Sustainability and longevity of existing gas grid exploitation perspective are closely related to two fundamental issues: their ability to adopt to changing gas fuel production and supply landscape in the context of methane-based fuels, mostly, biomethane, and in the context of non-methane-based fuels, mostly, low carbon and green hydrogen. Renewable gases and their ever-growing presence in gas transmission and distribution systems open up a discussion about the necessity to revise and restructure the original - vertically integrated layout of the gas systems, where gas supply is only technically possible from the transmission system towards distribution one, and not vice versa. Development of numerous decentralized biomethane production facilities connected to the gas distribution system causes a necessity to ensure the possibility to pass biomethane surplus of a certain production area into the gas transmission grid, thus avoiding necessity to install biomethane storage capacities locally and granting other regions an opportunity to use said surplus in their gas consumption immediately. The article addresses biomethane production trends and actions taken towards the development of reverse flow gas stations in France - one of biggest biomethane producers in Europe to date, and opportunities and challenges, which this technique might face in smaller and less active renewable gas markets as the one of Latvia.

Abstract The existing European Union (EU) natural gas network provides large capacity to integrate renewable (RGs) and low-carbon gases. Today, hydrogen contributes only a few percent to Europe’s energy consumption and is almost exclusively produced from fossil fuels and used in the industry. Nevertheless, hydrogen has a significant role to play in emission reduction in hard-to-decarbonize sectors, in particular, as a fuel in transport applications and as a fuel or feedstock in certain industrial processes (steel, refining or chemical industries, the production of “green fertilizers”). Carbon dioxide (CO2) in reaction with hydrogen can also be further processed into synthetic fuels, such as synthetic kerosene in aviation. In addition, hydrogen brings other environmental co-benefits when used as fuel, such as the lack of air pollutant emissions. However, in transitional phase from fossil to RG, namely, renewable or green hydrogen, natural gas/biomethane and hydrogen blends, are needed to gradually replace natural in existing gas transmission and distribution networks. The gas networks are believed to be able to use natural gas/biomethane and hydrogen blends with 5–20 % of hydrogen by volume. Most systems and applications are able to handle it without a need for major infrastructure upgrades or end-use appliance retrofits or replacements. The promotion of hydrogen network such as European Hydrogen backbone (EHB) is gaining momentum in Europe. To decarbonize the natural gas grids, the threshold of hydrogen in the existing grid systems must be increased, which can be done by means of wider natural gas/biomethane and hydrogen blending and simultaneous transportation in currently operational gas networks.

Hydrogen has been widely recognised as a versatile and environmentally-friendly energy carrier, with a broad range of potential applications across various sectors. The abundance of hydrogen in the universe and its high energy content makes it an attractive alternative to conventional fossil fuels. Moreover, the utilization of hydrogen does not produce greenhouse gases or other pollutants that contribute to air pollution and climate change. In recent years, there has been a growing interest in developing and deploying hydrogen technologies for a sustainable energy future. This paper provides an in-depth exploration of the potential of hydrogen as a clean energy source in different sectors, such as transportation, energy storage, power generation, industry, buildings, maritime transport, and aviation. The aim of the paper is to provide an overview of the current state of hydrogen applications in Europe and the Baltic States, including examples of ongoing projects and initiatives, and to assess the advantages and disadvantages of hydrogen technologies in different sectors. The main results of the paper highlight that hydrogen has the potential to significantly reduce greenhouse gas emissions and achieve carbon neutrality targets. However, the deployment of hydrogen technologies also faces various challenges such as high production costs, lack of infrastructure, and safety concerns. The tasks of the paper are to provide an insight into the potential of hydrogen, identify the challenges and limitations, and highlight ongoing research and development efforts in this field. The paper concludes that the widespread adoption of hydrogen technologies is a long-term goal that requires the cooperation of various stakeholders and the development of innovative and cost-effective solutions. Despite the challenges, the current state of hydrogen applications and ongoing projects in Europe and the Baltic States demonstrate that hydrogen has the potential to play a significant role in the transition to a sustainable and low-carbon future.

