Standalone Energy System


Design of a Standalone Energy System and its Comparison with Grid Connected System in Pakistan


During last few decades the investment and interest in the development of solar energy is being increased. PV is becoming more and more popular in those countries which can bear large investment cost and can offer economic incentives to the investors and almost in all those areas of world which are looking for a clean environment and working hard for green energy projects. This thesis work covers the design of a standalone power system and comparison of this designed system with already existing grid connected system in Pakpattan, Pakistan. After preliminary designing, an estimation of system and different components sizing was made and on the basis of this sizing, different energy sources like PV, wind and diesel generator were tested. Also if PV can fulfill the daily load or a backup diesel generator would be needed. For preliminary designing, Sandia sheets and PVSYST were used but for the actual designing, HOMER was used because HOMER is more accurate and precise tool for designing standalone power systems. Simulations were carried out and the cost of energy per kWh was 0.435$. Total initial capital cost was 6517$. Further economic evaluation was carried out and was compared with already existing grid connected system. On pure economic terms, this system does not seem to be economical feasible but when different recommendations were taken into account like government subsidy and carbon credit then this system was economically feasible over the 25 years which is the life of this project.

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1. Project background and Introduction

1.1 Introduction

The project with respect to this thesis is to design a standalone energy system and to compare it with already existing grid connected system. This system might be PV alone system, PV wind hybrid system, PV Diesel hybrid system or just diesel generator 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” [1]. 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 by heavy 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. [1]

1.2 Aim of the thesis

The main aim of the project is to design an independent and stand alone energy system for an Islamic center in Pakpattan, Pakistan. During the attempt to design this independent energy system, there could be sub aims as well, which are 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.

* To go through the core knowledge of the designing process.

* Obtaining data for the boundary conditions such as load, solar radiation wind data, available components, cost for fuel, electricity and components.

* Sizing of the system.

* Optimizing the cost.

* To get familiar with different tools used for designing and make selection between them.

* 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.

* Introductory part (Abstract, contents)

* Main part (Introduction, Background, Description, Analysis, Calculation of the primary load for this specific project. Boundary conditions and design parameters. Economical look on existed grid connected system and Comparative study between this newly design system and already existing grid connected system in terms of economics, Results and Conclusion )

* Reference part (Reference list and Appendices)

1.3 Method

As the aim of this thesis project is to design an independent energy system for Islamic center and then compare it with existed grid connected system. The main interest is to provide electricity for Islamic center without shortfall. To do so, first of all literature survey was carried out and was gone through different designing procedures for standalone independent systems. Different tools were also tried and testified, so that an appropriate design could be chosen. In this way Scandia sheets, PVSYST and HOMER were considered especially because these tools were used previously to design such systems. First of all load demand was calculated. Why these three tools were used, the reason is that Scandia sheets are very helpful in sizing different components of standalone energy system while PVSYST has very big database of PV modules, batteries, inverters and diesel generators in itself. After that when the sizing was done then specific components were chosen for this stand alone system. In HOMER there are different options to check weather PV, PV wind hybrid or PV diesel hybrid system is feasible

After designing the system, its economic analysis was carried out using different economic parameters like pay back periods, net present value, benefit to cost ratio and internal rate of return.

1.4 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. The reasons for this deficiency are limited fossil fuel resources, weak economy and mismanagement of the available energy sources. In 1.1, an overview of primary energy supplies in Pakistan is presented 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) [2]

From 1.1 it is clear that energy supply of Pakistan is highly dependent on Oil and Gas, both contribute more than 79% of total primary energy supplied. The other sources like hydro- electricity, coal, nuclear electricity and imported electricity contribute about 21% of the total share. 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. 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 develop its indigenous energy resources such as hydropower, wind and solar energy. Pakistan is one of the highest solar insulation areas of the world. [3]

Here are the main sources of energy in Pakistan right now;

* Natural Gas



* Oil

* Coal

* Nuclear Energy

1.5 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. Solar energy has 2.9 Million MW potential and wind energy has around 0.346 Million MW while Mini & Small Hydel has 2,000 MW. [4]

There is a significant potential of wind energy in Pakistan especially in the coastal belt of Baluchistan and Sindh, and also in deserts of Sindh and Punjab. 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” [4]. 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. [4]. In 1.2a and 1.2b wind and solar maps for Pakistan are shown.

