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Renewable and Sustainable Energy Reviews
journal homepage: www.elsevier.com/locate/rser
Biogas from animal manure: A sustainable energy opportunity in the Canary
Islands
J.L. Ramos-Suáreza,⁎, A. Ritterb, J. Mata Gonzáleza, A. Camacho Péreza
a Departamento de Ingeniería Agraria, Náutica, Civil y Marítima, Sección de Ingeniería Agraria de la Escuela Politécnica Superior de Ingeniería (EPSI), Universidad de La
Laguna (ULL), Carretera de Geneto, 2, 38071 La Laguna, Tenerife, Spain
bUniversidad de La Laguna, Área de Ingeniería Agroforestal, Ctra. de Geneto, 2, La Laguna, Tenerife 38200, Spain
A R T I C L E I N F O
Keywords:
Anaerobic digestion
Biogas
Canary Islands
Livestock wastes
Renewable Energy
A B S T R A C T
Biogas production from animal manure produced in farms in the Canary Islands may represent an additional
energy source for producing heat and/or electricity. Data of different animal farms distributed all around the
islands were used for evaluating the potential biogas generation and contribution to the production of renewable
energy in the Canary Islands. Total manure production is 495,622 tons per year. Results show that animal
manure as a source of biogas may be associated with an overall biogas potential of 27.1Mm3 year−1 with an
equivalent installed power capacity of 6.8MWe. Considering 0.5 t day−1 manure as the lowest limit for im-
plementing biogas projects, 546 farms raising different animal types (poultry, sheep, swine, cows or goats) have
potential for producing and using their own biogas for generating heat and/or electricity with electrical powers
ranging from 3 to 185 kWe. Potential GHG emissions savings due to the production of biogas from animal
manure could reach yearly 55,745.1 tons of carbon dioxide equivalents, including both substitution of fossil fuels
and appropriate management of animal manure.
The application of appropriate policies described in this study should contribute to overcome main challenges
identified for the development of the biogas industry in the Canary Islands, which are related to the small size of
the livestock holdings, the lack of a culture of association in the livestock sector and the lack of specific subsidies
for biogas production. This study could be used as a basis for further studies in other European outermost regions
with similar characteristics to the Canary Islands, such as Madeira and Azores.
1. Introduction
Biogas represents a renewable source of energy that results from the
anaerobic digestion of almost any kind of organic matter [1]. Since it is
mainly composed of methane [2] it can be used for any energy appli-
cations in which natural gas is employed [3]. The simplest applications
of biogas are the generation of heat and/or electricity using boilers,
generators or with Combined Heat and Power (CHP) units [4]. Biogas
production has made significant progress worldwide, both in large-scale
biogas plants and in small-scale domestic digesters [5]. In Europe, the
biogas industry has been in constant growth during the last decade
driven by several countries that today are a world reference in the
sector. In 2016 primary energy production from biogas increased 3%
compared to 2015, reaching 16.1 Mtoe [6]. Almost half of it is produced
in Germany, which is the leader of the biogas industry. After Germany,
UK and Italy contribute about 2.4 and 2.0 Mtoe, respectively. Spain is
far away from the leading countries, with only 230.8 ktoe of primary
energy production from biogas, 80.6% coming from landfills and
sewage [6].
Germany produced 33.07 TWh of electricity from biogas during
2015, most of it (93.1%) coming from agricultural biogas plants using
energy crops and manures [5,7]. According to Daniel-Gromke et al. [7]
there were 8200 agricultural biogas plants in Germany in 2016 with an
average installed capacity of 520 kWe. Biogas plants treating manure as
sole substrate produced only 12.4% of the total electricity coming from
biogas in 2016 [7]. In 2011 29% of the manure produced in Germany
was treated through anaerobic digestion, all of them in farm size in-
stallations, whereas this percentage was only 6.4% of the livestock
manure in the EU [8]. The percentage of manure treated by anaerobic
digestion should be now much higher, since only 3800 biogas plants
https://doi.org/10.1016/j.rser.2019.01.025
Received 13 April 2018; Received in revised form 26 December 2018; Accepted 10 January 2019
Abbreviations: CHP, combined heat and power; GDP, Gross domestic product; GHG, Greenhouse gases; GIS, Geographic information system; LSU, livestock units;
OFMSW, organic fraction of municipal solid waste; WWTP, wastewater treatment plants
⁎ Corresponding author.
E-mail address: jramossu@ull.es (J.L. Ramos-Suárez).
Renewable and Sustainable Energy Reviews 104 (2019) 137–150
1364-0321/ © 2019 Elsevier Ltd. All rights reserved.
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were accounted in Germany for 2011. However, in recent years the
development of the biogas industry in Germany has been slowed down
by the change in the compensation conditions of this type of facilities
and the limitation to the use of energy crops [6,7].
In contrast to Germany and other countries like Italy or UK, in Spain
the agricultural biogas potential remains untapped, and the near future
does not look any better. Nowadays, there are 46 biogas plants in Spain,
excluding sewage and landfill biogas, summing up only 20MW [9].
However, Spain is the 2nd producer of swine, the 4th producer of
poultry and the 6th producer of cattle in Europe. As a consequence,
Spain is the 4th largest manure producer in the EU, with more than 118
millions of tons per year, close to that of UK (more than 139 millions of
tons) and higher to that of Italy (98.5 millions of tons) [10]. Therefore,
potential biogas production from animal manure in Spain is largely
wasted. As an example, in the UK the primary energy production from
biogas has increased from zero in 2011 up to 660.9 in 2016, whereas in
Italy it has increased from 323.9 in 2011 up to 1570.8 in 2016 (in-
cluding agricultural, agri-industrial and OFMSW biogas plants) [11,6].
This shows that with a similar manure production it is possible to de-
velop the biogas industry if appropriate policies are implemented.
According to Foged et al. [8] only 0.69% of the manure produced in
Spain was treated through anaerobic digestion in 2011. The poor de-
velopment of the biogas industry in Spain is the result of national po-
licies. Today there is no specific support scheme for the generation of
electricity or heat from biogas and, before 2012, when the feed-in tariffs
system was suspended, the maximum bonus for biogas plants (14c
€/kWh) was not enough to attract investments in biogas energy [12].
Bangalore et al. [13] showed that the state of development of the biogas
industry in different countries is not dependent on feedstock avail-
ability or technological advantage, but rather the policy incentives.
Currently, renewable power enters the Spanish energy system through
auctions, in which the maximum working hours per year that are paid
are below what a biogas plant can work per year, therefore, being
detrimental to biogas. In fact, out of 3000MW auctioned at the end of
May, only 4.8 MW were allocated to agricultural biogas, 4.5MW cor-
responding to the same plant located in Asturias (in the North of the
Iberian Peninsula).
Although in Spain the biogas industry is at a standstill, in the rest of
Europe the industry current trend is the production of biomethane
thanks to the improvements in the upgrading technology [5]. This si-
tuation is also a consequence of cuts or uncertainties regarding feed-in
tariffs for electricity
production from biogas plants in countries such as
UK, Italy and Germany [14,12], leading to a low profitability of elec-
tricity biogas plants [5]. Biomethane can be used for transport or for
injection in the natural gas grid, substituting fossil fuels. Meyer et al.
[15] estimated the potential substitution in the EU of natural gas with
biogas produced from animal manure, straw and grass to be 9–16%.
Increase in biomethane production in 2016 was 40% compared to
2015, more than 10 times higher the increase in primary energy pro-
duction from biogas [6]. Investment costs of such facilities are still high,
and the capital costs are inversely related to the plant size [16],
therefore, implementation of biogas upgrading in small-scale biogas
plants is still difficult.
Despite the several hindrances observed in Europe for the continued
development of the biogas industry in the last years, biogas and bio-
methane still have a high potential and represent an opportunity for
Europe. Biogas can be used for grid stabilization when high renewable,
variable electricity is introduced in an energy system, such as solar and
wind energy, as biogas can be easily stored or produced on-demand
[17–19]. In an island context, this differentiating quality of biogas with
respect to most renewable energies could be the driving force of its
production, especially when there are no continuous sources of re-
newable energy such as geothermal and/or hydroelectric. European
outermost regions, constituted by Guadeloupe, French Guiana, Marti-
nique, Réunion, Saint-Martin, the Azores, Madeira and the Canary Is-
lands face several challenges for widespread of renewable energies,
such as isolation from continental grids and even from other islands
from the same archipelago and lack of energy storage capability, which
leads to system instability [20].
The aim of this study is to evaluate the biogas potential from
anaerobic digestion of animal manures in the Canary Islands to explore
its potential contribution to the production of renewable electricity.
The main contributions of this study to the scientific knowledge and the
development of the biogas industry are: (i) the analysis of the current
situation of the biogas technology in the region and with similar regions
in the European context, such as the Autonomous regions of Azores and
Madeira; (ii) the analysis of the potential production of biogas from
manure, (iii) the geolocation of animal manures production sources,
(iv) the identification of the factors that slow down the development of
the biogas industry in the Canary Islands; and (v) the proposal of cor-
rective measures aiming to promote the development of the biogas
industry in the agricultural and livestock sector, proposals which could
be used as a model for other European outermost regions similar to the
Canary Islands.
