Design and Operation of Microgrid with Renewable Energy

Sources and Energy Storage System: A Case Study

1
Anis Ur Rehman, 2Shah Zeb 3
Hanif Ullah Khan, 4S. Shahbaz U. Shah, 5Atta Ullah
1,2 3,4,5
Electrical Engineering Department Electrical Engineering Department
Balochistan University of Engineering and Technology, Balochistan University of Engineering and Technology,
Khuzdar, Pakistan Khuzdar, Pakistan
Email: haroon.uetp@yahoo.com Email: hanifkhan34143@gmail.com
Email: rajaglt4534@yahoo.com Email: khidraniatta@gmail.com

Abstract—Modern power system experts attentions have been energy sources for large power generation are the
diverted from the centralized power generation to the microgrid unreliability and huge capital costs. It relates voltage and
system due to availability of high potentials of renewable energy frequency fluctuations of renewable energies availability (e.g.
resources. Microgrid is designed so that a little dependency on from wind, solar, micro hydro and biomass etc.) and the
national grid. In this paper a microgrid design guidelines,
amount of these energies depends on the environmental
procedures and techniques have been presented where the
renewable energy resources are available in abundant. A case impacts (like climate and weather), place and time [3]. The
study of an educational institute with academic blocks has been optimal renewable technology unit size is the other main
taken for which a microgrid is designed with available resources constraint in the design and planning of smart and microgrids.
(solar and wind) and energy storage system. Optimal sizes and Different techniques have been presented to design and
sites for wind and solar PV units were investigated using an plan the microgrids with optimal renewable energy sources to
analytical approach. The proposed scheme presents the effective meet the electrical load satisfactory. R. Nazir et.al [3]
utilization of energy sources with a ranked load distribution analyzed the possibility to develop the simple microgrid
system. The results obtained in this research work clearly model to optimize the local available renewable energy
demonstrates the cost effectiveness of microgrid compare to the
sources in operating microgrid with on-grid mode. Micro
dependency on power utility grid. Cost analysis of the microgrid
with proposed renewable sources, batteries and diesel hydro power unit and Photovoltaic (PV) system were
generators has also been carried out. considered and the model analysis was performed with
HOMER and MATLAB/Simulink software. The previous
Index Terms—Microgrid, Distributed Energy resources, Solar work in [4, 5] also focused on HOMER software in the
PV system, Wind turbine, Energy storage system. optimization of units for the rural electrification with hybrid
renewable energy based isolated microgrid systems. The
1. INTRODUCTION options of research work in paper [4] were biomass, PV and
wind while other performed the optimization of wind, solar,
Renewable energy sources (RES) are now recognize globally
micro hydro and non-renewable diesel hybrid system for the
as important alternative options in supplying the electrical
electrification of remote areas.
loads of microgrids [1]. Renewable energy based design and
development of microgrids have attained a greater attention The PV system and energy storage units (batteries) were
of power researchers and electric energy experts. Operating integrated with traditional electric power system using
distributing method in [6]. The two PV units of 190kW each
costs of renewable sources like wind, solar PV, fuel cells,
and batteries output voltage of 380V were coupled on a single
biomass etc. are lesser than conventional energy sources
bus to complete an on-grid microgrid project. The on-grid
(Nuclear, coal, oil and gas based) comparatively. Renewable
and off-grid operation were checked with harmonic detecting
energy sources are clean and pollution free and therefore are
the prior options for the designers and planners of smart and techniques by controllers. The work in [7] highlighted the
necessity of primary, secondary and tertiary control levels
microgrids.
with the generation from the PV and energy systems and
Microgrids not only provide onsite power to the local
SVC and STATCOM converters.
users but may sell surplus energy to power utility grid during
A more related work to the study in this paper was
light loads or surplus generation. As energy demands are
increasing rapidly worldwide due the economic developments presented in [8] for the design of microgrid system derived
and gradual growth in rate of populations, requiring energy from the prospective scheme that was designed for the
Sustainable Building research center (SBRC) at the
resources to meet the daily energy demands [2]. The
University of Wollongong University, Australia. The work
significant issues that have made hard to grow renewable
was to contribute in in the design and operation of microgrid
of SRBC with net-zero energy target. The MG was designed • Combination of co-located power generation sources
with the considerations of PV system, small wind generators and inter-connected loads
and Li-ion batteries to meet the dynamic and static load. • Provide different levels of the power quality and
This paper mainly focused on the design and operational supply continuity (reliability) for the end users
planning of an island mode microgrid. An educational • They are designed to accommodate the total system
institute with administration and departmental blocks with energy requirement
different load characteristics has been taken as a case study.
A complete load survey and statistical approaches were used
B. Microgrid enabling Technologies
to investigate the electrical load demand in summer, winter
and spring season. On the basis of maximum demand of the The key feature and capability of a designed microgrid is the
administration and engineering laboratories, class rooms and ability to operate in an island mode (off-grid) when the power
offices the optimal renewable energy sources have been supply from the distribution system of utility’s grid is
optimized for the effective utilization of units and to satisfy suddenly interrupted or then blackouts for longer duration.
the load demands. A hybrid system with energy storage The microgrid should be designed so that it may satisfy the
system and backup diesel generators set up is optimized very load demand [8]. There should be an intelligent control and
effectively and cost analysis is also carried out for the life protective system to handle and operate the microgrid with
cycle cost and overall project estimated expanses. A dynamic behavior of load. The control system will control the
microgrid protection and effective operation strategies, bus voltages, reactive power in peak load duration and
guidelines and planning have also been presented in this maintained the frequency within standard limits while
research work. protective system avoid the MG from faults and overloading.
However to operate the microgrid in an island mode in
expected manner following technologies will be required:
2. OVERVIEW OF MICROGRID SYSTEM • Distributed generation (DG)
A microgrid is actually a subset of electric power system. It is • Distribution Automation (DA)
a power distribution network of that consists of several local • Smart energy meters and other measuring meters
distributed generation resources (DER) or generators with • Islanding and bi-directional inverters
energy storage system and controllable loads and can operate • Substation Automation (SA)
both in an island mode (off-grid) and in parallel with utility • Microgrid control system (voltage, frequency etc.)
grid (on-grid). The local generating sources may be
• Smart transfer and change over Switches
conventional fossil fuels or then renewable energy sources. A
• Advanced energy storage system (batteries/super
simple model of a microgrid with DERs and loads is shown
capacitors)
in figure 1.
According to IEEE and the study performed by Zyprme et.al
[10], the most important enabling technologies for the design
and operation of microgrid are the; 1) energy management
system, 2) distribution management system, 3) sensors and 4)
communication systems. The one limitation in this study is to
neglect the controllers and protection system.

