading is low, it means electron making chemistry is lacking. Why this happened? Actually it is resting on the electrode plates and when we recharge the battery that sulfur will return to electrolyte.
Types Of Lead Acid Batteries
1. SLI: These are used in automotive and vehicle applications and have very high discharge and charge rates. They supply high peak powers for very short time. These batteries have poor life under deep cycling but have very good life time under shallow-cycling. These should not be used in PV systems because their properties are not optimized for the use in a renewable energy system (lifetime in PV systems is very low).
2. Motive power batteries or Traction: These batteries are used for providing electric power to small transport vehicles like golf carts. If we compare these to SLI batteries, they are designed in a way that they have greater ability of deep and frequent cycling but still these can maintain a long lifetime. This feature makes them attractive for the use in PV system but due to their motive power batteries should not be used in any PV systems since their self discharge rate is very high due to the use of special electrodes of lead antimony. High self discharging rates will effectively cause high power losses and will make the PV system inefficient as whole, unless batteries experience a large depth of discharge (DOD) on daily basis. Their ability to withstand deep cycling is far below than that of true deep-cycle batteries. Therefore, these are not suitable for PV systems.
Stationary batteries: These batteries are usually used for emergency power supplies or the applications where the power supply is uninterruptable. These are shallow-cycle batteries and they intend to remain very close to fully charged state for the majority of lifetime with just only occasional deep discharges. They could be or may be used for a PV system if battery bank is properly sized so that it will never fall below the DOD of between 10% & 25%. 
- Low cost.
- Reliable, a long history of development.
- Tremendous tolerance for abuse.
- It can tolerate overcharging.
- The world's most recycled item
- Capacity to deliver very high currents.
- If stored without electrolyte it has indefinite shelf life.
- Very wide range of capacities and sizes available
- Low internal impedance.
- Many suppliers worldwide.
- Very bulky and heavy.
- Has columbic charge efficiency only 70%.
- During charging there is danger of overheating.
- It is not suitable for quick charging
- Typical cycle life is 300-500 cycles.
System meters first measures and then display many different aspects of PV energy system. Like system's performance, status, information about how much full is battery bank, how much electricity has been generated or generating and how much power is in use. System without metering is just like a running car without any gauges, although it is possible to do, but it is always better to know the status of the system and fuel.
The function of inverters is to convert DC electricity produced PV modules into AC electricity (alternating current). It is very common and mostly used in homes for powering different appliances. Grid connected inverters combine the electricity they generate with grid's utility AC electricity and allow the system to give back electricity made from solar to the utility grid. Grid connected inverters operate without batteries, but some battery operated models also are available. Battery-based inverters for grid connected or off-grid systems often include a battery charger. This battery charger is capable of charging the battery bank either from the grid or from a backup generator during bad cloudy weather.
Mostly grid connected inverters can be installed outdoors (like in the shade). But most off-grid inverters are not capable to operate outdoor and are not weatherproof and they must be install indoors and close to the battery bank.
Most homes with a grid connected solar energy system will have AC electricity which is both way coming from and going to electricity utility grid. A bidirectional KWh meter can very easily track the record electricity flow in each of the two directions simultaneously. We just need to know the information of how much electricity we are using and how much our solar energy system is generating.
Generator is a device which consumes fuel to produce energy for domestic and commercial use. Diesel generator is a combination of diesel engine and alternator (electrical generator). They are usually used as power generating unit for remote areas or an auxiliary source of energy. Generally diesel engine is an internal combustion engine but more specifically we can say it a compression ignition engine. The ignition in a diesel engine takes place between fuel and highly pressurized hot compressed air. The fuel in the engine is suddenly exposed to this pressurized air, rather than to use a different ignition source (such as spark plug). This process is called “the diesel cycle” (Rudolf Diesel invented it in 1892). The flow of the fuel is the factor by which we can control the operating speed of diesel engines, which determines the frequency of output AC voltage.
The fuel cost of the diesel generator governs the operating cost while the maintenance cost depends on the load of engine and operating hours. Mechanical wear increases with the frequent start of diesel generator. In order to minimize these costs following points should be kept in mind.
1. Once engine is started, it should run for minimum period of time which is at least 20 minutes of continuous operation. It will decrease the engine wear and will eventually minimize maintenance costs.
2. The generator should not be operated below minimum power level for a long time. Minimum load is selected as 40%of rated capacity which protects glazing on cylinder walls and avoids low fuel efficiency.
