Report
May 2022

Green
Gas

The Green Economy
under our feet.

1

2

Contents
Foreword by Founder of Ecotricity, Dale Vince

4-5Part One
Green Gas – The opportunity for Britain

7-34

Independent analysis by Dr Gbemi Oluleye and Dr Semra Bakkaloglu from
Imperial College London, via Imperial Consultants.

Part Two
Domestic Heat Pumps in the UK – The implications of awholesale switch to heat pumps and the potential forinterface with Green Gas

36-48

Independent analysis by NRS Griffiths

Appendix
Appendix 1 – Green Gas – The opportunity for Britain
Appendix 2 – Biographies

49-54
55

3

Foreword
by Founder of Ecotricity, Dale Vince
Seven years ago we published our first green gas
report. In it, we flagged the amazing opportunitythat gas made from grass offers us as a nation.
Essentially we believed that it was possible to
make all the gas we need to heat Britain’s homes,
right here in Britain, from a new approach using a
proven technology - grass fed anaerobic digesters.
Our desktop study told us there was enoughgrassland in Britain to do this, that we could create
100k jobs and a £10 billion annual contribution to
the rural economy. We would end our use of fossil
gas for home heating - worth some 15% of ourcarbon emissions and since domestic use of gas
is 2/3 of our national total - it would be a big step
towards Energy Independence.
We struggled to get traction for some reason, while
we also struggled to build our demonstration
project, for lots of reasons - planning, patchy
government support, a pandemic followed byan energy crisis followed by a war in Europe - allcomplicated the picture.
But we finally started work on that demonstration
project, the same day we launched this new report.
We commissioned this second green gas report tovalidate our first one, or not - as the case may be.
We also wanted a deeper dive into the data, tolook more closely at the availability of land andgrid connections, the economics of green gas, thejob creation potential - the whole works really. And
we wanted the impact that an independent andacademic voice could add to this.
Because to us gas from grass is an amazing
opportunity - right beneath our feet.

4This new study doesn’t just validate our original
position - it shows that the opportunity is evenbigger than we said it was seven years ago.
The key findings for me are these;
There is enough grassland to make all the gas
Britain’s homes use - without taking any land out offood production.
In the process we would create 160k jobs and a£15 billion contribution to rural economies.
If we model in changes to our diet, the reductionof animal consumption and therefore farming - theopportunity gets even bigger, green gas from grass
could actually power the whole country’s homes
and businesses.
In fact by 2050 we could be making nearly twice
as much gas this way as we currently get from theNorth Sea.
Green gas made this way would have almost 90%
less greenhouse emissions when compared tonorth sea gas and synthetic fertiliser use - green
gasmills produce natural fertiliser as a by product.
With process improvements it looks possible toachieve an emissions reduction of 99%, comparedto North Sea gas and current fertiliser production.
These are stunning findings. We could be Energy
Independent in gas, freeing us from the global
commodity markets that set prices beyond ourcontrol - and from our dependency on unreliable
or unethical sources of fossil fuels, such as Russia
and the Middle East.
Making all the gas we need from the grass we havean abundance of is the perfect complement tomaking all the electricity we need from the wind
and the sun - which we also have an abundance of.
In combination we can achieve complete Energy
Independence and enormously strengthen our
economy, which pre the energy crisis was depletedby £50 billion every year - that’s how much we
spent to bring fossil fuels to Britain just to burnthem. £1 billion each week. That’s like the lie on theside of Johnson’s Brexit bus (£350m per week for
the NHS if we exit the EU) - but three times bigger
and real.
In the process we can create an enormous amountof new sustainable jobs here, help farmers
diversify from animal agriculture, save ourselvesa shedload of money every year - and do what wehave to do, to avoid the worst of the climate crisis
into the bargain - get to net zero carbon.
It’s a plan with no downsides. It even creates
habitats for wildlife, on a vast scale - over andabove those that exist on grassland now.
The second part of this new report looks for the
first time in depth at the government’s alternativeplan - a national air source heat pump program.
The key findings for me are these;
It will require the scrapping of tens of millions ofexisting devices, gas cookers and boilers.
The scrapping of our national gas grid.
A tripling of renewable energy generation to makethe electricity to power nearly 30 million heatpumps. And a massive grid upgrade to deliver thatextra electricity.
A home that uses a heat pump will have annual
energy bills that are higher by over 40% - than thesame home using a gas boiler.
Heat pumps won’t work in 20% of our homes
without significant home upgrades - while foranother 20% they won’t work full stop.
A national air source heat pump program will cost
six times as much as a green gas program - almost£300 billion versus £50 billion.
These are also stunning findings.
This report could not be more timely - we’re deep
into an energy security crisis that has exacerbatedan existing energy price crisis - while we urgently
need to deal with the role of energy in the climate
crisis anyway. The answer is not to throw away
our national gas grid and the tens of millions ofappliances that use it, imposing vast costs on the
public - the answer is simply to change the gas we
put into the grid. And carry on as normal.
Green gas is cheaper, faster and far less wastefulthan a switch to heat pumps. And it will work forevery home - no exceptions. It will give us a morebalanced and diverse outcome in terms of energy
supply, and form an essential part of the smart grid
we need - with gas and electricity grids supporting
each other, sharing the energy load of the country.
Today we announced a new gas field ‘discovered’ in
Britain - this report shows that Britain’s grassland
could actually be be our new North Sea - but with asignificant difference - it will never run out.

Dle Vnce
Dale Vince
Founder, Ecotricity

5

6

Part One

Green Gas – The opportunity for Britain
An independent report by Dr Gbemi Oluleye and Dr Semra Bakkaloglu of
Imperial College London

7

Green Gas – The opportunity for Britain
Table of Contents
Executive Summary

9Green Gas Potential in the UK

9

Benefits of Green Gas

10

How can we support Green Gas Mills?

10Introduction: The new frontier for decarbonisation

11

A beginner’s guide to the Green Gas Mill

12

1

How much grassland is available?

13

1.1

How much grassland is suitable?

14

1.2

Biomethane potential of suitable grassland

142

Is Green Gas capable of meeting the UK’s gas demand?

17

3

How economic is green gas?

20

3.1

Feedstock cost

20

3.2

Feedstock transport cost

20

3.3

Biomethane production cost

20

3.4

Price unit of biomethane

21

3.5

Employment opportunities from green gas

23

3.6

Reducing our reliance on fossil fuel imports

23

4

5

8

Biodiversity gain

24

4.1

Enhancing the soil health and structure

25

4.2

Creating habitats for wildlife

25

Greenhouse gas savings

26

5.1

Upstream GHG emissions

27

5.2

Average emission intensity of the UK Natural Gas Supply

27

5.3

Downstream GHG emissions

27

5.4

Lifecycle emissions from biomethane production (A, B, C)

28

5.5

GHG emission savings from Green Gas Mills compared to business-as-usual emissions

28

6

Achieving Our Green Potential: summary of becoming Green Britain

30

7Bibliography

31

Executive Summary
The UK Government’s new Net Zero Strategy1 , UK Heat and Building Strategy2 and British Energy Security
Strategy3 lays out for the first time how the government plans to cut UK emissions in half in less than adecade and eradicate them entirely by 2050, while also ensuring the UK can be largely independent ofchanges in global fuel prices. It is a feasible proposal that will bring employment, investment, and broader
advantages to the UK. However, as the UK Climate Change Committee pointed out, there are significant
gaps between these ambitions and a clear policy and delivery pathway. A number of key decisions have yet
to be made, with aspects of this pathway relying on ongoing studies (low carbon hydrogen) and technology
yet to be developed (new and advanced nuclear power), let alone brought to the market.
The Government has proposed deployment levels of low-carbon options. Recognising that future
demand for gas will decline4 as we decarbonise implies that the gas system will need to change to meet
net zero targets. This will allow us to identify how the gas market will need to develop to guarantee thatthe required market and regulatory signals are in place to provide the requisite level of investment andmaintenance during the transition.
A new Green Gas Support Scheme (GGSS) has been introduced to encourage the injection of biomethanefrom anaerobic digesters (AD) as well as investigate the development of commercial-scale gasification andthe replacement of the GGSS with a long-term biomethane support scheme.
To get there, we are going to have to work on a new frontier – to remove the carbon emissions from ournation’s heating. Ecotricity believe that they have found a solution that could play a significant part in this:Green Gas Mills.
Through the process of Anaerobic Digestion, Ecotricity’s Green Gas Mills will use species rich herbal leys
as fuel to produce biomethane (or ‘Green Gas’). The big benefits of Green Gas are that it is a fuel sourcethat will never run out, it’s low carbon, it reduces the need to import fossil fuels from overseas or frack thecountryside, and it uses existing infrastructure such as the gas grid (there is no need to upgrade the gas
grid to stop hydrogen leaking from the old pipe network) and household heating systems. Grass/herbal
ley biogas/biomethane is a viable solution for meeting renewable energy targets in the UK in terms ofavailable technology, energy balance, greenhouse gas (GHG) savings, and policy constraints.

Green Gas Potential in the UK
Green Gas can immediately contribute significantly to meeting the UK’s Net Zero target. We assessedthat the UK has 6.46 million hectares of suitable grassland. This is enough suitable grassland for around
5,400 Green Gas Mills to be built. This would provide up to 236.5 TWh - enough energy to heat 98.8% of
British homes if made energy efficient - while also boosting the rural economy by nearly 162,000 jobs andgenerating £16 billion for the rural economy.
Green Gas Mills also save nearly 87% of greenhouse gas (GHG) emissions when compared to usage andgeneration of natural gas and synthetic fertiliser, as business-as usual scenarios, which could be further
reduced with proper automation and well monitored systems by 2050 to emission saving up to 99%.
We are now working on the second phase of the green gas mill project with Ecotricity to assess the Life
Cycle Analysis (LCA) of green gas mills. This will be completed when the plant at Reading is operational in
2023/24.
The above assumes Green Gas Mills with 5MW capacity, and requiring 1200 hectares of land each in linewith current technology. Total energy output could be increased further if Green Gas Mills become more
efficient. If this was not a constraint, the gas potential of herbal ley species on the suitable UK grassland
itself is 247.2 to 482.5 TWh, with an average of 288.5 TWh. This green gas potential could be increased to579.2 TWh by adding seaweed and even 923.1 TWh by 2050 if diet habits also change, allowing for more
grassland to be used for green gas generation on top of the use of seaweed. This significantly exceeds UK
gross natural gas production from the North Sea (438.3 TWh).

9

According to various studies we have reviewed, an additional 6.86 million hectares of land would beavailable if the total population became vegan. Assuming that just 10% of the population adopts a plantbased diet now, we could re-purpose 664 thousand hectares of current grazing land to produce 318.2
TWh energy per year on average. Even without changing diets, with seaweed addition the UK’s suitable
grassland could meet up to 71.6% of total current natural gas demand including industrial use. There ispotential to produce more than enough biomethane to supply every household in the UK and replace theneed for natural gas for our domestic gas needs. If 20% of hydrogen is blended into the gas grid, 76.5% of
total natural gas demand could be offset.
The price of a unit of Green Gas is expected to be around £70 per MWh, but this can be reduced to £54
per MWh with technological advancements and the addition of seaweed, which is half the cost of current
natural gas prices. Given the cost of heat pumps and the electrification of the entire gas grid (which
includes all heating and hot water requirements), Green Gas is a safe and cost-effective solution to thecurrent energy price crisis.

Benefits of Green Gas
Green Gas Mills can help us decarbonise our heating and contribute to the fight against climate change.
They also provide additional benefits, including the following•

Boosting rural economies: each Green Gas Mill will generate approximately 30 jobs and £3 million in
annual feedstock contracts for farmers.

•

Increasing food productivity: when grass feedstocks are grown in rotation with crops on arable land,soil health is improved.

•

Supporting wildlife and biodiversity by providing a pollen and nectar-rich habitat for bees and otherinsects in areas growing feedstock species, such as rich herbal leys.

•

Weaning the UK off reliance on imported gas as North Sea production declines, thereby eliminating theneed for fracking.

•Utilising existing gas infrastructure: This enables us to easily switch from fossil fuel to grass-based gas.