2. Potential benefits of the introduction of biogas in the Canary
Islands
The Canary Islands are a Spanish archipelago made up by eight is-
lands that are located next to the southwest coast of Morocco, on the
African continent. With a total area of 7446.95 km2 and 2,108,121 in-
habitants [21], it constitutes an independent energy systems that is
isolated from both Europe and Africa. In fact, only the islands Tenerife
and La Gomera, and Fuerteventura and Lanzarote are interconnected by
submarine power cables. These and the rest of islands constitute in-
dependent energy systems.
According to the latest Canary Islands Energy Yearbook [22] the
primary and the final energy consumption in 2016 was 4,728,936 and
3,504,302 toe, respectively, with an increase of 4.87% and 6.07%
compared to 2015. The trend of the primary and final energy con-
sumption during the last years is shown in Fig. 1a. Inner production of
energy in 2016, which corresponded entirely to renewable energy
(wind, photovoltaic, solar thermal, hydroelectric, mini-hydraulic and
landfill biogas) was 68,189 toe, with an increase compared to 2015 of
1.21%. The contribution of the renewable energy sector to the energy
production in the Canary Islands is low, being 1.95% of the final energy
consumption during 2016 (Fig. 1a). There was a constant increase of
the renewable energy production since 2011 and the aim of the Gov-
ernment of the Canary Islands is to maintain this increase in the coming
years even at higher rates.
In 2016 electricity corresponded to 20.08% of the final energy
consumption in the Canary Islands [22]. The electricity production has
decreased in the last years as a consequence of the world economic
crisis suffered from 2008 (Fig. 1b). Contrarily, contribution of renew-
able energies has increased significantly since 2000 (3.6%) until 2016
(7.6%). However, this percentage is still far away from the contribution
of the renewable energy sector to the national electricity production:
38.9% of the electricity produced in Spain during 2016 came from re-
newable energies [23].
Most electricity generated in the Canary Islands during 2016
(92.5%) is produced in thermal power plants using gas oil, diesel oil
and fuel. These oil-derived products are all imported and used in
combined cycles, steam turbines, diesel motors, and gas turbines
thermal power plants [22]. Fig. 1e shows the gross electricity produc-
tion in each island according to the type of technology used, which
summed up 9213.53 GWh in 2016. It should be noted that in isolated
electrical systems, production and consumption of electricity must be
the same to achieve a stable system. Therefore, on each island, gross
electricity production matches electricity consumption plus the elec-
tricity losses. Electricity consumption was 8771.39 GWh during 2016,
with an increase of 1.2% compared to 2015. Electricity demand is
variable by islands, since not all are equally populated or have the same
J.L. Ramos-Suárez et al. Renewable and Sustainable Energy Reviews 104 (2019) 137–150
138
economic activity. The two capital islands, Gran Canaria and Tenerife,
account for 79% of total electricity consumption [22]. Maximum net
power demand is also variable in each island, oscillating from 8.1MWe
in El Hierro up to 549.0MWe in Tenerife. In terms of electricity demand
by economic sectors, the domestic sector and the hotel industry with
36.90% and 16.97%, respectively, represented the highest demand,
whereas the primary sector electricity demand was only 1.94% in 2016
[22]. In summary, the energy system of the Canary Islands is
characterized by being isolated and by a high dependence on imported
fossil fuels. Consequently, the cost of the electricity production is the
highest in the country. During 2016 the production cost was 135.8 € per
MWh in the Canary Islands [22], with a decrease of 10% compared to
2015. Meanwhile, the average price of electricity in the electricity
market in Spain during the same period was 48.40 € per MWh [24].
Besides the high price of generation, thermal power plants using oils
have the greatest pollution indexes compared to other fossil fuels,
Fig. 1. Energy and electricity panorama in the Canary Islands, based on [22]. (a) Primary (brown) and final (orange) energy consumption and contribution of
renewable energy (green) in the Canary Islands between 2011 and 2016; (b) Electricity production based on conventional (orange) and renewable (green) energy
between 2000 and 2016. (c) Average electricity production costs between 2008 and 2016; (d) renewable energy production in the Canary Islands during 2016; (e)
gross electricity production in each island based on technology used: thermal steam power plant (blue), thermal diesel power plant (orange), thermal gas power plant
(grey), thermal combined cycle power plant (yellow), refinery and cogeneration (brown), renewable energy (green).
J.L. Ramos-Suárez et al. Renewable and Sustainable Energy Reviews 104 (2019) 137–150
139
excluding coal and lignite [25,26].
The Government of the Canary Islands established in its latest
Energy Plan the production of 30% of the electricity consumed on the
islands from renewable
sources as a target for 2015 [27]. Based on the
information discussed above, this goal was not accomplished by far,
thus jeopardizing the compliance with the European directives for the
use of renewables in Spain [28].
The contribution of renewable energies to the production of elec-
tricity in the Canary Islands is mainly due to wind and solar energy,
with 391.2 and 273.2 GWh in 2016, respectively. Mini-hydraulic, the
combination of hydro and wind energy and biomass energy completed
the contribution of renewables to the electrical system in 2016 (Fig. 1d)
[22]. Nowadays biomass energy is solely represented by the biogas
produced in two landfills of Tenerife and Lanzarote, with 1.6 and
2.1MW of installed power, respectively [22]. In future months, it is
expected the connection of the electricity produced in one landfill of
Gran Canaria to the network of the island, thus increasing electricity
production from biomass up to more than 6MW. This last plant will
also use the biogas produced in four anaerobic digesters treating the
organic fraction of municipal solid waste (OFMSW) and the sludge
produced in almost all wastewater treatment plants (WWTP) on the
island.
As mentioned above, electricity generated in the Canary Islands is
produced primarily based on imported fossil fuels and the renewable
electricity comes mainly from solar and wind energy (95.6%). A greater
penetration of renewable energies in the system would need stable,
non-fluctuating renewable energy sources, especially necessary in in-
dependent island systems. Biogas plants can provide a constant elec-
tricity supply [29] or can even be converted into modular/flexible
systems that are able to adapt electricity production depending on peak
demands [17,18]. This would give biogas energy a higher added value
compared to other renewable electricity sources due to its ability to
balance demand and supply in the islands energy systems. Despite the
significant generation of organic waste, no relevance has been given to
biogas energy in research and/or policies aiming at a higher penetra-
tion of renewable energy in the Canary Islands, nor in other similar
energy systems in the EU such as Madeira and Azores, where biogas is
an untapped source of energy [30–33]. In the Autonomous Region of
Madeira there is no electricity production from biogas [34], despite
having participated in European projects aiming at promoting tech-
nologies for energy production from biogas from municipal waste [35].
In fact, in Madeira island municipal solid waste are incinerated, with
the production of 5% of the electricity in the electricity mix [34]. On
the island São Miguel (Azores) biogas is produced from swine slurry,
representing the only agricultural biogas plant with electricity pro-
duction and injection to the grid in the Macaronesia. The company
Agraçor-Suinos dos Açores SA has two biodigesters of 1500m3 treating
the swine slurry produced by 15,000 swine [36]. This biogas plant has
an installed power of 760 kWe and produced 0.07% of the electricity in
São Miguel during 2017 [37].
The status of the biogas industry in these three European outermost
regions reflects the status in Spain and Portugal, where biogas energy
production is very low [38] compared to other European countries. This
is a logical consequence of national policies that do not consider out-
ermost regions particularities regarding their energy system and elec-
tricity production costs, already mentioned above [20].
The development of the biogas industry does not only influence the
energy system, but also the cattle and the agricultural industry and the
environment of the region. On the one hand, the primary sector is a
minor economic sector in the Canary Islands, being 1.21% of the total
GDP (Gross Domestic Product) [39] and employing more than 25,000
persons, which is equivalent to 2.3% of occupied [40]. Total agri-
cultural production amounted to 904,316 t year−1 in 2016 in 40,063.5
cultivated hectares. Tenerife, Gran Canaria and La Palma are the islands
with the largest cultivated surface, with banana as the dominant crop
with more than 9,000 ha [41]. Despite the low relative importance of
the sector, during 2016, Canarian farmers imported more than 39,000
tons of mineral fertilizers valued at more than 26M€ [42]. The anae-
robic digestion of animal manures, besides biogas production, leads to
the conversion of animal manures into digestates, which has some
benefits such as improvement of fertilizer quality, reduction of odors
and pathogens and possible novel uses in agriculture such as hydro-
ponics [43,44]. The anaerobic digestion of manures could therefore
lead to a higher acceptance of digestate by the farmers, a decrease in
the use of imported mineral fertilizers and an increase of savings for
Canarian farmers. Moreover, the use of digestates for agriculture can
have a positive effect in resource conservation and soil quality main-
tenance [45], which is crucial for agriculture in sub-tropical regions
within a climate change context.
On the other hand, more than 40% of the territory of the Canary
Islands is protected, which means that the Canary Islands have a great
environmental value in terms of flora, fauna and landscape. The man-
agement of livestock wastes is a pending issue in the Canary Islands,
leading to pollution of soils and aquifers. In fact, it is considered as one
of the priorities in the regional Rural Development Plan [46]. In this
context anaerobic digestion can play a key role in the development of
new management strategies, both on-farm or centralized, increasing the
environmental awareness of farmers about their wastes and the op-
portunity that these wastes represent if proper management is carried
out.
In addition, since the energy production in the Canary Islands is
highly dependent on fossil fuels, the generation of electricity from
biogas can substitute part of the fossil fuels currently used, thus de-
creasing GHG emissions. Moreover, substitution of mineral fertilizers by
digestate and controlled degradation of manure could further reduce
GHG emissions.
