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Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
OASYS SOUTH ASIA Research Project
Peer-reviewed Published Papers
(pre-publication version)
Off-grid Electricity Generation with Renewable Energy
Technologies in India: An Application of HOMER
Rohit Sen
The Energy and Resources Institute, New Delhi India
and Subhes C Bhattacharyya
Institute of Energy and Sustainable Development
De Montfort University
Leicester LE1 9BH, UK
(Renewable Energy DOI: 10.1016/j.renene.2013.07.028)
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
Abstract
Renewable energy-based off-grid or decentralised electricity supply has traditionally
considered a single technology-based limited level of supply to meet the basic needs,
without considering reliable energy provision to rural consumers. The purpose of this paper
is to propose the best hybrid technology combination for electricity generation from a mix
of renewable energy resources to satisfy the electrical needs in a reliable manner of an off-
grid remote village, Palari in the state of Chhattisgarh, India. Four renewable resources,
namely, small-scale hydropower, solar photovoltaic systems, wind turbines and bio-diesel
generators are considered. The paper estimates the residential, institutional, commercial,
agricultural and small-scale industrial demand in the pre-HOMER analysis. Using HOMER,
the paper identifies the optimal off-grid option and compares this with conventional grid
extension. The solution obtained shows that a hybrid combination of renewable energy
generators at an off-grid location can be a cost-effective alternative to grid extension and it
is sustainable, techno-economically viable and environmentally sound. The paper also
presents a post-HOMER analysis and discusses issues that are likely to affect/ influence the
realisation of the optimal solution.
Keywords: hybrid systems, off-grid electrification, HOMER, India.
Acknowledgement: The work reported in this paper is funded by an EPSRC/ DfID research grant
(EP/G063826/1) from the RCUK Energy Programme. The Energy Programme is a RCUK cross-council
initiative led by EPSRC and contributed to by ESRC, NERC, BBSRC and STFC. The author gratefully
acknowledges the funding support.
Disclaimers: The views presented here are those of the authors and do not necessarily represent the
views of the institutions they are affiliated with or that of the funding agencies. The authors are
solely responsible for remaining errors or omissions, if any.
Abbreviations
COE: Cost of Energy
Km: Kilometre
EDL: Economical Distance Limit
RET: Renewable Energy Technology
RES: Renewable Energy Sources
GHG: Green House Gases
LCC: Life Cycle Cost
LUCE: Levelized Unit Cost of Electricity
NPC: Net Present Cost
O&M: Operation and Maintenance
BET: Bio Energy Technology
T&D: Transmission and Distribution
SPV: Solar Photovoltaic’s
BDG: Bio-Diesel Generator
SHP: Small Hydro Power
B100: 100% Pure Biodiesel
DG: Diesel Generator
MNRE: Ministry of New & Renewable Energy, India.
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
2
1. Introduction
With about 1.3 billion people in the world (or about 1 in 5) without access to
electricity in 2010 [1], the challenge of providing reliable and cost-effective services remains
one of the major global challenges facing the world in this century. Although grid extension
still remains the preferred mode of rural electrification [2], extension of the central
electricity grid to geographically remote and sparsely populated rural areas can either be
financially unviable or practically infeasible. Off-grid options can be helpful in such cases.
Moreover, the efforts in using renewable energies have often focussed on single
technologies. For example, Solar Home Systems (SHS), solar photovoltaic systems and
micro-hydro power have been widely used, but such options are often unable to cater to
consumers’ needs adequately and reliably due to limited resource availability arising from
variability of resources. Reliance on a single technology generally results in an over-sizing of
the system, thereby increasing the initial costs. A hybrid system design can overcome the
intermittent nature of renewable energy sources (RES), the over-sizing issue and enhance
reliability of supply. Yet, hybrid systems have received limited attention due to their
increased complexity and hardly any work has considered the issue of reliable supply of
electricity in a rural context
1
.
The purpose of this study is to find the best combination of RET from the available
resources in a given village location that can meet the electricity demand in a reliable and
sustainable manner and to analyse whether such a hybrid option is a cost effective solution
or not. To achieve this objective, we use an example of an Indian village, estimate the
potential demand, identify the available resources, model electricity generation based on
multiple combinations of RETs with the application of HOMER software, select the best
option based on the cost of electricity generation and then compare these performance
indicators to grid extension related costs. Our choice of the tool is influenced by its
popularity, ease of use and flexibility. Despite our reliance on HOMER, our contribution
arises from four novel features: 1) most of the studies in the past have considered wind
turbines, solar power and diesel technologies whereas we have considered four renewable
1
By reliable supply we imply round-the-clock supply or supply on demand. In most studies, a limited period
of supply is considered for rural areas. This is not the case in this study.
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
3
technologies namely micro-hydro, solar PV, wind turbines and bio-diesel thereby pushing
the hybrid technology combinations; 2) the reliability of supply, which has not received
adequate attention in the literature, is considered as a main supply objective; 3) we have
included productive use of electricity in commercial and agricultural activities in addition to
domestic energy needs, thereby enlarging the scope of the study; and 4) we have gone
beyond a typical HOMER application by considering pre and post HOMER analysis (discussed
in sections 3.1 and 5 in more detail).
The organisation of the paper is as follows: section 2 presents a review of related
studies; section 3 briefly presents HOMER, section 4 presents the case study and results
obtained from the study. Section 5 then presents the post-HOMER analysis, while
concluding remarks are presented in section 6.