Green Gas Mills are the antithesis of fracking: they are low carbon, a truly renewable source of indigenous
gas, provide an infinite, rather than limited, supply, and boost local economic benefits without jeopardisingwater supply, air quality, local communities, or climate targets. Indeed, Green Gas Mills have a sizable
environmental benefit.
We are aware of concerns about ‘energy crops,’ which are another method of producing biomethane; if the
incentives are not right, farmers may abandon food production on arable land in favour of crop production
for biogas production. This is a legitimate concern – the farmland in the UK is valuable and must be
protected.
The other frequently discussed method of producing green gas is from food waste. While this method
presents its own set of complications such as the need of source segregation, it will clearly need to be partof the plan for future energy security.
In the United Kingdom, we are developing another method of producing green gas - from species richgrassland, known as herbal ley. It has none of the drawbacks associated with food waste, energy crops, or
fracking, but it has significant advantages over all three. This is a significant opportunity for the UK.

How can the UK support Green Gas Mills?
Green gas mills are a relatively new technology. We believe they have tremendous potential, but in order toget started and demonstrate what they are capable of, they will require policymaker support. As a priority,
we hope the government will:

10•

Maintain support for biomethane producers through the Green Gas Support Scheme (GGSS).

•

Clarify the regulation and classification of permitted feedstocks under the Green Gas Support Scheme
to ensure that feedstocks such as herbal leys that do not threaten food production are supported.

•

Avoid duplicating the regulations already in place for biomethane injection with additional rules under
the Green Gas Support Scheme.

•

Provide additional clarity on targets post-2035.

The next major challenge in our quest to become a Green Britain is decarbonising the gas network andproviding carbon-neutral heating and hot water systems. Green Gas Mills, we believe, can play a criticalrole in meeting that challenge.

Introduction: The new frontier for decarbonisation
The Prime Minister, Boris Johnson, has made further pledges to ensure that the UK remains at theforefront of the green industrial revolution over the next decade5. He unveiled a ten-point strategy fora green industrial revolution in 2020 to make the UK a global leader in renewable energy generating
employment, reducing emissions and increasing exports. The target is to power the country with 100%
clean energy sources by 2035. The announcement is part of the government’s pledge to achieve net zero
emissions by 2050, and it will sustain 60,000 jobs.
But the UK is now approaching the next chapter of this challenge: decarbonising heating.

1+25+2118161142D

Heating accounts for 37% of total energy consumption in the UK and is responsible for the majority ofresidential emissions, which account for 16% of the UK’s annual greenhouse gas emissions (Figure 1). It’s
straightforward: unless and until we can decarbonise our heating and hot water, we will never achieve
Green Britain.

2%

2%

1%

Public

LULUCF

Industrial processes

4%

Waste management

11%

25%
Transport

Agriculture

16%
Residential

21%

Energy supply

18%
Business

Figure 1. Final UK greenhouse gas emissions for 20206
Note: LULUCF is land use, land use change and forestry

11

A beginner’s guide to the Green Gas Mill
Ecotricity have been working on Green Gas Mills for a while now, and are not the only ones. These GreenGas Mills are potentially revolutionary: using herbal leys as fuel they produce biomethane (Green Gas),
which is both renewable and virtually carbon-neutral but can be used just like natural gas, replacing gas
from the North Sea, Saudi Arabia or even Russia. The big difference is that biomethane recycles existing
carbon in the atmosphere which has been absorbed by the grass within the last year, rather than fossil fuelgas which releases carbon when it is burned after being safely stored underground for at least 65 million
years, and methane (CH4) from incomplete combustion or fugitives from venting and flaring events.
The way the Green Gas Mills work is pretty simple. They can be fuelled with organic feedstocks - in
Ecotricity’s case species rich grassland known as herbal leys - which bacteria then break down in anoxygen-free environment through a process of Anaerobic Digestion (AD). From the process of AD, we
get two main outputs: biogas and a ‘digestate’ which isn’t actually wasted at all, but can be used as a richsource of organic fertiliser.
In many ways the process is just like a cow: the grass goes in one end, and gas and fertiliser come out
the other. But in this case, rather than the gas ‘escaping’ like it does from cows, it is collected and used toreplace natural gas.
Some people use the biogas directly in gas boilers for heating or burn it in an engine to generate combined
heat and power (CHP). Our Green Gas Mills go one step further. Once we have the biogas it is then‘upgraded’: purified and brought up to the UK’s high environmental and safety standards as biomethane.
After being upgraded to biomethane, it can be fed directly into the national gas network to be used forheating in gas heating boilers, cooking on a standard gas hob, or even as vehicle fuel.
That’s one beauty of the Green Gas Mill concept: you can be cooking on Green Gas, and you won’t evennotice.
Grasslands are found across large area of the UK ranging from natural upland grassland, through lowland
hay meadows, semi-improved grasslands to intensively managed single species grasslands cut for silage or
intensive cattle grazing. Grasslands also contribute to a region’s cultural heritage and recreational benefits,
as well as providing a vital regulating ecological function and supporting biodiversity and cultural services7.
Grassland is a significant carbon sink8 as well as a feedstock for renewable energy generation in the formof grass biomethane. It also has other benefits (e.g., long persistency of high dry matter yield, intercropping
potential with legumes and subsequent reduction in fertiliser application rates9, protection of soil from
erosion, and groundwater formation10-13).
Ecotricity believes that “green gas from grass” will provide the UK with a new type of low-carbon,
sustainable energy.

121. How much grassland is available?
The first crucial question is not how much land one Green Gas Mill will require, but how much land will be
required across the UK to replace natural gas for home heating and hot water with “green gas from grass.”
There are many different land types, but not all of them are suitable for green gas generation.
There is a total 17.46 million hectares of agricultural land in the UK. This consists of arable andhorticultural land, improved grassland, neutral grassland, calcareous grassland, and acid grassland areas(see Figure 2 and Table 1).

Figure 2. This represents available grassland in the UK14. Surface hill shade demonstrates the steepness of surface15, which can vary inlocal areas16. Because soil characteristics are influenced by the slope of the surface, acid grasslands are found on more steeply sloped
areas. Solid and dashed black lines show the natural gas (NG) pipeline (© National Grid UK, 2022)17. See Appendix A1 for details of the
UK land cover, Appendix A2 and A3 for the steepness of the surfaces.

Table 1. The UKCEH Land Cover class and area for UK in 202016
UKCEH Land Cover Class

Area (million hectares)

Arable and horticulture

5.38

Improved grassland

7.10

Neutral grassland

0.27

Calcareous grassland

0.13

Acid grassland

2.21

Upland heather moorland

1.03

Heather grassland

1.35

Excluding land used for food production and horticultural activities, the total of potentially available
grassland area in 2020 would be 12.08 million hectares.

13

1.1

How much grassland is suitable?

However, not all of the potential 12.08 million hectares of grassland would be harvestable or close enoughto a suitable gas grid connection.
The slope of the surface is critical for determining the type of equipment that can be used in a given area,
identifying areas that are more susceptible to surface runoff, and even determining the feasibility of green
gas generation in that area. There is approximately 2.16 million hectares of acid grassland and 1 million
hectares of upland heather land in Great Britain that exceeds a 12-degree threshold17, making it unsuitablefor harvesting, leaving an area of 8.92 million hectares of potentially suitable grassland. Furthermore, themajority of Scotland’s heather grassland (1.26 million hectares) is located outside the gas grid, and thus is
excluded.
Of the remaining 7.65 million hectares, a significant area is used for common grazing (1.19 million
hectares of grassland based on agricultural statistics for the UK in 202018) and therefore also consideredunsuitable. Thus, it is estimated that a maximum 6.46 million hectares of grassland can potentially be
used to produce green gas (see Appendix A4 for details). This would of course exclude any permanent
species rich grassland nature reserves or Sites of Special Scientific Interest (SSSI) .

1.2

Biomethane potential of suitable grassland

Anaerobic digestion (AD) is a technique for producing biogas from biomass (i.e., grass, legume and herbs
for Green Gas Mills), which can then be upgraded into biomethane of the same quality as natural gas.
Biomethane, which contains 97% CH4, 2% CO2, and some minor constituents, plays a significant role inproviding renewable energy as biomethane and natural gas can be mixed and interchanged. Green Gas
Mills are designed to produce biomethane, which is used to replace natural gas in the gas grid.
The UK has a high potential for green gas, with temperate climates and a high proportion of grassland.
There is growing interest in utilising grassland for bioenergy generation in Europe and North America19,
focusing on various grass species20,21. Despite this, methane yield from grass species is generally modest
due to them containing relatively low and imbalanced nutrients22. Herbal ley mixtures can improvemethane yield by including diverse chemical compositions, such as concentrations of structural and nonstructural carbohydrates, as well as mineral nutrients (e.g., nitrogen, N)23-25, which are linked to biomass
digestibility in Green Gas Mills. Recent studies21,26 indicate that some deep-rooting herb species such as
chicory are rich in macro and micronutrients (potassium, sulphur, zinc and boron) because of absorption
from deeper soil layers, which is significant for the health of microorganisms in Green Gas Mills, whereas
legume species (i.e., white, red clovers) are high in nitrogen in plant tissues. Anaerobic digestion ofgrass, herb and legume with complementary nutrient composition has potential to increase methane
generation27. Hence, Ecotricity have decided to feed Green Gas Mills with herbal leys, made up of grass,legume and herbs or wildflower species, by working with farmers (see Appendix A5 and A6 for details).
Ecotricity will also conduct ecological surveys so as to maintain herbal ley mixture quality and increase thebiodiversity of the land. The herbal ley mixture is suitable for medium to light soil types with a pH of 6-828
and the UK’s climate conditions, and is thus a good fit with the UK’s 6.46 million hectares of grasslands
identified above.
The yield and quality of biomass from herbal leys for Green Gas Mills can be improved by land
management practices such as cutting period, harvest time and frequency25-27. Recent studies reported thata two-cut strategy in a year for multi-species grass, legume and herbs mixtures can increase biodiversity
and methane yield27,29, while also lowering cost and energy inputs30. Ecotricity aim to apply the two-cut
strategy for Green Gas Mills. Although the methane yield per hectare may vary from field to field andyear to year due to difference in species composition (and yearly rainfall31), the aim is to obtain a range of
methane yield of herbal species which would be the main feedstock for Green Gas Mills (see the Appendix
A6 for the details of herbal species mix to be used).
Table 2 depicts the UK’s biomethane potential from suitable grassland. Based on 6.46 million hectares ofsuitable grassland potential and 13 tonnes of dry solids yield per hectare of herbal ley mixture in a year, 84
million tonnes of dry solids and 75.6 million tonnes of volatile dry solids could be the feedstock of Green14

Gas Mills. The average methane yield of a herbal ley mixture is 375 m3 CH4 per tonne of volatile dry solids(see Appendix 5 for more information), which can produce 47.2 billions m3 of biogas that is further
refined into 28.3 billion m3 of biomethane from AD. Before injecting this produced gas into the gas grid,
it should be upgraded. The biomethane loss from upgrading processes such as pressure swing adsorption(PSA), membrane, chemical and water scrubbing processes, and chemical absorption systems ranges
from 0.001 to 5.5% of gas generation32. Due to the high technology of Green Gas Mills, we assumed thatmethane slips would be in the lower range. According to recent studies, PSA technology can result in thehighest methane loss, and chemical absorptions32,33 can yield lower methane loss from upgrading systems;
therefore, Ecotricity will consider using chemical absorption for biogas upgrading systems in order tominimize methane loss from the system, resulting in lower methane emissions and thus lower GHG
emissions. So, we assumed 0.5% of methane slip from the biogas upgrading facility on average. As a result,
before considering the capacity of Green Gas Mills themselves, the UK’s suitable grassland could in theory
generate 288.5 TWh (ranging between 247.2 and 482.5 TWh) energy per year based on biomethane
higher heating value. Because these calculations are based on 6.46 million hectares of suitable grassland,
the biomethane yield from per hectare of grassland would be 160.8 GJ per hectare on average, ranging
from 137.8 to 268.9 GJ ha-1 per year (see Appendix A7 for the details of these calculations).
The estimated biomethane from the current AD under construction by Ecotricity is 65,538 kWh per hectare(235.75 GJ ha-1), and falls within this range, although this does include the addition of seaweed extract(Ascophyllum Nodosum) to boost methane production. If this method were applicable across the board,
it would result in 482.5 TWh from 6.46 million ha, which is near the upper end of the range estimatedin Table 2. Also, Shin et al.34 reported that adding seaweed to anaerobic digestion of food waste andsewage sludge enhances anaerobic digestion performance and increases methane yield by 24% and 20%
respectively, at high substrate concentrations. We assume that seaweed addition to Green Gas Mills may
improve biomethane yield by 20%. Thus, the UK’s suitable grassland has a great potential to generate 296.6
to 579 TWh of biomethane per year, with an average of 346.2 TWh.
Table 2. The biomethane potential of the UK
Grassland

