Economic Justification for a V2G Facility in a Radial Distribution Network

Volume 13, Issue 3 2012 Article 5

International Journal of EmergingElectric Power Systems

Economic Justification for a V2G Facility in aRadial Distribution Network

Uwakwe C. Chukwu, Tennessee Technological UniversitySatish M. Mahajan, Tennessee Technological University

Recommended Citation:Chukwu, Uwakwe C. and Mahajan, Satish M. (2012) "Economic Justification for a V2G Facilityin a Radial Distribution Network," International Journal of Emerging Electric Power Systems:Vol. 13: Iss. 3, Article 5.

DOI: 10.1515/1553-779X.2990

©2012 De Gruyter. All rights reserved.

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Economic Justification for a V2G Facility in aRadial Distribution Network

Uwakwe C. Chukwu and Satish M. Mahajan

AbstractA V2G facility has the potential to reduce losses and loading in the power distribution

network, thereby effecting savings and an increase in the generator, line and substation capacityfor additional loading. In this paper, economic models are developed to compute the amount ofeconomic incentives accruable from the penetration of V2G into the distribution network subjectto two potential benefits of V2G: released generation capacity and reduced energy losses. Thedeveloped models were tested using IEEE test systems. Results from the test systems reveal thatoperational choice affects economic incentives. Hence, further analytical expression was developedto model operational formulation that will lead to economic incentives. This principal model wasformulated to indicate the manner in which economic incentives can be impacted by decisionvariables, namely: loading pattern, V2G location and capacity injection. More than 95% releasedgeneration capacity was obtained. In addition, $37,775/year of economic incentive due to reducedpower losses in the IEEE 123 Node test Feeder was observed. The results from the principal modelshowed that V2G promises significant economic incentives. It may be concluded, based on theresults obtained, that proper system studies are necessary at the planning stage before installing aV2G facility.

KEYWORDS: distribution system, released generation capacity, energy/power loss, economics,V2G parking lot

Author Notes: This work was supported by office of Research and graduate studies, TennesseeTechnological University, Cookeville, TN 38501, U.S.A. Uwakwe Christian Chukwu is a doctoralstudent at Electrical and Computer Engineering Department, Tennessee Technological University,Cookeville, TN 38501, U.S.A.(e-mail: [email protected]). Satish M. Mahajan isa professor of Electrical and Computer engineering, Tennessee Technological University,Cookeville, TN 38501, U.S.A.(e-mail: [email protected]).



I. INTRODUCTION

Many studies have investigated power capacity and economic potentials of V2G PHEV units, especially the works of Han and Sezaki (2011), Chukwu and Mahajan (2011), and Kempton and Tomic (2005). As noted by Yiyun (2011), and Kempton and Tomic (2005), V2G promises economic incentives over the contemporary internal combustion engine units. Economic potential of V2G was calculated for peak power, spinning reserves, and regulation services as noted in the literature- Chukwu and Mahajan (2011), and Kempton and Tomic (2005). According to Kempton and Tomic (2005), V2G units could provide additional revenue to owners who wish to sell power back to the grid. Other work of Kempton et al (2008) estimated that ancillary electric services may amount up to $12 billion per year, some of which would go to V2G owners. Other studies reported in Sovacool (2009) show that additional annual revenue accruable from V2G ancillary services is between $3,777 and $4,000 per vehicle.

While the purchase price of electric cars (V2G hybrid vehicles) can be high, the operation and maintenance cost is considerably insignificant compared to the cost of maintaining a gasoline engine. For example, Roy (2008) stated that with a V2G vehicle, there is no need to change engine oil, filters, gaskets, hoses, plugs, belts; no catalytic converters or exhaust pipe to replace. Therefore, maintenance issues arising from heat and vibration of gasoline cars causing wear and tear are not part of the V2G hybrid vehicles. More so, there is no need for a radiator to cool things down (some battery packs still need cooling, but that may no longer be needed with future batteries). In addition to this economic motivation, Sovacool, B. K. and Hirsh, R. F. (2009) indicated that the gasoline needed by a car using internal combustion engine technology to drive the same distance as V2G PHEV unit would cost more than four times as much (assuming a gasoline price of $3 per gallon). Sovacool (2009) showed that PHEVs would save about $600 per year for an average driver.

