Legislative background
International agreements
In the past three decades, governments around the world have set out to decarbonise electricity and heat generation, industrial processes, and transport by moving away from fossil fuels and increasingly adopting low carbon energy sources. Decarbonisation initiatives are based on landmark international agreements like the 1997 Kyoto Protocol, or the 2015 Paris Climate Accords facilitated by the United Nations Framework Convention on Climate (UNFCC).
National legislation
Individual countries have their own climate change legislation based on the above agreements, which define the unique path a country aims to take to fulfil its climate goals. In the United Kingdom the most important piece of climate legislation is the Climate Change Act 2008, while for Northern Ireland it is the Climate Change Act (Northern Ireland) 2022. The Republic of Ireland adopted its own climate legislation in 2021, which is part of the European Climate Law. In short these laws aim to drastically reduce carbon emissions by 2030, and to balance the remaining emissions by greenhouse gas removal from the atmosphere by 2050, the latter of which is also referred to as net zero.
National strategies and schemes
In practice, the aims of these laws are going to be delivered through net zero strategies and schemes. The United Kingdom’s Net Zero Strategy published in 2021, updated in 2023, aims to fully decarbonise power generation in Great Britain. The Northern Ireland Department for the Economy’s (DfE) Climate Change Act (Northern Ireland) 2022 sets out the aim of meeting at least 80% of Northern Ireland’s electricity demand from renewable sources by 2030. The Republic of Ireland aims to achieve net zero greenhouse gas emissions by 2050; this is reflected by the 2019 Climate Action Plan. This involves ending the usage of coal and peat for power generation, increasing reliance on renewable electricity generation from 30% to 70%, and committing to a 51% reduction in greenhouse gas emissions by 2030. In addition to this, the Climate Action and Low Carbon Development (Amendment) Act 2021 commits to a 51% reduction in greenhouse gas emissions by 2030 compared to 2018.
Subsidising renewable electricity production in Great Britain currently happens though a Contracts for Difference (CfD) scheme. The scheme is made up of a series of auctions, where eligible low carbon electricity suppliers can bid for funding. Successful applicants of allocation rounds are paid a flat rate for the low carbon electricity they produce for 15 years. The rate is equal to the difference between the average market price for electricity in Great Britain, also called reference price, and what is called a strike price. When the market price for electricity is lower than the strike price, the generator receives a payment to bring revenue up to the strike price. When the market price for electricity is above the strike price, the generator pays back the difference between the two.
The Republic of Ireland subsidises low carbon electricity generation through the Renewable Electricity Support Scheme (RESS), which was designed in line with the European Union’s Clean Energy Package, carrying out the aims of the European Green Deal. The RESS is also a CfD scheme and it provides financial support for onshore wind, solar, hydro, and some biomass, biogas, and waste heat harvesting electricity projects of capacities above 0.5 MW.
Northern Ireland operated a subsidy scheme called Northern Ireland Renewables Obligation (NIRO) that was open for applications until 2017. Since the NIRO closed there has been no subsidy scheme in operation, but in line with the aims of the 2022 Energy Action Plan published by the Department for the Economy development of a potential new scheme has started. A consultation on this topic concluded in 2023, which along with internal and external research, pointed towards a CfD scheme being the most fitting for Northern Ireland.
It is also worth mentioning that both Great Britain and the Republic of Ireland subsidises microgeneration through separate schemes, which generally means low carbon energy applications below 0.5 MW. No comparable scheme is available in Northern Ireland. The Minister for the Economy noted in June 2024 that “options for microgeneration support, including domestic renewable generation, will continue to be evaluated as part of our net zero ambitions”.
Wind power
Wind power is one of the cheapest, cleanest renewable energy sources and the most abundant renewable power resource in the United Kingdom and the Republic of Ireland.
As the above map illustrates, the Republic of Ireland and the United Kingdom (and especially Northern Ireland) are some of the windiest regions of Europe. Accordingly, wind already plays a large part in generating the electricity used across the United Kingdom and the Republic of Ireland, illustrated by the below graphs.