2. Literature Review
The purpose of the literature review presented here is twofold: first, this provides
evidence of knowledge gap that justifies the need for this work; and second, it also provides
support for the methodology used in the study and is a source of information for
comparison, triangulation and referencing. Given the above purpose, we use the literature
to show the limitations of existing studies by focusing mainly on studies that relied on
HOMER as the analytical tool.
HOMER (Hybrid Optimisation Model for Electric Renewables), developed by NREL
(National Renewable Energy Laboratory, USA) appears repeatedly in the literature as a
preferred tool. It can handle a large set of technologies (including PV, wind, hydro, fuel cells,
and boilers), loads (AC/DC, thermal and hydrogen), and can perform hourly simulations.
HOMER is an optimization tool that is used to decide the system configuration for
decentralized systems. It has been used both to analyse the off-grid electrification issues in
the developed as well as developing countries. In the case of developed countries, often
advanced fuel systems such as hydrogen are considered. Examples of such studies include
the following Khan and Iqbal [3] who investigated the feasibility of a hybrid system with
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
4
hydrogen as energy carrier in Newfoundland, Canada; Barsoum and Vacent [4]; Karakoulidis
et al. [5], Giatrakos et al. [6] and Türkay and Telli [7].
For developing countries, a large number of studies exist and a detailed review of this
literature is beyond the scope of this paper. Instead we focus on a selected set for our
purpose. Givler and Lilienthal [8] conducted a case study of Sri Lanka where they identified
when a PV/ diesel hybrid becomes cost effective compared to a stand-alone small solar
home systems (50 W PV with battery). This study considers an individual household base
load of 5W with a peak of 40 W, leading to a daily load average of 305 watt-hours. Through
a large number of simulations, the study found that the PV-diesel hybrid becomes cost
effective as the demand increases. However, this study focuses on the basic needs as such
and does not include productive use of energy.
Munuswamy et al. [9] compared the cost of electricity from fuel cell-based electricity
generation against the cost of supply from the grid for a rural health centre in India,
applying HOMER simulations. The results showed beyond a distance of 44km from the grid,
the cost of supply from an off-grid source is cheaper. This work just considered the demand
of a rural health centre and was not part of any traditional rural electrification programme.
Hafez and Bhattacharya [10] analysed the optimal design and planning of renewable
energy-based micro-grid system for a hypothetical rural community where the base load is
600 kW and the peak load is 1183 kW, with a daily energy requirement of 5000 kWh/day.
The study considers solar, wind, hydro and diesel resources for electricity generation.
Although the study considers electricity demand over 24 hours, the purely hypothetical
nature of the assumptions make the work unrealistic for many off-grid areas of developing
countries.
Lau et al. [11] analysed the case of a remote residential area in Malaysia and used
HOMER to analyse the economic viability of a hybrid system. The study uses a hypothetical
case of 40 households with a peak demand of 2 kW. The peak demand is 80kW and the base
demand of around 30 kW is considered in the analysis. Although such high rural demand can
be typical for Malaysian conditions, it is certainly not true for others. The study also does
not consider any productive use of electricity.
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
5
Similar case studies are presented in other studies as well. For example, Himri et al. [12]
present a study of an Algerian village; Nandi and Ghosh [13] discuss the case of a
Bangladeshi village, while Nfah et al. [14] and Bekele and Palm [15] provide case studies of
Cameroon and Ethiopia respectively. Table 1 summarises the technology choices, demand
focus and country of application of these studies.
Table 1: Selected examples of hybrid technology analysis using HOMER
Reference
Technology
application
Country of
application
Supply duration/ type
Givler and
Lilienthal [8]
PV-battery -
diesel
Sri Lanka
Basic needs
Hafez and
Bhattacharya
[10]
PV, Wind, Hydro,
Diesel, Battery
Hypothetical
24 hour service but unrealistic
demand profile for a rural area
of developing countries.
Lau et al. [11]
(2010)
PV-diesel hybrid
Malaysia
24 hour service but uses a high
demand profile for a rural area
and does not use any productive
load.
Himri et al. [12]
Wind-diesel
hybrid
Algeria
Adding wind turbine to an
existing diesel-based supply;
Limited technology options.
Nandi and Ghosh
[13]
Wind-PV-Battery
Bangladesh
Solar and wind hybrid; no
productive demand
Nfah et al. [14]
PV, Micro-hydro,
LPG generator,
battery
Cameroon
Diesel as main generator
supplemented by PV and micro-
hydro, load based on grid-
connected urban households of
Uganda was used.
Bekele and Palm
[15]
PV-wind hybrid
Ethiopia
PV and wind hybrid, randomised
load profile from hypothetical
load data.
It can be seen that the hybrid options have often considered a limited set of
technologies. Moreover, most studies concentrate on supplying electricity merely for
domestic purposes and do not take into account the electricity demand for agricultural,
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
6
irrigation, community purposes and for small-scale business units for the socio-economic
development of the whole region. The load profiles are also not carefully considered in
many cases. These issues are considered in the present study, thereby bridging the
knowledge gap.
3. Methodology
3.1 Introduction
This study uses the HOMER software package developed by NREL for designing
micro-power systems but complements it by undertaking pre- and post- HOMER analyses.
This is indicated in Fig. 1. In the Pre-HOMER analysis phase, a detailed assessment of the
village load, site layout and available resources in the selected village is conducted. This is
carried out outside HOMER and data is fed into the software. In the HOMER analysis the
hybrid RET system is designed, followed by a techno-economic analysis. It compares a wide
range of equipment with different constraints and sensitivities to optimize the system
design. The analysis is based on the technical properties of the system and the life-cycle cost
(LCC) of the system. The LCC comprises of the initial capital cost, cost of installation and
operation costs over the system’s life span. HOMER performs simulations to satisfy the given
demand using alternative technology options and resource availability. Based on the
simulation results, the best suited configuration is selected. In the Post-HOMER phase, the
business-related analysis is performed to a limited extent (see section 5), which we intend
to strengthen in the future.