The annual fuel cost shown in Figure 1 shows that it costs less to drive PHEV or electric vehicles. Fixed number of charging/discharging cycles do limit the life of the battery. In spite of that, fueling with electricity instead of petroleum could be a sound financial decision from the operational perspectives.

1

Chukwu and Mahajan: Economic Justification for a V2G Facility

Published by De Gruyter, 2012



Figure 1. Annual fuel cost for various vehicle technologies (source: www.teslamotors.com/ goelectric)

Unfortunately, in all the state-of-the-art published materials related to economic justification for V2G units, emphasis centers only on economic incentives for the V2G owners, and revenue benefits from ancillary services to the system operators. There is no economic model available that deals with quantification of displaced expenses in the power system due to a V2G penetration. An attempt has been made to fill this void through this work. Models were developed to investigate the economic justification for V2G in a radial distribution network. Two benefits of V2G on distribution network were identified, and used to quantify the amount of dollars saved, namely: released generation capacity and reduced energy losses. When reactive power is provided only by generators, each system component (generators, transformers, transmission and distribution lines, switch gear and protective equipment, etc) has to be increased in size accordingly. A V2G facility may reduce losses and loading in all these equipment (assuming V2G is optimally installed in the network), thereby effecting savings through power loss reduction and increase in generator, line and substation capacity for additional load. The work of Zimmerman (1953) showed that capacitor installation in distribution network can release at least 30% additional capacity in generators, lines and transformers. Similar savings from a V2G facility may help offset increasing costs of the infrastructure.

The economic values of these benefits (actually, there are displaced expenses) are investigated in this paper. The paper is organized as follows: - In section II, the models for economic incentives due to V2G penetration in the distribution network are presented, whereas the results for different case studies are presented in Section III. Conclusions are presented in section IV.

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International Journal of Emerging Electric Power Systems, Vol. 13 [2012], Iss. 3, Art. 5



II. MODELING OF THE ECONOMIC INCENTIVES DUE TO V2G

In this section, models are developed to formulate economic incentives due to the V2G facility in a radial distribution network. The models considered and discussed next are: (1) modeling annual benefits due to V2G on the released generation capacity, (2) modeling annual benefits due to V2G on the reduced energy losses, and (3) impact of location, V2G capacity and feeder loading on annual economic incentives.

a) Modeling annual benefits due to V2G on the released generation capacity.

It is assumed in this investigation that V2G parking lot is injecting only reactive power, Qc, as depicted in Figure 2. The installation of V2G parking lot on the feeder line will result in improved power factor from cosθ1 to cosθ2 as illustrated in Figure 3, where cosθ1 and cosθ2 are power factors before and after injecting Qc kVAr, respectively. Taking Q1, Q2 as the load reactive power demand and source reactive power injection, respectively and S1, S2 as their respective complex powers, then for real power flow, P, the value of S1 and S2 are defined as

2 2

1 1S P Q (1)

222 1 cS P Q Q (2)

Figure 2. V2G parking lot injecting Qc kVAr on feeder line AB

Figure 3. Effect of injecting Qc kVAr on power factor (Gonen, 1987).

3





Defining the per unit (p.u) released generation capacity beyond maximum generation capacity (at original power factor), ΔSG, as

1 2

1

221

2 21

1

G

c

S SS

S

P Q Q

P Q

(3)

Let

11

( . )cQC p u

Q ; 2

1

( . )P

C p uQ

(4)

Then, substituting (4) into (3) and simplifying yields

22

2 122

11

1G

C CS

C

(5)

Note that C1 = 0 represents no reactive power injection from V2G parking

lot, while C1 = 1 represents reactive power injection equal to the load reactive power demand. Since reactive power injection Q2 supplements load reactive power demand Q1, the ratio C1 is defined by the range: 0 ≤ C1 ≤ 1. Furthermore, C2 = 0 represents no real power injection. Because of high kW demand in a distribution networks, situations may arise when C2 > 1.0. The annual economic incentive, Δ$G, due to released generation capacity due V2G installation is

/$ / $ /

1$ 8760

h yryr MWhMW

G G GS S pf C Av

(6)

where pf is power factor, CG, is the cost of generation, and Av is the

availability of V2G vehicle per day (taken as 96% according to Kempton and Tomic, 2005).

