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Optimization strategy for element sizing in hybrid power systems

Abstract

This paper presents a procedure to evaluate the optimal element sizing of hybrid power systems. In order to generalize the problem, this work is based on the “energy hub” concept and formulation previously presented in the literature. The resulting optimization minimizes an objective function based on costs and efficiencies of the system elements, while taking into account the hub model, energy and power constraints and estimated operational conditions, such as energy prices, input power flow availability and output energy demand. The resulting optimal architecture also constitutes a framework for further real–time control designs. Also, an example of a hybrid storage system is considered. In particular, the architecture of a hybrid plant incorporating a wind generator, batteries and intermediate hydrogen storage is optimized, based on real wind data and averaged residential demands. The hydrogen system integrates an electrolyzer, a fuel cell stack and hydrogen tanks. The resulting optimal cost of such hybrid power plant is compared with the equivalent hydrogen–only and battery–only systems, showing improvements in investment costs of almost 30% in the worst case.

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Optimization strategy for element sizing in hybrid power systems

Author: Arce Rubio, Alicia; Bordons Alba, Carlos; Real Torres, Alejandro del
Publisher: Elsevier
Year: 2009
DOI: 10.1016/j.jpowsour.2008.11.141
Source: https://idus.us.es/bitstreams/60363cc7-72f0-42f9-8e5c-71a5847614cc/download
Op imiza ion s a egy o elemen sizing in hyb id powe sys ems
Alejand o J. del Real, Alicia A ce and Ca los Bo dons
Abs ac — This pape p esen s a p ocedu e o e alua e he
op imal elemen sizing o hyb id powe sys ems. In o de o
gene alize he p oblem, his wo k is based on he “ene gy
hub” concep and o mula ion p e iously p esen ed in he
li e a u e. The esul ing op imiza ion minimizes an objec i e
unc ion based on cos s and e iciencies o he sys em elemen s,
while aking in o accoun he hub model, ene gy and powe
cons ain s and es ima ed ope a ional condi ions, such as ene gy
p ices, inpu powe low a ailabili y and ou pu ene gy demand.
The esul ing op imal a chi ec u e also cons i u es a amewo k
o u he eal– ime con ol designs.
Also, an example o a hyb id s o age sys em is conside ed.
In pa icula , he a chi ec u e o a hyb id plan inco po a ing
a wind gene a o , ba e ies and in e media e hyd ogen s o age
is op imized, based on eal wind da a and a e aged esiden ial
demands. The hyd ogen sys em in eg a es an elec olyze , a
uel cell s ack and hyd ogen anks. The esul ing op imal cos
o such hyb id powe plan is compa ed wi h he equi alen
hyd ogen–only and ba e y–only sys ems, showing imp o e-
men s in in es men cos s o almos 30% in he wo s case.
I. INTRODUCTION
The ene gy in as uc u es o oday a e abou o un-
de go a p o ound change: ossil uel p ices a e aising
e e y yea while, a he same ime, ene gy demand in-
c eases in e e y coun y. Mo eo e , he aim o educe
g eenhouse gas emissions is mo ing i s a en ion o mo e
en i onmen ally– iendly and sus ainable ene gy sou ces.
Wi h an inc eased u iliza ion o small dis ibu ed ene gy
esou ces o gene a ion o elec ici y and hea [1], enewable
ene gy gene a ion will cons i u e an impo an pa o he
o e all ene gy scena io in he coming yea s.
One o he main p oblems associa ed wi h hese kind o
sys ems is he eliabili y and quali y o he powe supply. As
a ma e o ac , since he enewable sou ce is in e mi en ,
unp edic able luc ua ions may appea in powe ou pu [2].
Also, elec ical gene a ion om enewable sou ces is no sub-
jec o demand, which c ea es imbalance in he sys em. One
way o o e come his p oblem is by including in e media e
s o age, such as ba e ies, wa e pumping, supe –capaci o s,
comp essed ai , ly wheels, supe conduc ing magne ic en-
e gy s o ages, e c [3]. Among he mos p omising s o age
echnologies a e hose based on hyd ogen p oduc ion and
u iliza ion, which is expec ed o be used o e y di e en
applica ions [4], [5] as hey cons i u e some in e es ing
This wo k was suppo ed by MEC-Spain (con ac DPI2008-04568) and
he Eu opean Commission (Hycon FPG-511368)
The au ho s a e wi h Escuela Supe io de Ingenie os, Depa amen o
de Ingenie ´
ıa de Sis emas y Au om´
a ica, Uni e si y o Se ille, 41092
Camino de los Descub imien os s/n, Se ille, Spain. e–mail:{adel eal,
aa ce}@ca uja.us.es, [email p o ec ed]