C. Microgrid design considerations

This section provides the general guidelines of design
considerations of microgrid and as applied here for institute
of Balochistan U.E.T Khuzdar, Pakistan. The especially
importance is given to the power generation system, energy
storage system and well control and protection system. The
load profile of all the concerned sections like labs, class
Figure. 1 simple schematic model of microgrid [7] rooms, offices, data centers, conference and examination
halls and administration block have been obtained using
A. Common features of Microgrid statistical load calculation method, measurements and from
the power rating of equipment and appliances. Fortunately the
• Operate in both the islanded mode and grid- behavior of load except laboratories were same as most of the
connected load is lightening, computers and Air conditioners. The labs
• Presentation to the microgrid as a single controlled
entity
have a large number of induction motors and DC motors. and Power factor meters are used. The collected load data is
Voltage buses are selected as most microgrid have both AC scaled to match with the design details regarding the load
and DC main buses. For the load and power system taken of site or institute etc. One more important
parameters measurements, C.Ts, P.Ts, Voltmeters, Wattmeter consideration in microgrid design is the future load growth
especially when the microgrid will have to operate in island duration of 16-18 hours a day. This make the wind as best
mode. However the issue of load shedding may not rise if the option for selecting a generation unit of microgrid. The solar
installed power generation units have capacities of 15-20% irradiations as noted are 900-1000W/m2 with average
more than the present load demand. temperature of 33-35C0. The details of characteristics of wind
speed and power obtained at different speed (m/sec) is
3. LOAD PROFILE, DEMAND AND RENEWABLE ENERGY presented in Figure 2.
SOURSES IN B.U.E.T KHUZDAR
A. Solar PV and Wind Turbine System
The first important consideration to design a microgrid
is to obtain the load profile, total demand of each section or A photovoltaic (PV) cell has a photovoltaic effect and is
block and the dynamic behavior of load. In this research work a non-linear electrical energy source. Its output voltage and
an educational institute has been taken as a case study and a current is DC and the basic elements are the PV cell, shunt
microgrid system is to be designed for this institute which resistance and a diode to block the reverse currents. The
will operate in an island mode only. The load will be supplied output of the PV solar module depends on the temperature,
power from the renewable energy sources and a well- light intensity and load magnitude [11]. The current obtained
protected system is also to be proposed for the survival of at the output may be evaluated using a simple Kirchhoff’s
microgrid system even in the situation of load growth. The current law (KCL) applied to the equivalent circuit of PV.
Balochistan University of Engineering & Technology have
four engineering departments comprises of teacher offices,
class rooms and laboratories. One administration block, an
auditorium, an access center and a central library. The load
profile and peak power demand during summer, winter and
spring season is presented in Table 1. Where
V: the output voltage, T: temperature, K: Boltzmann constant
TABLE 1. LOAD ENERGY DEMAND (SEASONWISE) OF BUET IL: the short circuit current, Q: Colombes constant, RS: line
resistance and RSh: shunt resistance. The maximum power
Academic Demand Demand Demand Power may be obtained at some specific voltage level at specific
Section in kW in kW in kW Factor
(Summer) (Winter) (Spring)
temperature and light intensity known as Maximum Power
Electrical point Tracking (MPPT).
Department 44.14 32.75 34.14 0.85 The photovoltaic solar panels that are selected here have
Mechanical output voltage of 24V-DC which is converted into AC
Department 47.350 29.00 33.60 0.82 thorough MTTP 50/100/150A inverters for a complete setup.
Civil The solar energy is available in BUET, Khuzdar with huge
Department 34.76 22.55 24.76 0.85 radiations and the cost per kW of solar panel in Pakistan is
Computer from $120-150 with inverter module. The useful life of solar
System/IT 68.42 17.69 26.67 0.83 panel may vary from 10-20 years.
Admin Block
20.97 16.26 14.57 0.87
The wind turbine convert the available wind energy into
mechanical energy that is again converted into an electrical
Library 3.5 3.75 3.5 0.92
Auditorium
energy by permanent magnet or induction type generators. A
(External) 08.81 08.12 03.63 0.85 simple mathematical expression to show that how much
Auditorium mechanical power is obtained from the wind turbine with
(Internal) 26.45 10.87 16.53 0.81 available wind speed.
Access V= wind velocity (m/sec)
Centre 12 6 8 0.86