b) Annual benefits due to V2G on the reduced energy losses

It is appropriate to quantify annual benefits due to reduced energy losses along feeder lines when ‘V2G is strategically installed’ to achieve reduced electrical losses. Electrical energy loss, Eloss, when I amps of current flows through a feeder line of resistance R for a given time, t, is defined as 2

lossE I Rt

4




Hence, considering 8760 hrs in a year, the total annual energy loss will be obtained by modifying the above equation as,

2 8760

/1000loss

I RE KWh yr

(7)

The above expression is actually the total annual energy loss without V2G installed. With V2G is installed, the total current Itotal flowing along the feeder line will be given by, total cI I I (8)

where Ic is the current injected into the feeder line by the V2G facility. For a line-line voltage, V, the phase current flowing along the feeder line is

3

SI

V

(9)

For a V2G facility injecting Qc kVAr of reactive power into the feeder line, the injected current may be expressed as

3

cc

QI

V

(10)

Substituting (10) and (9) into (8), the total current flow is

3

ctotal

QI I

V

(11)

Substituting (11) into (7) results in a new energy loss due to installation of V2G, EV2G_loss, given as

2

2 _

8760

1000 3c

V G loss

R QE I

V

(12)

The annual energy conserved or gained (ΔACE) as a result of V2G installation is 2 _loss V G lossACE E E (13)

Substituting (12) and (7) into (13) and using (9) yields,

22

87602 / /

3000 c c

RACE SQ Q KWh phase yr

V (14)

The total ΔACE due to three-phase distribution network is given by

2

3 87602 /3 /

3000c

c

RQACE S Q KWh phase yr

V

(15)

Next,

sin

cQS

(16)

where (taking pf as the operating power factor), 1cos pf

5





Substituting (16) into (15),

2

2

8760 21 /3 /

1000 sincRQ

ACE KWh phase yrV

(17)

The annual economic incentive Δ$ACE due to reduced annual energy loss as a result of V2G installation is defined as

/ $ /$ /

$

kWh yr kWhyr

ACE EACE C

(18)

where CE is the cost of electricity in $/kWh. The models presented in sub-sections a) and b) were tested using IEEE 13

and IEEE 123 test Node Feeder Systems (results presented and discussed in section III). In the study, the V2G parking lots are located only at the feeder buses (end of the feeder), and the amount of kW or kVAr power injections is constant (i.e., power injections of 2500 kW active power and 2500 kVAr reactive power). No attempt was made to consider the impact of V2G location, sizing, and feeder loading on the annual economic incentives.

c) Impact of Location, V2G Capacity and feeder loading on Annual Economic Incentives

In this sub-section, the impact of sizing, siting and feeder loading on the annual economic incentives was investigated. In this model, only reactive power injection on a feeder line was considered. The per unit power loss reduction due to V2G penetration, ΔPLS_V2G, is given by Gonen (1987) as _ 2 1 1 13 2LS V GP cx x x c (19)

where V2G siting (x1), sizing (c) and loading pattern, λ, are in the range 0 to 1.0 p.u. A zero loading pattern (i.e., λ = 0) represents uniformly distributed load, while λ = 1 represents lumped loads (Gonen, 1987). The quantity, α, is computed by the methodology presented in Gonen (1987) as

2

1

1

The economic incentive due to the reduced power loss (otherwise called conserved power) may be defined as

$ $

_ 2$ 8760

yr kWyrkW

ACP LS V G EAv P P C

(20)

where P is the kW power flowing in a feeder line segment before the installation of V2G in the system. Substituting (19) into (20) yields

6




$ $

1 1 1$ 3 2 8760

yr kWyrkW

ACP Ecx PAv x x c C

(21)

III. NUMERICAL RESULTS

The annual benefits due to released generation capacity were computed using (5) and presented in Figure 4 and Figure 5. Figure 4 represents the relationship between released generation capacity and the magnitude of per unit injected reactive power C1 from V2G parking lot for different values of load kW power demand (note: kW controlling ratio is C2). The result shows that released generation capacity increases with decreasing real power flow, and also tends to be linear. From the results (Figure 4), a released generation capacity of 95% is obtained when the load demands 0.1 p.u real power and V2G facility is injecting 1.0 pu reactive power. More so, about 25% released generation capacity will be relieved at 1.0 p.u real power demand when V2G parking lot facility injects 1.0 p.u reactive power. It is clear from the results that injecting reactive power increases the amount of system’s released generation capacity. Figure 5 presents the characteristics of released generation capacity versus load real power demand for various reactive power compensations injected from V2G unit. In this simulation, the range of C2 considered is 0 ≤ C2 ≤ 1 (higher range is feasible). Although this result shows that increasing reactive power (the contours of Figure 5) increases the released generation capacity, the later decreases with increasing kW load demand.

