lakshitha weerasinghe

Emerging Scenario with Renewable Energy in Sri Lanka. Meeting the Challenges in Power System Operations & Economic Consequences.

Lakshitha Weerasinghe Ceylon Electricity Board

∗Basics of Power System Operations in the Sri Lankan context.

∗Understanding the problem! ∗Solutions!

Contents

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Basics of Power System Operations

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Time Line of activities G

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Cons

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Gen

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Asse

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Cons

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of

Tran

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In

fras

truc

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Uni

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Freq

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Tran

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Pl

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Econ

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Dis

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Supp

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Seconds Minutes Hrs./ Days

Gov

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Years

Ope

ratio

ns P

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ing

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Time Line of activities U

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Freq

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Econ

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Dis

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Supp

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Seconds Minutes Hrs./ Days

Gov

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© Lakshitha Weerasinghe Ceylon Electricity Board 2014

50Hz

51Hz 49Hz

Demand Generation

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Supply-Demand Balancing

Supp

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Seconds

20:0

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16:0

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12:0

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08:0

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04:0

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00:0

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24:0

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Intermediate load

Peak load

Load MW

Base Load

1400MW 1600MW

2000MW

900 MW

Understanding the Demand curve

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Frequency (Hz)

Power (MW)

50Hz

100 MW

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Supp

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Seconds

Gov

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Minutes Hrs./ Days

Frequency (Hz)

Power (MW)

50Hz

100 MW

49.5Hz

110 MW © Lakshitha Weerasinghe Ceylon Electricity Board 2014

Supp

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Seconds

Gov

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Minutes Hrs./ Days

Freq. Error

Without Governor Control

With Governor Control

Frequency

50 Hz Time

Disturbance (Generator Trips!)

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Supp

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Gov

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Frequency Control

Supp

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Seconds

Gov

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Minutes Hrs./ Days

Freq

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© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Frequency

50 Hz Freq. Error

With Frequency Control

Time

Disturbance (Generator Trips!)

With Governor Control (Primary ALFC)

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Bringing Frequency back to 50Hz.

Hydro*

Thermal

CEB 1361 MW

•CEB 1164 MW

•IPP 771 MW

*Note :- Mini Hydro and wind not included

Understanding the Frequency Controller

0MW 67

Kothmale single unit maximum capacity = 67MW

Eg.

50 49 51

52 48

Hz

30 60

50Hz

51Hz 49Hz

Demand Generation

50Hz

51Hz 49Hz

Demand

Generation

50Hz

51Hz 49Hz

Demand Generation

Any one of the following power stations is assigned at any given time to look after the system frequency. 1. Victoria (unit size = 71MWx3) 2. Kothmale (Unit size x 67 x 3) 3. New Laxapana (50MW x 2) 4. Samanala Wewa (60MW x 2)

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Time Line of activities U

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omm

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Freq

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Econ

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Dis

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Supp

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Seconds Minutes Hrs./ Days

Gov

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© Lakshitha Weerasinghe Ceylon Electricity Board 2014

∗Economic Dispatch – What load to be kept on each machine that is already in operation. ∗Unit Commitment – What are the

machines to start or stop to serve load within a given period.

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Other Constraints/ Considerations (1) Hydro Power comes last in the water utilization Priority order

1. Water Service and Drainage 2. Environment 3. Irrigation 4. Power

(2) Pond balancing (3) Reservoir Operations

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Annual Inflow 3500 GWh

Annual Hydro Generation 3500 GWh

Spill

MOL

Storage Capacity ≅ 1250 GWh

Rese

rvoi

r 1

Rese

rvoi

r 7

Understanding the problem.

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Resource Attributes that causes problems to System Operations

Small Hydro Non Dispatchability.

Wind Non- Dispatchability and Intermittency.

Solar Non-Dispatchability and Intermittency.

Problems associated with Non Conventional Renewable Technologies.

Over 260 MW of Small NCRE generators are connected to the Distribution network. They appear as “Negative Loads” to system operators.

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Issues due to Non Dispatchability.

20:0

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Load MW

Minimum Demand

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Issues due to non Dispatchable nature

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Issues due to non Dispatchable nature

20:0

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Load MW

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Issues due to non Dispatchable nature

3 Base Load Coal plants. Minimum stable load is 180MW. Base Load Thermals such as Sapugaskanda HFO plant, CC plants. Frequency Controlling Hydro Plant Plants providing (Up/Down) Operating Reserves. “Must Run” Hydro plants Hydro plants operated to balance ponds. 360MW of non dispatchable small renewable plants.

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Issues due to Intermittency

Technical • Violation of operating frequency

limits. (±1%) • Operation of Under Frequency Load

Shedding (starting from 48.75Hz). • Severe Frequency instabilities leading

to cascaded total collapse.

Economical • Cost of maintaining high spinning

reserve. • Underutilization of energy from other

sources which may be cheaper or at zero cost (such as from Run-of-the-river plants that are spilling).

• Cycling of base load thermal plants.

How Intermittent is Wind SPEED ?

0.00

2.00

4.00

6.00

8.00

10.00

12.00

Jan

Feb

Mar

Apr

May Jun

Jul

Aug

Sep

Oct

Nov Dec

Velo

city

m/s

Seasonal Variation of Wind Velocity

8.80

9.00

9.20

9.40

9.60

9.80

10.00

10.20

10.40

1 2 3 4 5 6 7 8 9 101112131415161718192021222324

velo

city

m/s

Diurnal Variation of Wind Velocity

0123456789

10

0 50 100 150 200 250 300 350 400 450 500

Source: SEA

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

How Intermittent is Wind Power ? Minute to Minute variation of out put (MW) of a wind Farm over

3 hour period.

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

How Intermittent is Solar?

Perfect Solar Day Pre-monsoon Clouds Passing Over

Source - SEA

Cost of Spinning Reserves.

Gradient = Incremental cost Rs/kWh

Generation Cost per

hour

Output (MW)

No Load Cost per

hour

Plant No Load Cost per Hour (Rs million)

(September 2014)

Kalanitissa CCP (Diesel) 1.17 AES CCP 1.3 Kerawalapitiya Yougadanavi 1.6 Victoria 10 m3 /s (25% of full load )

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Cost of Cycling

Plant Start/Stop Cost (Rs million)

Hot (<8 h) Warm (8<h<48)

Cold (48<h)

Kalanithissa CC (Diesel)

3.9 4.6 5.3

AES CC 3.3 8.6 10.5 Kerawalapitiya Yougadanavi

5.9 7.1 9.5

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Solutions

© Lakshitha Weerasinghe Ceylon Electricity Board 2014

Solutions Supply Side Solutions

• Maintaining larger spinning reserve to do Load-Frequency Control on supply side. • Operating intermittent sources (such as Wind) below capable output and utilize the balance

capacity to cushion out fluctuations at the source itself. • Group Control & AGC at Load dispatch Centre. • Secondary Automatic Load-Frequency regulation using Integral Controllers.

Demand Side Solutions • Valley Filling measures to improve Low demand period • Introducing variable loads to be called upon low demand periods. • Changing Customer demand using smart Grid options. • Introducing local loads such as Hydrogen, Compressed Air and Battery technologies to utilize

part of the generation to cushion out intermittency/variability at the terminal.

Other Solutions • Forecasting Wind speeds to do improved Operations Planning. • Interconnect with neighboring Grids. • Geographical scattering of Wind and Solar park locations.