ad an ages in e ms o cos , au onomy, powe ange and
en i onmen al e ec s [6].
Howe e , hyb id ene gy s o age sys ems inc ease he com-
plexi y o he o e all powe plan , he con ol design ha ing
an impo an e ec on sys em pe o mance. Thus, he e a e
a numbe o con olle s a ailable in he li e a u e, such as
hose based on heu is ic ules and ial–and-e o echniques
[7], [8], [9], [10]. Fuzzy logic app oaches [11], [12] a e
equi alen o hose based on heu is ic ules in he sense
ha hey ely on sys em knowledge o ob ain he ‘bes ’
in ui i e powe managemen . None heless, o he app oaches
based on on–line op imiza ion can be ound, esul ing in
a mo e e–usable and igo ous design p ocess, so ha he
inal algo i hm achie es a gua an eed op imum le el [13].
Along hese lines, an on–line op imiza ion o minimize he
hyd ogen consump ion o esiden ial hyb id powe plan s
was p esen ed in [14] and [15]. As o enewable sou ces, he
in e mi ency o he a ailable powe also has a g ea impac
on sys em pe o mance. Al hough no being sui able o
eal– ime con ol as he designs ci ed, he e a e some con ol
algo i hms based on p io knowledge o u u e condi ions
(such as wind speed da a) which a e use ul as a basis o
compa ison o he e alua ion o eal– ime con ol s a egy
quali y [16].
As well as he con ol design, i is e y impo an ha
componen sizing be aken in o accoun in o de o educe
ins alla ion in es men cos s and o achie e good o e all
pe o mance. Howe e , e y ew pape s ha e add essed his
issue. To his end, [17] discusses he bes coupling me hods
o con en ional s o age ba e ies wi h hyd ogen ene gy s o -
age which includes an elec olyze , hyd ogen s o age ank,
and a uel cell. The esul ing s udy shows ha i mul iple
ene gy s o age de ices wi h complemen a y pe o mance
cha ac e is ics a e used oge he , he esul ing hyb id sys em
can d ama ically educe he cos o ene gy s o age o e
single s o age sys ems. Also, [18] p oposes a e y gene al
ma hema ical o mula ion o hese hyb id powe plan s, he
so–called “ene gy hubs”, which is u ilized o de e mine he
op imal coupling o ene gy in as uc u es.
This pape , ollowing he concep and ma hema ical o -
mula ion o he ene gy hubs p esen ed in [18] and o he
ela ed pape s by he same au ho s such as [16], [19], [20],
[21], p oposes a no el op imiza ion, which is no aimed o
es ablishing he op imal hub layou as done in [18] bu a
de e mining he op imal hub size o a de e mined layou .
In he ollowing sec ion, ene gy hub concep and ma h-
ema ical o mula ion a e b ie ly ou lined, as he e is an
ex ensi e li e a u e by he co esponding au ho s desc ib-
ing hem. Sec ion III p oposes an inno a i e gene al cos
1
P
2
P
i
P
1
L
2
L
j
L
inpu s ou pu s
ene gy hub
Fig. 1. Gene al ene gy hub diag am
i
Pj
L
con e e
in e ace
s o age
k
E
k
Q
k
Q
Fig. 2. Ene gy hub basic elemen s: con e e (le ) and s o age ( igh )
unc ion o minimize componen sizing based on cos s and
e iciencies. Sec ion IV applies he gene al op imiza ion
scena io o a wind gene a o /hyd ogen/ba e ies powe plan ,
also discussing he esul s ob ained. Las ly sec ion V is
dedica ed o he concluding ema ks.
II. ENERGY HUB CONCEPT AND FORMULATION
As an inc eased u iliza ion o dis ibu ed gene a ion ech-
nologies will cha ac e ize u u e ene gy sys ems, e ms like
“mul iple ene gy ca ie sys ems” [22] and “hyb id ene gy
sys ems” [23] ha e become he no m when e e ing o
sys ems including a ious o ms o ene gy. In his way,
as no ed in [21], he e a e a numbe o app oaches o
o mula e hese kind o sys ems, such as “ene gy–se ices
supply sys ems” [24], “basic uni s” [25], “mic og ids” [26]
and he so–called “hyb id ene gy hubs” [27].
The la e o mula ion is adop ed he ein, which is ex en-
si ely desc ibed in he PhD hesis [21] and ela ed pub-
lica ions. Acco ding o his o mula ion, ene gy hubs a e
de ined as in e aces among ene gy p oduce s, consume s,
and he anspo a ion in as uc u e (see ig. 1, whe e Pi
a e powe inpu s and Ljpowe ou pu s), and con ain h ee
basic elemen s: di ec connec ions, con e e s and s o age
(see ig. 2, wi h Qkbeing he powe exchange, ˜
Qk he in e nal
powe and Ek he s o ed ene gy).
Con e e s link inpu s and ou pu s h ough coupling ac-
o s ci,j, which can be conside ed o be he con e e ’s
s eady–s a e ene gy e iciency, exp essed as:
Lj=ci,jPi(1)
Conside ing all he ene gy hub inpu s Pand ou pu s L, he
ollowing con e e coupling ma ix C esul s:
i
P
n
1
2
i,1
P
i,2
P
i,n
P
Fig. 3. Inpu powe Pidispa ch
i
Pj
L
con e e
in e ace
i
Q
i
Q
s o age
in e ace
j
M
j
M
s o age
i
Pj
L
Fig. 4. Con e e wi h s o age a he inpu and he ou pu sides



