Power to gas and H₂/NG blend in SMART energy networks concept

• The impact of hydrogen on existing natural gas grid is discussed.

• The importance of power-to-gas technology for energy storage is discussed.

• The effect of H2/NG blends on the end-use equipment's performances is reviewed.

Abstract

In the last decade energy security and supply has become one of the main priorities for governments around the world. Energy sources diversification, proper mix of energy generation capacities and large penetration of renewables are crucial to achieve a sustainable energy future. Smart Energy Networks (SENs) is a new concept that will allow the integration of various energy networks including electricity, gas and heat into one network under common Information and Communications Technology (ICT) to allow better management, efficient utilization and increased participation of distributed generation and renewables. In order to bridge the networks, appropriate technologies have to be applied that will allow the energy vectors to interface and share the load. One such technology is Power to Gas utilizing the excess electricity on the grid to generate hydrogen. Hydrogen then either injected in the gas pipeline/storage or used to synthesize a renewable natural gas through methanation.

Introduction

In the last decade the energy security and supply has become one of the main priorities for governments around the world. Energy sources diversification, proper mix of energy generation capacities and large penetration of renewables have become crucial to achieve a sustainable energy future. Smart Energy Networks (SENs) is a new concept that will allow the integration of various energy networks including electricity, gas and heat into one network under common ICT to allow better management, efficient utilization and increased participation of distributed generation and renewables. In order to bridge the networks, appropriate technologies have to be applied that will allow the energy vectors to interface and share the load. There are various forms of renewable and non-renewable energy sources. Each has its own drawbacks. Non-renewable energy sources are pollutants and their amount is limited; renewable energy sources (RES) such as solar and wind are intermittent, weather dependent and expensive; geothermal energy is location specific and can cause surface instability. However, the presence of RES on the grid often leads to a surplus of electricity, especially in cases when the energy demand is low in comparison to the installed generation capacities including nuclear power stations. In fact, the electricity generated from nuclear power stations in 2016, increased by 35 TWh to 2476 TWh [1]. Canada is a long-time leader in nuclear energy research and development with approximately “16% of Canada's electricity comes from nuclear power, with 19 reactors (located mostly in Ontario) providing 13.5 GWe of power capacity” [2]. A common approach in case of surplus electricity on the grid is to sell it at discount or even negative pricing in order to keep the grid stability.

The other approach is to power electrolyzers with excess electricity and produce hydrogen [3]. In this way, surplus energy is stored in gas and then distributed to end users at different locations contributing to the grid decarburization. One hybrid solution is known as “Power-to-Gas” (P2G), technology that was pioneered in Japan producing hydrogen from seawater electrolysis [4]. This technology was later developed in Denmark and Netherlands [5]. Other European countries, led by Germany, are also actively involved in the development of P2G technology. Since 2004, “17 pilot and demonstrative projects” on P2G have been launched in Germany [5], as well as the world's first industrial P2G (e-gas) plant by Audi [6]. The USA only joined these initiatives in 2015. In 2016, Hydrogenics Corporation [7], located in Mississauga (Ontario, Canada) and Enbridge, Inc. (operated in Canada and USA) started collaboration on a 2 MW P2G project to build “North America's first and largest, utility-scale power-to-gas plant” in Ontario. In addition, “Canadian Gas Association (CGA) has created a Canada-U.S. P2Gas Task Force examining guidelines for blending hydrogen into the gas distribution network” [8]. For Ontario, it was calculated that the existing gas storage infrastructure can store almost 7.84*10⁵ MWh energy [9].

P2G is the world's most innovative way to store and transport energy. The key part of this technology is an electrolyzer, in which the surplus energy is used to split water molecules (H₂O) into hydrogen and oxygen. These gases evolve from the electrolyzer without any CO₂ emission. As a stable chemical, hydrogen can be stored for long time without degradation under pressure. Hydrogen is miscible with other gases and can be injected into the existing natural gas (NG) grid. In theory, hydrogen and NG can be mixed in any proportion, but the resulted blend should be compatible with existing NG transmission and distribution infrastructure, as well as end-use equipment specifics.

Another product of P2G is methane. Methane is obtained by coupling hydrogen and carbon dioxide, with the later being derived from biomass, waste products [10] or coal [11]. The “power to methane” is discussed in great detail in a review paper of Ghaib et al. [12]. Methane formed in this way has similar properties with NG and is called “substitute natural gas” [13,14] or “synthetic natural gas” [15,16] (in the present paper, both terms are referred as “SNG”). SNG can be, further mixed with hydrogen, injected in the existing NG infrastructure and delivered to end users. In this way, P2G could reduce the need for importing NG in some countries (e.g., France [17]).

Intensive experimental and simulative studies are conducted on P2G worldwide, including techno-economic and life cycle assessments. The benefits and drawbacks of P2G are presented in a number of research and review papers [5,[14], [15], [16], [18], [19],18,19]. These investigations have identified P2G as a solution for long term and large capacity electricity storage. It has also been shown that the significance of P2G will increase with intensive penetration of RES. Depending on electricity supply and CO₂ source, P2G can significantly lower GHG emission [15]. However, some technical and economic obstacles need to be addressed before P2G can be commercially successful [14]. This includes the high installation cost of electrolyzers, possible degradation of its components, the compatibility of materials with H2/NG blends, codes, standards and gaps in knowledge on hazards and safety on hydrogen transmission through existing NG infrastructure. The paper presents the status and recent developments of P2G technology and its applications around the world. The latest research findings from literature and scientific sources are presented and analyzed to provide a concise view of challenges the P2G technology and H₂/NG blends face and possible paths forward.