On the social side, in addition to contributing to the environment
improvement, biogas plants are known to be promoters of job creation
[47] and to increase or diversify the sources of income in rural areas
[48]. Furthermore, in the Canarian context, attending to remoteness,
high population density and unemployment rate, biogas plants can
have additional benefits: (i) increasing food and energy self-sufficiency;
(ii) improving the cohabitation of livestock farms and residential areas
due to odor and insect reduction; (iii) attracting professional and young
entrepreneurs to the primary sector, which is mainly occupied by
people of advanced age and cries out for a generational renewal [46];
(iv) encouraging the association and cooperatives among farmers,
which is one of the pending subjects of the primary sector for growing
at a greater pace [46].
3. Methodology
3.1. Determination of manure availability and biogas potential from animal
manure
Each farm was identified using the data from the Canary Islands
Livestock Register [49] that includes the geolocation (UTM co-
ordinates) and number of animals for each species and for each animal
type.
A manure production coefficient was assigned to each animal (ac-
cording to species and typology). Similarly, a biogas generation coef-
ficient was selected for each type of waste. These coefficients were
obtained from the Probiogas Project [50] and from the Biogas3 Project
[51]. For calculating and comparing animal census of livestock farms
with different animal species and types, LSU equivalents for each type
of animal were obtained, using the conversion tables that the Canary
Islands Government uses when planning subsidies for the livestock
sector [52]. The complete list of coefficients and LSU equivalent are
shown in Table 1.
Waste production and potential biogas generation were calculated
for each livestock farm according to Eqs. (1) and (2). Livestock
farms
were classified according to the electrical power that can be produced
J.L. Ramos-Suárez et al. Renewable and Sustainable Energy Reviews 104 (2019) 137–150
140
from their biogas potential, calculated based on Eqs. (3) and (4). These
data were then added up to a municipal level according to Eqs. (5) and
(6) to obtain the information that facilitates the adoption and execution
of policies for appropriate manure management and the promotion of
biogas production.
∑=R A Q·h
h
ij ij
(1)
where Rh is the daily amount of manure produced in livestock farm h
(kg day−1); Aij is the number of animals of the species i and type of
animal j in the livestock farm h; and Qij is the daily amount of manure
produced by type of animal j of the species i.
∑=B A Q TS VS Y· · · ·h
h
ij ij ij ij ij
(2)
where Bh is the daily biogas volume produced in the livestock farm h
(m3 day−1); TSij is the total solids content in manure Qij (%/100); VSij is
the volatile solids content, with respect to total solids, in manure Qij
(%/100); and Yij is the biogas yield for manure Qij (Lbiogas kgVS−1).
∑=Pb
LHW B CH
24
·h CH
h
ij ij
4
4
(3)
where Pbh is the gross power from biogas on farm h (kW); Bij is the daily
biogas volume produced in farm h from waste of the species i and an-
imal type j (m3 day−1); CH4ij is the methane content of biogas produced
in farm h from waste of the species i and animal type j (%); and LHWCH4
is the methane lower heating value (9.96 kWh m−3).
=Pe Pb
η
·
100h h
e
(4)
where Peh is the electrical power from biogas in farm h (kWe); and ηe is
the average electrical efficiency of biogas gensets and CHP units (30%).
∑=RM R
365
1000k k
hk
(5)
where RMk is the yearly amount of manure produced in municipality k
(t year−1); Rhk is the daily amount of manure produced in farm h of
municipality k (kg day−1).
∑=PM Pek
k
hk
(6)
where PMk is the electrical power from biogas in municipality k (kW);
and Pehk is the electrical power from biogas in farm h located in mu-
nicipality k.
All these data and results were used to discuss the potential con-
tribution of biogas to the energy system of the Canary Islands. The
evaluation was carried out using GIS and considering the external
elements that influence the development of the biogas industry in the
Canary Islands. In order to estimate the real contribution of biogas from
livestock waste to the Canarian energy system, certain corrections were
applied to the availability of manure to generate biogas. These cor-
rections are not only based on availability factors of manure, but also
on the financial limitations of a small farmer to invest in a biogas plant.
For cow manure, smallest farm (i.e., producing less than 0.5 t
day−1) were not considered for calculating the corrected biogas po-
tential. On the other hand, larger farms are able to use manure for
biogas production before any other application they have currently for
manure, such as agricultural use or solids recycling as bedding.
Therefore, for larger farms no availability factor was considered. In this
way, a correction was applied based on an economic point of view for
cow farms, since small farmers will not have the means for investing in
a biogas plant, and due to the small quantity of manure they produced
it is easier to find alternative management ways, such as direct appli-
cation in agricultural fields.
Goat and sheep manure produced in small farms (< 0.5 t day−1)
was also not considered. Furthermore, an availability factor of 40% was
applied to the rest of farms. The reason is that in the Canary Islands goat
and sheep farming is mostly intensive, but farms are normally poorly
conditioned: there is no roof covering the pens, whose soil is of sand or
ground, so that manure is not collected in any way. Only few farms,
those with larger number of animals, are well conditioned and would
have the chance to collect manure properly for biogas production.
Swine slurry produced in small farms (< 0.5 t day−1 of manure)
was also not considered based on an economic point of view. Besides
this limiting factor, no other correction factor was considered. In fact,
swine farms in the Canary Islands have serious problems for a proper
management of their residues since swine slurry is not appreciated for
agricultural use.
Several limitations for the use of hen and chicken manure for biogas
production were found. Firstly, small farms (< 0.5 t day−1 of manure)
were not considered due to economic reasons. Secondly, farms that
Table 1
Coefficients used for the calculation of manure production and biogas potential.
Animal Type W (kg) LSUe Rh (kg head−1 day−1) TS (%) VS (%TS) Y (L kgVS−1) CH4 (%)
Swine Boar 165.0 0.30 7.01 17.5 75.0 460.8 66.4
Sows 110.0 0.20 7.01 17.5 75.0 460.8 66.4
Replacement 77.0 0.14 3.34 17.5 75.0 469.8 57.9
Raising/Transition 66.0 0.12 3.34 17.5 75.0 469.8 57.9
Fattening 66.0 0.12 3.34 17.5 75.0 469.8 57.9
Piglet 11.0 0.02 0.38 17.5 75.0 469.8 57.9
Cows Breeding female 550.0 1.00 30.44 20.0 80.0 333.3 60.9
Breedig male 456.5 0.83 15.84 20.0 80.0 333.3 60.9
Replacement 401.5 0.73 13.29 20.0 80.0 333.3 60.9
Fattening 198.0 0.36 13.29 20.0 80.0 333.3 60.9
Goats Breeding female 82.5 0.15 2.30 30.0 80.0 449.3 60.0
Breedig male 82.5 0.15 2.30 30.0 80.0 449.3 60.0
No breeders between 4 and 12 months 27.5 0.05 1.29 30.0 80.0 449.3 60.0
No breeders under 4 months 27.5 0.05 1.29 30.0 80.0 449.3 60.0
Sheeps Breeding female 82.5 0.15 2.30 30.0 80.0 452.4 55.0
Breedig male 82.5 0.15 2.30 30.0 80.0 452.4 55.0
No breeders between 4 and 12 months 27.5 0.05 1.29 30.0 80.0 452.4 55.0
No breeders under 4 months 27.5 0.05 1.29 30.0 80.0 452.4 55.0
Poultry Laying hens in Cages 5.5 0.01 0.110 40 75 447.0 65.1
Laying hens in barns 5.5 0.01 0.110 40 75 447.0 65.1
Hens in breeders 2.75 0.005 0.110 40 75 447.0 65.1
Broilers 2.75 0.005 0.027 60 75 410.4 54.1
W: Average weight; LSUe: LSU equivalent; Rh: Manure production; TS: total solids content in manure; VS: volatile solids content, with respect to total solids; Y: biogas
yield; CH4: biogas methane content.
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produce free-range eggs were not considered due to the difficulty of
collecting clean manure for biogas production.
Finally, rabbit manure was not considered for the calculation of the
biogas production potential due to the small size of the farms.
Results are shown in tables and maps that were created using QGIS
software (v2.18).
3.2. Determination of potential GHG emissions savings
Potential GHG emissions savings were calculated for: (i) the sub-
stitution of conventional manure storage by anaerobic digestion treat-
ment and (ii) for the displacement of fossil fuels by renewable biogas in
the electricity mix of the Canary Islands.
On the one hand, GHG emissions for manure storage were calcu-
lated for the animals that are in farms producing more than 0.5 t day−1
of manure. For each type of animal (hens, chicken, dairy cattle, other
cattle, swine, goat and sheep) emissions factors were used according to
IPCC Guidelines for National Greenhouse Gas Inventories, Tier 1 sim-
plified method [53], considering Canary Islands as part of Western
Europe and with temperate climates, with mean annual temperatures of
21 ºC. The livestock heads for each species/category in farms produ-
cing> 0.5 t day−1 of manure were determined according to the Canary
Islands Livestock Register [49]. An availability factor of 40% was ap-
plied for goat and sheep herds, accordingly to manure availability for
biogas production (see Section 3.1).