We have considered a combination of the following technologies, namely small
hydropower (SHP), wind turbines, solar PV (SPV) systems, batteries, and a bio-diesel
generator (BDG) for back-up (see Fig. 2 for a schematic system configuration diagram). In
the hybrid system the demand from the village is AC-coupled, the SHP and the BDG are
connected to the AC side of the network and the SPV, wind turbine and the batteries are
connected to its DC side. Usually a conventional back-up diesel generator (DG) is used to
supplement the RE system for peak loads and during poor resource periods. In this study, a
BDG (B100) is used instead, making the whole system a sustainable, clean and carbon
neutral system, not only for the purpose of electricity generation but also for working
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
7
effectively towards GHG emissions mitigation by not burning any fossil fuels. This makes the
study different from others.
Fig. 1: Framework of analysis
Initial assessment
Detailed assessment
Load profile
Resources
Site layout
Techno-economic analysis using HOMER
Post HOMER Analysis
Business case
Regulatory issues
Other issues
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
8
Fig. 2: Design of the selected RET’s for the hybrid system
3.2 System Modelling
The selected off-grid remote rural village for this study is Palari, a small village in
Bastar district in the Indian state of Chhattisgarh. The details of the village are listed in table
2. The nearest town is Kondagaon, which is about 15 to 20 kilometres away, both Kodagaon
and Palari are located in close proximity to the national highway 43 (NH-43). The area
around the village is partially hilly with flat plains constituting the rest. The village has water
and drinking water facilities in the form of water-wells and hand pumps. The village has no
access to grid electricity, which offers an opportunity for off-grid electrification of the
village.
Table 2: Details about the selected village
Particulars
DETAILS
Village Name
Palari
Sub-District
Kondagaon
District
Bastar
State
Chhattisgarh
Country
India
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
9
Latitude
19°635’N
Longitude
81°672’E
Elevation (in meters)
587
Area of Village (in hectares)
370
Unirrigated area (in hectares)
> 200
Forest land (in hectares)
14
Culturable waste (in hectares)
7
Rivers Available
1
Water-wells
1
Grid Electricity
0
Number of households
304
Total Population
1,624
No. of Males
764
No. of Females
860
Education facilities (Primary School)
1
Medical Facilities (Primary Health Subc entre)
1
Post Office
1
Total Income (per annum)
Rs. 1,75,100 / $ 3892
Total Expenditure (per annum)
Rs. 1,13,400 / $ 2520
Source: Census 2001. (http://www.censusindia.gov.in/)
3.2.1 Village Load Assessment
In a remote rural village the demand for electricity is not high compared to urban
areas. Electricity is demanded for domestic use (for appliances like radio, compact
fluorescent lamps, ceiling fans, and table fans), agricultural activities (such as water
pumping), community activities (such as in community halls, schools, and clinics) and for
rural commercial and small-scale industrial activities (such as cold storage, small milk
processing plants and cottage industries).
In this study, the village energy load requirement is carefully estimated considering
existing load profile data available in state government records for similar rural areas. We
have also consulted previously published literature on Indian villages and triangulated with
expert opinions and personal judgements. The demand has been estimated separately for
two distinct seasons prevailing in this area, namely summer (April to October) and winter
(November to March) considering the appliance holding and use patterns for households,
potential commercial activities, and energy use in productive applications. Table 3 provides
the summary of estimated demand for summer and winter seasons. Clearly, the demand
estimation is a crucial element of the entire system design and further improvement is
possible here by incorporating social information of the users as well as their preferences.
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
10
Table 3: Estimated electricity demand for Palari village
S.
No.
LOAD
No.
in
use
Power
(watts)
SUMMER (April -
Oct.)
Winter (Nov. -
March)
Hrs/Day
Watt-
hrs/Day
Hrs/Day
Watt-
hrs/Day
Domestic Purposes
1
Low-energy lights
(CFL)
1
20
6
120
7
140
2
Low-energy lights
(CFL)
1
20
6
120
7
140
3
Low-energy lights
(CFL)
1
11
5
55
6
66
4
Radio
1
10
3
30
4
40
5
Ceiling Fan
1
30
15
450
0
0
6
Table Fan
1
15
9
135
0
0
TOTAL
910
386
A
No. of Houses
304
276640
117344
Industrial/ Commercial/Community
Purposes
1
Shops
10
500
8
40000
7
35000
2
Community Centre
1
1000
8
8000
6
6000
3
Small Manufacturing
Units
5
3000
12
180000
10
150000
4
Street Lights (CFL)
5
30
10
1500
12
1800
B
TOTAL
229500
192800
Agriculture & Irrigation Purposes
1
water pump
8
745.6
5
29824
3
17894.4
2
Irrigation pump
4
1491.2
6
35788.8
4
23859.2
3
well
1
745.6
4
2982.4
2
1491.2
C
TOTAL
68595.2
43244.8
Medical Centre
1
Low-energy lights
(CFL)
4
20
4
320
6
480
2
Ceiling Fan
4
30
6
720
0
0
3
Refrigerator
1
600
20
12000
16
9600
D
TOTAL
13040
10080
School
1
Compact Fluorescent
Lights
5
20
2
200
4
400
2
Ceiling Fan
2
30
6
360
0
0
3
Computer (desktop)
1
300
2
600
2
600
4
Television
1
100
2
200
2
200
E
TOTAL
1360
1200
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
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Knowing that the load factor in such locations tends to be poor, some demand has
been distributed strategically over the 24 hour period to improve the system load factor.
