performance and economic study of interconnected pv system with
TRANSCRIPT
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
1/31
1
Faculty of Engineering, Elminia University,
Elminia, Egypt
Performance and Economic Study ofInterconnected PV System with Electric
Utility Accompanied with Battery Storage
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
2/31
2
This paper presents a complete study from economic and
reliability point of view to determine the impact of
interconnecting PVPS with electric utility, EU taking into
consideration battery storage, BS, all radiation and variation of
the load demand during the day. Three different configurations of
PVPS have been investigated. The first PVPS is stand-alone
PVPS accompanied with BS. The second PVPS is PVPS
interconnected with EU without BS. Grid-connected PVPS
accompanied with BS represents the third alternative.
Object of this paper
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
3/31
3
A comparative study between these three different configurations
has been carried out from economic and reliability points of view
with the main goal of selecting suitable one, to be installed atZafarna site to feed the load requirement. A simulation is carried
out over one year using the hourly data of the load demand,
insolation and temperature at Zafarna site, Egypt as a case study.
System ConfigurationThe electrical power generated and terminal voltage of PV module
depends on solar radiation and ambient temperature. The
equivalent electrical circuit describing the solar cells array used inthe analysis is shown in Fig. 1.
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
4/31
4
Fig.1 Equivalent circuit of PV solar cells array.
The mathematical equation describing the I-V
characteristics of a PV solar cells array is given by:
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
5/31
5
where, I(t)- is the output current, Amp, V(t) is the output voltage,
Volt, A is the ideality factor for p-n junction, T(t) is the
temperature, Kelvin, K is the Boltzman's constant in Joules per
Kelvin, and, q is the charge of the electron in Coulombs. Rsh is
the internal shunt resistance, and Rs is the series resistance.
Io(t) : The hourly reverse saturation current, Amp. This current
varies with temperature as follows:
shR
sR*I(t))t(V
)t(+
+
=
1
T(t)KA
sR*I(t)V(t)q
expoIph(t)II(t)
( ) ( )
= 1/T
r1/T
I/K
goE*qexp
3
rT(t)/TorI)t(o
I
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
6/31
6
Iph(t) : The hourly generated current of solar cells module. This
current varies with temperature according to the following equation:
where, Tr is the reference temperature, oK, Ego is the band-gapenergy of the semiconductor used in solar cell array, KI is the
short circuit current temperature coefficient, and, Ior is the
saturation current at Tr, Amp. (t) is the average hourly
radiation on the tilted surface, kW/m2. Isc is the PV cell short-
circuit current at 25o C and 100 mW/cm2.
The output of the solar cell module can be calculated by the
following equation:
100/)t(T
H*298)))t(T(I
Ksc(I)t(
phI +=
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
7/31
7
)t(I*)t(V)t(out,pv
P =
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
8/31
8
The energy balance between the load and the output of PV system must be
carried out to compute the optimum number of PV modules, Npv. The
output power from PV system must satisfy the load power demand. The
hourly generated power, Ppv,out(t), and hourly load power, PLoad(t), are
compared with each other. If Ppv,out(t) is larger than the load power
demand then there is an hourly surplus power, but if Ppv,out(t) is smaller
than the load power demand then there is an hourly deficit power. At any
value of Npv, if the summation of hourly surplus power equals to thesummation of hourly deficit power then this value of Npv represents the
optimum number of PV modules. The following equations have been used to
get the optimum number of PV modules [7].
Calculation of Optimum Number of PV Modules
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
9/31
9
08760t
1t
)]t(Load
P)t(out,pv
P*pv
N[=
=
>IF
Then, number of PV modules must be decreased by one module
and repeating the foregoing process[7]:
08760t
1t
)]t(LoadP)t(
out,pvP*
pvN[=
=
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
10/31
10
Then, Npv is the optimum number of PV modules satisfies the
energy balance condition.2-2 Sizing of BS
The size of battery bank in a stand-alone PVPS, PVPS
interconnected with EU accompanied with or without BS is
dependent on three main factors [8], [9]:-
The number of hours that the battery bank should provide the
critical load without input from PV system or EU.
