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Net Zero and Domestic Hydrogen: An Imminent Marriage?

A series of obstacles must be overcome if hydrogen is to really contribute to reducing electricity demand.

Since pure hydrogen is not present in the Earth’s atmosphere, we must manufacture it. Regardless of the method used, the energy released from the resulting hydrogen is always significantly less than the energy required to make it. Unlike natural gas, hydrogen is not an energy source, but a rather poor energy carrier. The two techniques most commonly used to produce hydrogen are water electrolysis and steam reforming of natural gas. The former requires 50-55 kWh of electricity to produce 1 kg of hydrogen with a specific energy of 40 kWh, making it 70-80 percent efficient; the latter is 65-75 percent efficient. An October 2018 report from the Department for Business, Energy & Industrial Strategy estimated that greenhouse gas emissions from the construction and use of an electrolyser equate to 122 g of carbon dioxide per kWh of hydrogen produced, 96 percent of which is caused by the manufacture of electrolysers. For steam reforming, without carbon capture and storage, the figure is between 222 g and 325 g CO2 equivalent / kWh. Few examples use carbon capture and storage on a large scale, and none in the UK, but a few of them claim 37g and 45g CO2 / kWh of hydrogen. The short life of electrolysers and the periods of low load when supplied by wind turbines also increase the associated greenhouse gas emissions.The Climate Change Committee and the UK Government are beginning to focus closely on expanding the use of hydrogen as part of the path to achieving “net zero” emissions. The UK’s annual energy demand for electricity is around 350 TWh, while transportation requires 660 TWh and 730 TWh heating, so it is clear that today’s electricity grid cannot handle transportation and / or heat. Is there an economically and technically feasible role for hydrogen to alleviate our future electricity demand while aiming for a net zero? The government’s Hydrogen Task Force was launched last March in response to previous research into decarbonising heat. It recognizes that the hydrogen route is not flawless and will require massive investment, with an initial report claiming that “achieving net zero is not possible at all without hydrogen [and] investment should be an immediate priority.” National Grid has confirmed “it is still investigating the conversion capabilities of our infrastructure to transport hydrogen / natural gas blends and 100 percent hydrogen.” This assessment is still in its infancy and it is building a test facility in Cumbria with decommissioned assets, where testing will begin in 2022. In late March 2021, National Grid announced that it plans to acquire a majority stake in its UK gas transmission business later in the year; Whether this will affect the proposed testing program remains to be seen.Switching our natural gas grid to 100 percent hydrogen – or even high concentrations of hydrogen – is a major challenge. The potential problem of hydrogen embrittlement of existing gas lines, distribution lines and welds is a well-known problem. Cyclic variation in pressure is believed to be a contributing factor and the introduction of hydrogen into the gas network may prove to be a major technical and financial challenge. Depending on the type and quality of the steel, coupled with the amount of atomic hydrogen entering pipe surfaces, progressive embrittlement can amplify the spread of existing cracks and, according to some experts, shorten the life of the affected pipes by 50 percent or more. . The UK aims to complete the transition from widespread smaller diameter iron pipes to polyethylene, which is considered hydrogen compatible, for medium and low pressure urban distribution in the next five years. A recent major study, H21, to convert the city of Leeds to 100 percent hydrogen, considers this replacement to be relatively affordable, as the switchover is fortunately well advanced.The scope of the investigation was not required to address the UK’s large bore network. Converting existing large-bore natural gas pipelines to transport 100 percent hydrogen introduces another factor. At standard temperature and pressure, the methane density is about eight times that of hydrogen with three times the calorific heating value, so hydrogen needs a flow rate three times that of natural gas to provide the same amount of energy. However, these properties partially offset each other, because hydrogen is much lighter. Existing pressures for plant and piping, control equipment, system operation and compression plants will need to be investigated and the level of investment determined by determining whether hydrogen transport conditions require grid design to change significantly. We may be lucky and achieve this under the current pressure, but the studies are currently incomplete. Blending with natural gas is seen as a possible way to heat homes and bring hydrogen to the market by installing a downstream plant to extract hydrogen from the combined gas mixture. It is considered possible to do this by the end of 2022. There are at least three reasonably established technical methods that could be used, but all of them would be expensive. In addition, the UK will have to amend the existing Gas Safety Management Regulations to make this possible.The UK’s position on the European Commission’s new hydrogen strategy, in the wake of Brexit, and the role it could play in the European Clean Hydrogen Alliance has yet to become clear. Germany has already started serious studies in this area and the prospect of divergence of standards may become a problem; there is a shortage of Euro standards for hydrogen combustion and the UK is likely to seek pipelines with Europe. In any case, the creation of the UK Task Force shows that we are starting to seriously address these and other issues. Reportedly, the EU expects to have 6 GW of electrolysers in operation by 2024 and 500 GW by 2050 – a huge ambition with less than 0.1 GW currently operational. Associated plans to store large amounts of hydrogen in salt caverns represent another area of ​​technical challenges and related costs. In my previous article – ‘Are hydrogen vehicles a waste of our time and energy?’ (Published February 2021), I looked at how some new wind farm developments apply hydrogen production through electrolysis when their power exceeds the demand for the electricity grid. This approach, seen as a means of eventually providing energy storage through the UK gas grid and compensating for wind variations, is not a panacea. Infrastructure costs will be enormous given the amount of hydrogen production needed to match the domestic heating demand currently met by natural gas and National Grid estimates that 75 GW of wind turbines would be required by 2050 to reach net zero through this route. to make it a viable prospect. . That is three times the existing full installed wind capacity in the UK, much of which will reach the end of its life in the next 30 years and will need to be replaced. Commercial viability, of course, depends on being able to earn higher revenues than penalties.National Grid’s Future Energy Scenarios 2020 report expects more than the vast majority of homes to be heated with hydrogen by 2050 under the ‘System Transformation’ scenario as a projected path to net zero, but this, combined with projections of its use in the domestic kitchen present major challenges. Hydrogen is a suffocating agent that, at 1/14 the weight of air, spreads very quickly and rises on escape, mixes with air and becomes dangerous due to its wide flammability range (from about 4 percent to 75 percent); a very low ignition energy; high combustion energy and an almost invisible flame that can reach 2,000 ° C. Burning invisibly, there are known challenges in adding a fragrance that can keep up with the inherent very fast hydrogen dispersion rates, allowing us to detect the odor before the hydrogen concentration becomes flammable; cooking risks will need to be seriously assessed and the development of related appliances worldwide is currently quite minimal. In addition, 60 percent more water vapor is produced with the same energy compared to natural gas. When hydrogen is burned into pure oxygen, the chemistry is simple and we get water and heat. When combusted in air, which is 78 percent nitrogen – as in an existing flame-burning boiler – the higher hydrogen flame rate means that the oxygen combines with nitrogen in the air to produce up to six times the NOx emissions compared to natural combustion. gas in the air. This poses a seriously increased health risk compared to natural gas.NOx emissions can be reduced by using catalytic combustion designs that require the use of precious metals such as platinum. Leading boiler manufacturers believe they can develop the technology for the domestic market and some have prototypes under test and are urging the government to commit to 100 percent hydrogen ready boilers by 2025, although much of the current literature is light on the engineering of NOx minimization. Indicative costs were not available for the H21 Leeds study. However, world production of platinum last year was about 130 tons, compared to about 1,800 tons of gold, which represents a very limited supply chain if platinum is to be widely used. The placement of household water heaters in the home will be another concern as some will currently be in bedrooms or a garage. No housing in the UK has electrical equipment certified for use in hydrogen atmospheres, so many existing boiler locations will have to change. The technology is still in the development phase and has a long way to go. All domestic water heaters sold since 1996 must be able to tolerate 23 percent hydrogen; Keele University has conducted a substantial trial with a 20/80 hydrogen / natural gas mixture. 650 homes near Gateshead will start trials this spring, also using a 20/80 blend, while a four-year test in Levenmouth, Fife, to run 300 homes on 100 percent hydrogen, is currently in the stages of approval.Unsurprisingly, this year National Grid considered four future energy scenarios to address net zero by 2050, following a government policy shift of 80 percent decarbonization. “Steady Progression,” as the name implies, largely pushes aside new initiatives and is generally a worst-case struggle. In two of the remaining three scenarios, “Consumer Transformation” and “Leading”, the heating and transport of homes is mainly modeled by electricity and not by hydrogen boilers, the latter with predominantly hybrid heat pumps. “System Transformation” is the only scenario involving a high rate of adoption of domestic hydrogen boilers, where natural gas steam reforming with carbon uptake must significantly outperform wind farms to meet estimated demand. This keeps the use of the planet’s fossil resources at a very high level and makes the UK highly dependent on gas imports. However, we should not forget that since April 2018, Clean Energy Growth legislation dictates that new domestic gas boilers must be at least 92 percent efficient. By instead using gas turbines to provide electricity to heat our homes, the efficient use of the gas is reduced to 65 percent, creating a massive increase in related greenhouse gas emissions for the equivalent amount of electrical heat energy supplied.If we can’t switch to a mixed 20/80 hydrogen / natural gas mix for domestic heating or anything closer to “System Transformation”, National Grid and the big gas companies could be left with billions of pounds in stranded assets. Given the challenges of hydrogen, it is currently unclear whether we can overcome the technical hurdles and at prices that the public can afford without major government subsidies. Some leading academics and engineers believe that the key outlook for hydrogen in 2050 is likely to be hydrogen-carrying ammonia for marine propulsion and high-temperature industrial processes such as steel production. The results of the net zero survey will determine our future. David B Watson is a licensed electrical engineer who was a project manager at Foster Wheeler Energy, based in Glasgow, before retirement, and responsible for managing project execution at the company’s Scottish facility. This article was updated on May 7, 2021 with National Grid’s March announcement of its intention to sell a majority stake in its UK gas transmission business.