Figure 2: Electricity generation by source in the UK
Figure 3: Electricity generation by source in Northern Ireland
Figure 4: Electricity generation by source in the Republic of Ireland
Wind is an unpredictably intermittent energy source, meaning that it is highly variable and does not follow periodic patterns. Compare this to solar energy which follows daily and yearly patterns and so is predictably intermittent. The graph on the left below shows the annual average wind speeds measured at the Lough Fea weather station, the black dots being the average, while the blue line indicates the variation in wind speed. This data showcases a near best case scenario for Northern Ireland onshore wind resource. This graph shows that the average is flat over the course of a day, but the variation is very large, so it is equally likely that the wind speed will be 2-3 m/s and 14-15 m/s at any time of the day. For reference, the minimum wind speed for generating electricity is about 4 m/s. The problem posed by this unpredictability becomes apparent when we consider the patterns in daily energy use.
The graph on the right above shows the overall energy demand versus time of day. Energy demand goes through predictable daily patterns with small variations. Because of this, large‑scale electricity production from wind turbines without energy storage could lead to reliability issues, especially when wind speeds are low, but energy demand is high. To increase the efficiency of using the available wind resource there is significant interest in coupling the increasing adoption of wind power to large-scale energy storage methods. This would mean energy harvested at any time of the day could be stored and then used at times of high energy demand.
Northern Ireland currently has a sum of 1447 MW of installed capacity for wind power, and the most important new project, North Channel Wind, aims to increase this by more than 1000 MW of off‑shore capacity. This project is part of the Department for the Economy’s Offshore Renewable Energy Action Plan.
Energy storage
Up until recent decades, large-scale energy storage was unnecessary, as fossil fuel and nuclear power plants generated the majority of most country’s electricity, and these generated a predictable output. Due to current decarbonisation initiatives, countries are moving away from fossil fuels, and the optimal usage of intermittent low carbon energy sources like wind requires large-scale energy storage methods. The remainder of this article will present an overview of the two main types of large-scale energy storage methods: mechanical and chemical.
Mechanical energy storage
The simplest grid scale energy storage methods use some kind of mechanical process to store the intermittent energy of renewables, like pumped hydro or compressed air energy storage. These methods tend to be capital intensive, have long lead times, and can only be used on a grid scale. Nonetheless, they also provide energy storage with low operational costs and a decades’ long operational life.
Pumped hydro energy storage (PHES) works by using surplus energy to pump water from a lower reservoir to a higher one, and so the water can then flow back down through turbines and generate electricity when demand is high. To enable PHES, the local geology should mainly be made up of hard rock, in order to allow for the construction of robust underground halls and tunnels. In the case of the United Kingdom, this means that the best candidates for PHES sites are in the Scottish Highlands and Snowdonia. One site was in development near Camlough, County Armagh, but this was later abandoned, some 50 years ago.
The other relevant mechanical energy storage method is the use of surplus energy to compress air, often to the point of liquefying it. The high-pressure air can then be used to drive turbines to generate electricity. In such compressed air energy storage (CAES), air is often pumped into large, airtight underground caverns, which can be created by removing most of the salt from underground deposits. This is quite relevant for Northern Ireland because the coast of Belfast Lough and the wider Lagan Valley are rich in deep salt deposits[1].
There are additional deep salt deposits under Larne Lough in County Antrim, which have been deemed suitable for gas storage and because of this there has been a lot of interest in the development of these sites. Most recently, Islandmagee Energy announced plans to develop a natural gas storage site under Larne Lough. This project has since been challenged on environmental and legal grounds. An environmental campaign group, won a legal bid against Islandmagee Energy, claiming the marine construction licence was given in error. This means it is uncertain if construction can ever begin on this project, and these events might have an impact on the development of this site for storage of other gases like compressed air.
Chemical energy storage
Chemical energy storage refers to methods where electricity is used to bring about a lasting chemical change, like producing a molecule or charging a battery. Strictly speaking, chemical energy storage is used to mean the production of hydrogen, but other molecules can be produced through subsequent processes, like ammonia, methane or methanol. All of these materials can be used as either fuels or industrial resources.
Hydrogen
Hydrogen is a very important resource and energy carrier of global heavy industries. Its use as a fuel is most common in fuel cells of electric vehicles, which combine hydrogen and oxygen to generate an electric current.
There are several ways of producing hydrogen with varying amounts of associated emissions. This article will only discuss the lowest emissions scenario, which is hydrogen produced from splitting water into hydrogen and oxygen using electricity. This is also called green hydrogen.
The production of green hydrogen is a promising energy storage method as the intermittent energy from renewables could be used to generate hydrogen in an environmentally friendly way. It should be noted, that for maximum efficiency the oxygen generated from water splitting should be used as well.
