Power-to-Gas-to-Power: Round-Trip Efficiency, Costs, and When It Makes Sense

By Green Gas Turbines Team · Published November 27, 2025 · 14 min read

Power-to-Gas-to-Power in One Minute

Power-to-gas-to-power (PtG-P)—sometimes called power-to-hydrogen-to-power (PtH₂P)—uses surplus electricity to make hydrogen, stores it for hours to months, and then converts it back to electricity through a gas turbine or fuel cell. On paper it looks brutally inefficient; in practice it may be the only scalable way to store terawatt-hours of clean energy over seasons.

This article breaks down how the cycle works, realistic round-trip efficiency ranges, why PtG-P looks bad next to batteries—and why grid planners still care about it for 60–100% renewables scenarios.

What Is Power-to-Gas-to-Power, Exactly?

In a power system context, PtG-P usually refers to the following four-step chain:

Power-to-Hydrogen (P2H): Use surplus or low-cost electricity from wind, solar, nuclear, or hydro to run an electrolyser (alkaline, PEM, or SOEC). The electrolyser splits water into hydrogen and oxygen.
Hydrogen Conditioning & Storage: Compress or liquefy hydrogen, or inject it into underground salt caverns, depleted gas fields, or large above-ground tanks. The goal is low-cost storage for long durations.
Hydrogen-to-Power (H2P): When the grid needs power, hydrogen is fed to a gas turbine (simple-cycle or combined-cycle), internal combustion engine, or fuel cell.
Grid Dispatch & Ancillary Services: The power block provides energy, capacity, and potentially spinning reserve, inertia, or fast frequency response—depending on the technology.

On GreenGasTurbines.com, we focus on the turbine pathway: electrolyser → H₂ storage → hydrogen-ready gas turbine. It is less efficient than fuel cells but better aligned with existing peaker fleets and grid operator workflows.

Round-Trip Efficiency: Where the Energy Goes

Round-trip efficiency (RTE) is the ratio of electric energy you get back to the electric energy you originally put into the system. For PtG-P, three stages dominate losses:

Electrolysis (power → H₂): System-level efficiency ~60–75% (lower heating value, including auxiliaries for AC/DC conversion and cooling) for mature alkaline and PEM electrolysers.
Storage & Handling (H₂ → stored H₂): 90–98% efficient depending on whether you use high-pressure cylinders, pipelines, or underground storage. Energy is consumed in compression, liquefaction, or pumping, plus any boil-off or leak losses.
Conversion Back to Power (H₂ → electricity):
- Hydrogen gas turbine in simple-cycle peaker configuration: ~35–40% efficiency.
- Hydrogen combined-cycle plant: ~50–60% efficiency in future designs, higher CAPEX.
- Fuel cell power plant: ~45–60% electrical efficiency today, with potential for more in the long term.

Realistic Round-Trip Efficiency Ranges

Several system-level studies have estimated full-chain PtG-P RTE under realistic assumptions (including auxiliaries and storage overheads):

Electrolyser → H₂ storage → gas turbine: roughly 24–27% round-trip efficiency for grid-scale plants.
Electrolyser → H₂ storage → fuel cell: typically 30–45% round-trip efficiency; higher in best-case designs.
Electrolyser → H₂ storage → ICE generator: similar to or slightly above the gas turbine path for smaller units.

As an engineering rule of thumb for hydrogen-turbine storage projects, many developers assume:

20–30% RTE for PtG-P with hydrogen gas turbines
30–40% RTE for PtG-P with fuel cells

That is clearly worse than lithium-ion battery storage (commonly 70–90% round-trip) or pumped hydro (70–85%). So why bother?

Why Use Such an Inefficient Cycle?

Despite the efficiency penalty, PtG-P offers several unique advantages that become critical in very high-renewables systems:

1. True Seasonal and Multi-Week Storage at Scale

Battery storage is excellent for seconds-to-hours timescales. But storing energy for weeks or months quickly becomes uneconomic with batteries because you pay for both power and energy capacity.

With hydrogen, you pay heavily for the conversion equipment (electrolysers, turbines, or fuel cells), but the incremental cost of adding more storage—larger tanks, bigger salt caverns, additional linepack—is comparatively low. That makes PtG-P attractive where you need:

Coverage for seasonal variability in wind and solar output
Storage of terawatt-hours of energy across months
Firm capacity to ride through multi-day weather events (“dunkelflaute”)

2. Massive Energy Capacity in a Small Physical Footprint

Hydrogen has very high specific energy (energy per unit mass). Underground storage in salt caverns or depleted gas fields can offer enormous capacity without the land-use constraints of new pumped hydro or the safety issues of building gigantic battery fields near urban load centers.

3. Asset Reuse: Turbines, Pipelines, and Storage

PtG-P reuses a large portion of existing gas infrastructure:

Existing peaker or combined-cycle plants can be retrofitted as hydrogen-ready.
Gas pipelines and underground storage can be repurposed or partially used for hydrogen.
Permitting and grid interconnection are often easier for brownfield conversions than for entirely new assets.