Unit

AverageMin

Max

million ha

6.46

6.46

6.46

Herbal leys yieldt DS/ ha/y

13

13

20

Annual Feedstockt DS/ y8.40 x107

8.40 x 107

12.92 x 107

Herbal leys yieldb

t VS/ t DS

0.9b

0.9b

0.9b

Volatile dry solids yieldt VS/ y7.56 x107

7.56 x107

11.63 x107aMethane yield of herbal leysc

m3 CH4/ t VS

375

340

408

Methane production

m3 / y28.3 x109

25.7 x109

47.4 x109

Biogas productiond

m3/ y47.2 x109

42.8 x109

79.1 x109

Biomethane loss in upgradinge

%

0.5

1

0.1

Biomethane after upgradingf

m3/y27.49 x109

23.56 x109

45.97 x109

Biomethane energy yield

GJ/y839.6 x106

275.6 x106

1670.2 x106

Biomethane energy yield

TWh/ y

288.5

247.2

482.5

Biomethane energy yield

GJ/ ha/ y

160.8

137.8

268.9

Biomethane yield after seaweed additiong

TWh/ y

346.2

296.6

579.0

Biomethane energy yield by
2050h

TWh/ y

460.0

394.2

769.3

Biomethane energy yield by
2050 after seaweed additioni

TWh/ y

552

473.0

923.1

Herbal ley mixture yield per hectare was obtained from the Cotswold Grass Seed webpage which states that herbal ley yields 13
tonnes of dry matter (DM) per hectare28; bIt is assumed that 0.9 total volatile dry solids (t VS) in total dry solids (t DS)35; cMethane yield
was derived from the literature; more information can be found in Appendix A5 and A6; dBiogas includes 60% of methane; eDifferent
biogas upgrading technologies have varying gas loss rate36,37, but we assume methane slip from Green Gas Mills would account for no
more than 1% of total biomethane production; f97% CH4 in biomethane was assumed38; gSeaweed addition increase biomethane yieldby 20%; hAdditional 4.18 million hectares of land will be available by 2050; iA 20% increase in biomethane yield is assumed.
aNotes: MethaneHHV: 38.1 MJ/ m3; 1 MJ: 0.000278 MWh

15According to the Committee on Climate Change (CCC) analysis39, 22% of the land currently used for
agriculture (the total UK agricultural area is 17.46 million hectares39) will be available by 2050 due toa variety of factors, including increased sustainable crop productivity and livestock grazing intensity,
decreasing beef, lamb, and dairy consumption, reducing food waste, and moving horticulture productionindoors. Therefore, an additional 3.84 million hectares of land will be available for use in green gas
generation, resulting in an additional 146.9 to 286.8 TWh energy capacity per year.
To sum up, the green gas potential of the UK’s suitable grassland could reach 769.3 TWh without
seaweed addition by 2050 (see Table 2), and 923.1 TWh by 2050 (ranging from 473.0 to 923.1 TWh, withan average of 552.0 TWh) with the addition of seaweed and future land availability in the UK (see Figure 4).
In this study, it is assumed that Gas Mills have a capacity of 5MW and require 1200 hectares of land each.
This means that with current mill technology and efficiency, 5,400 Green Gas Mills could be built on the 6.46
million hectares of suitable grassland identified above, providing up to 236.5 TWh of green gas. At present,
Green Gas Mills have capacities ranging from 3 MW to 6 MW, requiring around 1000 hectares of feedstock
growing land. Ecotricity has the most recent technology and efficiency to further utilise the UK’s green gas
potential.

1000

800

600

400

200

0

Biomethane yield

Biomethane yield after seaweed
addition

Biomethane yield by 2050

Biomethane yield by 2050 with
seaweed addition

Figure 3. Green Gas potential of the UK (TWh). It is assumed that the addition of seaweed increases methane yield by 20%. Figure 3
represents that grey line is 20% higher than pale green line; and bright green line is 20% greater than blue line.

16

2. Is Green Gas capable of meeting the UK’s natural gas
demand?
Based on BEIS data (2021)40, the UK’s total natural gas demand was 808.7 TWh in 2020 (Table 4),a 6%
decrease from 2019 due to reduced activity across the economy during the Covid-19 restrictions.
Of this 808.7 TWh of gas, 231.6 TWh was used to generate electricity of which approximately 29% is fordomestic electricity demand (90 TWh) and 61% for business and industry electricity demand (141 TWh).
In 2020, domestic house gas demand for heating and hot water was 299.3 TWh, and 189 TWh was used bybusiness.
Table 3. UK Natural Gas demand, TWh40
2019

2020

Electricity generators

272.3

231.6

Energy industries

91.2

88.6

Industry

108

99.3

Domestic

294.9

299.3

Services

93.2

89.6

Transport

0.2

0.3

858.9

808.7

Total

0+11+11122937D
0%Transport

11%

Energy industries

37%
Domestic

29%

11%
Services

12%
Industry

Electricity generators

Figure 4. Natural gas demand percentage for each sector, adapting from Table 3.

17

Green gas from the UK’s suitable grasslands has the potential to meet between 30.6 and 59.7% of the
UK’s total natural gas demand in 2020 (37.1% to 71%.6 of total natural gas demand if seaweed is added
to AD). If an additional 1.19 million hectares of common grazing areas are used for grassland production,
biomethane production could reach 292.7 to 571.3 TWh, replacing 36.2 to 70.6% of natural gas demand,
depending on herbal ley biomass yield per hectare of grassland and gas production unit loss.
2.71, 5.41, and 10.8 million hectares of grassland respectively would be required to meet 25%, 50%, and100% of the UK’s total demand for natural gas (see Table 5). Currently, suitable grassland cannot replace
100% of natural gas demand; however, shifting to vegan diets will reduce meat and dairy demand, affecting
the land requirement. The researchers41 estimate that if the entire world adopted a vegan diet, our total
agricultural land use would fall from 4.1 billion to 1 billion hectares (a 75% reduction in land use)42. If weapply this ratio to the UK’s agricultural land (so 75% of the 17.46 million hectares of agricultural land will
become available for green gas production), we get 13.1 million hectares of land available for green gas
production, which can yield twice as much biomethane as the present estimate. As a result, all the natural
gas demand could be met with green gas.
Table 4. Minimum area of grassland required to meet UK’s total natural gas demand% UK total natural
gas demand

UK natural gas demand, TWh(2020)

Min. required grassland, million
hectares (without seaweed
addition)25%

202.182.71

50%404.35

5.41

100%

808.7

10.8

In 2020, UK gross natural gas production from the North Sea was 438.3 TWh; however, 51 TWh was usedby the extraction industry and 105 TWh was exported, resulting in 282.3 TWh being injected into the grid,with further 6.3 TWh biomethane injection43. A minimum of 1.1, 2.2 or 4.6 million hectares of grassland
could compensate for 25%, 50% or 100% of North Sea natural gas production without industrial extraction,
respectively (see Table 5).
Table 5. Minimum area of grassland required to meet the UK’s North Sea natural gas production.
% UK total North Sea gas
production (minus amountrequired for extraction) andassuming no exports

UK North Sea gas production,
TWh (2020)

Min. required grassland, million
hectares (without seaweed
addition)

25%

83.3

1.1

50%

166.7

2.2

100%

333.3

4.6

The UK’s Green Gas potential can also meet the domestic natural gas demand if at least 1, 2 or 4 million
hectares of grassland were used to meet 25%, 50% or 100% of domestic natural gas demand, respectively(See Table 6).
Additionally, according to the UK Government’s Net-Zero Strategy40, heat and building energy demand is
expected to fall by 15-20% by 2050 as a result of energy efficiency measures such as improving homes tomeet Minimum Energy Efficiency Standards to EPC band C and building new homes with a high standardof energy efficiency. The British Energy Security Strategy aims to go further with “as many homes to reach
EPC B and C by 2035”. Therefore, when compared to the 2020 domestic natural gas demand in Table 3,
the energy requirements for domestic consumption in 2035 would range between 239.4 and 254.4 TWh,requiring a minimum of 3.21 to 3.41 million hectares of grassland.

18

Table 6. Minimum area of grassland required for UK’s domestic natural gas demand% UK domestic natural gas
demandDomestic natural gas demand,
TWh (2020)

Min. required grassland, million
hectares (without seaweed
addition)

25%

74.8

1.0

50%

149.7

2.0

100%

299.3

4.0

100%

75%

25%

61.9%
Total natural gas
domestic demand

31%
15.5%

69.7%
North Sea natural
gas production

34.1%
17.0%
167%

Total natural gas
demand83.7%
42%

Figure 5. The minimum % of suitable grassland (6.46 million hectares) required to meet the 25%, 50% and 100% natural gas demands

The Prime Minister announced a Ten Point Plan for a Green Industrial Revolution in November 2020 andstated that the government will “work with industry to complete testing necessary to allow up to 20%
blending of hydrogen into the gas distribution grid for all homes on the gas grid” by 202344. We also
analysed the minimum land requirement for Green Gas production assuming hydrogen is blended into
the gas grid at a rate of 20%. As shown in Table 4, the natural gas demand for 2020 is 808.7 TWh, which
equates to 72.9 billion m3 natural gas (assuming the higher heating value of natural gas is 11.1 KWh perm3). 20% of this volume could be compensated by hydrogen, which is approximately 14.6 billion m3. Withhydrogen’s higher heating value of 3.55 KWh per m3, this 20% hydrogen blending can offset 51.7 TWh ofenergy. Therefore, the demand of natural gas would be reduced to 757 TWh, requiring a minimum of
10.1 million hectares of grassland to replace natural gas with a green gas (Table 7).

19

Table 7. Minimum area of grassland required to meet UK’s total natural gas demand (2020) if 20% ofhydrogen is blended into the gas grid
% UK total natural gas
demandUK natural gas demand, TWh(2020)

Min. required grassland, million
hectares (without seaweed addition)

25%

189.3

2.53

50%

378.5

5.06

100%

757

10.14

According to the CCC’s analysis of the most cost-effective strategy for meeting the UK’s 2050 emissions
goal, natural gas consumption in industry, buildings, and electricity may decline from approximately 700
TWh in 2030 to around 370 TWh in 2050 (290 TWh based on CCC central scenario45). If efficient enoughGreen Gas Mills were built in sufficient number, this demand for green gas in 2050 could be easily met
by utilizing 76.6% of currently suitable grassland without changes in diets or adding seaweed.

3. How economic is green gas?
Grass from the previously identified suitable grassland has to be converted into biomethane. Anaerobic
digestion plants have to be built, and the grass must be collected and transported to the plants. The
production of biomethane depends on the geographical location and the type of grass available to produce
biomethane.
The cost of biomethane production is an important pillar because it affects the competitiveness of theenergy vector. The cost of biomethane relies on the following components:•

Feedstock costs include feedstock collection costs and costs of transporting the feedstock from thecollection location to the conversion location.

•

Operating expenses (OPEX) including conversion and upgrading costs.

•

Capital expenditure (CAPEX) including conversion, upgrading and injection costs.

3.1

Feedstock cost

The average cost of the simple herbal ley mixture was estimated to be around £6.47 per kg (£194 perhectare)46 although this will vary from year to year.

3.2

Feedstock transport cost

Typically, herbal leys for biomethane production are collected and transported to the conversion plant. It is
assumed that herbal ley will be transported over a maximum of 5 miles from a Green Gas Mill to grasslandand back. The haulage rate per mile for an 18/27 tonne vehicle is £2.547. However, in most new Green Gas
plants the aim will be to harvest as much as possible from the farm where the Green Gas Mill is locatedand neighbouring farms.

3.3

Biomethane production cost

Bioenergy costs, efficiencies, and emission intensities can change over time, but they are not expected tochange across scenarios. The full cost data for biogas and biomethane production are adapted from CCC
analysis48.
20

The cost of biogas production from anaerobic digestion is forecast to be £29 per MWh in both 2020
and 2050; biogas upgrading to biomethane technology costs £38 and £35 per MWh in 2020 and 2050,
respectively. The total cost of producing biomethane from the feedstock would be £67 per MWh in 2020and £64 per MWh in 2050. However, with development of technology and the addition of enzymes toboost biomethane, costs are expected to fall considerably, with some estimates for new plants to becommissioned this year already suggesting £54 per MWh.

