Building Research Establishment 20 th June 2007 Integrating a large solar array to enhance the performance of a low energy building. - A Case Study Keith

Building Research Establishment 20th June 2007

Integrating a large solar array to enhance the performance of a low energy building.

- A Case Study

Keith Tovey ( 杜伟贤 ) M.A., PhD, CEng, MICE, CEnvHSBC Director of Low Carbon Innovation: and Charlotte Turner: School of Environmental SciencesCRed

Why go Solar PV?

Original buildings

Teaching wall

Library

Student residences

Nelson Court

Constable Terrace

Low Energy Educational Buildings

Elizabeth Fry Building

ZICER

Nursing and Midwifery

School

Medical School

Medical School Phase 2

• The ZICER Building

• The Solar Arrays

• Performance of PV

• Issues of Shadowing

• Electrical Integration

• Economic Issues

• Life Cycle Issues


ZICER Building

Heating Energy consumption as new in 2003 was reduced by further 50% by careful record keeping, management techniques and an adaptive approach to control.Incorporates 34 kW of Solar Panels on top floor

Low Energy Building of the Year Award 2005 awarded by the Carbon Trust.

Two large open plan offices: Note: extensive use of computers

• Top floor is an exhibition area – also to promote PV

• Windows are semi transparent

• Mono-crystalline PV on roof ~ 17 kW in 10 arrays

• Poly- crystalline on façade ~ 6/7 kW in 3 arrays

ZICER Building

0

500

1000

1500

2000

2500

3000

3500

Jan Apr Jul Oct Jan Apr Jul Oct

2004 2005

kWh

Façade Roof

ZICER Building PV performance

Façade (kWh) Roof (kWh) Total (kWh)

2004 2650 19401 22051

2005 2840 19809 22649

Summer day (27th June 2005)

0

5

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25

05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20

Time of Day (starting time)

PV

(A

C)

ou

tpu

t (k

Wh

)

0100

200300

400500600

700800

9001000

Mea

n R

adia

tio

n (

W/m

2 )PV Output Solar Radiation

Cloudy Summer day (04/05/2005)

0.0

0.5

1.0

1.5

2.0

2.5

05 07 09 11 13 15 17 19


PV

AC

ou

tpu

t (k

Wh

)

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100M

ea

n r

ad

iati

on

(W/m

2 )PV OutputSolar Radiation

Winter Sunny Day (19th Jan 2005)

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08 09 10 11 12 13 14 15 16


PV

(A

C)

ou

tpu

t (k

Wh

)

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1400

Mea

n R

adia

tio

n (

W/m

2)

PV output

Solar Radiation

Performance of PV cells on ZICER

0%

2%

4%

6%

8%

10%

12%

14%

16%

Jan Mar May Jul Sep Nov Jan Mar May Jul Sep Nov

2004 2005

Lo

ad

Fa

cto

rfaçade roof average

0

2

4

6

8

10

12

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16

18

Jan Mar May Jul Sep Nov Jan Mar May Jul Sep Nov

2004 2005

kWh

/ m

2

Façade Roof

Load factors

Façade:

2% in winter

~8% in summer

Roof

2% in winter

15% in summer

Output per unit area

Little difference between orientations in winter months


0

2040

6080

100120140

160180200

9 10 11 12 13 14 15Time of Day

Wh

01020

3040506070

8090100

%

Top Row

Middle Row

Bottom Row

radiation

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9 10 11 12 13 14 15Time of day

Wh

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%

Block1

Block 2

Block 3

Block 4

Block 5

Block 6

Block 7

Block 8

Block 9

Block 10

radiation

All arrays of cells on roof have similar performance respond to actual solar radiation

The three arrays on the façade respond differently


0

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8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00

Elev

ation

in th

e sky

(deg

rees)

120 150 180 210 240Orientation relative to True North

0

5

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25

6.00 7.00 8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00Time (hours)

Elev

ation

in th

e sky

(deg

rees)

January February March AprilMay June July AugustSeptember October November DecemberP1 - bottom PV row P2 - middle PV row P3 - top PV row

0

5

10

15

20

25

8.00 9.00 10.00 11.00 12.00 13.00 14.00 15.00 16.00

Time (hours)

Elev

ation

in th

e sky

(deg

rees)

January February November DecemberP1 - bottom PV row P2 - middle PV row P3 - top PV row

Arrangement of Cells on Facade

Individual cells are connected horizontally

As shadow covers one column all cells are inactive

If individual cells are connected vertically, only those cells actually in shadow are affected.