The village load has been divided into three important categories:
1) Primary Load 1 – This includes the domestic load, medical centre and school demand. The
load demand is approximately 222kWh/day and 51.2 kW peak. It has a load factor of 0.181
(see Fig. 3).
2) Primary Load 2 – This includes the demand load for the community centre, shops, local
business and small manufacturing units. It is approximately 212kWh/day and 39.4 kW peak.
It has a load factor of 0.224 (see Fig. 4).
3). Deferred Load – This includes the agricultural load of the village. The scaled annual
average deferred load is 58.6kWh/day and has a peak load of 68.6kW. It has a storage
capacity designed for 30 kW and is also connected on the AC side.
Fig. 3: Load profile of primary load 1
Fig. 4: Load profile of primary load 2
The load assessment was done in Excel worksheet, using customised data templates
for this purpose. This is an area of further work which can produce a generic pre-HOMER
tool for wider applications.
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
12
3.2.2 Resources Assessment
We have considered solar, wind, micro-hydro and bio-diesel resources in this
simulation. The resource assessment is presented below.
The solar resource used for Palari village at a location of 19°59' N latitude and 81°59'
E longitude was taken from NASA Surface Meteorology and Solar Energy website
2
. The
annual average solar radiation was scaled to be 5.17kWh/m2/Day and the average clearness
index was found to be 0.548. The solar radiation is available throughout the year; therefore
a considerable amount of PV power output can be obtained (see Fig. 5).
Fig. 5: Solar energy profile at the selected village
The monthly average wind resource data from an average of ten years was taken
from the above NASA resource website based on the longitude and latitude of the village
location. The annual average wind speed for the location is 3.5 m/sec with the anemometer
height at 50 meters. The wind speed probability and average monthly speed throughout the
year is also observed. It shows that there are 15 hours of peak wind speed. The wind speed
variation over a day (diurnal pattern strength) is 0.25 and the randomness in wind speed
(autocorrelation factor) is 0.85 (see Fig. 6).
2
http://eosweb.larc.nasa.gov/sse/
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
13
Fig. 6: Wind energy resource at the selected village
The Alternate Hydro Energy Centre (AHEC), India, has identified a number of
locations for the development of Small Hydropower projects in Chhattisgarh [18]. One of
the projects, Kondagaon on Narangi River near Palari village, is identified with a potential
output of 500kW at 5 meters head. The monthly average flow has been carefully estimated
based on the average precipitation, average temperatures and topography of the region.
The residual flow was assumed to be 4000 l/s. The flow in the river drops from September
to May, and rapidly increases up to 58,000 l/sec in August due to heavy rainfall in the area.
Hence power generation from the hydro source varies depending on the water availability
during the year.
Biodiesel is a bio fuel predominantly made from vegetable oil and sometimes animal
fat. Biodiesel can be used to run diesel engines with minor engine modifications (if
required). In India, with the help of extensive agricultural research, Jatropha Curcas oilseed
was chosen as main feedstock for the biodiesel production in India’s Biodiesel programme.
The most commonly available are B20 (containing 20% of biodiesel and 80% petroleum
diesel in the blend), and B100 which is pure biodiesel. Biodiesel has a shelf life of 6 months,
after which it has to be tested again.
As there is a biodiesel plant in the neighbouring city of Raigarh, it is assumed that the
fuel will be available from this plant. The fuel price is considered to be 0.6 $/L. The current
market price of biodiesel in India is about 0.58 $/L, though it varies regionally due to tax and
other costs.
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
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3.2.3 Components Assessment
In a micro-power system, a component generates, delivers, converts and stores
energy. In this HOMER analysis, solar PV, wind turbines, and run-off river hydropower are
the intermittent resources and the bio-diesel is kept for backup. Batteries and Converter are
for storing, converting electricity respectively. The grid connection in this study is only used
as a comparison for the analysis and determination of the economic distance to grid (EDL).
The performance and cost of each of the system’s components is a major factor for the cost
results and the design
3
.
The SPV panels are connected in series. The power generated by SPV is more than
wind turbines at this location due to better solar insolation. The capital cost and
replacement cost for a 1kW SPV is taken as $6000 and $5000 respectively. As there is very
little maintenance required for PV, only $10/year is taken for O&M costs. Like for all other
components considered in the following paragraphs, the costs per kW considered include
installation, logistics and dealer mark-ups. The SPV is connected to a DC output with a
lifetime of 20 years. The de-rating factor considered is 90% for each panel to approximate
the varying affects of temperature and dust on the panels. The panels have no tracking
system and are modelled as fixed titled south at 19°59' N latitude of the location with the
slope of 45°.
A Generic 10kW horizontal-axes wind turbine is considered. The amount of
electricity generated by the wind turbine greatly depends on the availability of and
variations in the wind speed. The G10 wind turbine selected gives a 10kW of DC output. The
cost of one unit is taken as $40,000, while the replacement and the maintenance cost are
considered to be $32,000 and $200/year respectively. The wind turbine has a hub height of
25 meters and a lifetime of 25 years.
3
The components’ technical and cost parameters for this study are based on data collected from The Ministry
of Non-Conventional Energy Sources (GoI), The Energy Research Institute (TERI) in India, previous published
literatures, information from personal sources of Indian manufactures, and assumptions.
