The hydrogen city: clean, green & another nail in the fossil fuel coffin
David Thorpe | 12 April 2016
Hydrogen produces only water and heat when burnt and, if made using renewable fuels, is zero carbon.
Leeds in the UK is investigating the potential to convert its natural gas to hydrogen in a £55 million (AU$102.6m) pilot project. The “hydrogen city” proposal is a leading example of how some cities and energy supply companies are considering ways to decarbonise heating and cooking in the future and become less dependent on fossil fuels.
Northern Gas Networks is responsible for maintaining the gas grid infrastructure for 2.7 million homes in the north of England. In this area, 85 per cent of buildings use gas for heating space and water and for cooking.
The company sees the conversion of this network to take hydrogen as affordable and possible on an incremental scale. It also sees potential for using hydrogen for a vehicle refuelling network and for heating, possibly using micro-combined heat and power, as part of the UK Government’s “Northern Powerhouse” project.
The plan to make Leeds a “hydrogen city” would eventually cost about £2 billion and involve converting all domestic gas boilers and cookers to run on hydrogen. NGN has already received £300,000 (AU$559,670) funding from energy regulator Ofgem to develop the idea.
A report commissioned by NGN from KPMG consultants says that what is named the H21 Leeds City Gate Hydrogen Project would position natural gas as more than a “transitional fuel” on the UK’s pathway to a low carbon economy. Desktop modelling has shown that the current gas network in the UK and particular in Leeds is large enough to convert hydrogen, and that because of its unique positioning, Leeds should be the first city to convert.
“Households in Leeds could potentially cook and heat their homes using pure hydrogen within 10 to 15 years,” a spokesman for NGN said. The city would then become a centre of excellence for the hydrogen economy, it is thought.
The project is now looking to secure £55 million to develop a roadmap to hydrogen consisting of evidence that would back up the project’s viability. The work is seen as split into 16 work packages, covering over 50 projects. Part of this work will be to determine an overall strategy for UK-wide conversion over time.
Conversion would be a major infrastructural transformation, and many hydrogen compatible appliances and burners would need to be installed or converted, and a workforce trained to undertake the process. Hydrogen and electricity would become the dominant heating fuels by 2050.
The gas grid
The UK benefits from an extensive natural gas pipeline network that supplies 84 per cent of homes. Worldwide, natural gas supplies around 20 per cent of residential heat, primarily in OECD countries.
Many of the old local low-pressure distribution iron pipes are having to be replaced by polyethylene, and by 2030 this will be complete and they will be able to take hydrogen.
The national high-pressure gas distribution pipes on the other hand are made of steel, which is unsuitable to transport hydrogen, so a separate network would have to be constructed. This has happened before, when the network was converted from town gas to natural gas over a 10-year period, so it is known to be feasible.
Using hydrogen in the network is just one idea for its future, rather than decommission it completely, after the use of natural gas has to be abandoned to meet the constraints of climate change. Other possible uses are to carry bio-methane from the anaerobic digestion of organic waste, and hydrogen injection.
A 2013 academic study on the future of the UK gas network determined that from a cost point of view, hydrogen conversion was the cheapest option, and recommended that the government adopted a long-term strategy to do so. It concluded that renewable methane from anaerobic digestion could probably only ever meet around 10 per cent of total gas demand due to the limited availability of the waste organic matter (food and agricultural waste).
One of the drivers for the project is the UK’s 2008 Climate Change Act, which requires the government to reduce UK greenhouse gas emissions in 2050 by 80 per cent relative to 1990 levels.
A major stumbling block for this strategy is the problem of carbon capture and storage. If the hydrogen is produced by reforming methane, which is composed of carbon and hydrogen, the hydrogen would be pumped into the gas grid, but the carbon would need to be stored underground to prevent it entering the atmosphere. The likeliest place for storing it is back underneath the North Sea, where the gas came from in the first place.
However, last year the government scrapped a £1 billion (AU$1.87b) carbon capture and storage pilot project that would test out this idea, so no one yet knows whether this will work.
The use of hydrogen in the gas grid does have the backing of the Institution of Gas Engineers and Managers, which has already said it will help in developing standards for the construction and testing of hydrogen gas distribution systems and safety.
The role of hydrogen in decarbonising buildings
A study published two years ago criticised governments for not considering the role hydrogen could play in decarbonising buildings and heating. It concluded that fuel cells could especially offer wider energy system benefits for high-latitude countries because of their peak electricity demands in winter; but the same could be true in low latitude countries that have a high electricity demand for airconditioning.
The study argued that gas networks could prove difficult to displace with alternatives, particularly because consumers who have them like their gas boilers, which they perceive as safe, cheap, effective and easy to control, so why not adapt the existing markets and infrastructure for gaseous heating fuels and convert these to use hydrogen?
Both of the above academic studies are co-authored by Paul Dodds of University College London, an expert in energy economics. But the UK government also appears to be backing the idea, building on a 2012 strategy paper on The Future of Heating: A strategic framework for low carbon heat in the UK.
This paper argues that although constructing a high-pressure national grid for delivering hydrogen to households could be very costly, as intercity pipes would need to resist high-pressure hydrogen and corrosion, low-pressure local grids may be a more viable solution. This will potentially enable them to be connected to other local means of supplying the gas, for example by the electrolytic splitting of water using renewable electricity when more of it is being generated than is required at the time, such as by wind power at night.
