Renewable Energy and Inter-isla

Power Transmission Power Transmission

Vahan GNational ReLaboratoryCIEMADeS IConferenceUniv. of TuraGurabo, Pu

Pu

May 06, 2011

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the 

NREL/PR-5500-51

Composite photo created by NREL
NREL’s Role in Variable Renewable Energy I

• Integration studies and operational impacts;• Wind/solar 

pg ; lant modelin

g and interconnection;

• Transmission planning and analysis; • Resource assessment and forecasting. Energy Development for Island Nations (EDIN)• U.S. Virgin Islands (reduce dependency on fossil 

fuel by 60% by 2025).

• Iceland and Dominica collaboration.• Pacific Islands.Wind/PV/Energy storage projects in Hawaii

NATIONAL RENEWABLE ENERGY LABORATORY

Wind/PV/Energy storage projects in Hawaii. 
Overview

• Submarine Power Transmission Technologie• Hawaii Wind Integration and Transmission S• Caribbean Work.

NATIONAL RENEWABLE ENERGY LABORATORY 
HVAC vs. HVDC

NATIONAL RENEWABLE ENERGY LABORATORY 

+
HVDC Pros and Cons

Advantages Long distance transmission with lower costs and losses;

 No high capacitance effect on DC (no reactive losses);

 More power per conductor, no skin effect,

2 conductors only;

 Connecting unsynchronized grids, rapid power flow control;

 Buffer for some disturbances disturbances, stabilization stabilization of power flows; Multi‐terminal operation;

 Good for weaker grids;

 Helps integrating large amount of variable generation.

Disadvantages



Hi hg

h cost

o

f power converters;

 Complexity of control, communications, etc.;

 Maintenance cost higher than for AC, spare parts needed;

NATIONAL RENEWABLE ENERGY LABORATORY

 HVDC circuit breaker reliability issue.
HVDC Technologies

HVDC Classic – LCC Converters (bipole shown)

HVDC VSC Technology (bipole shown)

NATIONAL RENEWABLE ENERGY LABORATORY
HVDC Configurations

NATIONAL RENEWABLE ENERGY LABORATORY
Submarine Cables - How Dee

 The current experience is limited to water depths  HVDC ultra

‐deep technology up to 2000

m possib

experience so far;

 Based on published literature, 80 kVDC / 100 MW 

even at 2200 m;

 Additional development and testing including ful

ti l r

al is nee

d de

d

for hi hg

her d th ep s.

NATIONAL RENEWABLE ENERGY LABORATORY
Oahu Wind Integration and Transmission Stu

H ii Cl E I iti ti (HCEI) Hawaii Clean 

Energy Initi

ative (HCEI) – O t b 2008 O

c

t

o

ber 2008

– Multi-year initiative;– 70% clean energy by 2030 (40% by renewables);– Agreement between state of Hawaii and HECO:

• 400 MW of wind from Lanai and/or Molokai to Oahu (Stage 1• 200 MW of wind from Maui to Oahu (Stage 2).

OWITS Study• Support to HCEI and HECO;• FY 09/10;

• TRC consists of regional, national,

and international experts;

• TRC h ld e 5 i

n‐person meetings;

• Reviewed and provided feedback

on study methods, data needs, and

results.

NATIONAL RENEWABLE ENERGY LABORATORY
Big Wind Scenarios for HCEI (St

Wind (MW) 

Scenario

(MW) 

Oahu Lanai Molokai 

1. Oahu Wind 100 2. Off‐island Wind 100 200

3. Concentrated Wind 100 400 

4. Oahu Solar 5. High Renewables 100 200 200 

Stageinterc

NATIONAL RENEWABLE ENERGY LABORATORY 
OWITS Cable Study Inpu

• Potential cable landing points and

inter‐island routes have been identified

in Ocean Floor Survey Report (DBEDT);

• Maximum water depth – around 800

m;

• Sending and receiving end voltages

–

138 kV;

• PSSE load flow data from HECO;

• Contract between NREL and NREL and Electranix Electranix

for transmission modeling.

NATIONAL RENEWABLE ENERGY LABORATORY 
OWITS Option Screening Metho

C t os

t

s (HVAC) C 

o

AC Cables DC 

AC substations DC 

18 options analyzed (AC, DC, or combination of both).

