Azadeh Kamjoo

Alireza Maheri

Ghanim Putrus

Arash Dizqah

School of Computing Engineering and Information Sciences

Northumbria University

Newcastle upon Tyne, UK

Email: azadeh.kamjoo@northumbria.ac.uk

OPTIMAL SIZING OF GRID-CONNECTED HYBRID WIND-PV

SYSTEMS WITH BATTERY BANK STORAGE

Outline:

Introduction

Hybrid Renewable Energy Systems (HRES) Components

Design of HRES

Energy Flow in Grid-connected HRES with a Battery

HRES Components & Design Data

Model Development

Optimisation Problem & Design Scenarios

Case Study- Kent, UK

Results

Conclusions

Drivers

Climate changes and greenhouse effect

Global increase in electricity demand

Limitations in Fossil fuel resources

Remote places with no Grid

connection

Renewable energy resources

available, green and free

Find other energy resources Climate dependent & unpredictable

Wind Solar

Use more than one renewable energy resource

With a proper backup system such as DG or battery bank

Hybrid Renewable

Energy Systems

(HRES)

Introduction

Hybrid Renewable Energy Systems (HRES) Components:

HRES

Power production sources

Renewable- based

Non renewable- based

Wind

Solar Thermal

PV

Backup Auxiliary

Grid connected

Stand-alone

Battery bank Hydrogen

Diesel generator

Hydro

Storage

Ground Source

Design Inputs

Load profile

Meteorological data (Solar irradiance and wind speed)

Wind turbine, PV system and battery bank technical specifications

Grid electricity prices (peak and off-peak hours)

Feed-in tariffs (if applicable)

Design of HRES

Design Candidates Analysis

Components modelling

Cost Analysis

Optimisation process and choosing the best (optimum) solution

Energy Flow in Grid-Connected HRES with a Battery

Load

Scenario1:

a) From PV and WT towards the load

b) Sell the surplus to the grid

c) Buy the shortage from grid

(off-peak and peak)

Scenario2:

a) From PV and WT towards the load

b) Charge the battery with excess

power

c) Sell the excess to the grid if the

battery is charged

d) Use grid for power shortage in off-

peak hours and battery for

shortages in peak hours

HRES Components & Design Data

HRES Components

Deterministic

Design Methodology

Under uncertainties

Stand-alone

System Type

Grid-connected

Return On Investment

Assessment Criteria

Reliability

Model Development

To Analyse the overall HRES performance the individual components need to be modelled:

Wind Turbine

PV Panel

Battery Bank

HRES Components Modelling:

Economic Analysis:

Income Modelling

Cost Modelling

Return On Investment

wtwpwtAVCρP 3

2

1

Wind Turbine Model

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 210

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Wind Speed (m/s)

Po

wer

Co

eff

icie

nt

(Cp

)

HRES Components Modelling: Wind Turbine System

: Wind’s available power

: Air density

: Power coefficient

: Hourly average wind speed

: Rotor disk area

pC

wtP

wV

wtA

0

ref

0

hub

refw

z

zln

zz

ln

VV

PV Panel Model

PVPVPVηAIP

HRES Components Modelling: PV Panel System

I : Horizontal irradiance

: PV panel’s area

: efficiency of the PV arrays

PVA

PV

Battery Bank Model

bat

Cbat

C

ttItSOCtSOC

)((t))1)(()1(

bat

bat

C

ttItSOCtSOC

)((t))1)(()1(

V

tPtPtPtI loadwtPV

bat

)()()()(

V

tPtPtPtI wtPVload

bat

)()()()(

t

cSOCtSOCtSOCSOCcCItI batbat

)1)()(())(((,min,0max)( min

maxmaxmax,

HRES Components Modelling: Battery Bank

While discharging

While charging

where

where

with constraint of:

Economic Analysis:

Cost Modelling

Initial Capital Cost

Replacement Cost

O & M Cost

Cost of Buying Elec. from Grid

Income Modelling

Feed-in Tariff

Selling Elec. to Grid

Return On Invest.

grid,SellFIT IITI

gridbuyMOrepIC CCCCTC ,&

Optimisation Problem and Design Scenarios

Design scenario1: The power shortage will be maintained from grid in off-peak

and peak hours

Design Scenario2: The power shortage will be maintained from grid in off-peak

hours and from battery bank during peak hours

,PPP

,PPP

gridPVwt

PVwt

HRES_Total

Bat

grid

PVWT

PVWT

HRESTotal

P

PPP

PP

P

,

_

100TC

TCTIROImax

The optimisation problem can be formulated as:

If power generated by wind turbine and PV is sufficient to

cover the load demand.