4. Multi-Sector Coupling and Revenue Stacking

Hydrogen is a cross-sector energy carrier. A PtG-P system can:

Provide grid services (firm capacity, balancing, black-start)
Supply hydrogen for industry, heavy transport, or synthetic fuels
Help de-risk investments in hydrogen infrastructure by creating a stable “anchor” demand

When hydrogen serves both power and molecules markets, the economics may work even with low round-trip efficiency.

Comparing PtG-P to Other Storage Options

For system planners, the key question is not “What is the highest efficiency?” but “What is the lowest cost way to deliver reliable, decarbonized power over the required timescales?”

Duration vs. Best-Fit Storage Technology

Storage Duration Need	Typical Best-Fit Technology	Notes
Seconds to 4 hours	Lithium-ion and other batteries	High efficiency, high cycling; ideal for frequency response and short peak shaving.
4–12 hours	Batteries, pumped hydro, some thermal storage	Choice depends on geography and siting constraints.
12–100 hours	Pumped hydro, compressed air (CAES), flow batteries, early hydrogen projects	Hydrogen begins to compete in certain locations with good geology.
Multi-week to seasonal	Hydrogen PtG-P, synthetic methane, and other chemical storage	Hydrogen’s low $/kWh storage cost can outweigh low round-trip efficiency.

Rule-of-Thumb Economics

Although exact numbers are project-specific, developers often use these heuristics:

Short duration (< 10–12 hours): Batteries and pumped hydro usually beat PtG-P on cost and efficiency.
Medium duration (12–100 hours): Mixed portfolio; PtG-P may be competitive where geology allows cheap caverns and curtailment is high.
Seasonal duration (weeks to months): PtG-P and hydrogen-based variants are often the only practical scalable options.

Design Choices That Drive Performance

Round-trip efficiency and cost are not fixed. They depend on design decisions across the whole chain.

1. Electrolyser Technology and Operating Strategy

Alkaline electrolysers offer relatively low CAPEX and good efficiency at steady, baseload operation. PEM electrolysers are more flexible, handle dynamic operation better (following wind and solar), and have a compact footprint, often at a slightly higher cost per kW. Solid oxide electrolysers (SOEC) promise very high efficiency but are still emerging.

Project developers must decide whether the electrolyser will:

Run as a baseload off-taker of cheap renewables with high utilization, or
Operate flexibly to soak up otherwise-curtailed energy and provide additional grid services.

Higher utilization generally reduces hydrogen cost per kilogram, but grid value may be higher if electrolysers are dispatchable loads that track system needs.

2. Storage Method: Tanks vs Caverns vs Pipelines

Hydrogen storage options include:

High-pressure tanks (350–700 bar): Scalable for small to medium projects, but compression consumes roughly 10–15% of the hydrogen’s energy content and tanks become expensive at very large capacities.
Liquid hydrogen: Higher energy density but significant energy penalty and boil-off losses—better for transport than stationary, multi-month storage.
Underground storage (salt caverns, depleted fields): Very low cost per kWh for large volumes and high storage efficiency when properly designed.
Pipeline “linepack”: Using existing gas networks as a distributed hydrogen storage and transport system in blending scenarios.

For power-sector PtG-P projects, underground storage in suitable geology is usually what unlocks the real advantage of hydrogen as a long-duration storage medium.

3. Power Block: Turbine vs Fuel Cell vs Hybrid

For grid applications, there are three main pathways for converting hydrogen back to electricity:

Hydrogen gas turbines: Lower efficiency but high power ratings and familiar technology for utilities. Simple-cycle machines favor fast-start peaking; combined-cycle configurations raise efficiency at higher CAPEX and complexity.
Fuel cell power plants: Higher efficiency and lower local emissions, but currently higher costs and generally smaller unit sizes. They are more common in distributed or industrial applications than in bulk peaking plants.
Hybrid configurations: Pairing a hydrogen turbine with a battery to provide extremely fast ramping and frequency support while using hydrogen mostly for longer-duration energy delivery and capacity adequacy.

Worked Example: 100 MWh of Surplus Wind

Consider a simplified, idealized PtG-P system connected to a high-wind grid:

Electrolyser efficiency: 70%
Storage plus handling efficiency: 95%
Hydrogen gas turbine electrical efficiency: 38%

Starting with 100 MWh of surplus wind power:

Electrolysis: 100 MWh × 0.70 = 70 MWh_H2 stored in chemical form.
Storage: 70 MWh_H2 × 0.95 ≈ 66.5 MWh_H2 after compression and storage.
Back to power: 66.5 MWh_H2 × 0.38 ≈ 25.3 MWh of electricity delivered.

That’s a round-trip efficiency of about 25%. In practice, auxiliary loads and part-load operation may reduce this further. The question for planners is: Is 25 MWh of clean, dispatchable power at the right time worth the cost of “spending” 100 MWh upfront? In high-renewables systems with substantial curtailment, the answer can be yes.

