Renewable energy is starting to make a significant impact on the way we create, transfer and consume energy and the possibilities for the future look like they have only just begun to present themselves. As the world starts to narrow in on the final objective of zero carbon emissions across every sector, and in every country, engineers and scientists are starting to develop a tangible motivation to overcome the technological constraints that currently limit our ability to reduce overall emissions, and to allow an orderly transition away from fossil energy. The realisation that fossil fuels play an integral role in the fabric of modern society presents obvious difficulties for a complete transition to renewable energy. For this reason, much thought has been invested in what alternatives may exist in the place of niche markets in transport, heating, fertilizer, plastics and heavy industies which all heavily depend on refined oil or natural gas, and have been found to be increasingly difficult to replace effectively with renewable alternatives.
As well as this numerous barriers exist both in the production and consumption of energy, and the transfer and storage of energy which require considerable changes to maintain effective operation within our current energy system. Given this set of problems; finding a single, base solution remains the ultimate objective: and it looks like we are now closer than ever to this goal.
Hydrogen produced via the electrolysis of water is an emerging technology which ticks all the boxes required of a zero-carbon energy medium and recent developments are gathering momentum as the need for fossil fuel substitutes increases. Ninety percent of hydrogen today is produced using steam reforming where 25% of the embodied energy of the fuel is used to extract hydrogen from gas oil or coal. Given the traditionally low price of fossil fuels, this is the dominant method of production in a global hydrogen industry producing 58 million tons of hydrogen per year for a range of niche markets such as the chemical industry, fertilizers and manufacturing. Further methods of hydrogen production use feedstocks such as biogas and bio-SNG (synthetic natural gas) produced from municiple solid waste as well as a variety of other sources. However, very little of this hydrogen is used to produce energy, and the market for hydrogen has not seen a signficant demand for growth, as current production volumes remain sufficient.
The need to store energy from excess renewable electricity production is starting to provide the opportunity for the growth of a completely new industry that converts this energy to gas, and stores it in large amounts for extended durations for later use in all the use cases where it may be impossible to completely replace fossil energy with electricity – with the vital addition of a newly discovered characteristic: the ability to reverse the flow of hydrogen through an electrolyser.
The first enabler of the power-to-gas process is the low or negative cost of electricity during periods of low demand when plants cannot ramp down energy output, or they are needed to provide heat within district heat networks. The need to utilise excess energy produced by renewables grows markedly as the share of renewable energy surpasses 20%, which provides a strong motivation to transfer this energy to the storage medium of hydrogen, which can later be converted to SNG for widespread use or as has been recently discovered; used directly as a fuel within the electrolyser to return electricity to the grid.
Synthetic natural gas
One motivation to convert electricity to SNG is the artificially low cost of natural gas. If this cost more accurately reflected the true cost of extraction and delivery, we would remove subsidies for gas which are often much higher than for electricity. This means that with a power-to-gas efficiency of approximately 65%, the cost of artificially produced gas could end up being much closer to the real cost of natural gas. Including historical subsidies, the cost of artificially produced gas is likely to be lower than conventional NG.
The advantages of decarbonising the existing natural gas network using SNG are obvious, as no major disruption to infrastructure or appliances is necessary, and in combination with biogas products, an incremental transition is relatively straightforward. Such thinking is also very much the topic of the moment among fossil fuel executives who recently met at the Gas Meets Wind North Sea Energy Symposium to discuss the innovative use of electrolysers to produce hydrogen offshore using disused gas platforms, distributed via existing gas pipelines. Such a scenario could give a new lease of life to an industry faced with both dwindling reserves and enevitable regulatory issues surrounding carbon emissions management.
Because hydrogen via electrolysis is still an expensive option despite better exploitation of low or negative prices – even where renewables providers may recieve capacity payments when they are unable to distribute generated electricity – further incentives may need to be presented to enable a more speedy transition away from carbon-intensive technologies. However, given the flexibility of hydrogen, many such incentives for switching to hydrogen exist.