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
15
The SHP is designed for a power output of 30kW depending on the village load. The
turbine is designed for a net head available of 5m and has a design flow of 815 l/s. The
turbine efficiency is 75% and has a pipe head loss of 5.68%. The SHP gives an AC output and
has a lifetime of 25 years. The capital cost for a 30kW SHP is taken as $42,000 while the
replacement cost and O&M cost are considered to be $35,000 and $4,000 respectively.
The capital cost, replacement cost, O&M costs of a 1kW BDG are taken as $1200,
$1000, and $1.03/hr respectively.
4
A normal old DG can be used as well, but it might need
certain modifications. The per kW costs are for a new modern DG that can be used for
biodiesel as fuel as well and include the costs of installation, logistics and dealer mark-ups.
The generator is connected to an AC output with a lifetime of 15,000 operating hours. The
minimum load ratio is taken to be 30% of the capacity; moreover, HOMER requires the
partial load efficiency to simulate this component. HOMER calculates the total operating
cost of the generator based on the amount of time it has to be used in a year.
Batteries are used as a backup in the system and to maintain a constant voltage
during peak loads or a shortfall in generation capacity. The battery chosen for this study is
Surrette 6CS25P. It is a 6V battery with a nominal capacity of 1,156 Ah (6.94 kWh). It has a
lifetime throughput of 9,645kWh. The capital cost, replacement cost and O&M costs for one
unit of this battery were considered as $1000, $800, and $50/year respectively.
5
HOMER
models the batteries on charging and discharging cycles.
The capital cost, replacement cost and O&M costs of the converter for 1kW systems
were considered as $700, $550, and $100/year respectively [16]. The lifetime of the
converter is 15 years, inverter efficiency of 90% and rectifier efficiency of 85%.
4
The prices considered are an interpolation of data (quotations) obtained from local Indian manufactures and
distributors.
5
The prices considered are an interpolation of data (quotations) obtained from local Indian manufactures,
distributors and previous published literatures.
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
16
3.2.4 Sensitivity of Inputs
The key variables for the micro-power system are, however, often uncertain. This is a
major problem to be overcome in the designing of the system. Here the uncertainties in the
RES (wind, hydro, solar and biomass) have been taken into account. The sensitivities entered
for the Biodiesel price in $/l are 0.60, 0.714, and 0.804. For wind speed 3.5m/s and 5.0m/s
are the two values entered. Similarly for the design flow rate 815 l/s and 0 l/s were entered
for the SHP.
3.3 Economic Modelling
As HOMER aims to minimise the total net present cost (NPC) both in finding the
optimal system configuration and in operating the system, economics play a crucial role in
the simulation. The indicator chosen to compare the different configurations’ economics is
the life-cycle cost (LCC), and the total NPC is taken as the economic figure of merit. All
economic calculations are in constant dollar terms.
3.4.1 Economic Inputs
The project’s lifetime is considered to be 25 years with an annual discount rate of
10%. The system fixed capital cost is considered to be $10,000 for the whole project and the
system fixed O&M cost is estimated to be $500/year for the project lifetime.
6
The system
fixed capital costs include various civil constructions, logistics, labour wages, required
licenses, administration and government approvals and other miscellaneous costs.
3.4.2 The Grid
In this study the grid is used as standard benchmark by HOMER, to be compared
with the technical and cost parameters of the off-grid hybrid RETs system. Therefore the
cost of grid extension is taken in the analysis to see whether a grid extension is viable or an
off-grid system is more appropriate. The capital cost of grid extension per kilometre for the
6
These costs are an interpolation from previous literature, estimates from TERI and quotations from local
Indian civil contractors.
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
17
Palari village terrain is considered to be $8000/km. The annual O&M cost per kilometre is
considered to be $1500/year/km
7
and the grid power price is assumed from an interpolation
as $0.44/kWh [17].
3.4.3 Analysis
HOMER performs the simulation for a number of prospective design configurations.
After examining every design, it selects the one that meets the load with the system
constraints at the least life cycle cost. HOMER performs its optimization and sensitivity
analysis across all mentioned components and their resources, technical and cost
parameters, and system constraints and sensitivity data over a range of exogenous
variables. The competitiveness of the best suited hybrid RET system for rural electrification
is compared with the conventional option of grid extension, based on the COE for both
options and based on this the economic distance limit (EDL) is determined. The cost of low
tension transmission distribution lines within villages has been excluded, since it is the same
in all the cases.
4. Results and discussion
This section presents the results of our analysis. First, the optimisation results are
presented, which is followed by the outcomes of our sensitivity analysis. The economic and
environmental aspects are also considered.
4.1 Optimization results
The optimal combination of RET system components for our case study is a 20kW
PV-Array, 30kW SHP, 10kW BDG, 40 Surrette 6CS25P Batteries, 20kW Inverter and a 20kW
Rectifier with a dispatch strategy of cycle charging. No wind turbine is selected at this site
7
The costs are an estimated assumption based on the interpolation from previous publishes literatures.
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
18
(see Fig. 7). This system is considered at 3.5m/s of wind speed, $0.6/l of biodiesel cost and
815 l/s of design flow rate for the SHP. The total net present cost, capital cost and the cost
of electricity (COE) for such a hybrid system are $673,147, $238,000 and $0.420/kWh,
respectively. The COE of $0.420/kWh from this hybrid system is cheaper than that of
$0.44/kWh from grid extension as considered for this study. Therefore grid extension does
not appear to be a viable option to meet the village load. But, if the cost of electricity from
the grid supply falls below $0.420/kWh, grid extension becomes viable.
Fig. 7: Optimal least cost hybrid system for the case study
Figure 8 shows the monthly distribution of the electricity produced in kW by the SPV,
SHP and BDG. From December to February, the biodiesel generator is mostly used combined
with SPV as hydropower is unavailable due to low flow in the river. Also, from June to
August the peak load is met by SPV and BDG.
