"Every energy technology that now powers the world was once 'emerging.' Coal was a curiosity in the 1700s. Oil was a novelty in the 1850s. Solar was a laboratory experiment in 1954. The future of energy is being built in laboratories, demonstration plants, and startup garages right now. We document what exists — not what we wish for."
— The Energy Codex · observation without advocacy · thecodex.expert
Cluster 9 · What is known — epistemic status
How to read this page — the four readiness levels
Every technology on this page is assigned a readiness level based on what institutional and peer-reviewed sources document. This is not optimism or pessimism — it is accuracy.
Commercial
Operating at commercial scale, generating revenue
Multiple installations exist. Technology is proven. Costs are documented. Can be financed by commercial banks without guarantees. Examples: ammonia synthesis (industrial), grid-scale batteries, flywheels for frequency regulation.
Demonstration
Pilot projects operating, commercial scale not yet reached
Technology works at small-to-medium scale. Real energy generated. Costs still falling toward commercial viability. Examples: green ammonia fuel, gravity storage (Energy Vault), compressed air (some plants).
Research
Active R&D. No commercial plant operating.
Physics or engineering proven in laboratory. Pathways to commercialisation identified. Significant investment occurring. Examples: space-based solar power, long-duration compressed air, advanced flywheels.
Theoretical
Confirmed physics but no extraction demonstrated
The phenomenon exists and is measured by science. No working energy device exists. Examples: zero-point energy (quantum vacuum fluctuations are real and measured — no extraction demonstrated). Claims in this category should be evaluated with extreme care.
Cluster 3 · Ammonia fuel
Ammonia — the energy carrier for shipping and heavy industry
What is ammonia fuel? Ammonia (NH₃) is a molecule made of nitrogen and hydrogen. It doesn't contain carbon, so when burned it produces water and nitrogen — no CO₂. Today most ammonia is made from natural gas (grey ammonia), which releases CO₂. "Green ammonia" is made using green hydrogen (from renewable electricity) and nitrogen from the air. Green ammonia can be used as fuel for ships, power plants, and fertiliser factories. It is much easier to transport and store than hydrogen — liquid at −33°C (versus −253°C for liquid hydrogen). Several shipping companies have ordered ammonia-fuelled vessels for delivery in 2025–2030.
Why ammonia matters for shipping: International shipping produces approximately 2.5% of global CO₂ and cannot easily electrify — ships need too much energy over too long a range for batteries. Ammonia has energy density of approximately 4.3 kWh/litre (versus 9.6 kWh/litre for diesel). Current major projects:
Yara International (Norway) + Ørsted: Planned green ammonia plant at Esbjerg, Denmark — 100,000 tonnes/year green ammonia target. Source: Yara International
MAN Energy Solutions: Two-stroke ammonia engine for large ships — first delivery 2024. Approved by all major classification societies.
IMO strategy: The International Maritime Organization's 2023 strategy targets net-zero greenhouse gas emissions from shipping by 2050. Green ammonia is one of the primary candidate fuels. Source: IMO 2023 Strategy
Yara International (Norway) + Ørsted: Planned green ammonia plant at Esbjerg, Denmark — 100,000 tonnes/year green ammonia target. Source: Yara International
MAN Energy Solutions: Two-stroke ammonia engine for large ships — first delivery 2024. Approved by all major classification societies.
IMO strategy: The International Maritime Organization's 2023 strategy targets net-zero greenhouse gas emissions from shipping by 2050. Green ammonia is one of the primary candidate fuels. Source: IMO 2023 Strategy
Source: IEA — The Future of Hydrogen · IMO GHG Strategy 2023
Ammonia synthesis: N₂ + 3H₂ → 2NH₃ (Haber-Bosch process, ΔH = −92 kJ/mol). Green ammonia replaces fossil-derived H₂ with electrolytic H₂ from renewable electricity. Energy requirement: ~10 MWh/tonne NH₃ for electrolysis + ~1 MWh/tonne for synthesis. Current green ammonia cost: ~$700–1,200/tonne (vs. grey ammonia ~$200–400/tonne). Ammonia combustion: 4NH₃ + 3O₂ → 2N₂ + 6H₂O. NOx formation is the primary combustion challenge — requires selective catalytic reduction. Ammonia toxicity: LC50 ~300 ppm (inhalation), requiring marine safety protocols. Classification: SOLAS Annex II IGC Code (under revision for fuel use). IEA projects green ammonia trade reaching 150–400 Mt/year by 2050 in various scenarios.