Fuel Efficiency And Fuel Cost Of A Diesel Generator
A medium size diesel generator has fuel efficiency if about 3kWh/liter when it runs above 80% of its rated capacity. Fuel efficiency of diesel engine decreases in the operations of lower output power, which is shown in the following . The figure shows a sharp increase in the cost of fuel below a minimum generator load of about 40%. Diesel fuel cost is assumed 0.5US$ . The fuel cost may differ due to local infrastructure and fuel subsidies, global supply situations and remoteness of the location. When the diesel generator is operated at low power levels, not only fuel efficiency decreases but maintenance requirements also increases. Very simple reason for increasing these maintenance costs is that when it is operated at low power levels, the temperature does not reach to the normal operating temperature in the combustion chamber, which leads to carbon deposits on cylinder walls and increases the acidity level of lubrication oil.
There is another option to use gasoline generator is as well, here is some comparative study and after that it would be decided that either gasoline or diesel generator should be used.
Gasoline & Diesel Generator's Performance, Safety & Cost Comparison
Both diesel and gasoline generators can supply electrical power for different applications. It is hard to compare performance of these two but the usage factor can help to have comparative study. Performance is not very important and vital factor for backup generators because they are not used on daily basis. But when the generator usage is continuous in the case of portable generators, performance can be measured. The life time of diesel generators is long as compared to gasoline generators and also they are more fuel efficient. The reason is that normally diesel generators operate at lower RPM and can produce more torque at lower speeds which increases engine life. We will study this comparison with the help of an example, which is “Guardian's QUIETPACT® RV generators”. The gasoline fueled generator with power of 7500 W runs at RPM of 2571 while a diesel fueled generator of same power rating runs at RPM of 1950. So with performance point of view, it depends on the type of application and how good the generator is being used with manufacturer settings.
As far as safety is concerned, gasoline can be ignited with static electricity and is more combustible, as usually we see signs to turn off car engine and to avoid the usage of cell phones during gas filling. Diesel and gasoline both can produce harmful and dangerous fumes including CO which can be a cause of serious problems. The diesel has more safety margin.
If we compare the overall cost of diesel and gasoline generators, a lot of issues must be discussed. First, the cost of diesel generators can be three times as high as gasoline generators because more expensive parts are used in their manufacturing and automatically it increases the cost of repair when they break down. The next is fuel cost. The cost of diesel is usually more than gasoline and also they need some additives for longer shelf life. The consumption of fuel is relatively less for diesel generators as compared to gasoline generators and they can save some amount of fuel. Diesel generators have longer engine lifetime and low maintenance but when maintenance and repair is needed, it is more expensive than to repair gasoline generator. Diesel generators can save more money as compared to gasoline generators in the long run.
So after comparing these two, I have decided to choose diesel generator instead of gasoline generator.
3. Types Of PV And PV Hybrid Systems
Generally the classification of PV systems is based on their operational and functional requirements, the configuration of their components and the connectivity of the equipment to power sources and electrical loads. There are two main types of PV systems are
1. Grid-connected PV systems
2. Stand alone PV systems
PV systems are designed to supply DC and/or AC power and can operate interconnected with utility grid or independent of it. These can also be connected with other energy storage systems and energy sources.
Grid-Connected PV Systems
Grid-connected PV systems are designed to operate parallel with the interconnection of electric utility grid. Inverter or Power conditioning unit (PCU) is the basic component in grid-connected PV systems. PV array produces DC power supply and the PCU converts it into AC power supply which is consistent with the power and voltage requirements of the utility grid. PCU automatically stops the power supply to the grid when utility grid is not energized.
The grid connected PV systems act as producers and/or consumers of electrical energy. When the system (could be domestic or industrial) produces more energy than its needs, the excess energy is than passed to the utility grid company. It is added into the system and counted with a special "debit" meter by that utility grid company. But if the system does not produce enough energy to overcome its own needs as it could be during night times then that depictive amount of energy is taken from utility grid company or network with a special "credit" meter.
Stand Alone PV Systems
Stand alone PV systems are designed to operate independent of electric grid. Mainly stand alone PV systems are used in isolated and remote areas where the connection with grid or electricity network is not possible. In this type of systems the storage system (batter bank) is very important component and storage is guaranteed by batteries. The design and sizing of such system should be done in such a way that it could supply and meet the required load even in bad weather conditions or during winter months.
For this surety these systems could be coupled with diesel generator, wind turbine or hydro generator and the systems after this type of coupling is called PV Hybrid systems. There could be different arrangements and designing methods of PV systems depending on the requirements and type of load to be fulfilled. The simplest one is that in which DC power supply directly from PV array is connected directly to a DC load. In direct coupled systems there is no energy storage or battery bank, that's why these type of systems can operate in sunlight hours and this feature makes them suitable for common applications like water pumps, ventilation fans and small circulation pumps used in solar thermal heating systems. There is a critical part in designing the coupled systems that matching the impedance of electric load with the maximum power output from PV generator.
