Pressure is mounting to decarbonize the economy, and momentum may be building around hydrogen as an energy resource and energy carrier. Hydrogen could be used with natural gas pipelines and power grids, along with associated markets, in an interconnected fashion.
Though this idea is more theoretical than practical at this stage, models are taking shape that could point the way to a future hydrogen economy. Utilities are used to applying models to plan large capital investments and operate power grids safely and reliably. They may use similar models developed by institutions such as CIGRE, the IEEE and the International Organization for Standardization one day to make reality out of theory.
Why Hydrogen?
Currently, about 95% of hydrogen made today is produced using fossil fuels like natural gas or coal. Electrolyzers fueled by low-carbon electricity, such as renewables, hydropower or nuclear energy, could reduce life-cycle greenhouse gas emissions. Of course, economic hurdles remain. It is still too costly to produce hydrogen in quantities necessary for utility-scale generation. Still, the International Energy Agency (IEA), European Commission and U.S. Department of Energy (DOE), along with states such as Washington and Massachusetts as well as cities such as Los Angeles, are including hydrogen in their decarbonization plans because of the benefits it could offer them.
As a carbon-free fuel, hydrogen could addressWhat is notable about this representation is the interplay between gas pipelines and electric grids. The electric grid is evident in providing energy to produce hydrogen from water molecules using electrolyzers — an electricity-intensive process. Products of electrolysis and methanation are injected into the gas grid and could be used to fuel turbines with hydrogen. At this time, the hydrogen generators being used can run on some mixture of hydrogen, but not at very high percentages yet. Most are smaller-sized generators today, with utilities planning to scale them up to the megawatt level in the future.
Coordinating Power and Gas
Utilities are participating in research and development efforts to show the potential benefits of hydrogen energy. To date, North American utilities are involved in at least 15 demonstration projects to test the technical and economic feasibility of hydrogen production. Among the utilities involved are APS, Exelon Corp., the Los Angeles Department of Water & Power (LADWP) along with other municipalities, the New York Power Authority, NextEra Energy Inc., San Diego Gas & Electric, Southern California Gas Co.Now introduce hydrogen into the system. First, electricity is needed to power the electrolyzers that produce clean hydrogen. Hydrogen produced by electrolyzers may be blended with natural gas for delivery by gas pipelines. Blending has an impact on energy content (caloric value) and pressure. There may be a need for electricity to power additional compressors along the pipelines if the hydrogen production site is far from the point of off-take.
In another application that may be further down the road, hydrogen could fuel natural gas peaking plants to generate power when low wind and solar are insufficient to meet peak demand. The industry is still a long way from seeing turbines completely fueled by hydrogen, and turbines that use hydrogen today run on a mixture of H2 and natural gas with low percentages of hydrogen. General Electric Co. (GE), Siemens AG, Caterpillar and others are working along these lines on hydrogen generators; however, the companies estimate it could take until 2030 to develop 100% hydrogen turbine designs. Meanwhile, natural gas is a highly mature generation technology, widely used and inexpensive on a megawatt scale.
Also, retrofitting existing turbine technology to accommodate burning hydrogen also presents challenges, according to the Electric Power Research Institute’s (EPRI’s) research on hydrogen-capable gas turbines for deep decarbonization. Lower volumetric energy density of a blend will require investment in larger fuel supply lines to maintain the same power output. It will be important to understand how an increase in the flow of H2 and natural gas to one plant might affect the availability of gas at other gas-fired plants and, accordingly, electric production at those plants.
Power-To-Gas Projects
In Utah’s Intermountain Power Project (IPP) Renewed, LADWP along with some Utah municipals plan to make hydrogen and use it to generate electricity. The power station’s new 840-MW combined cycle gas turbine is expected to take a 30-to-70 blend of hydrogen and gas by 2025 and be 100% hydrogen by 2045. Site preparation began in October 2021. When the project is complete, wind and solar power — possibly from neighboring states — will power electrolyzers to produce clean hydrogen. A salt dome formation is nearby that could be used to store excess hydrogen for off-take by others. Advanced Clean Energy Storage (ACES) was invited to submit a proposal to DOE for financing the development of salt cavern storage.
Power-to-gas (P2G) projects like IPP Renewed raise all kinds of questions about the safe operation of power and gas as well as market issues like the price of electricity, natural gas- When is the best time to take renewable electricity from the grid to power electrolyzers?
- What are optimal locations for P2G facilities?
- Are there ways to avoid building new infrastructure through flexible operations?
- What is the impact on the networks if components fail or exceed operating limits?
The P2G scenario is only one of several potential scenarios being put forward, raising additional questions:
- How will power and gas networks be impacted as hydrogen production scales?
- Will peak energy demand need to be reduced or flow rates increased with hydrogen injections into gas pipelines?
- What will be the net impact of hydrogen on carbon emissions?
- Which natural gas pipelines, if any, should be repurposed to transport hydrogen?
What’s Needed For Modeling?