L1
.
.
.
Li



| {z }
L
=


c1,1... ci,1
.
.
.....
.
.
c1,j... ci,j



| {z }
C



P1
.
.
.
Pj



| {z }
P
(2)
As he inpu low Pican be dis ibu ed among a ious
con e e de ices (see ig. 3), dispa ch ac o s
ν
i,nspeci y
how much o he inpu powe Pi lows in o he con e e n:
Pi,n=
ν
i,nPi(3)
Conse a ion o powe also in oduces he cons ain s
0⩽
ν
i,n⩽1∀i,∀n(4a)
∑
n
ν
i,n=1∀i(4b)
Wi h espec o s o age, powe exchange Qkand s o ed
ene gy Eka e linked h ough he equa ion:
e
Qk=ekQk=dEk/d ≈ 4Ek/4 ,˙
Ek(5)
ekbeing he e iciency o he cha ge/discha ge s o age in e -
aces, exp essed as
ek=½e+
ki Qk≥0(cha ging/s andby)
1/e−
kelse (discha ging)(6)
When s o age elemen s exis , powe conse a ion leads o
he ollowing, depending on which side o he con e e he
s o age is loca ed (see ig. 4):
e
Pi=Pi−Qi(7a)
e
Lj=Lj+Mj(7b)
Adding he s o age o he hub equa ion (2) leads o:
[L+M] = C[P−Q](8)
Hub layou
design
Hub size
design
Hub con ol
design
Op imal powe
dispa ch
Es ima ed
ope a ional condi ions
OPTIMAL ENERGY HUB DESIGN
Fig. 5. Op imal ene gy hub design s eps
Assuming a cons an con e e coupling ma ix Cand ap-
plying supe posi ion, he equi alen s o age lows a e:
Meq =C Q +M(9)
Rew i ing (8) in a mo e condensed o m,
L=C P −Meq (10)
De ining he s o age coupling ma ix S o desc ibe how
changes o he s o age ene gy de i a i es a ec he hub
ou pu lows, he equi alen s o age powe lows Meq can
be s a ed as