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 hotter months of summer, it cannot meet the energy requirements due to less productive. Also 70% of population lives in around 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. [4]

1.6 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 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. [5]

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 400W 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. [6]

1.6.1 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. [6] Off-grid or stand-alone sector

Stand-alone or off grid 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. [6] Grid-connected sector

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. [6]

1.6.2 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. [5] Photovoltaics

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. [5] Solar thermal applications

There are many applications which utilize the heat characteristics of solar energy directly. These applications are very simple, low price and easily to adoptable. These include heating and cooling of residential and commercial buildings, cooking, water heating for domestic and industrial use and drying agricultural products. A brief description of such applications in Pakistan is given here. [5] 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. [5] Solar cooker

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. [5] Solar dryers

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. [5] Solar desalination

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. [5]

2. 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. PV systems are designed to supply DC and/or AC power and can operate interconnected with utility grid or independent of it. There are classified as;

· Grid-connected Photovoltaic systems

· Stand alone Photovoltaic systems

2.1 Grid-connected PV systems

Grid-connected PV systems are designed to operate parallel with the interconnection of electric utility grid. Power conditioning unit (PCU) or inverter is very basic component in grid-connected PV systems. PV array produces DC power supply and the PCU converts it in to 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. [7]

2.2 Stand alone PV systems

Stand alone PV systems or off grid systems are designed to operate independently. 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 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. In direct coupled system, DC power is supplied directly from PV array to DC load and there is no energy storage, that’s why this type of systems can operate in sunlight hours which make them suitable for common applications like water pumps, ventilation fans and small circulation pumps used in solar thermal heating systems.

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. [7]

2.3 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. [8]

2.4 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 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. [9]

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. [9]

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

* Increase or decrease of population;

* Special community events;

* Seasonal change in environmental conditions ( summer, humidity);

* 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. [9]

2.5 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

· Series hybrid energy systems

· Switched energy systems

· Parallel energy systems

2.5.1 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. [9]

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. The gain in energy is marginal for a good 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. [9]

There are certain merits and demerits of these configurations, they are as below.


* It has simplified electrical output interface as no switching of AC supply is required between different energy sources.

* The supplied power to the load is not interrupted when diesel generator starts.

* The inverter can produce a square wave, modified square wave or a sine wave depending on application.


* The cycling of the battery bank increases which decreases the life time.

* As diesel cannot supply power directly to the load, that’s why system efficiency is low.

* 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.

* The cycling profile requires the large battery bank to limit the depth of discharge.

2.5.2 Switched configurations

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” [9]. The 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. [9]

This configuration has also certain advantages and disadvantages as


* As the generator can fulfill the load directly, it improves the efficiency and reduces the fuel consumption.

* The inverter can make a square wave, modified square wave or a sine wave depending on application.


* Power supply is interrupted time by time as AC power sources are transferred.

2.5.3 Parallel configuration

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

* It can charge battery bank when excess energy is available from diesel generator (rectifier operation).

* 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 ”[19]

Parallel configuration hybrid systems have also merits and demerits over other systems, like


* The efficiency of diesel generator could be maximized.

* The maintenance of diesel generator could be minimized.

* The system load could be fulfilled by optional ways.


* It should be controlled by automatic control unit in order to make the operation of the system more reliable.

* Operation of the system is much complex for untrained users

2.6 Power conditioning

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 cond 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 cond 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: [9]

* 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.

2.7 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;

* Decrease the number of cycles and depth of discharge of the battery bank.

* To run the generator within its most efficient operating range.

* To ensure high reliability of the system.

* Maximum utilization of renewable energy.

The nature of load to be fulfilled could be varying and due to this fluctuations in PV generator occurs which results in the variation of SOC of the battery. The hybrid energy system controller must respond to these changing operating conditions. There are different operating modes for a PV single diesel system which is shown in . 2.8

Mode (I): Base load (at night and early in the morning) is supplied by the stored energy. PV power is not available and generator is not started yet

Mode (II): PV energy is supplemented by stored energy to meet medium load.

Mode (III): Excess PV energy is available and is stored and medium load demand is fulfilled by PV

Mode (IV): diesel generator is operated at its nominal power to fulfill evening load. Excess energy from diesel generator is being used to recharge the batteries.

Mode (V): The power of diesel generator is insufficient to meet the peak load demand. Additional power is supplied from battery by synchronizing the inverter AC output voltage with the alternating waveform.

Mode (VI): Power from diesel generator exceeds the load demand and but it is kept operational until the batteries are recharged at high state of recharge level.

The most efficient system would be that which supply the power directly from the generator (PV or diesel) to the load. It will decrease the cycling of the battery. [9]

3. Sizing and designing of standalone energy system

3.1 Boundary conditions

There are two main boundary conditions, in the circle of these boundary conditions we have to design our system, these are

1. Available solar radiations (input)

2. Primary load to be fulfilled (output)

3. Government subsidies

4. Carbon credit tax

5. Energy availability must be 100%

6. Mood of local people to choose weather PV, PV wind hybrid or PV diesel system

7. Cost of energy/kWh

3.2 Introduction and background of the project site

The site of this project is a Mosque and the total area is around 6000 square feet (50*120 feet long), out of which 1000 (20*50 feet) feet is covered by roof which is shown as label 3 and the rest is without roof. There is a 97 feet long tower attached with this roof covered area which is labeled as 1 and the width of this round tower is 12 feet. There is another small room attached with this tower and covered area which is labeled as 2 in the following . The plan is to set whole system in this room because it is near to the main distribution unit and quite safe place for all components and very easy to connect PV panels with the rest of system. The roof is constructed with concrete and steel reinforcement, which means roof is also very safe to carry weight. In this building 4, 5 and 6 shows three entrance gates. Label 7 shows the water pump and label 8 shows the place for washing taps. Label 9 shows three lines of ceiling fans which includes total 12 fans inside the roof covered area while label 11 shows two rows of ceiling fans in uncovered area of mosque. Label 12 is the main power supply line from grid utility but it is decided to shift it in that small linked room in label 2.