On the other hand, emissions savings due to substitution of fossil
fuels in the electricity mix of the Canary Islands was calculated using
the emission factor for the Canary Islands estimated by IDAE [54] and
considering the corrected biogas potential from animal manure ob-
tained in this study, considering that a conventional operation time for
biogas plants is 8000 h per year [55].
4. Results and discussion
4.1. Analysis of the
endogenous factors of the livestock industry in the
Canary Islands
According to the Canary Islands Livestock Register [49], there are
3,834,383 animals (excluding horses) raised in the Archipelago
(Table 2). While poultry contribute with more than 3.4 M animals, they
represent only 30% in terms of Livestock Units (LSU). Goats represent
the main LSU type (36%) and they are specially appreciated in the
Canary Islands for their milk, which is used primarily for cheese pro-
duction.
The livestock distribution is not equal for each island (Table 2).
Gran Canaria and Tenerife gather most of the livestock industry, with
more than 92% of the animals raising (68.8% in terms of LSU) and more
than 60% of the livestock farms. There are 2767 livestock farms in the
Canary Islands, excluding equine farms that were not considered in this
study. Most farms raise goats as the main species followed by bovine
and ovine farms.
Most farms in the Canary Islands are family size farms, with less
than 30 LSU each (Fig. 2) regardless of the main animal type in the
farm. In fact, average farm size for cow and swine farms are 25 and 223
animals per farm, respectively, an indicator that clearly shows the small
size of most of them (Table 2). In the Canary Islands holdings with less
than 100 LSU are 93.8%, whereas holdings with 500 LSU or higher are
only 0.4% (Fig. 2). Comparing these percentages to the European li-
vestock industry pattern [56] differences are evident: Holdings with
less than 100 LSU in Spain are 86.9%, whereas holdings with 500 LSU
or higher represent 2.3%. In other countries with a higher penetration
of biogas energy these figures are like that of Spain. In Germany and UK
holdings with less than 100 LSU are close to 75%, whereas holdings
with 500 LSU or higher are 2.6%. Italy, with a much higher penetration
of biogas, has 90.5% of the holdings with less than 100 LSU and only
1.8% of the holdings with 500 LSU or more. The small size of the farms
in the Canary Islands implies a large dissemination of livestock manure
production on each island. Moreover, in order to have a higher pene-
tration of biogas, small farmers should play an important role given
their importance in the livestock sector in the Canary Islands. However,
small farmers are often reluctant to make investments. Consequently,
the structure of the livestock holdings in the Canary Islands could
jeopardize the introduction of the biogas industry.
Similar outermost regions, such as Madeira and Azores, show the
same limitation for the development of the biogas industry. In Madeira
small farms dominate livestock industry. This is also the case in Azores
where the agriculture and livestock sector contributes 9.5% to GDP
[57]. In addition to the small farm size there is a significant fraction of
extensive livestock [58], which represents another limitation for
manure utilization for biogas production.
Contrarily, almost all manure produced in most farms of the Canary
Islands could be collected for feeding biogas plants because extensive
farming does not represent a relevant percentage over total. However,
as explained in the Methodology section, we have considered some
limitations for its use due to economic reasons and farm types.
Fig. 3 shows the spatial distribution of all the farms and the con-
centration of LSU on each island. In most islands, the topography and
the territorial protection regulations determine the distribution of the
farms: on Gran Canaria, most farms are located on the north and the
east sides of the island, whereas on Tenerife most farms are located in
the north side and in the lower areas of the island. This is also the case
on La Palma, with most of the farms located near the coast. By contrast,
Fuerteventura is an island with a gentle topography and with farms
distributed over its entire surface. In terms of livestock concentration,
there are few areas, mainly located on Gran Canaria and Tenerife,
where there is a high concentration of livestock (> 699 LSU) (Fig. 3).
These areas are indicators of possible locations for centralized biogas
plants due to the proximity of manure production sources.
More than 40% of the territory of the Canary Islands is protected
due to its high natural value. The high level of protection creates a high
competition for land use, where residential, livestock, agricultural and
industrial uses converge. Consequently, livestock farms must be ex-
tremely careful with the management of their waste, since in addition
to environmental problems, it is common to observe social problems
due to the vicinity of residences or industries.
4.2. Manure availability estimates for biogas production
Table 3 shows the most relevant data on manure production in the
Canary Islands. Total manure production is 495,622 t year−1, most of it
being produced on Gran Canaria and Tenerife (ca. 69% between both).
The highest contribution to this production corresponds to goats
(32.9%), followed by cows (29.8%), poultry (17.8%) and swine
(11.6%).
Fig. 4 shows manure production in each municipality. Only twelve
municipalities produce more than 12,500 tons of manure per year,
eight of them being located on Gran Canaria, two on Tenerife and other
two on Fuerteventura. The highest manure production occurs in Las
Palmas de Gran Canaria (Gran Canaria), with more than 29,517 t
year−1. On a lower level, with a manure production between 7000 and
12,500 t year−1 there are ten municipalities, four on Tenerife, three on
Fuerteventura, two on Gran Canaria and one on Lanzarote.
In order to determine the potential use of manure for biogas pro-
duction it is convenient to know its production distribution by farm. In
the biogas industry the size matters, and there is a strong inverse cor-
relation between the installed power and the investment costs in biogas
plants [59,60]: highest installed power leads to a decrease in invest-
ment costs in terms of € kWe−1. In fact, one of the challenges to be
faced by the biogas industry in developed countries is to increase the
implementation of projects for small-scale anaerobic digestion
(< 100 kWe) [61]. Most farms in the Canary Islands (2223 representing
80% of the total farms) produce less than 0.5 t day−1 of manure. This
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means that in most farms it is not possible to install biogas plants since
biogas production would be too low for making the investment profit-
able. If we consider 0.5 t day−1 manure as the lowest limit for executing
biogas projects (this is equivalent to nearly 3 kWe depending on the
substrate type and concentration), only 546 farms have enough po-
tential for producing and using their own biogas. For each type of farm
(classified according to its main animal type in terms of LSU) the in-
fluence of this lowest limit is different: for poultry (hens and chickens)
34.8% of the farms could have their own biogas plant, however this
percentage is reduced to 0% for rabbits, 10.5% for sheep, 17.0% for
swine, 19.2% for cattle and 21.3% for goats.
The low number of farms that are likely to have their own biogas
plant limits the implementation of biogas projects on the Canary
Islands. However, farms producing more than 0.5 t day−1 manure
generate 80.6% of the total manure in the Canary Islands. Therefore,
from an environmental and economic point of view, it is suggested to
focus on these larger farms which can contribute to solve the problem of
livestock waste in the Canary Islands. In addition, this gives a chance to
every small farm to take their waste to nearby biogas plants of larger
farms.
4.3. Evaluation of biogas and energy potential production from animal
manure
Total biogas production potential from animal manure in million
cubic meters (Mm3) is shown in Table 4, for each island and for each
type of manure. Without considering any type of restriction for using
animal manure for biogas production, total biogas potential is 44.7
Mm3 year−1. The major biogas contribution comes
from goat manure,
with 18.2 Mm3 year−1, followed by poultry manure with 11.9 Mm3
year−1. In terms of production on each island, Gran Canaria and Te-
nerife have the greatest potential, with 17.6 and 12.2 Mm3 year−1,
respectively. Far away is Fuerteventura with 8.0 Mm3 year−1. How-
ever, it is well known that total manure production in a region is not
always available for biogas plants due to alternative uses of manure for
other applications [62]. Unlike other studies [62,63] where a general
and, apparently, arbitrary availability coefficient for all types of
manure was used, regardless of the manure and farm type, in this study
a different procedure was carried out for estimating a more realistic
biogas potential production. This correction procedure is explained in
detail in the Methodology section.
Table 2
Number of animals, number of livestock farms and number of Livestock Units (LSU) per island a for each type of animal raising.
Animalc Variable GC T LP F L EH LG Totalb
Swine Animals 10,043 24,346 4214 8093 2414 493 357 49,960
LSU 1100 2643 438 891 269 50 42 5433
Farms 69 62 33 14 20 21 5 224
Animals/Farm 145.6 392.7 127.7 578.1 120.7 23.5 71.4 223.0
Poultryd Animals 1,462,778 1,871,327 43,725 19,458 57,018 2019 7926 3464,251
LSU 10,021 11,730 436 194 568 12 79 23,040
Farms 67 111 13 5 22 4 2 224
Animals/Farm 21,832.5 16,858.8 3363.5 3891.6 2591.7 504.8 3963.0 15,465.4
Cows Animals 11,887 4395 1387 314 257 665 50 18,955
LSU 8781 3263 952 212 199 535 40 13,982
Farms 353 203 111 22 8 45 8 750
Animals/Farm 33.7 21.7 12.5 14.3 32.1 14.8 6.3 25.3
Goats Animals 54,076 33,893 17,825 79,385 18,052 4243 5335 212,809
LSU 7056 4424 2351 10158 2364 564 710 27,627
Farms 343 247 152 212 72 63 58 1147
Animals/Farm 157.7 137.2 117.3 374.5 250.7 67.3 92.0 185.5
Sheeps Animals 21,383 6756 1802 9484 5091 4266 1337 50,119
LSU 2764 835 241 1159 631 589 178 6397
Farms 128 46 35 41 37 60 24 371
Animals/Farm 167.1 146.9 51.5 231.3 137.6 71.1 55.7 135.1
Rabbits Animals 2019 24,162 5730 21 382 665 5310 38,289
LSU 15 150 33 0 3 4 31 236
Farms 7 25 6 0 3 9 1 51
Animals/Farm 288.4 966.5 955.0 0 127.3 73.9 5310.0 750.8
Total Animals 1,562,186 1,964,879 74,683 116,755 83,214 12,351 20,315 3,834,383
LSU 29,737 23,045 4451 12,614 4034 1754 1080 76,715
Farms 967 694 350 294 162 202 98 2767
Animals/Farm 1615.5 2831.2 213.4 397.1 513.7 61.1 207.3 1385.8
a GC: Gran Canaria, T: Tenerife LP: La Palma, F: Fuerteventura, L: Lanzarote, EH: El Hierro, LG: La Gomera.
b La Graciosa Island was not considered since it has no livestock farms.
c Each livestock farm was classified according to its main animal type in terms of Livestock Unit (LSU). Equine farms were not considered for this study.
d Includes only chickens and hens.
