When the UK ran for a full day without relying on coal-fired fossil fuel generation, as happened last April, it was a milestone moment. After all, burning coal primarily powered Britain through the industrial revolution and much of the 20th Century. Although today, carbon targets and other environmental issues dictate the use of alternative fuel sources.
TABLE OF CONTENTS
- – How Green is the UK’s Fuel Mix?
- – Decarbonising Electricity
- – What About Decarbonising Heat?
- THE STRATEGIC ROLE OF GAS
- – Cleaner Than Coal, Less Dirty Than Oil
- – The Strategic Role of Gas
- FUTURE ENERGY SCENARIOS FOR GAS
- – 1: A High Electrification Scenario
- – 2: Two Degrees future energy
- – 3: Decarbonised Gas
- DECARBONISING HEAT CHALLENGES
- – The Role of Renewable Gas Sources
- – First Steps for Decarbonising Heat
- CURRENT GAS HEATING APPROACH
- – Biogas and Biomethane
- – Biomethane Production Advances
- HEATING INNOVATIONS
- – District Heating
- – Hybrid Heating
- – Predictive Demand Control
- LONGER-TERM OPTIONS
- – Heat Pumps
- – Low-Carbon Hydrogen
- PILOTS AND FEASIBILITY STUDIES
- – Natural Gas to Hydrogen
- – Hydrogen and Natural Gas Blend
How Green is the UK’s Fuel Mix?
During the 24-hour coal-free period on 21 April 2017, electricity came mainly from solar power although the onshore and offshore wind farms also played their part.
Coal-free periods are expected to occur with more frequency before the UK shuts its last coal plant in 2025, as the prevalence of renewable energy sources in the overall mix grows.
Few would argue that progress so far in decarbonising our electricity generation mix has been a significant achievement over recent years.
But deep and extensive decarbonisation of our economy entails using available energy more efficiently and moving away from hydrocarbon fuels, not only for transport but heating too.
What About Decarbonising Heat?
Decarbonising heat has not become part of the public discourse in the way that decarbonising transport has.
Heating and hot water for UK buildings make up around 40% of our energy consumption and 20% of our greenhouse gas emissions (GHGs), according to the statutory advisor, the Committee on Climate Change (CCC).
Nearly 30% of the UK’s energy comes from renewable sources with wind turbines generating 14.8%.
A recent report by the National Grid (pdf) points out that policy clarity on how the decarbonising of heat will have to emerge by the early 2020s if the UK is to meet its 2050 carbon target to reduce emissions by at least 80% from 1990 levels (Climate Change Act 2008). The document reiterates similar statements made in an earlier report by the CCC, published in 2016.
The Strategic Role of Gas
From a whole energy system perspective that considers electricity, heating, transport and industrial activity, the role of gas is fundamental, so to replace its use with the mass electrification of heating and transportation would likely come at a huge cost and also disruption.
- According to the Department for Business, Energy and Industrial Strategy (BEIS), the UK generated 42% of its electricity from gas in 2016.
- Eight out of 10 homes use natural gas for heating.
UK Electricity Generation Sources
|1. Coal (M Tonnes)||49.84||38.22||29.31||12.04||8.70|
|2. Oil (M Tonnes)||0.19||0.17||0.17||0.19||0.14|
|3. Gas (TWh)||175.21||189.92||185.95||271.56||257.60|
Source of UK electricity production 2016
The use of gas may become more prevalent in transport as it decarbonises, especially when we are talking public transport, like buses, or haulage and shipping.
Gas is also used by industry, either for heat or as part of production processes, for manufacturing ceramics and fertilisers, for example.
Cleaner Than Coal, Less Dirty Than Oil
Conversely, efforts to eradicate the more carbon-intensive fossil fuels – oil as well as coal – to reduce emissions, have led to more burning of natural gas, seen as a ‘bridging fuel’ on route to fully decarbonised economies.
Oil and gas companies are investing heavily in new gas extraction and production facilities to meet rising demand gas. Government policies focused on decarbonisation emphasise renewables, nuclear and natural gas. That doesn’t make it a ‘green gas’ though.