Source: IEA — The Future of Hydrogen 2023 · IMO 2023 GHG Strategy · MAN Energy Solutions product documentation
Demonstration
Green ammonia production at scale: multiple pilot plants operating. First commercial ammonia-fuelled ships: delivery 2025–2027. Commercial green ammonia at competitive cost: projected 2030+. Source: IEA Hydrogen 2023.
Cluster 3 · Compressed air energy storage
Compressed Air Energy Storage (CAES) — underground grid batteries
How CAES works
During excess electricity periods, electric motors compress air and pump it into underground caverns (salt caverns, depleted gas fields, aquifers). When electricity is needed, the compressed air is released, heated (using gas or the heat stored from compression), and expanded through a turbine to generate electricity.
Advantages: Large capacity, long duration (hours to days), uses existing geology, relatively low cost per MWh of storage.
Operating CAES plants:
• McIntosh CAES, Alabama, USA (110 MW, GPS: 31.27°N 87.65°W, operating since 1991)
• Huntorf CAES, Germany (321 MW, GPS: 53.44°N 8.50°E, operating since 1978 — the world's first)
Adiabatic CAES (A-CAES): Stores the heat of compression (instead of venting it) and uses it to reheat the air on expansion — eliminating the need for gas and making it fully renewable. RWE's ADELE project in Germany was a major A-CAES research effort.
Advantages: Large capacity, long duration (hours to days), uses existing geology, relatively low cost per MWh of storage.
Operating CAES plants:
• McIntosh CAES, Alabama, USA (110 MW, GPS: 31.27°N 87.65°W, operating since 1991)
• Huntorf CAES, Germany (321 MW, GPS: 53.44°N 8.50°E, operating since 1978 — the world's first)
Adiabatic CAES (A-CAES): Stores the heat of compression (instead of venting it) and uses it to reheat the air on expansion — eliminating the need for gas and making it fully renewable. RWE's ADELE project in Germany was a major A-CAES research effort.
Demonstration Two plants operating since 1978/1991. A-CAES not yet commercial.
Liquid Air Energy Storage (LAES)
A variant using liquefied air (cooled to −196°C). Air liquefies and is stored in insulated tanks. When needed, it is allowed to re-expand, driving a turbine. Highview Power (UK) operates a 50 MW / 250 MWh LAES demonstration plant in Manchester (53.43°N 2.24°W) — the world's largest liquid air storage plant. Advantages: No geological requirement (tanks can be placed anywhere), longer duration than batteries. Source: Highview Power
Demonstration 50 MW Manchester plant operational. Multiple larger projects in development.
Cluster 3 · Flywheel energy storage
Flywheel storage — kinetic energy for fast grid response
How flywheels work and where they are used
A flywheel stores energy as the kinetic energy of a spinning mass. Electric motors accelerate the flywheel (charging). When electricity is needed, the flywheel's rotational energy drives a generator (discharging). Modern flywheels spin at 20,000–50,000 rpm in a vacuum, using magnetic bearings to minimise friction. They can respond in milliseconds — faster than any other storage technology.
Key characteristics: Very fast response (milliseconds), unlimited cycles, very low degradation — but can only store energy for minutes to a few hours. Best suited for: frequency regulation, smoothing renewable output fluctuations, UPS (uninterruptible power supply) for data centres.