Fig. 2. Size distribution in terms of Livestock Units (LSU) of farms in the Canary
Islands. The n indicates the total number of farms. The term ‘All farms’ include
rabbit farms too, but these have a low contribution to the livestock population
and are not shown separately.
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143
Fig. 3. Spatial distribution of livestock farms and Livestock Unit density on each island: a) Gran Canaria; b) Tenerife; c) La Palma; d) Fuerteventura; e) Lanzarote; f)
El Hierro; g) La Gomera. For each farm a radius of 2 km of influence was considered.
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After applying these correction factors for each type of manure,
potential biogas production reduces substantially, from 44.7 Mm3
year−1 to 27.1 Mm3 year−1 (Table 4 as ‘Corrected Biogas Potential’).
Moreover, poultry manure has the largest contribution to the total
biogas production (43.95%), followed by cow manure (24.91%) and
goat manure (20.28%). Gran Canaria and Tenerife still have the
greatest biogas potential with 12.4 Mm3 year−1 and 8.9 Mm3 year−1,
respectively. Biogas potential on Fuerteventura decreased dramatically
(more than 60%) due to the low availability of goat manure for biogas
production. Although the availability factor of 40% applied to goat and
sheep manures is an estimate, it is similar to factors applied in other
studies to the same type of manure [62]. The choice of this correction
factor was based on authors’ knowledge on the Canarian livestock in-
dustry, whereas, a more precise factor would need a thorough backup
study which is far beyond the scope of this study.
In terms of primary energy, corrected biogas potential can con-
tribute up to 14.6 toe year−1, i.e., 0.31% and 0.42% of the primary and
final energy consumption during 2016 in the Canary Islands. These
percentages are high compared to other regions where similar studies
were performed. Moreda et al. [64] estimated that energy from biogas
in Uruguay could potentially reach 1.3–2.1% of total primary energy,
being the contribution of manure to the whole biogas matrix only
around 2%. In terms of electricity, potential electrical power obtained
from animal manure biogas is 6.8MWe (Table 4) considering an overall
electrical efficiency of CHP and gensets units of 30%. This power is
0.22% and 1.84% of the current total and renewable installed power in
the Canary Islands, respectively, which were 3064MW and 367.7MW
in 2016 [22]. Biogas plants are considered to be able to work 8000 h
yearly [55], therefore, potential electricity production from biogas
obtained from animal manures is 54.21 GWh year−1, equivalent to
0.62% and 7.80% of the total electricity consumption and renewable
electricity production, respectively, during 2016 in the Canary Islands.
According to the last Energy Plan of the Government of the Canary
Islands [27], the electrical power installed in 2015 in the Archipelago
based on biogas (including landfill biogas) was expected to be ca.
30MW. Animal manure can contribute significantly to the consecution
of these goals, which right now are far away. Furthermore, the
Government of the Canary Islands would like to enhance the primary
sector of the islands in order to reach a higher proportion of food self-
sufficiency [46], which would lead to a higher biogas potential due to
higher manure production. Moreover, agricultural waste, organic waste
produced in agri-food industries, OFMSW and wastewater sludge could
increase substantially the potential contribution of biogas to the energy
system of the Canary Islands. However, these substrates are out of the
scope of this work.
To increase the influence of this study and to carry out specific field
actions, farms producing more than 0.5 t day−1 manure were identified
and geo-located on maps for each island, which can contribute for a
better planning of biogas plants facilities or even cooperation between
different farmers (Fig. 5). Moreover, land protection is also shown on
these maps in order to ease possible locations for biogas plants outside
the farms.
Totally, there are 546 farms with real potential for installing their
own biogas plants. In terms of type of farms, 246 are goat farms, fol-
lowed by cow (144), poultry (78), swine (38) and sheep farms (40),
whereas these farms are mostly located on Gran Canaria (192), Tenerife
(143) and Fuerteventura (102). No farms are located inside any
National Park, which is the highest level of land protection. Only a
small number of farms (6) are located inside Natural Parks, which is the
second protection level. Integral Natural Reserve is a very restrictive
type of protection, with almost all uses of land forbidden, therefore, no
farms are located on this land. Farms located in Rural Parks, Sites of
Scientific Interest, Natural Monuments and Protected Areas might have
their own biogas plant although special measures are likely necessary
for complying with local legislation [65]. Areas with major density of
farms with potential for installing their own biogas plant are not subject
to any type of protection.
4.4. Potential contribution of biogas generation and use to the reduction of
GHG emissions
The estimation of potential
GHG emissions savings are limited in
this study to those saved due to a proper management of manure and
due to fossil fuel substitution by biogas energy, considering that biogas
Table 3
Manure production (t year−1) for each animal type on each island.
Manure Type GC T LP F L EH LG TOTAL
Swine 11,615 27,870 4619 9498 2925 537 465 57,527
Cow 93,391 34,412 10,406 2173 1895 5336 386 147,998
Goat 41,519 26,028 13,780 60,209 13,892 3296 4149 162,873
Sheep 16,322 5014 1406 6990 3786 3397 1040 37,955
Poultry 42,816 40,180 1743 776 2271 33 317 88,135
Rabbit 107 696 154 2 19 25 132 1134
TOTAL 205,770 134,200 32,108 79,648 24,788 12,624 6489 495,622
GC: Gran Canaria, T: Tenerife LP: La Palma, F: Fuerteventura, L: Lanzarote, EH: El Hierro, LG: La Gomera.
Fig. 4. Manure production (t year−1) for each municipality on each island (horse and rabbit manure were not considered).
J.L. Ramos-Suárez et al. Renewable and Sustainable Energy Reviews 104 (2019) 137–150
145
potential is used for electricity production. A detailed determination of
GHG emissions savings due to biogas energy from animal manures in
the Canary Islands is out of the scope of this study and would lead to a
comprehensive study including other potential savings such as mineral
fertilizer substitution, nitrous oxide emissions during manure/digestate
storage and/or application on agricultural fields, etc.
On the one hand, the livestock industry produces significant GHG
emissions, as a consequence of the enteric fermentation and methane
and nitrous oxide emissions from manure management [53]. Emissions
due to manure management are especially significant in intensive sys-
tems and in those systems where manure is handled in liquid form [53].
Anaerobic digestion of animal manure is associated with a reduction of
greenhouse GHG emissions, because of avoidance of the methane
emissions from natural decomposition during storage [66].
GHG emissions due to manure storage are shown in Table 5 for each
island and for each animal type, considering only animals raised in
those livestock holdings with a daily manure production greater than
0.5 t, the lowest limit established for executing biogas projects (see
Section 4.2). Yearly total methane emissions (expressed as carbon di-
oxide, CO2e) due to animal manure storage are 27,362.2 t CO2e.
Highest emissions are due to swine slurry (48.2%) and dairy cattle
manure (33.5%), whereas most of the GHG are emitted in Gran Canaria
(42.8%) and Tenerife (37.6%). According to Steinfeld [67] up to 50% of
these emissions could be saved if an appropriate anaerobic treatment
for biogas production is performed compared to a conventional manure
storage system. Consequently, we can assume that at least 50% of the
emissions calculated above could be avoided if a full deployment of
biogas energy is achieved in the Canary Islands. This is equivalent to
13,681.1 t CO2e year−1.
On the other hand, the use of this biogas for energy generation
displaces the use of fossil fuels and, therefore, contributes to the re-
duction of GHG emissions and other pollutants. Considering the CO2
emission conversion for electricity of 0.776 kg CO2e kWh−1 established
by IDAE [54] for the Canary Islands, the use of biogas instead of fossil
fuels would imply a reduction of 5.26 t CO2e h−1 (Table 6). To this
amount contribute mainly the largest islands (45.6% in Gran Canaria;
33.5% in Tenerife). According to animal manure, the largest
contribution corresponds to poultry manure (43.8%) and cow manure
(24.1%).
Operation time for biogas plants is conventionally estimated in
8000 h per year [55], therefore, in order to obtain the total GHG
emission savings for the Canary Islands due to biogas use for electricity
production, the factor 5.26 t CO2e h−1 should be multiplied by 8000 h,
leading to potential savings of 42,064 t CO2e year−1, higher than those
expected due to proper manure management. Total GHG emissions
savings, including manure management and renewable energy pro-
duction are 55,745.1 t CO2e year−1.
This is equivalent to a reduction in GHG emissions of 1.03 kgCO2e
per kWh, higher than for other renewable energies which GHG emis-
sions savings are limited to that of fossil fuel substitution.
