DC and AC coupling:
which one is the best solution?
1W.
Suponthana, 2V. Salas and 3W. Pokakul
1Leonics Co., Ltd. Thailand.
2UC3M PV-Lab, Universidad Carlos III de Madrid, Spain
3SERT, Naresuan University, Thailand
Phone: +66 8 1815 3787/+34 916248867
Email:
wuthipong@leonics.com/vicente.salas@uc3m.es/wilailuk@leonics.com
Agendas
-
DC and AC coupling PV energy of systems
Efficiency of each type
Which one is better, DC or AC coupling?
Load profile impact performance and energy cost
What is the best solution?
Real performance from system in operation
Conclusion
Agendas
-
DC and AC coupling PV energy of systems
Efficiency of each type
Which one is better, DC or AC coupling?
Load profile impact performance and energy cost
What is the best solution?
Real performance from system in operation
Conclusion
Stand-Alone PV system Design Concept using
DC Coupling : PV energy goes into system at DC Bus
Stand-Alone PV system Design Concept using
AC Coupling
:
PV
energy
goes
into
system
at
AC
Bus
AC coupling Stand Alone
PV-WT Hybrid System
Grid Connect Inverter
AC Bus
Bi-Directional Inverter
AC Load
Agendas
-
DC and AC coupling PV energy of systems
Efficiency of each type
Which one is better, DC or AC coupling?
Load profile impact performance and energy cost
What is the best solution?
Real performance from system in operation
Conclusion
AC Coupling VS DC Coupling
Day time system efficiency when PV supply Load
Efficiency from PV to supply load = 96%
AC coupling Stand Alone
PV-WT Hybrid System
Efficiency from PV to supply load = 93.1%
DC coupling Stand Alone
PV-WT Hybrid System
Charge Controller
Grid Connect Inverter
96%
Bi-Directional Inverter
Inverter
95%
AC Load
Real Load = Load + BDI Loss
98%
AC Load
AC Coupling VS DC Coupling
Day time system efficiency when PV charge battery
Efficiency of PV energy path
Efficiency of PV energy path
to charge Battery = 82.08%
to charge Battery = 88.2%
AC coupling Stand Alone
PV-WT Hybrid System
DC coupling Stand Alone
PV-WT Hybrid System
Charge Controller
Grid Connect Inverter
AC Load
98%
96%
Bi-Directional Inverter
Inverter
AC Load
95%
90%
88.20% from 100% of PV output
90%
82.08% from 100% of PV output
AC Coupling VS DC Coupling
Night time system overall efficiency when battery supply load
Efficiency from PV to battery and
Backcoupling
to supply load
= 74.07%
AC
Stand
Alone
PV-WT Hybrid System
Efficiency from PV to battery and
Back to
supply
load = 79.6%
DC
coupling
Stand Alone
PV-WT Hybrid System
Charge Controller
Grid Connect Inverter
98%
Bi-Directional Inverter
Inverter
AC Load
95%
AC Load
95%
95%
88.20% from 100% of PV output
95%
82.08% from 100% of PV output
Agendas
-
DC and AC coupling PV energy of systems
Efficiency of each type
Which one is better, DC or AC coupling?
Load profile impact performance and energy cost
What is the best solution?
Real performance from system in operation
Conclusion
-
Both of them are good in different times
DC coupling is better when PV is used to charge battery
AC coupling is better when PV is used to direct supply
load
System
Efficiency
Day time charge Day time supply Night time round
in to Battery
to Load
trip supply load
DC Coupling
88.20%
93.1%
79.60%
AC Coupling
82.08%
96.0%
74.07%
-
DC or AC coupling which one is better should be
effected by Load profile that the PV system operates.
Agendas
-
DC and AC coupling PV energy of systems
Efficiency of each type
Which one is better, DC or AC coupling?
Load profile impact performance and energy cost
What is the best solution?
Real performance from system in operation
Conclusion
Cost of Energy
from using DC or AC Coupling
when
Load Profiles are different
Simulated by using HOMER
1. Uses HOMER to simulate cost of energy
2. Same load energy consumption per day
3. Same PV power, Converter, Battery capacity
4. Change Load Profile
-
Flat Load,
-
High Day time Load,
- High Night time Load
5. Change PV configuration
- PV on AC bus
- PV on DC bus
PV AC Coupling
Cost of Energy
(USD/kWh)
PV AC coupling
PV DC Coupling
PV DC coupling
Flat Load
0.217
0.208
USD/kWh
0.425
USD/kWh
0.401
USD/kWh
USD/kWh
0.354
USD/kWh
USD/kWh
High Nigh time load
High Day time load
0.191
HOMER simulation with DC and AC coupling
with real village load profile
Agendas
-
DC and AC coupling PV energy of systems
Efficiency of each type
Which one is better, DC or AC coupling?