Risk is associated with the introduction of hydrogen gas for utilities. According to the IEA, “Although hydrogen’s high versatility makes a wide range of possibilities and solutions available across diverse sectors, inadequate planning could result in the construction of inefficient and costly infrastructure. Thus, integrated analysis at the system level is needed to design efficient infrastructure for producing hydrogen and transporting it to end users.”Today, electric and gas grid operations are mostly modeled independently, even by utilities that operate both electric and gas assets. Several mature commercial modeling software offerings are available for steady-state and dynamic simulations of electricity networks (such as from Siemens, GE, DigSILENT GmbH and PowerWorld Corp.), power system production cost modeling (such as from Hitachi Energy Ltd., Energy Exemplar and PSR Inc.), and natural gas steady-state and dynamic hydraulic simulations of gas pipeline networks (such as from DNV, Gregg Engineering Inc. and SIMONE Research Group).
However, the data engineering necessary to get models to share data is difficult and time consuming. It is even more difficult to get the models to sync spatially and temporally or to be solved simultaneously. According to one scientist, loose coupling can miss issues that may cause reliability challenges. The results may be too conservative and result in an economically inefficient use of resources.Co-simulation and combined simulation are two approaches to running scenarios on coupled networks that incorporate multiple models. Simulation models help utilities to understand the impact of one grid’s behavior on another under dynamic conditions. These models quantify the physical interdependencies between electricity grids and gas pipeline networks, including operational constraints (that can impact costs), as well as impacts on reliability and security of supply. Simulations help to identify potential bottlenecks in the system, such as not enough gas to power gas generators at a certain node, at a certain point in time. Optimization models provide insight into least-cost approaches to investment to meet decarbonization goals.
Simulation Scenarios
The co-simulation method iterates between electric and gas models. In a co-simulation (traditional) modeling approach to solving a problem, there are two different modeling platforms — each one representing an energy network. For example, the results of a gas model are fed into an independent electric model. The electric model runs and gives an output, which may require more gas than what the gas model suggested. That requires another iteration where electric results are fed back into the gas model. The gas analysis provides changed outputs, which are then fed back into the electric model, and so on.
The DOE’s national laboratories have been testing co-simulation in conjunction with a consortium of other organizations. The Hierarchical Engine for Large-scale Infrastructure Co-Simulation (HELICS) platform brings together commercial and open-source modeling tools to perform co-simulation.
The National Renewable Energy Laboratory (NREL) recently completed a natural gas and power system co-simulation with data from Coloradoto understand how Xcel Energy Inc. could meet its decarbonization targets. The study looked at an increased penetration of renewables. It found that in a month characterized by highly variable wind conditions, co-simulation could achieve lower emissions through better gas delivery and dispatch of natural gas power plants and a 22% reduction in curtailment of wind and solar. The study was limited in that it could not accommodate entire systems or multiple iterations.Combined simulation solves a set of electric network models, gas network models and coupled models all at once. Instead of having two different models iterate between each other, combined simulation solves one set of equations that considers all the connection points between the gas and electric networks. Each time the model is run, there is one solution for both networks. Each network considers how the other network will react to a change.
Combined simulation makes more accurate results with less computational time. In contrast, co-simulation requires multiple iterations and powerful computing capacity. Back and forth iterations can continue indefinitely, never getting closer to a settled or optimal value for both gas pipelines and electric grids.
An American-German start-up encoord GmbH uses the combined simulation approach. The company’s commercial planning software, Scenario Analysis Interface (SAInt) for energy systems, is built on a modern underlying architecture more flexible than most legacy applications. The platform brings together power system production cost modeling, power flow simulations as well as steady-state and transient hydraulic simulations of gas pipeline networks with gas composition and quality tracking capabilities. Users perform combined physical simulations of electricity and gas networks to better quantify their interdependencies and synergies as well as understand their coupled performance in the context of hydrogen production, storage and delivery. One major European electricity transmission system operator has used the platform to analyze the optimal location and sizing of electrolyzers, considering both the gas and electric networks.
Still To Come
Advancements in modeling coupled grids will continue. With more real-world data, results can be further validated. There is still work to be done to enhance the precision of open-source and commercial tools.
With advances in analytics, modeling will be more easily accessible to nonacademic users. As hydrogen scales, expect to see dedicated hydrogen grids, and even other types of transportation, added to the mix.
Jill Feblowitz is president of Feblowitz Energy Consulting, which provides advice to energy providers including utilities (regulated and unregulated), generators, competitive energy retailers, DER providers and suppliers to the industry. Prior to Feblowitz Energy Consulting, she was Vice President of the energy vertical at IDC. As an analyst, she advised energy executives on business and technology strategy and suppliers on product development, marketing and sales. Areas of coverage included key business initiatives (reliable and efficient operations & maintenance, energy trading & risk management, security, customer engagement, energy efficiency, etc.) and technologies (cloud, Big Data, analytics, mobility, and edge computing). She also worked as an associate analyst at the Meta Group (now Gartner) and as Director of the Energy Practice at AMR (now Gartner), and as a senior consultant at XENERGY (now DNV GL) Feblowitz holds a B.S.in Urban Planning from MIT, an electrician's license, and is a certified women's enterprise (WBE) in the Commonwealth of Massachusetts. She is also the chair of the MIT Enterprise Forum CleanTech Committee.
For More Information
Caterpillar | www.cat.com
DigSILENT | www.digsilent.de
DNV | www.dnv.com
encoord | www.encoord.com
Energy Exemplar | www.energyexemplar.com
GE | www.ge.com
Gregg Engineering | www.greggeng.com
Hitachi Energy | www.hitachienergy.com
PowerWorld | www.powerworld.com
PSR | www.psr-inc.com
Siemens | www.siemens.com
SIMONE Research Group | www.simone.eu