Meq
1
.
.
.
Meq
k



| {z }
Meq
=


s1,1... s1,k
.
.
.....
.
.
s1,k... sk,k



| {z }
S



˙
E1
.
.
.
˙
Ek



| {z }
P
(11)
Summa izing all he p e ious equa ions, he comple e hub
ene gy model would be:
L=C P −S˙
E(12)
III. OPTIMAL HUB SIZE
Op imal hub design can be di ided in o wo di e en s eps:
op imal hub a chi ec u e design and hub con ol design (see
ig. 5). Mos o he pape s in he li e a u e, as men ioned
in sec ion I, a e dedica ed solely o he con olle design,
no add essing a chi ec u e design. Acco dingly, di e en
ypes o con olle s a e p oposed: heu is ic ules, uzzy logic,
on–line op imiza ion, e c. The be e he con olle design,
he be e he pe o mance o a gi en sys em. Howe e ,
hub a chi ec u e and con ol designs a e no independen
om one ano he . As a ma e o ac , he pe o mance o
he o e all sys em no only depends on he quali y o he
con olle bu also on he hub a chi ec u e.
Op imal hub sizing o any gi en hub layou en ails
op imiza ion o con e e and s o age elemen sizes. To ha
end, cos and e iciencies associa ed wi h each componen , as
well as he es ima ed wo king condi ions o he hub (such as
ene gy p ices, inpu ene gy lows a ailabili y, ou pu powe
demand, e c.) ha e o be aken in o accoun . The o e all
op imal a chi ec u al design esul s in an i e a i e p ocess,
e alua ing he op imal cos o each hub layou in o de
o selec he one ha minimizes he in es men cos while
assu ing a de e mined pe o mance le el based on he agen s
a ec ing he sys em.
Gi en he op imal hub a chi ec u e, and supposing knowl-
edge o he sys em ope a ional condi ions, a sui able op i-
miza ion p oblem minimizing a de e mined objec i e unc-
ion would hen ep esen he basis o compa ison o he
e alua ion o eal– ime con ol s a egy quali y. This ype
o op imiza ion p oblem is e e ed o as “op imal powe
dispa ch” [16].
The p oblem p esen ed by op imal hub sizing, which is
he objec i e o his wo k, can be basically exp essed wi h
h ee ela ions: an objec i e unc ion which accoun s o he
minimiza ion o he sys em in es men cos ; physical laws
ep esen ing he hub; and echnical limi a ions. By making
he op imiza ion ho izon as la ge as possible o co e he
highes numbe o possible ope a ional condi ions and si ua-
ions, he op imiza ion is s a ed as a mul i–pe iod nonlinea
cons ained p oblem including an objec i e unc ion, equali y
and inequali y cons ain s.
The ene gy hub is desc ibed by he equali y cons ain s
p esen ed in sec ion II. Ex ending ha o mula ion o con-
side mul iple ime pe iods, he model would be:
L( )=C( )P( )−S( )˙
E( )∀ (13)
whe e
˙
E( )
k=e( )
kQ( )
k−e( −1)
kQ( −1)
k(14)
also aking in o accoun he dispa ch ac o p ope ies gi en
by (4).
Inequali y cons ain s co espond o he echnical limi a-
ions o he con e e and s o age elemen s. Equa ion (15a)
exp esses powe limi s o he con e e s. Equa ions (15b) and
(15c) co espond o change in s o age ene gy limi s, which
a e a esul o he echnical cha ac e is ics o he s o age
in e aces, while (15d) conside s he ene gy capaci y limi s
o he s o age elemen s. The las inequali y (15e) is also
included so ha s o ed ene gy a he end o he op imiza ion
pe iod N is equal o o g ea e han he ini ial amoun , in