Abstract The future of the European Union’s (EU) gas sector and gas distribution systems in particular is under review as a necessity to move away from conventional natural gas is strictly outlined in its strategical energy framework. The main questions of future gas sector layout are largely related to gas decarbonization paths – whether they will include simultaneous transportation, distribution and storage of methane-based and non-methane based renewable gases or not. In general, this question is left for different Member States to decide, because as alternatives to it there are two options – decommissioning of all gas distribution and partially gas transportation and storage systems on the one hand and total replacement of existing gas transportation system with brand new hydrogen transportation and distribution system on the other. The first option leaves only liquified renewable gases (including, hydrogen) that are transported via truck and the second – pipeline transportation and distribution only for hydrogen, limiting methane-based renewable gases to road transportation solutions only. The Latvian gas distribution system is also facing imminent transformation in foreseeable future; thus, at the moment its sustainability priority is the maintenance of the existing system in a safe and secure manner by improving it in accordance with technical necessities and immediate customer requests. The current research shows two sides of gas distribution system priorities in Latvia – its maintenance and development trends prior to fundamental transformations of gaseous fuel transition and general transitional challenges laying ahead.

Abstract Natural gas is relatively clean energy source, which emits less greenhouse gases (hereinafter – GHG), compared to other fossil fuels, such as hard and brown coal, and therefore it may be the most feasible resource to ensure smooth energy transition towards Europe’s climate neutrality by 2050. Traditional natural gas can be easily transported and used in liquefied (hereinafter – LNG) or compressed form. As for biomethane, in future it also can be used in liquefied (hereinafter – bioLNG) and compressed form, as well as transported by means of the current natural gas infrastructure. It can also significantly enhance regional and national energy security and independence, which has been challenging for the European Union (hereinafter – EU) over at least several decades. Issue on energy independence, security of supply, alternative natural gas sources has been in a hotspot of the Baltic energy policy makers as well. Now, considering Russia’s invasion in Ukraine, since late February 2022, a problem of the EU natural gas dependency on the Russian Federation has escalated again and with force never before experienced. The European natural gas prices also hit records, as the natural gas prices in the Netherlands Title Transfer Facility reached 345 euros per megawatt-hour (hereinafter – EUR/MWh) in March 2022. Therefore, LNG import terminal is the only viable option to reduce national dependency of the so-called pipe gas which in some cases, due to the insufficient interconnections, may be delivered from very limited number of sources. The European policy makers and relevant institutions are currently working towards radical EU natural gas supply diversification, where LNG deliveries coming from outside of Russia will certainly take a central stage. In case of Latvia, the potential benefits of the LNG terminal development in Skulte were evaluated in order to reduce energy independence of the Russian natural gas deliveries in the Baltic region and to introduce new ways and sources of the natural gas flows to the Baltics. LNG terminal in Skulte could ensure significant capital investment cost reduction comparing to other projects proposed for Latvia in different periods, due to already existing natural gas transmission infrastructure and the relative closeness to the Incukalns underground gas storage (hereinafter – UGS). Various aspects, such as technical, political and economic ones, were analysed to assure that Skulte LNG terminal would be a real asset not only to customers of Latvia, but also to those of the whole Baltic region, where in future it would be possible to use biomethane for efficient utilisation of existing and developing natural gas infrastructure.

