GREEN GAS - IEA Bioenergy Task 37
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
GREEN GAS
Facilitating a future green gas grid
through the production of renewable gas
IEA Bioenergy Task 37
IEA Bioenergy: Task 37: 2018 : 2
Green gas Title page
Green Gas
Facilitating a future green gas grid through the production of renewable gas
David M. Wall, (MaREI centre, University College Cork, Ireland)
Mathieu Dumont (Netherlands Enterprise Agency, Utrecht, The Netherlands)
Jerry D. Murphy (Director MaREI centre, ERI, University College Cork, Ireland)
EDITED BY
Jerry D. Murphy
ACKNOWLEDGEMENTS:
We acknowledge the following for their country specific input: James Browne (Gas Networks Ireland),
Morten Gyllenborg (Nature Energy, Denmark), Stefano Bozzetto (Biogas Refinery Development SRL, Italy)
Copyright © 2018 IEA Bioenergy. All rights Reserved
ISBN: 978-1-910154-37-3 (printed paper edition)
ISBN: 978-1-910154-38-0 (eBook electronic edition)
Cover photo: Lars Huigen, Wjister Green Gas Hub http://www.attero.nl/klanten-leveranciers/locaties/wijster
Published by IEA Bioenergy
IEA Bioenergy, also known as the Technology Collaboration Programme (TCP) for a Programme of Research, Development and Demonstration on
Bioenergy, functions within a Framework created by the International Energy Agency (IEA). Views, findings and publications of IEA Bioenergy do
not necessarily represent the views or policies of the IEA Secretariat or of its individual Member countries
Table of contents Green gas Table of contents 1. Executive summary 4 2. Introduction 5 2.1 What is green gas? 5 2.2 Coupling biomass availability with technology application 5 2.3 Benefits of a biomethane economy 6 2.4 Biogas and biomethane deployment 7 2.5 Advanced technologies for biomethane production 9 3. Algal biofuels 9 3.1 The role of seaweed in future biomethane production 9 3.2 Micro-algae and the circular economy 10 4. Gasification to expand the biomass and biomethane resource 11 5. Advanced smart grid technologies 12 5.1 Facilitating intermittent renewable electricity 12 5.2 Demand driven biogas systems 13 5.3 Power to Gas 13 6. Country case studies: future strategies for biomethane 15 6.1 Ireland 15 6.2 The Netherlands 18 6.3 The United Kingdom (UK) 20 6.4 Italy 21 6.5 Denmark 22 7. Integration of renewable green gas systems 24 8. Grid injection: challenges and solutions 25 8.1 Biomethane injection to the natural gas grid 25 8.2 Approaches to balancing the gas grid in biomethane injection 25 9. Conclusion and Outlook 27
4
Green gas Executive summary
1. Executive summary
To mitigate climate change, it is essential to develop natural gas demand in these countries respectively and thus
integrated and sustainable decarbonised renewable energy indicates a significant source of clean renewable energy and
systems. Heat and transport together, account for about the role that gas energy and infrastructure can play in the
80% of final energy consumption. Significant progress has future. It is suggested that in 2050 the same gas demand will
been made in renewable electricity but decarbonisation of be needed in Europe as today, however potentially 76% of
transport fuel is problematic. Gaseous renewable energy the gas could be green (EURATIV, 2017).
carriers, such as renewable ‘green gas’ can have a considera-
ble impact in future energy systems and play a key role in Cascading bioenergy
decarbonising heat and transport. Green gas at present is Cascading renewable gas systems will become a very
dominated by biomethane, which can be generated from the important tool in maximising the quantities of green gas
anaerobic digestion of organic biomass and residues pro- production and ensuring sufficient sustainability. An exam-
duced in agriculture, food production and waste processing. ple of cascading bioenergy could include integration of
green gas technologies, to maximise sustainable renewable
Biomethane present and future gaseous fuel production whilst minimising greenhouse gas
In 2015, there were 459 biogas-upgrading plants in emissions. The technologies investigated in this report
operation producing 1,230 M Nm3 of biomethane (Euro- (anaerobic digestion, gasification-methanation, power to
pean Biogas Association, 2016). The market for biomethane gas, micro-algae biogas upgrading) and feedstocks (energy
is still growing. Sweden, the UK, Switzerland, France and crops, agricultural residues and wastes, food waste, micro-
the Netherlands have all increased their biomethane pro- algae, seaweed, woody crops) when integrated can optimise
duction significantly in the last five years. In the short term, a system producing decarbonised indigenous renewable
the development of green gas projects, including the injec- energy. By-products of the different technologies maybe
tion of biomethane to gas networks will be the primary further amalgamated to ensure the use of the full supply
focus of this developing industry. Future renewable gas chain and circular economy concepts. Examples of this
technologies such as gasification-methanation and power include CO2 from biogas used in a power to gas system to
to gas systems have been identified as methods that could produce more green gas; solid digestate from a biogas plant
contribute substantially to greening natural gas grids of the used as a feedstock for gasification; oxygen produced from
future. Recent EU policy measures facilitate the develop- electrolysis used for the gasification process; and micro-
ment of such pathways with progressively increasing obli- algae biogas upgrading as a method of offsetting the costs
gations on decarbonisation. The share in renewable and of traditional upgrading methods.
low-carbon transport fuels (excluding first generation bio-
fuels and including for electrification) is required to The biomethane economy
increase from 1.5% in 2021 to 6.8% in 2030, with advanced As indicated in this report, an indigenous biomethane
biofuels to make up at least 3.6% by that time (EC, 2016). resource can potentially replace significant amounts of
natural gas. Particularly in countries with well-established
Country roadmaps and technology deployment and closely linked gas grids, there are good opportunities
Many countries are currently dependent on fossil fuels for cross-border trade and to create a market for biometh-
(including natural gas) to meet their national energy ane, thus lowering dependency on fossil fuels. Biomethane
demand. The concept of renewable electricity is well under- is very flexible in its application. Its may be injected direct-
stood. However a number of countries are now in the pro- ly into the existing natural gas grid allowing for energy-
cess of generating roadmaps for the deployment of renew- efficient and cost-effective transportation. Gas grid opera-
able green gas; these roadmaps highlight the potential tors can switch to a renewable gas source in a straightfor-
availability of biomass and technological innovation. This ward manner and provide energy for an array of applica-
report outlines the various substrates and technologies for tions including electricity generation, heat and transport.
green gas production and examines how much natural gas The production of biomethane from regional resources
can be replaced by green gas in specific countries. The logis- creates jobs, especially in agriculture, supply logistics, engi-
tics of injecting green gas in to existing gas grid infrastruc- neering, plant construction and maintenance. Farmers can
ture are also examined. The roadmaps developed for accel- profit in “non-food” related sectors with an alternative
erating the use of green gas thus far in specific countries are source of revenue through biomethane.
analysed. Utilising all of the available deployment pathways,
future production of green gas may account for 41PJ in This report was produced by IEA Bioenergy Task 37,
Ireland, 77PJ in the Netherlands, 280PJ in the UK, 1260PJ which addresses the challenges related to the economic and
in Italy and over 100PJ in Denmark. This represents environmental sustainability of green gas production and
approximately 26%, 24%, 8%, 44% and 75% of current utilisation.
