Analysis of wind energy with pumped storage systems in autonomous islands George Caralis Mechanical Engineer NTUA National Technical University of Athens

Analysis of wind energy with pumped storage systems in

autonomous islands

George CaralisMechanical Engineer NTUA

National Technical University of AthensDepartment of Mechanical EngineerFluids Section, Wind Energy Laboratory

Contents of the presentation

• Description of the problem• Methodological approach• Evaluation criteria • Application in three autonomous Greek islands• 1st case

– Analysis of the wind power penetration in autonomous islands without pumped storage

• 2nd case – Analysis of the combined use of wind energy with

pumped storage systems– Operational targets and Architecture of WPS– Optimization procedure

• Conclusions - RecommendationsG.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 2

Description of the problem

• Autonomous islands face the problem of wind energy rejection during the hours of low demand from the system operator.

• The ability of local power stations to balance out both the variability of the demand and the wind power, defines the wind power which can be directly absorbed by the grid.

G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 3

Methodological approach

• The simulation of the whole electrical system based on the steady-state (non-dynamic) analysis and the convolution of the demand and the wind data is proposed as the main methodological approach for the design and the decision process.

• The following data are needed for the application:– the special characteristics of the energy demand (hourly

data series), – the local conventional units (technical minimums, cost, fuel

consumption) – the technical restrictions for the smooth and safe operation

of the network – the wind characteristics (hourly data series) – the wind installed capacity and – the design of the Pumped Storage Unit.


Objectives of the current work

• Create a computational tool – Simulation of the autonomous electrical system – Simulation of the various subsystems (conventional units,

wind farms, pumping station, hydro-turbine, etc)

• Present comparable results for three Greek islands– Analysis of wind power penetration (without storage) and– Analysis of the combined use of wind power with pumped

storage systems.


Current situation in the autonomous Greek islands

• 4% of the national demand with 1 million citizens• Weak autonomous electrical grids, based almost entirely on

oil • High rates of increase of the energy demand (due to tourism

development)

• High variation of demand between summer and winter and during the day (low load factor of the conventional units, high Electricity Production Cost)

• Abundant wind potential (annual wind speed 8-9m/s)

• High investor’s interest for wind applications • Constrain in the wind installed capacity• Wind power rejection during low demand


0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Ele

ctr

icit

y P

rod

uc

tio

n C

os

t (

€/k

Wh

)

30%

40%

50%

60%

70%

80%

90%

10 100 1000 10000 100000 1000000

peak demand (kW)

Sh

are

of

Fu

el C

ost

to

E

lect

rici

ty P

rod

uci

ton

Co

st

CreteLesvos

Serifos

8 micro 10 medium 1 Large

Crete

LesvosSerifos

11 small

Current situation in the autonomous Greek islands

1st Case study: Analysis of the wind power penetration in autonomous Greek islands


Case study: Analysis of the wind power penetration in autonomous Greek islands

Simulation

• Wind power is absorbed in priority

• with respect to the technical minimums of the conventional units

• and until the maximum permitted instantaneous wind penetration (i.e. 30%)

• The maximum ability of the committed conventional units should be able to meet the demand (even all the wind power is lost)


Case study: Evaluation of the wind power penetration in autonomous Greek islands

• In order to take comparable results, the wind installed capacity should be introduced dimensionless:

• by the peak demand, or by the mean annual load?