3.4

Price per unit of biomethane

Table 8 shows the total costs associated with utilising the entire biomethane potential of the UK. The priceof a unit of biomethane was calculated based on the average biomethane potential of the UK.
Table 8. The total costs of if UK’s biomethane potential is fully utilised
Feedstock cost
Grass to biomethane
conversion technology cost
Transportation cost
Total cost

Unit

Costs, £ billion£194 / hectare

1.25£67/ MWh(£64/ MWh for 2050)(£54/ MWh for enzyme addition)

19.3(18.5)£2.5 / mile for 27 tonne truck

0.039(15.6)
20.6

The total grassland area is assumed to be 6.46 million hectares, with a herbal ley yield of 13 tonne DS/year.
Assuming that the average UK’s biomethane potential is 288.5 TWh/ year (see Table 2), the price unit ofbiomethane would be £71.4 per MWh, which could fall to £69.5 per MWh by 2050. The unit cost will be
reduced to £58.5 per MWh through the development of new technology and the addition of seaweed
enzymes.
According to the IEA World Energy Outlook report extract on prices and affordability49, spot natural gas
prices have been steadily rising around the world, reaching their highest levels in Europe during thesecond half of 2021. Natural gas prices fell significantly during the pandemic but have recently climbed
dramatically (see Figure 6). In 2021, the EU’s natural gas price is around £42.6 per MWh (15.8 USD/MBtu,
one USD is currently worth around £0.79 on April 26, 2022). As shown in Figure 6.b, natural gas prices
soared to around 45 USD/MBtu (£121 per MWh)50 in 2022, more than twice the unit price of green gas
because Russia’s invasion of Ukraine has added further pressure and uncertainty to energy prices.
According to the IEA51, annual upstream investment in natural gas supply will be around 240 and 125
billion USD (2020) for Net Zero Emissions by 2050 and Stated Policies scenarios (STEPS), respectively. The
IEA also warns that demand uncertainty caused by the energy transition, global pandemics, and investor
pressure to diversify away from fossil fuels could result in higher prices. Under these circumstances, as
illustrated in Figure 6, the future natural gas unit price cannot be easily predicted. On March 20, 2022,
the IEA announced a 10-point plan to reduce reliance on Russian natural gas52, which encourages thereplacement of natural gas with alternative sources such as green gas and gas grid electrification52.
However, electrification of the gas grid has its own challenges with high associated costs.
Element Energy Limited and E4tech conducted a cost analysis of future heat infrastructure options for the
National Infrastructure Commission and discovered that low carbon heating will be more expensive thanfossil fuel heating today53. The cost of decarbonising the UK’s heating and hot water is estimated to be
between £120 and £300 billion under their central cost assumption, and between £100 and £200 billion
under their best-case assumptions. They also stated that in 2050, the average cost of heating per homewould be £100-300 higher. The CCC also estimates in its Sixth Carbon Budget report that £250 billion
investments will be needed to fully decarbonise homes54. The decarbonisation of heating and hot water
system includes different technologies such as heat pumps and direct electric heating. According to the
Element Energy Limited and E4tech study53, the electrification using heat pump requires upgrades to theelectricity distribution network and the transmissions network, for a mid-case range total of £44 billion.

21

Oil

Coal

Gas - European Union

Gas - United States

Gas - Japan

30

25

20

15

10

5

0
Figure 6a. Oil, natural gas and coal prices by region from 210 to 2021 in terms of USD per million BTU obtained from IEA49.

Asian spot LNG

Henry Hub - US gas price

TTF- European gas price

70
60
50
40
30
20

Figure 6b. IEA estimation of natural gas prices in Europe, Asia and the United States50.

2204-02-2021

16-12-2021

03-11-2021

21-09-2021

06-08-2021

24-06-2021

11-05-2021

24-03-2021

08-02-2021

08-02-2021

22-12-2020

09-11-2020

25-09-2020

12-08-2020

30-06-2020

30-03-2020

14-02-2020

0

02-01-2020

10

These high energy prices indicate that supply is struggling to keep up with demand. Green Gas is a simple
and straightforward solution to address the high cost of electrification and the unexpected cost of natural
gas prices.

3.5

Employment opportunities from green gas

Green Gas Mills have a large economic impact on rural regions. Each Green Gas Mill will generate around30 jobs in agriculture and feedstock collection, operation and maintenance, and site management. We
predict that each Green Gas Mill will provide £3 million per year, to the local agricultural economy via
contracts for grass feedstock. This would provide a significant boost to rural towns at a difficult time.
The first Green Gas Mill, with a capacity of 5MW, requires on average 1,200 hectares (3,000 acres) of
grassland (see Table 2 for average energy production), and costs £11.3 million to heat 3,600 homes in
the UK (The median gas consumption per meter in 2020 is 1.39 kW /12,145 kWh55). That equates to 0.33
hectare (0.82 acres) per house. That is less than one acre per household.
By 2050, energy efficiency is expected to reduce heat and building energy demand by 15-20%40, implyingthat 0.27 hectares (0.67 acres) of grassland would be required per home. Thus, a typical Green Gas Mill
could heat 4,500 homes efficiently.
Nearly 5,400 (5,383) Green Gas Mills could be built in the UK’s 6.46 million hectares of suitable grassland,
providing enough energy to heat 24.3 million homes (98.8% of British households) with well-insulated
systems, or 19.5 million homes without energy efficiency modifications. As a result, the rural economy
would gain nearly 162,000 jobs and £16 billion in annual investment.
To heat the entirety of the UK’s 29 million homes56 (87% or 25.4 million residential buildings are currently
connected to the gas grid; the remaining 13% or 3.8 million rely on oil, or liquid petroleum gas (LPG) orcoal)57. In 2020, the median domestic gas consumption per meter in 2020 is 12,145 kWh55. Considering
the total domestic gas demand in 2020 (299.3 TWh), 24.6 million homes would be heating by natural gas
demand. The remaining homes (756,000) would be heated by heat pumps or biomass heating, which
requires approximately 5,500 (5,466) Green Gas Mills would need to be built. We believe that by adding
seaweed or shifting to a vegan diet by 2050, Green Gas Mills will be able to heat all homes in the UK if they
are insulated for energy efficiency.

3.6

Reducing our reliance on fossil fuel imports

Natural gas prices have risen sharply in the last year, causing the British government to struggle to reducethe impact of energy prices on citizens’ energy bills. Ofgem announced a 54% increase in the energy pricecap from April 2022 due to a spike in wholesale gas prices affected by the war in Ukraine, and a further
increase is expected in October 202258. However, rapid biomethane scaling-up could provide both a shortterm and long-term solution.
While the UK’s overall gas usage is decreasing, the quantity imported is increasing as the North Sea
depletes (Figure 6). According to the UK Oil and Gas Authority, the UK’s natural gas imports could rise tonearly 70% by 2030. As a result, rather than benefiting the British economy, more and more of the money
we spend on importing fossil fuels will be spent overseas, making us larger clients for the Netherlands,
Norway, and Qatar. Rising costs for fossil fuel imports have led in recent years to a current accountdeficit, which narrowed to £11.4 billion (1.9% of GDP) in Quarter 4 2021, from £26.1 billion in the previous
quarter59.

23

Net production

Imports

120

100

80

60

40

20

2035

2034

2033

2032

2031

2030

2029

2028

2027

2026

2025

2024

2023

2022

2021

2020

2019

2018

2017

2016

2015

2014

2013

2012

2011

2010

2009

2008

2007

2006

2005

2004

2003

2002

2001

2000

0

Figure 7. The UK gas consumption by source (million tonnes of oil equivalent) 60

Biomethane produced in Europe is currently 30% cheaper than natural gas61 and can reduce the UK’s
energy dependency on external suppliers. Capable of being produced from £58.5 per MWh of biomethane,(with cost expected to decline, in addition to being a cheaper alternative, biomethane could provide
the steppingstone to green hydrogen, which requires more time and cost to adequately scale-up61. The
ongoing Russia-Ukraine crisis has prompted the UK’s decision to phase out Russian imports (less than 4%of its natural gas supply, 32 TWh)62; biomethane could very quickly replace these imports and help stabilise
rising gas prices in the UK. It would take just 430 thousand hectares of grassland and 358 Green Gas Mills
to replace all the gas imported from Russia.
Green Gas Mills can not only get us on the road to a greener Britain, but they can also aid our farmers,
increase food yield, create employment, protect wildlife, and reduce our dependency on fossil fuel imports.

4. Biodiversity gain
According to the House of Commons report “Biodiversity in the UK: bloom or bust?”, the population sizesof birds, mammals, amphibians, reptiles, and fish have declined by 68% since 1970. The UK is one of theworld’s most environmentally devastated nations with 15% of UK species on the verge of extinction. Amongthe G7 nations, the UK has the lowest amount of biodiversity surviving63. At the very least, the UK has
failed to reach 14 of the 19 Aichi biodiversity objectives, which are global environmental goals that the UK
agreed to meet by 202063. The reason for the dramatic decrease in biodiversity could be the intensificationof both arable land and monoculture grasslands; additionally, the UK lost nearly 2 million acres ofgrassland due to urban area expansion64.
The House of Commons report recommends that an urgent revolutionary change is necessary to reverse
the trajectory of biodiversity loss63, which cannot be addressed simply by better using natural resources.
In 2020, the UK Government unveiled the Ten Point Plan for a Green Industrial Revolution, with the ninth
point focusing on the protection of our natural environment44. The UK government allocates funding to24

create more green jobs, with a £40 million second round of the Green Recovery Challenge fund to improvebiodiversity and tackle climate change44.
Ecotricity’s vision is to plant herbal ley species not only to generate green gas but also to address the UK’s
biodiversity crisis. Herbal ley mixture species do not require agricultural land, so they do not competewith food production. They do, however, provide specific added environmental values, such as promoting
biodiversity and soil fertility. Herbal leys on grasslands even have the potential to enhance biodiversity65,66
and to provide additional benefits such as increased carbon capture from the atmosphere and foodproduction for pollinators like bees, butterflies and hoverflies 66-69.

4.1

Enhancing the soil health and structure

Herbal leys, which are composed of grass, legumes, herbs, or wildflowers, have numerous advantages
for improving soil health and structure. Plants like grass, legumes, herbs, and wildflowers provide energy,
protein, and minerals, as do plants like sainfoin, chicory, or bird’s-foot-trefoil70. Legumes do add nitrogen to
the soil, which can reduce the need for synthetic N fertilizer71. Additionally, they absorb more carbon fromthe atmosphere and store it in the soil as organic matter.
When used in crop rotation cycles, the varieties of native grass species we use in our Green Gas Mills
can increase food productivity on arable farmland and improve soil health while breaking disease andfungal cycles that can persist in the soil72 because herbal leys build soil carbon, fix nitrogen and mobilise
phosphate for the following crop, all of which benefit soil fauna. Deep-rooted grassland has the ability
to create and restore healthy organic matter to the topsoil in a way that cannot be duplicated by addingorganic topsoil or manures alone, as they can reach water deeper in soil. Also, growing herbal leys creates
an absorbent layer on the surface, which has the benefit of impeding rainfall runoff, thereby providing
greater community benefit from reduced flood risk.

Digestate as a biofertilizer
Ecotricity’s Green Gas Mills will contribute not only to renewable energy but also to renewable fertilisers.
Green Gas Mills produce a digestate as a by-product, which may influence water, land and biodiversity.
Converting digestate into biofertiliser can provide economic benefit as well as increase microbial biomass
and activity in soil 73,74.
Digestate biofertilisers can also boost herbal leys growth. According to an Irish study, the quality of
biofertilisers varies significantly depending on the feedstock used 75. The development of biofertilisers fromdigestate is becoming increasingly important for Green Gas Mills in order to meet regulatory requirements
and generate additional revenue.
Green Gas Mills have the necessary technical performance and infrastructure to recover nutrients fromdigestate which can be marketed as a biofertiliser. Digestate from Green Gas Mills will be accredited to thestandard of PAS 11076 which ensures safe and reliable organic fertilisers while also eliminating methane
emissions, as it requires closed digestate storage.