Fig. 8: - Monthly average electricity production from the best hybrid configuration system.
.
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
19
It is evident from Fig. 8 and table 4 that small hydro station dominates the electricity
output in this case. The SHP operates at full load for 9 months and produces 186,649
kWh/year, achieving a capacity factor of 71%. At this level of operation, the levelised cost of
hydro-only system becomes just 4.62 cents/ kWh. Only during the winter months when
water is inadequate, bio-diesel plant becomes the dominant producer. For the selected
system the biodiesel plant operates for 2663 hours (capacity factor 28.9%), produces 25,294
kWh/year and consumes 13,646 litres of bio-fuel. However, this is a costlier option than
hydropower and the marginal cost of electricity from the bio-diesel plant is $0.21/ kWh. The
penetration of solar energy reduces the biodiesel output, particularly outside winter
months. The solar panels produce 34,439 kWh/year, operating for 4357 hours (or recording
a capacity factor of 19.7%). The levelised cost of solar electricity turns out to be
$0.415/kWh.
Table 4: - Techno-Economic details of the three hybrids system configurations
Configurations
Unit
Best Hybrid
2nd best
Hybrid
3rd best Hybrid
Wind Speed
m/s
3.5
3.5
5
Bio Diesel-
(B100) Price
$/L
0.6
0.6
0.6
Design Flow
Rate
L/s
815
0
0
Solar PV
kW
20
100
120
Wind Turbine
(G10 kW)
no.
0
0
6
Hydro
kW
29.98
0
0
Bio D
kW
10
20
10
Batteries -
Surrette 6CS25P
40
180
200
Converter
kW
20
50
70
Dispatch
Strategy
no.
CC
CC
CC
Total Capital
Cost
$
2,38,000
8,49,000
12,31,000
Total NPC
$
6,73,147
19,84,485
18,98,258
Total Annual
Capacity Cost
$/yr
26,220
93,533
1,35,617
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
20
Total Annual
Replacement
Cost
$/yr
3,623
14,232
17,815
Total O&M Cost
$/yr
36,129
89,701
47,937
Total Fuel Cost
$/yr
8,188
21,161
7,759
Total Annual
Cost
$/yr
74,159
2,18,627
2,09,127
Operating Cost
$/yr
47,939
1,25,094
73,511
COE
$/kWh
0.42
1.23
1.192
PV Production
kWh/yr
34,439
1,72,196
2,06,636
Wind
Production
kWh/yr
0
0
53,004
Hydro
Production
kWh/yr
1,86,649
0
0
Bio D
Production
kWh/yr
25,294
63,719
22,950
Total Electrical
Production
kWh/yr
2,46,382
2,35,916
2,82,589
AC Primary
Load Served
kWh/yr
1,55,444
1,56,290
1,54,027
Deferrable Load
Served
kWh/yr
21,308
21,383
21,350
Renewable
Fraction
%
0.9
0.73
0.92
Capacity
Shortage
kWh/yr
4,393
2,805
5,522
Capacity
Shortage
Fraction
%
0
0
0
Unmet Load
kWh/yr
3,056
2,144
4,440
Unmet Load
Fraction
%
0.02
0.01
0.02
Excess
Electricity
kWh/yr
62,412
25,258
73,398
BioDiesel-
(B100)
L/yr
13,646
35,268
12,932
Breakeven Grid
Extension
Distance
km
-2.09
58.58
54.59
62,412 kWh/year of electricity which is 25% of total electricity generated goes
unused due to low demand and is fed to dump loads. This is particularly high in summer
months when the hydro plant operates fully. This shows that this system has the capability
in meeting the demand growth in the future. The demand can also be increased by serving
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
21
the demand of other nearby villages, because as the demand increase the load factor
increases and hence the cost per kWh will decrease.
Fig. 9: Cash flow summary based on the selected components
Figure 9 shows the cash flow summary for the optimal system. The capital cost of the
bio-diesel generator makes up only 5% of the system’s total capital cost, whereas almost
50% of the initial investments go to the SPV arrays. Once installed, however, SPV is cheap to
maintain and operate compared to the BDG, which in the end is responsible for 51.5% of the
system’s total annual cost of $74,159. Small hydro plant on the other hand is relatively
cheaper and contributes less to the overall cost.
4.2 Sensitivity Results
Sensitivity analysis eliminates all infeasible combinations and ranks the feasible
combinations taking into account uncertainty of parameters. HOMER allows taking into
account future developments, such as increasing or decreasing load demand as well as
changes regarding the resources, for example fluctuations in the river’s water flow rate,
wind speed variations or the biodiesel prices. Here, various sensitive variables are
considered to select the best suited combination for the hybrid system to serve the load
demand.
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
22
If the hydropower option is not available, the second-best hybrid configuration will
comprise of 100kW SPV, 20kW BDG and 180 batteries and will have a cost of electricity of
$1.230/kWh. This hybrid system has an economic distance to grid of 58.6 kilometres and
generates 25,258 kWh/year of excess electricity. This configuration can be used at off-grid
locations where hydropower is not available. The third hybrid configuration adds wind
turbines to the configuration when the wind speed increases from 3.5m/s to 5m/s and no
hydro is available. Hence with an increasing number of components the capital cost and
total NPC also increase. The third hybrid configuration of wind turbines, SPV, BDG and
batteries has a COE of $1.192/kWh
8
. Table 4 shows all the relevant techno-economic details
considering the best three hybrid system configurations considered on HOMER for this
paper.