Abstract Hydrogen is the most abundant chemical element on the Earth, and it has really a wide variety of applications, starting from use in refining, petrochemical industry, steel manufacturing, and ending with use in energy production and renewable gas (hereinafter – RG) blending for gradual replacement of natural gas in all sectors of the national economy. Being practically emission-free, if produced in sustainable way or from renewable energy sources (hereinafter – RES), hydrogen is regarded as one of the most promising energy sources for decarbonisation of practically the entire segment of industrial and energy production. Growing pressure of the European climate neutrality targets has triggered special interest in production, use, storage and transportation of hydrogen – especially the green one, which can be used in at least four fundamental ways: as a basic material, a fuel, an energy carrier and an energy storage medium. In the context of sector coupling, however, hydrogen facilitates decarbonisation of those industrial processes and economic sectors in which carbon dioxide (hereinafter – CO2) emissions can either not be reduced by electrification or this reduction would be minimal and linked to very high implementation costs. At the same time, development of an extensive hydrogen economy is the key to the achievement of the European climate protection targets, with the European Commission’s (hereinafter – EC) Hydrogen Strategy, a framework created in 2020 to develop and promote sustainable hydrogen economy in the European Union (hereinafter – EU), in its centre. Green hydrogen also will take its legitimate place in the gaseous fuel diversification risk management strategy, as this gaseous fuel is not only one of the most perspective future energy sources, but also one of the most volatile and demanding sources. In the process of gaseous fuel diversification in the EU and worldwide, new logistical chains and supply – demand networks of green hydrogen will emerge. Therefore, adequate addressing of potential challenges of this new regional and global production, delivery and consumption framework will be of utmost importance for secure, safe and predictable functioning of future energy systems.

Hydrogen is regarded as one of the best solutions for energy storage, especially, for energy coming from variable renewable energy sources, which currently lack large-scale cost-effective and universally approved storage solutions. Electricity production from renewable energy sources can be rather unstable, as it is governed by ever changing weather patterns. These changes, however, can result in shortages of energy production, in particular, for regions, where renewable energy sources form considerable share of all electricity generation capacity. In such regions, hydrogen combined with large-scale underground storage can be a key for stable and timely energy deliveries, as well as balancing out the impacts of variable renewable energy sources. Apart from hydrogen storage in existing natural gas grids and on-ground storage facilities, there are three general options for hydrogen underground storages in future, and all of them coincide with options available for the natural gas storage today. This article overviews hydrogen underground storage options theoretically available in the EU and worldwide, bring forward a few challenging points in hydrogen underground storage development, and outlines the Latvian underground hydrogen storage potential. Economic feasibility studies and technical evaluation is planned to be carried out in the following researches.

Abstract In Latvia, heat supply is provided in three different ways: using district heating (hereinafter – DH), local heating and individual heating systems. Heat energy consumption consists of heat energy consumption for heating, hot water and heat energy technological processes. The structure of DH consumers has not changed in recent years and the largest consumers of heat are households – 70 % of the total energy consumption. The district heating system accounts for approximately 29 % of the total consumption. There is also the so-called tertiary sector, which is made of municipal and state buildings with a minor total heat consumption of about 1 %. It should be noted that 65–70 % of energy is used for heating needs, and 30–35% for hot water preparation. In Latvia, heat of DH consumers is produced both in boiler houses (hereinafter – BHs) and cogeneration plants (hereinafter – CHPs). The latter also produce electricity. Over the past 10 years, the distribution of heat produced in BHs and CHPs has changed significantly. The heat supply of the Latvian energy sector is a system consisting of three main elements – heat source, transmission and distribution networks, and end consumer. Low efficiency of heat supply system elements creates risks to security of heat supply, resource sustainability and competitiveness. Increasing energy efficiency in the system as a whole, or in individual elements of the system, will promote the enhancement of the heat supply sector, while promoting economic growth as well. The research attempts to evaluate the energy efficiency of DH systems in the so-called left bank (hereinafter – LB) DH area (located on the left bank of the Daugava River in Riga).

Abstract A common natural gas market in the Baltic region, which is in operation since 1 January 2020, means a single entry–exit tariff system for the natural gas transmission among Finland, Estonia, Latvia, and a common Latvian–Estonian balancing zone. Finland joined the market with a separate balancing zone, certain rules, contracts, invoices and billing, with a decision for full integration to be taken not earlier than in 2022. Lithuania is not currently the common market participant, because it is not ready to join it with such revenue splitting conditions as Finland, Estonia and Latvia. But still common entry–exit tariff zone countries are actively working to find a viable solution for market expansion. Lithuania and other neighbouring Member States of the European Union (hereinafter – the EU), first and foremost, Poland, are welcome to join. The creation of an integrated regional natural gas market in the Baltics in the long term will stimulate the interest of traders in the region, strengthen security of supply and improve market liquidity. Increased market competition, predictable prices in the long term, transparent tariffs, digital communication and customer-oriented business strategies are just a small part of benefits that will inevitably develop with time.