5
Introduction Green gas
2. Introduction
2.1 What is green gas? generated can be used directly in CHP units to produce
Green gas refers to renewable gas, which can be gen- electricity and heat or upgraded to biomethane and used
erated from the anaerobic digestion of organic biomass in the same manner as natural gas. The supply of biogas
and residues produced in agriculture, food production or biomethane can be maintained year-round by ensur-
and waste processing. The digestion process involves a ing a constant supply of feedstock. Slurries, manures
series of biological processes in which microorganisms (Figure 2.1a) and organic wastes from food processing
break down the biodegradable material in the absence of can be accumulated and stored. Similarly, harvested crop-
oxygen. Typically the biogas produced is approximately biomass can be preserved in silos and designed with suf-
60% methane (CH4) and 40% carbon dioxide (CO2). The ficient scale to supply the required quantity of feedstock
biogas can be combusted directly in a combined heat and annually. Thus, the production of biogas and biomethane
power (CHP) plant or upgraded to biomethane through can be considered a stable and reliable energy source.
the removal of CO2 to leave a product similar to natural The biological process for producing biogas reflects
gas (with greater than 95% CH4 content). a natural process present in ruminant animals (Figure
Renewable gas can also be produced from high-tem- 2.1b). Naturally occurring bacteria breakdown the bio-
perature gasification of woody crops with methanation of mass in the digester (similar to the way crops are digested
the syngas. Renewable gas may also be produced through in the stomach of a cow) producing biogas consisting
power to gas technologies using electricity; preferably of CH4 and CO2. Minimal amounts of other trace gases
(but not always) this electricity would be both renewable such as ammonia and hydrogen sulphide (H2S) can also
to ensure sustainability and surplus electricity which may be produced in digestion.
otherwise be curtailed or constrained to ensure financial Of late, there has been an academic focus on algal bio-
sustainability. Algae are also a proposed source of biom- fuels. Algae are an additional biomass source with signifi-
ethane; this includes for both seaweed and micro-algae. cant growth rates, which may be cultivated in the form of
Gas of biomethane standard is considered a very flex- seaweed (macro-algae) in a marine environment or as a
ible energy vector as it can be injected directly in to exist- means of capture of CO2 through cultivation of micro-
ing gas grid infrastructure. It is an important fuel in terms algae typically in raceway type ponds situated on mar-
of contributing to future renewable energy strategies in ginal land. The production of biomethane is suggested as
electricity, transport and heat whilst abating greenhouse a beneficial route to sustainable energy for algae and is
gas (GHG) emissions in these sectors. described in detail in the IEA Bioenergy report entitled “A
This report outlines the potential for biomethane perspective on algal biogas” (Murphy et al., 2015).
(and renewable gas) as a multifaceted solution in “green- An additional technology pathway for renewable gas
ing” future gas grids. production is gasification-methanation. Gasification is
a low-carbon pathway to produce energy, fuels, chemi-
2.2 Coupling biomass availability with technology cals, and fertilisers. A large variety of biomass, typically
application with higher dry solids content greater than 40%, such as
Biomass is a finite but wide ranging resource. It can come agri-forestry residues, black bin waste, indigenous energy
in the form of specifically grown crops, or by-products crops grown on marginal land, and sewage sludge can
generated in agriculture (slurries/manures) or from in- be used in this process. Gasification involves the partial
dustrial applications such as paper, wood, and furniture combustion of carbonaceous feeds to produce a synthetic
manufacturing. Biomass will play an important role in gas (known as syngas). For biomethane, a methanation
the future realisation of a sustainable energy system and step is used to create synthetic natural gas (bio-SNG)
considering its finite nature, it is important to maximise with a CH4 content greater than 95%.
the available resource. One of the most auspicious appli- Furthermore, power to gas is a technology that con-
cations of available biomass is the generation of biogas verts electricity to hydrogen gas (through electrolysis of
or biomethane. Wet biomass (with dry solids content in water), which can be subsequently converted to CH4 in a
the range of 5-30%) can be used as input feed to produce methanation step. The theoretical advantage in this tech-
biogas in an anaerobic digester. As indicated, the biogas nology is the use of surplus electricity associated with
6
Green gas Introduction
Figure 2.1 (a) Slurries and manures generated in agriculture can be used as feedstocks for anaerobic digestion; (b) Ruminants stomach digests
crops similar to biological digestion process
(From DEN EELDER FARM: Small farm scale mono-digestion of dairy slurry, March 2017 available in http://task37.ieabioenergy.com/case-stud-
ies.html)
intermittent renewable electricity sources such as from biomass derived energy. The utilisation of agricultural
wind turbines and solar energy devices. Electricity, which wastes for biomethane production can make a further
would otherwise be curtailed and/or constrained, may contribution to climate protection and contributes to
be available at a cheaper rate. This advantage of cheap the overall ideology of greening agriculture and diver-
excess electricity may also be associated with transmis- sifying the rural economy. For instance, the digestion of
sion grid constraints. In practice the power to gas sys- freshly collected manure can potentially reduce methane
tem would be oversized or under capacity in terms of emissions from manure storage on farms. The European
equipment if the only source of electricity were surplus Commission’s Joint Research Centre (JRC) methodology
electricity. It is expected that such systems will be sized assumes a 17% methane emissions savings through re-
for long term operation and as such will bid for electric- placing open slurry storage with digestion as described
ity alongside other users (Ahern et al., 2015). However in the 2017 IEA Bioenergy report on methane emissions
power to gas offers a storage solution for electricity in the from biogas plants (Liebetrau et al., 2017). In essence
form of renewable gas whilst changing the energy vector slurry biomethane systems (or indeed other combined
to one available to transport fuel. This fuel is termed gas- waste management biogas systems) can be carbon nega-
eous fuel from non-biological origin in the EU Renew- tive. It is recommended by the authors that crop diges-
able Energy Directive (RED) and is seen as an advanced tion systems include for co-digestion with slurries to
biofuel (EC, 2017). ensure the maximum possible decarbonisation. This
positive attribute is unique to biomethane production
2.3 Benefits of a biomethane economy technologies. As such biomethane systems are an effec-
Biomethane generated from biological processes sub- tive measure in contributing to key European renewable
stitute fossil-natural gas as a source of electricity, heat or energy supply (RES) targets and also alleviating GHG
transport fuel. It can abate GHG emissions through for emissions in problematic sectors such as transport and
example reduction of fugitive methane emissions from agriculture.
