IJRRAS 7 (1) ● April 2011
www.arpapress.com/Volumes/Vol7Issue1/IJRRAS_7_1_14.pdf
USING HOMER
POWER OPTIMIZATION SOFTWARE FOR COST
BENEFIT
ANALYSIS OF HYBRID-SOLAR POWER GENERATION
RELATIVE TO
UTILITY COST IN NIGERIA
K.R. Ajao,
O.A.Oladosu & O.T. Popoola
Department of
Mechanical Engineering, University of Ilorin, Ilorin, Nigeria
ABSTRACT
HOMER is a micro power optimization software used in evaluating
designs of both off-grid and grid-
connected
power systems for a variety of
applications. The cost benefit analysis of
a wind turbine-solar
hybrid system
was done using HOMER software and comparison was also made with the cost per kilowatt
of central
grid or utility supply. The hybrid system have a pay-back period of about
thirty-three years and at
current
costs, central grid
power is the least expensive
option but may not
be available to most
rural
households far
from the grid. Hence it is necessary to supply these areas from isolated power
sources.
1. INTRODUCTION
Nigeria
is endowed with
abundant renewable energy resources,
the significant ones being
solar energy, biomass,
wind, small
and large hydropower with potential for hydrogen fuel, geothermal and ocean
energies. Except for large
scale
hydropower which serves as a major source of electricity, the current state of
exploitation and utilization of the
renewable
energy resources in the country is very low, limited largely to demonstration
and pilot projects.
The main
constraints in the rapid
development and diffusion of
technologies for the exploitation
and
utilization of
renewable energy resources in the country are the absence of market and the
lack of appropriate
policy,
regulatory and institutional framework
to stimulate demand and attract
investors. The comparative
low quality of
the systems developed and the high
initial upfront cost
also constitute barriers to the
development of
markets.
The
transmission network is overloaded with a wheeling capacity less than 4,000 MW.
It has a poor voltage profile
in most parts
of the network, especially
in the North, inadequate dispatch and
control infrastructure, radial and
fragile grid
network, frequent system collapse, exceedingly high transmission losses.
Access to
electricity services is low in Nigeria. About 60 percent of the population
(approx. 80 million people) is not
served with
electricity. Per capita consumption of electricity is approximately 100kWh
against 4500kWh, 1934 kWh
and 1379 kWh
in South Africa, Brazil and China, respectively [1].
The objective
of this work is to analyze the cost benefit of a solar-wind power hybrid system
and determine the pay-
back period
when compared to cost per kilowatt of utility power supply.
2. WIND ENERGY
The energy
available in the wind depends on the
density and air velocity. The density,
as any other gas,
changes with
the temperature and pressure which varies with the high level of the sea. The
energy of a mass
of air which
is displaced is determined by the Kinetic Energy (K.E) flux [2].
1
P = rAV3
( )
0
2
When wind move
across the wind turbine, the static pressure drops to a lower pressure than the
atmospheric
pressure. As
the air follows its trajectory, it takes its
atmospheric value again, inducing an extra wind
deceleration.
By this way, in a distance between upstream of the turbine and downstream,
behind the turbine,
there is no
change in static pressure, but there is
a reduction in kinetics energy. This phenomenon is
represented by
the Betz law in eqn (2).
PMAX=
8
27
rAV3
( )
Wind is a
natural phenomenon related to the
movement of air
masses caused primarily by the differential
solar heating of
the earth's surface.
Seasonal variations in the energy
received from the sun affect the
strength and
direction of the wind. The ease with which wind turbines transform energy in moving air to
rotary
mechanical energy suggests the use of electrical devices to convert wind energy
to electricity. Wind
energy has
also been utilized, for decades, for water pumping as well as for the milling
of grains.