• Using the mean annual load, similar results for different in size systems are achieved


8.1m/s

0%

20%

40%

60%

80%

100%

120%

0% 20% 40% 60% 80% 100%wind installed capacity (dimensionless by the peak

demand)

Win

d e

ner

gy

abso

rbed

Crete

Lesvos

Serifos

8.1m/s

0%

20%

40%

60%

80%

100%

120%

0% 50% 100% 150% 200%wind installed capacity (dimensionless by the mean annual

load)

Win

d e

ner

gy

abso

rbed

Crete

Lesvos

Serifos

Case study: Evaluation of the wind power penetration in autonomous Greek islands

• Crete / Lesvos / Serifos• Three wind velocities (8.1 / 7.2 / 6.3m/s)

corresponding to different initial capacity factors (23%, 30% and 38%)

• Wind installed capacity: 0%-200% of the mean annual demand

• Evaluation indexes– The real capacity factor CFR (%) – The percentage of wind energy absorbed (%)– The contribution of wind energy (%)– The Conventional units production cost (EPCC - €/kWh)– The Electrical system’s production cost (EPCS - €/kWh)– The Wind power’s production cost (EPCW - €/kWh)



Crete

0%

5%

10%

15%

20%

25%

30%

35%

40%

0% 50% 100% 150% 200%wind installed capacity (dimensionless)

Cap

acit

y F

acto

r (%

)

6.3

7.2

8.1

Crete

0%

20%

40%

60%

80%

100%

120%


Win

d e

ner

gy

abso

rbed

(%

)

6.3

7.2

8.1

Crete

0.190

0.195

0.200

0.205

0.210

0.215

0.220


Co

nve

nti

on

al u

nit

s E

PC

(€

/kW

h)

6.3

7.2

8.1

Crete

0%

5%

10%

15%

20%

25%


win

d e

ner

gy

sup

ply

(%

)

6.3

7.2

8.1

Crete

0.180

0.182

0.184

0.186

0.188

0.190

0.192

0.194

0.196

0.198


Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

)

6.3

7.2

8.1

Crete

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14


Win

d p

ow

er's

EP

C (

€/kW

h)

6.3

7.2

8.1

Crete

Lesvos


Lesvos

0%

5%

10%

15%

20%

25%

30%

35%

40%


Cap

acit

y F

acto

r (%

)

6.3

7.2

8.1

Lesvos

0%

20%

40%

60%

80%

100%

120%


Win

d e

ner

gy

abso

rbed

(%

)

6.3

7.2

8.1

Lesvos

0.112

0.114

0.116

0.118

0.120

0.122

0.124

0.126

0.128

0.130


Co

nve

nti

on

al u

nit

s E

PC

(€

/kW

h)

6.3

7.2

8.1

Lesvos

0%

5%

10%

15%

20%

25%


win

d e

ner

gy

sup

ply

(%

)

6.3

7.2

8.1

Lesvos

0.108

0.110

0.112

0.114

0.116

0.118

0.120

0.122

0.124

0.126

0.128


Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

)

6.3

7.2

8.1

Lesvos

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14


Win

d p

ow

er's

EP

C (

€/kW

h)

6.3

7.2

8.1

Serifos


Serifos

0%

5%

10%

15%

20%

25%

30%

35%

40%


Cap

acit

y F

acto

r (%

)

6.3

7.2

8.1

Serifos

0%

20%

40%

60%

80%

100%

120%


Win

d e

ner

gy

abso

rbed

(%

)

6.3

7.2

8.1

Serifos

0.30

0.31

0.32

0.33

0.34

0.35

0.36

0.37

0.38

0.39

0.40


Co

nve

nti

on

al u

nit

s E

PC

(€

/kW

h)

6.3

7.2

8.1

Serifos

0%

5%

10%

15%

20%

25%


win

d e

ner

gy

sup

ply

(%

)

6.3

7.2

8.1

Serifos

0.318

0.320

0.322

0.324

0.326

0.328

0.330

0.332

0.334

0.336


Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

)

6.3

7.2

8.1

Serifos

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16


Win

d p

ow

er's

EP

C (

€/kW

h)

6.3

7.2

8.1

Sensitivity on the allowed instantaneous wind penetration


• allowed instantaneous wind penetration: 30% / 40% / 50%

• For wind velocity 8.1m/s• For Brent price: 54$/b (mean value 2005)

Crete


Crete

0.170

0.175

0.180

0.185

0.190

0.195

0.200


Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

)

