Global Energy Reserves and Future

Global energy systems form a multi-layered structure encompassing production, transmission, and consumption processes. These systems are shaped by objectives of economic growth, energy security, and environmental sustainability.

Global energy consumption has increased significantly over the past 50 years in parallel with economic growth and population expansion. Annual energy consumption, which stood at approximately 63 trillion kilowatt-hours (TWh) in the 1970s, reached about 180 trillion TWh by 2023. This increase has been accelerated particularly by the industrialization processes of developing countries.

By energy source, consumption distribution is 30 percent oil, 25 percent coal, 22 percent natural gas, 7 percent biomass, 6 percent hydropower, 4 percent nuclear, 3 percent wind, and 2 percent solar. In terms of sectoral distribution, the largest shares are held by the industrial, transportation, and residential sectors (Figure 2).

Energy Sources

The technical, economic, and environmental comparison of energy sources forms the foundation of energy policy. This evaluation is conducted using multidimensional indicators such as specific energy density (MJ/kg), capacity factor (%), capital investment cost ($/kW), production cost ($/MWh), carbon emissions (ton CO₂/GWh), land requirement (m²/MWh), and water consumption (L/MWh).

In this context, nuclear energy stands out due to its very high energy density, capacity factors approaching 90 percent, and low carbon emissions. However, nuclear energy technology is subdivided into different reactor types. The most common, Light Water Reactors (LWR), consume only the U-235 isotope, leaving the majority of the fuel unused and becoming waste. In contrast, Breeder reactors can convert not only the used fuel but also non-fissile isotopes such as U-238 or Th-232 into new fissile material. This increases fuel utilization efficiency and extends reserve lifetimes manyfold. The energy density of breeder reactors is approximately one order of magnitude higher than that of conventional LWRs (~8×10⁷ MJ/kg).

Although not yet commercialized, nuclear fusion is also considered a potential option in energy policy. Fusion has practically unlimited energy potential due to the abundant availability of hydrogen isotopes, particularly deuterium and tritium. Moreover, fusion reactions produce no carbon emissions and generate no long-lived radioactive waste, making them highly advantageous environmentally. However, the development of a fusion reactor capable of producing stable and net-positive energy remains in the research and development phase.

Solar and wind energy are based on infinite, renewable sources. Their investment costs are low and carbon emissions are minimal. However, their production depends on weather conditions, making them intermittent and potentially reducing system reliability due to capacity factors ranging from 10 to 45 percent.

Fossil fuels (coal, oil, and natural gas) offer high technical energy efficiency but are not a sustainable long-term solution due to high carbon emissions and declining reserves.

Table 3 presents a comparative analysis of major energy types based on these indicators.

_{Table 3 – Technical, Economic, and Environmental Comparison of Energy Sources}

*The stated reserve lifespans are calculated assuming the 2023 energy consumption rate remains constant. If annual consumption increases over time, reserve lifespans will shorten significantly.

*The specific energy calculation for nuclear energy is based on natural uranium.

*Energy density (MJ/kg): Represents the theoretical energy released per unit mass, indicating the energy-carrying capacity of the source.

*Reserves (ton): The estimated economically extractable resource quantity on Earth.

*Sustainability (years): The estimated time to depletion at current consumption rates.

*Capacity factor (%): The average production rate of a plant over a year relative to its maximum capacity.

 *OCC ($/kW): Overnight Capital Cost – Investment cost. Represents the total cost required to build a plant, excluding financial delays and inflation.

 *LCOE ($/MWh): Levelized Cost of Electricity – The average cost per unit of electricity generated over the plant’s lifetime, including all costs (investment, operation, maintenance, fuel) divided by total electricity output.

*Carbon emissions (ton CO₂/GWh): The amount of carbon dioxide emitted per unit of electricity generated.

*Land use (m²/MWh): The average land area required to produce one megawatt-hour of electricity.

*Water consumption (L/MWh): The total volume of water consumed per unit of electricity generated, including cooling and process needs. 

Fossil Fuels

Oil, natural gas, and coal still meet approximately 77 percent of global energy supply. However, the reserve lifespans and production efficiencies of these resources are gradually declining. At current consumption rates, oil reserves are projected to last about 58 years, natural gas 52 years, and coal 159 years. Detailed data are presented in Table 4.

_{Table 4 Global Fossil Fuel Reserves and Consumption Data (2023) (10)}

*R/P: Reserves-to-Production ratio. Data are calculated based on current consumption levels.

However, the Energy Return on Investment (EROI) of fossil fuels has declined over the years. For example, while the EROI for conventional oil was around 30:1 in the 1970s, it has now fallen to approximately 15:1. For shale oil and tight natural gas sources, this ratio is between 5–10:1. Similar declining trends are observed in coal and natural gas.

_{Table 5 EROI (Energy Return on Investment) Values for Fossil Fuels}

*EROI values vary widely in the literature; approximate trends are shown.

This trend is directly linked not only to the quantity of reserves but also to accessibility, extraction technology, rising costs, and environmental constraints. One of the key drivers of the energy transition is this declining efficiency.

