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Renewable Energy Integration Issues Roel Verlaan

DNV KEMA

21st PPA Annual Conference

Pre-conference Workshop

July 15th, 2012

Vanuatu

Agenda

Integration of Intermittent Renewable Energy

Generation on small island systems

Case Studies:

- Integration of Solar Energy Generation into the

VIWAPA Power System in St. Thomas

- Integration of Solar Energy Generation into the

NPC Power System in Niue

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Intermittent Renewable Energy Sources:

- Solar

- Wind

Non-intermittent (base load) Renewable Energy

Sources:

- Hydro

- Geothermal

- Waste to Energy

- Biomass

- Coconut oil

- Others (mostly not proven technologies)

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Renewable Energy Sources

4

Example of intermittent PV Output

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0.5

1

1.5

2

2.5

3

3.5

7:42 9:30 11:18 13:06 14:54 16:42 18:31

Time of Day

Ou

tpu

t (k

W)

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Example of Wind Power Output

Risks associated with high levels of

penetration must be understood

Solutions and their associated costs need to

be clearly defined

Exacerbating these issues, commercially

available power system simulation tools have

inherent limitations in performing the required

time domain simulations.

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High Level Penetration of Intermittent

Renewables

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Example of Wind Power Effects on

Combustion Generation Ramp Rates

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Effects on System Frequency Point “X” corresponds to the instant in time

when the system is in steady state, just before

the start of the renewable-ramping event.

Point “Y” corresponds to the time instant at

which the frequency is at its lowest, or where

the frequency deviation from its nominal value

of 60 Hz is maximum. Point “Z” corresponds

to the time instant when the frequency returns

to its nominal value for the first time.

Grid calculation software tools like for

example PSSE, ETAP, are not designed to

analyze an event of this duration.

KEMA developed software tool KERMIT as

a “screening” tool, in order to quickly decide at

which point during an event, an elaborate

analysis with for example PSSE is needed.

The term “screening” is used because

KERMIT can execute a 24-hour simulation in

5-10 minutes.

KERMIT – a KEMA developed tool

Developed by KEMA in Europe and the US

Simulates 24h Real Time Power System Dynamics

Quantifies Impact of Variable Power Sources on System Operation

Capabilities include:

- Visualize impact of volatility on system control

- Effect on system dynamic when adding wind or solar to the generation

mix

- Assess opportunities for energy storage

- Comparison of operation control strategies

- Investigate system response to outage or cable loss

- Test mitigation strategies for intermittent generation

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Time Step Increases

1 ms 1 cycle 1 second 1 minute 10 minutes 1 hour 1 day 1 month 1 year

Harmonics

Stability

Protection

Frequency Response

Regulation

Balancing /Dispatch

Capacity

Economics

Transient Stability

and Harmonics

Short Circuit

Power Factory

PSSE

others

Production Costing

Market Simulation

Expansion Planning

Statistical Analysis of AGC and

Balancing

Replacement Reserves

Governor Response

Spinning and Short

Term Reserves

Storage

Replacement

Reserves

Emissions

Performance

Long Term

Generation,

Transmission, DSM,

and DG Investments

KERMIT Simulation Tool KEMA Energy

Ecology Model

Traditional T-Planning

TOOLS

STUDIES

ISSUES

Ops Planning & Sched Realm Real Time Ops Realm Auto Control Realm

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Analysis Timeline

Useful in analyzing response AND in developing / assessing new solutions

- Governor controls and droop settings

- AGC algorithms

- Integration of fast storage

- New scheduling / dispatch paradigms

- Varying reserve levels

- Use of Demand Response

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KERMIT Dynamic Simulation Features

KERMIT allows testing various PV output patterns

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0 500 1000 1500-50

0

50

100

150

200

25027361

Smooth

0 500 1000 1500-50

0

50

100

150

200

2508641

Volatile

0 5 10 15 200

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4

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10

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14C:\Current Projects\Virgin Islands\KERMIT\Modeling\STX_Light_day_solar\TotalSolar.mat:: TotalSolar

Hours

MW

1

Typical

0 500 1000 1500-50

0

50

100

150

200

25033121

Temporary output drop

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KEMA ES-Select software

Input from KERMIT and (for

example) PSSE study results for

determining technical and

economical feasibility of Energy

Storage

CASE STUDIES

KEMA performed Renewables Integration Studies for island

systems like Oahu (Hawaii), Aruba, Niue, for a number of US

West Coast Utilities and currently a study is ongoing, using the

tools as mentioned again, for US Virgin Islands

Two case studies

Findings of the US Virgin Islands Study so far

Integration of Solar Energy Generation in the Power System of

the South Pacific Island of Niue

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US Virgin Islands KERMIT Modeling – preliminary results

St. Thomas basics

VI-WAPA requested study of

- Technical limits to maximum wind and PV

- Connection studies for six specific proposed projects

KEMA uses a unique computer tool (KERMIT) for evaluation

- Evaluates entire days in sub-second intervals

- Especially suited for evaluating random generation during entire day

- Evaluates dynamic response of system through entire day

System characteristics

- 80 MW peak load

- Six generators

- Total 132 MW

- Largest 39 MW

Proposed PVs

- Three sites total 9 MW

- Largest 5 MW

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KERMIT Simulation – St. Thomas

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Three PV sites on STT:

- Home Depot 5MW

- Mall roof 2MW

- Mall canopy 1.833MW

PV profiles are assumed as follows:

0 5 10 15 200

0.5

1

1.5

2

2.5

3

3.5

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4.5

5C:\Current Projects\Virgin Islands\KERMIT\Modeling\STT_Light_day_solar\MWsolarCnPV.mat:: MWsolar

Hours

MW

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9C:\Current Projects\Virgin Islands\KERMIT\Modeling\STT_Light_day_solar\TotalSolar.mat:: TotalSolar

Hours

MW

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Fig.1 Individual PV site output power Fig.2 Total PV output power

KERMIT Simulation – St. Thomas

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System frequency with and without PV

The frequency deviation is caused by the short term fluctuation of PV power that the

SCADA system and line engine are not fast enough to compensate.

