Hydrogen, Storage and Renewable Energy
In his book on the strategy needed to enable the UK to
address the threat from climate change, Chris Goodall mentions hydrogen more
than a hundred times (Goodall, 2020). Describing the connection between
renewable energy and hydrogen, he cites “ the great British biologist J.B.S.
Haldane, who foresaw the importance of renewable electricity combined with
hydrogen as the basis of the entire energy system as early as 1923”. Here is
part of Haldane’s lecture, given in Cambridge:
“Personally, I
think that … the power question in England may be solved somewhat as follows:
The country will be covered with rows of metallic windmills working electric
motors which in their turn supply current at a very high voltage to great
electric mains. At suitable distances, there will be great power stations where
during windy weather the surplus power will be used for the electrolytic
decomposition of water into oxygen and hydrogen. These gasses will be … stored
in … reservoirs, probably sunk in the ground …In times of calm, the gasses will
be recombined in explosion motors working dynamos which produce electrical
energy once more, or more probably in oxidation cells. These huge reservoirs …
will enable wind energy to be stored, so that it can be expended for industry,
transportation, heating and lighting, as desired.” (Haldane,1923).
The ‘power question’ for Haldane was the foreseeable “exhaustion
of our coal and oil-fields” and the solution was “to tap those intermittent but
inexhaustible sources of power, the wind and the sunlight. The
problem is simply one of storing their energy in a form as convenient as coal
or petrol.” The relevance of hydrogen for energy storage in our present
situation of climate change will be explored below, along with some of the
other uses which Goodall sees for hydrogen in the production of synthetic
fuels, as a replacement for coal in steel making, and in the manufacture of fertilisers,
ammonia and cement. A number of hydrogen-based projects will also be outlined.
Surplus power from renewables can occur in many different
ways: a brief period of high wind may lead to excessive output from wind
turbines, fine summer weather may cause daily surplus production from solar
installations, and tidal generation may exceed requirements several times per
day as water flow rates peak. Battery storage is one of the promising methods
of coping with short term variation in power output, but is (as yet) not a
suitable way of coping with longer term and seasonal variation. Pumped storage
of water for hydroelectric generation offers a solution in countries with
suitable climate and geography, but has only limited scope in the UK. The use
of surplus power to produce hydrogen may be an attractive option, provided that
a range of associated problems can be overcome. These problems may be divided
into groups: the efficient production of hydrogen, its storage and its
transportation; its uses both as fuel and in manufacture; economic, political and
environmental issues.
Production of hydrogen and associated energy
Almost 96% of the world’s hydrogen is produced from
fossil fuels, with the remainder produced by electrolysis (Catalan and Rezaei,
2019). Steam-methane reforming of natural gas accounts for 48% of the global
hydrogen production, and in this process methane and water react to produce
hydrogen and carbon dioxide. Without carbon capture, this method contributes to
global warming. Electrolysis of water, on the other hand, produces only hydrogen
and oxygen. The production of 1 kg of hydrogen using efficient methods of water
electrolysis requires 50–55 kWh of electricity (Wikipedia, 2020). The specific
energy of hydrogen (the energy released when it burns) is about 40 kWh per kg,
so that producing hydrogen for energy can be commercially viable only if the
price of electricity is sufficiently low, and ecologically sustainable only if
the electricity used has very low associated carbon emissions.
Storage and transport of hydrogen
Hydrogen can be stored in large amounts and for extended
periods. Storage methods include those based on either compression or cooling
or a combination of the two (hybrid storage), but “a large number of other new
hydrogen storage technologies are being pursued or investigated” (Hydrogen
Europe, 2017). For the industrial storage of hydrogen, salt caverns, exhausted
oil and gas fields or aquifers can be used as underground stores, but operational
experience of hydrogen storage caverns exists only in a few locations in the
USA and Europe.
The most common hydrogen transportation means are by compressed
gas cylinders, cryogenic liquid tankers and dedicated pipelines; but hydrogen
can also be transported in existing natural gas pipelines, by blending it with
the natural gas and separating it at the point of delivery (ibid.)
