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| Tue, 7th Sep 2021 7:00:00 |
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Why we need a hydrogen power network to reach net-zero carbon |
In August, the government announced its plan to provide the UK with low-carbon energy derived from hydrogen. What will the gas be used for, and will it really help us reach our emissions targets?
What is the government’s plan?
The main aim of the UK Hydrogen Strategy is to have the capacity to produce 5GW (five billion joules per second) of low-carbon power from hydrogen by 2030. This is equivalent to the amount of gas used by three million UK households.
This hydrogen could be used in a variety of ways. Perhaps the easiest to put into place will be replacing natural gas derived from fossil fuels. Natural gas, a mixture of methane and ethane, is used for heating, cooking and generating electricity. Hydrogen can be burned in exactly the same way, producing only water and no CO2, though you would need roughly three times as much to produce the same amount of energy.
The strategy outlines plans to test the use of hydrogen for heating in a neighbourhood by 2023, in a village by 2025 and a town by 2030.
Hydrogen can also be used in fuel cells. In this scenario, nothing is burned. Instead, chemical energy is turned directly into electrical energy, much like a battery. These cells can be used in place of a combustion engine in vehicles – even trains or aeroplanes – or instead of petrol or diesel generators.
Where will the hydrogen come from?
The gas can come from two sources, known as ‘blue’ and ‘green’ hydrogen. “So-called green hydrogen is produced by splitting water into its constituent parts, hydrogen and oxygen, using electricity derived from renewable energy sources such as wind or solar power,” says Dr Eike Thaysen, Experimental Geosciences Technical Research Assistant at the University of Edinburgh.
“Blue hydrogen is produced by the reaction of steam with methane, where the carbon emissions from this process are captured and stored.”
Since green hydrogen is produced using renewable energy, it can essentially be used as a way of storing surplus renewable energy.
Blue hydrogen, however, is produced using fossil fuels, and so creates carbon emissions. During the process, the CO2 is captured and stored permanently underground. However, The Guardian reported in August that the carbon capture technology fails to store between 5 and 15 per cent of emissions. Based on the government’s planned usage of blue hydrogen, this works out to eight million tonnes of CO2 annually by 2050, equivalent to what’s produced by 1.5 million fossil-fuel cars.
A separate study by scientists from Cornell University and Stanford University suggested that blue hydrogen could be even worse than that. They estimate that the emissions are equivalent to 139g of CO2 per million joules of energy, with a carbon footprint 20 per cent greater than burning natural gas or coal.
Why use blue hydrogen at all?
If using blue hydrogen still produces carbon emissions, why not just burn the natural gas directly?
Stuart Haszeldine, Professor of Carbon Capture & Storage at the University of Edinburgh, doesn’t believe the study from Cornell and Stanford is applicable to the UK. “[The study] takes worst possible case assumptions based on a leaky USA system – that lots of methane will leak, and very little CO2 will be captured – and so it is not surprising that leaks and poor processes end up with a very large CO2 emission per unit of hydrogen,” he says.
“Even so, I regard low carbon blue hydrogen as a transition to rapidly replace methane through diverse uses – its replacement by cleaner green hydrogen will be determined by the pace at which the price of electrolysis decreases.”
Thaysen says that a more accurate estimate of the emissions for blue hydrogen would be equivalent to 10 to 20g CO2 for each million joules of energy produced. For the same amount of energy, burning natural gas produces about 63g of CO2.
“This means that blue hydrogen is about three to six times cleaner than natural gas – on the condition that the carbon has been split off and permanently stored,” she says. So even if 15 per cent of the carbon dioxide escape into the atmosphere, the total emission is still much less.
Furthermore, Thaysen believes that blue hydrogen is essential on our journey to net zero. “Green hydrogen enables decarbonised storage of renewable energy, thereby fuelling increased use of zero-carbon energy sources and helping the transition to a net-zero society,” she says.
“However, blue hydrogen is currently more economical and uses well-established existing technologies, which helps develop value chains and can help industry cut emissions quickly. It also ensures there is a market for green hydrogen once it becomes cost-competitive.
“Therefore, a combination of green hydrogen and blue hydrogen will be essential to help us get to net zero fast.”
What infrastructure is still needed?
Converting the gas supply to our homes to accommodate hydrogen will be comparatively simple, thanks to the infrastructure that’s already in place.
Thaysen explains that hydrogen can be blended into the existing gas network without changing the infrastructure or our gas appliances, up to a total of 20 per cent of the gas volume. “This makes the conversion to hydrogen rapid and low-cost. However, this only results in a 7 per cent reduction on CO2 emissions, so we want to be aiming for 100 per cent hydrogen,” she says. “But to convert to 100 per cent hydrogen, adaptations to the current infrastructure are needed.
“To get the gas from the distribution sites into our homes, we are very fortunate because the yellow polyethylene pipes that are currently being installed across the country to replace the old iron pipes are suitable for use with hydrogen.”
For drivers, a Toyota Mirai or Hyundai Nexo powered with a hydrogen fuel cell might seem like the perfect compromise between the range of a fossil-fuel car and the emissions of a battery electric vehicle. However, the main problem for consumers is where to fill up.
UK H2Mobility lists only 11 hydrogen fuel stations available for cars around the country, mostly situated around London – fine if you’re staying in the capital, but once you head north from Sheffield, you can’t fill up again before Aberdeen.
So, is hydrogen the answer to reaching net zero?
The UK’s aim to reach net zero carbon emissions by 2050 will be essential in mitigating the effects of climate change. But will the government’s Hydrogen Strategy get us there?
“Hydrogen has the potential to be incredibly useful. It could literally reach the sectors other options can’t, in industry and aviation,” says Robert Gross, Professor of Energy Policy and Technology at Imperial College. “But we won’t be able to use it everywhere all at once.
“The sheer volume of energy needed in single sectors, like domestic heating or transport, is immense. Considering the minuscule amount of hydrogen we use for energy today, the challenge is huge. So hydrogen won’t be a quick fix or a universal panacea.”
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