o de o ensu e sus ainable s o age u iliza ion.
Pi,n≤
ν
( )
i,nP( )
i≤Pi,n∀ ,∀i,∀n(15a)
Qi≤Q( )
i≤Qi∀ ,∀i(15b)
Mj≤M( )
j≤Mj∀ ,∀j(15c)
Ek≤E( )
k≤Ek∀ ,∀k(15d)
E(0)
k≤E(N )
k∀k(15e)
The objec i e unc ion Fdepends on he con e e and
s o age elemen limi s, which a e ela ed o i s size. No e
ha , as he cha ging s o age in e ace may be di e en o he
discha ging in e ace, Qiand Mjco espond o he cha ging
limi s, while Qiand Mja e ela ed o he discha ging
Fig. 6. Hyb id ene gy s o age sys em
limi s. The solu ion o he op imiza ion p oblem p o ides
he op imal alues o he limi s o he cons ains (15). This
way, he o al objec i e can be exp essed as:
F=F¡Pi,Ek,Qi,Mj,Qi,Mj¢(16)
Conside ing a quad a ic unc ion, he objec i e emains:
F=∑
i
cPiP2
i+∑
k
cEkE2
k+∑
i¡cQiQ2
i+cQiQ2
i¢
+∑
j¡cMjM2
j+cMjM2
j¢(17)
cPibeing he cos pe W ins alled o he con e e i,cEk he
cos pe J ins alled o he s o age elemen k, and cQi,cMj,cQi
and cMj he cos pe W ins alled o he cha ging/discha ging
in e aces iand j.
The hub size op imiza ion p oblem can inally be s a ed
as:
Minimize objec i e unc ion (17)
subjec o ene gy hub model (4),(13),(14)
ene gy and powe cons ain s (15)
When he objec i e unc ion is con ex and he cons ain s
a e exp essed as linea equa ions, he global op imum can
be ound u ilizing nume ical me hods, as he solu ion space
is con ex.
IV. APPLICATION
Conside ing he sys em shown in ig. 6, he p ima y ene gy
sou ce is a wind gene a o , which is connec ed o a esiden ial
load (L ). The elec ici y p oduced ia wind (w) can be
deli e ed o he load and/o be di e ed o an elec olyze (E)
and ba e ies (B). The ene gy consumed by he elec olyze
(QE) is used o p oduce hyd ogen, which is s o ed in he
anks placed in he hyd ogen line (EH2). The uel cell s ack
(FC), ed by hose anks, can p oduce elec ici y (QFC).
Simila ly, he ba e ies can be cha ged (QB,ch), s o ing he
ene gy (EB), and discha ged (QB,dis), hus complemen ing
he o al powe supplied o he load.
De i ing his speci ic case om he gene al p oblem, and
assuming a ce ain se o ope a ional condi ions, he op imal
hub sizing o he p oposed sys em is calcula ed. To ha end,
he op imiza ion p oblem is o mula ed as in he p e ious
sec ion III
η
η
η
η
Fig. 7. Co esponding ene gy hub o a hyb id ene gy s o age sys em
TABLE I
HYBRID ENERGY STORAGE SYSTEM EFFICIENCIES
Hub elemen E iciency
Elec olyze
η
E=0.74
Fuel cell
η
FC =0.47
Ba e y cha ging
η
B,ch =0.7
Ba e y discha ging
η
B,dis =0.9
A. Ene gy hub model
Model equa ions a e based on he no a ion p esen ed in
sec ion II. This way, he speci ic ene gy hub is illus a ed in
ig. 7. Inpu , ou pu and s o age ene gy de i a i e ec o s o
mul iple ime pe iods, can be de ined as
P( )=hP( )
wi(18a)
L( )=hL( )
i(18b)
˙
E( )=h˙
E( )
H2˙
E( )
BiT(18c)
Also, ollowing he a o emen ioned no a ion, con e e
coupling ma ix C( )and s o age coupling ma ix S( )a e
s a ed as:
C( )=£1¤(19)
S( )=h1/e( )
H21/e( )
Bi(20)
whe e e( )
H2and e( )
Ba e he s o age in e ace e iciencies (see
able I), he elec olyze being he ‘cha ging’ in e ace and
he uel cell he ‘discha ging’ in e ace o he hyd ogen line.
Also, no ice ha di e en ba e y cha ging and discha ging
e iciencies a e conside ed, esul ing in he ollowing ela-