A report published in late 2017 found that governments have underestimated methane emissions from natural gas. According to the report, by the Tyndall Centre for Climate Change Research, it is "no longer viable to mitigate emissions at a global level" to limit a temperature increase to 1.5°C, and that an "urgent programme to phase out existing natural gas and other fossil fuel use across the EU" is needed to deliver on the Paris Agreement, as reported by The Chemical Engineer.
The Strategic Role of Gas
In March 2018 the National Grid published a report, titled The Future of Gas: How gas can support a low carbon future. The report concludes gas will play a crucial role in the future, but that clear policies from the government for decarbonising gas are urgently needed.
The document points out that decisions on how to decarbonise gas must consider all impacts that it could have on end consumers, in terms of cost, practicality, disruption and acceptability. Whatever approaches taken, consumers need access to secure and affordable energy for heat, power, transport and industry.
On the other hand, the energy infrastructure needs to be adapted and modified to connect new sources, including renewables, hydrogen, and biogases. It is an undertaking that will require more coordination across the different energy forms, such as gas and electricity, which some projects, discussed later in this article are doing.
Future Energy Scenarios for Gas
The report models three future energy scenarios, compared with today’s in terms of gas and electricity demand.
1: A High Electrification Scenario
The first option, where both heat and transport predominantly use electricity in future, would be a challenging undertaking and would need a high degree of policy intervention from the government. In this scenario, gas demand would reduce from 880TWh today to 200TWh in 2050. By then the UK’s electricity demand would be around 500TWh, up from just over 300TWh today.
2: Two Degrees future energy
In the Two Degrees future energy scenario, the 2050 carbon reduction target is met through a cost optimal approach across electricity, transport and heating.
Carbon Capture and Storage (CCS) enabled generation gets deployed along with nuclear and renewable technologies.
There is electrification of heat, although supported by more green gas, reducing the total requirements for electrification in order to hit the 2050 target. In 2050, gas demand and electricity will each be around 400TWh.
3: Decarbonised Gas
In the third future energy scenario, Decarbonised Gas, gas demand will increase to 1100TWh a year by 2050 while electricity demand would be a little lower than it is today.
The Challenges of Decarbonising Heat
The National Grid says heat is the most challenging energy sector to decarbonise because of the amount of energy required to do so, but also the direct impact on the end consumer in terms of change, infrastructure and cost.
As 80% of the UK’s 26 million homes use gas for heat, if decarbonisation of heat is to be successful by electrification, around 20,000 homes per week from 2025 to 2050 will need to move to a low carbon heat source. There is the risk that replacing gas will put more people in fuel poverty.
Therefore, a combination of solutions to decarbonising heat may emerge, including decarbonised gases, like hydrogen and biogases, alongside electric heat pumps, combined heat and power (CHP) and district heat networks, as well as energy efficiency measures.
The Role of Renewable Gas Sources
A report, titled Review of Bioenergy Potential (pdf), published in mid-2017 by Cadent, which operates the UK’s largest gas distribution network, estimates that by 2050 renewable gas, made from domestic and agricultural waste, energy crops, food waste and sewage, could produce up to 183TWh of biomethane a year, enough to heat up to 15 million homes.
According to KPMG the cost of decarbonisation via conversion to decarbonised gas, including hydrogen, costs around a third of the cost of full electrification, largely due to the gas grid’s ability to manage inter-seasonal demand fluctuations.
As acknowledged by BEIS in its Clean Growth Strategy, work is needed in this Parliament to set up decisions in the first half of the 2020s about the long-term future of heat. Along with its stakeholders, the National Grid agrees that "active experimentation is needed today to demonstrate and de-risk pathways to inform and deliver clear policy decisions in the early 2020s."
First Steps for Decarbonising Heat
According to the CCC report, Next Steps for UK Heat Policy (2016), decarbonising heating to meet 2050 targets could occur in a phased approach. Between now and 2030, the following measures need action:
- New buildings should be highly energy efficient and designed to accommodate low-carbon heating from the start.
- Energy efficiency improvements to existing buildings, such as installing insulation or a new boiler, should commence immediately.
- Low-carbon heat networks such as district heating schemes require a certain density of heat demand in order to be economical, which means that they are suited to urban areas, new-build developments and some rural areas. Low-carbon heat sources can include waste heat, large-scale heat pumps, geothermal heat and potentially hydrogen.
