Ene gy Repo s 6 (2020) 2627–2640
Con en s lis s a ailable a ScienceDi ec
Ene gy Repo s
jou nal homepage: www.else ie .com/loca e/egy
Sus ainable biomass pelle s using unk wood om oli e g o es a he
end o hei li e cycle
Víc o M. Sol e o a,∗, Lidia Román a, M. Es ela Pe al a a, Rica do Chaca egui b
aDepa men o Design Enginee ing, Uni e si y o Se ille, 41011 Se ille, Spain
bDepa men o Ene gy Enginee ing, Uni e si y o Se ille, 41092 Se ille, Spain
a icle in o
A icle his o y:
Recei ed 19 Sep embe 2019
Recei ed in e ised o m 4 Sep embe 2020
Accep ed 19 Sep embe 2020
A ailable online 1 Oc obe 2020
Keywo ds:
Sus ainabili y
Biomass
Bio uel
Pelle s
Oli e ee managemen
abs ac
Fo es biomass is he aw ma e ial mos commonly used o p oduce quali y pelle s o domes ic
households. Howe e , sus ainable o es biomass is no a ailable in all egions, bu he e a e o he
po en ial aw ma e ial sou ces o biomass hea ing sys ems, based on pelle s. The e a e a la ge numbe
o oli e ees in he Medi e anean a ea, bu hese a e no used as enewable pelle uel because he
ba k canno be used as aw ma e ial o p oduce quali y pelle s. The aim o his s udy is o ca y ou a
me hodology o es ima e he op imal sus ainable bioene gy li e cycle, and he amoun o sus ainable
esidue a ailable ( unk wood) a he end o he li e o he oli e g o e, by op imizing he bene i s,
h ough an analysis o cos s and income o he whole li e p ocess. The me hodology de e mines he
po en ial alue o he unks o oli e ees o be used as biomass, in he o m o pelle s in domes ic
con ex s and in a speci ic geog aphical a ea. In a case s udy applied o Andalusia, i has been shown
ha he op imal enewable li e-cycle is 97 yea s. I policies o ag icul u al and ene gy sus ainabili y
a ou ing his model we e adop ed, his egion would p oduce 160,000 onnes o pelle s pe yea , and
266,500 onnes pe yea , i ex ended o he whole o Spain. This has a po en ial o p o iding 70.17%
o he cu en o al pelle consump ion. The ex ension o he model o o he Medi e anean coun ies,
such as G eece and I aly, would esul in an addi ional 124,000 and 144,000 onnes o pelle s pe yea ,
espec i ely.
©2020 The Au ho s. Published by Else ie L d. This is an open access a icle unde he CC BY license
(h p://c ea i ecommons.o g/licenses/by/4.0/).
1. In oduc ion
Ene gy, as a esou ce, is one o he main indica o s o he
human de elopmen index le el (Gou eia e al.,2019;Insah and
Bha acha yya,2015;Neumaye ,2001). Cu en ly, 77.6% o he
Eu opean ene gy supply comes om ossil uels, whe eas 11.7%
is supplied by nuclea plan s, and 11.1% comes om enewable
ene gy sou ces. This high dependence on ossil esou ces p o-
duces signi ican en i onmen al impac s and a ec s he economy.
I mo i a es policies o p omo ing he de elopmen and use o
enewable al e na i e sou ces. In he case o he EU-28, he use
o enewable ene gies in 2015 accoun ed o 16.66% o g oss
inal consump ion, compa ed o 16.13% in 2014. Wi hin hese
da a, ega ding he p oduc ion o hea wi h biomass, in 2015,
bioene gy ep esen ed 10% o o al ene gy consumed and 61.34%
o he enewable ene gy used (AEBIOM,2017), making bio uels
cu en ly one o he main enewable ene gy al e na i es.
∗Co esponding au ho .
E-mail add esses: [email p o ec ed],[email p o ec ed] (V.M. Sol e o),
[email p o ec ed] (L. Román), [email p o ec ed] (M.E. Pe al a),
[email p o ec ed] (R. Chaca egui).
In his con ex , he use o ag icul u al, o es y o ood esidues,
o hei use in hea ing sys ems in buildings and indi idual
dwellings, is a was e managemen s a egy ha o e s ad an ages
o he ci cula economy (Valen ín e al.,2016) and educes he
dependence on ossil uels (Aga ,2017;Cheng,2017). Al hough
i in ol es combus ion and CO2emissions, he whole chain will
be CO2neu al, being compensa ed h oughou he use ul li e o
he ag icul u al esou ce by he p ocess o pho osyn hesis (Anon;
Wo king G oup III IPCC,2007).
The de elopmen o sus ainable s a egies and policies based
on hese aw ma e ials, assu ing he economic and echnical
iabili y o sys ems based on hei use and exploi a ion, equi es
he gua an ee o medium and long- e m supply, as well as a
minimum low hea alue (Hoogwijk e al.,2003;We he e al.,
2000). Cu en ly, wood chips, ag o-indus ial esidues, i ewood
and pelle s a e he main solid bio uels used o his pu pose
(Ka kania e al.,2012;Waheed e al.,2019). Fig. 1 shows he
dis ibu ion o pelle p oduc ion and global ade lows (Calde ón
e al.,2018).
As Fig. 1 shows, Eu ope is he wo ld’s la ges consume o
pelle s wi h 20.3 million onnes in 2015 (Eu opean Biomass As-
socia ion (AEBIOM),2016), o which, 6.2 million onnes we e
h ps://doi.o g/10.1016/j.egy .2020.09.017
2352-4847/©2020 The Au ho s. Published by Else ie L d. This is an open access a icle unde he CC BY license (h p://c ea i ecommons.o g/licenses/by/4.0/).
V.M. Sol e o, L. Román, M.E. Pe al a e al. Ene gy Repo s 6 (2020) 2627–2640
Fig. 1. Wo ld pelle map and ade lows in 2017 (Calde ón e al.,2018).
impo ed om Ame ica, Russia and Eas e n Eu ope. Op imal en-
e gy e iciency depends on he quali y o he pelle , de ined om
he p ope ies o he eeds ock and he pelle ing p ocess. The
ISO 17225-2 (ISO,2014a) de ines di e en pa ame e s o he
classi ica ion, acco ding o he quali y o he pelle and i s use
a an indus ial o domes ic le el.