Renewable Energy

Renewable energy sources, with their low carbon emissions and sustainable structure, are at the center of the energy transition. In 2023, approximately 510 GW of new renewable energy capacity was added globally, 75 percent of which came from solar photovoltaic systems. Total installed renewable capacity stands at around 3,800 GW.

_{Table 6 Global Renewable Energy Data (2023–2024)}

In Türkiye, 42 percent of total electricity generation comes from renewable sources. Total installed capacity is 106,668 MW, of which 56 percent is from renewables. In line with 2035 targets, Türkiye aims to increase the share of renewable energy in electricity generation to 55 percent and in installed capacity to 65 percent.

_{Table 7 Türkiye’s 2023 Electricity Generation}

However, the intermittent nature of sources such as solar and wind necessitates large-scale battery systems. The global target is to increase battery capacity to 970 GW by 2030.

_{Table 8 Türkiye’s 2035 Electricity and Capacity Targets}

Nuclear Energy

Nuclear energy holds strategic importance due to its low emissions and long fuel cycle. As of 2023, extractable uranium reserves amount to approximately 7.93 million tons, sufficient to supply energy for 120–160 years using current reactor technologies.

Breeder reactors can extend uranium reserve lifetimes by a factor of 30. Additionally, Mixed Oxide (MOX) fuel cycles and thorium-based systems can further extend this duration.

Fusion Energy

Fusion energy aims to harness energy released by the merging of hydrogen isotopes. Its fuel, derived from seawater, is theoretically unlimited. Due to zero carbon emissions and high energy efficiency, fusion holds a unique position among clean energy sources.

However, commercial use remains unfeasible. Projects such as ITER, STEP, CFETR, and DEMO aim to develop fusion technology. Fusion is expected to make a significant contribution to energy systems only after 2050, with a potential contribution of around 5 percent by 2100.

_{Table 9 Estimated Contribution Shares of Fusion and Breeder Systems (21; 22)}

*Values are scenario-based projections with uncertain realizations. Fusion cannot make commercial contributions before 2050 but may achieve limited shares by 2100. Breeder FBRs may enter operation in some countries by 2050 and could assume a major portion of nuclear production by century’s end.

Energy Consumption Projections

If current production trends continue, global energy demand could reach 203,000 TWh by 2050. Under net-zero scenarios, this is targeted to be capped at 175,000 TWh. In these scenarios, energy efficiency, electric transportation, industrial conservation technologies, and digital infrastructure advancements will play critical roles.

Projections for 2100 suggest energy consumption could rise to 300,000 TWh. This increase is driven by the widespread adoption of electric vehicles, hydrogen production, cooling systems, and artificial intelligence-based applications.

Projected reserve lifespans for fossil fuels are approximately 58 years for oil, 52 years for natural gas, and 159 years for coal. In contrast, nuclear energy can provide sustainable fuel for 120–160 years with current reactors and thousands of years with advanced systems. While renewable sources have unlimited potential, they face constraints related to infrastructure, investment, and intermittency.

Conclusion

Since 1970, global energy consumption has increased by 180 percent, and nearly 77 percent of this demand is still met by fossil fuels. However, the limited remaining reserves of oil, natural gas, and coal—only 58, 52, and 159 years respectively—combined with declining EROI values, rising production costs, and carbon pricing mechanisms, are undermining the sustainability of fossil-based energy systems. In this context, a transition to alternative energy technologies capable of simultaneously ensuring energy supply security, economic efficiency, and environmental goals is inevitable.

Nuclear energy plays a pivotal role in this transition. Uranium reserves can support energy production for 120–160 years with current light water reactors and for thousands of years with advanced closed fuel cycles in breeder reactors. Breeder systems enhance fuel utilization efficiency by converting U-238 into fissile Pu-239, while MOX fuel cycles and alternatives such as thorium strengthen resource diversity. Small Modular Reactors (SMRs) offer more flexible and scalable solutions, while MOX and fast breeder reactors reduce waste volume and ensure cycle sustainability. In the medium to long term, fusion projects such as ITER and DEMO will play a crucial role in restructuring energy systems with carbon-free, theoretically unlimited energy potential.

On the renewable side, a record 510 GW of new installations were added globally in 2023. However, due to the low capacity factors of solar and wind (10–35 percent), large-scale storage solutions have become essential. International projections indicate that global battery capacity must reach 970 GW by 2030.

For Türkiye, this transition represents a strategic opportunity. In the short term (2025–2030), investments of ≥80 GW in solar and wind capacity and ≥5 GW in battery storage can reduce fossil dependence in industry. In the medium term (2040–2060), a portfolio of ≥5 GW of SMRs and ≥20 GW of battery investment can further decarbonize industrial processes. In the long term (2060–2100), deployment of ≥3 GW of FBRs and a domestic DEMO fusion prototype can enable a closed-loop, sustainable energy architecture.

In conclusion, redesigning the energy system requires moving away from fossil fuels, establishing a secure and diverse resource structure supported by advanced nuclear technologies, and enhancing grid flexibility through battery systems. These goals will not only ensure supply security but also make possible a low-carbon future aligned with climate commitments.