**4.2 Simulation cases and results**

Simulations were performed for the standalone hybrid power system using the annual load profile for four systems: (i) diesel-battery system, (ii) PV-diesel-battery system, (iii) winddiesel-battery system, and (iv) PV-wind-diesel-battery system.

The following assumptions were used for the Kongiganak Village simulations:


Table 2 shows the installation costs (USD) for different components for the hybrid electric power system. The post simulation results obtained from the HARPSim model were compared with those obtained from the HOMER software. Table 3 shows the comparison of results from the HARPSim model with HOMER for the hybrid electric power system. It can be observed from the table that the wind-diesel-battery system is the most cost effective system with the lowest NPV, COE, and payback period. This is because of the high energy

Energy-Efficient Standalone Fossil-Fuel Based

**system** 

3.04 (11.48)

273,910 (72,463)

**Item Diesel-battery** 

3.11 (11.75)

267,662 (70,810)

System cost

Engine

kWh/liter (kWh/gallon) for the engine

Fuel consumed in liters (gallons)

Total cost of

(c) PV array

Operational life

(a) Generator

(b) Battery

Net present value (USD) with i = 7% and n = 20 years

Cost of Electricity (USD/kWh)

Payback period for renewable (years)

Emissions (a) CO2 in metric tons (US tons)

(b) NOx in kg

(c) PM10 in kg

7,322

(16,143) - 7,245

Table 3. Comparison of Results from HARPSim with HOMER.

(lbs)

Energy supplied to load (kWh)

Energy supplied (a) Diesel

Hybrid Power Systems Employing Renewable Energy Sources 135

(USD) 172,788 172,788 224,448 224,450 234,288 234,288 285,948 285,950

efficiency (%) 29.3 28.63 29.3 28.51 29.3 27.03 29.3 26.88

fuel (USD) 212,429 217,390 210,185 216,325 153,373 171,451 151,458 170,456

engine (kWh) 832,152 832,205 823,368 823,422 597145 619,504 588,362 612,287 (b) WTG (kWh) - - - - 235,007 238,000 235,007 238,000

(kWh) - - 8,784 8,783 - - 8,784 8,783

(years) 5 1.87 5 1.87 5 1.8 5 1.8

bank (years) 5 12 5.5 12 5.5 12 6 12

832,152 832,205 832,152 832,205 832,152 832,205 832,152 832,205


0.301 22.6 0.304 0.334 0.237 0.27 0.24 0.275


660 (728) 703 (775) 653 (720) 700 (772) 477 (526) 555 (612) 471 (519) <sup>552</sup>

(11,657) - 5,222

(15,972) - 5,288

(lbs) 308 (679) - 305 (672) - 222 (490) - 220 (484) -

3.02

272,568 (72,108)

3.11 (11.75)

264,834 (70,062)

HARPSim HOMER HARPSim HOMER HARPSim HOMER HARPSim HOMER

(11.43) 3.11 (11.75) 2.87

193,249 (51,124)

216,027 (57,150)

**Wind-diesel-battery system** 

**PV-wind-dieselbattery system** 

(10.78)

214,776 (56,819)

(608)

(11,512) -

(10.84) 3.11 (11.75) 2.85

190,837 (50,486)

**PV-diesel-battery system** 

available from the WTG. The WTG penetration level is observed as 28%. Due to its location, the solar flux available in this region is low resulting in low energy penetration from the PV array. The payback period of the WTG is obtained a little over a year and the payback period for the PV array and the WTG for the PV-wind-diesel-battery system is obtained as a little over two years. It can also be observed that the NPV of the wind-diesel-battery system using HARPSim is less than HOMER. This is because in HARPSim the battery bank charges and discharges while supplying the load. Therefore, the DEGs operate more efficiently resulting in fuel savings while emitting less pollutant. However, this fuel savings is achieved at the expense of the battery life.


Table 2. Installation Costs for Different Components.

Since the wind-diesel-battery system was observed to be the most cost effective system, further work was carried out to study the effect of installing another WTG into the winddiesel-battery system. The addition of a second WTG required an increase in the capacity of the battery bank to accommodate more energy storage. Therefore, the battery bank capacity and the inverter rating were increased from 100 kW and 100 kVA to 200 kW and 200 kVA, respectively.

available from the WTG. The WTG penetration level is observed as 28%. Due to its location, the solar flux available in this region is low resulting in low energy penetration from the PV array. The payback period of the WTG is obtained a little over a year and the payback period for the PV array and the WTG for the PV-wind-diesel-battery system is obtained as a little over two years. It can also be observed that the NPV of the wind-diesel-battery system using HARPSim is less than HOMER. This is because in HARPSim the battery bank charges and discharges while supplying the load. Therefore, the DEGs operate more efficiently resulting in fuel savings while emitting less pollutant. However, this fuel savings is