4.2

Creating habitats for wildlife

It is estimated that Britain has lost 97% of its species rich grassland with only isolated pockets remaining
since 193077. This has caused the decline of many species of farmland bird and insects, particularly bees,
which play a vital role in the ecosystem.
Green Gas Mills can enhance the wildlife values of land by replacing intensive monoculture grasslands
with species rich herbal leys. Green Gas Mill feedstocks, herbal leys, contain a greater diversity of species,
including herbs and wildflowers such as chicory, ribgrass, clovers, sainfoin, and lucerne, which provide
pollen and nectar-rich habitats that can help slow or halt the decline in pollinating bee populations
and species in the UK78. Herbal leys will support a much higher density of insects, bees, and otherpollinators than any intensively managed grassland because of the lack of use of synthetic pesticides or
agrochemicals. Those insects and insect larva offer food for voles, shrews, and mice, which are prey for25

mammalian predators such as weasels and stoats, as well as birds of prey such as kestrels, buzzards,
harriers, and owls and a variety of other species. Additionally, insectivorous birds such as skylarks, yellow
wagtails, whitethroats and grey partridges, as well as bats would benefit from herbal leys as a food source.
To summarise, the UK’s 25 Year Environment Plan, published in 201879, highlights the threats posed bylong-term trends in water quality, air quality, GHG emissions and biodiversity. This represents a greatchallenge to British agriculture. However, the development of successful Green Gas Mills coupled withenhanced nutrient management planning represents an excellent opportunity to reset and refine oursystems to deliver better environmental outcomes at a local and national level.

5

Greenhouse gas savings

The Climate Change Committee (CCC) recommends that the UK set its Sixth Carbon Budget to require a
78% reduction in emissions by 2035 compared to 199054. Net Zero Strategy: Build Back Greener lays out
policies and proposals for decarbonising all sectors of the UK economy in order to meet our net zero target
by 20501. The decarbonisation of the British gas network strategy covers the future injection of biomethaneand potential hydrogen blending. The availability of UK grassland potential for biomethane generation anddisplacement of natural gas in the current gas grid would make biomethane a more viable solution for
decarbonising the gas grid than hydrogen, which requires more cost and energy to produce and store.
The main emissions from green gas generation are methane emissions from anaerobic digesters, biogas
upgrading units, digestate storage and transmissions, distribution and storage of green gas, and nitrous
oxides from digestate handling stages. The emissions can come from fugitives, leaks on pipes, tanks,
vents or pressure relief vales. Methane emissions are the main concerns of biomethane production due
to higher 100-year global potential of 27.2 ±11 based on latest IPCC report79. Nitrous oxide (N2O) has
an even higher 100-year global warming potential of 273 ±13079 than CO2 which can also be emitted byincomplete combustion of engine and flare. Life cycle emissions should be thoroughly investigated in orderto generate sustainable green gas. In order to quantify GHG emission savings, total life cycle emissionsof Green Gas Mills should be compared to the alternative scenario of business as usual (BAU). The stages
associated with GHG emissions from the Green Gas Mills and the BAU alternatives are categorised in Table
9 below. The end-use emissions from natural gas and green gas are not included.
Table 9. Stage of life cycle emissions (LCE) from Green Gas Mills and BAU
Upstream emissions
On-site emissions:gas production,transmission, distribution
and storage

Downstream emissions:Fertiliser application
Total LCE

Green Gas Mills – GHG emissionsA) Emissions saving from grassland,as feedstockB) Biomethane production andutilisation on site: emissions fromsupply chain•

Biogas production•

Biogas upgrading: Biomethane
production•

Transmissions, distribution andstorageBAU Alternatives – GHG emissions
1) Land used for grazing, or grasslanduses business as usual2) North Sea emissions from domesticgas production, pipeline distribution
and LNG shippingC) Digestate transport and spreading on land

3) Life cycle emissions of synthetic
fertiliser production and spreading on
land

A+B+C

1+2+3

The GHG saving (%) can be calculated as the ratio of the differences between alternative scenarios andtotal LCE of Green Gas Mills compared to the alternative scenarios:

Total LCE from BAU alternatives (1+2+3) - Total Green Gas Mills LCE (A+B+C)
Total LCE from BAU alternatives (1+2+3)

26

5.1

Upstream GHG emissions

If the available grassland is not used for Green Gas Mills, the land would be used for grazing.
According to the UK National Atmospheric Emission Inventory (NAEI, 2022), the UK’s emissions fromgrazing are 1,037 kilotonnes of CO2-eq for 201980. The total grazing land in the UK in 2019 is 5.09 million
hectares, including rough and common grazing land. Therefore, emission intensities in 2019 would be
203.7 kg CO2-eq/ha. The emissions would be higher if methane emissions from manure management andnitrous oxide emissions from agricultural soils were included. We aim to assess the lowest possible rangeof GHG emissions savings by operating Green Gas Mills.
The grassland emission savings are 1,100 kilotonnes CO2-eq for 201980. Given the UK’s total grassland area of
12.08 million hectares, the grassland emission intensity in 2019 would be -91.1 kg CO2-eq/ha.

5.2

Average emission intensity of the UK Natural Gas Supply(On-site emissions – 2)

Green gas, as an Ecotricity goal, has the potential to replace natural gas. As a result, natural gas emissions
from the production, transportation and distribution stages should be compared to Green Gas Millemissions under the BAU conditions. The emission factor for natural gas assumed in the Ofgem Carbon
Calculator is 67.59 g CO2-eq /MJ (243 kg CO2-eq /MWh)81 for the EU mix with 4000 km of transportdistance and combustion emissions.

5.3

Downstream GHG emissions

Synthetic fertiliser is an alternative for biofertiliser obtained from Green Gas Mills. The Ofgem GHG
calculator is utilised to estimate GHG emissions from fertilisers81
Table 10. Lifecyle emission intensities from fertiliser production81
Parameters

Emission intensity

Unit

Fertiliser production LCE, N

4.57

kg CO2-eq / kg N

Fertiliser production LCE, P2O5

1.18

kg CO2-eq / kg P2O5

Fertiliser production LCE, K2O

0.64

kg CO2-eq / kg K2O

These parameters are combined with the amount of digestate (kg or tonnes) to calculate the fertiliser
counterfactual’s GHG emissions. In 2020, the fertiliser consumption given in Table 10 was used to estimate
total GHG emissions from fertiliser utilisation (see Table 12).
Table 11. Overall fertiliser usage on grassland per hectare in Great Britain for 202082
Nitrogen usage

53kg N/ haP2O5 usage

8kg P2O5 / ha

K2O

11

kg K2O / ha27

Table 12. Total emissions from fertiliser production and utilisation in Great Britain for 2020
Nitrogen fertiliser

242.21kg CO2-eq / ha

P2O5 fertiliser

9.44

kg CO2-eq / ha

K2O fertiliser

7.04

kg CO2-eq / haTotal emissions from fertiliser
production and utilisation

258.69kg CO2-eq / ha

5.4

Lifecycle emissions from biomethane production (A, B, C)

According to the DEFRA GHG conversion factors, lifecycle emissions of anaerobic digestion plants withbiomethane upgrade for the gas grid would account for 65 kg CO2-eq/ MWh in 2020 and 6 kg CO2-eq/
MWh in 205083. Green Gas Mills have been operating with advanced technology, so we believe methane
emissions from such facilities will be in the lower range. However, 6 kg CO2-eq/ MWh may be too ambitious,
so we decided to use an average GHG conversion factor for 2020 and 2050, which is 35.5 kg CO2-eq/MWh
for Green Gas Mills. As these are the default emission factors (which do not represent a specific grass type),
future research will be able to assess the comprehensive lifecycle emission estimate for a typical GreenGas mill. We are now working with Ecotricity to assess the Life Cycle Analysis (LCA) of green gas mills. This
will be completed when the plant at Reading is operational in 2023/24.

5.5

GHG emission savings from Green Gas Mills compared tobusiness-as-usual emissions

BAU (i) Grassland is used for•

Upstream emissions from grazing, (136.7 tonnes CO2-eq/ y for 1200 hectares land)•

On-site emissions from natural gas (10,643.4 tonnes CO2-eq /y for 5 MW energy production), and•Downstream emissions form chemical fertiliser utilisation (314.1 tonnes CO2-eq/ y for 1200 hectares
land)

Total LCE emissions would be 11,094.2 tonnes CO2-eq per year.
BAU (ii): Grassland is utilised for•

Upstream emissions as a native grassland (-110.6 tonnes CO2-eq/ y for 1200 hectares land),•On-site emissions from natural gas is used for energy (10,643.4 tonne CO2-eq / y for 5 MW energy
production), and•Downstream emissions from chemical fertiliser utilisation (314.1 tonne CO2-eq/ y for 1200 hectares
land).

Total LCE emissions would be 10,846.9 tonne CO2-eq per year.
How about the LCE emissions from Green Gas Mills?
One Green Gas Mill needs 1,200 hectares which saves 109.3 tonnes of CO2-eq/y. Green Gas Mills with acapacity of 5 MW generate 1,554.9 tonne CO2-eq/y from biogas production to biomethane generation.
Downstream emissions for digestate would be zero81. Each Green Gas Mill will produce 1,445.6 tonnes ofCO2-eq/y in total, although this is the upper end of the emission range for Green Gas Mills. We believe thatwith proper automation and well monitored systems, these emissions will be significantly reduced. Theseemissions will be reduced further to 153.5 tonne CO2-eq/y by 2050 using the DEFRA 2050 GHG conversion
factor48.

28

In comparison to the above-mentioned alternative use of grasslands with natural gas supply, Green Gas
Mills provides GHG savings ranging around 87%, which could account for up to 99% of GHG saving by
2050.

GHG Emissions, tonne CO2-eq per year

11,500

9,500

7,500

5,500

3,500

1,500

-500

BAU (i)Up-stream

BAU (ii)

On-stream

Green Gas Mill

Down-stream

Green Gas Mill

Total

By 2050

Figure 8. GHG from the Green Gas Mill and business as usual (BAU) scenarios

Green gas recycles atmospheric carbon and does not release any additional fossil carbon into theatmosphere as the carbon contained in biomethane is biogenic and part of the carbon cycle. As a ready touse technology, biomethane needs to be an urgent priority to ensure that we can cut emissions as much as
possible, as soon as possible. This needs to be done by Green Gas Mills.

29

6

Achieving Our Green Potential:
summary of becoming Green Britain

The UK has tremendous potential for green gas generation to be used not only to decarbonise heating andhot water, but also to meet its net zero emission commitments. Additionally, green gas can serve as a formof seasonal energy storage and provide support for other low-carbon electricity sources. The rise in energy
prices following the pandemic and the energy crisis caused by the Ukraine war have prompted the world tolook for suitable energy sources, one of which is Green Gas, readily available in the UK.
We believe that Green Gas Mills can directly contribute to the UK’s need for energy independence anddecarbonisation. Although low-carbon heating technologies such as heat pumps will also be critical, andthe National Grid’s ‘Leading the Way’ scenario includes a mix of hydrogen and electrification for heating84,
these will necessitate significant societal changes as well as significant investment in overall systeminfrastructure. We believe that Green Gas Mills can be easily adapted to the current natural gas gridwithout incurring significant costs, and that they can contribute to the UK’s net-zero goal.
To demonstrate how, we’ve created three scenarios (low, medium and maximum ambition represents
25%, 50% and 100% of total green gas production, respectively) that illustrate theoretically how far we
could go in decarbonising our heating by 2035 through the use of Green Gas Mills (Table 13). Green Gas
Mills are more than eight times less expensive than heat pump options, with up to £16 billion in revenue
and 162,000 jobs created, as well as a 52 million tonne CO2-eq GHG savings. These are not predictions. They
have nothing to do with what we believe is probable. They are about what is possible, ranging from what
we think is a bare minimum to the very ambitious. Ultimately, these scenarios are intended to demonstrate
how far we can go and to set the stage for a discussion about the potential benefits of Green Gas Mills.

Table 13. Green Gas Mills 2035 scenarios
Low ambition

Medium ambition

Maximum Green Gas

Green Gas Mills

1350

2700

5400

Green gas generated(TWh)1

59.1

118.3

236.5

UK energy-efficienthouseholds supplied (%)

24.7

49.4

98.8

Estimated carbon saving(million tonne CO2-eq)

13

26

52

Revenues generated
(£mn)

2025

4050

8100

Employees

40500

81000

162000

Green gas roll-out costs
(£bn)

14

28

56.1

Heat pump roll-out costs(£bn)2

65

130

260

Notes: 1 It is assumed that each green gas mill has 5 MW capacity. 2 The total cost of heat pump
replacement for 29 million homes is interpolated to the number of homes (24.6 million) heated by
Green Gas Mills.