ions:
e( )
H2=(
η
Ei Q( )
H2≥0(elec olyze )
1/
η
FC else ( uel cell)(21a)
e( )
B=½
η
B,ch i Q( )
B≥0(ba e y cha ging)
1/
η
B,dis else (ba e y discha ging)
(21b)
wi h he powe exchanges Q( )
H2,Q( )
Band s o age ene gy
de i a i es ˙
E( )
H2,˙
E( )
Bexp essed as:
˙
E( )
H2=e( )
H2Q( )
H2−e( −1)
H2Q( −1)
k(22a)
˙
E( )
B=e( )
BQ( )
B−e( −1)
BQ( −1)
B(22b)
B. Ene gy and powe cons ain s
Technical limi a ions a e modeled as hey we e in (15).
Inpu powe limi s, s o age in e aces powe exchange ca-
paci ies and s o ed ene gy limi a ions a e e alua ed nex .
Wi h espec o he inpu , wind powe P( )
wdepends on he
a ailable wind powe , as well as on he size o he wind
gene a o . De ining b
P( )
was he no malized powe p oduced
by a 1W wind gene a o gi en a ce ain wind speed a ime
, powe inpu limi s would be:
£0¤≤hP( )
wi≤hb
P( )
wPwi(23)
wi h Pwbeing he size o he wind gene a o o he p oposed
hyb id s o age plan .
Powe s o age exchange is also limi ed by he maximum
powe ha can be p o ided by he s o age in e aces:
·−QFC
−QB,dis ¸≤"Q( )
H2
Q( )
B#≤·QE
QB,ch ¸(24)
whe eas o he hyd ogen line, QEand QFC ep esen he
maximum capaci ies o elec olyze and uel cell espec-
i ely. Conce ning he ba e ies, QB,ch and QB,dis a e he
limi cha ging/discha ging a es. No ice ha hese a es a e
usually a unc ion o o al ba e y size E, assuming he e ha
QB,ch =0.2Eand QB,dis =2E.
Maximum s o ed ene gy depends on he size o he
hyd ogen anks EH2and he ba e ies EB. Due o echnical
cons ain s, he ba e ies should ne e be o ally d ained no
ully cha ged; hey should always be in a pa ially cha ged
s a e. Taking hese conside a ions in o accoun and assuming
a sa e cha ge le el, he cons ain can be exp essed as:
·0
0.2EB¸≤"E( )
H2
E( )
B#≤·EH2
0.9EB¸(25)
Finally, a cons ain o e i y sus ainable ene gy s o age is
also in oduced, so ha
"E(0)
H2
E(0)
B#≤"E(N )
H2
E(N )
B#(26)
C. Objec i e unc ion
Mo ing om he gene al (17) o he speci ic, he objec i e
unc ion, whose cos e ms a e shown in able II [17], would
be:
F=cPwP2
w+cEH2E2
H2+cEBP2
B+cQFC Q2
FC +cQEQ2
E(27)
TABLE II
HYBRID ENERGY STORAGE ELEMENT COSTS
Hub elemen Cos
Wind powe cPw=$2/W
Elec olyze cQE=$1.9/W
Fuel cell cQFC =$2.5/W
Hyd ogen ank cEH2=$0.03/Wh
Ba e y cEB=$0.2/Wh
0 500 1000 1500
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
ime (h)
no malized wind powe
Fig. 8. No malized wind powe da a se ( eco ded o e a wo-mon h pe iod)
D. Ope a ional condi ions
As he op imal hub a chi ec u e design is based on es i-
ma ed ope a ional condi ions, he mo e p ecise he u ilized
da a a e, he mo e accu a e a e he a chi ec u al esul s. As
o he powe inpu , a wo–mon h wind powe no malized
da a se b
P( )
wwas conside ed (see ig 8). Conce ning he load
L , he da a used is shown in ig. 9, which ep esen s he
a e age daily load o he esiden ial sec o in Spain [28].
The sampling ime o all he da a se s is 1h.
E. Op imiza ion esul s
The op imiza ion was done o h ee hub layou s: hyb id,
hyd ogen–only and ba e y–only s o age, and was imple-
men ed in Ma lab using he sol e ”CPLEX”, esul ing in a
0 5 10 15 20
0
100
200
300
400
500
600
ime (h)
esiden ial load (W)
Fig. 9. Residen ial sec o a e age daily loads