Abstract Considering the changes of gas transmission system (hereinafter – GTS) brought about by diversification of gas suppliers, new interconnections with European GTS and implementation of an open electricity market and then an open gas market, a steady-state GTS modelling tool has been developed for future implementation in the risk and resilience analysis and potentially operational planning for different GTS or other purposes. The developed method combines the linearized hydraulic conductivity approach with a technique, derived from a linear electrical circuit analysis and an additional pressure change term for modelling of active non-pipeline elements of GTS. This method also takes into consideration operational limits of compressors and pressure regulators and changes in compressibility factor and gas viscosity based on the gas composition, temperature and pressure. The paper includes part of the results obtained from a validation case study performed for the presented method.

Abstract Despite various benefits that the natural gas mobility can provide, CNG (hereinafter – compressed natural gas) and LNG (hereinafter – liquified natural gas) filling infrastructure both in Latvia and the Baltic States as a whole is still at the stage of active development. As a result, the natural gas fuelled vehicle fleet comprises less than 1 % of all registered road vehicles in the Baltics, but, with regards to transport and climate policies of the European Union (hereinafter – the EU), it has a significant potential for further growth. In order to estimate the perspectives of mobility of natural gas, including bioCNG and liquified biomethane (hereinafter – LBM), CNG has been chosen and analysed as a possible alternative fuel in Latvia with its environmental and economic benefits and payback distance for CNG vehicles compared to petrol and diesel cars. The review of various types of CNG filling stations is also presented, along with information on operating tax rates and currently registered vehicles divided by types of fuel in Latvia. It was established that with the Latvian fuel price reference of the late 2020, exploitation of CNG-powered vehicle was by 24 % cheaper per kilometre in comparison with diesel and by 66 % cheaper in comparison with petrol vehicles. CNG vehicles have smaller operational taxes, since they are based on carbon dioxide (hereinafter – CO) emissions, which are lower for CNG-powered vehicles. Calculation results also indicate that CNG vehicle payback time may fall within the warrant period, if at least 57650 kilometres as an alternative to a petrol vehicle or 71 531 kilometres as an alternative to a diesel vehicle are driven by it.

Abstract In the early 2010s, only 23 countries had access to the liquefied natural gas (hereinafter – LNG). Import terminals, despite attractive short-term economics, took long time to build, and rigid supply contracts made truly global use of LNG rather complicated. Concerns about geo-political risks also stunted demand growth from existing supply sources, even when new LNG export routes and sources became available. Current natural gas market is very different, both in terms of market participants and accessibility and diversity of services. In 2019, the number of LNG importing countries reached 43. Rising competition among suppliers and increasing liquidity of markets themselves created favourable conditions to diversify contract duration, size, and flexibility. In addition, development of floating storage and regasification unit (hereinafter – FSRU) technology provided LNG suppliers with a quick response option to sudden demand fluctuations in regional and local natural gas markets [1]. Moreover, LNG is one of the major options not only for bringing the natural gas to regions where its pipeline supply infrastructure is historically absent, limited or underdeveloped, but also for diversification of the natural gas supply routes and sources in regions with sufficient state of pipeline delivery possibilities. And it concerns smaller natural gas markets, like the Baltic States and Finland as well. Accordingly, prospects for use of LNG there in both mid and long-term perspective must be carefully evaluated, especially in regards to emerging bunkering business in the Baltic Sea aquatory and energy transition in Finland, replacing coal base-load generation with other, more sustainable and environmentally friendly alternatives.

Abstract Natural gas is an essential element of the Latvian and the Baltic energy portfolio, so its supply disruption can seriously affect the national economy and energy security of our country. The article focuses on a basic case study of the natural gas supply to one of the Latvian municipalities, when the energy crisis is announced. It also marks potential vulnerabilities factors that may cause the natural gas supply shortages or disruption periods of different length for a wide spectrum of the Latvian natural gas consumers – starting with households and finishing with large industrial consumers and energy producers. A legal framework analysis along with an emergency natural gas supply review has been proposed as well, taking into account the actual distribution of the natural gas consumption among the urban energy users, which can be compared with references included into the Cabinet of Ministers Regulation No. 312 “Procedures for the Supply of Energy Users and Sale of Heating Fuel during Declared Energy Crisis and in Case of Endangerment to the State” (hereinafter – Regulation 312).