4.5. Challenges and recommended policies for the development of biogas in
the Canary Islands
Biogas industry faces several barriers for its development all around
the world: legal regulations, financial issues, grid connection obstacles
and social rejection are common regardless of the development status of
the industry and the country [4,29,68]. Promoters in the Canary Is-
lands, who tried to construct biogas plants in the past, have faced all
these barriers [69,70]. But, the biogas industry in the Canary Islands
should face other important challenges:
(i) The high proportion of land protection limits the development of
biogas projects to certain areas, which at the same time are densely
populated. Residential and industrial uses converge in very little
surface, increasing price of land.
(ii) There is a lack of culture in the livestock sector for association and
cooperatives [46], which limits the size of plants to small scale due
to the size of the livestock holdings in the Canary Islands.
(iii) The high average age of livestock farmers [46] makes the execu-
tion of long-term investments such as biogas plants difficult.
(iv) The Spanish Government removed feed-in tariffs for renewable
energy in 2014 [71] and there is no evidence for a new regulation.
(v) The Government of the Canary Islands has no powers in the last-
Table 4
Total and corrected biogas potential (Mm3 year−1), potential energy (1) (toe year−1) and potential electrical power a (kWe).
Animal Variable GCc T LP F L EH LG Total
Swine Total Biogas Potential 0.66 1.66 0.26 0.41 0.08 0.02 0.01 3.09
Corrected Biogas Potential 0.55 1.54 0.21 0.38 0.06 0 0 2.74
Energy 313.0 873.1 116.7 216.3 33.0 0 0 1552.0
Electrical Power 145.4 405.7 54.2 100.5 15.3 0 0 721.2
Poultryb Total Biogas Potential 5.74 5.41 0.23 0.10 0.33 0 0.09 11.91
Corrected Biogas Potential 5.63 5.15 0.22 0.09 0.30 0 0.09 11.47
Energy 3138.7 2870.0 120.8 47.8 165.5 0 50.2 6393.1
Electrical Power 1458.5 1333.6 56.1 22.2 76.9 0 23.3 2970.7
Cows Total Biogas Potential 5.30 1.89 0.58 0.09 0.19 0.30 0.02 8.36
Corrected Biogas Potential 4.58 1.43 0.34 0.04 0.18 0.18 0 6.75
Energy 2378.4 746.3 175.1 21.6 94.3 94.6 0 3510.3
Electrical Power 1105.2 346.8 81.3 10.0 43.8 43.9 0 1631.1
Goats Total Biogas Potential 4.55 2.86 1.52 6.96 1.55 0.39 0.44 18.26
Corrected Biogas Potential 1.36 0.67 0.27 2.47 0.56 0.06 0.10 5.50
Energy 695.0 345.2 136.8 1267.1 288.0 74.9 52.1 2858.9
Electrical Power 322.9 160.4 63.5 588.7 133.8 13.9 24.2 1307.5
Sheeps Total Biogas Potential 1.37 0.40 0.10 0.48 0.33 0.34 0.10 3.12
Corrected Biogas Potential 0.32 0.11 0 0.11 0.08 0.04 0 0.65
Energy 150.0 50.6 0 54.8 39.0 18.8 0 313.2
Electrical Power 69.7 23.5 0 25.5 18.1 8.7 0 145.5
Total Total Biogas Potential 17.62 12.21 2.70 8.04 2.49 1.05 0.65 44.74
Corrected Biogas Potential 12.43 8.90 1.03 3.09 1.18 0.28 0.20 27.11
Energy 6675.1 4885.2 549.3 1607.6 619.8 188.3 102.3 14,627.6
Electrical Power 3101.7 2270.0 255.3 746.9 288.0 66.6 47.5 6776.0
a Calculated from corrected biogas potential.
b Hen and chickens.
c GC: Gran Canaria, T: Tenerife LP: La Palma, F: Fuerteventura, L: Lanzarote, EH: El Hierro, LG: La Gomera.
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146
Fig. 5. Geo-located livestock farms producing more than 0.5 t day−1 of animal wastes -classified according to animal type and its potential electrical power from
biogas- and land protection in Canary Islands: a) Gran Canaria; b) Tenerife; c) La Palma; d) Fuerteventura; e) Lanzarote; f) El Hierro; g) La Gomera. NOTE: some farms
are not shown in these maps due to coordinates missing in the official register.
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147
mentioned area, so its possible actions are limited
to direct sub-
sidies to renewable energy facilities.
All these facts limit the development of the biogas industry, but
specially the execution of large biogas plants, that have reduced in-
vestment costs in terms of installed power [59,60,72] and therefore
ease the return on the investment.
Some policies that could help are being already implemented, such
as subsidies to renewable energy facilities, to promote the insertion of
young farmers and for the modernization of livestock farms. However,
the work done in this study shows that the challenges for the devel-
opment of biogas in the Canary Islands are numerous. The aforemen-
tioned policies, suitably modified, together with a series of additional
policies that could be implemented at a regional / local level, can fa-
cilitate the development of biogas industry. The following are a series of
policies that could improve the situation and perspectives of biogas
energy from animal manures in the Canary Islands. These policies could
also be used for promoting biogas in other outermost regions in Europe,
such as Azores and Madeira, which have similar characteristics to
Canary Islands.
– Regarding the subsidies for renewable energy facilities for private
companies:
(i) The last subsidies were awarded according to the order of regis-
tration of the projects. The biogas projects have an added difficulty
due to the large number of factors that they contemplate (agri-
cultural, livestock, energy, and environmental), which requires
more planning time. Instead of the simple ‘order of registration’
methodology, the establishment of a scale providing that the pro-
jects with the greatest reduction in GHG emissions per kWh obtain
higher score would benefit biogas projects compared to other re-
newable energies.
(ii) A subsidy proportional to the size of the facility (greater subsidy for
smaller facilities) would favor small scale biogas plants, which
would allow a greater penetration of biogas in the Canarian live-
stock sector, clearly dominated by very small farms.
– Regarding the subsidies for the modernization of livestock farms:
(i) These subsidies are granted without considering if farmers comply
with current regulations regarding manure management.
Therefore, requiring a manure management plan before giving any
type of subsidy to farmers would improve the current management
of manures, where biogas could play an important role.
(ii) A significant subsidy for paving the pens would ease the collection
of clean manures and their use for biogas production whilst
avoiding pollution of soils and groundwaters.
– Regarding possible actions for increasing the co-operation between
farmers:
(i) Co-operation between farmers to establish communal biogas plants
would help to reduce the high investment costs associated with
small-scale biogas plants. This could be done by means of higher
subsidies for communal investments.
(ii) Moreover, the promotion of co-operation between livestock and
agricultural farmers would secure the profitability of biogas plants
by means of taking advantage of the synergies of co-digestion be-
tween manures and other agri-industrial wastes and by increasing
the utilization of the digestate in agriculture.
– Public Administration should make an effort in outreaching and
training activities for livestock and agricultural farmers and for the
society in general, in order to make known the benefits of biogas and
to overcome its social rejection.
5. Practical implications of this study
This study has shown that biogas from animal manure could be a
significant source of energy for the Canary Islands. However, due to the
structure of the livestock holdings of the Archipelago, the biogas po-
tential is widely spread among more than 546 farms, producing to-
gether more than 80% of the animal manure and yielding from 3 to
185 kWe of potential electrical power from biogas each.
In research and policies regarding biogas, small biogas plants are
considered those below 75–100 kWe. An example is the new regulation
for feeding biogas electricity into the German electrical network, which
focuses on the promotion of biogas between small farms, considering
only those with less than 75 kWe of biogas production and using mostly
manure as substrate [7]. On the other hand, other studies suggest
50 kWe as the minimum capacity that biogas plants should have to be
economically viable due to economics of scale [72].
The reality on the Canary Islands invites to think about what type of
biogas facilities to promote for treating animal manure: cooperation
between farmers, very small plants for energy self-sufficiency or cen-
tralized plants promoted and operated by the Public Administration.
Probably, a combination of all these options would be the best so-
lution for the Canarian Archipelago, considering the reality of each
island. In-depth studies on the economics of each option, which is out of
Table 5
GHG emissions (in t CO2e year−1) due to manure storage in livestock farms producing more than 0.5 t day−1 of manure in the Canary Islands.
GCa T LP F L EH LG Total
Hens 667.1 529.7 27.9 11.1 35.1 0.0 5.2 1276.1
Chicken 149.5 344.6 0.0 0.0 0.0 0.0 0.0 494.1
Dairy cattle 6369.3 1994.9 341.6 97.4 112.6 244.1 0.0 9159.9
Non-dairy cattle 1890.0 606.1 187.7 46.4 53.7 79.9 5.9 2869.7
Swine 2517.9 6775.3 961.6 2256.0 553.7 68.5 60.1 13,193.1
Goat 73.2 36.4 14.4 128.2 29.9 2.8 5.8 290.7
Sheep 34.3 12.0 1.6 17.9 8.9 3.3 0.7 78.8
Total 11,701.2 10,299.0 1534.7 2557.0 794.0 398.6 77.7 27,362.2
a GC: Gran Canaria, T: Tenerife LP: La Palma, F: Fuerteventura, L: Lanzarote, EH: El Hierro, LG: La Gomera.
Table 6
GHG emission reductions factor (kg CO2e h−1) by using biogas instead of fossil
fuels for electricity production.