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IJRRAS 7 (1) ● April 2011
Ajao & al. ● Cost Benefit Analysis Of Hybrid-Solar Power
Generation
A study on the wind energy potentials for a number
of Nigerian cities shows that the annual
wind speed
ranges from
2.32 m/s for Port Harcourt to 3.89 m/s for Sokoto [3]. The maximum extractable
power per unit
area, for the same two sites was estimated as 4.51 and 21.97 watts per square metre of blade area,
respectively.
When the duration of wind speeds greater than 3 m/s is considered, the energy
per unit area is
168.63 and
1,556.35 kWh per square metre of blade area, again for Port-Harcourt and
Sokoto.
Although
use of
wind energy for water supply has been known and used for hundreds of
years, in recent
times efforts
have been directed largely towards the use of wind power for the generation of
electricity and
in the past
twenty years or so rapid changes in technology have occurred and major wind
powered generating
plants have
been installed, especially in the rural areas of the developed countries.
3. SOLAR ENERGY
Solar energy is the most promising of
the renewable energy sources
in view
of its apparent unlimited
potential. The
sun radiates its energy at the rate of about 3.8 x 1023 kW per second. Most of this energy is
transmitted
radially as electromagnetic radiation which
comes to about 1.5kW/m2 at the boundary of the
atmosphere.
After traversing the atmosphere, a
square metre of the earth's surface can receive as much as
1kW of solar
power, averaging to about 0.5 over all hours of daylight. Studies relevant to
the availability of
the solar energy resource in Nigeria have indicated its
viability for practical use. Although solar radiation
intensity
appears rather dilute when compared with the volumetric concentration of energy
in fossil fuels.
Nigeria
receives 5.08 x 1012 kWh of energy per day from the sun and if
solar energy appliances with just 5%
efficiency are
used to cover only 1% of the country's surface area then 2.54 x 106 MWh of electrical energy
can be
obtained from solar energy [4]. This amount of electrical energy is equivalent
to 4.66 million barrels
of oil
per day. Typical
of such applications are in
drying, cooking, heating, distillation, cooling and
refrigeration
as well as electricity generation in thermal power plants.
In solar
photovoltaic applications, the solar radiation is converted directly into
electricity. The most common
method of doing
this is by the use of silicon solar cells. The power generating unit is the
solar module which
consists
of several solar
cells electrically linked together
on a base plate. On the whole the
major
components
of a photovoltaic system include
the arrays which consist of the
photovoltaic conversion
devices,
their interconnections and support,
power conditioning equipment
that convert the dc
to ac and
provides
regulated outputs of voltage and current; controller, which automatically
manages the operation of
the total
system; as well as the optional storage for stand alone (non-grid) systems.
4. HOMER SOFTWARE
HOMER, the micro
power optimization software
developed by Mistaya Engineering, Canada for
the National
Renewable
Energy Laboratory (NREL) USA, used in
this analysis simplifies the task of evaluating designs of both
off-grid and
grid-connected power systems for a variety of applications.
In designing a
power system, many decisions about the configuration of the system are to be
made: components to
include in the
system design, size of each component to use etc. The large number of
technology options and the
variation in
technology costs and
availability of energy
resources make these
decisions difficult. HOMER's
optimization
and sensitivity analysis algorithms make it easier to evaluate the many
possible system configurations
[5].
HOMER simulates
the operation of a system
by making energy
balance calculations and
displays a list of
configurations,
sorted by net present cost that can be used to compare system design.
5. ENERGY GENERATION SYSTEM
DESIGN
The 400W FD
Series wind turbine and solar module rated 100W are installed on the roof top
of Faculty of
Engineering,
University of Ilorin building (Block 10) as shown in Figure 1. These unit serves as a backup
power supply
to the Very Small Aperture Terminal (VSAT) equipment housed inside the VSAT
room where
the inverter
and battery bank are installed as shown in Figure 2.