> **Dieselbattery system (USD)**

generator 40,000 1 40,000 40,000 40,000 40,000 40,000 40,000

generator 45,000 1 45,000 45,000 45,000 45,000 45,000 45,000

Inversion 18,000 1 0 18,000 18,000 18,000 18,000 28,000

solar panels 262 180 0 0 47,160 0 47,160 0 Engineering 1 3,000 3,500 4,000 4,000 4,500 6,000

Since the wind-diesel-battery system was observed to be the most cost effective system, further work was carried out to study the effect of installing another WTG into the winddiesel-battery system. The addition of a second WTG required an increase in the capacity of the battery bank to accommodate more energy storage. Therefore, the battery bank capacity and the inverter rating were increased from 100 kW and 100 kVA to 200 kW and 200 kVA,

**PV-dieselbattery system (USD)** 

16,000 1 16,000 18,000 20,000 20,000 22,000 30,000

2,143 16 0 34,288 34,288 34,288 34,288 68,576

55,000 1 0 0 0 55,000 55,000 110,000

1 13,000 14,000 16,000 18,000 20,000 30,000

TOTAL 117,000 172,788 224,448 234,288 285,948 357,576

**Winddieselbattery system (USD)**

**PVwinddieselbattery system (USD)** 

**2 winddieselbattery system (USD)** 

achieved at the expense of the battery life.

**Cost per unit (USD)**

Table 2. Installation Costs for Different Components.

**No of units** 

**Dieselonly system (USD)**

**Item** 

140 kW diesel

190 kW diesel

Switch gear to automate control of the system

Rectification/

New Absolyte IIP 6-90A13 battery bank

AOC 15/50 wind turbine generator

Siemens M55

Commissioning, Installation, freight, travel, miscellaneous

respectively.


Table 3. Comparison of Results from HARPSim with HOMER.

Energy-Efficient Standalone Fossil-Fuel Based

and

money.

costs, and 'S' is the salvage value of the project.

Hybrid Power Systems Employing Renewable Energy Sources 137

where 'LCC' is the life cycle cost, 'C' is the installation cost (capital cost), 'M' is the overhead and maintenance cost, 'E' is the energy cost (fuel cost), 'R' is the replacement and repair

The net present value (NPV) is the money that will be spent in the future discounted to today's money. The NPV plays an important role in deciding the type of the system to be installed. The NPV of a system is used to calculate the total spending on the installation, maintenance, replacement, and fuel cost for the type of system over the life-cycle of the project. Knowing the NPV of different systems, the user can install a system with minimum

> 1 *<sup>N</sup> <sup>F</sup> <sup>P</sup> <sup>I</sup>*

<sup>N</sup> A[1 (1 I) ] <sup>P</sup> I

where 'P' is the present worth, 'F' is the money that will be spent in the future, 'I' is the discount rate, 'N' is the year in which the money will be spent, and 'A' is the annual sum of

Fig. 11 and Fig. 12 show the LCC analysis of the PV-wind-diesel-battery hybrid power system using HARPSim and HOMER, respectively. It can be seen that in HARPSim, the cost of DEGs is 4% less while the cost of the battery bank is 2% more than in HOMER. This is because in HARPSim, the battery bank acts as a source of power rather than as the backup

(15)

, (16)

NPV. The relationships used in the calculation of NPV are given as follows:

Fig. 11. 20-year LCC analysis of the hybrid power system using HARPSim.

Table 4 shows the comparison of results from the HARPSim model with HOMER for the two wind-diesel-battery hybrid power system. It can be observed that the addition of the second WTG into the wind-diesel-battery hybrid power system resulted in the further reduction in the NPV and the COE, while the payback period with the two WTGs increased slightly. The WTG penetration level increases to 50% for this case. The payback period of the WTGs has increased to 1.56 years due to the extra cost involved in the addition of the second WTG.


Table 4. Comparison of Results from HARPSim with HOMER for Two Wind-Diesel-Battery Hybrid Power System.

### **4.3 Life cycle cost and net present value analysis**

The life cycle cost (LCC) is the total cost of the system over the period of its life cycle including the cost of installation, operation, maintenance, replacement, and the fuel cost. The life cycle cost also includes the interest paid on the money borrowed from the bank or other financial institutes to start the project. The life cycle cost of the project can be calculated as follows:

$$L\text{CC} = \text{C} + M + E + R - S \tag{14}$$

where 'LCC' is the life cycle cost, 'C' is the installation cost (capital cost), 'M' is the overhead and maintenance cost, 'E' is the energy cost (fuel cost), 'R' is the replacement and repair costs, and 'S' is the salvage value of the project.