The European Union (hereafter - the EU) takes a strong position in the global fight against climate changes by setting ambitious targets on reduction of greenhouse gas (hereafter - GHG) emissions. A binding target is to reduce those emissions by at least 40 % below 1990 levels till 2030, which would help make Europe the first climate neutral continent by the mid-21st century. Consequently, the expected 2050 emission reduction target for the EU is 80 %-90 % below 1990 levels. The EU's new economy decarbonisation framework - The European Green Deal - outlines and summarises Europe's ambition to become a world's first climate neutral continent by 2050. This supposedly can be achieved by turning climate and environmental challenges into opportunities across all policy areas and making the energy transition just and inclusive for all. The transport, and particularly road transport, is one of the most significant fossil fuel dependent segments of national economies across the EU. Oil dependency of all segments of the transport sector makes it the single biggest source of GHG emissions in the united Europe as well. Road transport is responsible for about 73 % of total transport GHG emissions, as Europe's more than 308.3 million road vehicles are over 90 % reliant on conventional types of oil-based fuels (diesel, gasoline etc.). However, there is a wide range of low-emission alternative fuels for all kinds of transport that can reduce overall oil dependence of the EU's transport sector and significantly lower GHG in road transport. Among these alternatives a tandem of the natural gas and biomethane could be named as one of the most promising for short and mid-term transport decarbonisation solutions both in the EU and Latvia.

Abstract The successful implementation of smart metering in the European Union (hereinafter – EU) depends on criteria that are mostly determined by the Member States themselves. These criteria cover the regulatory framework and legislation necessary for the establishment and functioning of the smart metering system, the fulfilment of technical and commercial conditions, as well as the security of data collection, archiving and use. The introduction of the smart metering in different Member States has started at different times. In Latvia, its reference point was 2004, when the goal was set to maximise the use of telemetry in the natural gas metering. Currently, in the Latvian natural gas distribution system about 85 % of all consumption data are automatically processed. One of the most important components of the smart natural gas metering is natural gas commercial metering devices (hereinafter – smart meters). They differ in both the principle and type of operation. Depending on the technology used, the metering range changes, and thus the accuracy of the measurements. The article addresses some issues of further successful implementation of smart metering in the Latvian natural gas sector, as well as the measurement accuracy for smart natural gas meters.

Abstract A necessity to reduce greenhouse gas (hereinafter – GHG) emissions and energy import dependency, while coping with increasing energy demand, affordability issues and many other factors, causes the European Union (hereinafter – EU) energy policy makers to identify development trends that would help harmonize future energy market and technological changes with ever growing pressure of universal data processing digitalisation. In order to stimulate data processing digitalisation in energy, the European Commission has proclaimed a support to the development of all kind of the smart energy systems, where simultaneous use of the natural gas and renewable gases (hereinafter – RG) will play one of the major sustainability ensuring roles. Firstly, it will help achieve designated energy efficiency goals and, secondly, enable cost saving synergetic solutions at the early stages of the energy supply chain decarbonisation. Synergy of the natural gas and RG emphasises the need for a modern, smart and sustainable energy infrastructure to allow developing more flexible back-up and balancing power capacity, storage solutions and innovative demand-response mechanisms. This paper addresses some trends in development of the smart gas distribution (hereinafter – SGD) as part of the smart energy systems both in the EU and Latvia, with a particular focus on smart energy concepts, smart gas metering and grid modernisation.