The fact that modern plastic gas pipelines can carry hydrogen; as well as the relative ease of upgrading steel pipelines to plastic, means that hydrogen is well placed to provide a substitute for conventional gas boilers and gas cookers. The recent H21 Leeds City Gate report explains that in areas where the pipeline has been upgraded, it will be very easy to switch to hydrogen as:
– The gas network has the correct capacity for such a conversion
– It can be converted incrementally with minimal disruption to customers
– Minimal energy infrastructure will be required compared to alternatives (grid capacity)
– The existing heat demand for Leeds can be met via steam methane reforming and salt cavern storage using technology in use around the world today
The report focuses on the production of hydrogen via steam methane reforming utilising natural gas and CCS , although this could at some later date be swopped for hydrogen generated via electrolysis providing a 100% renewable and locally produced energy source.
The fact that heating carries a large seasonal demand for energy means that converting to a carbon neutral energy system 100% dependent on electricity would mean at least a doubling in the size of capacity just to cope with a few days of low temperatures. Given these facts, hydrogen appears to be a much cheaper option than many other alternatives, although district heating, biogas/SNG and other technologies are also likely to play a significant role in overall decarbonisation efforts.
Electrolysers for grid services to balance load
The power to gas industry is just starting to take advantage of excess electricity supply created by an increasing share of variable renewables output that cannot be stored and is therefore wasted at cost. Where P2G has until recently focused on remote locations that require hydrogen or SNG, the evolution of energy markets to more accurately balance supply and demand using storage; as well as the need to reduce carbon emissions; has led to an increasing interest in battery storage and power-to-gas. The ongoing development of a 100% renewable hydrogen production industry has also recently been strengthened by the announcement of a new set of EU directives to more easily allow the integration of power-to-gas plants and electrolyser-hydrogen refueling stations to sell stored energy to the electricity market, as well as the sale of hydrogen to the transport and gas sectors. This is immanently possible because the electrolyser stack works as a fuel cell in reverse, with the hydrogen being converted back into electricity. This skips the SNG-conversion stage, which offers much higher overall efficiencys as the 20% single-step efficiency loss is reduced.
Growth of the power-to-gas market
While 100 MW electrolyser configurations are due to be made available commercially this year from ITM and in 2018 from Siemens, smaller scale projects such as the 6 MW H2Future electrolyser power plant in Austria have already started to investigate the potential for electrolysers to provide hydrogen for the steel industry, as well as providing grid-balancing services to the electricity grid to improve overall cost effectiveness. As the project description explains; the overall findings will then go on to inform decisions made regarding larger production units around the EU27 in the steel and fertilizer industry.
Fuel cells and transport
The most visable use of hydrogen in the near term is likely to be as transport fuel in fuel cell vehicles, which are slowly beginning to arrive in showrooms around the world. Fuel cell vehicles have all the advantages of electric operation; while being faster to refuel, no plugs and wires for busy urban dwellers, greater range potential and a higher energy-to-weight ratio which translates as a cost saving. Renewably produced hydrogen as a fuel is also much cheaper than petrol per kilometer due to current fuel cell efficiencys; and these efficiencys are likely to increase. However, investments are needed to increase the number of electrolyser-hydrogen refueling stations (HRS) and hydrogen pumps, as well as incentives for buyers, if the number of hydrogen fueled vehicles is likely to increase.
The outlook for hydrogen
It is becoming inevitable that hydrogen will eventually represent the core component of a fully decarbonised modern energy system. While alternatives exist for many fossil energy use cases, significant inconsistancies appear where no realistic substitute exists to replace hydrocarbons, and many policymakers are starting to see CCS and even unproven negative emissions as the only other possible answer. Given that these technologies have not yet progressed beyond pilot stage, carrying such large risks may not continue to be feasible.
The hydrogen economy is a necessity, not an aspiration. Accepting the profound opportunity that hydrogen represents or relegating the industry to bit-part player is likely to decide the success of the energy transition, and with it our ability to limit global temperature increase.