0

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7000

(Jan ) 1 (Mar) 11 (May) 21 (Aug) 31 (Oct) 41 (Dec) 51

Time (week number)

Ele

ctri

city

use

d/ge

nera

ted

(kW

h)

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70

PV

per

cent

age

of th

e to

tal e

lect

rici

ty u

sage

Electricity from conventional sources PV electricity PV % of total


0

1

2

3

4

400 600 800 1000 1200 1400

Annual Average Solar Radiation (kWhm-2yr-1)

PC

cos

t (£

/kW

h) A

B

C

D

E

F

• (A) Actual ZICER costs – no grant• (B) Actual ZICER costs – with grant of £172 000• (C) Avoided costs (ZICER) – no grant• (D) Avoided costs (ZICER) with grant of £172 000• (E) Average EU costs in 2006• (F) as E with 50% capital grant

Performance of PV cells on ZICERCost of Generated Electricity

Actual Situation excluding Grant

Actual Situation with Grant

Discount rate 3% 5% 7% 3% 5% 7%

Unit energy cost per kWh (£) 1.29 1.58 1.88 0.84 1.02 1.22

Avoided cost exc. the Grant

Avoided Costs with Grant

Discount rate 3% 5% 7% 3% 5% 7%

Unit energy cost per kWh (£) 0.57 0.70 0.83 0.12 0.14 0.16

Grant was ~ £172 000 out of a total of ~ £480 000

Performance of PV cells on ZICERCost of Generated Electricity

• Peak Cell efficiency is ~ 9.5%.

• Average efficiency over year is 7.5%

Mono-crystalline Cell Efficiency Poly-crystalline Cell Efficiency

Efficiency of PV Cells

• Peak Cell efficiency is ~ 14% and close to standard test bed efficiency.

• Most projections of performance use this efficiency

• Average efficiency over year is 11.1%

Inverter Efficiencies reduce overall system efficiencies to 10.1% and 6.73% respectively

Comparison of other PV Systems

LocationMonitoring

Period

System Efficiency

(%)Source

Northumberland Building, University of Northumbria.

1995-1997 8.1 Pearsall

Solar Office Doxford International, Sunderland, UK

Mar 1998-May 2000

7.5-8 Jones

Jubilee Campus, Nottingham University, Nottingham, UK

Sept 2000-Aug 2001

8Riffat and

Gan

Eco Energy House, Nottingham University, Nottingham, UK

Sept 2000-May 2002

3.6 Omer et al.

Gaia Energy Centre, Delabole, Cornwall, UK

Jan 2003-June 2003

9-10 DTI

PV Domestic Installations, UK (Average of six systems)

12 – 25 months8.2 (range

6.5-10.4)Pearsall and

Hynes

ECOS Millennium Environmental Centre, Ballymena, Northern Ireland

Dec 2000-Dec 2003

7.7Smyth and

Mondol

Performance of Photo Voltaic Array

Inverters are only 91% efficient

Most use is for computers

DC power packs are inefficient typically less than 60% efficient

Need an integrated approach

Life Cycle Issues

Embodied Energy in PV Cells (most arising from Electricity use in manufacture) 3230 2750

Array supports and system connections 285 285

On site Installation energy 131.4 131.4

Transportation Spain > Germany > UK11250 vehicle-kilometres

453.2 453.2

Total MWh/kWp 4.1 3.4

Mono-crystalline

(kWh/kWp)

Poly-crystalline

(kWh/kWp)

Energy Yield Ratios

Mono-crystalline Cells 20 25 30

As add on features 3.2 3.8 4.6

Integrated into design 3.5 4.2 5.4

Life Time of cells (years)

Conclusions

• Economics of PV was only viable on ZICER because of Grant• Shading has some effect on façade, but improvements could be

made by different method of wiring cells• Overall Load Factor is 7.6% with 8.3% on roof and 4.7% on

façade. In summer Load Factor can reach 15%.• 9% of electricity is lost in inverters, and a further 50 – 60% is

lost in IT equipment.• Need to consider an integrated approach – possibly with DC

networks in similar buildings.• Important to use actual rather than test bed efficiencies in

design appraisal• Energy Yield Ratios are lower than many other forms of

generation. Long transportation distances associated with PVs do not necessarily lead to a low embodied carbon requirement.


Building Research Establishment 20th June 2007


- A Case Study


Why go Solar PV?

Documents

Building Research Establishment 20 th June 2007 Integrating a large solar array to enhance the performance of a low energy building. - A Case Study Keith