3.3 Weather data of the proposed project site

The weather data of the proposed project site was not available. So the weather data for the nearest big city is used and it is Lahore, which is about 150 km far away from Pakpattan which is the actual site of this project. There is no significant difference in the climate and weather situation of these two cities. The reference for this argues is my own experience. This weather data is taken from NASA and other available sources.

Table 3.1: weather data for the whole year [10]


Air temperature

Daily solar radiation, horizontal

Clearness Index

Sunshine hours [11]





































































In this table air temperature, daily solar radiation horizontal, clearness index and sunshine hours per month for the project site are listed.

3.4 Load profile

Before calculating load data, different appliances will be discussed here. The type and number of these appliances are the same as working over there. These include ceiling fans, water pump, loud speaker (amplifier) and energy saver lamp. Their details are;

3.4.1 Ceiling Fan

Ceiling fans which are already in use over there are of local made. The manufacturer is GFC Fans Gujarat, Pakistan. They are available in 220V & 127V at 50 c/s & 60 c/s. and different sizes, 36” (900mm), 48” (1200mm), 56” (1400mm). [12]

3.4.2 Water Pump

Water pump is also local made by Golden pumps Gujranwala, Pakistan. It is G-1 goldmatic pump with 0.5 HP motor (373W) and operates at 200 to 220 V. [13]

3.4.3 Loud speaker with amplifier

Already working amplifier was considered for this design. It is manufactured by JBL and suppliers are Punjab Electronics Lahore, Pakistan and it is a 520-Watt 4 Channel Power Amplifier [14]

3.4.4 Energy saver lamps

The energy savers manufactured by Philips are already working there and I have considered the same product. [15]

Here is the load profile and total electricity demand was divided into two parts or two load profiles. Load profile 1 and load profile 2. This division is based on the seasonal requirements, i.e. Load profile 1 is for winter months (January, February, November and December) while Load profile 2 is for summer and spring months (March, April, May, June, July, August, September and October).

3.4.5 Load profile 1

Table 3.2: load profile 1








Power (w)

Total Wh












Loud Speaker





water pump














Total wh/day


Total Wh/month

3.4.6 Load profile 2

Table 3.3: load profile 2










Appliances and their number

Power (W)

Total Wh


10 Lamps + 10 cieling Fans




10 Lamps + 10 cieling Fans




10 Cieling Fans +Loud Speaker

(10*55)+ 520



10 Cieling Fans + water pump

(10*55)+ 373



10 Lamps + 10 cieling Fans




10 Lamps + 10 cieling Fans



Total Wh/day


Total Wh/month


Total Wh for profile 1= 44790*4= 179160 Wh= 179.16 kWh

Total Wh for profile 2= 143790*8= 1150320 Wh= 1150.32 kWh

Total= 179.16 +1150.32 =1329.48 kWh/year

Average load per month= 1329.5/12= 110.8 kWh/month

Average per day=1329.48/365=3.64 kWh/day

In these two load profiles, theoretically designing load would be the higher one in order to run the system. So load profile 2 is the designing load.

3.5 Prefatory sizing and designing of the system

The main aim of this sizing was to have a rough idea of the size of the system and to see if the system is feasible or not. A preliminary sizing and designing is the first step to design all types of solar systems. It gives a quick and easy way to final designing. This designing was done within the circle of boundary conditions (solar radiation data and energy demand), which are already defined in section4.1.was performed and this sizing was used in the primary design. This design was made by Sandia sheets and PVSYST.

Sandia sheets consist of sizing work sheets and instructions. These worksheets are used for the specification of components which are required for a PV system. These were developed by experienced system designers and were published in a very comprehensive handbook for standalone systems. There are nine different work sheets, which help in sizing and designing a standalone or hybrid system. The first sheet is for the calculation of total load. This load is seasonal and details for each and every month are required. The second work sheet is to design current and tilt array, following with third sheet which is used for the calculation of battery size. Work sheet #4 is used for the calculation of system array size. There are also instructions to use these work sheets and how to calculate all these parameters. Work sheet #5 helps in determination of hybrid design. Work sheet # 6 is used for the battery and charge controller specifications and work sheet # 7 is for power conditioning unit specifications. Worksheet #8 is used for the specification of switches, fuses, and other devices for protection which are required for a safe operation of the system. At the end Worksheet #9 & #10 are used for the determination of wire sizing (DC or AC) for the system. There are more than one hundred columns which must be filled with appropriate data and all these are explained at the end of these work sheets. The method to size and design the system was easy to perform using these sheets. After filling up these sheets sizing of the system was completed and after that these sizing s were used to perform simulations for the designing of the system using PVSYST. [16]