A p esen , only o es esidues ha e easible echnologies and
associa ed ma ke s o exploi a ion in Eu ope (Ga cía-Ma a e
e al.,2015). In he case o he Medi e anean a ea, hose esidues
coming om he ac i i ies o he oli e-g owing sec o a e an
impo an sou ce o he manu ac u e o pelle s, he main by-
p oduc s o ene gy eco e y being pomace ‘‘o ujillo’’ (oli e cake
o pos oil-ex ac ion was e) (Valen i e al.,2017), ‘‘hojín’’ (d y
lea es ha all om he oli e ees and ha a e bu ied as a
na u al e ilize ), p uned emains and oli e pi s (Agencia An-
daluza de la Ene gía,2011;Conseje ía de Ag icucl u a Pesca y
Desa ollo Ru al,2015;Hansen,2019;Niaounakis and Hal adakis,
2006;Schip e and K anzl,2019). In Andalusia, in pa icula , he
o al ene gy po en ial o he by-p oduc s o he oli e ag oindus y
amoun o 567,702 oe/yea , in e ms o p ima y ene gy, da a
ha make he de elopmen o o ms o ene gy use om his
esou ce a p io i y (Ekman e al.,2013;Ga cía-Ma a e e al.,
2012). E en wi h hese bene i s and amewo k, hei use as a
bio uel is qui e educed (Ga cía-Ma a e e al.,2015), al hough
di e en s udies analyse he economic easibili y, mechanical
beha iou and physical–chemical p ope ies o pelle s ex ac ed
om di e en a ie ies o was e (Ca one e al.,2011;Ga cia-
Ma a e e al.,2014;Mi anda e al.,2010;Mani e al.,2006).
The e a e di e en easons o hei low use as a bio uel. Was es
a e p oduced locally and hei use in ol es high cos s, ei he
because o he logis ical p ocesses equi ed o hei ans e o
p ocessing o cen al combus ion plan s (high s o age olume
o he eeds ock), o he in es men equi ed on a small scale
in local ins alla ions (Ba eca and Fiche a,2013,2014;Capu o
e al.,2003;Kinab and Khou y,2015). Main limi a ions o i s
use a e associa ed wi h high mois u e con en , low bulk densi y,
low ash mel ing poin and high ola ile ma e con en (We he
e al.,2000). I should be no ed ha , i he p uning eeds ock
(lea es and b anches) o almond, black popla , holm oak and oli e
species a e compa ed, he pelle s om oli e esidues ha e op i-
mum lowe hea ing alue (LHV) and i s p oduc ion o e s g ea e
densi y and g ea e esis ance o ac ion han o he eeds ock.
Howe e , hey ha e a high ash con en , and e en hough i is
lowe han ha o sepa a e oli e lea es, i eaches a alue abo e
he h eshold o domes ic boile egula ion (1.5%). In e ms o
he di e en o ms o esidues [oli e wood (ba k and unk) and
oli e p uning (lea es and b anches)], he lea es a e esponsible
o p oducing he g ea es amoun o ash, ollowed by ba k and
b anches (Ga cia-Ma a e e al.,2014;Velázquez-Ma í e al.,
2011). On he o he hand, he unk wood o e s op imal esul s
ha mee he quali y equi ed in comme cial and esiden ial
applica ions and is he e o e he mos sui able pa o gene a ing
pelle s o domes ic use. Table 1 summa izes he cha ac e is ics
o he pelle s by aking in o accoun he o igin o he esidue and
he quali y (A1, A2 o B).
In o de o es ima e he a ailabili y o esidue and he po en-
ial o pelle gene a ion, i is necessa y o e alua e he whole
li ecycle o he oli e g o e, di e en ia ing be ween biological,
p oduc i e and ene gy cycles (Fig. 2). The biological cycle is
es ima ed o be o e 2000 yea s, al hough he con as ed alue in
scien i ic s udies is 700 yea s [27]. This cycle is di ided in o h ee
s ages: (i) you h (0–20 yea s); (ii) adul pe iod (20–100 yea s)
composed o he p oduc ion phase (20–50 yea s) and he de-
c easing phase (50–100 yea s); and (iii) senescence (>100 yea s).
None heless, he op imal p oduc ion cycle is educed o a ange o
40–50 yea s depending on he a ie y (Gucci and Can ini,2000).
Old ees can be e y p oduc i e as long as hey a e subjec ed
o a eju ena ion p ocess, al hough as old age is eached, i.e., a -
e 70 yea s, p uning and ha es ing cos s inc ease and annual
p oduc ion dec eases (Gucci and Can ini,2000;Pas o Muñoz
Cobo and Guillén,2015). Las ly, he ene gy li e cycle o an oli e
g o e is calcula ed as he op imum cos -bene i alue o he
exploi a ion, including he income om he sale o wood o i s
ene gy eco e y.
A p esen , he biological li e cycle is gene ally gi en p io i y
o e he p oduc i e li e cycle on oli e a ms and, in he Medi e -
anean a ea in pa icula , he p oduc i e cycle can be longe
han 200 yea s (Bo mann,1985;By ne owicz and Omasa,2007;
Paole i e al.,2010). In mos cases, he enewal o plan a ions
is no ca ied ou , due o a lack o knowledge o he op imum
cos -bene i alue, he e a e also no economic incen i es.
Unde his amewo k, i is o in e es o iden i y he op imum
p oduc i e and ene gy cycles o he oli e g o e, maximizing
esou ce p oduc i i y and, subsequen ly, o iden i y he capaci y
o exploi a ion o a ailable wood esidues a he end o li e s age
as an ene gy sou ce and economic oppo uni y o his ag i- ood
sec o .
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V.M. Sol e o, L. Román, M.E. Pe al a e al. Ene gy Repo s 6 (2020) 2627–2640
Table 1
Cha ac e is ics o he pelle s udies and ISO 17225-2:2014 (Ga cia-Ma a e e al.,2014;ISO,2014a).
