Energy Challenges and Fusion

Since the Industrial Revolution, humanity has built an energy system heavily dependent on fossil fuels. However, facing the dual challenges of resource depletion and global warming, establishing new energy sources has become urgent. Fusion energy is one of the most promising solutions to these challenges.

This chapter provides a comprehensive overview of global energy challenges and examines where fusion energy fits into the picture.

Current State of Global Energy Demand

Trends in Primary Energy Consumption

According to data from the International Energy Agency (IEA), global primary energy consumption reached approximately 604 EJ (exajoules, 10^18 J) in 2022. This is equivalent to about 14.4 billion tonnes of oil equivalent.

The historical trend of primary energy consumption shows remarkable growth since the Industrial Revolution.

Year	Primary Energy Consumption (EJ)	World Population (billions)	Per Capita (GJ)
1800	~20	1.0	20
1900	~40	1.6	25
1950	~100	2.5	40
1970	~250	3.7	68
2000	~420	6.1	69
2010	~520	6.9	75
2022	~604	8.0	76

From the latter half of the 20th century through the 21st century, energy consumption has increased dramatically. In approximately 70 years from 1950 to 2022, primary energy consumption has grown more than six-fold.

Energy Source Composition

Looking at global primary energy consumption by source in 2022, fossil fuels still dominate overwhelmingly.

Energy Source	Consumption (EJ)	Share
Oil	190.7	31.6%
Coal	161.5	26.7%
Natural Gas	140.0	23.2%
Hydropower	40.4	6.7%
Nuclear	24.7	4.1%
Renewables (excl. hydro)	39.9	6.6%
Biomass & Others	6.8	1.1%

The combined total of fossil fuels (oil, coal, and natural gas) is approximately 492 EJ, accounting for 81.5% of the total. Despite progress in renewable energy adoption, the global energy structure remains heavily dependent on fossil fuels.

Regional Energy Consumption

There are significant regional disparities in energy consumption.

Region	Primary Energy Consumption (EJ)	Population (billions)	Per Capita (GJ)
North America	110.3	0.37	298
Europe	82.4	0.75	110
Asia Pacific	294.2	4.22	70
Middle East	35.5	0.28	127
Central & South America	28.9	0.66	44
Africa	18.3	1.42	13
Former Soviet Union	34.4	0.29	119

North America’s per capita energy consumption of 298 GJ/person is approximately 23 times that of Africa (13 GJ/person). This disparity clearly demonstrates the correlation between economic development levels and energy consumption.

NASA satellite photos of Earth at night show developed countries shining brightly, visually confirming the uneven distribution of energy consumption. Conversely, as parts of Africa and Asia achieve economic development, global energy demand is expected to increase further.

Future Energy Demand Projections

According to the IEA’s World Energy Outlook 2023, global primary energy demand in 2050 is projected as follows under various scenarios.

Scenario	2050 Energy Demand (EJ)	Change from 2022
Stated Policies Scenario (STEPS)	750	+24%
Announced Pledges Scenario (APS)	620	+3%
Net Zero Emissions Scenario (NZE)	540	-11%

Under the Stated Policies Scenario, energy demand in 2050 is projected to increase by 24% compared to 2022, reaching 750 EJ. Meanwhile, under the Net Zero Scenario to achieve climate targets, demand decreases to 540 EJ through energy efficiency improvements, but massive energy supply is still required.

Particularly noteworthy is the increase in electricity demand. Due to electrification trends, global electricity demand in 2050 is projected to be approximately twice current levels. The main factors include the proliferation of electric vehicles, electrification of industrial processes, and growth of data centers.

Rising Energy Demand in Developing Countries

The world population is projected to reach approximately 9.7 billion by 2050 and approximately 10.9 billion by 2100 (UN medium projection). Most population growth will occur in Africa and Asia.

Let’s estimate the energy demand increase if developing countries improve energy access and aim for living standards comparable to developed nations.

Simply raising Africa’s current per capita energy consumption (13 GJ/person) to the global average (76 GJ/person) would increase Africa’s energy demand to about six times its current level. Furthermore, in a scenario where the global average rises to current European levels (110 GJ/person), global energy demand could increase to about 1.5 times current levels.