TABLE III
HYBRID ENERGY STORAGE SYSTEM COSTS
Hyb id Hyd ogen–only Ba e y–only
Equipmen cos cos cos
(size) (size) (size)
Wind gene a o $7600 $8600 $12500
(3800 W) (4300 W) (6250 W)
Elec olyze $656 $665 —
(345 W) (350 W)
Fuel cell $450 $1375 —
(180 W) (550 W)
H2 ank $1642 $3681 —
(54.730 kWh) (122.695 kWh)
Ba e ies $2268 —$3651
(11.34 kWh) (18.255 kWh)
To al cos $12616 $14321 $16151
Inc emen Baseline 11.91% 28.02%
0 500 1000 1500
0
100
200
300
400
ime (h)
ba e y ou pu powe (W)
0 500 1000 1500
0
50
100
150
200
ime (h)
uel cell powe (W)
Fig. 10. Op imal u ilisa ion o ba e y (uppe g aph) and uel cell (lowe
g aph) o a hyb id s o age powe sys em
Mixed In ege Quad a ic P og amming (MIQP). Con i ming
he s udies p esen ed in [17], hyb id s o age p o ed o be
signi ican ly cheape han o he possible s o age sys ems. In
pa icula , hyd ogen–only s o age cos is 11.91% highe han
he hyb id plan , he ba e y–only choice being 28.02% mo e
expensi e han such hyb id sys em (see able III o de ailed
in o ma ion).
As can be seen in ig. 10, hyb id s o age layou combines
he bes cha ac e is ics o bo h ene gy s o age de ices. In
pa icula , he uel cell is used as a base powe supplie ,
while ba e ies a e u ilized o deli e he powe peaks. In a
hyd ogen—only choice, he uel cell size has o be inc eased
in o de o c ea e he powe peaks, which esul s in a cos
inc ease due o he high cos o he equipmen . On he
o he hand, ba e y–only s o age equi es a la ge o al ene gy
capaci y, which is cos ly oo.
V. CONCLUDING REMARKS
In his pape , an op imiza ion s a egy o sizing hyb id
powe sys ems is p esen ed. The ma hema ical o mula ion is
based on he “ene gy hub” concep desc ibed in p e ious li -
e a u e. The op imiza ion p ocedu e was applied o a hyb id
powe plan inco po a ing a wind gene a o , con en ional
ba e ies and a hyd ogen s o age sys em comp ised o a
uel cell, an elec olyze and hyd ogen anks. The op imal
a chi ec u e esul ed in a 30% imp o emen among he
possible sys em layou s in e ms o cos e ec i eness.
VI. ACKNOWLEDGMENTS
The au ho s g a e ully acknowledge he con ibu ion o
Ca los Pa do, who is wo king on his mas e hesis in ela ed
issues.
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