Figure 4. Released generation capacity versus reactive power Injection for various fractions of kW demand

c1 (pu)

S

G (

pu)

0.1

0.2

0.3

0.4

0.50.6

0.70.8

0.91

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

7





Figure 5. Released generation capacity versus P demand for various reactive power compensations

The characteristic at higher reactive compensations have higher gradients than at lower compensation levels. Figure 4 and Figure 5 show that reactive power injection improves released generation capacity. This implies that distribution system operators may delay system upgrade by operating the V2G parking lot facility in reactive power injection mode. This is imperative if system capacity limit is being threatened.

The estimated cost of electricity by source for plants entering service in 2016 as reported by US Department of Energy was obtained from the published literature in EIA (2011). Based on this report (and for the purpose of this analysis), an average cost of electricity was assumed to be $100/MWh (i.e., 1$/kWh). The economic incentive, Δ$G, as a result of V2G integration resulting in released generation capacity was computed using (6), from where it is seen that

1$ , , ,G G Gf S pf S C

Fixing any two of the independent variables in the above expression, it is

possible to study how the remaining variables affect the extra dollar incentive (taking CG = $100/MWh). Wherever S1, pf or ΔSG, are fixed, the respective values are 0.1MVA, 0.8 and 1.0 p.u. The results are presented in Figure 6 and Figure 7.

c2 (pu)

S

G (

pu)

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0 0.2 0.4 0.6 0.8 10

0.2

0.4

0.6

0.8

1

8




Figure 6. Dollar Incentives with respect to: (3,1) ΔSG at constant pf, (3,2) ΔSG at constant S1, (3,1) pf at constant S1

From the results in Figure 6 and Figure 7, it is seen that the dollar incentives increase linearly with increasing ΔSG, S1, or pf. Results in Figure 7 were obtained by swapping the independent variables in the corresponding subplot in Figure 6. It can also be seen that in spite of swapping the independent variables, the dollar incentive are not different. In all the simulations, Δ$G versus ΔSG at constant pf (and the corresponding swapped plots) resulted in about 10 times less economic gain. The relationship between the annual conserved energy ΔACE and V2G reactive power injection was computed using (17), and the results presented in Figure 8. The results indicate that for any given power factor pf, the total ΔACE increases with increasing Qc injection in the system. More so, at higher power factor, the amount of saving in energy loss increases. Figure 9 shows a clearer picture of how ΔACE varies with power factor (at a given amount of Qc injection). The results show that the impact of power factor on ΔACE is not quite significant at low power factors; hence, operating at high power factor is a recommended practice.

$G versus SG at constant pf

SG (pu)

$ G

($) 0.8

0.60.40.2

0

5

x 104

$G versus SG at constant S1 (MVA)

SG (pu)

$ G

($) 0.8

0.60.40.2

0

5

x 105

$G versus pf at constant S1 (MVA)

power factor

$ G

($) 0.8

0.60.40.2

0.1 0.2 0.3 0.4 0.50

5

x 105

9





Figure 7. Dollar Incentives with respect to: (3,1) pf at constant ΔSG, (3,2) S1 at constant ΔSG, (3,1) S1 at constant pf.

Figure 8. The relationship between ΔACE and V2G Qc injection at constant pf

$G

versus pf at constant SG

power factor

$ G

($) 0.8

0.60.40.2

0

5

x 104

SG versus S1 (MVA) at constant SG

S1 (MVA)

$ G

($) 0.8

0.60.40.2

0

5

x 105

Plot of SG versus S1 (MVA) at constant pf

S1 (MVA)

$ G

($) 0.8

0.60.40.2

0.1 0.2 0.3 0.4 0.50

5

x 105

0 50 100 150 200 2500

20

40

60

80

100

Qc (KVAr)

A

CE

(K

Wh/

yr)

pf=0

pf=0.2

pf=0.4pf=0.6

pf=0.8

10




Figure 9. The relationship between ΔACE and pf at constant Qc.