- Heat pumps in buildings not connected to the gas grid – heat pumps have faced challenges to date, but remain the leading low-carbon option for buildings not connected to the gas grid.
Biomethane injected into the gas grid is a means of decarbonising supply without requiring changes from consumers, and provides a route for capture and use of methane emissions from biodegradable wastes. However, its potential is limited to around 5% of gas consumption, according to the CCC report.
The Current Gas Heating Approach
The two types of gas available for use in the National Grid are natural or renewable as follows:
- Natural gas which is distributed via the gas grid to heat homes and premises is high purity, with a methane content of at least 95%.
- Biogas gets produced from organic matter, including crops and some waste, is purified, or scrubbed, to get rid of traces of other gases to produce biomethane, which can then inject into the gas grid.
Biogas and Biomethane
Biomethane that supplies the gas grid is more energy efficient than using the gas to generate electricity. Around 90% of energy gets retained through grid injection, but only 65-70% when combusted to generate electricity.
Green energy retailers, including Good Energy and Ecotricity, have been sourcing a percentage of their gas supplies from biomethane sources, usually, small-scale anaerobic digestion (AD) plants that use agricultural waste and manure as feedstocks.
Ecotricity states that 12% of the gas it supplies is biogas sourced. The company will increase this amount by building what it calls green gas mills with the first one built in Hampshire.
The green gas, or biomethane, is made in an Anaerobic Digestion (AD) plant using grass, or rye in some cases, as the feedstock. A byproduct is a natural fertiliser on the side. The grass will come from sustainable sources, such as break crops on arable rotation or old grazing land.
Biomethane Production Advances
Advances in technology mean that a wider array of organic matter could be used as feedstocks to produce biomethane in future. Advanced Plasma Power has developed Gasplasma.
As the name suggests, the technology combines proven, established gasification and plasma treatment to convert waste and the outputs from any waste gasification process into a hydrogen-rich synthesis gas (syngas).
The syngas can be used to generate electricity directly in gas engines, turbines or fuel cells and it can also get converted into substitute natural gas, hydrogen or liquid fuels. The process also makes an inert byproduct for use in construction.
A £25 million commercial plant is under construction in Swindon that will make bio-substitute natural gas (BioSNG) using APP’s technology. The plant is expected to become operational in 2018.
If the technology can demonstrate scalability, it could mean that in the future waste can contribute up to a third of feedstock for biomethane with the rest coming from energy crops and agricultural residues.
If the UK is to decarbonise heating, then a mix of approaches will be needed.
One contender, for new buildings in densely populated urban areas, is district heating, which is not a new approach but is ripe for innovation to decarbonise these networks, especially when biogas gets used as a fuel source.
Scandinavia is at the forefront of district heating advances since district heating networks are more widely available in these countries, compared with the UK. In Finland, district heating using Finnish biogas made from waste is in production in Helsinki, aimed at business customers as well as apartment buildings.
In Wales, a project between Western Power Distribution and Wales & West Power Utilities is showing a hybrid heating approach, where cheap off-peak electricity can be used for heating in homes, switching to gas during peak times. UK firm PassivSystems is providing the software controls to switch between the two.
The project shows that carbon emissions reductions in excess of 87% from domestic heat are possible and at low investment, with no electricity grid upgrades, or expensive heat pump installations. Instead, a small, low-cost heat pump to provide the background heat, topped up by the gas boiler, which gets supplied with a blend of biogases, hydrogen and, at peak times, natural gas. By using the existing assets deployed there needs little additional investment to expand the scheme.
Predictive Demand Control
PassivSystems developed its Predictive Demand Control (PDC) technology over the last few years. The system learns the detailed thermal response of a property and builds a physics model of the house and heating system.
Demand is entirely automatically shifted to take advantage of the lowest prices while fitting within demand constraints and ensuring it meets the comfort requirements of the occupants.
Longer term main options for the decarbonisation of buildings on the gas grid in the 2030s and 2040s include heat pumps and low-carbon hydrogen.
According to the CCC report, heat pump deployment could be extended from applications off the gas grid to buildings on the grid. Alternatively, in some regions replacement of natural gas with low-carbon hydrogen may be preferable.