The net present value (NPV) is the money that will be spent in the future discounted to today's money. The NPV plays an important role in deciding the type of the system to be installed. The NPV of a system is used to calculate the total spending on the installation, maintenance, replacement, and fuel cost for the type of system over the life-cycle of the project. Knowing the NPV of different systems, the user can install a system with minimum NPV. The relationships used in the calculation of NPV are given as follows:

$$P = \frac{F}{\left(1 + I\right)^N} \tag{15}$$

and

136 Fossil Fuel and the Environment

Table 4 shows the comparison of results from the HARPSim model with HOMER for the two wind-diesel-battery hybrid power system. It can be observed that the addition of the second WTG into the wind-diesel-battery hybrid power system resulted in the further reduction in the NPV and the COE, while the payback period with the two WTGs increased slightly. The WTG penetration level increases to 50% for this case. The payback period of the WTGs has increased

> System cost (USD) 357,576 357,576 Engine efficiency (%) 29.3 26.6

> Total cost of fuel (USD) 119,883 159,876

(a) Diesel engine (kWh) 469,542 561,741

 (kWh) 470,015 475,999 Energy supplied to load (kWh) 832,152 832,205

(a) Generator (years) 5 1.8 (b) Battery bank (years) 5.5 12

i = 7% and n = 20 years 1,748,988 2,407,895 Cost of Electricity (USD/kWh) 0.22 0.273 Payback period for WTG (years) 1.56 -

(a) CO2 in metric tons (US ton) 367 (405) 517 (570)

The life cycle cost (LCC) is the total cost of the system over the period of its life cycle including the cost of installation, operation, maintenance, replacement, and the fuel cost. The life cycle cost also includes the interest paid on the money borrowed from the bank or other financial institutes to start the project. The life cycle cost of the project can be

(c) PM10 in kg (lbs) 171 (383) - Table 4. Comparison of Results from HARPSim with HOMER for Two Wind-Diesel-Battery

(b) NOx in kg (lbs) 4,068

**Item Two wind-diesel-battery** 

(11.75)

(39,961)

**system**  HARPSim HOMER

(9,112) -

*LCC C M E R S* (14)

2.78 ( 10.53)

201,444 (53,222)

to 1.56 years due to the extra cost involved in the addition of the second WTG.

kWh/liter (kWh/gallon) for the engine 3.11

Fuel consumed in liters (gallons) 151,252

Energy supplied

Operational life

Net present value (USD) with

**4.3 Life cycle cost and net present value analysis** 

(b) WTG

Emissions

Hybrid Power System.

calculated as follows:

$$\mathbf{P} = \frac{\mathbf{A} \left[\mathbf{1} - \left(\mathbf{1} + \mathbf{I}\right)^{-N}\right]}{\mathbf{I}},\tag{16}$$

where 'P' is the present worth, 'F' is the money that will be spent in the future, 'I' is the discount rate, 'N' is the year in which the money will be spent, and 'A' is the annual sum of money.

Fig. 11 and Fig. 12 show the LCC analysis of the PV-wind-diesel-battery hybrid power system using HARPSim and HOMER, respectively. It can be seen that in HARPSim, the cost of DEGs is 4% less while the cost of the battery bank is 2% more than in HOMER. This is because in HARPSim, the battery bank acts as a source of power rather than as the backup

Fig. 11. 20-year LCC analysis of the hybrid power system using HARPSim.

Energy-Efficient Standalone Fossil-Fuel Based

COEL =

COEH =

and

in the cost of fuel.

Table 2 and Table 3 as

A 1 = P 1 1

gallon) and an investment rate (%) is calculated as follows:

*L*

Fig. 13. Sensitivity analysis of fuel cost and investment rate on the NPV.

*A P*

Hybrid Power Systems Employing Renewable Energy Sources 139

The annual COE for different systems given a fuel price in USD per liter (4.00 USD per

*H*

where CPV-wind is the cost of the PV-wind-diesel-battery system from Table 2, CDB is the cost of the diesel-battery system from Table 2 and CF is the annual cost of fuel from Table 3.

The plot for sensitivity analysis of fuel costs and investment rate on the payback period for the PV-wind-diesel-battery system is shown in Fig. 15. It can be seen that the payback period of the PV array decreases as a function of a fifth order polynomial with the increase

The simple payback period (SPBT) for the PV array and WTG is calculated using data from

Extra cost of PV system SPBT= . rate of saving per year

*A P*

(CPV-wind - CDB) +

*n n i( i) ( i) -* 

*H*

*A P*

(17)

(CDB) + CF (18)

(20)

(CDB) + CF, (19)

20-year LCC analysis of the Kongiganak Village hybrid power system using HOMER

Fig. 12. 20-year LCC analysis of the hybrid power system using HOMER.

power source used in HOMER. Therefore, the life of the battery bank is less in HARPSim due to the annual increase in charge/discharge cycles. This results in more efficient operation of the DEGs while reducing the fuel consumption and saving in the cost of the DEGs. Overall, the LCC analysis shows a lower NPV in HARPSim than in HOMER.