The generators should have a capacity that during light load

an energy storage system (batteries) is to be charged for
future use. Renewable energy sources are considered as a The power variations with different wind speed in m/sec. The
best option in design and development of microgrid system. wind is available here in Khuzdar with an average speed of
Fortunately the location of BUET Khuzdar are such that it 10 m/sec. It can easily be depicted that maximum power is
has a huge potential of wind and solar potential is also in rising gradually, but practically a limited wind force is
abundant. The normal wind speed (as recorded by allowed to force the turbine blades. The blades may damage
meteorological instrument installed at the auditorium of with high wind force and therefore at different standard wind
University) is 10-12 m/sec. Wind is available for an average forces, the power generation may be at some fixed level.
A= Rotor swept area (m2) and ȡ = Air density (1.23 kg/m3)
 Figure: 1 Daily Load Curve of Academic sections of selected University of Khuzdar

D. Backup Energy Storage System units are Administration block, class rooms, data center and
laboratories. There is no need to install these units at
The energy storage system is essential part of the microgrid
auditorium or offices because for the auditorium and
since during peak loads and sudden interruptions the priority
conference rooms the best option is the diesel generator as it
load is normally feed from batteries or other storage system
is run for short duration in emergency cases like
(UPS). The proper selection of capacity of energy storage
convocations, monthly meetings etc. The air conditioners are
devices is one of the main constraint in design of the
operated with wind generators and for the class rooms first
microgrid. If the generation is lightly more than demand then
priority is the PV system. If the PV cells are working
it is uneconomical to install huge number of batteries system.
properly and sunshine is available then wind generators will
The batteries are selected normally for lightening and
charge the batteries.
computer laboratories in institutes instead of running air
For offices the solar PV is first option and in interruptions of
conditioners or heating load (as they consumed much more
supply from PV they will be feed from the energy storage
power). The batteries selected in this study have capacity per
system. The total PV panels that are required at each
unit of 200Ah and an uninterruptable power supply systems
engineering department, auditorium external section,
are installed at different optimum locations as discussed in
administration, central library and access center are approx.
the next sections.
700 and its total capacity is about 150-155kW as presented in
IV. IMPLEMENTATION OF PROPOSED DER TECHNOLOGIES
Table 2. The total units of wind generators that are to be
installed are 19 and total approximate capacity will be 97kW.
On the basis of proposed distributed energy resources (PV, The total battery units required are 6400Ah with 200Ah
wind and diesel generators) and energy storage system, the capacity per lead acid battery. The kVA capacity evaluated as
microgrid is to be given a final shape for its implementation. 69 kVA. This capacity of batteries will fully meet the
The load profile is matched and scaled with available emergency load and priority loads during a complete
generation sources and optimum units were selected. The interruptions. Each engineering department required 5-6Ah
next step is to implement these generating units with such an battery system (UPS) for their offices and class rooms. For
approach that overall load demand is meet. the emergency cases two diesel generators (30kVA/45kVA)
are to be installed. These diesel generators are suggested to be
mobile type which can easily be transferred to any required