To meet increasing energy demand while curbing climate change, substantial expansion of low-carbon energy sources is essential.

Limitations of Fossil Fuels

Reserves and Years of Remaining Supply

Fossil fuels are finite resources. The years of remaining supply calculated from proven recoverable reserves (amounts extractable with current technology and economic conditions) and annual consumption are as follows.

Resource	Proven Reserves	Annual Consumption	Years of Supply
Oil	1.744 trillion barrels	~100 billion barrels/year	~54 years
Natural Gas	210 trillion m³	~4 trillion m³/year	~53 years
Coal	1.0748 trillion tonnes	~8 billion tonnes/year	~134 years

These figures fluctuate with new resource discoveries and advances in extraction technology. During the 1970s oil shocks, it was said that “oil will be depleted in 30 years,” but subsequent technological innovations have extended the years of remaining supply.

However, the fact that fossil fuels are finite remains unchanged. Even including unconventional resources (shale oil, oil sands, shale gas, methane hydrates, etc.), major fossil fuel resources are projected to be depleted within 100-200 years at current consumption rates.

Rising Extraction Costs

Since easily accessible resources are developed first, the extraction cost of remaining resources is trending upward.

Conventional oil extraction costs range from $10-40 per barrel, but deepwater oil fields cost$40-80, oil sands cost $50-90, and Arctic oil fields cost$75-100 or more per barrel.

Rising extraction costs create long-term upward pressure on energy prices and impact economic activity. Additionally, resources that are more difficult to extract tend to have greater environmental impacts.

Declining Energy Return on Investment (EROI)

Energy Return on Investment (EROI) is an indicator showing how much energy is obtained relative to the energy invested in energy production.

$$\text{EROI} = \frac{\text{Energy Obtained}}{\text{Energy Invested}}$$

The EROI for various energy sources is as follows.

Energy Source	EROI
Conventional Oil (1930s)	100:1
Conventional Oil (current)	15-20:1
Deepwater Oil	5-10:1
Oil Sands	3-5:1
Shale Oil	2-5:1
Coal	20-80:1
Natural Gas	20-30:1
Nuclear (fission)	10-15:1
Wind Power	15-25:1
Solar Power	6-12:1
Fusion (projected)	25-50:1

The EROI of conventional oil in the 1930s exceeded 100:1, but has now declined to around 15-20:1. As easily extractable resources decrease, more energy must be invested to obtain new energy.

When EROI declines, the cost and environmental burden required to obtain the same amount of energy increases. Generally, energy sources with an EROI of 5:1 or higher are considered necessary to maintain civilization.

Geopolitical Risks

Fossil fuel resources are geographically concentrated, creating energy security risks.

Approximately 48% of oil reserves are concentrated in the Middle East. Natural gas reserves are also concentrated in the Middle East and Russia, with both regions accounting for about 58% of global reserves.

Russia’s invasion of Ukraine in 2022 highlighted the importance of energy security once again. European countries were forced to rapidly reduce their dependence on Russian natural gas, experiencing energy price spikes and supply uncertainty.

From an energy security perspective, securing diverse energy sources that do not depend on specific regions or resources is essential.

Global Warming and CO2 Emissions

The Mechanism of the Greenhouse Effect

Earth’s atmosphere contains greenhouse gases including carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and fluorinated gases. These gases absorb infrared radiation emitted from the Earth’s surface, warming the atmosphere.

The greenhouse effect itself is essential for maintaining Earth’s temperature. Without the greenhouse effect, Earth’s average temperature would drop from the current approximately 15°C to about -18°C, making life as we know it impossible.

The problem is that human activities have caused a rapid increase in greenhouse gas concentrations. The rise in CO2 concentration is particularly notable, increasing from approximately 280 ppm before the Industrial Revolution to approximately 420 ppm in 2023. This is a level unprecedented in the past 800,000 years.

Current and Projected Temperature Rise

According to the IPCC (Intergovernmental Panel on Climate Change) Sixth Assessment Report, Earth’s average temperature has risen approximately 1.1°C since the Industrial Revolution. It is scientifically virtually certain that human-caused greenhouse gas emissions are the main cause of this warming.