PVSYST is a very useful tool for the designing of a standalone PV system. Latest version of PVSYST was used for preliminary designing and it is Version 5.05. The start window of this software consists of three different options which includes

· Preliminary Design

· Project design

· Tools

Under the preliminary design option there are three types of systems which included grid connected, stand alone and water pumping systems. After choosing stand alone system, it gives pre-sizing steps of project. It evaluates the system and the size of components. System yield evaluations performed using monthly values. It gives a rough estimation of size and cost of system without any specific system components. There are three steps to go through this preliminary designing step. [17]

· Defining the Location

· System specifications and load data

· Results

The specific location of the project is defined for the first step and then the specification of system is defined. After that load data is inserted depending on different appliances and their usage. Finally it will give the results of preliminary designing.

Now the option of project design will be discussed. Under this option there is a choice of four different types of systems like grid connected, standalone, pumping and DC grid. Standalone was selected as for this specific project. In this section, location of the project, specification and conditions of project site are defined. Afterwards the load data is defined by appliances and their usage. The beauty in this software is that there is a big data base of all components used in standalone PV system and there is a big range to choose appropriate components like PV modules, battery, charge controller and it also gives an option to use backup generator. It also tells about array losses by calculating thermal properties in tabulated form and in graphical form as well. After that it performs simulations for detailed results. There is a good thing in this tool that it automatically indicates the red sign if there is some mistake in selection of components. All the tabs must be green, than the results can be trusted. After detailed simulation results, it performs economic evaluation. The economic evaluation is quite realistic in PVSYST because it includes all prices which one have to consider for practical implementation. It includes the price for PV modules, support and integration, batteries, charge controller, inverter, backup generator, transport and assembly and price of engineering. It also considers different taxes and subsides to finance the project. [17]

The third part of this software is tools, which includes meteo database, components database and measured data, “It gives a wide range to choose solar tools like solar geometry and meteo on the tilted planes, as well as a powerful mean of importing real data measured on existing PV systems for close comparisons with simulated values.” [17] After the initial preliminary design, I got some initial results which are listed in the following table 3.4. The total production of the system was around 1642 kWh. The initial capital cost for the whole system was around 15000$ and the cost of energy was around 1.87$/kWh.

Table 3.4: Main results and Balances from preliminary design using PVSYST.

This prilimenary sizing and design was very helpful to choose specific components for this system and to size them. This step lead me towards some leaterature survay in order to know more about the designing and economic evalution. The main goal was to find out acceptable price of solar energy/kWh, initial capital cost and payback period. Now a days the price of electricity though solar is 35.22 $ cents/kWh. [18]

3.6 Designing of the system

For the actual designing of the system an optimizing tool was used which is known as HOMER.

It is a micro power optimization model which simplifies process of evaluation and designs both grid connected and off grid power systems. In the designing of a power system, many steps and decisions must be taken carefully to con the system. For example

* Which components must be included in the system design?

* What is the size and number of each component used?

There are a lot of parameters, which we have to control during the designing of an energy system and there are a lot of variations in these parameters as well, like different technology options, availability of different energy resources and the variation in the cost of technology. All these parameters make the decision very difficult. But HOMER uses optimization and sensitivity analysis algorithms which make it much easier. It helps to evaluate different possible system configurations. In this tool there are lot of choices to design a PV system and after trying different choices, a final feasible and suitable design is selected. The economic data is fed according to the manufacturer of specified components. The economic evaluation is not as accurate as was in PVSYST. It is a general purpose tool which helps in designing and optimizing a hybrid system. Moreover HOMER require different inputs like, electrical load (yearly or monthly or hourly), renewable energy sources (like solar, wind and hydro), the technical details of different components and their costs, controls, constraints and different dispatch strategies. In the following table 3.5, it is presented in tabulated form. It performs hundreds and thousands of different simulations based on the input parameters and then to choose the most feasible and suitable solution for the desired system.

Table 3.5: Interface of HOMER [19]

Power sources



Solar photovoltaic (PV)

Battery bank

Daily profiles with seasonal variation

Wind turbine


Deferrable (water pumping, refrigeration)

Run-of-river hydro power

Flow batteries

Thermal (space heating, crop drying)

Diesel & gasoline generator


Efficiency measures

Electric utility grid

Micro turbine

Fuel cell

The option to use PVSYST is still valid if HOMER tells that there is no need to attach a backup generator or a wind turbine. All this options will be addressed in the next section. The reason to choose PVSYST is that it is more accurate and detailed tool for standalone systems in terms of economics. Now different options will be considered for this design which are available. First of all, 1kW wind turbine was added to the system and simulations were performed. The cost of 1 kW wind turbine with all necessary support and components (wind turbine, rectifier and inverter) is around 1300$ [20]. The optimization and sensitivity results were obtained as a result of simulations which are listed I the following table 3.6.