open slurry holding tanks and from displacement of fos- Many countries are dependent on the importation
sil fuels. Biomethane can promote a sustainable, circular of fossil fuels to meet their national energy demand. Bi-
economy. CO2 emissions resulting from the burning of omethane can be an indigenous resource, derived from
fossil-fuels and CH4 from slurry management and waste localised organic wastes and residues. Previous literature
facilities are primary causes of global warming. Biom- studies and developed roadmaps in member countries
ethane produced from crops release CO2, which was ab- have shown that biomethane can replace significant
sorbed from the atmosphere by the crops as they mature; amounts of natural gas. For example, utility compa-
this is known as short term carbon. Therefore, the provi- ny Engie estimates that biogas from agricultural and
sion of low carbon energy is conceivable through crop other waste (excluding crops) can provide for 100% of
7
Introduction Green gas
gas consumption in France by 2050 (Reuters, 2017). In plants. It can be used by heating systems with highly ef-
countries with a well-established and closely linked gas ficient conversion efficiencies, and employed as a regen-
grid, there are good opportunities for cross-border trade erative power source in gas-powered vehicles. The utilisa-
and to create a market for biomethane, thus lowering the tion of biomethane as a source of energy is a crucial step
import dependency of fossil fuels. The production of bi- towards a sustainable energy economy. A further pathway
omethane from regional resources creates jobs, especially for biomethane can be found in large industry energy
in agriculture, supply logistics, engineering, plant con- users. A growing demand for green gas has been evident
struction and maintenance. Farmers can profit in “non- from multinational companies who want to fulfil their
food” related sectors with an alternative source of revenue corporate social responsibilities. These industries would
through biomethane. typically include breweries, distilleries, milk processing
Anaerobic digestion plants are typically located in facilities and data centres. The substitution of natural gas
close proximity to areas where biomass is cultivated or with biomethane can lower the use of fossil materials and
sourced. This circumvents the need for energy-inten- support the intended change from a fossil to a bio-based
sive transportation of biomass to the plant location. It society without the need for expensive new infrastructure.
also minimises the cost of redistributing the digestate,
a commercial biofertiliser by-product, to the surround- 2.4 Biogas and biomethane deployment
ing cropland. The digestate can reduce the farmers’ costs Anaerobic digestion can now be considered a mature
associated with the purchase of manufactured chemical technology that is widespread particularly throughout
fertilisers. The use of all by-products generated in biom- Europe. If biomethane is produced, the preferred end-
ethane production systems can ensure the optimisation use typically varies by country and the extent of their gas
of the full value-added chain. grid infrastructure. For instance, Sweden has a gas grid
Biomethane is very flexible in its application, more restricted to one region in the country and so biometh-
so than other renewable sources of energy. Its ability to ane is used primarily as a vehicle fuel with set financial
be injected directly into the existing natural gas grid al- incentives (IEA Bioenergy Task 40 and Task 37, 2014). At
lows for energy-efficient and cost-effective transporta- the end of 2015 there was a total of 17,376 biogas plants
tion. This allows gas grid operators to enable consumers and 459 biomethane plants in operation in Europe (Eu-
to make an easy transition to a renewable source of gas. ropean Biogas Association, 2016). Figure 2.2 gives an
The diverse, flexible spectrum of applications in the ar- insight into the quantity of biogas plants in a number
eas of electricity generation, heat provision, and mobility of countries and the different types of facility (WWTP,
creates a broad base of potential customers. Biomethane agricultural/industrial or landfill). The estimated energy
can be used to generate electricity and heating from with- output (TWh) from the facilities in the same countries is
in smaller decentralised or large centrally-located CHP indicated in Figure 2.3.
Figure 2.2 Number and
type of biogas plants in
selected countries
(Source: IEA Bioenergy
Task 37 Country Report
summaries 2016,
http://task37.ieabioen-
ergy.com/country-
reports.html)
8
Green gas Introduction
Figure 2.3 Current energy output (TWh) from anaerobic digestion in selected countries
(Source: IEA Bioenergy Task 37 Country Report summaries 2016, http://task37.ieabioenergy.com/country-reports.html)
If biomethane, due to its flexibility as an energy carri- for biogas upgrading varies, however four main methods
er, is considered the future of renewable gas, the technol- are currently most practiced: water scrubbing; chemical
ogy for upgrading biogas becomes a key consideration. scrubbing; membrane separation; and pressure swing
Figure 2.4 gives the current breakdown of the number absorption (PSA). Figure 2.4 also illustrates the break-
of upgrading plants in specific countries with Germany down of CO2 removal technologies used for the coun-
and the UK leading the way in Europe, and South Korea tries listed and highlights the growth of upgrading tech-
also demonstrating high uptake. The technology used nologies since the turn of the century.