Beacon Power's Stephentown facility (New York, USA, 42.55°N 73.50°W): 20 MW flywheel park — provides frequency regulation for the New York ISO grid. 200 composite flywheel units operating since 2011. Source: Beacon Power · NREL
Amber Kinetics (USA): 8 kWh / 8 kW steel flywheel — 4 hours discharge. Deployed in 35+ sites including Hawaii and the Philippines. Longer duration than most flywheels.
Key characteristics: Very fast response (milliseconds), unlimited cycles, very low degradation — but can only store energy for minutes to a few hours. Best suited for: frequency regulation, smoothing renewable output fluctuations, UPS (uninterruptible power supply) for data centres.
Beacon Power's Stephentown facility (New York, USA, 42.55°N 73.50°W): 20 MW flywheel park — provides frequency regulation for the New York ISO grid. 200 composite flywheel units operating since 2011. Source: Beacon Power · NREL
Amber Kinetics (USA): 8 kWh / 8 kW steel flywheel — 4 hours discharge. Deployed in 35+ sites including Hawaii and the Philippines. Longer duration than most flywheels.
Commercial Flywheels for frequency regulation are commercially deployed. Long-duration flywheel: early commercial.
Cluster 3 · Gravity energy storage
Gravity storage — lifting weight to store energy
Energy Vault — concrete blocks and cranes
Energy Vault (Switzerland/USA, NYSE: NRGV) builds towers that stack heavy concrete blocks (35 tonnes each) using electric cranes. When electricity is cheap, cranes lift blocks to the top of the tower (storing gravitational potential energy). When electricity is expensive, the blocks are lowered, and the regenerative cranes generate electricity.
EVx system: 36-story towers, 50–500 MW power, 4–16 hours storage duration. First commercial project: 25 MWh demonstration in LaFarge, Switzerland (2022). Major project announced with SVC in China (100 MW / 400 MWh). Source: Energy Vault Annual Report 2023
EVx system: 36-story towers, 50–500 MW power, 4–16 hours storage duration. First commercial project: 25 MWh demonstration in LaFarge, Switzerland (2022). Major project announced with SVC in China (100 MW / 400 MWh). Source: Energy Vault Annual Report 2023
Demonstration First plants operating. Commercial-scale deployment beginning 2024.
Gravitricity — abandoned mine shafts
Gravitricity (UK) repurposes abandoned mine shafts by suspending heavy weights (500–5,000 tonnes) inside them. Lowering the weight generates electricity; raising it stores energy. Mine shafts can be 500–1,500 metres deep — providing significant head (height difference).
Why mine shafts: The shaft already exists (no civil construction). Many disused coal mines exist globally. Provides economic activity to post-industrial communities. Response time: under 1 second.
Demonstration system operating at port of Edinburgh (2022). Projects announced in former Czech and Slovak coal mines. Source: Gravitricity Ltd
Why mine shafts: The shaft already exists (no civil construction). Many disused coal mines exist globally. Provides economic activity to post-industrial communities. Response time: under 1 second.
Demonstration system operating at port of Edinburgh (2022). Projects announced in former Czech and Slovak coal mines. Source: Gravitricity Ltd
Demonstration Demonstration operating. Commercial deployments in planning across Europe.
Cluster 3 · Space-based solar power
Space-based solar power — sunlight without night or clouds
The concept and who is pursuing it
In space (geostationary orbit, ~36,000 km), solar panels receive sunlight 24 hours a day with no atmospheric absorption — approximately 8 times more energy per unit area than the best ground-based solar. The energy would be converted to microwaves (2.45 GHz) or laser beams and transmitted to a rectenna (receiving antenna) on Earth, converting microwave energy back to DC electricity.
JAXA (Japan): Demonstrated microwave wireless power transmission at 1.8 kW over 55 metres in 2015. Working toward a 1 GW orbital demonstration. Source: JAXA Space Solar Power Systems
ESA (European Space Agency): SOLARIS initiative — studying a space-based solar constellation. Formal feasibility study commissioned 2022. Source: ESA SOLARIS
UK Space Agency: Funded CASSIOPeiA concept study — a novel orientable satellite design avoiding moving parts.