Table 3.6: Sensitivity Analysis

Alternatives Used

PV (kW)

No. Of Batteries


OC $/Year

COE $/kWh


Capacity Shortage

PV only








PV and Wind








In this table

ICC: Initial capital cost

OC: Operation Cost

COE: Cost of energy

NPC: Net present cost

This table of results shows clearly that the addition of wind turbine to the system is not feasible because it increases the initial capital cost and cost of energy/kWh at the same time, which is not advisable to adopt. The detailed results of this optimization are in table 3.7.

Table 3.7: Detailed results


Capital cost $

Replacement $

O&M $

Fuel $

Salvage $

Total $







































PV array



Wind turbine



3 4

After these results wind turbine was removed and simulations were carried out with backup diesel generator of 1 kW. The reason to use diesel generator is that cost of diesel generator is less than wind turbine but there is an extra cost of fuel when diesel generator is being used. So the total initial capital cost was reduced but operational cost and cost of energy per year was increased. All the parameters were defined and simulations were carried out. Step by step simulations were refined in more detail and sensitivity analysis was also carried out with more parameters. The components for the system are already selected and these are used for all simulations. The detail of these components is in the next section. After different simulations, one thing was clear that diesel generator always increase the operating cost and overall cost of energy $/kWh due to the extra fuel cost. Another important thing is that the system is simpler in design without diesel generator. Four important things were observed in designing this system and these are;

* The system should be economically feasible and within the buying power of the people.

* It should be energy efficient.

* It should not be too complicated to handle for the people who will use it.

* It should not give a negative or harmful effect to the environment.

Several simulations were performed using HOMER, considering different PV capacities. PV capacity was allowed to vary in the range of 0 to 2kW. The capacity of the battery was selected 2.76kWh. The price of diesel is 48.10 Rs/l (0.57 $/l) [21] and 1 to 1.5 kW power generator was selected for simulations. The fraction of renewable energy is almost 100%. The COE/kWh is around 0.435$/kWh, which is quiet compromising. Sensitivity analyses were also completed and results are shown in 3.8. Furthermore the detailed economic results are shown in table 3.8.

The specific cost of energy/kWh was decreased to 0.435$/kWh and the initial capital cost was decreased to 4464$. These results show that in many simulations, HOMER has not selected diesel generator as a backup. It means that there is possibility to design this system without diesel generator. This will decrease the cost of the system and will also give positive impact on the environment and the reliability on conventional fuels will decrease but there will be uncertainty in the availability of energy all the time. For example if there is cloudy and foggy weather for consecutive five or six days then this system without generator backup will be failed and the main to make an independent and standalone energy system will not be fulfilled. So it was decided to add diesel generator as back up and finally PV diesel hybrid system was finalized. Here are the results obtained from simulations.

3.7 Results

After performing different simulations, results were elaborated and concluded. The main technical results of PV and diesel and emissions are in the following table shown in the following table.

Table 3.8: Main results of PV, Generator and Emissions


Diesel Generator

Rated capacity

1.00 kW

Mean output

0.35 kW

Mean output

8.33 kWh/d

Capacity factor


Total production


Maximum output

1.21 kW

PV penetration


Hours of operation

4,381 hr/yr

Levelized cost

0.435 $/kWh



Carbon dioxide


Carbon monoxide


Unburned hydrocarbons


Particulate matter


Sulfur dioxide


Nitrogen oxides


Hours of operation

20 hr/yr

Number of starts

13 starts/yr

Capacity factor


Fixed generation cost

0.920 $/hr

Marginal generation cost

2.00 $/kWh

Electrical production

9.67 kWh/yr

Mean electrical output

0.484 kW

Min. electrical output

0.200 kW

Max. electrical output

0.661 kW

Fuel consumption

44.2 L/yr

Specific fuel consumption

4.567 L/kWh

Fuel energy input

435 kWh/yr

Mean electrical efficiency

2.2 %

3.8 Schematic diagram of PV diesel hybrid system

Now the specific components in detail will be discussed which are selected for this system.

3.9 Selection of different components

Different components selected are as below.

3.9.1 Selection of PV Panels

After sizing the PV array, appropriate panels are selected for this system. These panels are manufactured by Kyocera and its model is SE185-72M and its nominal power is 185W. The reason to select 185 W panels is to decrease the cost and area to be occupied. The selection was made on the basis of sizing procedure in PVSYST. There were different options to choose PV panel but this panel was selected. The total number of panels is 6. Electrical and other specifications are described in the following table. The specifications and cost was confirmed via email which is attached in appendice A.