C
A
B
Water Scrubber Chemical Scrubber Membrane
PSA Organic physical scrubber Other + unknown
Cryogenic upgrading
Figure 2.4 A: Number of biogas upgrading plants per country; B: Breakdown of biogas upgrading technologies used at biomethane plants;
C: Biogas upgrading technologies uptake over time (IEA Task 37 Energy from Biogas, 2016)
9
Algal biofuels Green gas
3. Algal biofuels
2.5 Advanced technologies for biomethane production 3.1 The role of seaweed in future biomethane production
First generation biofuels, such as rapeseed biodiesel Third generation, advanced biofuel sources such as
and wheat ethanol, are now capped under the EU Re- macro-algae (seaweeds), do not require arable or agri-
newable Energy Directive (RED) at 7% in terms of con- cultural land for production. Moreover, seaweeds that are
tributing to renewable energy supply targets for trans- farm cultivated at sea may offer a sustainable alternative
port. This is to avoid a potential “food versus fuel” debate to more traditional crops with higher growth rates. Rich
and alleviate concerns over the sustainability of first gen- in carbohydrates and with low lignin content, seaweeds
eration biofuels in achieving sufficient GHG emissions represent an attractive feedstock for biomethane pro-
savings. It is proposed that the cap on first generation duction with a variety of seaweeds such as S. latissima,
biofuels may be even further reduced to 3.8% by 2030 L. digitata, S. polyschides and A. nodosum, investigated
under the most recent EU legislation proposals in the in literature (Tabassum et al., 2017). Table 3.1 presents
Recast RED (EC, 2016). Consequently, second genera- energy yields from a number of different seaweeds. How-
tion biofuel substrates, such as lignocellulosic crops (in- ever, different seaweed species vary in composition, with
cluding perennial ryegrass), organic municipal wastes respect to carbohydrate and protein content; this vari-
and agriculture residues, have become the main focus of ance is also influenced the time of year at which they are
renewable energy generation through anaerobic diges- harvested. Specific growth conditions such as tempera-
tion. The digestion of second generation feedstocks is ture, nutrient availability and sunlight alter this compo-
generally well understood. Typically, a form of pre-treat- sition. Thus, the time of harvest is critical in maximising
ment is required for lignocellulosic materials to enhance the total biomethane production from seaweed. Seasonal
their digestibility and improve biogas yields. However, variation of seaweeds is also an important characteristic
providing a renewable and decarbonised energy sys- in terms of the concentrations of polyphenols and ash,
tem (for electricity, heat and transport) through second both of which, in high concentrations, may inhibit the
generation (land based) biofuels may put a significant anaerobic digestion process and lower the attainable bi-
constraint on both arable and agricultural land. As the omethane yields. The ash in seaweeds is predominantly
world’s population increases, the total energy consump- salt (chloride) and is evident in much higher levels than
tion and demand for food will increase. Use of large more traditional crop feedstocks.
swathes of land for bioenergy may become questionable Procuring a secure source of feedstock is vital to the
with potential rises in food production prices. Since the development of a seaweed biomethane industry. In the
proportion of land that can be devoted to bioenergy is fi- short term, seaweeds from natural stocks may be di-
nite, future energy systems may need to shift to the sea to gested for their energy content and may even provide a
provide sufficient feedstock resources to meet increasing method of waste treatment. Eutrophication is a common
energy demand. More advanced feedstocks such as mi- cause of green tides, whereby green seaweed washes up
cro and macro-algae are now receiving attention as an al- on the shorelines of bays or estuaries due to excess ni-
ternative to the more traditional land based biofuel pro- trogen run-off into water streams, as occurs in Ireland,
duction. Non-biological sources of renewable gas such Japan and France. Green seaweed can pose a health risk
as power to gas are also considered to have high potential and must be removed; for instance, Ulva Lactuca (sea let-
in expanding the overall energy resource to 2050. Recent tuce) can generate high concentrations of the toxic gas
EU policy measures have encouraged the development H2S. Co-digestion of seaweeds such as Ulva Lactuca with
of such pathways suggesting progressively increasing farm slurry for example can provide a mutual synergy
obligations. The share in renewable and low-carbon by optimising carbon to nitrogen (C:N) ratios in the di-
transport fuels (excluding first generation biofuels and gestion process and supplying essential trace elements
including for electrification) is required to increase from required by the anaerobic microbial consortium (Allen
1.5% in 2021 to 6.8% in 2030, with advanced biofuels to et al., 2013).
make up at least 3.6% by that time (EC, 2016).
10
Green gas Algal biofuels
Table 3.1 Potential methane and energy yields from seaweed in
Ireland (Tabassum et al., 2017) increase in the digester loading rate and improvement of
biomethane yields as compared to the mono-digestion
Seaweed species L CH4 kg VS−1 GJ ha−1 yr−1 *
of micro-algae. Thermal, mechanical, chemical and bio-
S. latissima 342 52 – 384
logical pre-treatments have all been investigated to in-
S. Polyschides 263 52 – 191
crease the solubilisation of micro-algae by attacking the
A. Esculenta 226 41 – 307
cell walls and thus to increase the obtainable energy yield
L. digitata 254 38 – 96 from the feedstock.
L. hyperborean 253 38 – 96 Micro-algae are very interesting feedstock in that
*Dependent on the specific methane yield, volatile solids content and potentially they can also be used to upgrade biogas to
seaweed yield per hectare. These values account for both basic and biomethane. The CO2 in biogas (typically 40-50%) can
optimistic harvesting potentials.
be captured through micro-algae growth in a photosyn-
Cultivation of seaweeds for biomethane production may thetic process. This novel method of biogas upgrading
provide a more long-term strategy. One method of inter- may be advantageous in that it could potentially offset
est is combining seaweed cultivation with existing fish the cost of a traditional biogas upgrading system. Care
farms, known as integrated multitrophic aquaculture must be taken in situations wherby CH4 in the biogas
(IMTA). The advantage of IMTA is that a form of biore- and O2 from micro-algae respiration could exist together
mediation occurs, in that the seaweed absorbs the nutri- at explosive levels. This threat may be overcome in sys-
ent-rich waste produced from the fish in their growth. tems such as high rate algal ponds coupled with external
This can increase growth productivity of the seaweed. In absorption columns (containing alkaliphilic bacteria)
terms of seaweed preservation and storage, drying sea- or incorporating biofixation of CO2 in a bicarbonate/
weeds is energy intensive and relies on fossil fuels, which carbonate cycle. These microalgae biogas-upgrading
is unsustainable. An alternative approach involves the systems are at a low technology readiness level (TRL)
ensiling of seaweed, similar to methods in the ensiling of but can potentially provide a biomethane-standard end
crops on farms, and may even increase the available bi- product.
omethane yield from the seaweed by digesting any silage From a biorefinery perspective, micro-algae can be
effluent produced (Herrmann et al., 2015). Research in- used for biodiesel production through the transesterifica-
vestigating the seasonal variation of seaweed, combined tion of lipids with the remaining residues post extraction
with effective ensiling methods, will enable the provision utilised for biomethane production. The digestate pro-
of a year-round supply of high quality biomass. duced from the digestion process can potentially be used
as a nutrient source for the cultivation of micro-algae,
3.2 Micro-algae and the circular economy avoiding the external purchase of such nutrients. Other
Micro-algae are unicellular algal species that can be sources of CO2 generation besides biogas from anaerobic
cultivated and used for biomethane production through digestion include power plants and distilleries, which may
anaerobic digestion. As a feedstock, micro-algae of- also be taken into consideration for micro-algae growth.