US Department of Defense: AFRL successfully transmitted solar power wirelessly from orbit (Arachne experiment, 2023).
Challenges: Enormous cost of launching the mass of solar panels to orbit. Efficiency losses in wireless transmission (~15–30% round-trip). Safety of microwave beams. No commercial SBSP plant exists or is currently planned.
JAXA (Japan): Demonstrated microwave wireless power transmission at 1.8 kW over 55 metres in 2015. Working toward a 1 GW orbital demonstration. Source: JAXA Space Solar Power Systems
ESA (European Space Agency): SOLARIS initiative — studying a space-based solar constellation. Formal feasibility study commissioned 2022. Source: ESA SOLARIS
UK Space Agency: Funded CASSIOPeiA concept study — a novel orientable satellite design avoiding moving parts.
US Department of Defense: AFRL successfully transmitted solar power wirelessly from orbit (Arachne experiment, 2023).
Challenges: Enormous cost of launching the mass of solar panels to orbit. Efficiency losses in wireless transmission (~15–30% round-trip). Safety of microwave beams. No commercial SBSP plant exists or is currently planned.
Research Wireless power transmission from orbit demonstrated at small scale. Commercial SBSP: 2040s at the earliest.
Cluster 9 · Zero-point energy — what physics confirms and what it does not
Zero-point energy — what quantum mechanics actually says
Zero-point energy is a real, measured phenomenon of quantum mechanics. The claims made about it as an energy source are not. This section separates what is confirmed from what is not — precisely and without advocacy in either direction.
What quantum mechanics says — in plain English: According to quantum mechanics, even in a perfect vacuum at absolute zero temperature (−273.15°C, the coldest anything can ever be), space is not truly empty. It vibrates with a minimum energy that cannot be removed — called zero-point energy. This energy is real and has been measured: the Casimir effect (1948) demonstrates it by showing that two metal plates placed very close together are pushed together by the surrounding vacuum energy. This is confirmed physics, not speculation. What has not been demonstrated — despite many claims — is extracting useful energy from this vacuum energy. There is no working zero-point energy generator. Thermodynamics constrains extraction severely.
The confirmed physics:
Zero-point energy (ZPE): The lowest possible energy state of a quantum mechanical system is not zero — it is ½ħω per mode (where ħ is the reduced Planck constant and ω is the mode frequency). For a harmonic oscillator, ground state energy = ½ħω.
The Casimir effect (confirmed, measured): Two uncharged conducting plates in vacuum attract each other because the vacuum energy between them is lower than outside — the plates suppress some vacuum modes. Measured precisely by Lamoreaux (1997) and Mohideen (1998). Casimir force at 10 nm separation: ~1 atmosphere of pressure.
Lamb shift (confirmed): The slightly different energy levels of hydrogen's 2S and 2P states, caused by vacuum fluctuations interacting with the electron — measured to 12 decimal places and used to test quantum electrodynamics (QED).
What has not been demonstrated: Any device that extracts net useful energy from vacuum fluctuations. The Casimir effect demonstrates that vacuum energy is real, but using it to do useful work faces a fundamental thermodynamic constraint — you cannot extract net energy from a system at thermal equilibrium with its environment.
Zero-point energy (ZPE): The lowest possible energy state of a quantum mechanical system is not zero — it is ½ħω per mode (where ħ is the reduced Planck constant and ω is the mode frequency). For a harmonic oscillator, ground state energy = ½ħω.
The Casimir effect (confirmed, measured): Two uncharged conducting plates in vacuum attract each other because the vacuum energy between them is lower than outside — the plates suppress some vacuum modes. Measured precisely by Lamoreaux (1997) and Mohideen (1998). Casimir force at 10 nm separation: ~1 atmosphere of pressure.
Lamb shift (confirmed): The slightly different energy levels of hydrogen's 2S and 2P states, caused by vacuum fluctuations interacting with the electron — measured to 12 decimal places and used to test quantum electrodynamics (QED).