Hydrogen as fuel
Jessica Murray reported early in 2020 that “Zero-carbon
hydrogen has been injected into a UK gas network for the first time in a
ground-breaking trial that could help to reduce carbon dioxide emissions”
(Murray, 2020). She was referring to a trial of a blend of 20% hydrogen with natural
gas to heat homes and faculty buildings at Keele University. The article claims
that “Rolling the 20% hydrogen blend out across the country could save about 6m
tonnes of carbon dioxide emissions a year”. The use of the term “zero-carbon”
might be questioned; hydrogen produces no carbon when burned, but even when hydrogen
is produced by electrolysis using renewable electricity, there will be some
carbon burden: ‘green hydrogen’ might be a better description. The use of “zero-carbon”
hydrogen in the UK may be new, but hydrogen in the domestic gas supply is not;
it was “a major component in ‘town gas’, the gas created from coal and used
widely throughout Britain before the discovery of North Sea gas in the 1960s.
Up to 60% of the gas (by volume) being used by consumers was hydrogen” (Northern
Gas Networks, 2018).
A number of projects aim to deliver 100% green hydrogen
for heating. One of these is SGN H100, described by the Scottish Hydrogen and
Fuel Cell Association as a “world-first programme using green hydrogen to heat
homes” (SHFCA, 2020). The project “is intended to provide critical evidence for
a potential zero carbon energy source, helping to inform the UK’s long-term
policy decisions for decarbonisation”; subject to Ofgem approval, it will serve
300 homes at Levenmouth in Fife “within about three years.”
A wider perspective on the future of heating with green
hydrogen comes from the European Commission, which foresees that “Local
hydrogen clusters, such as remote areas or islands, or regional ecosystems –
so-called “Hydrogen Valleys” – will develop, relying on local production of
hydrogen from decentralised renewable energy production and local demand,
transported over short distances. In such cases, a dedicated hydrogen
infrastructure can use hydrogen not only for industrial and transport
applications, and electricity balancing, but also for the provision of heat for
residential and commercial buildings” (European Commission, 2020).
Hydrogen can be used to generate electricity in a number
of ways. Internal combustion engines can be made to run on hydrogen, and the
future of vehicles powered in this way has been a subject of discussion
(ScienceDirect, 2018). Clearly such an engine could be used to drive a
generator, but a hydrogen fuelled gas turbine would be more appropriate for large
scale electricity generation. Robb (2019) writes that gas turbines running on
100% hydrogen “have been a long-term dream”, and that the concept “has gained
momentum in tandem with the trend toward carbon neutrality.” He describes a
project to modify a gas turbine to run solely on hydrogen at a green hydrogen
power facility in Port Lincoln, South Australia. The project includes a water
electrolysis plant, a facility for sustainable ammonia production, and a 5 MW
hydrogen fuel cell. It can “either use grid supply, on-site solar power or
hydrogen-powered electricity as required.” Further details of the project are
given by RenewablesSA (undated).
Hydrogen can be used to generate electricity by means of
fuel cells, and an article from the U.S. Department of Energy provides an
introduction to them (EERE, 2017). A number of straightforward points are made:
hydrogen is earth’s most abundant element; the environmental impact and energy
efficiency of hydrogen depends on how it is produced; hydrogen and fuel cells
can be used in a broad range of applications; fuel cells can be
grid-independent, and so provide an attractive option for powering critical services.
Vehicles powered by hydrogen fuel cells can have a carbon footprint around half
that of conventional vehicles if the hydrogen is made from natural gas, or
about 10% if the hydrogen is produced by renewable energy, such as wind and
solar. A linked article from the same organisation provides a more detailed
perspective on fuel cells, including their use in forklift trucks, buses, cars,
trains and ships (EERE, 2019). Hydrogen fuel cells have been used to power
light aircraft, and demonstration flights between Cranfield and Kirkwall,
Orkney, are expect to begin shortly (Robinson, 2020). A further discussion
of the role of hydrogen in aviation is provided by Thompson (2020).
As stated by EERE, the efficiency of energy processes
which use hydrogen depends, among other things, on how it is produced. We saw
above that 50–55 kWh of electric energy was needed to produce by electrolysis
enough hydrogen to yield 40 kWh when burned, representing an efficiency of 80%
at best.. How much useful energy can be retrieved from hydrogen?
