optimization of sustainable solar-wind hybrid system for domestic electrification

7/30/2019 OPTIMIZATION OF SUSTAINABLE SOLAR-WIND HYBRID SYSTEM FOR DOMESTIC ELECTRIFICATION

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International Journal of Mechanical and Production

Engineering Research and Development (IJMPERD)

ISSN 2249-8001

Vol. 2 Issue 4 Dec - 2012 31-42 TJPRC Pvt. Ltd.,

OPTIMIZATION OF SUSTAINABLE SOLAR-WIND HYBRID SYSTEM FOR DOMESTIC

ELECTRIFICATION

1

KARAN SOOD,2

PROF PRAVEEN SINGH &3

PRASHANT BAREDAR1Assistant Professor, Patel Institute of Technology, Ratibad, Bhopal-462044, India

2Associate Professor, B.U. University Institute of Technology, Hoshangabad Road, Bhopal, India

3Associate Professor, Maulana Azad National Institute of Technology, Bhopal, India

ABSTRACT

Solarwind hybrid energy systems allow improving the system efficiency, power reliability and reduce the energy

storage requirements for stand-alone applications. Good compensation characters are usually found between solar energy

and wind energy. These hybrid systems are now becoming popular in urban area for power generation applications due to

advancements in renewable energy technologies and substantial rise in prices of petroleum products. This paper

recommend an optimal design model for hybrid solarwind systems employing battery bank for calculating the system

optimum configurations and ensuring that the annualized cost of the systems is minimized while satisfying the custom

requirements. The main decision variables included in this analysis are A.C. Primary Load Calculation, Global Solar

Resources, Wind Resources, Output of solar and Wind energy systems, Excess Electricity and State of battery charge.

First, we analyse above variables and finally we conclude the optimum design of the hybrid system along with its cost

estimation with expected life of battery bank. The optimization results of the hybrid system has good complementary

characteristics between the solar and wind energy and this system is expecting to perform very well throughout the year

with generally no battery over-discharge condition. The study presented here is also an attempt to promote the domestic

use of Solar-wind energy in this region of Bhopal, India (Longitude 77

.35and Latitude 23

.28).

KEYWORDS: Solar-wind hybrid system, Wind turbine, Solar-PV, Homer, Optimization

INTRODUCTION

The main benefit of solar-wind hybrid system is that when solar and wind powers are used together, the reliability

of the system is enhanced. Additionally, the size of battery storage can be reduced as there is less dependence on only one

source of power generation. Often, when there is no sun, there is plenty of wind in India (as in Monsoon season). Winds

are usually relatively strong in winter and solar radiations have higher intensity in summer. Muralikrishna &

Lakshminarayana (2008) have shown; for the same level of deficiency of power supply probability, the Solar-wind hybrid

energy system gives the lowest unit cost values as compared to standalone solar and wind energy systems.

Ding & Buckeridge (2000) presented a balanced system for getting stable output from available resources of

renewable energy, which minimized the dependency of the output upon the weather changes; moreover, it optimised the

exploitation of the renewable energy resources. Shaahid and Elhadidy (2007) used the Homer tool for minimizing of the

NPC of a SolarDieselBattery system to deliver the uninterrupted electricity to a shopping complex situated in Dhahran

(Saudi Arabia). Dalton et al. (2008) have also done the optimization for minimizing NPC by using Homer tool in a Solar

WindDieselBattery system in Australia. Muljadi & Butterfied (2001) and Ched et al. (1998) represented the useful

techniques, which were helpful for optimum sizing of solar-wind hybrid systems.


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32 Karan Sood, Praveen Singh & Prashant Baredar

PROBLEM FORMULATION

Muselli M et al. (1999) and Bagan & Billinton R. (2005) have shown in their study that the hybrid systems are

more consistent for uninterrupted power supply and less costly than the systems which are depend on single renewable

energy resource. But hybrid systems have higher failure rate due to improper optimization, components failure, poor

maintenance and inadequate support by suppliers after installation of the system. Although it has observed that generally

component failure occurs because of improper optimization of the system. The Homer tool from NREL

(www.nrel.gov/homer/) is the one of the best platform for optimizing of Solar-Wind hybrid system. The main motive of

this paper is to reduce such failures of the hybrid systems by implementing proper optimization techniques.