Table 3.9: Specification of SE185-72M Module. [22]

Electrical Performance under Standard Test Conditions (*STC)

Maximum Power (Pmax)

185W (+5W/-0W)

Maximum Power Voltage (Vmpp)


Maximum Power Current (Impp)


Open Circuit Voltage (Voc)


Short Circuit Current (Isc)


*STC: Irradiance 1000W/m2, AM1.5 spectrum, cell temperature 25°C

Number of cells per Module

72 (6*12)

Area of Module

1580×808 x46mm



IV curve against power for the selected module is shown below which shows maximum current and voltage of the module at the rated power. The selected site for project is located in hot region. The ambiant temperature varies from 22 to 250C but the tepmerature in summer reaches upto 450C. This increase in temperature can effect voltage output of PV panel.

3.9.2 Selection and sizing of Battery

The suggested capacity for this system is around 900 Ah and the voltage of battery is 24V because the appliances are of medium size. The reason to select 24V system, that the appliance’s maximum power should be less then 1000W for 24V system and the maximum power in this system is 572W for loud speaker, so 24V is feasible For this, Surrette S-460 deep cycle battery was selected. The capacity of this battery is 900Ah and the nominal voltage of the battery is 6V. It is very efficient battery and the average life of this battery is ten years with 1300 cycles. It contains three cells and fifteen plates. In the following table, the capacity of this battery at different hour rate is shown with current.

Table 3.10: capacity curve and lifetime curve of Surrette S-460 [23]

Capacity curve

Lifetime curve

Time (hrs)

Current (A)

Capacity (Ah)


































Depth of Discharge(%)

Cycle to Failure

















3.9.3 Sizing and selection of inverter

The sizing of appropriate inverter for this system is around 1kW. The selected inverter is manufactured by ExelTech and the model of this inverter is XP-1100-24 with power rating of 1.1Kw. The price of this converter is around 754$ per piece. Here are some electrical characteristics of this selected inverter. [24]

Table 3.11: Inverter Specifications. [24]


Nominal VDC

Minimum VDC Cut off Alarm

Maximum VDC

Rated Current

Peak Current

Efficiency@ full power








3.9.4 Selection of Charge Controller

Charge controller for this system is manufactured by The Xantrex. It manufactures C-Series charge controllers in three different models C35, C40 and C60. But C60 was selected for this system. It can control 60 amps of DC current. This charge controller can be used in three ways.

* As solar charge controllers or

* load controllers or

* Load diversion controllers.

When is used as solar charger, it can control 12 and 24 VDC operation and it has selectable and adjustable settings for lead acid and NiCad batteries. When it used as diversion load controller, it automatically directs extra energy to a dedicated load and ensures that the batteries are never overcharged. This is very popular series of charge controllers which can be use for all of these applications. It has a manual reset button for emergency low voltage operation. The price for this model charge controller is 170$. [25]

Table 3.12: Specifications of Xantrex C-60 [25]

3.9.5 Other specified Components

There are some other components which are essential for a complete PV hybrid system. There are as below. Iron ridge and mounting assembly

For mounting PV modules, a mounting assembly is required which is known as iron ridge. Iron ridge consists of aluminized

* Iron rails

* End clamps

* Mid clamps

* Under Clamps

* Internal Splice

* Stand-offs

* L-feet

* Grounding

* Tilt Legs (they support up to 400) [25]

1) 2) 3)4)5)

6) 7)8)

These items will be purchased local made and the estimated cost for this assembly is around 100$ which includes both material and engineering cost (60$ material cost and 40$ engineering cost). The advantage to use local made mounting assembly is that we can adjust the design of mounting according to the place available on the project site. Battery Rack

As batteries cost a lot and they are a major and important part of PV system. Their protection must be ensured so that they can have estimated long life. For this purpose, a battery rack is used. Batteries especially lead acid batteries are heavy and large in size. They need proper support in order to function properly and also to make the system more secure. Battery racks are also used to keep them safe from ambient high temperature and other environmental conditions. The battery racks will be used local made and it will cost around 100$ which includes material cost and engineering cost. Cables and Wires

Different cables and wires will be used in order to run the system and to complete different connection at different stages. The wire sizing is not possible right now because it will depend on the placement of the system components, length and sizing depends on the distance between the load distribution unit and power generation unit. Diesel Generator

In order to make the system more reliable, a backup generator is connected. This generator is connected within the system according to parallel configuration. In this type of configuration, the small load is fulfilled by separate sources of energy while the peak load would be fulfilled by both solar and diesel generator and the surplus energy will be used for charging the batteries. The diesel generator for this system is manufactured by Honda and the model is EP2500CX. The detailed specifications are in the following table.