Pa ame e Pine spain Oli e wood Oli e p uning Pelle A1 Pelle A2 Pelle B
P oxima e analysis (% w , as ecei ed)
Mois u e 10.1 7.6 8.0 ≤10 ≤10 ≤10
Ash 1.0 1.4 5.5 ≤0.7 ≤1.5 ≤3.0
Ul ima e analysis (% w , d y ash ee)
Ni ogen 0.3 0.3 1.1 ≤0.3 ≤0.5 ≤1.0
Sulphu 0.02 <0.01 0.05 ≤0.03 ≤0.03 ≤0.04
Lowe hea ing alue (MJ/kg) 16.9 16.0 16.5 16.5–19 16.3–19 16.0–19
Du abili y 91.88 98.09 98.92 ≥97.5 ≥97.5 ≥96.5
Bulk Densi y (kg/ m3) 544 638 610 ≥600 ≥600 ≥600
Ra io L/D 1.52 3.64 3.86 0.52–40 0.52–40 0.52-40
Fig. 2. Biological and bioene gy li e cycle o he oli e g o e.
Wi h his aim, his a icle de elops a me hodology o es i-
ma e he op imal bioene gy li e cycle and he amoun o esidue
a ailable ( unk wood), a he end o li e o he oli e g o e, by
op imizing he sus ainable exploi a ion o esou ces h ough an
analysis o cos s and income. Wi h he esul s, i is possible o
e alua e he po en ial alue o he oli e ee unks ha could
be used as biomass o domes ic use in a geog aphical a ea. In
addi ion, i is conside ed ha he ma ke alue o he pelle ed
unk wood will con ibu e o he equi ed in es men o oli e
ee eplacemen , eplan ing o he nex p oduc i e cycle.
The a icle is o ganized as ollows: Sec ion 2desc ibes he
p oposed me hodology; Sec ion 3de elops a case s udy o he
a ea o Andalusia; and inally, Sec ions 4and 5p esen he esul s,
discussion and main conclusions o he esea ch.
2. Ma e ials and me hods
This Sec ion de elops he me hodology o es ima e he op-
imal sus ainable bioene gy li e cycle and he amoun o sus-
ainable esidue a ailable ( unk wood) a he end o li e o he
oli e g o e, by op imizing he bene i , h ough an analysis o
cos s and income o he whole li e p ocess. The me hodology
de e mines he po en ial alue o he unks o oli e ees o be
used as biomass, in he o m o pelle s in domes ic con ex s in a
speci ic geog aphical a ea. In his way, he easibili y analysis se s
he enewal and eplan ing o he oli e g o e a he end o i s
op imum p oduc i e cycle. This in ol es an analysis o he cos s
and income in ol ed in he cul i a ion o he oli e ee o he
g owe , by aking in o accoun he ene gy alue o he pelle ed
unk wood a he end o he li e cycle o he oli e g o e. Fig. 3
illus a es he p oposed me hodology.
2.1. S ep 1: Delimi a ion and cha ac e iza ion o he s udy a ea
The s udy a ea is selec ed by calcula ing he op imum alue o
he li e cycle o he ees o an ene gy use as pelle s, he e a e
no limi s o su ace a ea, and i can be applied o di e en le els:
coun y, egion, locali y o c op.
Once selec ed, he ype o oli e g o e will be cha ac e ized. I
he e is mo e han one oli e a ie y in he a ea unde s udy, i
will be necessa y o de e mine hei pe cen age and dis ibu ion,
because p oduc ion da a will a y acco ding o ype o oli e.
A e ha , a descending o de o su ace a ea occupied by a ie y
is es ablished. Fo an adequa e le el o accu acy a de ini ion o
occupa ion abo e 90% o he o al is conside ed.
Fo he cha ac e iza ion o he a ea i will be necessa y o
collec da a on: o al a ea occupied [m2]; oli e ee a ie ies and
hei a ea occupied [ ype, m2]; p oduc ion by a ie y [kg/ ee];
cul i a ion egime (i iga ed o d y); densi y o plan a ion [oli e
ees/ha]; age a he s a o he p oduc ion cycle [yea ]; selling
p ice o he oli e [e/kg]; selling p ice o he ee [e/ ]; equency
o p oduc ion p uning [yea s]; beginning o p oduc ion p uning
[yea ]; unk pe ime e g ow h [cm/yea ]; and unk heigh [m].
These da a can be ob ained om s a is ical da a publica ions such
as Na e o e al. (2017), Fabb i (2004), Gucci and Can ini (2000),
Pas o Muñoz Cobo and Guillén (2015).
2.2. S ep 2: Calcula ion o economic a iables and es ima ion o
indi idual unc ions
The op imal p oduc i e cycle o he oli e g o e depends on
ou economic a iables: p oduc ion, unk wood mass, p uning
and ha es ing o oli es. As he objec i e is o de e mine he
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V.M. Sol e o, L. Román, M.E. Pe al a e al. Ene gy Repo s 6 (2020) 2627–2640
Fig. 3. P oposed me hodology o he e alua ion o biomass op imized po en ial o pelle p oduc ion.
op imum bioene gy cycle o he oli e g o e, all o hese a iables
depend on he age o he oli e ee, which implies a di ec ela-
ionship wi h he income and cos s o managing he plan a ion.
All hose economic a iables independen o he age o he oli e
ee a e disca ded, as hey emain cons an on any a m. Income
comes om: (i) annual income, due o he p oduc ion and sale o
oli es which a e p esen h oughou he p oduc i e li e cycle o
he oli e g o e; and, (ii) speci ic income, de ined as ha ob ained
om he sale o he ee a he end o he li e cycle o he oli e
ee. On he o he hand, he cos s o an oli e a m a e qui e
di e se: p uning, ha es ing, soil main enance, olia ea men s,
p e en ion o pes s and diseases, e iliza ion, e c. Howe e , only
hose ha depend on he age o he oli e ee a e ele an a
his s ep: (i) cos o annual ha es ing; and, (ii) cos o a iable
p uning, depending on he s age o he biological cycle o he ee.
In he ollowing sec ions, each economic a iable is de ined
and modelled h ough a ime-dependen unc ion. This s udy is
based on s a is ical da a ela ed o he di e en pa ame e s and
ac o s which a ec he gene a ion and use o oli e esidues.