SYSTEM DESIGN AND ITS OBJECTIVES

Yang et al. (2007, 2009) give the optimization approach for hybrid SolarWindBattery systems which is able to

reduce the LCE. Koutroulis et al. (2006) present a paper for economic optimization

by means of Genetic Algorithms on PVWindBattery systems. The main objective for designing a Solar-wind-battery

system is the optimum mixing of wind system and solar PV system to fulfil the load requirement of the consumer, at aminimum cost of installation and maintenance. In order to accomplish this, the hybrid system has been designed based on

the following steps:

(i) Power requirement, (ii) Availability of Solar and Wind Resources, (iii) Configure the inputs for generating sustainable

conditions (iv) Simulations of the sustainable Hybrid Systems, (v) Chosen of the optimum system for fulfilling the

consumer requirement.

POWER REQUIREMENT

Calculation of power requirement is essential for designing an sustainable hybrid system. AC Primary load is

electrical load that must be met immediately in order to avoid unmet load. To synthesize the electric data in Homer tool,

we must enter at least one load profile, which is the set of 24 hourly values of electric load, one for each hour of the day.

We can enter different load profiles for different months and for weekdays and weekends too.

Figure 1: AC Primary Load

By entering the whole year data in the Homer tool, we got the AC Primary load calculation graph for the whole

year (Figure 1). In this load calculation we considered two variables: Day-to-day variable and time-step-to-time-step


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Optimization of Sustainable Solar-Wind Hybrid System for Domestic Electrification 33

variable, where both variables are 15% and 20% respectively. Finally, we conclude that the scaled annual average and

average load are 3.25 kWh/d and 135W respectively, with the peak load of 1.55kW. Thus we should design a Solar-wind

hybrid system which can hold the 3.25kWh daily with the 135W average load and the peak load of 1.6kW.

AVAILABILITY OF SOLAR AND WIND RESOURCES

Solar Resource

Hourly solar radiation data with clearness index for the year 2011 collected from official website of NREL

[www.nrel.gov/homer/]. This online data for the particular year can gather by providing appropriate time zone, latitude and

longitude. The time zone for India is GMT +05:30 and latitude and longitude for the proposed site in Bhopal is 23 o28 and

77o35 respectively. The proposed site for installation of domestic hybrid system is Gandhi Nagar, Bhopal.

Figure 2: Average Daily Solar Radiation and Clearness Index

In Figure 2, we can see that in summer season solar radiations are higher than winter and in rainy season clearness

index and availability of solar radiations are lower than summer and winter season. From the above analysis of Solar

resource, we conclude that scaled annual average of solar radiation is 5.18kWh/m

2

/d.

Wind Resource

Figure 3: Wind Resource for Throughout the Year of 2011

Wind mast is used to measure the wind speed at a prospective wind turbine site. For this purpose anemometer is

fitted to the top of a mast, which is placed at same height as a expected hub height of the wind turbine to be used. The two

basic parameters: one is altitude from mean see level i.e. 530m and the height of anemometer i.e. 16m and the four

advanced parameters: Weibull k, Autocorrelation factor, Diurnal pattern strength and Hour of peak wind speed are 2, 0.85,

0.25 and 15 respectively (Figure 3). All the data and parameters for optimization of wind resource were collected from

weather monitoring station, UIT-RGPV, Gandhi Nagar, Bhopal.