30%

40%

50%

Crete

0%

5%

10%

15%

20%

25%

30%

35%


win

d e

ner

gy

sup

ply

(%

)

30%

40%

50%

Lesvos

SerifosSerifos

0.310

0.315

0.320

0.325

0.330

0.335

0.340


Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

)

30%

40%

50%

Serifos

0%

5%

10%

15%

20%

25%

30%

35%


win

d e

ner

gy

sup

ply

(%

)

30%

40%

50%

Lesvos

0.100

0.105

0.110

0.115

0.120

0.125

0.130


Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

)

30%

40%

50%

Lesvos

0%

5%

10%

15%

20%

25%

30%

35%


win

d e

ner

gy

sup

ply

(%

)

30%

40%

50%

Sensitivity on the electrical system’s EPC on the Brent price


• Allowed instantaneous wind penetration: 30% / 40% / 50%

• For wind velocity 8.1m/s• For Brent price: 54$/b / 75$/b / 100$/b (mean

value 2005)

Crete


Lesvos

Crete - 8.1m/s

54$/b

75$/b

100$/b

0.15

0.17

0.19

0.21

0.23

0.25

0.27

0.29

0.31

0.33

0.35

0% 50% 100% 150% 200%

wind installed capacity (dimensionless)

Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

)

without wind

100$/b-30%

100$/b-40%

100$/b-50%

75$/b-30%

75$/b-40%

75$/b-50%

54$/b-30%

54$/b-40%

54$/b-50%

Lesvos - 8.1m/s

54$/b

75$/b

100$/b

0.05

0.07

0.09

0.11

0.13

0.15

0.17

0.19

0.21

0.23

0.25

0% 50% 100% 150% 200%


Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

)

without wind

100$/b-30%

100$/b-40%

100$/b-50%

75$/b-30%

75$/b-40%

75$/b-50%

54$/b-30%

54$/b-40%

54$/b-50%


SerifosSerifos - 8.1m/s

54$/b

75$/b

100$/b

0.30

0.32

0.34

0.36

0.38

0.40

0.42

0.44

0.46

0.48

0.50

0% 50% 100% 150% 200%


Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

)

without wind

100$/b-30%

100$/b-40%

100$/b-50%

75$/b-30%

75$/b-40%

75$/b-50%

54$/b-30%

54$/b-40%

54$/b-50%

Conclusions

• There is a very specific level of penetration of wind energy which is different for each island and provides the maximum benefits to the electrical system.

• According to the existing infrastructure and the current technical constraints, even with significant wind penetration the decrease of the EPCS is negligible, and the dependence on the oil remains high.


2nd Case study: Analysis of the combined use of wind power with pumped storage systems in

autonomous Greek islands


Current electrical system


Wind energy combined with pumped storage unit (WPS)


Simulation

1. The hydro-turbine’s set-point, the number of conventional units committed

2. The wind power absorbed directly and the wind power rejected by the grid

3. The conventional units set-point, Available grid power for pumping

4. The pumping - turbine operations and the water flows


Parameters for optimization – Dimensioning The most important parameters:

– the wind potential (mean wind velocity) and– the hydraulic head between the two reservoirs.

The main parameters for optimization are: – the wind capacity to be installed, – the capacity of the two reservoirs, and– the capacity of the hydro-turbine

Less critical parameters are: – Rating and number of pumps– Diameter of the Penstock


Optimization procedure - Example: Crete


0

20000000

40000000

60000000

80000000

100000000

120000000

140000000

160000000

180000000

200000000

0% 20% 40% 60% 80%part of the peak to be covered with the turbine

Re

se

rvo

ir's

vo

lum

e (

m^

3)

31921532142753363974585195806417037648258869471008106911301191

0,00

0,05

0,10

0,15

0,20

0,25

0,30


Tu

rbin

e's

EP

C (

€/k

Wh

)

31921532142753363974585195806417037648258869471008106911301191

lower envelope curve

Operational design and Architecture of WPS

Issues to be defined:– Energy supply of the hydro-turbine

• Peak demand supply (when the demand exceeds one predefined level)