These da a come om s udies o species and he exploi a ion
o plan a ions in he Medi e anean a ea (Na e o e al.,2017;
Conse je ía de Ag icul u a y pesca,2002a;Fabb i,2004;Gucci and
Can ini,2000;Ins i u o de In es igación y Fo mación Ag a ia y
Pesque a (IFAPA),2010;Pas o Muñoz Cobo and Guillén,2015;
Tous e al.,2014). The unc ions a e app oxima ions o he be-
ha iou o hese da a, and a e chosen as he mos op imal o
ep esen each ac o .
2.2.1. Oli e g o e p oduc ion
Oli e g o e p oduc ion is de ined as he kilog ammes o oli es
p oduced pe hec a e, he a iables ha mos signi ican ly a ec
i a e: he a ie y o oli e ee, he cul i a ion egime and he age
o he ee (Conse je ía de Ag icul u a y pesca,2002a). I should
be no ed ha p oduc ion dec eases wi h ageing once he max-
imum p oduc i e age has been eached. The p oduc ion o new
plan a ion specimens is es ima ed a 1956 kg/ha; while ha o
adul ees is es ima ed a 2736 kg/ha (Conse je ía de Ag icul u a
y pesca,2002a). The use o i iga ed c ops inc eases p oduc ion
wi h espec o non-i iga ed c ops, o example, in he Picudo
a ie y, i iga ion p oduces 48 kg/ ee compa ed o 27.50 kg/ ee
wi hou i iga ion (Na e o e al.,2017;Fabb i,2004). Fo he la -
e case, wo al e na i es may be conside ed in he me hodology:
o selec he majo i y egime in he s udy a ea (d y o i iga ed),
o , o ake in o accoun he p oduc i e a iabili y by di iding in o
sub-a eas and assigning hem he occupied su ace wi h i iga ed
and d y egimes.
Income om p oduc ion he e o e depends on he p e ious
a iables ( a ie y o oli e ee, cul i a ion egime and age o he
oli e ee) and on he p oduc ion le el, conside ing: he densi y
o he plan a ion, he beginning o he p oduc ion cycle (age a
which he specimen begins o p oduce), and he selling p ice
o he oli es. The p ice o oli es a ies om season o season,
and hei yield is aken in o accoun in o de o income o be
es ima ed. The me hodology p o ides wo al e na i es: o use an
a e age es ima ion o he selling p ice o he oli e g o e, o o
use a di e en selling p ice o each a ie y o oli e ee. FIP [e/ha]
will be he ime e olu ion o income o each a ie y o oli e ee.
2.2.2. Income linked o unk wood mass
In his ene gy applica ion he op imal p oduc i e cycle o he
oli e ee ends wi h he use o he unk wood o he gene a ion
o pelle s o esiden ial use. The wood ha can be ha es ed is
he unk wi hou ba k.
This a iable allows us o de e mine he a ailabili y o e-
sou ces o ob aining biomass in he li e cycle o he oli e g o e
o , in o he wo ds, he po en ial o gene a ing pelle s om a
a m.
Volume and mass a e es ima ed om he diame e and heigh
o he oli e ee unk, which depend on he a ie y and age
o he oli e ee (excep cu ing p ocess, disease o acciden ). I
2630
V.M. Sol e o, L. Román, M.E. Pe al a e al. Ene gy Repo s 6 (2020) 2627–2640
Table 2
Va ia ion o unk diame e acco ding o he a ie y o oli e ee (Ins i u o de
In es igación y Fo mación Ag a ia y Pesque a (IFAPA),2010).
Oli e a ie y T unk diame e [cm]
Hojiblanca 10.5
A bequina 8.5
Picual 12
Picudo 12.5
A oniz 14
Neg al 18
is conside ed ha he pe ime e o he oli e ee g ows by ap-
p oxima ely 2.5 cm/yea (A nan e al.,2012), eaching maximum
p oduc i i y wi h he diame e s shown in Table 2, depending
on he a ie y, whe eas he maximum unk heigh can a y
be ween 0.8 and 1 m (Gucci and Can ini,2000;Ins i u o de
In es igación y Fo mación Ag a ia y Pesque a (IFAPA),2010).
In o de o calcula e he unk wood mass, he quan i y o
log wi hou ba k Mi[kg] is de e mined depending on he a ie y
io he oli e ee. Fi s o all, he diame e o he unk Di
[m] is calcula ed as a unc ion o he pe ime e Pi[m] wi h he
exp ession (1):
Di=Pi
π(1)
Then he olume o he unk Vi[m3] is calcula ed by geo-
me ic app oxima ion o a cylinde om he exp ession (2), i[m]
being he adius o he unk and hi[m] he heigh o he unk
[m], conside ing hmax be ween 0.8 and 1 m:
Vi=π· 2
i·hi(2)
Wi h he p e ious da a, he quan i y o wood Mi[Kg/ ee] is
calcula ed depending on he olume Vi[m3] and he densi y o
he wood dw[kg/ m3] depending on he ee a ie y:
Mi=dw·Vi(3)
Nex , he exp ession (4) p o ides in o ma ion on he o al
amoun o unk wood MT,i[kg/ha] ha a a ie y iwill be able
o p oduce in he li e cycle o he oli e g o e; and he exp ession
(5) gi es in o ma ion on he o al income om he sale o unk
wood Iw[e/ha]. Fo hese, he plan a ion densi y Dha [ ee/ha] and
he selling p ice o unk wood Pw[e/kg] mus be es ablished.
MT,i=Mi·Dha (4)
Iw=MT,i·Pw(5)
I he e a e di e en a ie ies o oli e ee in he same plan a-
ion, he o al mass o he a ailable unk wood will be calcula ed
wi h he sum o he quan i ies MT,iob ained o each a ie y i.
Finally, he annual income and he amoun o annual pelle s
a e calcula ed o he li e cycle o he oli e g o e. The annual
esul o incomes Iy [e/y ] is ob ained om he exp ession (6)
ha ela es he o al income o he oli e g o e Iw[e/ha] wi h he
conside ed p oduc i e cycle PCop [yea s/ha]:
Iy =Iw
PCop
(6)
The pelle gene a ion po en ial o he a m is de e mined om
he e iciency o he pelle ing p ocess, by aking in o accoun
he unk wood mass WT,i[kg], he pe cen age o wood mois u e
(25%) and he pe cen age o wood educ ion by he p ocess (15%).