However, the report acknowledges that heat pumps remain a niche option in the UK as previous policies have failed to deliver a significant increase in uptake. It also acknowledges that installations are often disruptive and heat pumps operate in different ways to gas and oil boilers, though once installed customer satisfaction is high.
And while low-carbon options to provide electricity for heat pumps are available, widespread deployment would bring significant challenges for meeting peak demand in winter. In addition, improved building efficiency is an essential part of effective heat pump roll-out, according to the report.
That leaves hydrogen.
Hydrogen is likely to be a key requisite in decarbonised gas future. Even though natural gas is the lowest carbon dioxide emitter of any fossil fuel, producing 180gm/kWh carbon dioxide equivalent, hydrogen emits zero at the point of use.
The National Grid notes in its report that hydrogen for heat is gaining momentum: "We believe that hydrogen will play a role in the future. It is seen as an attractive option for meeting the decarbonisation targets due to the potential lower cost and level of disruption compared to other routes."
Hydrogen for heating requires less change in behaviour from consumers since hydrogen shares many characteristics with natural gas.
Different Carbon Footprints
The carbon footprint of hydrogen depends on its source.
For example, grid power electrolysis has high emissions whereas hydrogen made from stripping the carbon atom from natural gas has about 50 gm/kWh carbon dioxide equivalent, including indirect emissions, which is a big reduction over natural gas. However, steam reforming using natural gas, also needs CCS and in the UK no large-scale CCS exists to date. Private Eye magazine describes viable CCS as like the unicorn, "everyone can describe it, some people believe in it, but it doesn’t (yet) exist" (Issue No. 1469).
Before discoveries of natural gas in the North Sea Continental Shelf in the 1960s and 1970s, the UK relied on locally manufactured town gas which contained around 50% hydrogen using coal, then oil, as fuel feedstock. As the UK embarked on natural gas extraction a nationwide programme to convert 40 million appliances was undertaken, resulting in 80% of UK homes relying on natural gas for heating and cooking today.
A hydrogen conversion could occur that would involve minimal disruption for customers, domestic or commercial, and require no large-scale modifications to properties.
The Key Benefits of Hydrogen
The use of hydrogen storage addresses inter-seasonal storage, one of the known problems of trying to use only electricity as the energy vector for heat. This benefit smooths out the UK’s significant variation in inter-seasonal energy demand as hydrogen is produced and stored ‘downstream’ at a relatively constant rate throughout the year. It also smooths out the production of carbon dioxide, simplifying sequestration.
Wholesale natural gas purchases are less susceptible to fluctuations as the demand is relatively constant over the year for hydrogen production, reducing the volume of natural gas required at periods of high demand, and cost.
As lower-cost pipeline quality hydrogen can get purified to the exceptionally high-quality gas required by fuel cells, a UK gas grid conversion to hydrogen could provide feedstock for automotive use, and via fuel cell CHP point to an alternative to centralised power generation.
Pilots and Feasibility Studies
Natural Gas to Hydrogen
The H21 Leeds City Gate project, run by gas utility Northern Gas Networks, is a feasibility study to see if it is technically and economically possible to convert the existing natural gas supply in Leeds, one of the largest UK cities, to 100% hydrogen. If successful, the project could stand as a blueprint for a potential UK-wide incremental rollout of a hydrogen gas system to decarbonise the production of heat.
Earlier in 2017, the project concluded it is both safe and economically viable to convert the city to a full supply of hydrogen gas. The project, awarded £9 million from the regulator Ofgem is also receiving £1.3 million from the UK’s gas distribution network operators, which will be used to finance controlled tests for a potential city-wide transition.
The first cities that convert to hydrogen will not do so before 2025 because of the number of preparations that need to be undertaken, in areas such as funding, planning, as well as regulatory and policy.
Hydrogen and Natural Gas Blend
Another project, HyDeploy, is establishing the potential for blending hydrogen, up to 20%, into the regular gas supply to reduce carbon dioxide emissions. The project will be the first in the UK to inject hydrogen into a natural gas network.
A key focus of HyDeploy is determining the level of hydrogen that can be used by gas consumers safely, with no changes to their behaviour or existing domestic appliances.
Subject to Health & Safety Executive approval, the aim is to run a year-long live trial of blended gas starting in 2019.