Sea/land cable transition SeaFixed compensation reactors ‐Other com

ponents Oth

Stage 1

p

AC losses (20 years) DC Total HVAC cost Tot

Only 6 selected for detailed simulation (AC and DC).

Stage 2 Stage

2

Only 3 final scenarios (including interconnections to Maui) selected for f h d il d d i i l i RF

Q

NATIONAL RENEWABLE ENERGY LABORATORY 

furt

her 

detail

e

d

dynamic simulation.

Q
All AC Option

• Simulat

for wors

138-kV Bus

70-mile AC 

under-sea 

34.5-kV Bus

600-V Bus

Spontaneous 

breakeropen 

operation

Operation due 

to overvoltage 

protection

for wors

• 230 kV 

• AC solut

230-kV Bus

cable

200 MW of 

Wind Turbines

operation

230-kV Bus

p

without enhancecompen

Fibre-optic link Receiving End Sending End • Depths 

challeng

cables.

NATIONAL RENEWABLE ENERGY LABORATORY 
HVDC Option

HVDC Option C3‐2 HVDC Option 

HVDC Option B3‐2 HVDC Optio

HVDC Option B1‐2 HVDC Opt

NATIONAL RENEWABLE ENERGY LABORATORY 
Range for Budgetary Capital costs for HVDC 

(including burial and termination)

Source: OWITS summary report NREL Nov 2010 (available at:

NATIONAL RENEWABLE ENERGY LABORATORY 

Source: OWITS summary report, NREL, Nov 2010 (available at:

www.nrel.gov/wind/systemsintegration/pdfs/2010/owits_summary_
OWITS Final Scenario 1

• 400‐MW bipole VCS link

between Molokai and

Oahu.

• AC cable between Molokai

and Lanai.

NATIONAL RENEWABLE ENERGY LABORATORY 
OWITS Final Scenario 2

• 200‐MW monopole VCS

link between Molokai and

Oahu.

• 200‐MW monopole VCS

link between Molokai and

Lanai.

• AC cabl b e

between Mlki o

o

k

ai,

Lanai, and Maui.

NATIONAL RENEWABLE ENERGY LABORATORY 
OWITS Final Scenario 3

• 400‐MW bipole VCS link

between Molokai and

Oahu.

• AC cable between Molokai,

Lanai, and Maui.

NATIONAL RENEWABLE ENERGY LABORATORY 
OWITS Cable Study Summa

• St t i d l d t h i t ti f bl f 

Stra

tegies were 

develope

d

to en

hance in

tegration o

f renewables 

fo

scenario:

• Wind power forecasting to improve commitment;• Refining the up-reserve requirements by using fast start units and loa• Reducing minimum power of the baseload units;• Seasonally cycling off some selected baseload units\Increasing the th

rate capability and enhancing the droop;

• Considering advanced wind turbine technologies (inertia and frequen

• Some aspects of short term storage were examined for implementing 

of wind plants.

• Adequate reserve requirements for sustained drops in wind over an • The largest drop in wind and solar power over 10-min. periods can 

with future improved AGC ramp rates; 

• Quick variations in wind and solar ( ) 1 to 5 min. time frame) mi

ght re

q

term storage for up/down ramp rate limiting;

• Detailed transient modeling to evaluate the system’s response to w

contingences (voltage faults at different locations) was conducted;

NATIONAL RENEWABLE ENERGY LABORATORY 

• PPAs were signed between HECO and Castle & Cook ($0.11 to 0.13/

transmission costs).
On-going Puerto Rico – USVI: BVI Interconne

Cable routes

are notional

The study is focused on options for:

•50‐mile interconnection between PR and STT;

•10‐mile interconnection between STT and BVI;

NATIONAL RENEWABLE ENERGY LABORATORY

10‐mile interconnection between STT and BVI;

•80+ mile interconnection between STT and STX; or

•Direct interconnection between PR and STX as an alternative.
PR-USVI Bathymetry

NATIONAL RENEWABLE ENERGY LABORATORY 

NREL‐developed map. Combination of 10, 30, and 100‐m horizontal resolution, and based on NOAA 
Puerto Rico – USVI Bathymetry

2200

m

1700

m

NATIONAL RENEWABLE ENERGY LABORATORY 

NREL‐developed map. Combination of 10, 30, and 100‐m horizontal resolution, and based 
Puerto Rico – USVI: BVI Interconnection Stud

• Determine power capacities, types, and requiremen

interconnections;

• P f er

form power sys

tem

s

t du

d

y an

d id tif en

y necessary 

reinforcements;

• Demonstrate Demonstrate potential potential benefits benefits (generation (generation costs

, r

r

• Estimate project costs.