This shows that the system configurations without SHP tend to be more costly than
other renewable technologies. Even if the wind speed increases, generating more electricity
from the wind turbine, the system costs do not reduce (see Fig. 10). The surface plot for the
levelized COE with total NPC superimposed is presented in Fig. 10. The biodiesel price is
fixed at $0.6/l, the hydropower design flow rate is depicted on the x-axis and wind speed
variation on the y-axis. It can be observed that as the design flow rate increases, the power
output from SHP increases and hence there is a reduction in total NPC. As the total NPC
decreases, the system’s COE decreases as well. This shows that with a change in sensitivity
variables the capacity of an individual component increases and hence the configuration of
the system changes. Therefore a hybrid system with SHP proves to be the cheapest option
compared to other RETs.
8
HOMER ranks options by net present value and not by cost of electricity.
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
23
Fig. 10: Surface plot of cost of electricity
Figure 11 shows the result for the breakeven distance for grid extension (or EDL). It
shows that the distance varies from a negative value to 60kms depending on the total NPC
and levelized COE. For the selected hybrid configuration of SPV, SHP, BDG, and batteries the
EDL comes out be a negative value as mentioned earlier. It is clearly evident from the line
graph that as the design flow rate increases with wind speed and biodiesel cost at a fixed
value of 3.5m/s and $0.6/l respectively, the total NPC of the system decreases. At 100l/s of
design flow rate the EDL comes out to be 50kms and at 800l/s the EDL comes out to be
negative distance of -2kms. Hence the total NPC and levelized COE of a system determine
the EDL with respect to the input parameters.
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
24
Fig. 11: - Line graph for total NPC vs. Design flow rate and Breakeven Grid Extension
distance.
4.3 Emissions
The optimal hybrid RET system would save 33,832 kg/yr of CO2 over one year in
operation compared to a central power generation plant or a stand-alone DG system. In
addition, emission of particulate matters and nitrogen oxides will be reduced due to reliance
on renewable energy systems (see table 5).
Table 5: Emission reduction
Pollutant
Emissions
(kg/yr)
Carbon dioxide
33,832
Carbon monoxide
44.3
Unburned hydrocarbons
0.688
Particulate matter
4.68
Sulphur dioxide
0.576
Nitrogen oxides
894
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
25
Based on the above analysis, it can be concluded that a hybrid system becomes a
viable option in an off-grid location in India. If small hydro power potential exists, it can
offer economically attractive power supply. In the absence of small hydro potential, the cost
of supply increases and interventions by the government may be required to make the
investment socially desirable.
5.0 Post HOMER Analysis
The optimal hybrid electricity supply system requires development of 60 kW of
power generating capacity (30 kW small hydro, 10 kW biodiesel and 20 kW solar PV) in a
remote location and arrange for necessary distribution to 304 households and other
customers in the village. Although HOMER suggests technical feasibility of such a system
and indicates the break even cost at which the investment can be recovered, the business
dimensions are generally not covered. The post HOMER analysis is required to develop a
complete understanding of the business case. In the following paragraphs, some such issues
are highlighted.
The first question that arises relates to financing of the investment. For example, in
the optimal case, an investment of $238,000 will be required for a 60 kW system (or an
average of $400 per kW approximately). Although the investment volume is not large either
for any conventional lender (such as banks) or for any utility investor, significant risks are
involved in the investment. First, a part of the investment is not re-deployable (e.g. the
investment for SHP). If the project does not succeed for any reason, the investment will be a
sunk cost for the investor and will represent a bad investment. Second, the electricity
market in the area is not developed and the assumptions related to the demand may not
materialise, or take longer to realise. This will adversely affect the cost recovery process.
Third, the business environment may be affected by political, regulatory and governance
challenges, thereby affecting such investments. Fourth, there are practical difficulties (e.g.
availability of skilled manpower, managing supply logistics, and poor transport facilities) that
can add to costs, delay project delivery and reduce profitability of the projects. In such
cases, appropriate incentives and support mechanisms will play an important role to attract
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
26
investment and mitigate risks. In the state of Chhattisgarh, capital grant is available for
solar, wind and biogas plants. Also, the state renewable energy agency is actively promoting
off-grid electrification and has trained technicians who work in rural areas. Therefore, some
risk mitigation is already underway.
A related issue that requires careful consideration is the choice of an appropriate
business model for delivering the project. While a private investor brings expertise and
innovative ideas, the cost of supply can be higher. Moreover, a private investor will
essentially be profit-driven and unless the business case suggests profitability, it is unlikely
that private investment will flow. On the other hand, state utility services have not been
successful in providing electricity in the remote areas and therefore such agencies are
unlikely to be interested in off-grid electricity delivery. A middle path may be found in the
form of local co-operatives or private-public partnership projects where both the social
dimension and the business-like approach are combined. In our particular case, the state
renewable energy agency is proactive in building joint ventures and promoting private
investment but further work is required to decide a specific business model.
Clearly, the tariff issue will play a crucial role but remains a challenging task in the
rural context due to the following factors. First, investors will be interested in recovering the
investment over a shorter period of time and very few lenders will consider a loan period of
25 years. As the cost recovery period reduces, the cost of supply will increase, which may in
turn make the project less attractive to the users. Second, the discount rate used for
business decisions depends on the investor. For example, a private investor is likely to use a
higher discount rate to reflect the cost of capital, riskiness of the investment and its desire
to recover the investment quickly. On the other hand, state agencies or local communities
may use a low discount considering the social nature of the investment. The tariff will
accordingly depend on this. Third, the grid-based electricity supply in other areas may be
subsidised and consumers in the off-grid area may expect similar tariff treatments.