If power generated by wind turbine and PV is insufficient to

cover the load demand.

If power generated by wind turbine and PV is sufficient to

cover the load demand.

If power generated by wind turbine and PV is insufficient to

cover the load demand during off-peak hours

If power generated by wind turbine and PV is insufficient to

cover the load demand during peak hours

Case Study( Kent, UK)- Design Inputs

COMPONENTS DESIGN PARAMETERS

Efficiency

(%)

Lifetime

(year) Initial Cost O&M Cost

Interest

Rate(%)

Inflation rate

(%)

Feed-in Tariff

(c/kWh)

PV panel 12.3 25 600 ($/m2) 1% of price 8 4 27

WT 20 700 ($/m2) 3% of price 8 4 44

Battery Bank 90 8 1.5 ($/Ah) 1% of price 8 4 -

BATTERY BANK’S SPECIFICATION

Nomial Capacity

(Ah)

Nominal Voltage

(V)

DOD

(%)

Number of

Cycles

Battery

Bank40 24 90 535

Components technical and economical data

Average solar radiation data

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 240

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

Hour

So

lar

Irra

dia

nce

(W

/m2

)

Apr

May

Jun

Jul

Aug

Sep

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 240

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

Hour

So

lar

Irra

dia

nce (

W/m

2)

Jan

Feb

Mar

Oct

Nov

Dec

Average wind speed data

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 240

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Hour

Win

d S

pee

d (

m/s

)

Apr

May

Jun

Jul

Aug

Sep

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 240

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Hour

Win

d S

peed

(m

/s)

Jan

Feb

Mar

Oct

Nov

Dec

Load profile

0 1 2 3 4 5 6 7 8 9 1011121314151617181920212223240

400

800

1200

1600

2000

2400

2800

3200

3600

4000

Hour

Dem

and

(W)

Summer

Winter

Grid electricity prices

GRID ELECTRICITY PRICES IN UK

GridStandard Tariff

(c/kWh)

First 900kWh 29

Consumptions after

first 900kWh17

Selling electricity to

grid (c/kWh)5

OPTIMUM CONFIGURATION OF EACH PRICE RATE

Peak price/Off-peak

price

WT Rotor Disk

Area (m2)

PV Panel

Area(m2)

Number of

Batteries

Grid Supply

for Peak hour

1.1 28.27 0 0 Yes

1.3 28.27 0 0 Yes

1.5 40.72 0 0 Yes

1.7 40.72 0 0 Yes

1.9 40.72 0 0 Yes

2.1 40.72 0 0 Yes

2.3 40.72 0 32 No

2.5 40.72 0 32 No

2.7 40.72 0 32 No

2.9 40.72 0 32 No

Standard electricity tariff in off-peak and peak hours in UK.

The HRES is designed under different assumptions for the peak hours price.

Below table shows the optimum solution for each of peak price assumption.

Results- Optimum Config. Under 10 different Peak hour Tariffs

PV Area vs. HRES Performance and Cost

0

100

200

300

400

40

50

60

701

2

3

4

x 105

PV Area (m2)WT & PV total sharein load satisfaction

Co

st

No PV in optimum configuration of any peak hour price assumptions.

The wind power is dominant in the desired site.

The figure shows the effect of adding PV panel on a sample for wind turbine with overall share of

45% in load satisfaction. It can be seen that by increasing the area of PV arrays from zero to 400 m2

the HRES share increases by 25% in the load demand satisfaction while the total cost of system

increases significantly

Results – Economical & Technical Aspects of Adding PV Panel

Adding 400 m2

of PV panel is capable of

adding 25% to produced

power of HRES which is

not cost effective comparing

to other configurations

without PV panel.

Peak price tariffs can be divided into three categories:

• Peak Prices<= 1.3Off-peak hours

The wind turbine size is small

The shortage is obtained from grid in off-peak and

peak hours

•1.3<Peak Prices< 2.3Off-peak hours

Larger wind turbine

Less power from grid in off-peak and peak hours.