The depth of discharge of the battery strongly depends on the
applications, and can vary from a few percent to as much as
80%. i.e. the energy can be taken from BS equal to 80% of itscharge.
The total ampere of the critical load current.
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
11/31
11
For stand-alone PVPS, the battery storage capacity can be
found as follows:
( ) )*bat
/()deficit(Min)Surplus(MaxPV
BS =
For PVPS interconnected with EU, the size of battery bank can
be expressed by the following Equation:
)*bat
Tcri/(*criticalL,
PEU
BS =Where;
PL,critical : The maximum critical load in the period Tcri. Tcri:The number of hours that the battery bank should provide the
critical load without input from PV system or EU. :The depthof discharge of the battery in percent. bat: The efficiency ofBS.
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
12/31
12
The major concern in the design of an electric power system that
utilizes renewable energy sources is the accurate selection of
system components that can economically satisfy the load
demand. The system's components are found subject to [10]:
1. Minimize the cost of electricity production ($/kWh).2- Ensure that the load is served according to a certain reliability
criteria.
3- Minimize the power purchased from the grid.
To evaluate the economics of the PV system, a Life Cycle Cost,
LCC methodology has been applied to obtain the ECF over life
span of PV system.
Calculation of Energy Cost Figure
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
13/31
13
The ECF is derived as the ratio of annual payment and annual
energy output of PVPS and it can be written as follows:
PVPSofoutputEnergy/APECF =Calculation of Reliability
Reliability issue has been considered as an important step in any
system design process. Generally, reliability is defined as the
probability that an item of power system component will performits specified function without failure for a specific period of time or
number of cycles [12].
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
14/31
14
Figure 2-a represents the layout block diagram of
PV/EU accompanied with BS, while Fig. 2-b shows
the reliability block diagram of grid-connected PVPS
system accompanied with BS. From Fig. 2-a and Fig.2-b the reliability of each configuration under study
can be calculated as follows:
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
15/31
15
U t i l i t yI n t e r f a c e
z
PVarray
(A)
T.L.(d)
132/66
C.B.(a)
Trans..
(b) C
.B
.(c)
Generation
Station(G)11
/132
C.B.(e)
Trans..
(t)C.B.(f)C.B.(h)
Trans..
(g)
Subsyste
m(1)
Subsyste
m(1)
Radiation
(I)
Inverter
(D)
C.B
.(E)
Trans..
(F)
Trans..
(O)
0.4/11
Distrib
Panal(L o a d
C.B.
(M)
C.B.(N)
C.B.(J)C.B.(K)
T.L.(
L)
Volatge
Regulator(V)
C.B.(B)
(S)
ControlUnit
(C)
K
L
M
N
O
H
L o a d
G
a
b
c
d
e
t
h
z
y
REU
I
A
B
C
D
E
F
J
V
S
P o w e rS w i t c h
y
Fig. 2
a : Block Diagram of
PVPS/EU accompanied
with BS.
b : System Reliability Block
Diagram of PVPS/EU
accompanied with BS.
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
16/31
16
Reliability of Stand-alone PVPS.
From Fig. 2-a & Fig. 2-b the reliability of PVPS accompanied with
BS can be calculated as follows:-
[ ]3
R)2
R1)(1
R1(1BS/PV
R =
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
17/31
17
Where;
R1=RI RA RB , R2=RI RA RB RV RS , R3= RC RD RE RF RJ
RK RL RM RN RO RH,RI : Reliability of the Irradiance= Probability(I Imin), RA :Reliability of the PVPS array, RB : Reliability of circuit breaker=
RE=RJ= RK= RM=RN= Ra= Rc= Re= Rf= Rh , RV : Reliability
of the Regulator, RS : Reliability of the Battery storage, RC :Reliability of the DC switch, RD : Reliability of the inverter, RF :
Reliability of the transformer= RO= Rb = Rt= Rg, RL :
Reliability of the transmission line, RH : Reliability of the
distributed panel.