Future temperature rise projections vary significantly depending on greenhouse gas emission scenarios.

Scenario	Temperature Rise by 2100 (from pre-industrial)
SSP1-1.9 (Sustainable Development - Low Emissions)	1.4°C (1.0-1.8°C)
SSP1-2.6 (Sustainable Development)	1.8°C (1.3-2.4°C)
SSP2-4.5 (Middle of the Road)	2.7°C (2.1-3.5°C)
SSP3-7.0 (Regional Rivalry)	3.6°C (2.8-4.6°C)
SSP5-8.5 (Fossil Fuel Development)	4.4°C (3.3-5.7°C)

The 2015 Paris Agreement agreed to hold temperature rise to well below 2°C above pre-industrial levels and pursue efforts to limit it to 1.5°C.

To achieve the 1.5°C target, the IPCC reports that CO2 emissions must be reduced by 45% from 2010 levels by 2030, and net zero (balance between emissions and absorption) must be achieved by around 2050.

Current State of CO2 Emissions

Global CO2 emissions reached approximately 36.8 billion tonnes in 2022. This is a record high.

The sectoral composition of CO2 emissions is as follows.

Sector	CO2 Emissions (billion tonnes)	Share
Power & Heat Generation	14.6	39.7%
Industry	9.2	25.0%
Transport	8.0	21.7%
Buildings	3.0	8.2%
Others	2.0	5.4%

Power and heat generation is the largest emission source, accounting for about 40% of the total. Decarbonizing the power sector is one of the most critical challenges in addressing climate change.

By country, China is the largest CO2 emitter accounting for about 30% of the global total, followed by the United States (~14%), EU (~8%), India (~7%), and Russia (~5%).

Impacts of Global Warming

Even at the current 1.1°C temperature rise, the effects of warming are being observed worldwide.

Arctic sea ice extent has been declining at a rate of about 13% per decade since satellite observations began in 1979. The minimum sea ice extent in September 2022 was approximately 4.72 million km², significantly reduced from the 1979-1990 average of approximately 7.1 million km².

Sea level rose approximately 20 cm between 1901 and 2018. Projections for rise by the end of the 21st century range from 43-84 cm (median) depending on the scenario. Island nations such as Tuvalu, Maldives, and Kiribati face the risk of losing their territories.

The frequency and intensity of extreme weather events are increasing. In the 2022 Pakistan floods, abnormally heavy monsoon rains submerged about one-third of the country, killing more than 1,700 people and affecting over 33 million. In the 2023 Canadian wildfires, a record area of over 180,000 km² was burned.

Impacts on ecosystems are also severe. Coral reef bleaching, changes in species distribution ranges, and shifts in biological seasons (flowering times, migration timing, etc.) are being observed.

Difficulty of Emission Reductions

The global economic shutdown during the 2020 COVID-19 pandemic highlighted the difficulty of reducing CO2 emissions. Despite grounded aircraft, factory shutdowns, and dramatic reductions in automobile traffic, CO2 emissions decreased by only 5.8% compared to the previous year.

UNEP (United Nations Environment Programme) estimates that achieving the 1.5°C target requires approximately 7.6% annual emission reductions continuing until 2030. Reducing emissions at this pace while maintaining economic activity is extremely difficult with current technology and energy systems.

Achieving “decoupling” - reconciling economic growth with CO2 emission reductions - requires breakthrough technological innovation and fundamental transformation of energy systems.

Challenges of Renewable Energy

Renewable energy is an important pillar of climate change measures, but faces several fundamental challenges.

The Intermittency Problem

Solar power generates electricity only during daylight hours, and wind power generates only when the wind blows. This intermittency (output variability) poses a major challenge for stable power grid operation.

The annual capacity factor for solar power is about 14% in Japan, about 11% in Germany, and around 25% even in the US Southwest. Wind power capacity factors range from 20-35% onshore and 35-50% offshore. In contrast, nuclear power has a capacity factor of 80-90%, and thermal power ranges from 40-80%.

A low capacity factor means that more installed capacity is needed to obtain the same amount of generated electricity. For example, to obtain an average output of 1 GW annually, solar power with a 14% capacity factor requires approximately 7.1 GW of installed capacity, while nuclear power with an 85% capacity factor requires only about 1.2 GW.