30

7

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34

35

Part Two

Domestic Heat Pumps in the UK – The
implications of a wholesale switch
to heat pumps and the potential forinterface with Green Gas
Independent analysis by NRS Griffiths

36

Domestic Heat Pumps in the UK – The implications of awholesale switch to heat pumps and the potential forinterface with Green Gas
Table of Contents
1

Introduction

38

2

The Cost Implications of a switch to Heat Pumps

39

2.1

Costs of heat pump installation

39

2.2

Costs of local grid upgrade

41

2.3

Costs of increased renewable energy production capacity

42

2.4

Total capital costs of heat pump installation

42

2.5

Other environmental costs

43

3

4

Constraints on heat pump deployment

43

3.1

Building typology

43

3.2

Impact of domestic hot water demand

44

3.3

Running costs & fuel poverty

44

Hybrid heat pump/boilers

45

4.1

Running cost effectiveness

45

4.2

Reduced capital costs

46

4.3

Reduced impact on the electricity grid

46

4.4

Interface with green gas

46

5Conclusions

47

6

Bibliography

48

37

Introduction
The UK Government’s Heat and Buildings Strategy (October 2021) rests on the Clean Growth Strategy(2017), the 2050 Net Zero commitment, and the Prime Minister’s Ten Point Plan for a Green Industrial
Revolution (2020).
The Heat and Buildings Strategy sets out a path for decarbonisation of heating, but there are significant
challenges along the way. This Strategy correctly recognises that demand reduction is needed as a firststep. Demand reduction ultimately reduces the need for new sources of low carbon energy production
to be built. All new construction has a carbon impact of its own - embodied carbon - as well as otherenvironmental impacts, so it is essential to minimise these impacts and not to rely on the single metric of“carbon emissions from buildings in use” during the decision-making process.
A further significant challenge is that the targets for demand reduction are framed in terms of a building’s
headline score on the Energy Performance Certificate (EPC). The problem is that the headline EPC score isan estimate of energy cost, not a measure of carbon emissions. Replacing gas central heating with a heatpump, for example, in order to reduce carbon emissions, will increase running costs for consumers and istherefore unlikely to improve the EPC score1. The Heat and Buildings Strategy includes a commitment torebalance the relative price of gas and electricity to address this issue, but serious concerns remain about
EPCs and hence their use as a policy tool2.
The Strategy sets out 5 policy areas to be developed during the next decade:•

Energy efficiency in buildings•

Heat pumps•

Hydrogen•Heat networks•

Bioenergy

The optimal path to net zero requires a mix of technologies and approaches - sustainability is the art of thepossible, making best use of what we have got. It is clear from the Heat and Buildings Strategy that there
is to be a heavy reliance on heat pumps as the optimal or only solution to the decarbonisation of heatingin many or most circumstances. For the purposes of comparison only, this brief analysis sets out the costs
and implications of a wholesale or partial switch to heat pumps as the primary source of space heating andhot water in domestic buildings.

38

2. The Capital Cost Implications of a switch to Heat Pumps
There are 3 elements to the capital cost of switching to heat pumps:•

cost of installation in each property;•

cost of upgrade to the local electricity distribution grid;•cost of increasing renewable electricity production.

2.1 The costs of installation
The cost of installing a heat pump of course varies according to the property - principally according to
the peak demand which the pump will be called upon to meet. The Heat and Buildings Strategy quotes
a cost of £7,000 - £14,000 for the cost of installing a domestic air source heat pump (ASHP), depending
on building size and fabric efficiency. Some buildings may of course be suitable for a ground source heatpump (GSHP), but the mass market is likely to be for ASHPs as there are constraints to GSHP installation inso many locations.
We cannot simply take an average of these figures and multiply by the number of dwellings in the UK to
derive an overall capital cost - for a number of reasons:a.

Some dwellings are already heated by heat pumps;b.

There are more smaller dwellings than larger ones, so the median cost will be lower than the
average;c.

The costs of installation may be expected to fall as market size increases;d.

Boilers need to be replaced on average every 15 years in any case, so the cost of the replacement
boiler should be deducted.

e.

In some cases, the switch from a gas boiler to a heat pump will require replacement of the heat
distribution system to allow for the lower temperatures which heat pumps require to operate
efficiently.

To examine each of these factors in detail:a) Market size
The current English domestic building stock is approximately 25.2m dwellings3, 1.4m in Wales4 and 2.6m in
Scotland5, making a total of 29.2m homes in the UK excluding Northern Ireland. In 2020 it was estimatedthat 200,000 heat pumps had been installed in UK homes. This leaves a net total of 29m homes where newheat pumps could in theory be deployed - in England, Scotland and Wales.
b) Costs of heat pumps
The cost of £7,000 - £14,000 for the cost of installing a domestic ASHP quoted in the Heat and Buildings
Strategy (P86) needs some interpretation. According to the BRE’s analysis of UK dwelling types, less than
20% of properties are detached, the majority being semi-detached, terraced, bungalows or flats. In otherwords, we can realistically conclude that average costs will be at the lower end of this cost spectrum.
Indeed, some small social housing units for example are heated by very small heat pumps which costconsiderably less than the lower estimate6. On this basis, it is safe to assume an average cost of £8,000 per
property, based on current prices.
These costs relate to air-water heat pumps - where water is the heat distribution system - as is the normin the UK with gas and oil boilers. Air distribution is of course common in non-domestic buildings as
a component of air conditioning systems, and used in housing in other countries, but rare at present
for dwellings in the UK. Costs for air-air heat pumps are lower but this would require a completely new
distribution system (air) to be installed. The additional cost of distribution would compensate for the lower
cost of the heat pump, so the total cost of a replacement air-air system is likely to be similar to an air-water
system using at least part of the existing distribution system.

39c) Savings from volume roll-out
The 2016 report7 “Potential Cost Reductions for Air Source Heat Pumps” derives a figure of 20% for
expected reductions if ASHPs are rolled out at mass scale. Similar reductions have been achieved in otherareas of technology in recent years, so we should therefore apply this reduction across the board to thetotal figures derived.
d) Natural replacement cycle
If a machine of any type is replaced before the end of its life - this creates a “wasted asset”. The impact ofwasted assets, and their embodied energy is completely missed in policy terms. If we replace boilers before
they have reached the end of their life, then we increase carbon emissions more than is necessary.
To minimise such wasted assets and their embodied carbon emissions, heat pumps should therefore be
introduced according to the “natural replacement cycle” of boilers, and not before. The exception to thismay be the introduction of hybrid heat pump/boilers - where an existing boiler can sometimes be retained- see the Section below on Hybrid Systems.
If the installed cost of a replacement gas boiler is taken on average to be £2,5008, this should be deductedfrom the cost of the air source heat pump installation - as a heating system will be required in any case.
In the UK, 87% of domestic properties are on the gas grid. Of the remaining 13%, we may assume thatthose on oil or coal would be replaced by a heat pump as this is demonstrably lower carbon. There would
be no point replacing biomass heating with electric heating until the grid is fully decarbonised, as biomass
would be both lower carbon and lower in running costs, but only a small percentage of domestic buildings
are currently heated by biomass. Oil boilers have a similar (or slightly higher) installed cost to gas boilers.
e) Heat distribution system replacement
Heat pumps work best with low temperature distribution systems. This is because they have to raise thetemperature of the heat by a lower amount, and can thus run more efficiently. It is perfectly possible to run
a heat pump with higher distribution temperatures but the efficiency level drops, so the carbon intensity
increases, as does running cost9.
Unless major thermal improvements are being made to the property at the same time as heat pumpinstallation, a lower temperature distribution system will be required. In most retrofit situations it isimpractical to fit underfloor distribution so in practice this means increasing emitter (radiator) sizes so thatthey can deliver the same comfort temperatures while using a lower temperature distribution system.
The cost of increasing radiator sizes of course depends on the size of the property, and not all properties
will require distribution system replacement, but it is realistic to add an average of £1,000 per property toallow for this.
Conclusions on heat pump roll-out costs
Taking into account the costs set out in (b) to (e) above, we can derive the following average cost perproperty for the switch to ASHPs:

Add

Subtract

Average cost of Domestic ASHP
Distribution system upgrade£8,000£1,000£9,000Replacement boiler cost

£2,500£6,500Volume discount20%£5,200Net Total

40

Total

£5,200Applying this average unit cost across the housing stock for England, Scotland and Wales, we can derive thefollowing costs:
No of dwellings

Total cost

25% of dwelling stock

7.25m

£38Bn

50% of dwelling stock

14.50m£75Bn

100% of dwelling stock

29m£151Bn

It is important to understand that the final figure in this table is purely notional as it would be impracticalto replace all heating systems with an ASHP. Firstly, there are lower carbon heating systems (biomass,
biogas, waste heat) already in use and their use should be expanded. Secondly, some properties will besuitable for a GSHP. Thirdly, there are constraints to the deployment of heat pumps, as many buildings are
not suitable for heat pumps, and cannot be made to be suitable in a cost-effective and environmentally
sustainable manner.

2.2

The costs of upgrade to the electricity distribution grid

The government recognises that a large scale switch to electric heating will require “significant additional
network capacity”, including a massive upgrade to the low voltage network which provides the connection
from local substations to dwellings.
No formal attempt has yet been made to quantify these costs, but the UK Government states that “Wehave been engaging with distribution network operators (DNOs) and the Energy Networks Association
to understand the potential scale of the need for local network reinforcement and preparations forelectrification of heat. For these reinforcements to be carried out effectively, we need to ensure that DNOs
can make strategic investments that reduce the need for network upgrades, investing ahead of need,
where possible and useful. DNOs were due to submit their final business plans to Ofgem in December
2021, setting out their proposed projects and actions for the 2023-2028 price control, RIIO-ED2.10”
These business plans clearly need to be analysed and summed. However, they do not contain the full
figures required because 100% electrification of heating has not been proposed and the DNOs are notallowed to include costs for speculative investment - they can only respond to proven levels of demand.
Furthermore, the demand will also be increased by the planned switch to electric vehicles, which will add
significantly to the requirements for electricity grid capacity. By contrast, smart grid management should
reduce overall costs somewhat.
100% heat pump deployment would require replacement of whole grid system components - including
provision of 3 phase power at local level - as many buildings have a larger heat demand than can be met
by a 240V heat pump. It is possible that (carefully selected) 25% heat pump deployment could impose
demands on the grid that can be met with only partial grid reinforcement, so it is conceivable that gridcosts for 100% deployment would be greater than they would be if scaled up from 25% (i.e. more than 4x
greater).
According to the Element Energy report “Cost analysis of future heat infrastructure options” (2018) the
worst case scenario (based on reduced heat pump efficiency and sub optimal consumer behaviour) is that
“This leads to total discounted distribution and transmission reinforcement costs of £62 bn.

41

2.3 The costs of increasing renewable electricity production
Electrification of heat will require a huge investment in renewable electricity production, in addition to theloads already to be imposed by decommissioning of fossil-fuel power plants, and the switch to electricvehicles.
The key to working out supply costs is an assessment of peak demand. Peak domestic demand for gas iscurrently 170GW, though according to other calculations referenced the peak demand may be more thandouble this11.
Based on a coefficient of performance (CoP) of 2.5 (which an ASHP is unlikely to achieve in mid winter), if
this peak demand were to be replaced by heat pumps, we would need 170GW/2.5 = 68GW of additional
electricity generating capacity. This ignores the potential impact of energy storage systems but as the CoP
in mid winter will be lower than 2.5 the peak demand on the grid is likely to be higher.
Note that solar cannot be used to provide this power for space heating - as it is not available when heat
demand is at its highest. In terms of low carbon electricity, we are therefore reliant on nuclear, wind power,hydro , geothermal or tidal power (if this is ever introduced, which it should be).
The installation cost of offshore wind power is recorded by BEIS at £1.3m per MW12 in 2030, excludingtransmission costs. This equates to £1.3Bn per GW.
On that basis, to add 68GW of further capacity would cost 68 x £1.3Bn = £88Bn, with no allowance fortransmission costs. Economies of scale may well bring this figure down, so we may crudely estimate afurther £88Bn in capacity costs for the supply of additional renewables capacity to provide complete
electrification of domestic heating via heat pumps.