Table 3.13: Specifications of Diesel Generator, EP2500CX [27]

Generator Type

Brush Type

Maximum AC Output (Watts)


VAC Voltage Available 120


Maximum Continuous AC Output (Watts)


Max. Rated AC Amperage @ 120 V / 240 V

19.2 / –

Frequency (Hertz)



OHV, 4-Stroke, Air-Cooled

Fuel Tank Capacity (litres)


3.9.6 Safety components and specification

In order to be assure that the system will function in a safe mood, different components for the safety of the system must be included in the system. These are as:

· Array output

Ø DC disconnect Switch

Ø DC fuse

· Controller to inverter

Ø DC fuse disconnect

Ø DC fuse

· Battery charger

Ø DC manuel Switch

· Battery

Ø DC in line fuse

· AC distribution

Ø AC circuits breakers

3.9.7 Installation cost

The estimation of installation is one week at the most and if two persons work for whole week than total installation cost will be 100$. The labor cost is very cheap over there. Daily wages are around 4 to 7$ per day depending upon level of expertise.

3.9.8 Transportation cost

The total transportation cost is estimated around 500$. PV modules, Inverter, charge controller and batteries will be exported from China and the rest of the components will be used local made or will be purchased from local market.

3.10 Total Initial Investment Cost

In this estimation and calculation of overall initial cost there are some fixed prices and some are assumptions. The price of PV module is 1.75$/Wp without shipment and 1.78/Wp with shipment [27]. This selected module is manufactured by Solar InerTech which is based in China and the price was confirmed on phone from sales department of this company. The price of battery is taken from web data and was compared with other companies who are selling the same model of battery. In the following table, there is complete list of all the costs which are involved in a PV diesel hybrid system.





Cost/piece $

Total cost $

PV module

Solar Inertech

SE 185-72M


330 [22]


Iron Ridge and Mounting

Local made







Surrete S-460


312 [28]


Battery Rack

Local made

Local made





Exel Tech



754 [29]


Charge Controller


Xantrex C-60


170 [30]


Cables, Wires and fuses

Local made

Local made




Installation Cost

Local made





Transport Charges




Back up Generator




691 [31]


Total initial capital cost


The total initial capital cost= C0 = 6517$ (547428Rs)

The life of project = 25 years.

4. Comparison with grid connected system

Load is an important consideration to evaluate the system in economic terms. For this system the daily average load is 3.7kWh/day. This average load represents off grid load, although system is in operation with grid utility electricity but after the design of this system and implementation, it will be converted into off grid system. Therefore, in order to have economic comparison, analysis of grid electricity in Pakistan is needed.

4.1 Grid electricity in Pakistan

WAPDA (water and power development authority) and PEPCO (Pakistan electric power company) are responsible for the production and distribution of electricity in Pakistan. PEPCO is mother distribution organization, under which different small companies work with coordination of each other, depending upon the location. The company which provides electricity in this region is MEPCO (Multan electric power company). There is specific procedure to get a new electricity connection and the connection varies with load. Here is a tariff according to which people of our region pay electricity bills. [32]

Table 4.1: Tariff for domestic and commercial units [32]

a) For Sanctioned load up to 20 kW


Up to 50 Units

1.60 Rs/kWh

For Consumption exceeding 50 Units


For first 100 Units

3.54 Rs/kWh


For next 200 Units

4.55 Rs/kWh


For next 700 Units

7.00 Rs/kWh


Above 1000 Units

8.00 Rs/kWh

b) For Sanctioned load exceeding 20 kW

Time Of Use




Under this tariff, there shall be minimum monthly charges at the following rates even if no energy is consumed.

a) Single Phase Connections:

Rs. 75/-

b) Three Phase Connections:

Rs. 150/-

According to the tariff above, the monthly bills and cost for year 2009 were calculated. These s were asked from the concerned person over there via phone and then total cost per year and total cost per kWh was calculated.

Table 4.2: Electricity usage and bill per month


Usage (kWh)

Line Rent (Rs)

Cost/Month (Rs)




















































Cost per year=14360.5 Rs/year=170.95 $/year (Rs: Pakistani Rupee (1$=84Rs)

Cost per kWh throughout the year: 14360.5/3000=4.78 Rs/kWh= 0.059$/kWh

4.2 PV Diesel Hybrid system

The economic evaluation has been performed on the bases of some assumptions and facts, which are described as;

Life of the project = 25 years

Annual increase in diesel price = 3%/year [33]

Increase in electricity price = 9%/year [assumed]

Fixed O&M costs have been calculated as $210 per annum and the project gives a salvage value of $28 per annum. These two costs were calculated by HOMER and are used for economic evaluation. Also Carbon Credit has been taken into account to further refine the economics thereby considering carbon release of 0.6083 kg/KWh [34], which gives a return of 2.2$/year. The calculation procedure is as follow.