The economic incentive due to reduced energy loss was computed using (18). The result is as presented in Figure 10, taking CE as $0.1099/KWh (National U.S. average cost per KWh of electricity is $0.1099 as of January 2011 as obtained from EIA. 2011). From the result, the amount of revenue accrued from reduced energy loss depends on the magnitude of energy loss gained, as expected.

Figure 10: Variation of Δ$ACE with ΔACE (taking CE as $0.1099/ KWH).

d) Case Studies: IEEE 13 Node Test Feeder

The quantification of reduced power loss and the associated economic incentives discussed above was applied to the IEEE 13 Node Test Feeder (see Figure 11). The impact of V2G penetration on power loss profile of the test system was

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

10

20

30

40

50

60

70

80

90

power factor

A

CE

(K

Wh/

yr)

Q

c=0 kVAr

Qc=50 kVAr

Qc=100 kVAr

Qc=150 kVAr

Qc=200 kVAr

Qc=250 kVAr

0 2000 4000 6000 8000 100000

200

400

600

800

1000

1200

ACE (KWh/yr)

$A

CE

($/

yr)

11





implemented using Radial Distribution Analysis Package (RDAP), and the results are as shown in Figure 12. Defining V2G penetration as a percentage of the substation capacity, the impact of each V2G penetration level on the network’s power loss was evaluated on every phase.

Figure 11. IEEE 13 Node Test Feeder (Kersting, 2000)

The magnitude of the active power injected/demanded or reactive power injected by each V2G parking unit is expressed in terms of the percentage of the main substation capacity. For this study, category A and category B classifications were defined to present an in-depth study and analysis. Category A is comprised of 3-phase V2G integrations with respect to the seven case studies presented in Table 1, while the category B comprised of scenarios 1 through 5.

12




Scenario-1: 2500kW V2G-load added to the entire distribution system at all load buses;

Scenario-2: 2500kW of V2G power is injected to the entire system at the load buses; Scenario-3: V2G consuming 2500kW power and injecting 2500 kVAr power; Scenario-4: 2500kVAr V2G reactive power is injected to entire system at load

buses ; Scenario-5: V2G simultaneously injecting 2500kW and 2500kVAr of real and

reactive power, respectively.

Results from RDAP (presented in Figure 12) show that there are power loss improvements in case 3, case 6, and case 7 of category A while category B expressed power loss improvements in scenario 2, scenario 4, and scenario 5. For example, 3 phase V2G integration in category A resulted in reduction of total system power loss by 69.6% when operated in case 7, 58.8% when operated in case 3 and 19% when operated in case 6. This finding is crucial as power system operators would seek system operations that result in low power loss (for security and economic advantage).

Figure 12. Real power Loss due to: (1,1) Category A, (2,1) category B V2G operation for IEEE 13 Node Test Feeder

Since active power loss is the quantity in Figure 12 to be conserved in this analysis (not annual energy), it will be appropriate to introduce a new quantity: conserved power, ΔP, to represent the amount of electrical kW power gained due to penetration of V2G. Conserved power is defined as

,0 ,ii Loss LossP P P (22)

where ΔPi and PLoss,i respectively represent the ith conserved power and

power loss corresponding to the ith case or ith scenario; PLoss,0 is the reference

13





power loss for the original system. From (22), it is possible to have situations when ΔPi could be a negative quantity (i.e., when PLoss,i > PLoss,0), indicating that no power is conserved for that operation. The computation of (22) is presented in Figure 13. From the results presented, power is conserved only at case 3, scenario 2 and scenario 5 operations. The annualized dollar incentive due to conserved power is

$ $

$ . 8760

yr kWyrkW

ACP i EAv P C

(23)

The unit of CE is the cost of electricity in $/kWh, but converted to $/kWyr to preserve unit consistency ($/kWyr x 8760 = $/kWh). Using (23), the annualized dollar incentive due to conserved power is presented in Figure14, for category A and category B operations. The results show that operating in case 2, case 5, case 6, scenario 1, scenario 3 and scenario 4 modes would result in economic loss, while operating the system in case 3, scenario 2 and scenario 5 modes would result in economic incentives.