The s udy o he e olu ion o his economic a iable, wi h
espec o ime, will esul in he unk wood income unc ion
FI.w [e/ha], which models he income de i ed om he sale o
he wood when he oli e g o e eaches he end o i s op imal
p oduc i e cycle. This s udy is ca ied ou in Sec ion 3.2.2.
2.2.3. P uning p ocess
Du ing he biological cycle o he oli e ee, h ee di e en
p uning ope a ions a e ca ied ou : o ma ion p uning, p oduc-
ion p uning and enewal p uning. The objec i e, and equency,
o each p uning ope a ion is shown in Fig. 4. Fo ma ion p uning
is ca ied ou app oxima ely e e y h ee yea s wi h he aim o
emodelling he s uc u e o he oli e ee, i is cha ac e ized by
being minimal because he da e o beginning o he p oduc ion
o he oli e ee depends on he numbe o lea es and b anches
espec ed in his p uning. The p oduc ion p uning is ca ied ou
du ing he adul phase o he oli e ee, in o de o ob ain a
su icien olume o c own o assu e he maximum amoun o
ha es s, and o leng hen he p oduc i e pe iod. A e ha es ing,
he oli e ee is p uned o enewal (main enance), which is ca -
ied ou when he specimen shows signs o ageing and ha dening,
wi h eco e y being a way o esol ing he p oblem o excess
wood. A his ime, a pe iod o imbalance in he lea /wood a io
begins, which causes a dec ease in ha es s, a g ea e al e na ion
o p oduc ion, and a de e io a ion in he quali y o he ui s
(Fabb i,2004). When he oli e ee eaches he senile s age,
p uning becomes mo e equen and enewals a e mo e se e e.
In o de o calcula e hese a iables, i is necessa y o se :
he beginning o p uning, he equency o he ypes o p uning
and he p uning mechanism. Fo he la e , i will be necessa y
o know he hou s in es ed and he hou ly cos o he ask.
I is conside ed ha all a ie ies o oli e ees use he same
mechanism, ype and cos o p uning.
The s udy o he e olu ion o hese a iables o e ime will
esul in he p uning cos unc ion FC.P[e/ha], which models he
cos s associa ed wi h he se o p uning ope a ions and asks in
he s udy a ea h oughou he biological cycle o he oli e g o e.
This s udy is ca ied ou in Sec ion 3.2.3.
2.2.4. Oli e ha es ing p ocess
The e a e di e en me hods o ha es ing oli es: adi ional
(soil ha es ing, milking and oli e knock down) and mechanical,
he choice depends on he cha ac e is ics o he soil, he c op and
he g ow h o he c own o he oli e ee (Sola-Gui ado e al.,
2014). The cos s associa ed wi h ha es ing depend on he a ie y
o oli e ee, he p oduc i i y o he oli e g o e [kg oli e/ha],
he ha es ing mechanism (which de ines he hou s equi ed, as
well as he hou ly cos o labou ) and he s a o he oli e g o e
p oduc ion cycle (Tous e al.,2014).
2.3. S ep 3: De ini ion o he bene i unc ion o each oli e a ie y
and global bene i unc ion
Once he s udy a ea and he economic a iables in ela ion o
he a m o be e alua ed ha e been selec ed, he bene i unc ion
is de ined o each o he oli e ee a ie ies FB,i o maximize om
he income and cos s o he oli e g o e:
MAX [FB,i]=FB,i=FI.P+FI.W
−FC.P−FC.H(7)
whe e:
•FBis he bene i unc ion
•FI.Pis he p oduc ion income unc ion [e/ha]
•FI.Wis he unk wood income unc ion [e/ha]
•FC.Pis he p uning cos unc ion [e/ha]
•FC.His he collec ion cos unc ion [e/ha]
• is ime [yea s]
I is necessa y o conside he di e en imings o he consid-
e ed p ocesses. The p oduc ion income and he cos o ha es ing
a e annual, and occu h oughou he p oduc i e cycle o he
oli e g o e. The cos o p uning depends on he equency o he
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Fig. 4. P uning and age o oli e g o es (Pas o Muñoz Cobo and Guillén,2015).
p ocess, usually e e y wo o h ee yea s, depending on he need
o main enance, so ans o ma ion o an annual alue is equi ed.
Finally, income om he sale o ees occu s a he end o he
p oduc i e cycle o he oli e g o e, he e o e, IWwill be used o
he annual cos pe unk wood, as epo ed in Sec ion 2.2.2.
2.4. S ep 4: Maximize bene i unc ion
Calcula ing he maximum alue o he de ined unc ion FB,i,
ob ains he op imal du a ion o he p oduc i e cycle o o each
a ie y o oli e g o e, and hus, he op imal bio-ene gy cycle
pe iod, in yea s. Wi h his da a i is possible o de e mine he
po en ial o biomass gene a ion o ene gy [kg/ha].
Finally, he da a o he selec ed s udy a ea can be p ojec ed o
o he a eas, depending on he cul i a ed su ace o he oli e g o e
and he oli e ee a ie ies, in o de o ob ain an app oxima ion
o he pelle po en ial o o he geog aphical a eas.
3. Resul s
This sec ion co e s he applica ion o he de eloped me hod-
ology o he egion o Andalusia, in he Sou h o Spain, in o de o
de e mine he po en ial o gene a ing pelle s om was e unk
wood om he oli e g o es in he egion.
3.1. S ep 1. Delimi a ion and cha ac e iza ion o he s udy a ea
The Medi e anean a ea, and Andalusia in pa icula , has sig-
ni ican ac s o oli e plan a ions and a e one o he main sec o s
o he economy, con ibu ing o he gene a ion o employmen
and social, e i o ial and cul u al cohesion, as well as p oducing
one o he main p oduc s o he Medi e anean die . The su ace
a ea o oli e ee g o es is app oxima ely 1,500,000 ha. Fig. 5
shows he biomass po en ial o he e i o y in /ha om he
Andalusian oli e g o es (Eu opean Union and Jun a de Andalucía,
2008).