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IJRRAS 7 (1) ● April 2011
Ajao & al. ● Cost Benefit Analysis Of Hybrid-Solar Power
Generation
Figure 1: PV Panel and FD series Turbine
6. ENERGY ANALYSIS
6.1. Load
profile
Figure 2: Battery Bank and Converter
The load
profile is based on a hypothetical apartment and the profile is shown in Figure
3. A small base load
of 10 W occurs
throughout the day and night and small peaks of 80 W occur in the evening. The
total daily
load average
903 Watt-hours per day.
Figure 3:
Hourly load profile
6.2. Solar
radiation profile
Figure 4 below
shows the solar resource profile over one year. The solar resource data for
Ilorin, Nigeria was
obtained from
NASA surface Meteorology and solar energy website [6]. The approximate location
of the site
used is 8° 26’
N and 4° 29’E. It has been observed that the solar intensity ranges from 550 W/m2 to 1075
W/m2 with total incident energy per day of 17 MJ/m2 to 25 MJ/m2 in Ilorin,
Nigeria [7].
Figure 4:
Solar Radiation profile for
6.3. Wind
resource data
Ilorin
Figure 5 shows the wind resource profile over a
year period for Ilorin. This
was obtained from NASA
surface
metrology and solar energy website [6].
The daily average wind speed is
2.5 m/s measured at
anemometer
height of 14.9 meters above ground level [8].
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IJRRAS 7 (1) ● April 2011
7. Economic Analysis
Ajao & al.
● Cost
Benefit Analysis Of Hybrid-Solar Power Generation
Figure 5.Wind Resource Profile of
Ilorin
An annual interest
rate of 6% was
considered, while the project
life year was taken as 20 years. All
calculations
are done with exchange rate of $1 to N160. The tariff of the
utility company in Nigeria, The
Power Holding
Company of Nigeria (PHCN), is N4 per kWh ($0.024).
Constraints
are conditions which a system must satisfy for it to be feasible. HOMER discards systems that
do not satisfy the specific constraints so that they do not
appear in the optimization
or sensitivity result.
Maximum
capacity shortage is set at 5%.
A survey
of ten households
having similar electricity
consumption pattern showed
that the
average
consumption
per month for a household is 400 units. This amount to N1, 736 ($0.026) per
month or N20,
832 ($130.2)
per annum and is equivalent to N416, 640 ($2,604) for twenty years of
consumption.
8. IMPLEMENTATION OF HOMER CODE
8.1 System
equipment configuration
Figure 6 shows
the equipment considered in the optimization. The equipments considered are
photovoltaic
solar cells,
wind turbine, converter, battery bank and loading system.
Figure 6:
Equipment considered in the optimization
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IJRRAS 7 (1) ● April 2011
Ajao & al. ● Cost Benefit Analysis Of Hybrid-Solar Power
Generation
The size
of the components under consideration, the acquisition cost, replacement cost, operation and
maintenance
cost and the expected lifetime as input into the HOMER software is depicted in
table 1 below.
Table 1:
System Components
Component
PV Panels
Size
0.05 – 0.4 kW
Capital
Cost($)
$7,500/kW
Replacement
Cost
$7,500kW
O&M Cost
($)
0.00
Lifetime
20 years
Vision6 FM200D
Battery
200 Ah / 12 volt ( bank size: 1-
8 batteries)
$175/battery $175/battery $2.00/year
917 kWh of throughput
per battery
FDseries Wind
Turbine
Converter
8.2 System
performance
8.2.1. PV system
0.4 kW DC
0.1 – 1.5 kW
$2,500/kW
$200/kW
$2,500/kW
$200/kW
$10/year
$20/year
15 years
15 years
The capital
and replacement costs were specified with $7.50/W. No maintenance cost was
considered for the
PV system
because little or no maintenance is needed for the panels. A derating factor of
90% and 20 years
lifetime was
considered as shown in Figure 7 below.
Figure 7:
Photovoltaic Solar Input
8.2.2. Wind
system
The FD Series Wind Turbine was considered for the simulation in Figure 8. The capital and replacement
costs of $2.50
were specified.