fer higher growth productivity than traditional energy Micro-algae, as a third generation, advanced biofuel sub-
crops, require no land and have the potential for carbon strate, can employ circular economy concepts and pro-
savings through sequestration. The cultivation of micro- vide a cascading bioenergy system with regards to feed-
algae can be achieved in growth systems such as open stock production, gas upgrading and nutrient recycling.
raceway ponds or more expensive photobioreactors. The It must be noted that these technologies are not ma-
advantage of using micro-algae for biomethane produc- ture and algal biomethane systems may be overly ex-
tion is that no specific algae strains are required, unlike pensive. Projects such as the EU funded All-Gas project
for biodiesel production. However, micro-algae are con- (http://www.all-gas.eu/en/home), which aim to dem-
sidered a more challenging substrate for digestion due to onstrate the integration of the full production chain of
a high nitrogen content, which results in a low C:N ratio algae to biofuels (including transport fuel) should ad-
(typically less than 10). To overcome this, co-digestion of vance the TRL significantly. Full scale application will
micro-algae with carbon rich feedstocks such as barley involve certain challenges such as technology costs and
straw, beet silage or brown seaweed has been proposed geographical and seasonal constraints of micro-algae
(Herrmann et al., 2016). Such methods can allow for an growth (Zhu et al., 2016).11
Gasification to expand the biomass and biomethane resource Green gas
4. Gasification to expand the biomass
and biomethane resource
Woody residues, such as forest thinnings, and crops A successful application of the technology has been
such as short rotation coppice (SRC) willow are consid- demonstrated in Gothenburg GoBiGas plant (Figure 4.1).
ered second generation biofuel substrates that are also This project was developed as a proof of concept for the
suitable for biomethane production. With high dry solids gasification-methanation technology in providing a po-
content (typically greater than 40%), such feedstocks are tential avenue for expanding the growth of biomethane
more suited to gasification technologies than anaerobic to meet the increasing demand in Sweden. Plant costs are
digestion for energy conversion. Gasification is a thermo- estimated at € 150 million and the system has the poten-
chemical process (using high temperatures in excess of tial to fuel 15,000 cars (GEODE, 2016). A second phase
700°C) that converts lignocellulosic biomass to syngas, is planned in which a much larger scale plant will be de-
which can be purified and upgraded in a methanation veloped; biomethane production will increase from 160
phase to produce biomethane. The technology when in- GWh/a (0.58 PJ/a) to a capacity of 800 GWh/a (2.88 PJ/a)
cluding methanation is not as mature as anaerobic diges- (Alamia et al., 2016). Ultimately the two plants could po-
tion; it is also operated on a much larger technology scale tentially provide up to 1TWh – a resource equivalent to
and hence requires substantially more capital investment. the total biogas produced in Sweden at present, enough to
Nonetheless, in terms of the future production of green fuel 100,000 cars (GEODE, 2016).
gas, gasification-methanation can play an important role.
Figure 4.1 The GoBiGas plant in Gothenburg is the first of its kind in the world, injecting biomethane from thermal gasifi-
cation and methanation to the natural gas grid of Gothenburg. At full production, the 20 MW methane plant will deliver
160 GWh/yr. (Photo: Used with permission of Rob Vanstone and Göteborg Energi, Sweden).12
Green gas Advanced smart grid technologies
5. Advanced smart grid technologies
5.1 Facilitating intermittent renewable electricity is highest in the winter (Tsupari et al., 2016). The UK
In the future our energy system will undergo a transi- has forecasted onshore wind capacity to increase almost
tion towards sustainable and renewable energy sources. four-fold by 2035 to 21GW, and this could be surpassed
Renewable energy sources are different from conven- by offshore wind capacity in the same time period, esti-
tional fossil energy sources due to their low life-cycle mated at 37.5GW (Qadrdan et al., 2015). In Denmark,
carbon emissions and their intermittent nature. Sus- Spain, Portugal, Ireland and Germany, an increase in
tainable electricity production is highly dependent on installed wind capacity has also been evident, already
weather conditions. The intermittent nature of solar contributing ca. 9-34% of the electricity supply (Götz
and wind energy means that matching the supply and et al., 2016). The intermittency of electricity generated
demand of sustainably generated electricity is challeng- through wind and solar platforms is problematic as of-
ing. Consequently there will be a greater need for energy ten, supply does not match with times of high consumer
storage and flexibility of the energy infrastructure in the demand. Although the current curtailment of renewable
future. During the winter season, the demand for energy electricity is typically due to constraints on the electricity
can be many times higher than in the summer in colder transmission lines, the increased share of electricity from
climates. However during the summer in warm climates, intermittent renewable sources is likely to compound
air conditioning can lead to very high energy demand. this problem. This is exemplified by considering wind
Energy carriers need to be available and flexible to match electricity providing 40% of a country’s electricity. If the
energy demand. capacity factor of wind generation is 30% then when the
The share of renewable electricity in the EU is ex- wind is blowing it can provide 133% of the average elec-
pected to increase significantly to 2050, potentially rep- tricity demand at a given time. If this resource coincides
resenting between 64-97% of the electricity mix (Collet with low demand by night, a significant storage capacity
et al., 2016). On a global scale, the total wind installation is required or a significant electricity spillage may tran-
has increased from 17GW to 318GW since the turn of spire.
the century (Götz et al., 2016). Storage of intermittent Opportunities to use and/or store the excess produc-
renewable electricity will be required in countries where tion of sustainable electricity must be found. Existing
the installation of wind and solar devices has been signif- electricity storage methods include batteries, flywheels,
icant. For instance, Finland has significant solar irradia- compressed air energy storage (CAES) and pumped
tion on long summer days meaning electricity generation hydroelectric storage (PHS). However these particular
could potentially be high; however, energy consumption technologies may be limited as they do not store large
Figure 5.1 Electricity storage capacity and duration (source: DNV GL)13
Advanced smart grid technologies Green gas
quantities of energy for long periods of time (Walker et production through such operation. Furthermore when
al., 2016) and often rely on specific geographical features. the biogas plant is not supporting the electrical grid it can
Figure 5.1 illustrates the different electricity storage meth- produce biomethane (via biogas upgrading). Thus po-
ods and their respective capacity. Renewable gas systems tentially an anaerobic digestion facility can support both
can support the increasing proportion of intermittent re- the electricity grid and gas grid (Figure 5.2). Previous lit-
newable electricity through two principle methods: 1) as erature studies have modelled a continuously operating
a storage mechanism for curtailed renewable electricity, 435 kWe continuously fed digestion system, which when
with conversion of the energy vector to gas (power to gas) converted to demand driven, operated as a 2 MWe CHP
which is available for similar use as that of natural gas; unit for 60 min per day, whereby 21% of biogas was used
and 2) as a support to intermittent renewable electricity in the CHP generator and 79% was supplied to the biogas
generation through demand driven biogas systems. upgrading system (O’Shea et al., 2016c).
