The integration of renewable energy sources into power grids has introduced variability that demands innovative solutions for balancing supply and demand. One such solution is the power-to-gas-to-power (P2G2P) concept, which uses hydrogen as an energy carrier to store excess electricity and regenerate it when needed. This approach is particularly valuable for grid stability, long-duration storage, and niche applications like industrial clusters.

At its core, P2G2P involves three main stages: electrolysis, storage, and reconversion. Excess electricity, often from wind or solar, powers electrolyzers to split water into hydrogen and oxygen. The hydrogen is then stored using methods like compressed gas, liquid hydrogen, or chemical carriers. When electricity demand rises, stored hydrogen is fed into fuel cells or hydrogen turbines to regenerate power. The entire cycle bridges temporal gaps between renewable generation and consumption.

Round-trip efficiency is a critical metric for P2G2P systems. Electrolysis typically achieves 60–80% efficiency, depending on the technology. Alkaline electrolyzers operate at 60–70%, while proton exchange membrane (PEM) systems reach 70–80%. Solid oxide electrolyzers (SOEC) can exceed 80% but require high temperatures. Storage efficiency varies with the method; compressed gas incurs minimal losses, while liquefaction consumes 30–40% of the stored energy. Reconversion via fuel cells adds another 40–60% efficiency loss, resulting in an overall round-trip efficiency of 30–50%. Hydrogen turbines, though less efficient than fuel cells, offer scalability for larger grid applications. These figures highlight the trade-off between energy losses and the unique benefits of hydrogen storage, such as long-duration capability and high energy density.

The technology chains within P2G2P systems are diverse. Electrolysis can be coupled with underground salt caverns for large-scale storage, offering low-cost, high-capacity solutions. Alternatively, chemical hydrides or liquid organic hydrogen carriers (LOHCs) enable safer transport and decentralized storage. Reconversion technologies also vary; stationary fuel cells suit small-scale applications, while hydrogen turbines integrate with existing gas infrastructure for grid-scale power. Each chain has distinct advantages, depending on scale, location, and use case.

Industrial clusters present a compelling niche for P2G2P. These zones often have high energy demands and existing hydrogen infrastructure, such as refineries or ammonia plants. Excess renewable energy can produce hydrogen for both grid balancing and industrial processes, creating synergies. For example, hydrogen stored for grid use can also feed into chemical production during low-demand periods. This dual-use approach improves the economics of P2G2P by leveraging existing demand and infrastructure.

Comparing P2G2P with other storage methods reveals its unique role. Lithium-ion batteries dominate short-duration storage with round-trip efficiencies of 85–95%, but their capacity fades over hours. Pumped hydro offers 70–85% efficiency and large-scale storage but is geographically constrained. Thermal storage systems achieve 50–70% efficiency but are limited to specific applications. P2G2P, while less efficient, excels in long-duration storage and scalability. It can store energy for weeks or months, unlike batteries, and does not rely on specific terrains, unlike pumped hydro. Additionally, hydrogen can be transported or repurposed for industrial use, adding flexibility.

The environmental impact of P2G2P depends on the hydrogen production source. Green hydrogen, produced with renewable electricity, has near-zero emissions. However, leakage during storage or transport can offset some climate benefits due to hydrogen’s global warming potential. Proper handling and monitoring are essential to minimize these effects.

Economic factors also play a role. The levelized cost of storage (LCOS) for P2G2P is higher than batteries for short durations but becomes competitive for long-duration needs. As electrolyzer and fuel cell costs decline, P2G2P is expected to gain traction in markets with high renewable penetration and industrial hydrogen demand.

In summary, P2G2P provides a versatile solution for grid balancing, particularly in scenarios requiring long-duration storage or industrial integration. Its round-trip efficiency lags behind batteries and pumped hydro, but its scalability and flexibility make it indispensable for a decarbonized energy system. Niche applications, like industrial clusters, further enhance its value by combining grid services with industrial feedstock supply. As technology advances and costs fall, P2G2P is poised to play a pivotal role in the future energy landscape.