A. Optimal size selection of DER to meet the power location. Therefore connections should not be permanent..
requirement The per kWp cost of PV in Pakistan is USD $1000-1200
The basic requirement of a microgrid that will be operated in (max) and same for 1.8 kVA with MTTP30A inverter.
an island mode should have a capacity of generation that not Similarly the cost of 5kW permanent magnet PMG700
meet the present demand but also satisfy future load with model, wind generator/turbine setup is approximately USD
ease. In order to design such a microgrid the wind turbine $5000. The 30kVA Diesel generator worth USD $ 7076
units of 3.5kW, 5kW and 7.5kW are proposed to be installed (approx.), while 45kVA Hyundai model worth USD $9386-
at different locations. The appropriate sites for these wind 9500. The overall cost of microgrid units and batteries is
USD $ 0.266 million.
 V. CONCLUSION
The work presented in this paper is focused on the design
considerations of a microgrid for an educational institute
having different sections with separate load profiles. Wind
based power and pv system are proposed to design the
microgrid. These units were selected in such a way to meet
the total demand in peak hours. The units placed at optimal
positions comfort the islanded microgrid. Mostly the priority
was given to utilize PV suystem as it is lesser costly as
Figure 4. Flowchart of operation of microgrid system
compared to wind in pakistan. Cost analysis make it easy to
decide which generating unit will be the economical option
while the performance of each unit is test by matching and
scalling with load curves. The outcomes of the study presents
the necessity of the proper generation, a backup generation
system and energy storage system. A complete guidelines and
procedure is presented make design easier for learners. The
design may withstand the future load growth as generation is
surplus than present demand of institute.
 TABLE: THE DETAILS OF LOAD CENTERS, REQUIRED GENERATION AND OPTIMAL PLACEMENT

Academic Section Generation Source No. of Units Size(s) of Units Placement

Solar PV System 145 145 x 200W = 29 kW Classes/Labs/offices

Electrical Department Wind Turbines 2 + 1=3 2×5kW+1×7.5kW=17.5kW Labs/Class rooms
Battery Storage/UPS 3 3 × 200 Ah/ 6kVA UPS Class rooms/offices
Solar PV System 131 131 × 200W = 26.2 kW Classes/Labs/offices
Mechanical Wind Turbines 5 5 × 5kW = 25 kW Labs/ Class rooms
Department Battery Storage/UPS 3 3 × 200 Ah/ 6kVA UPS Class rooms/offices
Solar PV System 138 138 × 200W = 27.6 kW Classes/Labs/offices
Civil Department Wind Turbines 2 + 2=4 2×3.5kW + 2×5kW=17kW Labs/class rooms
Battery Storage/UPS 3 3 × 200 Ah/ 6kVA UPS Class rooms/offices
Solar PV System 128 28×.2kW+100×.3kW=35.6kW Classes/Labs/offices
Computer System & IT Diesel Generator 1 1 × 50 kVA=40 kW,P.f=.80 Data center/conf. room
Wind Turbines 3 3 × 5kW = 15Kw Labs/classes/datacenter
Battery Storage/UPS 10 10×200Ah/25 kVA UPS Data center/conf. room
Solar PV System 50 50 × 200W = 10 kW Offices (lights, fans)
Admin Block Wind Turbines 3 3 × 5kW = 15 kW Offices (HVAC)
Battery Storage/UPS 6 6 × 200Ah/ 10 kVA UPS Offices(lights/LCD/fan)
Solar PV System 20 20 × 200W = 4 kW Lights/fans/LCDs
Central Library Wind Turbines NIL NIL NIL
Battery Storage/UPS 2 2 × 200 Ah/ 5kVA UPS Library lights/LCD/fans
Backup Generator 1 1 × 30kVA= 25kW, P.f=0.83 Auditorium Hall
(Auditorium Solar PV System 40 40 × 200W= 8 kW Auditorium Offices
Internal + External)
Wind Turbines NIL NIL NIL
Battery Storage/UPS 2 2 × 200Ah/ 5kVA Offices(fans/lights/LCD
Solar PV System 50 50 × 200W= 10 kW LCD/Routers/lights/fan
Access Centre Wind Turbines 1 1 × 7.5 kW = 7.5 kW HVAC/ Routers
Battery Storage/UPS 3 3 × 200 Ah/ 6 kVA UPS 50% LCD + 50%lights

Energy Storage System”. ICSGCE 2011: 27–30 September 2011,

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