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CONFIGURE THE INPUTS FOR GENERATING SUSTAINABLE CONDITIONS

PV Inputs

Figure 4: PV Inputs

Borowy & Salameh (1995) represent a methodology to optimize the size of the solar array and the capacity of the

battery bank in Solarwindbattery system. The two main factors were considered when selecting of PV array for the

sustainable hybrid system, are

1. The cost of the solar energy system is higher than the wind energy system for the same rated capacity (Wp).

2. There is plenty of wind in this region of city for the small domestic wind energy system.

Thus, we have to choose the small Solar PV system for this site. We added the small sizes (i.e. 0kWp to

0.500kWp) of PV array in the Homer tool, which we want to consider for the optimum system. Now Homer will use the

information which we entered in the cost table to calculate the costs of each PV array size, interpolating and extrapolating

as necessary. Capital and replacement costs include the cost of PV panels, mounting hardware, tracking system, control

system, wiring and installation. The cost analysis of the PV system in Figure 4.

Wind Turbine Inputs

The two main factors were considered when selecting a wind turbine for the sustainable hybrid system:

1. The rated capacity (Wp) of wind turbine should be larger because of expansive Solar PV system.

2. With the help of power curve and availability of wind resources, we have to select appropriate wind turbine for the small

domestic wind electric system.

Figure 5: Wind Turbine Inputs

First, we should select the appropriate size of turbine with the consideration of nature of wind and power curve of

implemented turbine. If power curve (Figure 5) fulfils the load requirement then we have to move towards the effect of


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cost of turbine. Power curve represents the turbine's power output over a range of wind speeds. We used this curve to

verify that the wind turbine which we have selected for the site is appropriate one or not. The turbine which is suitable for

this site is 1.3kWp Whisper Turbine. Capital cost of this turbine including all mounting and transmission accessories in

$1964 with O&M cost 30$/yr. The cost analysis for the Wind Turbine is shown in Figure 5.

Battery Inputs

Karaki et al. (1999) represented algorithms series for battery bank of solar wind hybrid system. These series show

the economic value of battery bank with respect to battery capacity and charging/discharging cycle time. The role of

battery is very important in off grid system because this is the only backup for the system. In case of day of autonomy, the

system will fully depend on the battery bank. Protogeropoulos et al. (1998) performed the optimization of the system;

adjust the size of the battery bank until an ultimate configuration occur that certified the enough autonomy. Kellogg et al.

(1998) show an iterative optimization method for SolarwindBattery hybrid system. A 200AH, 12V Tubular battery of G-

Tech India, is very effective and economic nowadays in the country. This battery is labelled with 2 year replacement

warranty. It has been observed that if this battery is used under good maintenance and proper state of charge condition, the

battery life may extend up to 5 to 9 years. The cost specified battery is $152 with the replacement cost of $40 and O&M

cost of 1$/yr. (Figure 6).

Figure 6: Battery Inputs

Inverter Inputs

The inverter is an electronic device which converts the DC electricity that comes from the hybrid system into AC

electricity, which matches the AC frequency of the power lines. The Cost analysis for the inverter is shown in Figure 7,

where lifetime of a unit is 15 years with an efficiency of 90%. The capital cost of inverter is 100$ with replacement cost of

55$ and O&M of 1$/yr.

Figure 7: Inverter Inputs


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RESULTS & DISCUSSIONS

Simulations of the Sustainable Hybrid Systems

Homer simulates the operation of a system by making energy balance calculations for each of the 8,760 hours in a

year. For each hour, Homer compares the electric demand in the hour to the energy that the system can supply in that hour,and calculates the flows of energy to and from each component of the system. All the resources and inputs simulated and

we got the 360 sustainable configurations. This simulation results eliminate all infeasible combinations and rank the

feasible systems according to increasing net present cost. There are 360 feasible designs for our site under desirable

conditions.

Figure 8: Simulation Calculation Window

Optimization of the Appropriate Hybrid System

Figure 9: Optimum Solar Wind Hybrid

After simulating all the possible system configurations, we should select at least one optimum hybrid system,

sorted by net present cost, battery life and payback period. A 1.6kW Solar wind hybrid system is the optimum system for

this site because this system has lower net present cost, higher battery life with less payback period.