In the case of vehicles powered by fuel cells, one claim
is that although “less efficient than electric batteries, today’s fuel cells
compare favourably with internal combustion engine technology, which converts
fuel into kinetic energy at roughly 25 per cent efficiency. A fuel cell, by
contrast, can mix hydrogen with air to produce electricity at up to 60 per cent
efficiency” (MEED, 2019). Combining the efficiencies of electrolytic hydrogen
production and fuel cell conversion to mechanical energy gives a best overall
efficiency figure of around 48%.
In January 2019, Siemens Energy signed a commitment with
the members of the industry body EUTurbines, to increase the hydrogen capability
in gas turbines to at least 20 percent by 2020 and to 100 percent by 2030
(Lindstrand, 2019). Manufacturers of conventional gas turbines claim efficiencies
of 55 percent or greater, but this is the efficiency at baseload power, and is
likely to involve recovery of waste heat. (Wartsila, 2020). If we assume that
turbine efficiencies using hydrogen fuel from electrolysis will be similar, we
reach an overall efficiency of around 33%. This figure, together with the
estimate for fuel cells, makes the point that the electricity used for
electrolysis may have to be available at very low cost to make either process
economically viable, and puts into perspective the use of hydrogen for energy
storage.
Hydrogen and synthetic fuel
Hydrogen from electrolysis can be used in the production
of synthetic fuels with a lower carbon footprint than conventionally produced
fuels. The following description comes from the aviation industry, but probably
has more general relevance.
The ‘Power-to-Liquid’ process allows the production of a
synthetic alternative to fossil kerosene through the use of renewable
electricity to produce hydrogen from water by electrolysis and combine it with
carbon from CO2 (ideally captured from the air). The process “can present a
favourable greenhouse gas balance relative to conventional and bio-based
aviation fuel streams with close to zero emissions” and is seen as “a technically
viable solution to help decarbonise the aviation sector.” However, such fuels
are more expensive than kerosene, and using them to meet the expected future demand
for aviation has been predicted to “require 95% of the electricity currently
generated using renewables in Europe” (EASA, undated).
Hydrogen and steel making
The Fuel Cell and Hydrogen Energy Association describes
traditional steel-making as a reduction process in which iron oxide reacts with
carbon monoxide sourced from heating coke fuel in a blast furnace. The Association
estimates that in 2017, the iron and steel industry produced seven to nine
percent of the total global GHG emissions, with every ton of steel resulting in
an average 1.83 tons of carbon dioxide emissions. “New production processes are
exploring the use of hydrogen gas instead of coke. Hydrogen reacts with iron
oxide in a similar fashion to carbon monoxide, but instead of producing carbon
dioxide, the only byproduct is water vapor. When hydrogen used in this process
is derived from renewable or decarbonized sources itself, the steel making
process can become completely emission-free, creating ‘green steel.’” (Homann,
2019).
Hydrogen, fertilisers and ammonia
Fertilizers Europe, which represents the interests of many
fertilizer manufacturers in the European Union, acknowledges that current
“production of nitrogen fertilizers is energy intensive” with ammonia
production “mainly based on natural gas as a raw material and steam methane reforming
… as the main technology.” Natural gas is split at high temperatures to obtain
hydrogen and CO₂,
and the hydrogen is then combined with atmospheric nitrogen to produce ammonia.
This process “generates large quantities of CO₂.” The association foresees that under the
right conditions “ammonia production could be based on decarbonised sources of
energy.” Ammonia made using hydrogen from the electrolysis of water could be
used not only in the manufacture of fertilisers, but in the wider chemicals
industry, and more generally as a storable energy carrier with a near zero carbon
footprint and multiple uses as fuel (Fertilizers Europe, 2020).
The relation between hydrogen and ammonia is discussed in
a recent post on Energy Central, which points out that: “Paradoxically ammonia
is a better carrier of hydrogen than hydrogen itself as its properties make
transportation and storage straightforward. In some ways it makes more sense to
transport hydrogen as ammonia, and then back to hydrogen” (Rattan, 2020). The connection
between hydrogen and ammonia will not however be pursued further in the present
post.