In many other type of PV stand alone systems battery bank is used for the storage of energy and power inverters which can fulfill AC/DC loads at the same time. 
PV Hybrid Systems
PV hybrid systems are composed of combined solar energy with some other electricity producing sources like wind turbines, diesel generators or small hydro plants. The choice of other source of energy to be combined depends on the needs and the geographic situation and other specifications. The hybrid systems are best for the remote areas like islands and remote villages, also for remote applications like communication stations and military installations.
Before go for designing a hybrid system, the specific energy needs and the available energy sources should be known. It means the potential for all available energy sources like solar energy, wind energy and hydro energy must be studied, so that the best combination could be made which can meet the specific energy requirements in best way of economy and availability.
This was a short description of PV hybrid systems but now we will discuss PV diesel Hybrid systems as it is the main part of this report.
PV Diesel Hybrid Systems
In remote areas the electricity has been produced by engine driven generators in the past. For those applications where we need a reliable and stationary generator is required, diesel generators are preferred. Petrol generators may provide electricity at lower cost due to their less frequent use. Engine driven generators are less efficient when driven at light loads (around 40 to 50% of their rated capacity) which can shorten their operating life and it results in high maintenance cost. When the engine is operated at light loads, the combustion temperature goes down which results incomplete combustion and carbon starts to deposit (glazing) on cylinder walls and this leads to premature engine wear and tear.
In recent years, the cost of renewable energy technology has been declined continuously and also the concept of usage of alternative energy is growing day by day. Due to these two factors, the utilization of renewable energy sources has been increased for remote areas. Typically PV modules with small to medium size wind turbine are being used, but for some locations small hydro electric generators are suitable. In simple words combination of renewable energy sources and conventional energy sources with energy storage (battery bank) makes a Hybrid system which can give reliable and economic electricity supply. If we compare a system only with PV generator with a PV hybrid system, the second one reduces the batter size and improves the reliability of overall power supply. In hybrid system, the renewable energy source and battery bank try to reduce the run time of diesel generator. There is sufficient storage in these systems which allow the load to be shifted. Generally these type of systems are installed in those locations where the logistics and costs of a reliable supply of fuel are not major contributing factors to overall system operation cost.
The displacement type systems are sized to decrease the fuel consumption of diesel generator by 70 to 90% as compared with a diesel battery system, so it relies mainly on renewable energy sources like solar. The engine driven generator still remains in the system to equalize the battery and it provides a backup for those periods when there is low solar input or high load demand. Such systems are installed in those locations where some attractive incentives for the use of renewable energy exist or fuel supplies are costly and unreliable.
Usually the conventional power supplies with diesel in remote areas are not flexible to react to the changes in load demand and varying operating conditions. This results in the compromises on reliability and efficiency. Significant changes in long term and short term load demand could happen as a result of
1. Increase or decrease of population;
2. Special community events;
3. Seasonal change in environmental conditions ( summer, humidity);
4. Change of consumer trends (increased use of home appliances)
But renewable energy sources and batteries are modular in nature and can be upgraded without any problem when in future the load demand is increased with time. It means that we do not need to change the whole system. But as far as other components of the systems are concerned, they are different in their nature. For example inverters, battery chargers and PV charge controllers should be in such a way that the future increased demand should not exceed their rated capacity. Power conditioning devices are also inherently modular and they facilitate convenient system upgrade.
Hybrid System Configurations
PV-Diesel hybrid systems produce AC power supply by the combination of PV array with inverter, which can be operated parallel or alternatively with engine driven generator. PV diesel hybrid systems can be classified as
1. Series hybrid energy systems
2. Switched energy systems
3. Parallel energy systems
Here is some discussion about these three types.
Series Hybrid Energy Systems
In this configuration, the power generated by generator is rectified first and then converted back to AC supply to fulfill AC demand which incurs much conversion looses. During low electricity demand periods, the diesel generator is powered off and the demand can be fulfilled from PV and stored energy. AC supply reaching to the load is converted from DC by an inverter. In series configuration the system efficiency is low because most systems pass large fraction of produced energy from battery bank which increases the cycling of the battery.
The SOC (state of charge) of the battery and actual load decide whether the diesel generator will operate or not, which depends on power supply from PV and diesel generator, load demand and the batteries are either charged or discharged. Solar controller is used to control such situations which prevent the overcharging of the batteries, when PV supply is more than the load and also the batteries are fully charged. Although energy gain is marginal for a well sized system but we can add a maximum tracking point which can improve the utilization of available PV energy. The system can be operated either in manual or automatic mode. This can be done by adding some extra components in the system.