As was de eloped in Sec ion 2, he de ini ion o he bene i
unc ion, and cos s and income o each a ie y o oli e ee,
as economic a iables, mus be de ined: p oduc ion, unk wood
mass, p uning and ha es ing. These depend on a se o ac o s
ha cha ac e ize he a ea o s udy and a e shown in Table 3:
a ie y o oli e ee, ype o p oduc ion, age o he oli e ee,
densi y o plan a ion, age a he beginning o he p oduc i e cycle
and sale p ice o he oli es. The da a ha e a high le el o eliabili y
due o he annual da a upda es made by g owe s when hey apply
o cul i a ion aids g an ed by he Eu opean Union, and he public
egis e , included in he Ag icul u al Plo s Geog aphical In o ma-
ion Sys em. SIGPAC (Andalucía,2018;Conseje ía de Ag icul u a
Pesca y Desa ollo Ru al,2019).
Fig. 5. Po en ial p oduc ion o esidual biomass om oli e g o es in Andalusia
(Eu opean Union and Jun a de Andalucía,2008).
3.2. S ep 2: Calcula ion o economic a iables and es ima ion o
indi idual unc ions
The ollowing conside a ions we e aken in o accoun o he
calcula ion o economic a iables. The a ie ies o oli e ee wi h
an occupa ion g ea e han 90% we e selec ed which, in his case,
coincides wi h hose lis ed in Table 3 as he main a ie ies: Picual,
Hojiblanca, Manzanilla de Se illa, Lechín de Se illa, Ne adillo Neg o,
Picudo and Ve dial de Hué a (Conse je ía de Ag icul u a y pesca,
2002a). These ha e an occupa ion o 90.58% o he o al su ace
a ea o he oli e g o e, dis ega ding he seconda y a iables. In
ela ion o he p oduc ion egime, mos o he Andalusian oli e
g o es a e cul i a ed wi hou i iga ion (1,102,485 ha, which
ep esen s 73.5% o he o al a ea), so he i iga ion egime is
dis ega ded. I is conside ed ha he beginning o he p oduc i e
cycle, o all he a ie ies o oli e ees, begins in he i h yea o
age. In addi ion, an a e age selling p ice o 0.65 e/kg is es ima ed
o oli es o all a ie ies (Andalucía,2018).
3.2.1. Oli e g o e p oduc ion
P oduc ion depends on he ype o oli e g o e. The da a o
he es ima ion o p oduc ion h oughou he li e cycle o he
oli e g o e a e aken om he analysis o he Andalusian oli e
g o es (Conse je ía de Ag icul u a y pesca,2002b), hese a e
included in Table 4. Al hough he mos p oduc i e a ie ies a e
Hojiblanca and Picudo, i should be no ed ha he yield pe oli e
ee depends, in addi ion o i s a ie y, on o he ac o s such
as clima e, soil quali y, p esence o pes s o plan ing densi y. In
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V.M. Sol e o, L. Román, M.E. Pe al a e al. Ene gy Repo s 6 (2020) 2627–2640
Table 3
Cha ac e iza ion o he s udy a ea.
Geog aphical a ea Andalusia 1,500,000 ha o oli e g o e plan a ion
Oli e a ie ies Main (1,358,684 ha; 90.58%): Picual, Hojiblanca, Manzanilla de
Se illa, Lechín de Se illa, Ne adillo Neg o, Picudo and Ve dial de
Hué a .
Seconda y (141,316; 9.42%): A bequina, Go dal Se illana, Alo eña,
Ve dial de Vélez-Málaga, Lechín de G anada, Pico Limón, Manzanilla
Se ana, Alameño Blanco.
Cul i a ion egime A ea: 73.5% d y land; 26.5% i iga ed land
Densi y o oli e wood 960 kg/m3
Plan a ion Densi y 100 oli e ees/ha
Age a he s a o he p oduc ion cycle Age 5
Oli e sale p ice 0.65 e/kg
T unk wood sale p ice 30 e/
P oduc ion p uning equency 2 yea s
S a o p oduc ion p uning 20 yea old oli e g o e
Renewal p uning equency 3 yea s
Renewal p uning s a 50 yea old oli e g o e
T unk pe ime e g ow h 2.5 cm/yea
T unk heigh 1 m
Table 4
A e age p oduc ion pe oli e a ie y (Conse je ía de Ag icul u a y pesca,2002b).
Oli e a ie y A e age p oduc ion [kg/ ee]
Hojiblanca 27.00
Lechín de Se illa 10.42
Manzanilla de Se illa 20.30
Ne adillo Neg o 14.35
Picual 29.04
Picudo 22.63
Ve dial de Hué a 12.06
Table 5
Es ima ion o he p oduc ion income unc ion.
FI.PPa ame e alues
Va ie y a b c
Picual 0.2878 54.55 306.76
Hojiblanca 0.2727 50.03 227.5
Manzanilla de Se illa 0.2142 39.146 154.45
Lechín de Se illa 0.1298 23.797 39.428
Ne adillo neg o 0.1644 30.084 90.9
Picudo 0.2705 51.384 160.28
Ve dial de Hué a 0.1515 27.952 71.133
addi ion, he choice o a ie y is made by aking in o accoun he
a y yield o he ui , wi h Ve dial de Hué a , Picual, Picudo and
Ne adillo Neg o being he a ie ies ha ha e be e a y yield
compa ed o Lechín de Se illa, Manzanilla and Hojiblanca.
Applying he p ocedu e de ined in Sec ion 2.2.2, he ime e o-
lu ion o he oli e g o e is calcula ed o each a iable, ob aining
he ime p oduc ion income unc ion FI.P. The esul s a e shown
in exp ession (8),Table 5 and Fig. 6.
FI.P= −a· 2+b· +c(8)
The ela ionship o p oduc ion income (e/ha) o he age o
he oli e ee (yea s), gi es a quad a ic unc ion whose g aphical
ep esen a ion is an in e ed pa abola (a<0). As Fig. 6 shows, he
same end is es ablished o all a ie ies. P oduc ion inc eases
as he oli e ee g ows o each he e ex o he pa abola,
coinciding wi h he maximum yield o he oli e ee, om which
ime, p oduc ion begins o dec ease.