When PtG-P Makes Sense (and When It Doesn’t)

Good Use Cases for Power-to-Gas-to-Power

Very high renewables penetration (60–100%): When curtailment of wind and solar is routine and the grid needs multi-day or seasonal balancing.
Limited geography for alternatives: No suitable sites for new pumped hydro or CAES, and battery fields would be massive and expensive for the durations required.
Stranded gas infrastructure: Regions with existing pipelines, storage, and gas plants that risk stranding under aggressive decarbonization policies. PtG-P offers a pathway to reuse these assets with low-carbon fuels.
Sector coupling strategies: Hydrogen from PtG-P is also used in refineries, steel plants, fertilizer production, or heavy transport, creating diversified revenue streams.

Situations Where PtG-P Is a Poor Fit

Short-duration flexibility needs: If your main issue is 2–6 hour evening peaks, lithium-ion batteries, demand response, or flexible CCGTs will almost always be cheaper and more efficient.
Low-curtailment systems: If surplus renewable energy is rare, running an electrolyser primarily on grid-priced power can make hydrogen very expensive.
No access to low-cost storage geology: Without salt caverns or suitable reservoirs, large-volume hydrogen storage can become too costly.
Weak policy support: Absent carbon pricing, low-carbon fuel standards, or hydrogen support schemes, PtG-P projects may struggle to reach positive economics.

Project Development Considerations for Asset Owners

For owners of existing gas turbines or peaker fleets considering PtG-P retrofits, key due diligence questions include:

Grid need: Are you solving a seasonal/long-duration problem, or a short-duration flexibility issue already better served by batteries?
Fuel supply strategy: Will hydrogen be produced on-site from colocated renewables, delivered by pipeline, or imported as a derivative (e.g., ammonia)?
Storage siting: Is there access to salt caverns or other geologic formations? If not, what are the CAPEX and safety implications of large above-ground storage?
Technology roadmap: How quickly will your turbines transition from blending (e.g., 20–40% H₂) to 100% hydrogen capability, and what CAPEX is required?
Revenue stacking: Beyond energy arbitrage, can the project earn from capacity markets, ancillary services, hydrogen offtake contracts, or industrial customers?

Frequently Asked Questions

What round-trip efficiency should I assume in planning models?

For early-stage planning, many system studies assume 20–30% round-trip efficiency for PtG-P using hydrogen gas turbines and 30–40% for fuel-cell-based systems. For detailed project development, you should model each component—electrolyser, storage, and power block—at expected operating conditions and part-load profiles.

Is power-to-gas-to-power always worse than batteries?

On efficiency, yes. On cost per kWh delivered over very long durations (weeks to months), not necessarily. Hydrogen’s value is less about efficiency and more about its ability to store very large amounts of energy cheaply and to reuse existing gas infrastructure.

Can my existing gas peaker plant become part of a PtG-P system?

In principle, yes. Many OEMs now market hydrogen-ready gas turbines that can start with modest hydrogen blends and progress toward 100% hydrogen. You would still need hydrogen production and storage infrastructure, as well as detailed combustion, materials, and safety assessments for high hydrogen fractions.

How does PtG-P compare to ammonia-based storage or synthetic methane?

Using hydrogen derivatives like ammonia or synthetic methane adds extra conversion steps (and losses) but may simplify transport or leverage existing handling infrastructure. For pure power applications, direct hydrogen cycles usually have better round-trip efficiency; derivatives are more compelling when long-distance transport or multi-sector use is the priority.

Does low round-trip efficiency mean PtG-P is “wasting” renewable energy?

It depends on context. If you would otherwise curtail large volumes of wind or solar, converting a fraction of that into dispatchable power via PtG-P can still be economically and environmentally attractive. The key is that the input electricity must be low-cost and low-carbon, and the stored energy must provide high system value at times of scarcity.

Is hydrogen-based storage compatible with net-zero targets?

Yes—provided the hydrogen itself is produced from low-carbon sources (renewable electricity, nuclear, or fossil hydrogen with very high CO₂ capture rates). If PtG-P systems use unabated fossil-derived hydrogen, they will not achieve the emissions reductions required for net-zero pathways.

Conclusion: A Niche, But an Important One

Power-to-gas-to-power is not a silver bullet, and it will not replace batteries or pumped hydro for most short- and medium-duration storage needs. Its strength lies in solving a different problem: providing deep, long-duration, seasonal flexibility in grids with very high shares of renewables, while reusing and decarbonizing existing gas infrastructure.

For asset owners and system planners, the key is to treat PtG-P as part of a portfolio strategy: batteries for fast, short-duration needs; flexible CCGTs and demand response for multi-hour balancing; and hydrogen-based storage systems for rare but critical multi-day and seasonal events. When evaluated in that context—rather than on efficiency alone—power-to-gas-to-power starts to make sense.