5.2 Demand driven biogas systems 5.3 Power to Gas
With increasing wind, wave and solar deployment, the Power to Gas (PtG) is an emerging smart grid con-
amount of variable renewable electricity on the electricity cept whereby electricity (preferably surplus renewable
grid will increase. Such renewable devices are not con- electricity) is converted to methane for storage purposes.
sidered “dispatchable” (cannot be turned on or switched When electricity storage is challenging and current infra-
off at any given time) and so electricity supply does not structure does not support long-term management of this
always match electricity demand – for example when the problem, the PtG process converts the energy vector from
wind is not blowing and the demand for electricity is high. electricity to gas, which can be injected into the gas grid.
Currently, carbon intensive fossil fuels (such as combined PtG uses electrolysis, powered by electricity, to split water
cycle gas turbines) are used to back up the electrical load (H2O) into hydrogen and oxygen. To convert the hydro-
when such intermittent devices cannot meet demand. gen from electrolysis to renewable green gas in the form
Bioenergy can be made dispatchable on demand. Bi- of methane, a source of CO2 and a methanation phase
ogas generated from anaerobic digestion can be stored are necessary. Figure 5.3 contains a flow diagram that de-
onsite and fed to a CHP unit for electricity production scribes the flows on a proportional basis. It visualises the
when required. Alternatively, to minimise the cost of bi- material flows and the mass efficiency of the process can
ogas storage onsite, the feeding regime of the digester can be estimated. The flow diagram also demonstrates that
be varied to generate biogas at a specific time to match only part of the electricity is converted to hydrogen and
high electricity demand. This is known as a demand only a proportion of the hydrogen is converted to meth-
driven biogas system and often the biogas plant opera- ane. Methane is then mixed with small quantities of other
tor may receive a premium rate (price) for the electricity gases (CO2 maybe used to reduce volumetric energy den-
Figure 5.2 Combination of (A) power to gas system with (B) demand driven biogas system (Ahern et al., 2015; Persson et al., 2014)14
Green gas Advanced smart grid technologies
Figure 5.3 Product flows in the Power-to-Gas concept (source: DNV GL)
sity and propane to rise it) in order to comply with the and water (4H2 + CO2 -> CH4 + 2H2O). For catalytic
local gas-quality specification before it can be injected in methanation, a form of catalyst (typically nickel-based)
to the gas grid. Both electrolysis and methanation pro- is used making it less robust than biological methana-
cesses release heat. tion to contaminants in biogas. Biogas used in catalytic
Three main technologies reported for electrolysis methanation typically requires a cleaning step between
are: the alkaline electrolyser; the polymer electrolyte production and methanation. Catalytic methanation
membrane (PEM); and the solid oxide electrolysis cell operates at a high temperature range of 200-500°C with
(SOEC). Alkaline and PEM are considered low tempera- high pressures of 1-100 bar (Götz et al., 2016). Biologi-
ture technologies; SOEC is a high temperature process cal methanation uses hydrogenotrophic methanogenic
at a low TRL and is intended to improve the efficiency archaea to convert the hydrogen and CO2 to methane,
considerably (Parra & Patel, 2016). Alkaline electrolysis as opposed to catalysts. The biological method can be
is at a more mature stage of development than PEM or “in-situ” whereby hydrogen is injected directly into an
SOEC and is commercially available with modules up anaerobic digester and combines with the CO2 in biogas;
to 2.5MWe (Schiebahn et al., 2015). However, in the or “ex-situ” in which both hydrogen and CO2 are intro-
future, higher process efficiencies may be potentially vi- duced to an external methanation reactor. The source of
able in PEM and SOEC technologies. When evaluating CO2 for PtG can be provided by biogas plants, large CO2
electrolysis units, the most important features for PtG emitters in industry (such as distilleries), or wastewater
include conversion efficiency to hydrogen, cold start up treatment plants (WWTPs) where cheap, concentrated
flexibility, and operational lifetime (Götz et al., 2016). sources of CO2 can be accessed (O’Shea et al., 2017).