There are a number of initiatives in Northern Ireland and the wider United Kingdom connected to hydrogen in various stages of development. Northern Ireland Water plans to build a 1 MW electrolyser, which would produce hydrogen to be used as a fuel and oxygen to be used in water treatment. Translink has introduced over 100 zero emission buses to its fleet, 23 of these being hydrogen fuel cell electric vehicles. There is also a large proposed development for the Kilroot power station which includes hydrogen generation.
Battery energy storage
Storing energy in industrial capacity battery farms can be achieved by storing energy at times of high renewable energy production, but low overall energy demand, and then using it at times of high overall energy demand. The batteries used in such energy storage can be dedicated stationary battery farms, or the batteries of electric vehicles, the latter of which is often referred to as vehicle to grid energy storage.
Stationary battery energy storage
The most important established battery chemistries are lead-acid and lithium ion batteries, but there are some emerging technologies worth mentioning as well. A battery’s chemistry defines technical parameters, like energy and power output, maximum capacity, maximum number of charge-discharge cycles, and durability and safety. By extension, battery chemistry also defines economic parameters like costs and reliability of production and cost of operation.
Lead‑acid batteries are a simple, relatively cheap and well-established energy storage method. Their robust battery chemistry allows for long-term energy storage with minimal long-term loss of charge. On the other hand lead‑acid batteries also tend to have much lower energy densities on both volume and mass bases than most other established battery types. This means that for any given capacity, lead-acid batteries will usually be larger and heavier than other battery types.
Lithium ion batteries (LIBs) are one of the most common battery types that have become widely used in almost all areas of life. LIBs offer the highest energy density both in terms of volume and mass, for any rechargeable battery type, but are also relatively expensive. Additionally, the most common cathode material used in LIBs contains nickel and cobalt, which along with lithium, come with significant ethical and supply chain issues. While it is possible to construct LIBs without nickel and cobalt this generally leads to worse performance and lithium would still pose the same problems. Another disadvantage of LIBs is that they can only be safely stored and transported while partially charged, and charging below 0 °C can be very slow and lead to permanent damage.
There are a few operational large-scale battery energy storage sites in Northern Ireland. For example, Northern Ireland Water has a 4.1 MW battery storage site at Dunore Point, which stores energy from the onsite solar farm, and another similar solar powered battery storage at the Ballykelly Wastewater Treatment Works.
Electric vehicles as a means of energy storage
The average car spends the vast majority of its time being parked somewhere; it is only used about 4% of the time. It makes sense then to think of electronic vehicles (EV) as a fleet of small-scale battery storage sites through which higher efficiency utilisation of renewables can be achieved while they also serve their primary function. This can be done by encouraging owners to recharge their batteries at times of high renewable production and low overall energy demand or even to sell energy to the grid at times of low EV usage and high overall energy demand.
According to a 2022 United Kingdom Government Department for Transport statistical dataset, the current average battery capacity is 50 kWh, which means that the entire EV stock of about 23000 in Northern Ireland has an approximate combined capacity of about 1 GWh. For reference, 1 GWh would be enough to power all of Northern Ireland for an hour at an average energy demand at the 17:30 peak, so the current EV stock is already significant on a regional scale. According to an Energy Systems Catapult report, most of the value offered by using electric vehicles as energy storage can be utilised by keeping EVs plugged in as much as possible and also by charging them at times of high renewable production and low overall electricity demand.
Conclusion
In the past decades the government of the United Kingdom, the Northern Ireland Executive and the government of the Republic of Ireland have all ratified landmark international climate change agreements. As a result all three jurisdictions implemented national strategies and schemes that aim to fulfil the goals set out in these agreements. Wind is an abundant resource in both the United Kingdom and the Republic of Ireland, and as such decarbonisation is expected to strongly rely on it. It is worth noting though, that wind is an intermittent energy source, so it is often coupled to energy storage methods like pumped hydro, stationary battery farms or even electric vehicles in order to enhance the efficiency of its use.
Further reading
Research and Information Service: Large-scale energy storage methods for wind energy (2024)
Research and Information Service: Topical Digest: Large-scale energy storage methods for wind energy (2025)
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[1] H. Blanco et al. A review at the role of storage in energy systems with a focus on Power to Gas and long-term storage. Renewable and Sustainable Energy Reviews 81 (2018) 1049–1086, Appendix C
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