A follow-up 2014 White Paper from the UK Hydrogen and Fuel Cell (H2FC) SUPERGEN Hub examined the roles and potential benefits of hydrogen and fuel cell technologies for heat provision in future low-carbon energy systems. It agreed with the idea and proposed that in the shorter term small amounts of hydrogen be injected into the gas networks to reduce the emissions intensity of grid gas.
It also criticised government policies on renewable heat for marginalising hydrogen and fuel cells.
This approach, together with the use of fuel cell micro-CHP, would reduce the need to depend on heat pumps as the main solution for decarbonising heating. Heat pumps have recently been criticised because they either require a lot of space or, in the case of air course heat pumps, are too noisy.
The options for micro-CHP
Micro-CHP (or cogeneration) is a boiler that not only heats a building but also generates electricity. It’s around the size of a small fridge or washing machine. Like its big brother, conventional CHP, it uses the gas more efficiently, making the boiler 90 per cent efficient.
The current crop of models are based on the Stirling engine, Organic Rankine Cycle (ORC) or internal combustion engine. The first two have high thermal efficiency and output but low electrical efficiency (10 per cent), and this is a sticking point.
A 2011 trial by the UK’s Carbon Trust concluded that micro-CHP can cut electricity bills and overall CO2 emissions by 15-20 per cent when they’re the lead boiler in larger contexts like care homes, district schemes, apartment blocks and leisure centres. The best application for them therefore is a medium-to-large, moderately well-insulated building, perhaps with solid walls, solid floors and no loft space, that is hard to insulate well and has a relatively large heat demand; or a cluster of buildings.
Micro-CHP offers more limited benefits for smaller and newer dwellings, however, because they are more energy-efficient or have too little requirement for heat.
The key to success in micro-CHP is matching the thermal output to the building’s pattern of use, so that they operate not intermittently but for many hours at a time, making the value of electricity generated pay for the marginal investment as quickly as possible. It therefore works best with a buffer storage tank to save the surplus heat for later. Grid connection for electricity export is crucial to micro-CHP’s widespread acceptance.
On average, half of all electricity generated by a typical 1kWe micro-CHP device is exported to the grid, as it’s not needed at the time. Reliability is also a key issue; service agreements will be essential.
Superinsulated homes will have to wait until the next generation of machines, based on fuel cells. These generally come in two types – proton exchange membrane fuel cells (PEMFCs) and solid oxide fuel cells (SOFCs). They have a heat-to-power ratio that is approximately equal.
CO2 savings from fuel cells are therefore country- and site-specific, depending on the carbon intensity of grid electricity and on the heating system that is displaced.
At five times the installation cost of residential gas boilers (around £12,000 for 1kW residential systems, but costs are falling 10-15 per cent per year), they’re not cheap but are beginning to compete with other low-carbon heating technologies, and their running costs are lower, even without public policy support.
Hydrogen in the home
By contrast, could we live with hydrogen? The physical properties of hydrogen differ from natural gas, so switching to hydrogen would require changes not only to the gas network but to heating and cooking appliances.
Gas appliances designed for natural gas cannot generally be used directly with hydrogen, mainly because the combustion velocity or flame speed is higher for hydrogen than for natural gas. Conversion would mean replacing the burner heads. Hydrogen also spontaneously ignites much more quickly than natural gas, which will necessitate modifications to spark-ignition gas engines and gas turbines to avoid flashback and knocking.
Hydrogen has a lower calorific value than natural gas per unit of volume, so a greater volume of gas must be burned for the same heat level. But this is made up for by the fact that the gas flows quicker under the same pressure due to its lighter molecules. Hydrogen is also invisible and odourless, so would need odourants to be added to it to enable detection for safety reasons.
However, because hydrogen can be burnt directly in a combi-boiler, it requires no additional space in the home. Hydrogen boilers are also much cheaper than heat pumps. They could therefore provide zero-carbon heat without much disruption to living patterns, while being affordable.
Hydrogen may also be used for district heating. Boilers designed specifically for hydrogen are under development.
Gas heat pumps may also be converted to hydrogen. These are already commercially available in some countries for household or commercial use, and have much higher efficiencies than gas boilers.
The road to a hydrogen city is clearly a long one that is not without difficulties. However, Northern Gas Networks is one gas network operator that is not going to give up the value of its assets easily and is determined to explore the options.
Leeds, a pioneer city of the first industrial revolution, could yet become a pioneer of the post-carbon revolution.
David Thorpe is the author of:
- Best Practices and Case Studies for Industrial Energy Efficiency Improvement (with Oung, K. and Fawkes, S. UNEP, 2016)
- A London Conversation: Business Briefing on Green Bonds (The Fifth Estate, 2015)
- The One Planet Life (Introduction: Jane Davidson. Routledge, 2015)
- Earthscan Expert Guide to Energy Management in Buildings (Earthscan, 2013)
- Earthscan Expert Guide to Energy Management in Industry (Earthscan, 2013)
- Earthscan Expert Guide to Solar Technology (Earthscan, 2011)
- Earthscan Expert Guide to Sustainable Home Refurbishment (Earthscan, 2010)