On he o he hand, as Table 5 shows, he alue o p oduc ion
di e s be ween a ie ies (pa ame e s a, b and c), wi h he o e-
seeable esul as discussed in Table 4, wi h he highes p oducing
oli e a ie ies being Picual, Picudo, Hojiblanca and Manzanilla
de Se illa, ollowed by Ne adillo Neg o, Ve dial de Hué a and
Lechín de Se illa.
3.2.2. Income by quan i y o unk wood mass
Fo he calcula ion o he unk wood mass, he ollowing
ac o s we e equi ed: a ie y o oli e, pe ime e o he unk,
maximum heigh o he unk, and, densi y o he wood. Fo he
se en selec ed a ie ies, i was conside ed ha he pe ime e o
he unk g ows by 2.5 cm annually, ha he e is a maximum
heigh o 1 m and a wood densi y o 960 Kg/m3. Also, o de-
e mine he income o unk wood, he plan a ion densi y da a
(100 oli e ees/ha) and sale p ice (30 e/ ) we e used. Applying
he p ocedu e epo ed in Sec ion 2.2.2, he e olu ion o he oli e
g o e is calcula ed o he economic a iable s udied, ob aining
he ime unc ions o unk wood mass MW, and income o unk
wood FI.W, he esul s a e shown in exp essions (9) and (10),
Table 6 and Fig. 7.
MW=a· 2+b· −c(9)
FI.W=a· 2+b· −c(10)
The ela ionship be ween income (e/ha) and he age o he
oli e ee (yea s) esul s in a simila inc easing unc ion o all
a ie ies, which can be seen om he pa ame e s lis ed in Table 6.
As Fig. 7 shows, he amoun o unk is di ec ly p opo ional o
he age o he oli e ee, wi h he same end being es ablished
o all a ie ies. This is due o an inc ease in he pe ime e , when
he inc ease in heigh o he oli e ee is limi ed o 1 me e.
In his case, he a ie y is no a de e mining ac o . In he i s
yea s o he oli e ee cycle, he amoun o unk is simila o
all a ie ies, bu only in hose in he ange o 50–100 yea s can
some di e ence be seen. I can he e o e be es ablished ha he
ela ionship be ween income om he sale o he ee and he
a ie y is no signi ican . The e is a di e ence o only 100e/ha
be ween he a ie ies o oli e ees a 100 yea s o age.
3.2.3. Oli e g o e p uning p ocess
Fo he p uning o he se en a ie ies o oli e ee, he same
mechanism, ype and cos was used. The ollowing da a we e
aken o cha ac e ize he p ocess: beginning o o ma ion p uning
a 2 yea s o age o he ee, ca ied ou wi h a iennial equency;
beginning o p oduc ion p uning a 20 yea s o age, wi h a bien-
nial equency; beginning o eno a ion p uning a 50 yea s, wi h
iennial equency. Finally, Table 7 lis s he p uning ac i i ies,
he hou s dedica ed o hese ac i i ies, depending on he g ow h
phase o he oli e ee, and he cos associa ed wi h he p ocess.
As Table 7 shows, and aking in o accoun he assump ions
desc ibed, a p uning cos o 135.38 ee e y h ee yea s is o eseen,
2633
V.M. Sol e o, L. Román, M.E. Pe al a e al. Ene gy Repo s 6 (2020) 2627–2640
Fig. 6. Dis ibu ion o alues o p oduc ion income unc ion.
Table 6
Es ima ion o unk wood mass and unk wood income unc ion.
Va ie y Pa ame e alues o MWPa ame e alues o FI.W
a b c a b c
Picual 14.827 433.66 7130.8 0.0445 1.301 21.392
Hojiblanca 14.798 426.83 707.6 0.0444 1.2805 21.224
Manzanilla de Se illa 13.598 358.29 6013.2 0.0408 1.1049 18.04
Lechín de Se illa 13.598 368.29 6013.2 0.0408 1.1049 18.08
Ne adillo neg o 13.598 368.29 6013.2 0.0408 1.1049 18.04
Picudo 14.829 433.91 7132.1 0.0445 1.3017 21.396
Ve dial de Hué a 13.6 367.93 5998.5 0.0408 1.038 17.995
Fig. 7. Dis ibu ion o alues o unk wood income unc ion.
Table 7
P uning mechanism, hou ly cos and hou s in es ed (Fundación CITOLIVA,2007).
Ac i i y Cos [e/h] Fo ma ion
p uning [h]
P oduc ion
p uning [h]
Reno a ion
p uning [h]
P uning wi h chainsaw 12.95 6 12 18
Cleaning and collec ion o i ewood 7.21 4 9 15
Bu ning o p uning was e 7.21 4 9 15
TOTAL [e/ha]135.38 285.18 449.4
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V.M. Sol e o, L. Román, M.E. Pe al a e al. Ene gy Repo s 6 (2020) 2627–2640
Table 8
Es ima ion o he p uning cos unc ion.
Va ie y Pa ame e alues o FC.P
a b
Picual, Hojiblanca, Manzanilla de Se illa,
Lechín de Se illa, ne adillo neg o,
picudo, e dial de Hué a
0.5085 96.368
om yea 2 o yea 19 o he oli e ee. In yea 20, he biennial
p uning cos inc eases o 285.18 eun il yea 50, hen becoming
iennial and amoun ing o 449.40 e.
Applying he p ocedu e de ined in Sec ion 2.2.3, he e olu ion
o he oli e g o e is calcula ed o he a iable s udied, ob aining
he p uning cos unc ion FC.P[e/ha]. The esul s a e shown in
exp ession (11),Table 8 and Fig. 8. The unc ion is de ined, a
in e als, al hough an annual ans o ma ion is made o he
di e en equencies (biennial and iennial).
FC.P=a· +b(11)
The ela ionship be ween p uning cos s (e/ha) and he age o
he oli e ee (yea s) gi es a unc ion de ined a in e als. This is
due o he ac ha p uning ope a ions a e biennial, o iennial,
depending on he li e cycle o he oli e g o e, hus he e is a ze o
cos in pe iods wi hou p uning. In o de o de ine he p uning
cos unc ion, app op ia e o he objec i e o he s udy, he a e -
age annual cos was conside ed, gi ing he ep esen a ion shown
in Fig. 8. As Table 8 shows, a linea ela ionship is es ablished
be ween he cos o p uning and he age o he oli e ee, wi h he
same end o all a ie ies. As he age o he oli e ee inc eases,
mo e nume ous and in ensi e p uning ope a ions a e equi ed
o compensa e o he loss o he yield o he ee wi h age (as
desc ibed in he p oduc ion income unc ion in Sec ion 3.2.1).
