When we think about energy storage, we often think about batteries, compressed air or flywheels, but Power to Gas (P2G) has begun to enter the conversation more frequently in North America.
One glance over the ocean to our European counterparts shows that P2G is being seriously considered as a mainstream component of the energy storage mix, where a consortium of 11 leading energy companies have established the North Sea Power to Gas platform, to help move toward a carbon-neutral gas supply in 2050.
In North America, Power to Gas is often dismissed as expensive, complicated or lacking infrastructure. But before brushing aside this technology's potential, it's important to understand some of the technical drivers behind its adoption, and when P2G might provide a valuable outlet for excess energy production.
What is P2G?
Power to Gas (P2G) refers to the process of generating hydrogen from water, by running an electrical current through water with ions (electrolysis). Similar in many ways to a fuel cell run in reverse, most common electrolyzers are either based on Alkaline or Proton Exchange Membrane (PEM) technology. Both of these processes produce hydrogen that is 99.9% pure. Once the hydrogen gas has been generated, it can be stored almost indefinitely in hydrogen storage tanks, or injected into a natural gas system in order to lower the carbon content of one of our most commonly used fuels.
In the future, when the energy is required, stored hydrogen gas can be retrieved to produce electricity using a gas-fired electricity generation plant, fuel cell or most other processes that currently use natural gas.
Why consider P2G?
When you compare P2G to other technologies, it offers a few benefits:
Longer storage: with time-shifting electrons, we consider storing energy for peak loads, from hour to hour and night to day. But the efficiency of storing hydrogen in the natural gas stream offers an expanded range of annual energy planning options – consider storing spring-time energy to meet peak loads during summer heatwaves, or transfer lower summertime usage to meet wintertime demandFootnote1.
Widespread natural gas infrastructure: In some configurations, P2G can use the existing natural gas grid. This enables the use of existing components and technologies that support it, allowing for distributed energy storage without building significant additional infrastructure, bypassing some of the locational issues of other longterm storage technologies, and avoiding some of the complexities of managing a "real-time" system such as the electricity grid.
Fewer capacity concerns: With direct access to the natural gas stream, P2G can help store large amounts of energy from variable generation resources like wind and solar for immediate response to market demands. Most studies indicate that terra watt scales of storage are available for P2G even with only 2% H2 content in the natural gas system.
Synergies with other energy systems: As alternative vehicle technologies gain traction, generating a cost effective, renewable source of hydrogen becomes increasingly important. P2G is certainly an option to consider for fuel cell vehicle refueling, along with a variety of industrial processes that utilize hydrogen directly as opposed to generating it from other sources.
What else needs to be considered?
As with any emerging technology, there are often multiple items to consider when evaluating or deploying P2G:
Technology Options: From a technology stand-point, water electrolysis has been well-known for over 200 years. There are a few types of electrolyzers in use or development today, including Alkaline, Proton Exchange Membrane and Solid Oxide technologies. Each of these has advantages and disadvantagesFootnote2, and users must evaluate which technology is right for them. In addition, when reviewing their options users should consider the relative technology readiness level; components currently range from bench-scale testing to established commercial technologies.
System Configuration: P2G is a catch-all term for many different system and storage configurations, which can include the electrolysis technologies outlined above, the storage medium or the generation device. Each configuration has its pluses and minuses, and must be evaluated for a specific site, market or user. Much work has already been completed on optimizing these pathways; however a true market leader has not yet emerged.
Techno-economics: Each year, industrial applications draw upon billions of cubic metres of hydrogen produced by methane steam reforming, whereas less than 1% of supply is currently generated by water electrolytic process. Why isn't electrolysis more common, given that it's a mature technology? In short: cost and durability. The challenge lies in scaling-up hydrogen generation on a sound economic basis while considering capital and operating costs, overall efficiency, and durability.
Does P2G make sense for you?
To decide whether P2G would be a valuable complement to your energy storage mix, consider the relative strengths and weaknesses of your application, and the other technologies under consideration. In particular, you might want to take a closer look at P2G if you have any of the following scenarios:
Remote communities: Remote communities and remote mining sites often rely on diesel, which is expensive and often difficult to transport. With ready access to solar and wind energy, these communities could benefit from an electrolyzer and P2G system, with costs that compare to diesel transportation.
Natural gas infrastructure in place: One of the perceived barriers to P2G is the capital investment required to develop a viable system. But in many parts of Canada, natural gas infrastructure is already in place. Using existing pipeline networks to store and transport hydrogen makes financial sense, particularly when renewables are nearby.
Renewables near infrastructure: Provinces such as Alberta have strong natural gas networks in place. By installing wind turbines nearby, energy can be converted on the spot and transported to where it is needed.
In the end, "It's a strategic decision," says Kourosh Malek, a Technical Leader for NRC's Energy Storage program. "How does the P2G solution compare to other technologies you could use in its place?"
What challenges are you trying to address? Do you have any of the favourable scenarios for P2G?
With those answers in hand, the next step is a detailed Technical Economic Analysis, to ascertain what specific benefits could be realized from this technology. Until recently, there was little industry support for this type of analysis. As part of its mandate to help build a more competitive energy storage industry in Canada, NRC is working with EPRI to develop a free tool for those considering P2G opportunities.
In 2015, NRC began work with EPRI and several industry partners to enhance an existing Energy Storage Valuation Tool (ESVT), with a model for evaluating P2G opportunities.
In collaboration with the Department of Energy, the National Renewable Energy Laboratory, Atomic Energy of Canada Limited, Enbridge, Hydrogenics and Electric Power Research Institute, under the support of Industry Canada, the tool fills a critical gap for exploring the viability and potential benefits of P2G opportunities.