0 5 10 15 2059.92

59.94

59.96

59.98

60

60.02

60.04

60.06

60.08C:\Current Projects\Virgin Islands\KERMIT\Modeling\STT_Peak_day_solar\allAreasFrequencyDeviationRaw.mat:: allAreasFreqDeviationInHertzRaw

Hours

Fre

quency D

evia

tion,

in H

z

1

0 5 10 15 2059.92

59.94

59.96

59.98

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60.02

60.04

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60.08C:\Current Projects\Virgin Islands\KERMIT\Modeling\STT_Peak_day\allAreasFrequencyDeviationRaw.mat:: allAreasFreqDeviationInHertzRaw

Hours

Fre

quency D

evia

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in H

z

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Fig.3 System frequency with PV Fig.4 System frequency without PV

KERMIT Simulation – St. Thomas

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System frequency in the case the largest PV site (5 MW) is tripped

System frequency drops due to the lack of generation. Then the line engine is

picking up the imbalance by increasing the dispatch.

0 5 10 15 200

1

2

3

4

5

6

7

8

9Total Renewable

Hours

MW

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0 5 10 15 2059.7

59.75

59.8

59.85

59.9

59.95

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60.05

60.1C:\Current Projects\Virgin Islands\KERMIT\Modeling\STT_Peak_day_solar_AOG\allAreasFrequencyDeviationRaw.mat:: allAreasFreqDeviationInHertzRaw

Hours

Fre

quency D

evia

tion,

in H

z

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Fig.5 Disturbance in PV generation Fig.6 System frequency with PV disturbance

Looking for solutions

For mitigating solutions, we will look at the existing solution and the new solution—in

that order.

For the existing solution it is likely to review the policy of maintaining spinning

reserves. More simulation are currently ongoing to determine whether there is

enough capacity and units to meet the new spinning reserve requirement.

An alternative solution is energy storage, which is more effective at maintaining the

frequency.

On both solutions a cost/benefit analysis will be worked out.

US-VI does not have a “frequency standard”. In fact, like in many islands, they don’t

record the frequency, while such historical record would be needed for model

calibration. All UFLS is set at below 59Hz for St Thomas. This means that as long

as the fluctuations in wind and solar power are not too large, spinning reserve

should be able to keep the UFLS from being triggered.

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NPC Niue Preliminary results

Niue system basics

Very small system

- 500 kW peak load

- Population about 1,600

- Limited commercial activity

Four 500 kW diesel generating units

Some ‘difficult’ motor loads

- Water pumping

- Rock crusher at quarry

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Niue challenge

Must be able to support rock crusher and water pumping

Now must operate second diesel to support motor starting

Want to avoid running second diesel for motor starting

Want to integrate maximum amount of renewables

These are preliminary results

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One diesel is not enough for motor starting now

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0.82

0.84

0.86

0.88

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0.92

0.94

0.96

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pu

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Time (sec)

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0.4

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1.2

0 12

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Vo

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pu

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Time (sec)

One Diesel Online; 60 kW PV, 150 hp motor start

Voltage is OK But the system will collapse

Increased PV puts more reserve in the diesel

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0.98

0.985

0.99

0.995

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1.005

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Fre

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pu

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Time (sec)

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1.2

0 12

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Vo

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pu

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Time (sec)

One Diesel Online; 120 kW PV, 150 hp motor start

Voltage is a little better The frequency dips to 99%, but holds on

Also works with max PV and loss of large PV

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0.993

0.994

0.995

0.996

0.997

0.998

0.999

1

1.001

0 12

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Fre

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pu

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Time (sec)

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0.4

0.6

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1.2

0 12

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Vo

ltag

e (

pu

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Time (sec)

One Diesel Online; 400 kW PV (80% system peak load); loss of large PV (40 kW)

Voltage is fine The frequency dips to 99.6%, and holds on

Preliminary findings

NPC must always operate one diesel generator

100% supply with solar is not possible

One diesel should handle normal renewable output variations

System frequency variations because of high solar power fluctuations can most

likely be covered by one diesel generator as it looks now (no UFLS). If not, a second

diesel generator should run as spinning reserves during the hours per day with most

solar power

Renewable inverters susceptible to low-voltage drop-out during motor starts

- Will require low-voltage ride-through

Motor starting is a problem

- PV instead of a second generator online provides limited starting current (105% max output)

- With increased PV however more reserve in diesel is allowed

- Solution with capacitors is currently being studies

Maximum of renewables is limited by minimum load on diesel (≈100 kW)

Will review results with NPC in Niue at end of July

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