Figure 8: Wind
Turbine Input
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IJRRAS 7 (1) ● April 2011
8.2.3. Battery
storage
Ajao & al. ● Cost Benefit Analysis Of Hybrid-Solar Power
Generation
The battery
chosen is the 6FM200D series. It has a nominal
voltage of 12 Volts and nominal capacity of
200Ah (2.4 kWh).
Two batteries were considered by HOMER in the simulation shown if Figure 9
below.
Figure 9:
Storage Batteries Input
8.2.4. Converter
and Inverter
The
inverter and the rectifier efficiencies were assumed to be 90% and 85%
respectively for all the sizes
considered.The
sizes considered varied from 0.1 kW to 1.5kW. The converter input is shown in
Figure 10.
Figure 10:
Converter Input
8.2.5. Load
Levels
A typical
household load was considered. The consumption includes 8-bulb points, television, DVD,
refrigerator,
4-fans, washing machine and pressing iron as shown in Figure 11.
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IJRRAS 7 (1) ● April 2011
9. RESULTS
Ajao & al. ● Cost Benefit Analysis Of Hybrid-Solar Power
Generation
Figure 11:
Load Input
The total net
present cost is HOMER's
main economic output. All systems
are ranked according to net
present cost,
and all other economic outputs are calculated for the purpose of finding the net present cost.
The result
obtained from the optimization gives the initial capital cost as $3,455 while
operating cost is 69
$/year. Total
net present cost (NPC) is $4251 and the cost of energy (COE) is 1.74 $/kWh.
The utility
tariff bill of was compared with the hybrid system net cost. At this rate, the
system will have a
pay back
period of about thirty-three (33) years and not twenty years as specified by
many manufacturers.
10. DISCUSSION
The cost
benefit analysis of a wind turbine-solar hybrid system in comparison with
utility tariff showed that
the hybrid
system is not economically cheap and have a system payback time of thirty-three
years. At current
costs, central
grid power is the least expensive option but will not be available to most
rural households.
A wind-solar
cell hybrid energy system would be cost effective if there is reduction in component cost by
installation
of many of this hybrid system in a farm
thereby lowering the investment cost per kilowatts. Its
availability,
sustainability and environmental friendliness make it a desirable source of
energy supply.
The model
developed is fairly general and may be adequate for preliminary results for
energy consumption
cost for
household and industrial sector willing to adopt renewable energy sources.
11. REFERENCES
[1]. International
Centre for Energy, Environment and Development Report (2006). Renewable
Electricity Action
Program, Federal
Ministry of Power and Steel, Abuja, Nigeria
[2]. Victor L and
Ricardo A (2004). Interfas TIMEO – ANSYS, for the modeling one and
modal analysis
of an
airfoil of
turbine of wind IV, Conferencia de Diseño e Ingeniería por Computadora, San Miguel
de Allende
[3]. Adegoke C.O and
Anjorin A.S (1996). Wind as an alternative energy source. J.Sci.Engr.Tech
3(2), pp. 511-524.
[4]. Chiemeka I. U and
Chineke T. C (2009). Evaluating the global solar
energy potential at Uturu,
Nigeria,
International
Journal of Physical Sciences Vol. 4 (3), pp. 115-119
[5]. Givler, T. and
Lilienthal, P. (2005). Using
HOMER Software, NREL’s Micropower Optimization Model, to
explore the Role of Gen-sets in Small Solar Power Systems; Case Study: Sri
Lanka Technical Report, National
Renewable
Energy Laboratory, USA
[7]. Lasode O.A
(2004). An Improved Solar Cabinet
Dryer with Convective
heat Transfer. Journal of
Applied
Science,
Engineering and Technology, Vol.4 No.2; pp.32-39
[8]. Ajao K.R and Adegun I.K
(2009). Development and Power Performance Test of a Small Three-Blade
Horizontal-Axis
Wind Turbine. Heat
Transfer Research, Vol. 40, No. 8, pp.777-792
102
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