2.4 Total capital costs of heat pump installation
Based on the analysis of individual heat pump costs set out above, it is necessary to add the costs ofincreasing renewables capacity to meet this additional demand.
At present, good data is not available, and there are other sectors of the economy (such as transport)
where a switch from fossil fuels to electricity is envisaged, so it is difficult to isolate costs. Nonetheless, it isessential to include an estimate, so that the cost is recognised - and this estimate can be refined as betterdata becomes available.
Based on housing stock for England, Scotland and Wales:
Heat Pump
installation
estimate

Grid upgrade
Estimate*

Renewables
capacity
estimate

Total costestimate before
grid upgrade

25% of dwelling stock

£38Bn

£11Bn

£22Bn

£71Bn

50% of dwelling stock

£75Bn

£22Bn

£44Bn

£141Bn100% of dwelling stock£151Bn

£44Bn

£88Bn

£283Bn* https://nic.org.uk/app/uploads/Element-Energy-and-E4techCost-analysis-of-future-heat-infrastructure-Final.pdf

As previously stressed these figures are purely notional as 100% switch to heat pumps is not proposed.
These figures suggest that the cost of heat pump deployment could be doubled by the costs of grid
upgrade and the costs of providing additional renewable electricity generation capacity to meet theincreased demand.

42

2.5 Other environmental costs
Ultimately, sustainability is about the kind of tomorrow we want to leave to the next generation. This is the
key message of the famous Brundtland definition of 1987 that sustainable development is:“development which meets the needs of current generations without compromising the ability of future
generations to meet their own needs.”
We therefore need to think carefully about the implications of our different options and carry out a muchfuller cost-benefit analysis before making decisions about the future of heating and electricity supply in theUK.
There is a tendency to measure carbon emissions solely at the point of use. This serves an industrial
agenda as it tends to promote the maximum amount of change - i.e. switch from A to B and the emissions
will fall. This ignores the carbon cost of making the change - the embodied carbon. When considering awholesale switch to renewable energy this impact will be very significant indeed, and it will take some time
simply to pay back the carbon cost of making the change. In other words, decarbonisation of heating will
actually increase carbon emissions in the short term, so we need to be careful how this is done.
Capital costs are not the only costs. Resource scarcity is an issue and all change has an impact. If we aredeveloping vast new capacity of low carbon generation plant, be it nuclear, tidal or wind power, this all
consumes resources and certain resources are constrained - especially metals. Land use is a further costwhich does not easily translate into financial values despite the efforts of economists.
Decarbonisation is also not the only environmental priority. Many people have been reminded through the
pandemic that we value both our natural and built heritage, and time spent outdoors is vital for mental
and physical health. New sources of low carbon energy have an impact on our landscape, and this has tobe weighed against the decarbonisation aim. Regeneration should deliver not only a low carbon future, but
one where communities thrive, employment is available, heritage is enhanced, flood risk is reduced, andwhere we re-green and protect our natural environment

3. Constraints on heat pump deployment
3.1 Building typology
Heat pumps work best in well insulated and airtight buildings but many existing buildings cannot be
retrofitted to modern thermal standards. There are many details on buildings which make insulation very
difficult at reveals and junctions between walls/floors and roof structures, meaning that heat will continue
to escape at these points - via unavoidable thermal bridging. Added to this, the way that some buildings
are constructed makes it very hard to prevent air leakage, so they will continue to have a high heat demand- you can’t retrofit an air tightness membrane, it needs to be built in from the word go.
Low temperature distribution systems such as underfloor heating cannot be installed in many buildings
because there is no insulation in the floor slab and the floor level cannot be raised, or because not allsuspended floors can take the required insulation and pipework. In such buildings, all other things being
equal (i.e. heat demand not reduced), the radiator sizes will have to be increased, taking up more internal
wall space, but delivery temperatures will also be higher than when underfloor heat distribution is used,making heat pumps run less efficiently. At least 20% of the UK’s dwellings are of traditional construction13 i.e. solid walled, and these are not ideally suited to the low temperatures delivered by heat pumps.
There comes a point where the impact of the insulation and airtightness work to reduce space heat
demand (i.e. the embodied energy & emissions) becomes so great that in carbon (and cost) terms it is43better to insulate up to a certain point only, and accept that some buildings will always have a significant
residual heat demand. Only when the electricity grid is fully decarbonised and gas is no longer in use to
make electricity would it make sense to switch these buildings to a heat pump. This is explored further inthe section on hybrid heat pumps.
Approximately 20% of UK dwellings are flats (there is some limited crossover with the 20% traditional
construction mentioned above, but most flats were constructed after 1919). Many would not be suitablefor individual heat pump installations because it would not be possible to install ASHPs on the exteriorof these buildings at height. However, flats can be heated by a communal heat pump - with the heatbeing piped through the building. Many large office blocks and other non-domestic buildings are alreadyheated by heat pumps, so this is not necessarily a barrier. Heat can be metered just as easily as gas andelectricity, so individual dwellings can still be responsible for their actual heat use. This would require a
new distribution network to be installed within each block, which is not impossible, but could be costly. In
some blocks of flats, there may not be sufficient space to install the ASHP even at ground level. Planningbarriers might also apply.

3.2 Impact of domestic hot water demand
As fabric insulation standards improve and space heating demand falls, hot water for washing and bathing
becomes a much more significant proportion of domestic energy use. We also take more showers than we
did 50 years ago.
Domestic hot water is delivered at around 50ºC (and raised to 60ºC for periodic sterilization), much higher
than the ideal space heating distribution temperatures when a heat pump is in use (30-40ºC). A heat pumpis therefore less efficient at delivering domestic hot water than space heating as it has to do more work toraise the temperature of the delivery medium to a higher level.
The net effect is that the heat pump will be running at lower efficiencies for a greater percentage of its
operation time. This increases both the carbon emissions and the cost of running the heat pump. Whenconsidering the costs of running heat pumps, the percentage of hot water load as opposed to spaceheating therefore needs to be taken into account.

3.3 Running costs & fuel poverty
As things stand, changing from a gas boiler to a heat pump won’t save consumers any money. In fact, it willalmost certainly increase bills. Given the recent doubling of fuel prices across the UK, the percentage ofhouseholds in fuel poverty is climbing rapidly so this is a serious concern.
The ratio of the kW of heat energy produced by the system to the kW of electrical energy needed to power
the pump is known as the “Coefficient of Performance” (CoP). If the system runs at a CoP of 3, this meansthat it produces 3 units of heat energy for each unit of electricity input. When summed over an entire
heating season, the ratio of total energy input to total heat output is known as the Seasonal Performance
Factor or SPF.
Good quality independently verified data on heat pump performance is scarce. The heat pump trials fromthe Energy Saving Trust (already a decade old) put the SPF at around 2.5 for ASHPs14 . A very limited studyof installations under the Renewable Heat Premium Payment scheme15 put the figure slightly higher, but
the sample size was small. SPFs quoted by manufacturers are usually much higher than what is achievedin practice - it is the actual performance of the whole system over a year which matters. Good quality
metered data for electricity input and heat output has been collected under the Non-Domestic Renewable
Heat Incentive from 2016 onwards, but for some reason this data has not been analysed and published.
The Electrification of Heat Demonstration Project is ongoing and this should provide some more robust
data soon.
At the time of writing, the capped prices are 28.34p/kWh for electricity and 7.37p/kWh for gas - and these
are the rates that most domestic customers are paying. Electricity is therefore roughly 4 x the price of gas
per kWh.
44

Based on an SPF of 2.5, over a year you might get an average of 2.5 units of heat for each unit of electricity
used by an ASHP. If electricity is 4 x the price of gas, then by simply switching from a gas boiler to an ASHP,
and allowing for - say - 90% efficiency of gas boilers, you would currently increase your bill for heating
space and water by 4/2.5 x 0.9, which is a 44% increase.
Switching to a heat pump on top of a doubling of energy prices will add a significant further cost to space
and water heating, which is clearly unsustainable, and will increase fuel poverty yet further.
The demand for space heating can be reduced by insulation measures, but these have already been
installed in many properties - double glazing, loft insulation and cavity wall insulation all have very highpercentage penetration across the UK. There is a limit to what can be achieved by further measures insulation suffers from the law of diminishing returns - a little insulation goes a long way and it takes a lot
more insulation to do only a little more work. None of this will affect demand for domestic hot water.
Even for hybrid heat pump/boilers, the savings are not obvious. The Freedom Project (2018) which tested
out hybrids in Bridgend, South Wales16, concluded that “it is rarely cost-effective to operate the heat pump;and even in the scenario that gas prices increase by 50%, it is only worthwhile for the heat pump to take
40–50% of the heat load.”

4. Hybrid heat pump/boilers
ASHPs perform less efficiently when the temperature of the heat source (i.e. the external air) is low.
Unfortunately this coincides with the time of peak demand for space heating - i.e. in mid winter. This has
led to growing interest in hybrid heat pumps.
In simplest terms, hybrids include a backup boiler (gas, LPG or oil) which takes over when the airtemperature is low - the system controller automatically selects which is the most efficient mode to use. In
this case, the ASHP component would be used mostly during the “shoulder months” of the heating season i.e. at either end of winter when the air temperature is warmer, and the backup boiler would be used in thecoldest periods.
The hybrid approach has numerous advantages:•

ASHPs can be sized smaller, reducing installation costs;•

Existing boilers can be retained - avoiding a wasted asset;•

Energy security is improved, as a backup is in place (since the main current sources of renewableelectricity are notoriously intermittent);•

Running costs can be slightly lower;•

Peak demand on the electricity grid is far lower - resulting in:»less cost to upgrade the distribution network;»

less cost of installing new renewable generation plant.

We already have a very effective gas distribution network in place to 87% of the UK’s homes, so it makes
practical and economic sense to make use of this at least while we progress towards decarbonisation ofboth the electricity and gas grids.

4.1 Running cost effectivenessAs an ASHP is less effective in mid winter, it follows that it is more effective when the air temperatures arewarmer, and the COP should be well above 2.5. If used correctly as part of a hybrid system, an ASHP candeliver not only carbon savings but also cost savings on space heating, when it’s not too cold outside. At
current prices, and ignoring time of use pricing, an ASHP would deliver a saving when the COP is above 4.

45

During the coldest months, the backup boiler takes over and the consumer is at least no worse off thanthey are already. Over the course of a whole heating season the hybrid therefore produces a small net
saving.
Hybrid systems can be used in a much more sophisticated way if the controller is linked to variable timeof-use pricing, enabling the householder to make best use of low priced electricity when available, andsimultaneously benefiting the grid by load spreading. This is explored in much more detail in the Freedom
Project17 which concluded in 2018.

4.2 Reduced capital costs of installation
In a hybrid system, the heat pump does not have to provide the full peak space heating demand. Thismeans that the heat pump can be sized smaller - to meet demand at lower levels and when the airtemperature is warmer - so that it can run more efficiently. A smaller heat pump is going to cost less than alarge heat pump, so the capital cost of installing the heat pump side of the hybrid system can be reduced.
Some hybrid heat pump/boilers are sold as a package, but others can make use of the existing gas (or oil,
LPG) boiler as the backup system. This means that relatively new boilers, which have not reached the endof their working life, can continue to be used. This of course significantly reduces the capital cost of thehybrid system, as only a heat pump and a new controller need to be installed.

4.3 Reduced impact on the electricity grid and generation costs
By reducing peak demand on the electricity grid, smart optimised hybrid systems (as trialled under theFreedom Project) will substantially reduce the costs of electricity grid upgrade. If peak demand is not sohigh, the local and national transmission networks will require less investment to reinforce them, and there
will be greater capacity for electrification of vehicles - if managed correctly.
Although the cost of energy storage is falling rapidly, electricity storage still adds cost, and batteries haveother environmental impacts; they also lie idle much of the time. The gas grid already has capacity to store
significant quantities of gas by means of “linepack” - i.e. increasing the pressure within the distribution
network - as already occurs. This means that the gas grid can more easily take care of sudden surges
in demand, while predicted peaks can be reduced in any case by smart use of heat pumps to pre-heatdwellings.
Lastly, a reduction in peak electricity demand reduces the total generation capacity that will be required, so
substantially reduces the capital cost of providing renewable power. As it is accepted that renewables areintermittent and backup systems will need to remain in place, it makes not only economic sense but also
environmental sense to plan for a lower total generation capacity - as all new generation capacity has anenvironmental impact of its own.

4.4 Interface with green gas
The backup boiler element to hybrid heat pumps currently uses fossil fuels, in most cases.
For installations off the gas grid, the most common backup boiler will be oil or LPG. However, oil can now
be replaced with biodiesel, and LPG with bioLPG, so there is no reason why a hybrid heat pump/boiler
should have any carbon emissions other than the electricity component still produced using fossil fuels.
For on-gas-grid installations (87% of the dwelling stock), the situation is evolving. There are increasing
sources of hydrogen and biogas which can be injected into the gas grid, thus decarbonising the gas grid toa degree.

