Hydrogen Energy Storage: The Future of Renewable Energy

Hydrogen is the most abundant element in the universe and has the potential to play a major role in the future of clean energy. Being the lightest element, hydrogen has a high energy density by weight and can be used as an energy carrier in various applications like transportation, power generation and industrial processes. Some key advantages of using hydrogen as an energy carrier include its renewable origins through water electrolysis, zero direct carbon emissions when used in fuel cells and ability to store energy over long durations.

Electrolysis for Hydrogen Production

One of the major ways to produce hydrogen is through the electrolysis of water, where an electric current is passed through water splitting it into hydrogen and oxygen. Electrolysis offers a clean, renewable way of generating hydrogen using electricity from sources like solar, wind and hydro. As renewable power generation increases globally, excess electricity can be used to produce hydrogen through electrolysis, providing an effective means of energy storage. Research is ongoing to develop more efficient and affordable electrolysis technologies like solid oxide electrolysis cells to enable large-scale hydrogen production from renewables.

Above Ground Hydrogen Energy Storage

Once produced, hydrogen needs to be efficiently stored and transported for usage in different applications. Some common above ground hydrogen storage methods include:

- Compressed Gas Storage: Hydrogen can be compressed and stored in high-pressure gas cylinders or tanks up to 700 bars. Though energy intensive, compressed gas storage provides high volumetric density and is suitable for small-scale mobile applications.

- Liquid Hydrogen Storage: Hydrogen Energy Storage can be liquefied at -253°C for easier storage in wellinsulated cryogenic tanks. Liquefaction increases the energy density by a factor of three but incurs significant cooling energy costs. Liquid hydrogen is used for large stationary storage and transportation.

- Metal Hydrides: Certain metals and alloys can absorb and store hydrogen within their crystal structures. Reversible metal hydrides offer high gravimetric density storage but require high pressures and temperatures for hydrogen absorption/desorption.

- Chemical Hydrogen Storage: Hydrogen can also be stored chemically in liquid organic carriers through reversible hydrogenation/ dehydrogenation. These carriers have high energy density and could find applications in portable devices and fuel cell vehicles.

Underground Hydrogen Energy Storage

For large-scale stationary storage, underground storage of hydrogen offers distinct advantages over above ground options. Depleted oil and gas reservoirs, aquifers and salt caverns deep underground provide naturally isolated geological structures that can safely store hydrogen in huge volumes for long durations. Some key benefits of underground hydrogen storage include:

- Vast Storage Capacity: A single depleted gas field can store hundreds of tonnes of hydrogen, sufficient to balance supply-demand mismatches over seasonal timescales.

- Minimal Energy Losses: Being insulated underground, hydrogen stored incurs negligible thermal losses compared to above ground cryogenic tanks.

- Security & Safety: Geological storages provide a naturally safe, secure containment for hydrogen far away from populated areas.

- Equivalent Infrastructure: Existing natural gas transmission and storage infrastructure can be retrofitted for hydrogen with minimal modifications.

Several pilot projects globally are demonstrating the feasibility and economics of underground hydrogen storage. As renewable hydrogen supply scales up, vast underground reservoirs will play a critical role in balancing seasonal energy demands through long-term storage.

Transportation and Distribution of Hydrogen

For hydrogen to become widely used as an energy carrier, efficient transportation and distribution systems need to be established. This requires:

- Pipeline Networks: Existing natural gas pipelines can be repurposed for hydrogen transmission with minor steel upgrades. New pipelines will also be required to distribute hydrogen over long distances.

- Tankers & Trucks: Hydrogen can be transported via tankers for marine distribution and cryogenic tank trucks for local deliveries, much like liquefied natural gas (LNG).

- Fueling Stations: Widespread rollout of hydrogen refueling infrastructure similar to current gasoline stations will enable fuel cell vehicles and decentralised energy applications.

- Blending into Natural Gas Grids: Options to blend hydrogen into natural gas pipelines up to certain percentages are being evaluated for utilizing existing gas networks.

Demonstration projects across Asia, Europe and America are testing different distribution methods to establish hydrogen supply corridors. Development of common refueling standards, safety protocols and international transportation regulations will help scale up global hydrogen trade.

Future Applications of Hydrogen Energy Storage

With secure large-scale storage and distribution networks in place, hydrogen is expected to play a key role across various sectors in the low-carbon economy of the future:

- Transportation: Fuel cell electric vehicles (FCEVs), trucks, ships and trains running on hydrogen fuel cells offer a clean alternative to gasoline and diesel with similar refueling speeds.

- Power Generation: Hydrogen can complement renewable energy by powering flexible gridscale fuel cells, turbines and blending into natural gas power plants.

- Industrial Feedstock: Significant amounts of hydrogen are used in oil refining, fertilizer production and other industrial processes. Renewable hydrogen can help decarbonize these hard-to-abate sectors.

- Heating Buildings: Fuel cells and hydrogen-powered boilers provide an alternative to natural gas heating of homes and commercial buildings.

With the rising share of variable renewable power, hydrogen offers one of the most promising solutions for long-duration bulk energy storage and distribution. Advancements across the entire hydrogen value chain from production to end-use applications indicate hydrogen will play a pivotal role in transitioning to a net-zero, sustainable energy future. Coordinated global investments and cross-industry collaboration hold the key to commercializing hydrogen technologies at scale.