Hydrogen and cement
A BBC Science and Environment article claimed that concrete
“is the most widely used man-made material in existence. It is second only to
water as the most-consumed resource on the planet.” (Rodgers, 2018). Cement is
the key ingredient in concrete, and the report quotes Chatham House as stating
that in “2016, world cement production generated around 2.2 billion tonnes of
CO2 - equivalent to 8% of the global total.” Much of this comes from the calcination
process - heating the raw materials to high temperatures to split them into
calcium oxide and CO2.
One of the projects intended to reduce the amount of CO2
from cement manufacture stems from a government-funded feasibility study in
2019 which found that a combination of 70% biomass, 20% hydrogen and 10% plasma
energy could be used to eliminate fossil fuel CO₂ emissions from cement manufacturing. A UK government
grant to the Mineral Products Association will be used to test the results of
the study (Gerrard, 2020). The use of plasma energy in gas
conversion is discussed by Bogaerts and Neyts (2018).
Some further projects based on hydrogen will be briefly
outlined:
“In 2016, Northern Gas Networks, the gas distributer for
the North of England, produced the H21 Leeds City Gate feasibility study. Based
on a blueprint of the city of Leeds, this pioneering industry first concluded
it was technically possible and economically viable to decarbonise the UK’s gas
distribution networks by converting them from natural gas to 100% hydrogen.” (H21,
2020).
Northern Gas Networks, Cadent, SGN and Wales & West
Utilities submitted a bid to Ofgem in 2017 for funding to provide evidence that
the proposed conversion can be safely carried through. The bid to the Network
Innovation Competition on behalf of UK gas networks was successful, and “H21
NIC is working to present the quantified safety evidence between natural gas
and 100% hydrogen used within the existing GB as distribution networks.”
The BEIS Low Carbon Hydrogen Supply Competition resulted
in funding for the five following projects; Dolphyn, HyNet, Gigastack, Acorn
Hydrogen and HyPER (BEIS, 2020).
The Dolphyn project aims to produce hydrogen from
offshore floating wind turbines in deep water locations. UK offshore wind power
will be used to produce ‘green’ hydrogen by electrolysis of seawater, and pipe
it directly to shore. A floating 10 MW wind turbine is envisaged, and the
funding will enable the detailed design of a 2 MW prototype system (Dolphyn,
2020).
The HyNet project will develop a clean hydrogen
production facility as part of the HyNet Cluster, using Johnson Matthey’s low
carbon hydrogen technology for carbon capture and storage. This technology has
become the basis for analysis by BEIS and the Committee on Climate Change (Hynet,
2020).
Gigastack will demonstrate the delivery of bulk, low-cost
and zero-carbon hydrogen through gigawatt scale polymer electrolyte membrane
electrolysers, manufactured in the UK. The project aims to dramatically reduce
the cost of electrolytic hydrogen. This funding will enable ITM Power to work
towards developing a system that uses electricity from Orsted’s Hornsea Two
offshore wind farm to generate renewable hydrogen for the Phillips 66 Humber
Refinery (Gigastack, 2020).
The Acorn Hydrogen Project will evaluate and develop an
advanced reformation process, including assessment of Johnson Matthey’s low
carbon hydrogen technology. This will deliver an energy and cost-efficient
process for hydrogen production from North Sea Gas, while capturing and
sequestering the associated CO2 emissions to prevent climate change. The
funding will enable further engineering studies (Acorn, 2020).
The HyPER project led by Cranfield University proposes to develop a low carbon bulk
hydrogen supply through pilot scale demonstration of the sorption enhanced
steam reforming process, based on a novel technology invented by the Gas
Technology Institute (GTI). This phase of the funding will enable the detailed
design and build of the system at Cranfield University (HyPER, 2020).
Hydrogen may be seen as a partial solution to the problem
of intermittency in renewable energy supply, since it can be stored, but there
is a reciprocal relationship, since many of the roles which hydrogen could play
in a low carbon economy depend on the growth of renewable energy as a way of
providing very low cost electricity in quantity for electrolysis.
References
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BEIS, 2020, Low Carbon Hydrogen Supply Competition, BEIS,
Updated 23 April 2020
https://www.gov.uk/government/publications/hydrogen-supply-competition
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