46

The Pathfinder project18 is a full system analysis tool developed by Wales & West Utilities and this kind oftool holds the key to predicting demand and optimising the grid to deliver lowest cost and carbon, evolving
over time. This simulation clearly concludes that the gas network is essential to delivering a low carbon
energy network at reasonable cost, based on smart use of hybrid boiler/heat pumps. As new sources ofbiomethane or other low carbon biogas become available, the gas grid can decarbonise further, providing
the balance to a decarbonising electricity grid.

5. Conclusions
Full electrification of domestic heating and delivery via heat pumps makes no sense in environmental,
economic or social terms - the three original pillars of sustainability. The capital cost is likely to exceed£300Bn even before provision for grid upgrade costs, and consumers will face significantly higher runningcosts - a burden that cannot be acceptable given current high levels of fuel poverty. There will be verysignificant embodied carbon costs of grid reinforcement and of providing the required new supplies ofrenewable power.
By contrast, partial electrification of heating and the intelligent deployment of hybrid heat pump/boilers
can deliver better levels of energy security, lower running costs, and greatly reduced infrastructure costs.
This also allows change to happen gradually and be better managed, prevents wasted assets and makes
best use of the existing gas grid, which is also able to decarbonise. At reduced demand for gas, theproportion of gas coming from renewable and low carbon sources will be even higher, offering a costeffective route towards decarbonisation over a realistic timescale.
Straight heat pumps will work effectively in new buildings which are airtight and highly insulated, so have
low space heating demand. There should be minimal concerns over fuel poverty for occupants of suchbuildings - even if the unit cost of heat is high, consumption will be very low. For existing buildings which
are not so well insulated, hybrids are the optimal solution in many cases, and at the very least an importantinterim step on the path to full decarbonisation.

47

6

Bibliography

1. EPCs and the Whole Building Approach to Retrofit (STBA 2018) https://stbauk.org/stba-research/
2. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/
file/987564/Dwelling_Stock_Estimates_31_March_2020_Release.pdf (with 2 years added)
3. https://gov.wales/dwelling-stock-estimates-31-march-2020
4. https://www.gov.scot/publications/housing-statistics-stock-by-tenure/
5. https://www.boilerguide.co.uk/articles/boiler-replacement
6.

UK Govt Heat & Buildings Strategy 2021 https://www.gov.uk/government/publications/heat-and-buildings-strategy

7. “Decarbonising domestic heating: What is the peak GB demand?” - S.D.Watson, K.J.Lomas, R.A.Buswell
Published in Energy Policy Vol 126 March 2019 – https://www.sciencedirect.com/science/article/pii/
S0301421518307249
8. https://www.briefingsforbritain.co.uk/the-costs-offshore-wind-power-blindness-and-insight/#_ftn1
quoting https://www.gov.uk/government/publications/beis-electricity-generation-costs-2020
9. https://www.wwutilities.co.uk/media/3860/freedom-project-final-report.pdf
10. UK Govt Heat & Buildings Strategy 2021 https://www.gov.uk/government/publications/heat-and-buildings-strategy
11. Decarbonising domestic heating: What is the peak GB demand?” - S.D.Watson, K.J.Lomas, R.A.Buswell
Published in Energy Policy Vol 126 March 201912. https://www.briefingsforbritain.co.uk/the-costs-offshore-wind-power-blindness-and-insight/#_ftn1
quoting https://www.gov.uk/government/publications/beis-electricity-generation-costs-2020
13. https://files.bregroup.com/bretrust/The-Housing-Stock-of-the-United-Kingdom_Report_BRE-Trust.pdf
14. https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/
file/48327/5045-heat-pump-field-trials.pdf
15. https://www.gov.uk/government/publications/detailed-analysis-of-data-from-heat-pumps-installed-viathe-renewable-heat-premium-payment-scheme-rhpp
16. https://www.wwutilities.co.uk/media/3860/freedom-project-final-report.pdf
17. https://www.wwutilities.co.uk/media/3860/freedom-project-final-report.pdf
18. https://www.wwutilities.co.uk/about-us/our-company/future-of-energy/

48Appendix for Green Gas – The opportunity for Britain
Appendix item A1 - UK Land Cover details

49Appendix item A2 – OS Terrain 50 – Slope17

50

Appendix item A3 – Surface slope (12 degree threshold)1751

Appendix item A4 – The UK Land Cover details14 in million hectares wereobtained from QGIS raster data
Great Britain

IrelandUK

Deciduous woodland

1.79

0.10

1.88

Coniferous woodland

1.32

0.06

1.38

Arable

5.25

0.13

5.38

Improved grassland

6.47

0.62

7.10

Neutral grassland

0.14

0.13

0.27

Calcareous grassland

0.13

0.00

0.13

Acid grassland

2.16

0.05

2.21

Fen

0.02

0.00

0.02

Heather

1.00

0.02

1.03

Heather grassland

1.26

0.08

1.35

Bog

0.89

0.09

0.97

Inland rock

0.23

0.01

0.25

Saltwater

0.20

0.02

0.22

Freshwater

0.25

0.06

0.31

Supralittoral rock

0.06

0.00

0.06

Supralittoral sediment

0.08

0.01

0.09

Littoral rock

0.06

0.00

0.06

Littoral sediment

0.24

0.01

0.25

Saltmarsh

0.12

0.00

0.12

Urban

0.40

0.01

0.41

Suburban

1.44

0.05

1.49

Appendix item A5 – Mimimum, maximum and average methane yields ofvarious types of grass, legumes and herbs consisting of herbal leys mixture,in m3 CH4 kg-1 VS

52

Type

Min

Max

Average

References

Chicory

Herb

0.245

0.326

0.336

Wahid et al26

CloverLegume

0.140

0.558

0.298

Zhang et al 85

Cocksfoot

Grass

0.291

0.446

0.369

Tilvikiene et al86

Cow parsley

Herb

0.135

0.412

0.274

Kosse et al87

Fescue

Grass

0.259

0.446

0.354

Zhang et al 85

Festulolium

Grass

0.381

0.464

0.423

Kandel et al25

Grass lay

Grass

0.250

0.307

0.279

Lfl88

LucerneLegume

0.265

0.432

0.349

Kaiser et al89

Meadow foxtail

Grass

0.310

Mähnert et al90

Meadow grass

Grass

0.290

0.322

0.320

Zhang et al 85

Pasture grass

Grass

0.307

0.322

0.315

Lfl88

Red clover

Legume

0.236

0.344

0.290

Zhang et al 85

Ribwort plantain,
ribgrass

Herb

0.273

0.296

0.285

Wahid et al26

Ryegrass

Grass

0.390

0.409

0.400

Zhang et al 85

Sainfoin

Legume

0.267

0.292

0.280

Lfl88

Tall fescue

Grass

0.401

0.428

0.415

Kandel et al25

Timothy

Grass

0.308

0.365

0.337

Zhang et al 85

White sweet clover

Legume

0.162

0.183

0.173

Huňady et al91

Herb

0.265

0.290

0.278

Kosse et al87

Yarrow

Appendix item A6 – According to the Cotswoldseed, the methane yield of
typical herbal ley mix to be utilised in Green Gas Mill, in m3 CH4 kg-1 VS.
Type

Percentage in the mixture, %

Min

Max

Average

Festulolium

20.8

0.079

0.097

0.088

Ryegrass

40.3

0.157

0.165

0.161

Cocksfoot

8.3

0.024

0.037

0.031

Timothy

12.5

0.039

0.046

0.042

Fescue

6.7

0.017

0.030

0.024

White clover

4.2

0.007

0.008

0.007

Red clover

2.1

0.005

0.007

0.006

Alsike clover

1.3

0.002

0.007

0.004

Chicory

2.5

0.006

0.008

0.008

Ribgrass

1.3

0.004

0.004

0.004

Total

100

0.340

0.408

0.375

Herbal ley yield is reported to be 13 tonne dry matter per hectare (0-20 t DM ha-1) and chicory yield is reported to be 10 t DM ha-1. The percentage values in the herbal ley mixture (Cotswold mix23- Simple Herbal
ley45) are multiplied by the minimum, maximum, and average values given in Table A5.

Appendix item A7 – Details of Table 2 calculations
The average biomethane potential was calculated as shown below. The same calculation was performed
for the maximum and minimum biomethane potentials, taking into account the maximum and minimum
values in Table 2.
Available grassland: 6.46 x106 hectares
Herbal ley yield: 13 tonne dry solids per hectare
Annual feedstock become 83.98 x106 dry solids ( 6.46 x106 × 13 = 83.98 x106)
Volatile dry soils yield is assumed as 0.9 in total dry solids. The total volatile dry solids become: 83.98 x106 ×
0.9 = 75.58 x106 volatile dry solids
The average methane yield for herbal ley species is 375 m3 CH4 in volatile dry solids.
Therefore, methane production from 75.58 x106 volatile dry solids become 28.3 billion m3 methane (75.58
x106 VS × 375 m3 CH4 VS-1 = 28.34 x109 m3 CH4).
Methane in biogas is assumed as 60%; therefore, biogas amount will be 47.24 billion m3 (28.34 x109 m3

53

CH4 ÷ 0.6 m3 CH4 biogas-1= 47.23 x109 m3 biogas)
During the biogas upgrading process to biomethane, it is assumed that 0.5% of produced gas is lost. Therefore, the biomethane amount become 27.49 billion m3.
(28.34 x109 m3× 0.005 = 27.49 x109 m3 CH4 )Biomethane energy yield:
27.49 x109 m3 × 37.78 MJ m-3 (CH4 energy content) × 0.00027778 MWh MJ-1 × 10-6 TWh MWh-1 = 288.5 TWh
288.5 x103 GWh ÷ (6.46 x106 hectares) ÷ 0.0002778 GJ GWh-1 = 160.8 GJ / ha54

Appendix 2 – Biographies
Dr Gbemi Oluleye
Dr Oluleye is an Assistant Professor (Lecturer) in the Centre for Environmental Policy and a member of
the Sargent Centre for Process Systems Engineering with over 15 years combined experience in academia
and as a consultant for the process industry, and innovations to support decarbonisation. She has a BSc
in Chemical Engineering from the Obafemi Awolowo University, Nigeria in 2008, completed an MSc in
Advanced Chemical Process Design at the University of Manchester in 2010, worked as a Process Engineer
before beginning her PhD in 2012. Dr Oluleye research is centred on developing frameworks to supportmodelling, integration, assessment (both economic and environmental) and adoption of low-to-zerocarbon innovations including alternative fuels and technologies.
Dr Oluleye is working with Ecotricity on an independent basis capacity via Imperial Consultants.

Dr Semra Bakkaloglu
Dr Semra Bakkaloglu is a Research Associate at the Sustainable Gas Institute with over 10 years ofcombined academic, industry and consultancy experience. Dr Semra double majored in Environmental
Engineering and Chemical Engineering at Middle East Technical University (METU) in 2011 and 2012,
respectively. She attended Clemson University as a Fulbright Scholar, where she earned a master’s degree
in Environmental Engineering & Earth Science in 2014. She completed her PhD at Royal Holloway Universityof London as a Marie Curie Early-Stage Researcher. Dr Bakkaloglu’s research focuses on environmental
process engineering, life cycle assessments, and modelling of biomethane production, as well as methaneand hydrogen emissions from its supply chains.
Dr Bakkaloglu is working with Ecotricity on an independent basis capacity via Imperial Consultants.

Nigel Griffiths
Nigel Griffiths is a sustainability and energy efficiency expert in the built environment with over 25 years’
experience as a practitioner, project manager, author and consultant. As Director of the Sustainable
Traditional Buildings Alliance, he works at the cutting edge of sustainability for heritage buildings. As
a Principal Consultant with Ricardo, he provided practical energy efficiency, renewable energy andsustainability strategies for numerous buildings and large property portfolios. He has also worked
extensively on policy development in this sector in the UK and overseas. He continues to inspect
Renewable Heat installations on behalf of Ofgem, and is a lead technical expert to BEIS on the Social
Housing Decarbonisation Fund. He is the author of several books including the Haynes Eco House Manual,
writes for the Build-it monthly self-build magazine and is the resident sustainability expert at their UK
exhibitions.

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We only print on recycled paper.

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