System Architecture

System Architecture which will bear 3.2kWh/day and 1.6kWp (Figure 9):

(i) 1 Solar PV Array, 0.3kWp (ii) 1Whisper 200b Wind Turbine, 1.3kWp

(iii) 5 G-Tech Tubular Batteries, each 200AH, 12V (iv) Inverter for 1.6kW peak load


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Annualized Cost Summary

It is clearly marked in Figure 10 that PV module of 0.3kWp has the capital cost of $562 with $1/yr O&M. The

total annual cost of PV module in first year is $563. Similarly we can observe the investment cost for wind turbine,

batteries and converter. Thus total capital cost is $3386 and Total NPC is $3424 for the whole system.

Figure 10: Cost Flow Summary

Electrical Output of the Whole System

As we can see in the Figure 11, the optimum mixing for solar (PV array) and wind energy (Wind turbine) is 14%

and 86% respectively, where PV array will generate 654kWh/yr and Wind turbine will generate 3918kWh/yr. The total

power produced by both the systems is 4573 kWh/yr. On the other hand total AC primary load is 1186kWh/yr i.e.

3.25kWh/day with very few unmet load. In this way excess electricity is 3134kWh/yr. This excess electricity can supply to

grid. Renewable fraction value is 1.00, which is the maximum fraction value for any renewable energy source.

Figure 11: Electrical Output


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Solar Output of 0.3kwp Solar Array

Figure 12: Solar Output

A 0.3kWp rated capacity solar array is used in the system. As we can clearly see in Figure 12, there is generally

no power generation in between 06:00 PM to 06:00 AM and there is plenty of power generation in day time. Power

generation by the PV array is less in monsoon season, which will compensated by the wind turbine (in Figure 13). This PV

array works effectively from October to May.

Some important solar outputs are:

Quantity Value Units Quantity Value Units

Rated capacity 0.300 kW Minimum output 0.00 kW

Mean output 0.07 kW Maximum output 0.32 kW

Mean output 1.79 kWh/d PV penetration 55.2 %

Capacity factor 24.9 % Hours of operation 4,373 hr/yr

Total production 654 kWh/yr Levelized cost 0.860 $/kWh

Wind Output of 1.3kwp wind Turbine

Figure 13: Wind Output

Rated capacity of wind turbine is 1.3kWp. As we can see in the Figure 13, there is plenty of power output by wind

resource in between April to September. This is the time when the seasonal changes take place in the country due to the

monsoon.


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Some important wind outputs are:

Quantity Value Units Quantity Value Units

Total rated capacity 1.30 kW Minimum output 0.00 kW

Mean output 0.45 kW Maximum output 1.24 kW

Capacity factor 34.4 % Wind penetration 330 %

Total production 3,918 kWh/yr Hours of operation 7,312 hr/yr

Levelized cost 0.509 $/kWh

State of Battery

Figure 14: State of Battery Bank Charge

For an optimum hybrid system, we should use 5 parallel strings in a battery bank and each string has one battery

in it. Each battery should have the potential of 12V. We are designing this battery bank in such a way that both solar and

wind energy systems are not supplying the power (i.e. power generation by the hybrid system is 0 W). In above condition

of design consideration, we can take the whole load of primary load by battery bank. In a full charging condition, this

battery bank will able to give the constant power supply to the system for 2 days, 5hrs and 12mins. We can see the detail

state of battery bank charge for throughout the year in Figure 14 and state of battery bank charge on the monthly basis in

Figure 15.

Figure 15: Monthly Statistics of State of Battery Bank Charge


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Some important outputs for battery bank:

Quantity (Units) Value Quantity (Units) Value

String size 1 Lifetime throughput (kWh) 4,434

Strings in parallel 5 Battery wear cost ($/kWh) 0.050

Batteries 5 Energy in (kWh/yr) 606

Bus voltage (V) 12 Energy out (kWh/yr) 485

Nominal capacity (kWh) 12.0 Losses (kWh/yr) 121

Usable nominal capacity (kWh) 7.20 Annual throughput (kWh/yr) 542

Autonomy (hr) 53.2 Expected (life yr) 8.19

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optimization of sustainable solar-wind hybrid system for domestic electrification

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