Animal GCb T LP F L EH LG Total
Swine 112.8 314.8 42.1 78.0 11.9 0.0 0.0 559.6
Poultrya 1131.8 1034.9 43.5 17.2 59.7 0.0 18.1 2305.2
Cows 857.6 269.1 63.1 7.8 34.0 34.1 0.0 1265.7
Goats 250.6 124.5 49.3 456.8 103.8 10.8 18.8 1014.6
Sheeps 54.1 18.2 0.0 19.8 14.0 6.8 0.0 112.9
Total 2406.9 1761.5 198 579.6 223.4 51.7 36.9 5258.0
a Hen and chickens.
b GC: Gran Canaria, T: Tenerife LP: La Palma, F: Fuerteventura, L: Lanzarote,
EH: El Hierro, LG: La Gomera.
J.L. Ramos-Suárez et al. Renewable and Sustainable Energy Reviews 104 (2019) 137–150
148
the scope of this paper, should be performed to determine the best
combination of the above-mentioned possibilities for each island. Such
a study should address at least the following issues: (i) Selection of the
most appropriate site for constructing biogas plants, what will depend
on the available land surface, land protection or constraints, livestock
intensity and distance to nearby towns or villages [73,74]; (ii) De-
termination of the distance from each farm to a possible centralized
biogas plant, which, depending on the TS concentration of each manure
type, may influence greatly the transport costs of the livestock waste
[73–75]; (iii) Size of a possible centralized biogas plant [59,73–75]; (iv)
Investment, operation and maintenance costs [74,75]; (v) Availability
of nearby agricultural land to spread digestate, and the cost of trans-
porting the digestate [74]; and, finally, (vi) Possible income sources
[59,74].
Based on this study, future work should focus on: (i) cost analysis for
the public funds of promoting centralized vs. small, private biogas
plants; (ii) determination of the best locations on each island for joint or
centralized biogas plants; (iii) evaluation of other agri-industrial
wastes, such as crop residues, whey or specific energy crops, and their
co-digestion with animal manure, which would increase the potential
biogas production and the profitability of small biogas plants; (iv) de-
velopment of technological models of biogas plants specially adapted to
the Canary Islands context, where livestock farms are very small; (v)
studies on biogas as a tool to stabilize isolated electrical systems, such
as those we have in the outermost European regions; and, finally, (vi)
studies
on the use of digestate for typical crops of the Canary Islands,
such as tomato and banana.
6. Conclusions
This work presents the current situation of the primary sector in the
Canarian Archipelago regarding the management of animal manures,
and more specifically, with respect to the production of biogas from
these wastes. There are several challenges to face when implementing
biogas in the Canary Islands as a solution for the treatment of livestock
waste, and this work has highlighted them thanks to an exhaustive
analysis of the livestock sector reality and the potential for biogas
production in this archipelago. Biogas potential generated from animal
manure was shown to be an energy opportunity in the Canary Islands.
Yearly total manure production achieves 495,622 t, most of it being
produced on Gran Canaria and Tenerife. Highest contribution to this
production corresponds to goats (32.9%), cows (29.8%), poultry
(17.8%) and swine (11.6%). The evaluation of the biogas potential from
animal manure on a farm basis yielded 44.7 Mm3 year−1. However,
limitations for manure usage as biogas source, such as farm size and
manure availability should be taken into consideration. After applying
the availability coefficients to each type of manure, the real potential
for the production of biogas from manure in the Canary Islands resulted
in 27.1 Mm3 year−1 with an equivalent installed power capacity of
6.8 MWe. In terms of electricity share this is equivalent to 0.22% of the
installed power. This potential biogas production is spread widely
among 546 farms located all around the seven islands, which have real
potential for installing their own biogas plant for electricity and/or heat
production with electrical power ranging from 3 to 185 kWe.
In terms of GHG emissions savings, the production of electricity
from biogas could contribute in a greater extent compared to other
types of renewable energies to the reduction of GHG emissions. Yearly
GHG emissions savings were estimated in 55,745.1 t CO2e, including
both, substitution of fossil fuels and reduction of emissions due to ap-
propriate manure treatment.
The challenges identified for the development of biogas in the
Canary Islands are mainly related to the small size of the livestock
holdings, the lack of a culture of association in the livestock sector and
the lack of specific subsidies for biogas production. The application of
the specific policies proposed would substantially promote the devel-
opment of the biogas industry in the Canary Islands. This study may
represent the first step of a long way to facilitate the diffusion of biogas
exploitation in the Canary Islands and could be used also as a basis for
further studies in other European outermost regions with similar
characteristics of the Canary Islands, such as Madeira and Azores.
Acknowledgements
This work was financially supported by the Cabildo de Tenerife
(Spain) through the program ‘Agustín de Betancourt 2016-2020’.
Authors would like to thank the Consejería de Agricultura, Ganadería y
Pesca del Gobierno de Canarias (Spain), and especially, the Dirección
General de Ganadería, for contributing to this study by sharing valuable
data and statistics.
References
[1] Mao C, Feng Y, Wang X, Ren G. Review on research achievements of biogas from
anaerobic digestion. Renew Sustain Energy Rev 2015;45:540–55.
[2] Yentekakis IV, Goula G. Biogas management: advanced utilization for production of
renewable energy and added-value chemicals. Front Environ Sci 2017;5:1–7.
[3] Kadam R, Panwar NL. Recent advancement in biogas enrichment and its applica-
tions. Renew Sustain Energy Rev 2017;73:892–903.
[4] Capodaglio AG, Callegari A, Lopez MV. European framework for the diffusion of
biogas uses: emerging technologies, acceptance, incentive strategies, and institu-
tional-regulatory support. Sustainability 2016;8:298–316.
[5] Scarlat N, Dallemand J-F, Fahl F. Biogas: developments and perspectives in Europe.
Renew Energy 2018;129:457–72.
[6] Eurobserv’er. Biogas Barometer; 2017. 〈https://www.eurobserv-er.org/biogas-
barometer-2017/〉 [Accessed 25 July 2018].
[7] Daniel-Gromke J, Rensberg N, Denysenko V, Stinner W, Schmalfuß T, Scheftelowitz
M, Nelles M, Liebetrau J. Current developments in production and utilization of
biogas and biomethane in Germany. Chem Ing Tech 2018;90:17–35.
[8] Foged HL, Flotats X, Bonmati Blasi A, Palatsi J, Magri A, Schelde KM Inventory of
manure processing activities in Europe. Technical Report No. I concerning Manure
Processing Activities in Europe to the European Commission, Directorate-General
Environment; 2011. 138 pp.
[9] European Biogas Association. Statistical Report 2016. In: Stambasky J, Pfluger S,
Deremince B, Scheidl S, editors. Statistical Report of the European Biogas
Association. Brussels: EBA Statistical Report; 2016.
[10] Teresa Fernández M, Herrero Mallén E, Bescós Roy B. Evaluation of manure man-
agement systems in Europe. Zaragoza: SARGA 2015:180.
[11] Eurobserv’er. Biogas Barometer; 2012. Available at: 〈https://www.eurobserv-er.
org/biogas-barometer-2012/〉 [Accessed 26 July 2018].
[12] Kampman B, Leguijt C, Scholten T, Tallat-Kelpsaite J, Brückmann R, Maroulis G
et al. Optimal use of biogas from waste streams. An assessment of the potential of
biogas from digestion in the EU beyond 2020. Luxembourg: European Commision;
2017. 158 pp.
[13] Bangalore M, Hochman G, Zilberman D. Policy incentives and adoption of agri-
cultural anaerobic digestion: a survey of Europe and the United States. Renew
Energy 2016;97:559–71.
[14] Lukehurst C, ADBA UK. Country Report. IEA Bioenergy; 2017. 〈http://task37.
ieabioenergy.com/country-reports.html〉 [Accessed 3 August 2018].
[15] Meyer AKP, Ehimen EA, Holm-Nielsen JB. The potential of animal manure, straw
and grass for European biogas production in 2030. Proceedings of the 24th
European Biomass Conference and Exhibition; 2016. 〈http://www.etaflorence.it/
proceedings/?Detail=12749〉 [Accessed 3 August 2018].
[16] Sun Q, Li H, Yan J, Liu L, Yu Z, Yu X. Selection of appropriate biogas upgrading
technology-a review of biogas cleaning, upgrading and utilization. Renew Sustain
Energy Rev 2015;51:521–32.
[17] Hahn H, Hartmann B, Wachendorf K. M. Review of concepts for a demand-driven
biogas supply for flexible power generation. Renew Sustain Energy Rev
2014;29:383–93.
[18] Szarka N, Scholwin F, Trommler M, Jacobi HF, Eichhorn M, Ortwein A, Thrän D. A
novel role for bioenergy: a flexible, demand-oriented power supply. Energy
2013;61:18–26.
[19] European Biomass Association. AEBIOM Statistical Report 207. Key Findings; 2017.
〈http://www.aebiom.org/statistical-report-2017/statistical-report-2017-17-10-17/
〉 [Accessed 3 August 2017].
[20] Maldonado E Final Report. Energy in the EU Outermost Regions. Renewable
Energy, Energy Efficiency. 〈http://ec.europa.eu/regional_policy/sources/policy/
themes/outermost-regions/pdf/energy_report_en.pdf〉 ; Date unknown [Accessed 3
August 2018].
