1

A large pumped storage scheme for seasonal reliability of national

power supply?

Earl Bardsley (University of Waikato)Bryan Leyland (LCL Ltd)Sarah Bear (URS Ltd)

Acknowledgements

We thank Contact Energy Ltd and Meridian Energy Ltd for kind provision of generating and discharge data and financial support.

2

The dry-year issue

• Most of NZ power will remain hydro• Only 4,000 GWh storage capacity• Insufficient storage to use wet years to

offset low inflows later

1500

2000

2500

3000

3500

4000

4500

Jan Apr Jul Oct Jan Apr Jul Oct

GW

h

Electricity savings call

Spill

Jan Apr Jul Oct Jan Apr Jul Oct

2003 2004

4,000

2,000

Sto

rage

(GW

h)

New Zealand Hydro Storage 2003-04

3

Stand-by coal-fired stations?

• Expensive to maintain• No guarantee of new gas finds

Increase storage capacity?

• Capacity increase of about 10,000 GWh• Not possible with existing lakes• Pumped storage as an alternative?

4

Conventional pumped storage

• Load-following for thermal stations• Frequency control and voltage support

(Small water volumes shifted between upper and lower reservoirs)

Turlough Hill Pumped Storage Scheme, Ireland

5

The Saurdal seasonal pumped storage scheme (Norway) : A model for New Zealand?

10.5 kmTunnel length

82 km2Upper Reservoir area

125 metresReservoir level range

7,760 GWhEnergy storage

New ZealandLocation of Onslow-Manorburn basin (Central Otago)

Alexandra

Roxburgh

Lake Roxburgh

ManorburnReservoir

Lake Onslow

Roxburgh Dam

Clutha River N

6

Onslow Dam

Clutha River

Lake Roxburgh

N

km0 6 12 18

Tunnel

Reservoir area: 120 km2

Energy storage :12,000 GWh

Level range: 80 m

Tunnel length: 20 km

Head range: 590-720 m

Proposed Onslow-Manorburn seasonal pumped storage scheme

Alexandra

Manorburn Dam

Southern portion of Lake Onslow

800-metre contour

Onslow Dam

7

Northern portion of Lake Onslow

800-metre contour

40 metres

Proposed northern dam site

800-metre contour

Upper Manorburn reservoir

8

Simulation

• As if scheme was in operation 1990-2003

• Seek to smooth Clutha + Waitaki power yield through dry periods

• Move existing hydro lakes toward mid-range levels (spill reduction)

Pumped Storage Discharge or Pumping Rates at Roxburgh Dam (m3s-1)

-200-150

-100-50

050

100

150200

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Dis

char

ge o

r Pum

ping

Pumped storage daily water uptake or release to Clutha River (1990-2003)

0

+150

-150

Release (m3 s-1)

Pumping (m3 s-1)

1990 20031997

9

Pumped Storage Discharge or Pumping Rates at Roxburgh Dam (m3s-1)

-200

-150-100

-500

50100

150200

1992 1993

Dis

char

ge o

r Pum

ping

Pumped storage daily water uptake or release to Clutha River (1992 dry year)

Pumping (m3 s-1)

+150

-150

0

Release (m3 s-1)

Jan July Dec

Pumped storage daily power generated or used for pumping (1990-2003)

Mean: - 84 MW

Pumped Storage Power Inputs and Outputs (MW)

-1500

-1000

-500

0

500

1000

1500

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Pow

er (M

W)

+1000

-1000

0

Pow

er (M

W)

1990 1997 2003

Generating

Pumping

10

Clutha + Waitaki Power Schemes: Power Output (1990-2003)

0

500

1000

1500

2000

2500

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Pow

er (M

W)

Example Simulation of Pumped Storage Smoothing (case of Constant Power Output)

0

500

1000

1500

2000

2500

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Pow

er (M

W)

Mean: 1269 MW

Mean:1262 MW

Actual

Simulated

0

2000

Pow

er (M

W)

1990 20030

2000

Pow

er (M

W)

Simulation result: Clutha + Waitaki power yield maintained (1990 – 2003)

1000

1000

1997

Recorded

1990 1992 1994 1996 1998 2000 20020

2000

4000

6000

8000

10000

12000

14000

Time (years)

Pow

er (G

Wh)

Actual65 %75 %85%

Cum

ulat

ive

Ene

rgy

(GW

h)

Actual Waitaki + Cluthaspill losses

Simulated losses with pumped storage

Cumulative energy gain from alternative lake operating mode (1990-2003)

12,000

8,000

4,000

1990 1994 1998 2000

11

Water levels of simulated Onslow-Manorburn Reservoir (1990-2003)

Water Levels of Simulated Onslow-Manorburn Pumped Storage Reservoir

720

730

740

750

760

770

780

790

800

1990 1992 1994 1996 1998 2000 2002

800

740

780

760

720Wat

er L

evel

(met

res)

Maximum water level variation: 50 metres

Lake Pukaki Water Levels as Simulated with Pumped Storage (1990-2003)

518520522524526528530532534536

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Lake

Lev

el (m

etre

s)

Recorded Lake Pukaki Water Levels 1990-2003

518

520

522

524

526528

530

532

534

536

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Lake

Lev

el (m

etre

s)

Recorded and simulated Lake Pukakiwater levels (1990-2003)

518

536

518

536

Wat

er L

evel

(met

res)

1990 2003

Recorded

Simulated

12

Lake Rotoaira (0.5 metre operating range)

Lake Moawhango, 15 metres operating range

13

• Spinning reserve and frequency-keeping

• Supporting wind energy and small hydro

• Some reduction in Lower Clutha flood peaks

• Water supply for Dunedin city

Related Benefits of the Onslow-ManorburnScheme:

Onslow-Manorburn pumped storage: Conclusions

• Energy-neutral

• Could buffer hydro power output through future climatic variations

• Reduced hydro lake seasonal fluctuations

• But would it fit into the market?