Electricity generated from generator = 9.67 kWh/year

Carbon generated = 116 kg/year

Annual electricity consumption = 3000 kWh/year

PV generation = 3039 kWh/year

Carbon generation = 1.341Pounds/kWh [34]

Carbon generated = 1.341*0.4536 = 0.6083 kg/kWh

Carbon generated by grid system (if thermal by power systems) = 0.6083*3000 = 1824.8 kg

Carbon saving = 1824.8-116 = 1708.8 kg/year

Carbon saving = 1708.8/1000 = 1.7088 Ton/year

Carbon Credit as per the international market = 11€ [35]

Carbon Credit as per the international market = 11*118*1.7088 = 2218.06 Rs

Carbon Credit = 2218.06/12 = 184.8 Rs/year

Carbon Credit = 184.8/84 = 2.2 $/year)

Over the period of 25 years the project economics shows a deficit of $3744 against the total capital cost of $6517. Therefore it can be seen that on pure economic terms the project is found not economical compared with the grid connected power system.

There is a need that government should subsidize these types of renewable power systems to facilitate the consumers to switch towards standalone and environmental friendly power systems. Therefore to be compatible with the grid connected power system government needs to finance around 60% of the initial capital cost (3910.2$) to let the project become economically feasible over the life period of 25 years.

The detailed economic calculations and results are attached as Appendix B.

5. Discussion and Conclusion

Although there are tremendous resources of energy in Pakistan but at the moment country is energy deficient and the development of renewable energy sources is a need in order to overcome the energy demands. Due to this energy deficiency, domestic and industrial sectors are being affecting very badly. Pakistan has a big potential for renewable energy especially solar and wind energy. Wind and solar energy is in service in Pakistan since 1980’s but it needs to be adopted and developed on a higher scale. This thesis work is a part of this effort to design a standalone power system so that the price of energy could be decreased.

The pre-designing process was carried out with the help of Sandia sheets and PVSYST and final designing was done with HOMER. Different energy options were considered during pre designing. Wind turbine, PV and diesel generator were chosen and simulations were performed. With the combination of wind turbine and PV, the initial capital cost, net present cost and cost of energy per kWh were increased. This shows that this combination of PV and wind is not cost effective. After that just PV was selected for the design, it gave good results but there was uncertainty in the fulfillment of load in rainy and foggy weather during winter days. So in order to assure the 100% availability of energy, a backup energy system was attached with PV, so PV Diesel Hybrid system was finalized and chosen. The final designing was done with HOMER. The designing parameters and boundary conditions were defined and simulations were carried out. After that different calculations were done to perform economic evaluation. Final results were collected and are discussed in more detail in section 3.7. Technical and economic results were concluded. The economic data was collected for the existing grid connected system and calculations were done according to latest electricity tariff in Pakistan.

The specific cost of energy was 0.435$/kWh and the cost of energy from grid utility is around 0.0595$/kWh. The operating cost per year for this designed system is 217$/year and the cost of electricity for grid connected system is 170.9$/year. This is just 46$/year more which is not so big difference. But the difference in the cost of energy/kWh is big. The specific cost of energy per kWh is very high in case of PV Diesel hybrid system. The reason is high cost of system components and especially PV panels and batteries. Another fact that PV is not an economical solution on small scale power systems up till now, but may be in future the costs will come down due to development of efficient solar cells materials. The advantage of this standalone system hybrid system is that the availability of energy is 100%, the dependency on conventional fuels will be less and there will be a positive effect on the environment by decreasing carbon emissions as the fraction of renewable in this design is 1.

The economic results of this study show that this is not an economically feasible system. It can be made economical feasible by considering three important recommendations.

1. If the government give 60% subsidy to the project

2. Carbon credit tax

3. Loan from bank or some investor at 3 or 4% discount rate

After these three recommendations the system seems to be economical feasible. This is shown in the detailed economic evaluation in appendice A. It is a fact that the initial capital cost for a PV system is much higher but through life cycle cost method, it was noticed that the cost of energy through grid utility is higher over the entire life of the project. This system justifies all the economics parameters after recommendations. The initial investment in PV system is many times higher than the conventional grid connected systems. There are no taxes on solar applications and production at the moment in Pakistan which is a type of incentive to use renewable resources but is not sufficient. Government should provide subsidies, so that people over there can have their own small PV systems. This step will help in lowering the price of energy in Pakistan, as the number of users on thermal or conventional power system will decrease and the load will decrease automatically, this will lower the energy prices.

PV systems are environment friendly and they can be a very effective tool against global warming and CO2 emissions, because it is possible to reduce CO2 emission with the use of renewable energy sources. Table 3.7 explains more about the emissions. The adoption and development of renewable energy sources has advantage that they will minimize the dependency level on the fossil fuels as they are gradually decreasing all around the world. There will be no danger of theft or vandalism because the location of this project is very specific and it is very common and social place. So it is sure that it will not happen ever.

PV Diesel Hybrid systems on large scale for a medium size family can be very economical solution against the energy crises in Pakistan.

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Cite this page

Standalone Energy System. (2017, Jun 26). Retrieved December 3, 2022 , from

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