Project Timeline • October 2010 – Project kickoff• January 2010 – Interim report #1 

• HVAC/HVDC requirement• Submarine cable study

• April 2011 – Interim report #2 

NATIONAL RENEWABLE ENERGY LABORATORY

• Power system study 

• July 2011 – Final report.

Example of AC and DCInterconnection option
Adding 30 MW of Wind (Extreme Scenario

7080

STT Load Hourly Data and 30MW Wind

7080

STT Load Hourly Data and 30MW Wind

30405060

POWER (MW) 304050

60

POWER (MW)

• Baselo

0

1020

0 24 48 72 96 120 144 168

TIME (HR)

0

1020

0 24 48 72 96 120 144 168

TIME (HR) Baselo

genera

MW;

• 60 MW 

• N d o

day 

• Big cha

system 

NATIONAL RENEWABLE ENERGY LABORATORY 
How PREPA Interconnection Can Help?

• PREPA can p

load and/or 

to WAPA.

• Different en

may be asso

service.

NATIONAL RENEWABLE ENERGY LABORATORY 
PV Variability Will Contribute to Regulation Requ

23.3MW PV in Trujillo, 

2.5‐MW PV, measured in Las Vegas, NV area Single‐axis tracking

NATIONAL RENEWABLE ENERGY LABORATORY 
Submarine Interconnection Can Help with Fa

HVDC Interconnection Example

• PREPA maintains large reserve capacity for Autom

Generation Control (AGC). Generation Control (AGC).

• Faster (sub-second) power control is possible with 

(built-in feature).

NATIONAL RENEWABLE ENERGY LABORATORY 

• Voltage control simultaneous with power control.
Interconnection & Variable Generation – Possible 

Short self

recoverin

g

Voltage dip

HVAC Interconnection Example

g

fault

• Short self

‐recovering faults will create voltage dips in WAPA s

• May be

a serious reliability issue during times of large power 

• Wind power low voltage ride

‐through (LVRT) capability is ess

operation;

• Overall LVRT capability of WAPA system can be improved by 

HVAC interconnection;

NATIONAL RENEWABLE ENERGY LABORATORY 

• Modeling is necessary for various contingency scenarios, targ

and wind turbine topologies, etc.
Larger Regional Interconnection

USVI Benefits:• Diversified supply of energy;

• Clean baseload geothermal power from St. Kitts/Nevis;

• LNG‐generated power from PR;

NREL d

Cable 

LNG generated power from PR;

• Higher reliability;

• Lower energy costs.

NATIONAL RENEWABLE ENERGY LABORATORY 
Caribbean Power Interconnection and Renewa

• Th

e energy sol ti u ons

for th

e C ibb ar ean region i ld nc

u

d

e new 

new energy resources, and electrical interconnections betw

• Geothermal

power is considered as

a main driver for the 

• Caribbean wind energy (estimated at 3.7 GW) as

a driver 

interconnection?

• Variability of wind power represents significant challenge

baseload geothermal power.

NATIONAL RENEWABLE ENERGY LABORATORY 
Caribbean Bathymetry

NREL‐developed map , 1‐km horizontal resolution, based on GEBCO data.

NATIONAL RENEWABLE ENERGY LABORATORY 

Areas 1, 2, and

3 – may have gaps deeper than 1650 
Caribbean Bathymetry and Slopes

Depths l

and slop

NREL‐developed map , 1‐km horizontal resolution, based on GEBCO data.

NATIONAL RENEWABLE ENERGY LABORATORY 
Potential Benefits of Regional Interconnection

• Deliver lower cost electrical power from the island 

has such power to an island (or country) that does n

•

Possibilit

y

o

f

t itti ransmitting l t f arge amoun

t

s

o

f

el ti 

ec

t

ric

generated by renewable sources;

• Increased Increased reliability reliability, reduced reduced spinning spinning reserve reserve requ

requ

shared frequency regulation without adding new ge

• Increase the

potential for hi

g

h

‐

penetration variable 

generation;

• Reduce dependence on high price imported oil and 

level utilization of renewable energy sources on the 

• Integrating fiber

‐optic communication cables.

NATIONAL RENEWABLE ENERGY LABORATORY 
Thank you !

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the