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
18/31
18
Reliability of PVPS interconnected with EU.
From Fig. 2-a and Fig. 2-b the reliability of PVPS interconnectedwith EU can be calculated as follows:-
g3
R)
g2
R1)(
g1
R1(1
EU/PV
R
=
Where;
R1g= RG Ra Rb Rc Rd Re Rt Rh Rz Ry
R2g = RI RA RB RC RD RE RF RJR3g = RK RL RM RN RO RH
Rz: Reliability of power switch, Ry: Reliability of utility
interface.
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
19/31
19
Reliability of grid-connected PVPS accompanied withBS.
Also, from Fig. 2-a and Fig. 2-b the reliability of PVPS
interconnected with EU accompanied with BS can be
calculated as follows:-
[ ] 4R)g1R1)(PVBSR1(1BS/EU/PVR =
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
20/31
20
1.Applications and Results
A new proposed computer program has been used based on the
above methodology for calculating optimum design of stand-
alone PVPS with BS, PVPS interconnected with EU without BS,and PVPS interconnected with EU accompanied with BS.
The input data of this program are:
1. Hourly radiation, kW/m2.The average radiation of the horizontal surface and the ambient
temperature for the selected site has obtained from the Egyptian
Metrological Authority for Zafarna site.
2- Characteristics of PV module ASE-300-DGF/17 type [14].
3-Site latitude, Degrees.
Zafarna site is located on the western coast of the Seuz Gulf,
latitude 29.07o N and longitude 31.36o E, Egypt.
4- Hourly load demand, kW.
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
21/31
21
The price of selected components.
Price of PV solar module =$2/Wp, Price of Batteries=$120/kWh,
Price of Inverter= $400/kW, Price of Regulator= $100/kW, Price
of electrical Equipment = 10% of PV modules cost, Price of
Civil work = 10% of PV modules cost, Annual fixed cost of
O&M of PV=1% of Pv system cost [11].
Economic assumptions as follows:
Interest rate of 8%, General inflation 3%, Real discount
rate=interest rate-General inflation=5% [11].
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
22/31
22
1- Optimum number of PV modules.
The outputs of this program are:
The output of the proposed computer program is the optimum
total number of PV modules, number of series modules per string,
and finally number of inverter units. Total Number o
Modules=14760, Number of series Modules/string=20, Number
of parallel strings/subsystem=18, Number of Modules
/subsystem=360, Number of inverter units=41 with its rating o
100kW.
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
23/31
23
Battery Sizing
A battery with capacity of 1312 Ah and nominal voltage of 24V
was used in this study.BS capacity for stand-alone PVPS
The BS capacity for stand-alone PVPS can be found by using Eq.
(8) as follows:
( ) Mwh53.70.8)*/(0.8)948.14(421.19PVBS ==BS capacity for PVPS Interconnected with EU
The size of BS for PVPS interconnected with EU can be found
from Eq. (9) by changing the critical load PL,critical during one
hour from 0% to 100% of maximum load demand. (ba=80% ,
=80%). Table (1) shows the relation between BS capacity for
PVPS interconnected with EU and critical load.
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
24/31
24
Table (1) Economic of PVPS/EU Under Different Values of BS
ECF Cent/kWhCost of BS, $BS capacity, kWhP
L,critical=
% Pmax-LoadkW
9.35050000%
9.380637500312.520010%
9.404667500562.536018%
9.41067500062540020%9.4407112500937.560030%
9.4707150000125080040%
9.50071875001562.5100050%
9.53082250001875120060%
9.56082625002187.5140070%
9.59083000002500160080%
9.62093375002812.5180090%
9.650937500031252000100%
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
25/31
25
3- Cost of kWh generated, $/kWh.The generation cost of the system is estimated based on the
methodology of LCC. The PVPS output annual energy is equal to
9,370,269 kWh. As a result of the estimation, the ECF is calculatedas 15.7967 cent/kWh for stand-alone PVPS, 9.3505 Cent/kWh for
PVPS interconnected with EU without BS. Table (1) shows the
relation between ECF and BS capacity.