PtG requires a quick start up time from the perspec- PtG has been demonstrated for proof of concept in
tive that the system may be turned off and on to match laboratory studies. On a larger scale, two projects aim-
times when electricity is cheap (as would be the case if ing for commercial viability with regards to PtG with
the electricity source was curtailed electricity). PEM is biological methanation are the Electrochaea – BioCat
a faster technology than alkaline but is more expensive project (Denmark) and MicrobEnergy – BioPower2Gas
since the technology requires noble catalysts such as Pt, project (Germany); with both utilising biogas plants
Ir, Ru (Schiebahn et al., 2015). Any future enhancements for the source of CO2 (Bailera et al., 2017). The cost of
in electrolysis may depend on the high efficiency associ- electricity is deemed to be a very significant factor in the
ated with SOEC technology (greater than 90%), which is development of PtG systems. As discussed, lower elec-
currently at a low technology maturity. tricity prices could be available through curtailed renew-
The methanation step can be catalytic or biological; able electricity. A system conflict exists between: short
both methods adhere to the process of combining hy- operating times using cheap electricity and oversized
drogen and CO2 (at a ratio of 4:1) to produce methane electrolysis systems; and long operation times with more15
Country case studies: future strategies for biomethane Green gas
6. Country case studies: future
strategies for biomethane
expensive electricity and cheaper capital costs. Literature 6.1 Ireland
studies give examples whereby green gas can be produced To date, the Republic of Ireland (with a population
from a PtG system at €1.80/m3 when the price of electric- of ca. 4.5 million people) has made significant progress
ity is €0.05/kWeh, decreasing to €1.10/m3 when electricity in generating renewable electricity; approximately 25%
is purchased at €0.02/kWeh (Vo et al., 2017). of power generation comes from renewable sources such
PtG systems can provide a valuable control function as wind. However, Ireland has struggled to make progress
for the electrical grid in its capability to utilise curtailed in renewable heat and transport. In 2013, the total final
electricity in real time and produce green gas. The tech- energy consumption in Ireland for transport and ther-
nology costs for electrolysis and methanation must be de- mal energy was 179PJ (55 TWh) and 187PJ (52 TWh),
fined as the levels of curtailed electricity become apparent respectively. Currently there is a 6% gap to reach the 12%
in the future. Utilising the full value chain of PtG systems renewable energy supply in heat (RES-H) target for Ire-
can make such projects more financially viable (Breyer et land, which equates to about 3 TWh a-1 (10.8 PJ). Many
al., 2015). For instance, oxygen generated through elec- large energy users in the food and beverage industry are
trolysis can offer a valuable by-product with a monetary committed to procuring green energy through their en-
value. The cascading bioenergy system could use this ergy supplier. The Irish Renewable Heat Incentive (RHI)
oxygen in a gasification plant. For example a study by for biomethane injection is expected to be announced by
McDonagh et al. (2018) suggested an levelised cost of en- the government in 2018. This commodity support will
ergy (LCOE) of a catalytic PtG system of €124/MWh with potentially act as the catalyst to mobilise growth in the
costs dominated by electricity charges (56%) and CAPEX biomethane sector in the coming years. Although there
(33%). Valorisation of the produced oxygen could reduce has been a relatively small uptake so far in biogas and bi-
the LCOE to €105/MWh. An additional payment for an- omethane in Ireland, a variety of biomass resources such
cillary services to the electricity grid (€15/MWe for 8500h as grass, agricultural residues and food waste are available
p.a) would further lower the LCOE to €87/MWh. which could substantially increase renewable gas produc-
In 2012, the European Power to Gas Platform was tion. The total theoretical resource is assessed as per Fig-
founded by DNV GL. Its members are European Trans- ure 6.1.
mission and Distribution System operators, branch or- Grass is the predominant crop feedstock available in
ganisations and technology suppliers. The Platform Ireland. Ireland has 4.4 Mha of agricultural land, which is
facilitates the dialogue between these stakeholders and comprised of over 90% grassland. With a temperate cli-
provides them with a forum to gain and exchange knowl- mate, high yields of grass per hectare (10 tDM ha-1) are
edge and explore the conditions under which PtG can be readily achievable. Grass silage (preserved grass) is tradi-
successful. Within the Platform, knowledge gaps related tionally used as a feed for Ireland’s livestock. Ireland has
to the PtG concept and its implementation are identi- a large agricultural industry that will account for ca. 35%
fied and, where possible, investigated in internal stud- of the country’s total GHG emissions by 2020. Production
ies. These studies include expected curtailments in dif- of grass in excess of the quantity required for livestock
ferent European countries towards 2030, business cases feed has been identified as the biomass of most poten-
of PtG pathways and compatibility aspects of different tial for anaerobic digestion. This grass resource has pre-
CO2 sources for methanation. Recently, a study has been viously been estimated in literature at ca. 1.7 Mt DM a-1
finalised which investigated the role of PtG in a purely (McEniry et al., 2013), available in excess of livestock
renewables based European energy system. The Platform requirements and could be used for biomethane produc-
member’s common goal is to realize the energy transition tion.
as cost-effectively as possible.16
Green gas Country case studies: future strategies for biomethane
Legislation on the collection of food waste and the Residues from agriculture in Ireland include for farm
introduction of high landfill levies has encouraged its slurries, slaughterhouse wastes and processing wastes
disposal through other means in Ireland. Food waste from the production of milk and cheese. Typically these
(and the organic fraction of municipal solid waste) is a residues are land spread; however, such wastes can also
commonly identified feedstock for anaerobic digestion, be considered a valuable resource for energy production
as it can achieve high specific methane yields (SMYs). as they incur no cost and can achieve very high GHG
It is considered the low hanging fruit as a digestion emissions savings on a whole life cycle basis (compared
feedstock as it is a waste stream that can potentially to the fossil fuel displaced) due to the removal of fugi-
accrue a gate fee (for the operator) as opposed to en- tive methane emissions in open slurry storage tanks. The
ergy crops which have a production cost, supporting majority of slurry will come from Ireland’s dairy herd,
the economic feasibility of such digesters. The composi- where slurry is collected in pits when the animals are
tion of food waste is variable depending on origin, that housed inside in winter. Pig slurry may also be a viable
is, whether it is sourced from rural or urban areas. Es- feedstock as it is collected year round. Slaughterhouse
timates of the collectable household food and garden wastes typically comprise of paunch (material extracted
waste have been made for Ireland by multiplying popu- from the stomach of the animal) and sludge (from the
lation numbers by the quantity of waste available; it has wastewater treatment process), both organic by-prod-
been assessed that 138,588 t Volatile Solids (VS) a-1 of ucts suitable for digestion and biomethane production.
food waste is potentially available in Ireland (O’Shea et Milk processing waste is generated at dairy produce fa-
al., 2016a). cilities and typically comes in the form of an effluent or
Micro-algae (rudimentary) is
an approximate resource,
Gas, 181.26 which does not include for
weather conditions or actual
time based CO2 availability
from power stations; micro-
Total, 153.8 Power to gas, 1.43 algae (in-depth) includes for
weather conditions, daylight
Microalgae (in-depth), 1.75 hours and actual production
of CO2 from power plants
Microalgae (rudimentary), 9.76
Diesel, 114.18 Grass silage, 128.40
Source separated household organic waste, 1.50
Milk processing waste, 0.17
Slaughterhouse waste, 0.21
Chicken manure, 0.12
Pig slurry, 0.27
Sheep manure, 0.61
Cattle slurry, 9.59
Gas Diesel Total theoretical renewable
gas resource
Figure 6.1 Ireland’s total theoretical biomethane potential resource from identified feedstocks as compared to natural gas consumption and diesel consumption.