• Peak Prices>= 2.3Off-peak hours

The battery bank is added for peak hours shortage

The grid provides the power shortage in off-peak

hours

Results- Resources Share Vs. Peak Hour Tariffs

Share vs. Peak Hour Price Rate

1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 30

10

20

30

40

50

60

70

80

90

100

Peak Hour Price/Off-peak hour Price

Sh

are

(%)

Battery Bank

Grid

Wind Turbine

(1) Peak price=1.1 Off-peak (2) Peak price=1.9 Off-peak (3) Peak price= 2.3 Off-peak

5 5.25 5.5 5.75 6 6.25 6.5 6.75 7 7.25 7.5

x 104

0

10

20

30

40

50

60

70

80

90

100

Share

(%

)

Total Cost ($)

5 5.25 5.5 5.75 6 6.25 6.5 6.75 7 7.25 7.5

x 104

0

10

20

30

40

50

60

70

80

90

100

Retu

rn o

n I

nvestm

ent

(%)

Battery Share

Grid Share

Renewable Share

ROI

6.85 6.9 6.95 7 7.05 7.1 7.15 7.2 7.25

x 104

0

10

20

30

40

50

60

70

80

90

100

Sh

are

(%

)

Total Cost ($)

6.85 6.9 6.95 7 7.05 7.1 7.15 7.2 7.25

x 104

0

10

20

30

40

50

60

70

80

90

100

Retu

rn o

n I

nv

estm

en

t (%

)

Battery Share

Grid Share

Renewable Share

ROI

6.9 6.95 7 7.05 7.1 7.15 7.2 7.25 7.3 7.35 7.4 7.45 7.5

x 104

0

10

20

30

40

50

60

70

80

90

100

Sh

are

(%

)

Total Cost ($)

6.9 6.95 7 7.05 7.1 7.15 7.2 7.25 7.3 7.35 7.4 7.45 7.5

x 104

0

10

20

30

40

50

60

70

80

90

100

Retu

rn o

n I

nv

estm

en

t (%

)

Battery Share

Grid Share

Renewable Share

ROI

Comparison between two best solutions of three different Peak prices

The figure shows that at peak tariffs less than 1.5 there is no justification to add the battery

bank.

As the peak hour price increases to 1.5 times the off-peak hour the configuration with batteries

appear as the second best options yet not the best one.

The configuration with the battery bank becomes the optimum configuration when the peak

hour price reaches to 2.3 times more than the off-peak hour price.

Results- Comparison Between 2 Best Config. Of 3 Peak Hour Tariff

The produced power of each source for typical months

Hour (February)

Pow

er (W

)

0 1 2 3 4 5 6 7 8 9 10 11 1213 14 15 16 17 18 19 20 21 22 23 240

500

1000

1500

2000

2500

3000

3500

4000

Demand

WT Power

Battery Power

Grid Power

Hour (October)

Pow

er (W

)

0 1 2 3 4 5 6 7 8 9 1011 12 13 1415 16 1718 19 20 2122 23 240

500

1000

1500

2000

2500

3000

3500

4000

Demand

WT Power

Battery Power

Grid Power

Hour (November)

Pow

er (

W)

0 1 2 3 4 5 6 7 8 9 1011 12 13 14 1516 17 18 19 2021 22 23 240

500

1000

1500

2000

2500

3000

3500

4000

Demand

WT Power

Battery Power

Grid Power

Hour (December)

Pow

er (

W)

0 1 2 3 4 5 6 7 8 9 10 11 1213 14 15 16 17 1819 20 21 22 23 240

500

1000

1500

2000

2500

3000

3500

4000

Demand

WT Power

Battery Power

Grid Power

• The battery bank is used in four months of the year in which the wind speed is low.

• In other months either the wind turbine produces sufficient power or the shortage occurs in off-

peak hours and the shortage is maintained from the grid.

Results- Demand & Power Of Each Resource

• Based on desired site meteorological characteristic adding a renewable

resource may not be economically viable. (Ex. PV panels in current case study)

• Different prices at different hours requires development of new design methods

in grid-connected HRES, where the grid is required to provide electricity

during the shortage hours.

• At some grid electricity prices adding the battery may have no justification

• Adding a small storage system to cover the electricity shortage during peak

hours can be a good solution at peak hour tariffs.

• The outcome of the design would be economically more profitable

• The HRES owner would be less dependent on the grid.

Conclusions

Thank You.