From this Table, it can be seen that the ECF increases linearly
against BS capacity. Also, BS capacity is increased linearly with
critical load. Grid failure and low radiation produces 1.10 %
losses of annual energy from PVPS. This value has been obtained
from a new computer program. If we convert these losses to
money we will buy a BS by this amount of money.
The cost of 1.10% losses of annual energy from PVPS can be
found as follows:
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
26/31
26
Cost_loss=0.011*9,370,269*0.093505*7= $67465.20
The BS capacity purchased by this money =67465.20/120=562.21 kWh. Assuming life span of BS is 7 year.
So, the optimum BS accompanied with PVPS interconnected
with EU equal to 18 % of maximum load demand or 30% of
average load demand.
4- Reliability Calculation
As a result of computer program, the reliability of eachcomponent of the system under study is calculated and tabulated
in Table (2).
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
27/31
27
Table (2) The Calculated Reliability of Each Component
of PVPS/EU/BS
Reliabilityaverage=10-6Component
0.987383562716RA
0.9999100043R
B= R
E= R
J= R
K= R
M
= RN
= Ra= R
c= R
e= R
h
0.999971RC
= RD
0.9999850.5R
F= R
O= R
b= R
t
RL=R
d
0.9994001799200RH
0.99790220370RV
0.9999760.8RS
0.99850112450RG
0.999971Rz
0.9999940.2Ry
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
28/31
28
Comparative Study Table (3) reveals the comparative study between stand-alone
PVPS, PVPS interconnected with EU without BS and Grid-
connected PVPS with BS combinations. From this table, it can
be seen that the reliability of the grid-connected PVPS with
BS not only is higher than that of stand-alone PVPS with
1.30222905% but also is higher than that of PVPSinterconnected with EU without BS with 0.0191590% w.r.t.
the reliability of the later. On the other hand, the ECF o
stand-alone PVPS not only is higher that of PVPS/EU with
68.939% but also is higher that of PVPS/EU/BS with67.967%w.r.t. the ECF of the later. Then, it can be concluded
that the most techno-economical combination is PVPS
interconnected with EU for Zafarna site.
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
29/31
29
Table (3) Comparative Study between Stand-alonePVPS, PV/EU and PV/EU/BS
PVPS /EU/BSPVPS/EUStand-alone
PVPSCombinations
0.999075450.998884070.986232446Reliability
9.40469.350515.7967
ECF,
Cent/kWh
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
30/31
30
Conclusions
This computer program can be applied in any site of the world. In
this paper, the computer program has been applied to study
different configurations of PVPS to feed a load of 2MW located at
Zafarna site, Egypt as a case study. The following are the salient
discussions and conclusions that can be drawn from this study:-
This paper presents a new complete study from economic and
reliability point of view to determine the impact of interconnecting
PVPS with EU taking into consideration BS all radiation and
variation of the load demand during the day. Three different
configurations of PVPS have been investigated. A new computerprogram based on Matlab software introduces in this paper
-
8/14/2019 Performance and Economic Study of Interconnected PV System With
31/31
31
1- Using of BS with the configuration of PVPS/EU has saved
about 1.1% of the system energy losses.
2-The optimum size of BS accompanied with PVPSinterconnected with EU equal to 18 % of maximum loaddemand or 30% of average load demand.3-The ECF of stand-alone PVPS was 15.7967 Cent/kWh, 9.3505
Cent/kWh for grid-connected PVPS and 9.4046 Cent/kWh for
PVPS/EU accompanied with BS.
4-The PVPS/EU interconnected with BS has a higher reliability
level than that of stand-alone PVPS or Grid-connected PVPS
without BS.5-The price of kWh produced from PVPS has been decreased by
full utilization of PVPS energy through the year using BS.