Impact on Grid Stability

In power grids, generation (supply) and consumption (demand) must always be balanced. If this balance is disrupted, frequency fluctuates, potentially leading to large-scale blackouts in the worst case.

As the share of Variable Renewable Energy (VRE) increases, maintaining supply-demand balance becomes more difficult. On sunny days, solar power output surges during midday, creating “surplus electricity” exceeding demand, while after sunset, output drops to zero and must be compensated by other power sources.

This problem is visualized by the load curve shape known as the “duck curve.” In California, the massive introduction of solar power during daytime causes net demand (demand minus solar output) to dip significantly during the day and surge rapidly in the evening.

Large-Scale Energy Storage Challenges

The most direct way to solve intermittency is to store surplus electricity and discharge it when needed. However, large-scale electricity storage currently faces economic and technical challenges.

The most widely deployed storage system today is lithium-ion batteries, but they are expensive as grid-scale storage facilities and have energy density limitations.

Comparing storage technology costs and characteristics:

Storage Technology	Capital Cost ($/kWh)	Round-Trip Efficiency	Discharge Duration	Lifespan
Lithium-Ion Batteries	200-400	85-95%	2-8 hours	10-15 years
Pumped Hydro	50-150	75-85%	6-12 hours	50+ years
Compressed Air (CAES)	50-100	50-70%	8-26 hours	30+ years
Flow Batteries	300-500	65-80%	4-12 hours	15-20 years

Pumped hydro is the most mature large-scale storage technology, but suitable terrain is limited. Japan has approximately 27 GW of pumped hydro capacity, but sites for new development are limited.

Seasonal energy storage (using summer surplus in winter) is even more challenging. Conversion to and storage of hydrogen is a promising option, but the electricity-to-hydrogen-to-electricity conversion efficiency is only about 30-40%, and cost remains an issue.

Energy Density Constraints

Renewable energy has an inherently lower energy density compared to fossil fuels or nuclear power.

Comparing power generation per unit area for each energy source:

Energy Source	Power Density (W/m²)
Nuclear Power Plant	500-1,000
Coal Power Plant	100-1,000
Natural Gas Power Plant	200-2,000
Solar Power (ground-mounted)	5-20
Wind Power (onshore)	1-3
Wind Power (offshore)	2-5
Biomass Power	0.5-1

Nuclear power plants have a power density 50-100 times that of solar and 200-500 times that of wind power. Renewable energy requires far more land area to generate the same amount of electricity.

Approximate land area required for 1 GW of generation capacity:

Energy Source	Required Area (km²)
Nuclear Power Plant	1-3
Coal Power Plant	5-10
Solar Power	15-30
Onshore Wind Power	100-300

In countries like Japan with limited land area and available space, energy density constraints are particularly severe.

Resource and Material Constraints

Manufacturing renewable energy equipment requires specific mineral resources.

Solar panels use silicon, silver, tellurium, indium, gallium, and other materials. Wind power uses rare earth elements such as neodymium and dysprosium in permanent magnets. Batteries require lithium, cobalt, nickel, manganese, and other materials.

Many of these resources are concentrated in specific countries. Australia, Chile, and China account for about 90% of lithium production, while the Democratic Republic of Congo produces about 70% of cobalt. China accounts for about 60% of rare earth element production.

The volume of resources needed for large-scale renewable energy deployment is enormous. According to IEA estimates, demand for critical minerals needed for the clean energy transition could increase 4-6 times current levels by 2040.

Need for Backup Power

Backup power sources are needed to compensate for the variability of renewable energy. Currently, natural gas power plants often fill this role, but they produce CO2 emissions.

In Germany, the Energiewende (energy transition policy) has actively promoted renewable energy deployment, but combined with the phased shutdown of nuclear power plants, the country continues to rely on coal and natural gas power on windless days or cloudy weather.

Aiming for 100% renewable energy requires restructuring the entire system, including large-scale storage facilities, wide-area transmission networks, and improved demand-side flexibility. This requires enormous investment and time.