Load profile impact performance and energy cost
What is the best solution?
Real performance from system in operation
Conclusion
The Hybrid DC and AC coupling can benefit by using
better point of both PV at DC and AC coupling.
96%
Direct Supply load 96%
form AC Coupling
Balance fluctuation
of the Sun
98%
Direct Charge Battery 98%
From DC Coupling
The Hybrid DC and AC coupling can benefit by using
better point of both PV at DC and AC coupling.
Supply Night time Load
With efficiency 95%
form Battery
95%
Agendas
-
DC and AC coupling PV energy of systems
Efficiency of each type
Which one is better, DC or AC coupling?
Load profile impact performance and energy cost
What is the best solution?
Real performance from system in operation
Conclusion
Grid Connect Inverter
MPPT Charge Controller
Bidirectional Inverter
Grid Connect Inverter
MPPT Charge Controller
Bidirectional Inverter
MPPT Charge Controller
Bidirectional Inverter
A performance evaluation experiment on a
Hybrid DC and AC coupling to comparing system
efficiency using IEC 61724 concept has result as follow
𝜂𝑙𝑜𝑎𝑑 =
𝐸𝑢𝑠𝑒
𝐸𝑖𝑛
=𝐸
𝐸𝑓𝑟𝑜𝑚𝑃𝐶𝐸 +𝐸𝑡𝑜_𝐵𝐴𝑇𝑇𝑇
𝐴_𝑡𝑜𝑏𝑎𝑡𝑡 +𝐸𝐴(𝐷𝐶) +𝐸𝑓𝑟𝑜𝑚_𝐵𝐴𝑇𝑇
𝑃𝑅 =
𝑌𝑓
𝑌𝑟
=
(𝐸𝐴𝑡𝑜𝐿𝑜𝑎𝑑 +𝐸𝐴𝑡𝑜𝐵𝑎𝑡𝑡 . 𝜂𝐵𝐷𝐼+𝐸𝐴(𝐷𝐶) .𝜂𝑙𝑜𝑎𝑑)/𝑃𝑜
EA(AC)
EfromPCE
EA_toBatt EA_toLoad
EA(DC)
Eto_BATT
Efrom_BATT
EL(AC)
𝑌𝑟
EA(AC)
𝜂= 89%, PR = 69.64%
EL(AC)
Eto_BATT
Efrom_BATT
𝜂 = 90% , PR = 74.78%
EL(AC)
EA(DC)
Eto_BATT
Efrom_BATT
EA(AC)
𝜂 = 92% , PR = 75.54%
EL(AC)
EA(DC)
Eto_BATT
Efrom_BATT
New design approach
Hybrid DC-AC Coupling can improve system efficient 3-7% by
Use AC Coupling for Day time Load
Use DC Coupling to Charge Battery
for Night time Load
Design DC Couple side by using nigh time energy consumption
and AC Coupling side using day time energy consumption
Load Profile of haminadhoo
Night
0:00
160.14
1:00
Day
Pattern load
Real load
160.14
160.14
159.36
2:00
159.19
3:00
157.34
4:00
163.41
5:00
172.91
6:00
159.77
7:00
134.07
8:00
9:00
10:00
11:00
12:00
13:00
14:00
15:00
16:00
17:00
162.66
18:00
222.78
19:00
247.30
20:00
222.51
21:00
210.96
22:00
194.16
23:00
182.50
kWh
2,709.06
Ratio
70.20%
Average Load/h
Add Increase factory 40%
136.86
130.50
131.74
122.52
113.62
109.95
124.35
133.20
147.33
159.36
159.36
159.19
157.34
163.41
172.91
159.77
134.07
136.86
130.50
131.74
122.52
113.62
109.95
124.35
133.20
147.33
162.66
222.78
247.30
222.51
210.96
194.16
182.50
3859.13
159.19
157.34
163.41
172.91
159.77
134.07
136.86
130.50
131.74
122.52
113.62
109.95
124.35
133.20
147.33
162.66
222.78
247.30
222.51
210.96
194.16
182.50
3859.2
247.30
160.8
1,150.07
29.80% Peak power
160.80 Cal Average
225.12 kWh per hours
182.5
194.2
211.0
222.5
247.3
222.8
162.7
147.3
133.2
124.4
110.0
113.6
122.5
131.7
130.5
159.8
134.1
0.00%
136.9
Real load Profile
172.9
163.4
157.3
159.2
159.4
200.00
kW
100.00%
% of Fuel
160.1
300.00
% pf PV
Produce CO2
-
kg/day
100.00
Irra di a ti on
Ambi ent Temp.