Data on gas demand and diesel demand adapted from (Howley & Holland, 2016; O’Shea et al., 2016a; O’Shea et al., 2016b).17
Country case studies: future strategies for biomethane Green gas
sludge. The residual sludge from primary and second- highlights Ireland’s potential to produce the most renew-
ary wastewater treatment processes may also be digested able gas per capita within the EU by 2030, with a realistic
for biomethane in Ireland. Many wastewater treatment potential of 13 TWh a-1 (47 PJ a-1).
plants already have digesters onsite as part of their treat- Mobilising Ireland’s biomethane potential has been
ment process in reducing the organic content of their the focus of much research, strategy development and so-
effluent streams. lution design within Gas Networks Ireland (GNI). GNI
Several studies have been published on Ireland’s to- owns and operates over 13,500 km of transmission and
tal biomethane production potential, which ranges from distribution gas pipelines in Ireland (with approximately
about 4 – 50 TWh a-1 (15 to 180 PJ a-1) depending on feed- 680,000 connections to homes and businesses). GNI are
stock mobilisation assumptions. The total practical re- committed to facilitating renewable gas in decarbonis-
source (as opposed to potential resource) of biomethane ing energy supply to customers, particularly in the heat
identified by O’Shea et al., (O’Shea et al., 2016a; O’Shea and transport sectors. Based on detailed assessments of
et al., 2016b) based on currently available resources in the many biomethane solutions throughout Europe, GNI
Ireland was 27.8PJ as indicted in Figure 6.2. If this biom- identifies the “Hub and Pod model” as the model with the
ethane resource was used for transport or thermal energy most potential to maximise the mobilisation of biometh-
it could provide ca. 15% renewables in either sector. A ane in Ireland. This model incorporates road transport of
recent study by the Sustainable Energy Authority of Ire- biomethane in compressed trailer units from biogas pro-
land (SEAI) on Ireland’s renewable gas potential has indi- duction facilities located remotely from the gas network
cated that as many as 900 digesters, ranging in size from (Pods) to centralised injections facilities connected to the
500 kWe (CHP) to 6000 kWe (biomethane), would be gas network (Hubs). Such a solution could maximise the
required to exploit the existing and future biomass avail- potential for Irish farmers, as biogas production can be
able nationally (SEAI, 2017). The future resource from located remote from the gas network on farm scale biogas
biomethane was reported in this study as ca. 22 PJ which Pods, with clusters of biogas Pods feeding biomethane
would result in GHG emissions savings of 2 Mt CO2eq, to centralised grid Injection Hubs. Assuming ongoing
equivalent to 3.7% of the total national GHG emissions biomethane policy supports, GNI predicts the growth
in the baseline year 1990. A recent study published by the rate of biomethane injection facilities to grow with up to
EU Commission in March 2017 (Kampman et al., 2017) 43 centralised Hubs in place by 2030, with an average of
Table 6.1 Gasification-methanation of willow for biomethane in Ireland
(Gallagher & Murphy, 2013)
Gasification Conversion Unit
feedstock
6,800 Required for one 50MWth gasifier ha a-1
74,800 For eleven 50MWth gasifiers ha a-1
SRC
1,795,200 assuming 24 t/ha t a-1
willow
15.8 Lower heating value (LHV) 8.8 GJ/t PJ a-1
10.3 Process efficiency @ 65% PJ a-1
Table 6.2 Potential methane resource from power to gas in Ireland
adapted from (Ahern et al., 2015)
Electricity Conversion Unit
4.5 consumption in 2015 Mtoe a-1
188 consumption in 2015 PJ a-1
75 assuming 40% renewable electricity (RES-E) PJ a-1
5.3 assuming 7% curtailment PJ a-1
4.0 assume 75% efficiency conversion to H2 PJ a-1
Figure 6.2 Irelands practical biomethane resource from identified feedstocks
(O’Shea et al., 2016a; O’Shea et al., 2016b), 3.0 assume 75% methanation efficiency PJ a-118
Green gas Country case studies: future strategies for biomethane
8 biomethane production Pods supplying each hub (over grid; each gasifier would require 6,800 ha of willow (Gal-
300 on-farm anaerobic digestion Pods nationwide). This lagher & Murphy, 2013). The energy resource from gasi-
scenario would see 11.5 TWh a-1 (41.4 PJ a-1) of biom- fication is extrapolated in Table 6.1. Future renewable gas
ethane supplied to energy customers which would be production could increase by 10.3 PJ a-1 by the introduc-
approximately 20% of predicted natural gas demand in tion of eleven 50MWth gasifiers, increasing Irelands total
2030. theoretical energy resource to ca. 38 PJ a-1. Ireland is also
In addition to this, GNI are supporting the creation examining the concept of storing surplus electricity as a
of a biomethane market in Ireland by co-funding other gas through PtG systems. A recent literature study (Ta-
major projects through the Gas Innovation Fund. The ble 6.2) indicates that a resource of ca. 3 PJ a-1 would be
Causeway Project will examine the impact of increased available based on 7% renewable electricity curtailment
levels of Compressed Natural Gas (CNG) fast refill sta- in 2015. It is not feasible to operate based solely on cur-
tions and renewable gas injection on the operation of the tailed electricity as the CAPEX based on low run hours
gas network in Ireland and is co-funded by the European would generate a low capacity factor and expensive re-
Union through the Connecting Europe Facility. The pro- newable gas (McDonagh et al., 2018). The theoretical
ject will deliver 14 fast fill public access CNG stations in- resource is assessed as 1.43PJ in Figure 6.1.
stalled by the end of 2019.
Furthermore the Green Gas Certification Scheme 6.2 The Netherlands
project which is co-funded by the Department of Com- At present, the Netherlands produces ca. 4 TWh a-1
munications, Climate Action and Environment, Depart- (14.4 PJ a-1) of biogas, which is primarily used for elec-
ment of Jobs, Enterprise and Innovation as well as GNI tricity and heat. Approximately 900 GWh a-1 (3.24 PJ a-1)
and the Renewable Gas Forum of Ireland was launched of biomethane is also injected to the natural gas grid.
in April 2017, and aims to devel-
op a comprehensive meth-
odology for a certification
scheme that facilitates bi-
omethane trading for both
renewable heat and trans-
port markets. It is antici-
pated that such certification
and independent traceabil-
ity of Guarantees of Origin
and sustainability criteria
will be mandated in the up-
dated RED as well as dem-
onstrating compliance with
EU and national targets.
For advanced technolo-
gies in Ireland, gasification
studies have shown an in-
digenous supply of willow
could feed eleven 50MWth
gasifiers located on the gas
Figure 6.3 Biogas resource potential
in the Netherlands (Green Gas Forum,
2014) (Groen Gas Nederland (GGNL))You can also read