Challenges of Nuclear Fission Power

Nuclear power (fission) can contribute to climate change countermeasures as a low-carbon power source, but faces several fundamental challenges.

The Radioactive Waste Problem

Nuclear power plants generate high-level radioactive waste (spent nuclear fuel) during operation. This waste must be safely managed and isolated for tens of thousands to hundreds of thousands of years until radioactivity decays sufficiently.

The composition and half-lives of spent nuclear fuel are as follows:

Nuclide	Half-Life	Characteristics
Cesium-137 (Cs-137)	~30 years	Major heat source, main cause of environmental contamination
Strontium-90 (Sr-90)	~29 years	Accumulates in bones, high biological hazard
Plutonium-239 (Pu-239)	~24,000 years	Nuclear weapons material, highly toxic
Neptunium-237 (Np-237)	~2.14 million years	Long-lived, major challenge for geological disposal
Technetium-99 (Tc-99)	~210,000 years	Soluble, groundwater contamination risk

Deep geological disposal (burial in stable bedrock hundreds of meters underground) is internationally recommended as the final disposal method for high-level radioactive waste, but selection of final disposal sites has been difficult in many countries.

As of 2024, the only operational final disposal facility for high-level radioactive waste is Finland’s Onkalo repository. In Japan, the site selection process for a final repository is underway, but no candidate site has been determined.

Safety and Accident Risk

Nuclear power plant accidents can have severe impacts over wide areas.

In the 1986 Chernobyl disaster, core meltdown and explosion released massive amounts of radioactive material. Direct fatalities numbered in the dozens, but long-term health effects from radiation exposure are estimated to affect thousands to tens of thousands of people. Approximately 350,000 people were forced to evacuate, and the 30-km radius zone remains a restricted area today.

In the 2011 Fukushima Daiichi accident, an earthquake and tsunami caused meltdowns in three reactors. Approximately 160,000 people evacuated, and some areas remain designated as difficult-to-return zones. Accident cleanup costs are estimated at over 20 trillion yen.

Nuclear power plant safety continues to improve, but accident risk cannot be reduced to zero. Furthermore, when accidents do occur, the social and economic impacts are incomparably larger than those of other energy sources.

Nuclear Proliferation Risk

Nuclear power technology and nuclear weapons technology are closely related. Plutonium contained in spent nuclear fuel can be used as material for nuclear weapons.

Uranium enrichment technology is also commonly used for both low-enriched uranium for power generation (U-235 concentration 3-5%) and weapons-grade highly enriched uranium (U-235 concentration 90% or higher).

The expansion of nuclear power could increase the risk of nuclear weapons technology proliferation. Safeguards (inspection and monitoring) by the International Atomic Energy Agency (IAEA) are implemented, but complete monitoring is difficult.

Finite Uranium Resources

Uranium, the fuel for nuclear power, is also a finite resource.

As of 2021, proven uranium reserves were approximately 6.2 million tonnes (recovery cost under $130/kg). Calculated with annual consumption of approximately 60,000 tonnes, the years of supply is about 100 years.

Uranium resources are also geographically concentrated. Six countries - Australia, Kazakhstan, Canada, Russia, Namibia, and Uzbekistan - account for approximately 85% of global proven reserves.

Technologies such as fast breeder reactors and thorium fuel cycles that could dramatically improve uranium resource utilization efficiency are being researched but have not been commercialized.

Construction Cost and Schedule Issues

Nuclear power plant construction costs have been trending upward.

Recent projects in Europe and the United States have experienced significant cost overruns. Finland’s Olkiluoto 3 escalated from an initial estimate of about EUR 3.2 billion to over EUR 11 billion, taking more than 18 years to complete. The UK’s Hinkley Point C has increased from an initial estimate of about GBP 18 billion to over GBP 32-33 billion.

Rising construction costs and schedule delays undermine the economics of nuclear power and increase investment recovery uncertainty.

Advantages of Fusion Energy

Fusion energy has the potential to solve many of the challenges facing each energy source described above.

Abundant and Evenly Distributed Fuel

Deuterium (D), the primary fuel for fusion, exists at a ratio of 1 in every 6,700 ordinary hydrogen atoms and is contained in Earth’s seawater at approximately 0.015%.