What has not been demonstrated: Any device that extracts net useful energy from vacuum fluctuations. The Casimir effect demonstrates that vacuum energy is real, but using it to do useful work faces a fundamental thermodynamic constraint — you cannot extract net energy from a system at thermal equilibrium with its environment.
Source: Lamoreaux, S.K. (1997) "Demonstration of the Casimir Force in the 0.6 to 6 μm Range." Physical Review Letters 78, 5. · Lamb, W.E. & Retherford, R.C. (1947), Physical Review.
In quantum field theory, the vacuum is characterised by a non-zero expectation value of the stress-energy tensor: ⟨0|T_μν|0⟩ ≠ 0. The vacuum energy density is formally infinite (the sum of ½ħω over all modes diverges), requiring renormalisation. In practice, the physically measurable quantity is the difference in vacuum energy between two configurations (e.g., parallel plates vs. infinite separation) — this finite difference is the Casimir energy. The cosmological constant problem — why the observed vacuum energy density (~10⁻⁹ J/m³ inferred from dark energy observations) is ~120 orders of magnitude smaller than naive quantum field theory predictions — remains one of the deepest unsolved problems in physics. This does not mean ZPE is extractable. The second law of thermodynamics applies: a device in thermal equilibrium with the vacuum cannot extract net work from vacuum fluctuations without an external temperature differential. No experimental violation of this has been observed.
Source: Weinberg, S. (1989) "The cosmological constant problem." Reviews of Modern Physics 61(1). · Casimir, H.B.G. (1948), Proceedings of the Royal Netherlands Academy of Sciences.
Theoretical
Confirmed: Zero-point energy exists, is measured, and has real physical effects (Casimir effect, Lamb shift). Not demonstrated: Any working device that extracts useful energy from vacuum fluctuations. Claims of "free energy" from the quantum vacuum are not supported by any peer-reviewed experimental evidence as of . Source: Physical Review Letters · Reviews of Modern Physics.
Cluster 12 · Questions
Six questions people ask — answered
What is the most promising emerging energy technology?
By institutional assessment, the two emerging technologies with the highest near-term impact potential are: (1) Green ammonia — addressing the decarbonisation of shipping, fertiliser production, and long-duration energy storage. Multiple commercial projects active; first ammonia-fuelled ships entering service 2025–2027. (2) Enhanced Geothermal Systems (EGS) — potentially making geothermal energy available globally, not just near volcanic zones. Fervo Energy's Project Red (2023) was the first commercial EGS grid delivery in the USA. Both are documented in the IEA's technology roadmaps. Source: IEA Technology Perspectives 2024 · IRENA.
Source: IEA Technology Perspectives 2024 · IRENA Innovation Outlook
Is zero-point energy real?
Yes, zero-point energy is a real phenomenon confirmed by quantum mechanics and measured experimentally. The Casimir effect — first measured precisely in 1997 — demonstrates that vacuum fluctuations exert real force between metal plates. The Lamb shift in hydrogen's spectrum is caused by vacuum fluctuations interacting with electrons, and has been measured to 12 decimal places. What has not been demonstrated is any device that extracts useful net energy from vacuum fluctuations. This distinction — between ZPE existing and ZPE being extractable as a practical energy source — is critical. No peer-reviewed experimental evidence supports the latter as of . Source: Physical Review Letters (Lamoreaux 1997) · Reviews of Modern Physics.
Source: Lamoreaux (1997), Physical Review Letters · Casimir (1948), Proceedings KNAW
What is gravity storage and does it work?
Gravity storage stores energy by lifting heavy objects and releases it by lowering them through a generator. The physics is simple and reliable — this is how pumped hydro works, and pumped hydro is the world's largest form of grid-scale energy storage at ~170 GW globally. Newer approaches (Energy Vault's concrete blocks, Gravitricity's mine shafts) apply the same principle without requiring natural geography. Energy Vault and Gravitricity both have operating demonstration plants (2022–2023). The physics is proven. The economic question is whether the cost per MWh stored competes with lithium-ion batteries and pumped hydro as those technologies also continue to improve. Source: Energy Vault Annual Report 2023 · Gravitricity Ltd.
