On Frequency Stability in the Future Renewable Nordic Power System with

Gas Sector Integration

Jussi Ikäheimo (VTT) Juha Kiviluoma (VTT)

Contents

• Motivation – New reserve requirements in the Nordic system

• Frequency stability – Research methods – Results for a 100 % renewable scenario

The Nordic synchronous grid • Annual demand 400 TWh • Peak load 70 GW

Frequency deviations per week

Managing frequency excursions

50

49

48

47

51

52

53

Emergency power via HVDC links

Emergency power via HVDC links

Power plants disconnecting

Power plants disconnecting

Emergency load control Splitting of the transmission grid

mFRR

FCR-D FCR-N & aFRR

Maximum excursion as result of single fault

Freq

uenc

y H

z

Types of reserves

Types of reserves in Nordic countries

(Source Fingrid Oyj)

Proposal of new technical requirements for FCR

• Frequency controlled disturbance reserve

(FCR-D) – Stationary performance requirement – Dynamic performance requirement (in time

domain) – Stability requirement (in frequency domain)

• Frequency controlled normal operation reserve FCR-N – Similar structure but dynamic performance

in frequency domain

FCR-D dynamic performance • If specified energy

or power ramping requirement is not fulfilled, the paid capacity is penalized accordingly

𝐶𝐶𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 = 𝑚𝑚𝑚𝑚𝑚𝑚 ∆𝑃𝑃𝑠𝑠𝑠𝑠,∆𝑃𝑃5𝑠𝑠0.93

,𝐸𝐸5𝑠𝑠1.8𝑠𝑠

Methods

Workflow

0

20 000

40 000

60 000

80 000

100 000

120 000

140 000

ge

ne

rati

on

MW 1 natural gas

2 coal

3 wood

4 water

5 sun

6 wind

7 nuclear

Power system model

(Simulink)

Unit commitment

and economic dispatch

(Wilmar JMM)

Frequency nadir

Frequency rate of change

System set-up

Dimensioning incident

Capacity expansion simulation

Reserve requirement Plant scheduling

and reserves allocation

FCR-D 1500 MW 1400 MW

Dispatch model structure

heat pump

heat boiler

CHP plant

heat storage

elec

trici

ty

heat

Photovoltaic

Wind

Hydro

Power-to-gas

Condensing

EV

SNG

FCR

Dynamic plant models overview

Frequency measurement

Frequency measurement

Grid frequency

Governor model

Response model

Plant model

FCR-D

FCR-N

Power output

Dynamic plant models Plant Model type for FCR-D

Hydro plants The most common turbine model with water starting time TW = 1 s ; and gate servo delay Tg = 0.2 s

Steam & gas turbines

Based on the IEEEG1 model, with time constants for steam inlet and three boiler passes

Wind turbines Simplified model with consideration on blade pitching speed

PV plants First-order lag model with T1 = 1.5 s

Electrolysis First-order lag model with T1 = 2 s

Heat pumps First-order lag model with T1 = 2 s

Performance of the simulated plants

Plant type ΔP5s / ΔPss E5s / ΔPss Cfcrd / ΔPss

Hydro power plants 0.75 1.6 0.81

Steam and gas turbines 0.6 2.4 0.65

Wind turbines 0.97 2.6 1

PV plants 1.0 3.5 1

Heat pumps 1.0 2.8 1

Electrolysis plants 1.0 3.2 1

Generation capacity

wind

hydro CHP

electrolysis

PV

Gas turbines

Generation capacity (2) • Assumption on 100 %

renewable power and district heat system

• Capacity mix is a result of a separate optimization and used as input in this simulation

• Wind and hydropower based system

• Nuclear power was also not available in this scenario

Generation capacity (non-power)

• Wood-fired CHP and heat pumps as sources of heat

• Electrolysis (synthetic fuel generation) concentrated in Norway

0

200

400

600

800

1000

1200

1400

Norway - north Norway - south

MW

P2G

0

5

10

15

20

25

30

Denmark Finland Norway Sweden

Hea

t gen

erat

ion

capa

city

GW

country

heat boiler

heat storage

heat pump

CHP - wood

Results

Power generation

• Power generation is dominated by wind power and hydro power

WIND44 %

CONDENSINGBACKPR

3 %EXTRACTION

5 %

HYDRORES33 %

HYDRORUN10 %

SOLAR5 %

WIND

CONDENSING

BACKPR

EXTRACTION

HYDRORES

HYDRORUN

SOLAR

System kinetic energy in the 100 % renewable case

• Minimum kinetic energy (40 GWs) half of previous ENTSO-E (2016) study

0

50

100

150

200

250

300

350

0 2000 4000 6000 8000

kine

tif e

nerg

y [G

Ws]

hours per year

ENTSO-E 2025

base 2050

Reserves allocation • Heat pumps are

preferred because of their good availability

• Electrolysis geographically concentrated

• Wind and PV are possible as reserves but not used as much

0

100

200

300

400

500

600

aver

age

capa

city

(MW

)

FCR-D

FCR-N

Frequency nadir

48.8 49 49.2 49.4 49.6 49.8

Frequency nadir Hz

0

1000

2000

3000

4000

Hou

rs p

er y

ear

49.2 49.25 49.3 49.35 49.4 49.45 49.5

Frequency nadir Hz

0

1000

2000

3000

4000

5000

6000

Hou

rs p

er y

ear

0 50 100 150 200 250 300

Kinetic energy GWs

0.4

0.5

0.6

0.7

0.8

0.9

1

Freq

uenc

y dr

op H

z

0 50 100 150 200 250 300

Kinetic energy GWs

0.45

0.5

0.55

0.6

0.65

Freq

uenc

y dr

op H

z

Base case Wind inertia

Conclusion • 100 % Renewable Nordic power and heat sector modeled with new

reserve requirements • There was a considerably drop in the system kinetic energy minimum • Wind and solar power play only a small role in FCR-D • Single fault (1400 MW) lead to violation of the lowest allowed frequency

bound of 49.0Hz during 7 hours of the year – Increase of FCR-D to 1500 MW total was assumed

• When synthetic wind inertia was included, no violation of the allowed frequency bound took place

• Loads and EV’s were not considered as providers of FCR-D

Thank you