Figure 13: Conserved Power due to (1,1): Category A; (2,1): category B V2G operation for IEEE 13 Node Test Feeder

A critical look shows that huge economic losses are incurred in operations where V2G parking lots were consuming kW load (demanding power from grid, when battery is charged), while significant economic incentives are supported by operations where V2G parking lots are exporting either kW power, or both kW and kVAr (discharging power to grid). The insignificant economic loss in scenario 4 shows that injecting only kVAr into the distribution network may

14




promise economic incentive if the optimal amount of kVAr is injected (optimal sizing and siting of the parking lot was discussed in section II). Furthermore, operating in case 4 resulted in no loss/gain because case 4 and the original system (case 1) have the same system loss (hence null differential loss).

Figure 14: Dollar Incentive due to Conserved Power (1,1): Category A; (2,1): category B V2G operation

e) Case Studies: IEEE 123 Node Test Feeder

Using RDAP software package, the power loss in an IEEE 123 Node Test Feeder (see Figure 15) was computed and presented in Figure 16 and Figure 17 for different categories. The reduced power losses as well as the associated economic incentives were calculated, and the results are as shown in Figure 16 and Figure 17. The conserved power was computed using (22), while the annual dollar incentive due to conserved power was calculated using (23). Additional scenarios (Category C and Category D) are considered in this segment of analysis to obtain insight into power losses in the IEEE 123 test system for both single phase and 3-phase V2G interconnection. Category C comprises of scenario 6 through scenario 9, each scenario constituting case 1, case 2, case 3 and case 6 (i.e., 16 investigations for category C). Category D, however, comprises of case 1, scenario 1, scenario 2 and scenario 4. The assignments of the scenarios are: Scenario-6:

V2G injecting and/or demanding kW when interconnected to Phase A

V2G injecting only kVAr when interconnected to Phase A line Scenario-7:

V2G injecting and/or demanding kW when interconnected to

15





Phase B V2G injecting only kVAr when interconnected to Phase B line

Scenario-8: V2G injecting and/or demanding kW when interconnected to

Phase C V2G injecting only kVAr when interconnected to Phase C line

Scenario-9: V2G injecting and/or demanding kW when interconnected to

3-Phase V2G injecting only kVAr when interconnected to 3-Phases lines

Figure 15. IEEE 123 Node Test Feeder (Kersting, 2000).

From the above categorizations, the impact of injecting/ demanding kW (or injecting kVAr) on the system was studied for the power loss and the economic interest. The results in Figure 16 reveal that there is less power loss in 3-phase V2G interconnection than single-phase connection.

1

3

4

5 6

2

7 8

12

1114

10

2019

2221

1835

37

40

135

33

32

31

2726

25

28

2930

250

4847

4950

51

44

4546

42

43

41

3638

39

66

6564

63

62

60160 67

5758

59

54535255 56

13

34

15

16

17

96

95

94

93

152

92 90 88

91 89 87 86

80

81

8283

84

78

8572

7374

75

77

79

300111 110

108

109 107

112 113 114

105

106

101

102

103104

450

100

97

99

6869

70

71197

151

150

61 610

9

24

23

251

195

451

149

350

76

98

76

16




Figure 16. Total Power Loss for Category C interconnection of V2G on IEEE 123 system

It would be observed from Figure 18 that while different degrees of economic loss in all the cases took place in scenarios 6, scenario 7 and scenario 8, the results in scenario 9 indicate economic incentive at case 3 (positive Δ$ACP). More so, there are economic incentives in scenario 2 and scenario 4 of category B. The reason for this is clear: scenarios 6, scenario 7 and scenario 8 are single phase V2G integrations, which result in more power losses due to high unbalance effect, while scenario 4 is a three phase operation, which raises the ‘balanced’ integrity profile of the distribution network- thereby leading to both less power loss per phase and improved conserved power. This further indicates that three-phase integration and operation has more economic advantage than single-phase integrations. In all the scenarios, case 2 results in the highest economic loss because of the high loss swing in this mode of operation due to V2G units in charging mode. From Figure 18, the economic incentive for operating in case 3 of scenario 4 is $21,250.00 per annum.