Source: Energy Vault Annual Report 2023 · Gravitricity technical documentation · IEA Storage Report 2024
Can we generate electricity from space using solar power?
The concept is physically sound: solar panels in geostationary orbit receive approximately 8 times more energy per unit area than ground-based panels (no night, no clouds, no atmosphere). The energy would be transmitted to Earth as microwaves or laser beams. The US Air Force Research Laboratory's Arachne experiment (2023) successfully transmitted solar power wirelessly from orbit for the first time. JAXA (Japan) and ESA (Europe) have active research programmes. The challenge is economics: launching the mass of solar panels to orbit costs enormous amounts of energy and money — making space-based solar far more expensive than ground-based solar today. No commercial space-based solar plant is under construction. The IEA considers it a possible long-term technology. Source: JAXA · ESA SOLARIS · US AFRL.
Source: JAXA Space Solar Power Systems · ESA SOLARIS · US Air Force Research Laboratory (2023)
What is the difference between a battery and a flywheel?
A battery stores energy chemically — in the bonds of lithium compounds. A flywheel stores energy as kinetic energy — in the rotation of a spinning mass. Key differences: Batteries have high energy density (can store a lot of energy in small space) but degrade over thousands of charge cycles. Flywheels can spin up and down millions of times without degradation, respond in milliseconds, and last decades — but can only store energy for minutes to hours. Batteries are better for long-duration storage (overnight solar buffering); flywheels are better for rapid, short-duration grid frequency regulation. Some grids use both: flywheels for instant response and batteries for longer storage. Source: NREL Energy Storage · IEA Storage 2024.
Source: NREL Energy Storage Technology Characterisation · IEA Batteries and Secure Energy Transitions 2024
What is green ammonia and why does it matter?
Green ammonia is ammonia (NH₃) made using green hydrogen — hydrogen produced by electrolysis of water using renewable electricity — combined with nitrogen from the air. Conventional ammonia (grey) uses natural gas as the hydrogen source, releasing CO₂. Green ammonia contains no carbon, so when burned it produces only water and nitrogen — no CO₂. It matters because: (1) Shipping cannot easily electrify, and ammonia is a practical carbon-free fuel that existing ship engines can be modified to use. (2) Fertiliser production consumes ~2% of global energy — green ammonia could decarbonise this. (3) Ammonia is far easier to store and transport than hydrogen (liquid at −33°C vs −253°C for liquid hydrogen). Multiple green ammonia plants are under development globally. First commercial ammonia-fuelled ships are due for delivery 2025–2027. Source: IEA Future of Hydrogen 2023 · IMO 2023 GHG Strategy.
Source: IEA — The Future of Hydrogen 2023 · IMO 2023 Revised GHG Strategy
Cluster 10
Explore further
Source register
Every source used on this page
Primary sources
IEAThe Future of Hydrogen 2023 · Technology Perspectives 2024 · Batteries 2024 · WEO 2024iea.org/future-of-hydrogen
IMOInternational Maritime Organization · 2023 Revised GHG Strategyimo.org/revised-ghg-strategy
IRENAInnovation Outlook: Ammonia · Energy Storage 2024irena.org/ammonia
Physical Review LettersLamoreaux (1997) — Casimir force measurement · Zero-point energy confirmationjournals.aps.org/prl
NRELEnergy Storage Technology Characterisation · Flywheel and CAES datanrel.gov/grid/energy-storage
JAXASpace Solar Power Systems research programmejaxa.jp/ssps
ESASOLARIS initiative — space-based solar power studyesa.int/SOLARIS
Energy VaultAnnual Report 2023 · EVx gravity storage systemenergyvault.com
Fervo EnergyProject Red EGS demonstration results 2023fervoenergy.com
Highview PowerLiquid air energy storage — Manchester demonstration planthighviewpower.com