• Supply of a stable percentage of the demand• Stable operation at the technical minimums (as a spinning reserve)

– Single or double penstock– Definition of the allowed wind penetration

• Stable instantaneous wind penetration (simple control)• Increasing the wind penetration use the hydro-turbine as a

spinning reserve (advanced control)

– Pumping using conventional power• At the hours of low demand• Given the rest ability of the committed conventional units• Whenever (aiming at the minimization of the reservoir volume)



a. Peak demand supply (when the demand exceeds one value)

b. Supply of a stable percentage of the demand

c. Stable operation of the turbine at its technical minimums as a spinning reserve


050

100150200250300350400

73 81 89 97 105 113hours

Po

we

r d

em

an

d (

MW

)

050

100150200250300350400

73 81 89 97 105 113

Po

we

r D

em

an

d (

MW

)

050

100150200250300350400

73 81 89 97 105 113

Po

we

r D

em

an

d (

MW

)

other sources turbine

last 24hours' peak

Options of the hydro turbine operation


Single or double penstock • Single penstock

– Cheaper solution– Turbine priority– Pumping priority

• Double penstock– Operational flexibility– Independent pumping and

turbine operation– Quick response of the

turbine when it is needed



Instantaneous wind penetration permitted • “Simple control”: Stable maximum instantaneous

wind penetration “δ”– (i.e. δ = 30%), as it is used today in most autonomous

islands with concrete wind installed capacity.

• “Advanced control”: Increase the wind penetration by an amount equal to the rest ability of the hydro-turbine. – Two-sided communication (The EUO should know the

rest capacity of the hydro-turbine, in order to permit equal increase of wind penetration).

– The turbine should be in operation.


Scenarios definition


Scenario

Single/ Double penstock

Operational target Wind penetration permitted

1 Single penstock/ turbine priority

Peak demand supply Stable δ=30%

2 Double penstock Peak demand supply Stable δ=30%

3 Double penstock Peak demand supply Advanced control

4 Double penstock Stable supply of a percentage of the demand

Stable δ=30%

5 Double penstock Stable supply of a percentage of the demand

Advanced control

6 Double penstock Stable operation of the turbine at its technical minimums

Advanced control

Conventional power given the rest ability of the committed conventional units is used for complementary pumping

Main assumptions

• H=300m, L=3000m • Wind velocity: 8.1m/s at the hub-height. • Financial evaluation without any subsidy• Oil price: 54$/b (annual mean for 2005)• Basic parameters introduced dimensionless:

– The wind installed capacity as a share of the mean annual load demand (50% - 430% by step 20%)

– The volume of the reservoir in respect with the maximum hourly water pumping ability (30 to 100 by step 10).

– The maximum operational target (as a percentage of the peak) is calculated using an iterative procedure. A bigger target could be set, but it would be achieved in less than 100% of the year.


Indexes for the evaluation • Turbine’s EPC

• Conventional unit’s EPC

• Electrical system’s EPC

• Energy supply


Results - Crete


Crete

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35


Tu

rbin

e's

EP

C (

€/kW

h)

1

2

3

4

5

6

Crete

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35


Co

nve

nti

on

al u

nit

s' E

PC

(€

/kW

h)

1

2

3

4

5

6

Crete

0%

10%

20%

30%

40%

50%

60%

70%

80%


Hyb

rid

's e

ner

gy

sup

ply

(%

)

1

2

3

4

5

6

Crete

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35


Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

)

1

2

3

4

5

6

Results - Lesvos


Lesvos

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40


Tu

rbin

e's

EP

C (

€/kW

h)

1

2

3

4

5

6

Lesvos

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40


Co

nve

nti

on

al u

nit

s' E

PC

(€

/kW

h)

1

2

3

4

5

6

Lesvos

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%


Hyb

rid

's e

ner

gy

sup

ply

(%

)