There are certain merits and demerits of these configurations, they are as below.
1. It has simplified electrical output interface as no switching of AC supply is required between different energy sources.
2. The supplied power to the load is not interrupted when diesel generator starts.
3. The inverter can produce a square wave, modified square wave or a sine wave depending on application.
1. The cycling of the battery bank increases which decreases the life time.
2. As diesel cannot supply power directly to the load, that's why system efficiency is low.
3. If there is some problem in inverter or in case of its failure, it results in complete loss of power. In this case diesel generator has to supply power directly for emergency purposes.
4. The cycling profile requires the large battery bank to limit the depth of discharge.
It is one of the most common configurations used, but it has some operational limitations. As the name shows, it operates either with diesel generator or inverter as AC source but no parallel operation of the main power generation source is possible. Switched configuration hybrid systems can be operated in manual mode but it makes the system more complex. In order to get rid of this complexity, it is desirable to add some automatic control unit. This automatic control unit can work by adding appropriate battery voltage sensor and start/stop control unit of diesel generator. The main advantage of this configuration is that the load can be fulfilled directly from diesel generator, which gives overall higher conversion efficiency. In this configuration both PV array and diesel generator can charge the battery.
This configuration has also certain advantages and disadvantages as
1. As the generator can fulfill the load directly, it improves the efficiency and reduces the fuel consumption.
2. The inverter can make a square wave, modified square wave or a sine wave depending on application.
1. Power supply is interrupted time by time as AC power sources are transferred.
In this type of system PV and diesel generator supply the load separately when the load demand is low or medium. But when the load demand reaches at peck point, then PV and diesel generator combine and supply that peak load. In this configuration we use a Bi-directional inverter which has two functions
1. It can charge battery bank when excess energy is available from diesel generator (rectifier operation).
2. DC/AC converter (inverter operation).
The bi directional inverter can also provide “peak shaving” which is defined as “the ability of parallel hybrid energy systems to supply load that exceed the power rating of the engine driven generator of the inverter from combine sources as part of the control strategy when the engine driven generator is overloaded ”
Parallel configuration hybrid systems have also merits and demerits over other systems, like
1. The efficiency of diesel generator could be maximized.
2. The maintenance of diesel generator could be minimized.
3. The system load could be fulfilled by optional ways.
1. It should be controlled by automatic control unit in order to make the operation of the system more reliable.
2. Operation of the system is much complex for untrained users
In PV diesel hybrid energy systems three types of conversion devices are used to control and conditioning of power flow. They are battery charge regulator, inverter and a rectifier. The rectifier or battery charger is included in the system to convert AC power generated by diesel generator to DC voltage. This is done to recharge the battery bank. Series type hybrid systems have always low efficiency because they use two conversions AC/DC and DC/AC. If we assume that both efficiencies of rectification and subsequent inversion of DC voltage are very high, let's say 90%, it will result a loss of 19% of total power gained in these conversions. This is the reason why parallel and switched configured systems have always more overall system efficiency.
In hybrid energy system operation, usually the generator operates at 80% of its rated capacity. In switched or parallel configured energy systems AC power is supplied directly from diesel generator but the excess power which is more than the required load is used to recharge battery bank. This supply of power to battery bank is according to a defined battery charge strategy which takes the battery to high state of charge.
In some modern parallel hybrid systems, a bi directional inverter unit is used. This bi directional inverter unit consists of solar controller, inverter and rectifier. Automatic system management is also applied as a part of control functions to switch different electronic devices micro controller is implemented which included automatic management system. This central controller system in parallel hybrid system has following tasks:
- Continuous control of power flow;
- Automatic on/off control of diesel generator;
- To disconnect the loads at low voltages in order to prevent deep discharging;
- To share the load between diesel generator and inverter at peak loads exceeding the rating of inverter or diesel engine;
- To control battery charging from diesel generator;
- To ensure fast charging but avoiding excessive gassing because of overcharging;
- To limit the charging of the battery from PV generator when the batteries are at high state of charge and available power is more than required load.
Control And Simulation
The design of a hybrid energy system requires the best combination of energy sources, power conditioning devices and energy storage systems followed by an efficient energy dispatch strategy. To analyze and compare best possible system combinations, simulation software is needed as a tool. The purpose of the control strategy is to get optimal operational performance. In many RAPS (remote area power supply) systems, dumping of excess energy and inefficient operation is very common. Maintenance and replacement of different components also contribute to the lifecycle cost of the system. All these aspects of system operation are related to the selected control strategy and must be considered in system design.
In advance system control strategies;
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