6.37 kWh/m2.da y
o
31.8 C
0.00
247.30 kW
Pea k Loa d
160.80 kW/h
Aver. Loa d
Tota l Loa d
3859.20
kWh/Da y
Grid Connected Inverter
# of Inverter
Bidirectiona Inverter
300.00
Ba ck Up DG Power ra ti ng
Cons ume Di es el Fuel
Fuel Cons umpti on ra te
250 kW
3 Uni ts
Uni ts
1 units
300.00 kW
700.00 kWp
2
5967.50 m
AC Coupling PV
Li ters /da y
0.28 Liter/kWh
Installation Area
MPPT charger
Ba ttery
8
Uni ts
9000.00 Ah
480 Vdc
240.00 Cel l s
Annua l Loa d Energy cons umpti on
Annua l Energy genera ted form PV
5.95 Yea rs
Expect Ba tt Li fe
Annua l Di es el fuel cons umpti on
0.347
Repl a ce fuel @ Energy Pri ce
500.00 kWp
2
4262.50 m
DC Coupling PV
Installation Area
IPP
Annua l Di es el fuel reducti on
Annua l Di es el fuel a mount s a vi ng
Tota l Inves tment
Si mpl e Pa y ba ck peri od
Project Li fe
Confi denti a l i nforma ti on, thi s hybri d mi ni gri d des i gn i s property of Leoni cs Co., Ltd., ma y not reproduce wi thout pri o noti ce to Leoni cs Co., Ltd.
Project IRR reduce us e of fuel
Averag daily system operation condition and consumptions
Site Name : TG. La bi a n
Site Location (Lat./Long.) :
Project Owner :
Des i gn by
Wuthipong
:
S.
Vers i on/Rev. :
1A
Da te
:16-Sep-14
Al ti tude :
10.19%
5.18
Meter (ASL)
IPP
o
N
1,408,608
1,901,181
0.340
0
0
2,747,641
5.62
18
kWh
kWh
Li ters
USD/kWh
Li ters
USD
USD
Yea rs
Yea r
9.69%
%
o
119.24 E
MW scale Stand-Alone Hybrid Mini-Grid System
(PV) = Photovoltaic Module,
(B) = Battery,
(I)
= BDI + GCI,
(DG) = Diesel Generator
X.xx
MW
Total Power of INV+DG+PV
T&C 25-Jan-14
MW
T&C 14-Nov-12
MW
3.45
3.30
Kema
850 kWp (PV)
850 kW (I)
4,800 kWh (B)
1600 kW (DG)
MW
4.93
Bario
906 kWp (PV)
1,100 kW (I)
3,860 kWh (B)
1,443 kVA (DG)
4.45
MW
T&C 19-Nov-12
Banggi
1,200 kWp (PV)
2,075 kW (I)
2,880 kWh (B)
1,650 kVA (DG)
Tanjung Labian
1,212 kWp (PV)
1,650 kW (I)
4,320 kWh (B)
1250 kW (DG)
4.45
MW
Tg. Labian
Grid Connect
Inverter
250kW x 3 = 750kW
Bi-directional
Battery Inverter
300kW x 3 = 900kW
Diesel Generator
350kW 500kW 500kW
GS
GS
MPPT Charge
Controller
70 kW x9 = 630kW
PV on AC Coupling
Remote Station
255 kWp (Phase 2)
PV on AC Coupling
750 kWp
Battery
480Vdc 4,320 kWh
PV on DC Coupling 512 kWp
GS
Grid Connect
Inverter
75kW x 3 = 225kW
Grid Connect
Inverter
250kW x 3 = 750kW
Bi-directional
Battery Inverter
300kW x 3 = 900kW
Diesel Generator
350kW 500kW 500kW
GS
GS
4.93
PV on AC Coupling
Remote Station
MW
Banggi
Battery
480Vdc 720 kWh
Battery
480Vdc 2,880 kWh
MPPT Charge
Controller
70 kW x3 = 210kW
GS
Main Contractor : USAHA SIRIMAS SDN. BHD.
COD on
: 25 January 2014
BDI 3
BDI 2
BDI 1
Charge Controller
GCI 1
GCI 2
GCI 3
SMU 1
HCCU
ISC
DC Combiner
Battery Bank 3
Battery Bank 1
Battery Bank 2
AC Bus Combiner
MV TF 1
MV TF 2
Agendas
-
DC and AC coupling PV energy of systems
Efficiency of each type
Which one is better, DC or AC coupling?
Load profile impact performance and energy cost
What is the best solution?
Real performance from system in operation
Conclusion
Conclusions
-
Both DC and AC coupling are good in different time
DC coupling is better when using with high nigh time load
AC coupling is better when using directly supply load at day time
The best performance is using both DC and AC coupling together
in a PV system.
Load profile is useful in determining portion of DC and AC
coupling to supply energy to PV system
The performance of Hybrid DC and AC coupling is higher than DC
or AC coupling only in a PV system
Real plant performance designed by using Hybrid DC and AC
coupling confirm the calculation and simulation.
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Children in Papua, Indonesia at the moment that they have electricity, Dec 2012