However, the cost of supply for the off-grid case may be quite different from the grid-based
supply and the consumer base is significantly small. Therefore, there is very limited cross-
subsidy potential in the off-grid case and unless there is direct subsidy support from the
government, price parity with the grid-based supply can only jeopardise the viability of the
project. In this particular case, the state allows subsidy for rural areas and the support is
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
27
available for off-grid consumers at a fixed rate ($0.5 per household per month). While this
may reduce the tariff burden on the consumer, it is unclear whether this level of subsidy is
sufficient for cost recovery or not and whether the subsidy will be available over the entire
life of the project.
Finally, the issue of regulating the off-grid supply through a mini-grid system as is
envisaged in the case study requires careful consideration. The business will not function
effectively unless the rules of the game are clearly laid out and the compliance with the
rules is monitored through a supervisory system. As the consumers are likely to be illiterate
and vulnerable, protecting them against any monopoly abuse, health and safety risks and
other unfair treatments assumes greater importance. Simultaneously, the investor needs to
be protected and encouraged to provide the desired level of service. However, unclear
regulatory environment and lack of regulatory capacity can hinder developing such projects.
This is an area of concern for the present case study where no specific regulatory
arrangement exists for mini-grids.
6. Conclusion
Our search for a technically feasible and economically viable hybrid solution for off-
grid electricity supply to a remote village such as Palari resulted in a least-cost combination
of small hydro power, solar PV, bio-diesel and batteries that can meet the demand in a
dependable manner at a cost of $0.420/kWh. Given the availability of small hydro power in
this location, most of the electricity in the optimal solution comes from the hydro plant and
it provides a cheap source of power to the locality. However, the system reliability cannot
be ensured due to variable nature of water availability and lack of adequate water flow in
winter unless other technology options are considered. The bio-diesel plant and the solar PV
plants contribute 10% and 14% respectively to electricity generation but being costlier
options than small hydropower, they raise the overall cost of electricity. If the small hydro
plant is not available (or no hydro resources are available), the electricity demand can be
met with a hybrid system comprising of solar PV, small wind turbines and bio-diesel plants.
But the cost of electricity supply will increase three folds, thereby making the system less
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
28
attractive to users. Thus three main lessons from this case study are: 1) where hydro
potential exists, it is important to take advantage of the resource; 2) a combination of
technologies improves supply reliability and hence makes better business sense; 3) the cost
of supply of renewable-energy based electricity may not always be a cost effective option
for remote applications unless appropriately supported by the government.
Although our work is based on a standard software HOMER, it goes beyond the
conventional applications of the software by systematically considering the pre and post
application phases. In the pre-HOMER stage, we have considered the local demand in detail
and have included multiple types of users (residential, institutional, commercial, agricultural
and industrial) and considered seasonal variation in the demand. As HOMER takes the
demand as given and finds the least cost combination of supply options to meet the
demand, realistic demand estimation assumes an important role. Our study contributes in
this area by highlighting this aspect and incorporating a detailed demand analysis feature in
the study. In the post-HOMER phase we highlight the business-related dimensions that
influence the project delivery. We have briefly considered the financing challenge, business
model selection, tariff issue, and the regulatory concerns. This is an attempt to go beyond
the techno-economic analysis.
Surely further work is required in both pre and post HOMER areas. We believe that a
standard template can be designed for a systematic estimation of demand for off-grid areas
and to capture the stakeholder perspectives. Even demand scenarios can be included to
take the simulations to another level of iteration. Similarly, a systematic approach of
considering the business case of the optimal solution and its delivery-related issues can
enhance the overall appreciation of the micro-energy systems.
Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
HOMER
29
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Off-grid Electricity Generation with Renewable Energy Technologies In India: An application of
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OASYS South Asia project
The Off-grid Access Systems for South Asia (or OASYS South Asia) is a research project funded by the
Engineering and Physical Sciences Research Council of UK and the Department for International
Development, UK. This research is investigating off-grid electrification in South Asia from a multi-
dimensional perspective, considering techno-economic, governance, socio-political and
environmental dimensions. A consortium of universities and research institutes led by De Montfort
University (originally by University of Dundee until end of August 2012) is carrying out this research.
The partner teams include Edinburgh Napier University, University of Manchester, the Energy and
Resources Institute (TERI) and TERI University (India).
The project has carried out a detailed review of status of off-grid electrification in the region and
around the world. It has also considered the financial challenges, participatory models and
governance issues. Based on these, an edited book titled “Rural Electrification through Decentralised
Off-grid Systems in Developing Countries” was published in 2013 (Springer-Verlag, UK). As opposed
to individual systems for off-grid electrification, such as solar home systems, the research under this
project is focusing on enabling income generating activities through electrification and accordingly,
investing decentralised mini-grids as a solution. Various local level solutions for the region have been
looked into, including husk-based power, micro-hydro, solar PV-based mini-grids and hybrid
systems. The project is also carrying out demonstration projects using alternative business models
(community-based, private led and local government led) and technologies to develop a better
understanding of the challenges. It is also looking at replication and scale-up challenges and options
and will provide policy recommendations based on the research.
More details about the project and its outputs can be obtained from www.oasyssouthasia.dmu.ac.uk
or by contacting the principal investigator Prof. Subhes Bhattacharyya (subhesb@dmu.ac.uk).
OASYS South Asia Project
Institute of Energy and Sustainable Development,
De Montfort University,
The Gateway, Leicester LE1 9BH, UK
Tel: 44(0) 116 257 7975