3.2.4. Oli e ha es ing p ocess
To calcula e he cos o ha es ing, he ollowing ac o s we e
aken in o accoun : a ie y, p oduc ion [kg/ha], ha es ing mech-
anism, and, he beginning o he p oduc i e cycle (5 yea s). The
ha es ing mechanism a ies depending on he ype o oli e
g o e. Fo a adi ional mechanized oli e g o e, (i) milking, (ii)
b anch ib a o wi h complemen a y p ocess (knock down), and,
(iii) collec ion wi h can ases, depending on he age o he spec-
imens, a e used (AEMO (Asociación Española de Municipios de
Oli o),2012;Ag icul u e and Ru al De elopmen ,2012). Speci -
ically, o young oli e ees and up o he age o 50, adi ional
me hods such as milking a e used which, in his case, and bea ing
in mind ha he ope a o s collec 250 kg/day in a 7-hou day
wi h es , he cos amoun s o 54.42 e/day. F om he age o 50
un il he end o he p oduc i e li e, a b anch ib a o is used
wi h a complemen a y p ocess (knock down) and collec ed wi h
can ases, as long as he oli e ees ha e a non-bi u ca ed unk,
a unk heigh g ea e han 0.7 m, h ee o ou main b anches
and an up igh pos u e, he cos being 0.17 e/kg in non-i iga ed
c ops (Na e o e al.,2017;Fabb i,2004).
Applying he p ocedu e de ined in Sec ion 2.2.4, he e olu ion
o he oli e g o e is calcula ed o he a iables s udied in o de
o ob ain he collec ion cos unc ion FC.H. The esul s a e shown
in exp ession (12),Table 9 and Fig. 9.
FC.H=a· 3−b· 2+c· +d(12)
The ela ionship be ween he p uning cos (e/ha), and he age
o he oli e ee (yea s), p o ides he se o pa ame e s lis ed in
Table 9, which ep esen he ha es ing cos unc ion. As Fig. 9
shows, he ha es ing cos is di ec ly p opo ional o p oduc i i y
(kg ui /oli e ee), g owing exponen ially up o he maximum
poin o he cu e, om which poin i begins o dec ease. The
Table 9
Es ima ion o he ha es ing cos unc ion.
Va ie y Pa ame e alues o FC.H
a b c d
Picual 0.0019 0.4684 31.108 175.15
Hojiblanca 0.0018 0.4544 30.677 97.981
Manzanilla de Se illa 0.0014 0.3564 24.034 76.323
Lechín de Se illa 0.0008 0.2052 14.352 21.705
Ne adillo neg o 0.001 0.2692 18.756 24.603
Picudo 0.0016 0.0414 29.213 82.833
Ve dial de Hué a 0.0009 0.2257 15.966 36.568
di e en yields o each a ie y also a ec ha es ing cos s. Finally,
he cos depends on he ha es ing echnique used, which is mo e
e icien acco ding o he le el o p oduc ion, and he size o he
c own. Picking by hand, when he specimens a e young, in ol es
a highe cos , and a b anch ib a o , op imal when he oli e ee
is mo e p oduc i e, educes ha es ing ime and cos s.
3.3. S ep 3 and 4: De ini ion o he bene i unc ion and he op imum
li e cycle o each oli e a ie y
Wi h he da a ob ained in S ep 2, and wi h he indi idual
unc ions o he ou economic a iables, he bene i unc ion
FB,iis ob ained o each oli e a ie y. A e ha , he maximum
bene i unc ion is calcula ed and, hus, he op imal li e cycle
o each a ie y. The esul s a e shown in exp ession (13). The
esul s shown in Table 10 a e ob ained by maximizing his ex-
p ession: he PCop alue co esponds o he op imum cycle o an
oli e g o e, in yea s, o each a ie y. As can be seen om he
esul s, he di e ences be ween a ie ies a e small, and Picudo,
wi h 100.31 yea s, and Picual and Ve dial, wi h 97.5 yea s, a e
highligh ed.
MAX [FB,i]=FIP,i+FIW,i
−FCP,i−FCH,i(13)
= −αi· 2+βi· −γi
−δi
I is possible o calcula e da a on he exploi a ion o he oli e
g o e, by using he PCop. This demons a es he o al ons o wood
a ailable in each egion. As an example, he Picual a ie y would
p oduce 155,590.21 ons o unk wood pe yea , wi h espec o
he op imal li e cycle o 97.41 yea s, wi h an annual eplan ing
need o 8652.51 ha.
Conside ing he op imum li e cycle, he a ea occupied and
he plan a ion densi y o each a ie y, he unk wood mass is
es ima ed o be ob ained a he end o he p oduc i e cycle o he
oli e g o e, wi h he exp ession (9) de eloped in Sec ion 3.2.2.
The esul s a e summa ized in Table 11.
The alues shown in Table 11 a e associa ed wi h 90% o he
a ea occupied by he oli e g o es in Andalusia. Co ec ing his
da a, he Andalusian oli e g o es could p o ide a o al o 266,664
onnes/yea . On he o he hand, aking in o accoun ha oli e
wood con ains 20%–25% humidi y and es ima ing a 15% dec ease,
in he was e pelle ing p ocess, 159,998.50 pelle s/yea would be
ob ained.
To analyse he in luence o each o he incomes and cos s ha
appea in he exp ession (13), he case is made o he Picual
a ie y. I is possible o iden i y which is he de e minan ac o
among he cos s o incomes o de ine he op imal li e cycle o he
oli e ee. Fig. 10 shows he income, cos s and bene i s o e he
yea s. The p o i line will each i s maximum when he op imal
li e cycle o he oli e ee is eached.
As can be seen in Fig. 10, he a iable ha has he mos in lu-
ence in de e mining he op imal ime o exploi a ion o he oli e
ee is he income pe p oduc ion. Ha es ing cos s a e he nex
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