Figure 17. Total Power Loss for Category D interconnection of V2G on IEEE 123 system

17





Figure 18. Dollar Incentive due to Conserved Power for Category C V2G Interconnection on IEEE 123 test system

In Figure 19, the economic incentives of scenario 2 and scenario 4 operations amount to $37,775.00/year and $12,012.00/year, respectively (for the IEEE 123 test system). Economic loss is expected in scenario 1, because scenario 1 operation loads the distribution system due to V2G charging demand of 2500 kW, thereby leading to more power loss in the system than in the original system. This is contrary to scenario 2 and scenario 4 operations where V2G injection of 2500 kW and 2500 kVAr are respectively injected. The dollar incentive due to conserved power for scenario 2, scenario 4 and scenario 9 operations further suggest the advantage of operating the distribution system in three phase modes and/or balanced system wide operation, while taking additional advantage of kW or kVAr power injections.

Figure 19. Dollar Incentive due to Conserved Power for Category D V2G Interconnection on IEEE 123 system

18




Results of the economic incentives from the case studies presented in Figure 14, Figure 18 and Figure 19 may be summarized as follows:

1. operating V2G in a charging mode leads to significant economic loss. 2. operating V2G in a discharging mode leads to economic incentive. 3. amount of loading affects the economic incentives 4. injecting kVAr promises economic incentives.

The impact of location, V2G capacity and feeder loading on annual economic incentives will be investigated next.

f) Impact of Location, V2G Capacity and feeder loading on Annual Economic Incentives

Equation (21) was computed to study how different values of x1, c, λ and α may impact the annualized dollar incentive. The result is presented in Figure 20, taking λ from 0.4 to 1 in the steps of 0.2, for each subplot. First, for various V2G reactive power capacity, c, the extent of dollar incentive was quantified, while varying the position of V2G parking lot along the feeder. It was observed that dollar incentive increases as V2G location increases at a given λ and capacity, c. The Δ$ACP versus V2G location characteristics tend to be more linear at higher λ and higher c. However, at lower λ, a limiting revenue exists, beyond which increasing the V2G location away from the source end results in decreasing economic incentive. The results show that it will be more advantageous to operate the system at lower feeder loading and higher reactive capacity injection for more revenue to be obtained. For instance, more revenue is accruable in operating the system in the operating state presented in the subplot (2,1) where λ=0.2 than in subplot (3,2), where λ=1.0. In all the computations, P was assumed to be 500 kW.

The optimal value of reactive compensation, c, that will result in optimal reduced power is given by c=0.67 p.u. (Gonen, 1987.). Substituting c=0.67 into (21) results in the dollar incentive (revenue) due to optimum V2G capacity injected on a feeder with various combinations of load types (0.4 ≤ λ ≤ 1) and various V2G locations, given as

1 1 1$ 8760 3 2 3 2ACP Ecx C PAv x x (24)

When (24) was computed for P equals 7,000 kW and 10,000 kW, the

results are as shown in Figure 21. The results show that revenue increases as loading pattern, λ, becomes more uniformly distributed (i.e., as λ →0), although a limiting dollar incentive sets in. This result is expected, since power loss reduction increases as λ→0. More so, revenue increases as P increases. Comparing Figure 20 and Figure 21, it can be noticed that optimal value of c lead to increase in revenue.

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Figure 20. Dollar Incentive due to power los reduction versus V2G location for c, and feeder line loading patterns, λ.

It can be concluded from the results obtained in this sub-section c that the amount of dollar incentive from aV2G integration in a distribution network can be impacted significantly by the location of the V2G as well as capacity injection and loading pattern. The results in this sub- section indicate that proper system studies are necessary before installing a V2G parking lot for efficient and economical operation. Hence, the economic losses (i.e., negative Δ$ACP) observed in sub-sections a and b can turn into economic incentives, should optimal kVAr injection and optimal location of the V2G facility be taken into consideration.