Let’s calculate the amount of deuterium in seawater.

The total volume of seawater on Earth is approximately 1.4 billion km³ (1.4 × 10^21 liters). With a deuterium concentration in seawater of 0.015%, the total deuterium amounts to approximately 4.6 × 10^16 kg.

The energy release from D-T fusion reaction is approximately 3.4 × 10^14 J per kilogram of deuterium. Dividing this by global annual primary energy consumption (approximately 6 × 10^20 J), deuterium in seawater alone could meet energy demand for billions of years.

Tritium (T), the other fuel, hardly exists naturally but can be produced by irradiating lithium with neutrons.

$$^6\text{Li} + n \rightarrow {}^4\text{He} + \text{T} + 4.78 \text{ MeV}$$

Lithium is also abundant in seawater and the Earth’s crust, with total lithium in seawater estimated at approximately 230 billion tonnes.

Importantly, these resources are evenly distributed in seawater worldwide. Unlike fossil fuels or uranium concentrated in specific countries or regions, fusion fuel is accessible to all maritime nations. This represents a major energy security advantage.

Overwhelming Energy Density

The energy released by fusion reactions is millions of times greater than chemical reactions (combustion).

Reaction	Energy Release (MeV/reaction)	Energy per kg of Fuel
Oil Combustion	~0.00004	~4.2 × 10^7 J (42 MJ)
Uranium Fission (U-235)	~200	~8.2 × 10^13 J (82 TJ)
D-T Fusion	17.6	~3.4 × 10^14 J (340 TJ)

The energy density of D-T fusion is about 8 million times that of oil and about 4 times that of uranium fission.

Specifically, the energy from 1 gram of deuterium is equivalent to about 8 tonnes of oil or about 12 tonnes of coal. If Japan’s annual electricity consumption (approximately 1 trillion kWh) were supplied by fusion, only about 100 tonnes of deuterium would be needed.

Low Environmental Impact

Fusion power does not emit CO2 during operation. The reaction products are helium (an inert gas) and neutrons, and no air pollutants are generated.

$$\text{D} + \text{T} \rightarrow {}^4\text{He} (3.52 \text{ MeV}) + n (14.07 \text{ MeV})$$

The lifecycle CO2 emissions from fusion power (including construction, fuel production, and decommissioning) are estimated to be comparable to or lower than solar or wind power.

Generation Method	Lifecycle CO2 Emissions (g-CO2/kWh)
Coal Power	820-1,200
Natural Gas (Combined Cycle)	410-520
Solar Power	20-50
Wind Power (offshore)	10-25
Nuclear (fission)	5-20
Fusion (projected)	5-15

Fusion reactor structural materials become activated by neutron irradiation, but this differs in nature from spent fuel in fission reactors. With appropriate material selection, development of “reduced-activation materials” whose radioactivity levels become equivalent to general waste in about 100 years is progressing.

The fact that no high-level radioactive waste (spent nuclear fuel) is generated is a major advantage of fusion.

Inherent Safety

Fusion reactors have fundamentally different safety characteristics from fission reactors.

Fission reactions are chain reactions that can potentially run away if not controlled. In contrast, fusion reactions are non-chain reactions. If plasma conditions change even slightly, the reaction stops, making runaway reactions physically impossible.

Fusion reactor plasma is extremely dilute, with only a few grams of fuel in the reactor at any time. If any abnormality occurs, the plasma rapidly cools and the reaction automatically stops. Events like core meltdown cannot occur.

Additionally, fusion fuel (deuterium, tritium) cannot be directly used as nuclear weapons material, reducing nuclear proliferation risk.

Stable Baseload Power Source

Fusion power generation does not have the intermittency of renewable energy and can supply stable electricity regardless of weather or time. A capacity factor of 80-90% is expected.

Baseload power sources (sources that operate stably at all times) play an important role in power grids. Currently, this role is mainly filled by coal, natural gas, and nuclear power, but from a decarbonization perspective, these are problematic.

Fusion is an ideal baseload power source that can supply large amounts of stable power without emitting CO2 and without fuel supply concerns. It is expected to complement renewable energy and ensure power system stability.