1

2

3

4

5

6

Lesvos

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40


Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

)

1

2

3

4

5

6

Results - Serifos


Serifos

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

0% 20% 40% 60% 80% 100%part of the peak to be covered with the turbine

Tu

rbin

e's

EP

C (

€/kW

h)

1

2

3

4

5

6

Serifos

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90


Co

nve

nti

on

al u

nit

s' E

PC

(€

/kW

h)

1

2

3

4

5

6

Serifos

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%


Hyb

rid

's e

ner

gy

sup

ply

(%

)

1

2

3

4

5

6

Serifos

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90


Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

)

1

2

3

4

5

6

Comparison of the three islands (scenario 3)


scenario 3

Lesvos

Crete

Serifos

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40


Tu

rbin

e's

EP

C (

€/kW

h)

Crete

Lesvos

Serifos

scenario 3

Serifos

Crete

Lesvos

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40


Co

nve

nti

on

al u

nit

s' E

PC

(€

/kW

h)

Crete

Lesvos

Serifos

scenario 3

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%


Hyb

rid

's e

ner

gy

sup

ply

(%

)

Crete

Lesvos

Serifos

scenario 3

Serifos

Crete

Lesvos

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40


Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

)Crete

Lesvos

Serifos

Proposed solutions for the examined islands


Island Peak (MW)

Wind Capacity (MW)

Reservoir (•106 m3)

Turbine (MW)

% peak supply

% energy supply

Crete 563 825-1314 60-120 310-405 55-75% 46-72%

Lesvos 58 84-145 4.4-14 30-46 57-81% 51-79%

Serifos 2.9 2.2-3.6 0.2-0.3 2.3-2.9 75-100% 80-98%

Sensitivity analysis of the allowed instantaneous wind penetration


Crete

0.00

0.020.04

0.060.08

0.10

0.120.14

0.160.18

0.20

0% 20% 40% 60% 80%

part of the peak to be covered with the turbine

Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

) 30%

40%

50%

withoutWPS

Crete

0%

10%

20%

30%

40%

50%

60%

70%

80%

0% 20% 40% 60% 80%


Hyb

rid

's e

ner

gy

sup

ply

(%

)

30%

40%

50%

Crete

Sensitivity analysis of the allowed instantaneous wind penetration


Lesvos

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0% 20% 40% 60% 80%


Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

)

30%

40%

50%

withoutWPS

Lesvos

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

0% 20% 40% 60% 80%


Hyb

rid

's e

ner

gy

sup

ply

(%

)

30%

40%

50%

Serifos

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0% 20% 40% 60% 80% 100%


Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

)

30%

40%

50%

withoutWPS

Serifos

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

0% 20% 40% 60% 80% 100%


Hyb

rid

's e

ner

gy

sup

ply

(%

)

30%

40%

50%

Lesvos

Serifos

Sensitivity analysis of the Brent price


Crete

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0% 20% 40% 60% 80%


Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

)

54

75

100

withoutWPS



Lesvos

54$/b

75$/b

100$/b

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0% 20% 40% 60% 80%


Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

) 54

75

100

withoutWPS



Serifos

54$/b

75$/b

100$/b

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0% 20% 40% 60% 80% 100%


Ele

ctri

cal

syst

em's

EP

C

(€/k

Wh

)

54

75

100

withoutWPS

Conclusions• The proposed architecture of the WPS (scenario

3):– Double penstock / “Peak demand supply” / “Advanced

control”• With the introduction of the WPS the system’s EPC

is decreased• This benefit should be shared between the pubic

utility and the investor, by the definition of a suitable price.

• The basic parameters in issue are: – Hydraulic head and the Wind potential– Plant size, Island size– Current cost– Duration curve of the demand.

• The production cost is quietly defined• The introduction of the WPS is proposed and

expected to have very positive results


Thank you for your attention

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Documents

Analysis of wind energy with pumped storage systems in autonomous islands George Caralis Mechanical Engineer NTUA National Technical University of Athens