Figure 21. Dollar Incentive for power loss reduction due to optimum-sized V2G capacity located on a line for various λ

1

1

=0.4

$A

CP

($/

yr)

0.10.20.30.40.5

0 0.5 10

2

4x 10

5

1

1=0.6

$A

CP

($/

yr)

0.10.20.30.4

0.5

0 0.50

2

4

x 105

1

1=0.8

$A

CP

($/

yr)

V2G location (pu)

0.10.20.3

0.50.6

0 0.5 10

2

4

x 105

1

1=1

$A

CP

($/

yr)

V2G location (pu)

0.10.20.3

0.40.50.6

0 0.50

2

4

x 105

1

1

P=7000kW

$A

CP

($/

yr)

V2G location (pu)

0.8

0.70.40.2

0.1

0 0.5 10

2

4

6x 10

6

1

1

P=10000kW

$A

CP

($/

yr)

V2G location (pu)

0.80.6

0.40.2

0.1

0 0.5 10

2

4

6

8

x 106

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IV. CONCLUSIONS

This paper investigated the economic justification for installing V2G facility in a radial distribution network. Two principal promises of V2G on the distribution system are considered to justify the economic incentives, namely: released generation capacity and reduced energy losses. Mathematical models were developed to answer the question: what is the economic justification for V2G penetration in a distribution system. The developed models were tested using two IEEE test systems: IEEE 13 test node system and IEEE 123 test system. The results from the test systems reveal that economic incentive as well as economic losses may be incurred, depending on the operational practice. Sequel to this, mathematical model was developed to consider operational decisions that may lead to economic incentives, for all operations. The model showed that the amount of economic incentive may be substantially affected by the amount of power injections, the location of the parking lot on the feeder as well as the loading patterns of the feeder. It can be concluded from the results that the economic motivation and engineering rationale for V2G power are compelling, and may be considered as a catalyst to move V2G innovation forward. In the future, this work could be extended to consider the fact that V2G can improve system voltage profile, which will usually result in increased power consumption thereby enhancing the revenue from energy sales obtainable from improved voltage profile.

V. REFERENCES

Chukwu, U. C. and Mahajan, S. M. 2011. “V2G Electric Power Capacity Estimation & Ancillary Service Market Evaluation.” IEEE PES GM, pp. 1-8.

EIA. 2011. Levelized Cost of New Generation Resources in the Annual Energy Outlook. [Online]. Available: http://www.eia.gov/oiaf/aeo/electricity_ generation.html

Gonen, T. 1987. Electric Power Distributed System Engineering, 2nd Ed. New York: McGraw-Hill, pp. 384.

Han, S. and Sezaki, K. 2011. “Estimation of Achievable Power Capacity From Plug-in Electric Vehicles for V2G Frequency Regulation: Case Studies for Market Participation.” IEEE Trans. on SmartGrid, Vol. 2, (4), pp. 632 – 641. Kempton, W and Tomic, J. 2005. "Vehicle to Grid power fundamentals: calculating capacity and net revenue." J. Power Sources Vol. 144, Iss.1, pp. 268-279.

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Kempton, W., Victor, U., Huber, K., Kevin, K., Letendre, S., Baker, S., Brunner, D., Pearre, N. 2008. “A Test of Vehicle-to-Grid (V2G) for Energy Storage and Frequency Regulation in the PJM System.” [Online]. Available: http://www.udel.edu/V2G/resources/test-v2g-in-pjm-jan09.pdf.

Kersting, W. H. 2000. “Radial Distribution Test Feeders.” [Online]. Available: http://ewh.ieee.org/soc/pes/dsacom/testfeeders.html

Morrison, R., 2008. “V2G - Vehicle to Grid.” in Policy Innovations. [Online]. http://politics.gather.com/viewArticle.action?articleId=281474977351060

Sovacool, B. K. 2009a. “The Benefits of Plugging-In Your Vehicle.” [Online]. Available: http://scitizen.com/future-energies/the-benefits-of-plugging-in-your-vehicle_a-14-2587.html

Sovacool, B. K. and Hirsh, R. F. 2009. “Beyond Batteries: An Examination of the Benefits and Barriers to Plug-in Hybrid Electric Vehicles (PHEVs) and a Vehicle-to-Grid (V2G) Transition.” Energy Policy 37(3) pp. 1095-1103.

Yiyun, Tu. 2011.“Research on Vehicle-to-Grid Technology.” IEEE International Conference on Computer Distributed Control and Intelligent Environmental Monitoring (CDCIEM), pp. 1013 - 1016.

Zimmerman, R. A. 1953. “Economic merits of secondary capacitors.” AIEE Trans., Vol. 72, pp. 694-697.

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Economic Justification for a V2G Facility in a Radial Distribution Network