Meaning and Target Values of Energy Gain (Q Value)

Definition of Q Value

In evaluating the feasibility of fusion energy, energy gain (Q value, or energy multiplication factor) is one of the most important indicators.

Q value is defined as the ratio of energy generated by fusion reactions (P_fusion) to the energy externally input to heat and sustain the plasma (P_input).

$$Q = \frac{P_{\text{fusion}}}{P_{\text{input}}}$$

Q = 1 is called “breakeven,” where input energy equals output energy. Q > 1 means more energy is obtained from the fusion reaction than was input.

Scientific Q and Engineering Q

There is a distinction between “scientific Q (Q_sci)” and “engineering Q (Q_eng).”

Scientific Q is the ratio of heating power input to the plasma to fusion output. This is an indicator from the plasma physics perspective and is used to evaluate experimental device performance.

Engineering Q, on the other hand, considers the energy balance of the entire power plant. It is the ratio of total input, including power needed for heating devices, cooling systems, superconducting magnet cooling, and other auxiliary equipment, to power output from the generator.

$$Q_{\text{eng}} = \frac{P_{\text{electric output}}}{P_{\text{electric input (total)}}}$$

For a commercial power plant to be viable, the engineering Q must be significantly greater than 1. Generally, Q_eng > 5-10 is considered the benchmark for an economically viable power plant.

Achieved Values to Date

Let’s look at the progression of Q values achieved in fusion research.

Device	Year	Q Value (Scientific)	Notes
TFTR (USA)	1994	0.27	D-T experiments
JET (EU)	1997	0.67	D-T experiments, world record at the time
JET (EU)	2021	0.33	59 MJ output (5 seconds), energy record
NIF (USA)	2022	1.5 (target)	Inertial confinement, target basis

In December 2022, the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory in the United States achieved scientific breakeven (Q > 1) for the first time in the world using laser inertial confinement. Against 2.05 MJ of energy input to the target (fuel capsule) from the laser, fusion output was 3.15 MJ (Q approximately 1.5).

However, including laser generation efficiency in the total input, the Q value is less than 0.01. NIF’s primary purpose is nuclear weapons research, and the path to power generation differs from magnetic confinement approaches.

ITER’s Goals

ITER (International Thermonuclear Experimental Reactor), currently under construction, aims for Q = 10. The goal is to achieve 500 MW of fusion output with 50 MW of heating input.

ITER’s design parameters are as follows:

Parameter	Value
Plasma Volume	840 m³
Plasma Major Radius	6.2 m
Plasma Current	15 MA
Magnetic Field Strength (toroidal)	5.3 T
Fusion Output	500 MW
Heating Input	50 MW
Q Value Target	10
Pulse Duration	400-3,000 seconds

ITER aims to be the world’s first device to achieve Q > 1 using magnetic confinement. Full operation is scheduled to begin around 2035.

Q Value Required for Power Plants

Commercial fusion power plants require even higher Q values.

Assuming a power plant thermal efficiency of 35% and an auxiliary power ratio (proportion of generated power consumed on-site) of 25%, a scientific Q value of approximately 15 or higher is needed to achieve an engineering Q of 1.

For an economically viable power plant, an engineering Q of 5-10 or higher, meaning a scientific Q of about 25-50, is considered necessary. Many designs for demonstration reactors (DEMO) after ITER target Q greater than or equal to 30.

Meanwhile, research continues toward achieving the “ignition” condition (Q = infinity, where the plasma is self-sustaining without external heating).

Future Cost Projections for Power Generation

Current Power Generation Cost Comparison

Let’s compare the Levelized Cost of Electricity (LCOE) for various generation methods. LCOE is the total cost of building, operating, and decommissioning a power plant divided by the electricity generated, and is a standard metric for comparing different generation methods.

Representative LCOE values as of 2023 (USA, $/MWh) are as follows:

Generation Method	LCOE ($/MWh)	Notes
Onshore Wind	24-50	Varies by location
Utility-Scale Solar	28-44	Varies by solar conditions
Natural Gas Combined Cycle	39-67	Fuel price volatility
Coal	65-150	Depends on CO2 price
Nuclear (new build)	119-192	Rising construction costs
Offshore Wind	72-140	Costs declining rapidly
Solar with Storage	46-102	4-hour battery

Renewable energy costs (especially solar and onshore wind) have declined dramatically over the past decade and are now the cheapest generation methods in many regions. Meanwhile, new nuclear (fission) construction costs are trending upward.