Abstract Biomethane is one of the most promising renewable gases (hereafter – RG) – a flexible and easily storable fuel, and, when used along with the natural gas in any mixing proportion, no adjustments on equipment designed to use natural gas are required. In regions where natural gas grids already exist, there is a system suitable for distribution of the biomethane as well. Moreover, improving energy efficiency and sustainability of the gas infrastructure, it can be used as total substitute for natural gas. Since it has the same chemical properties as natural gas, with methane content level greater than 96 %, biomethane is suitable both for heat and electricity generation, and the use in transport. Biomethane is injected into the natural gas networks of many Member States of the European Union (hereafter – the EU) on a regular basis for more than a decade, with the Netherlands, Germany, Austria, Sweden and France being among pioneers in this field. In most early cases, permission to inject biomethane into the natural gas grids came as part of a policy to decarbonize the road transport sector and was granted on a case-by-case basis. The intention to legally frame and standardise the EU’s biomethane injection into the natural gas networks came much later and was fulfilled in the second half of the present decade. This paper addresses the biomethane injection into the natural gas grids in some EU countries, highlights a few crucial aspects in this process, including but not limited to trends in standardisation and legal framework, injection conditions and pressure levels, as well as centralised biogas feedstock collection points and the biomethane injection facilities. In a wider context, the paper deals with the role of biomethane in the EU energy transition and further use of the existing natural gas networks.

Currently, problems related to the operation and exploitation of safe gas distribution networks are deepening in Latvia and Eastern Europe, as the number of outworn underground gas pipelines is steadily increasing. It should be noted that there is a rather wide choice of technology and materials for gas distribution pipeline reconstruction, while at the same time there is no universal method that equally meets all possible work requirements. Therefore, it is an urgent task to understand the operational algorithm, while choosing optimal reconstruction option. classifying and determining the criteria affecting the choice, and determining the scope of each reconstruction method. For this reason, it is necessary to develop a scientifically based methodology for selecting the optimal method for the reconstruction of outworn gas distribution pipelines. Therefore, there are the following tasks that need to be accomplished: to carry out a complex analysis of reconstruction methods and factors determining the choice of an optimal gas distribution pipeline reconstruction method as well as perform the analysis of current state and development of gas supply network; to develop an algorithm for selecting an optimal gas distribution pipeline reconstruction method based on a multi-criteria approach; to develop a mathematical model for the selection of an optimal reconstruction method and scientifically based complex evaluation procedures taking into account technical and economic criteria; to analyse the interaction of the polyethylene gas pipeline with the steel frame during the post-reconstruction process using U-shaped pipe; to develop recommendations for the optimisation of gas distribution network reconstruction programmes. As a result of these tasks, a scientifically justified methodology for the selection of an optimal method for the reconstruction of the gas distribution pipes has been developed.

The Latvian natural gas system is interconnected with transmission networks located in Lithuania. Estonia and Russia Natural gas commercial metering is provided by GMS "Karksi" (Estonia) and by GMS "Kiemenai" (Lithuania). Natural gas is supplied to all larger urban areas in Latvia. Natural gas is supplied to Latvia along the Latvian-Russian pipeline only during the warm period of the year (April-September). and it is accumulated in the underground gas storage facility in Incukalns. During winter, gas from the underground facility is delivered to Latvian customers, as well as transmitted to Estonia and back to Russia There is also a connection to Lithuania. Out of the gas supply disruption risks that are assessed at different levels, the essential one with a trans-border impact potential consists in the insufficient technical capacity of Incukalns UGS. Given the current technical possibilities, IUGS cannot pass the gas volume required for the Baltic States to compensate the gas supply deficit. The paper performs system recovery analysis after selected critical events. The paper provides a report describing the steps to be followed in order to restore the gas transmission system to normal operation after selected critical events. Avery significant region of the power system of Latvia is the central part of Latvia and Riga region, where both of Riga CHPs, as well as Riga HPP, is located. The restoration time of the gas system of Latvia depends on the gravity of the situation and damage in the gas system and may range from several hours to several days.

In the present research, the main critical points of gas transmission and storage system of Latvia have been determined to ensure secure and reliable gas supply among the Baltic States to fulfil the core objectives of the EU energy policies. Technical data of critical points of the gas transmission and storage system of Latvia have been collected and analysed with the SWOT method and solutions have been provided to increase the reliability of the regional natural gas system.