[21] Instituto Canario de Estadística (ISTAC). Cifras oficiales de población; 2017.
〈http://www.gobiernodecanarias.org/istac/〉 [Accessed 27 February 2018].
[22] Gobierno de Canarias. Anuario Energético de Canarias 2016; 2017. 〈http://www.
gobiernodecanarias.org/ceic/energia/doc/Publicaciones/
AnuarioEnergeticoCanarias/ANUARIO-ENERGETICO-CANARIAS-2016.pdf〉
[Accessed 25 July 2018].
[23] Red Eléctrica de España. Las energías renovables en el sistema eléctrico español;
2017. 〈http://www.ree.es/es/estadisticas-del-sistema-electrico-espanol/informe-
de-energias-renovables〉 [Accessed 11 January 2018].
J.L. Ramos-Suárez et al. Renewable and Sustainable Energy Reviews 104 (2019) 137–150
149
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref1
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref1
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref2
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref2
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref3
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref3
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref4
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref4
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref4
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref5
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref5
https://www.eurobserv-er.org/biogas-barometer-2017/
https://www.eurobserv-er.org/biogas-barometer-2017/
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref6
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref6
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref6
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref7
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref7
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref7
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref8
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref8
https://www.eurobserv-er.org/biogas-barometer-2012/
https://www.eurobserv-er.org/biogas-barometer-2012/
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref9
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref9
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref9
http://task37.ieabioenergy.com/country-reports.html
http://task37.ieabioenergy.com/country-reports.html
http://www.etaflorence.it/proceedings/?Detail=12749
http://www.etaflorence.it/proceedings/?Detail=12749
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref10
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref10
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref10
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref11
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref11
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref11
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref12
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref12
http://refhub.elsevier.com/S1364-0321(19)30036-X/sbref12
http://www.aebiom.org/statistical-report-2017/statistical-report-2017-17-10-17/
http://www.aebiom.org/statistical-report-2017/statistical-report-2017-17-10-17/
http://ec.europa.eu/regional_policy/sources/policy/themes/outermost-regions/pdf/energy_report_en.pdf
http://ec.europa.eu/regional_policy/sources/policy/themes/outermost-regions/pdf/energy_report_en.pdf
http://www.gobiernodecanarias.org/istac/
http://www.gobiernodecanarias.org/ceic/energia/doc/Publicaciones/AnuarioEnergeticoCanarias/ANUARIO-ENERGETICO-CANARIAS-2016.pdf
http://www.gobiernodecanarias.org/ceic/energia/doc/Publicaciones/AnuarioEnergeticoCanarias/ANUARIO-ENERGETICO-CANARIAS-2016.pdf
http://www.gobiernodecanarias.org/ceic/energia/doc/Publicaciones/AnuarioEnergeticoCanarias/ANUARIO-ENERGETICO-CANARIAS-2016.pdf
http://www.ree.es/es/estadisticas-del-sistema-electrico-espanol/informe-de-energias-renovables
http://www.ree.es/es/estadisticas-del-sistema-electrico-espanol/informe-de-energias-renovables
[24] Red Eléctrica de España. El sistema eléctrico español 2016; 2017. 〈http://www.ree.
es/es/estadisticas-del-sistema-electrico-espanol/informe-anual/informe-del-
sistema-electrico-espanol-2016〉 [Accessed 13 August 2018].
[25] World Energy Council. Comparison of energy systems using life cycle assessment.
London: World Energy Council; 2004.
[26] Hondo H. Life cycle GHG emission analysis of power generation systems: japanese
case. Energy 2005;30:2042–56.
[27] Gobierno de Canarias. Plan Energético de Canarias (PECAN 2007); 2007. 〈http://
www.gobcan.es/ceic/energia/temas/planificacion/pecan/index.html〉 [Accessed
12 January 2018].
[28] Directive 2009/28/EC of the European Parliament and of the Council of 23 April
2009 on the promotion of the use of energy from renewable sources and amending
and subsequently repealing Directives 2001/77/EC and 2003/30/EC.
[29] Iglinski B, Buczkowski R, Iglinska A, Cichosz M, Piechota G, Kujawski W.
Agricultural biogas plants in Poland: investment process, economical and en-
vironmental aspects, biogas potential. Renew Sustain Energy Rev
2012;16:4890–900.
[30] Chen F, Duic N, Alves LM, Carvalho MC. Renewislands—renewable energy solu-
tions for islands. Renew Sustain Energy Rev 2007;11:1888–902.
[31] Miguel M, Nogueira T, Martins F. Energy storage for renewable energy integration:
the case of Madeira Island, Portugal. Energy Procedia 2017;136:251–7.
[32] Stenzel P, Schreiber A, Marx J, Wulf C, Schreieder M, Stephan L. Renewable en-
ergies for Graciosa Island, Azores – Life Cycle Assessment of electricity generation.
Energy Procedia 2017;135:62–74.
[33] Duic N, Carvalho MC. Increasing renewable energy sources in island energy supply:
case study Porto Santo. Renew Sustain Energy Rev 2004;8:383–99.
[34] EEM – Electricidade da Madeira. Evolução mensal do mix de produção e das
emissões de CO2. 〈https://www.eem.pt/pt/conteudo/sistema-elétrico/produção/〉
[Accessed 7 August 2018].
[35] Bourka O. BIORES – Reinforcing investments in Biogas technologies for small scale
RES applications in islands; 2014. 〈https://ec.europa.eu/energy/intelligent/
projects/en/projects/biores〉 [Accessed 7 August 2018].
[36] Rezendes V. Produção de Energia Elétrica por Biogás; 2012. 〈http://siaram.azores.
gov.pt/energia/biogas/_texto.html〉 [Accessed 7 August 2018].
[37] EDA – Electricidade dos Açores. Procura e Oferta de Energia Elétrica dezembro;
2017. 〈https://www.eda.pt/Mediateca/Publicacoes〉 [Accessed 7 August 2018].
[38] Ferreira M, Marques IP, Malico I. Biogas in Portugal: status and public policies in a
European context. Energy Policy 2012;43:267–74.
[39] Instituto Nacional de Estadística (INE). Contabilidad regional de España; 2017.
〈http://www.ine.es/dyngs/INEbase/es/operacion.htm?C=Estadistica_C&cid=
1254736167628&menu=resultados&idp=1254735576581〉 [Accessed 1 March
2018].
[40] Instituto Canario de Estadística (ISTAC). Empleos y relación con la actividad
económica; 2018. 〈http://www.gobiernodecanarias.org/istac/〉 [Accessed 1 March
2018].
[41] Instituto Canario de Estadística (ISTAC). Estadística Agraria de Canarias; 2018.
〈http://www.gobiernodecanarias.org/istac/〉 [Accessed 1 March 2018].
[42] Instituto Canario de Estadística (ISTAC). Importaciones y exportaciones según
capítulos y partidas arancelarias; 2018. 〈http://www.gobiernodecanarias.org/
istac/〉 [Accessed 1 March 2018].
[43] Holm-Nielsen JB, Al-Seadi T, Oleskowicz-Popiel P. The future of anaerobic diges-
tion and biogas utilization. Bioresour Technol 2009;100:5478–84.
[44] Möller K, Müller T. Effects of anaerobic digestion on digestate nutrient availability
and crop growth: a review. Eng Life Sci 2012;12:242–57.
[45] Alburquerque JA, de la Fuente C, Campoy M, Carrasco L, Nájera I, Baixauli C,
Caravaca F, Roldán A, Cegarra J, Bernal MP. Agricultural use of digestate for
horticultural crop production and improvement of soil properties. Eur J Agron
2012;43:119–28.
[46] Dirección General de Agricultura de la Consejería de Agricultura, Ganadería, Pesca
y Aguas del Gobierno de Canarias. Spain - Rural Development Programme
(Regional) – Canarias; 2014–2020. 〈http://www.pdrcanarias.es/index.php/el-pdr-
de-canarias-2014-2020〉 [Accessed 28 February 2018].
[47] Longo S, Malamis S, Katsou E, Costa CN, Theologides CP, Fatone F. Social aspects of
livestock waste management in Cyprus. Waste Biomass- Valor 2016;7:765–77.
[48] Brudermann T, Mitterhuber C, Posch A. Agricultural biogas plants – a systematic
analysis of strengths, weaknesses, opportunities and threats. Energy Policy
2015;76:107–11.
[49] Gobierno de Canarias. Registro de Explotaciones Ganaderas de Canarias (REGA);
2017.
[50] Alfonso D, Brines N, Peñalvo E, Vargas CA, Pérez-Navarro A, Gómez P, Pascual A,
Ruiz B. Cuantificación de materias primas de origen ganadero; 2009. 〈http://www.
probiogas.es/〉, PSE Probiogas [Accessed 27 February 2018].
[51] Biogas3. Small Biogas Web Application; 2014. 〈http://smallbiogas.biogas3.eu/
Acceso.aspx〉 [Accessed 27 February 2018].
[52] Gobierno de Canarias. Anexo II de la Orden de 15 de septiembre de 2016, por la que
se aprueban las bases reguladoras de la concesión de determinadas subvenciones
previstas en el Programa de Desarrollo Rural de la región de Canarias, para el
periodo 2014–2020.
[53] Dong H, Mangino J, McAllister TA, Hatfield