Fusion Power Cost Projections

Predicting fusion power plant costs is difficult since no commercial reactors exist yet. However, several research institutions have published projections.

A 2021 US Department of Energy (DOE) report projected LCOE for commercial fusion power plants at approximately $50-100/MWh. This is significantly cheaper than current nuclear plants but higher than the lowest renewable energy costs.

A 2020 UK Atomic Energy Authority (UKAEA) study estimated LCOE for fusion power plants based on STEP (the UK’s demonstration reactor program) at GBP 60-100/MWh.

Cost Reduction Factors

Several factors could potentially reduce fusion power costs.

Adoption of High-Temperature Superconducting (HTS) magnets can increase magnetic field strength compared to conventional low-temperature superconducting magnets, allowing device size reduction. Commonwealth Fusion Systems, an MIT spinoff, is developing the compact SPARC reactor using HTS magnets, aiming for significant construction cost reductions.

Mass production effects are also important. Major fusion reactor components (magnets, vacuum vessels, blankets, etc.) are currently custom-built, but standardization and mass production as commercial reactors proliferate could reduce manufacturing costs.

Learning curve effects may lead to schedule compression and cost reduction as construction experience accumulates. Solar panels achieved approximately 90% cost reduction over the past 20 years, a cumulative effect of mass production and technical improvements.

Considering External Costs

When evaluating power generation costs, it is important to consider social costs from CO2 emissions and air pollution (external costs).

The Social Cost of Carbon varies widely depending on estimation methods, but the US Environmental Protection Agency’s (EPA) 2023 estimate is $51/tonne CO2. Meanwhile, the Stern Review (2006) and more recent studies suggest values of$100-200/tonne CO2 or higher.

With a social cost of carbon of $100/tonne, coal power has$82-120/MWh in additional external costs, and natural gas power has $41-52/MWh. Including these, fusion power’s relative competitiveness improves significantly.

As carbon pricing systems (emissions trading and carbon taxes) strengthen, fossil fuel power costs will rise, improving the economics of low-carbon power sources.

Values Beyond Economics

The value of fusion power cannot be measured by generation costs alone.

From an energy security perspective, power generation using domestic fuel (extracting deuterium from seawater) eliminates dependence on imported fuels and reduces geopolitical risk.

The value of stable supply is also important. Baseload power sources that complement renewable energy variability and ensure power grid stability have value that cannot be expressed in simple LCOE comparisons.

Long-term fuel price stability is another feature of fusion. Unlike fossil fuels exposed to fuel price volatility, fusion can achieve stable long-term generation costs.

Summary

The global energy problem is becoming increasingly severe under the triple constraints of rising demand, finite fossil fuels, and climate change.

Renewable energy is an important solution, but it has intermittency and energy density constraints, making it difficult to meet modern society’s energy demand alone. Nuclear power (fission) is a stable low-carbon power source but faces challenges including radioactive waste, accident risk, and nuclear proliferation.

Fusion energy has the potential to fundamentally solve these challenges.

• Fuel is inexhaustibly available from seawater and evenly distributed worldwide
• Energy density is millions of times greater than fossil fuels
• No CO2 emissions and extremely low environmental impact
• Inherently safe with no runaway accident risk
• Does not generate high-level radioactive waste
• Complements renewable energy as a stable baseload power source

Technical challenges remain for realizing fusion energy, but research and development is accelerating with ITER construction and the emergence of private fusion companies.

Toward solving the energy problem, fusion is not competing with other energy sources but complementing them. By maximizing renewable energy utilization while adding fusion as a stable large-scale power source, a sustainable energy system can be built.

Next Steps

Toward realizing fusion energy, international projects including ITER are underway. Technology development to heat plasma to over 100 million degrees and sustain it for extended periods is progressing on a global scale.

For basic principles of fusion, see What is Fusion; for conditions to achieve fusion, see Lawson Criterion; for plasma confinement methods, see Confinement Methods.