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What type of energy will never run out?

With the rising costs of fossil fuels and concerns over climate change, many people are looking for energy sources that are renewable and will never run out. Some renewable energy sources like solar, wind, geothermal and hydroelectric power seem endless, since they harness energy from the sun, wind, earth’s heat and water currents. However, no energy source lasts forever. Even renewable sources could potentially run out or lose efficiency over time. So what type of energy will literally never run out?

Nuclear Fusion

Nuclear fusion has the potential to provide an endless supply of energy by replicating the nuclear reactions that occur in the sun and stars. Fusion involves joining together light atomic nuclei to form heavier nuclei, releasing massive amounts of energy in the process. The most efficient fusion reaction combines deuterium and tritium, which are two isotopes of hydrogen.

This reaction produces helium atoms and neutrons, along with a huge output of energy. Deuterium can be distilled from all forms of water, while tritium can be produced during the fusion reaction as neutrons interact with lithium. Therefore, nuclear fusion relies on hydrogen and lithium, two of the most abundant elements in the universe.

With access to seawater alone, there are enough deuterium reserves to provide the world’s electricity needs for billions of years. The key challenge is building a fusion reactor that can produce a net energy gain – generating more energy than it takes to initiate the reaction. But if this hurdle can be overcome, nuclear fusion may provide limitless energy with minimal negative impacts.

Advantages of Fusion Power

– Virtually inexhaustible fuel reserves from seawater and lithium

– No greenhouse gas emissions or air pollution

– Less radioactive waste than nuclear fission

– Abundant fuel materials evenly distributed globally

– No risk of meltdown or runaway reactions

Disadvantages of Fusion Power

– No commercial fusion reactor yet exists

– Prototypes require more energy input than they produce

– Extremely high temperatures and pressures required

– High development costs with uncertain timeline

– Use of tritium raises proliferation and safety concerns

Geothermal Energy

Another candidate for inexhaustible energy is geothermal power. Geothermal energy harnesses the heat generated and stored within the Earth to produce steam to drive turbines and generate electricity. Hot water or steam can also be used directly for heating buildings, growing plants in greenhouses, and various industrial processes.

The source of geothermal energy is the primordial heat leftover from the Earth’s formation over 4 billion years ago, along with heat continuously generated by radioactive decay of minerals in the planet’s core. This makes geothermal essentially limitless, unlike fossil fuels which regenerate very slowly. The Earth contains enough residual heat to provide energy for billions of years.

Advantages of Geothermal Power

– Renewable – core heat regenerates over time

– Reliable – available consistently day and night

– Environmentally friendly – low emissions

– Cost effective – inexpensive to operate

– Sustainable for future generations

Disadvantages of Geothermal Power

– High upfront costs for drilling and installation

– Limited to geographical areas with subsurface heat and water

– Geologic uncertainty over resource size and longevity

– Hydrothermal areas may become depleted over time

– Chance of subsidence or small earthquakes

Ocean Thermal Energy

Another renewable resource that could provide endless energy is ocean thermal energy conversion (OTEC). This process harnesses energy from temperature differences between warm surface seawater and cold deep ocean water. In the tropics, surface water can exceed 25°C (77°F), while water just 1000 meters down is around 4°C (39°F).

OTEC systems use this 20°C differential to generate electricity. Warm surface water is pumped through a heat exchanger to vaporize a working fluid with a low boiling point. The expanding vapor turns a turbine attached to a generator. Cold deep seawater then condenses the vapor back to liquid. The cycle is continuously repeated.

The tropical oceans receive enough solar energy every hour to equal the world’s annual energy needs. Since solar heating causes these temperature differences, OTEC is an indirect form of solar energy. But it avoids intermittency issues of direct solar collection.

Advantages of OTEC

– Renewable – uses constant ocean temperature differences

– Massive potential capacity from tropical seas

– Does not require high-tech solar cells

– Generating capacity factors over 90%

– Integrates with desalination and agriculture

Disadvantages of OTEC

– Complex systems required for deep water access

– High upfront investment costs

– Potential environmental impact on sea life

– Limited to tropical regions near coasts

– Low efficiencies of 1-3% from small temperature differences

Space-Based Solar Power

Space-based solar power involves placing large solar arrays in space to collect sunlight and transmit the energy wirelessly to Earth. A constellation of satellites in geostationary orbit could provide continuous 24/7 power. Since the arrays sit above the atmosphere, they can collect sunlight far more efficiently than ground-based panels. The energy is converted to microwaves or laser beams and pointed at receiving antennas on Earth.

While the upfront costs of such a system are immense, the potential payoff is even larger. The sun bombards Earth with 173,000 terawatts of solar energy – dwarfing global energy demand. Harnessing even a fraction of this in space could meet civilization’s needs for eons. Once the infrastructure is built, operational costs are relatively low while energy output remains high.

Advantages of Space-Based Solar

– Effectively unlimited energy potential

– 24/7 baseload power production

– Avoid intermittency issues of ground solar

– No weather impacts on output

– stationed in stable geostationary orbit

Disadvantages of Space-Based Solar

– Extremely high upfront launch and construction costs

– Requirement for heavy lift launch vehicles

– Untested wireless power transmission at scale

– Need for space construction and maintenance

– Energy losses from beaming over long distances

Tidal Power

Tidal energy utilizes the natural rise and fall of ocean tides to generate electricity. Coastal tidal power plants capture the potential energy of powerful tidal currents with submerged turbines, similar to wind turbines. Tidal barrages also exploit difference in height between high and low tides.

Tides are driven by the gravitational forces exerted by the Moon and Sun. Tidal forces are actually strengthening over time, which enhances the appeal of tidal power. Since tides are tied to lunar orbits, they are completely predictable decades or centuries in advance. Tidal energy output is highly consistent and reliable.

Advantages of Tidal Power

– Renewable – driven by lunar gravity

– Highly predictable and constant energy

– Flood protection from tidal barrages

– Does not deplete fish stocks or biodiversity

– Pairs well with wind and solar to balance grid

Disadvantages of Tidal Power

– Limited to coastal regions with high tides

– High capital costs for tidal dams and turbines

– Potential impact on marine ecosystems

– Sediment build-up can limit dam efficiency

– Intermittency on tidal timescales

Radioisotope Thermoelectric Generators

One niche energy technology that could outlast all others is the radioisotope thermoelectric generator (RTG). RTGs are used to power unmanned remote facilities like spacecraft, lunar bases, or arctic sensors for decades at a time. They convert heat from radioactive decay into electricity using thermocouples.

RTGs contain radioactive isotopes like plutonium-238 which release alpha particles as they decay. The alpha particles deposit kinetic energy as heat, which is converted to electricity with no moving parts. RTGs have exceptional longevity – the Voyager probes have RTGs that have been providing power for over 40 years in deep space. Their usable lifetime is several decades to centuries.

Advantages of RTGs

– Very long operational lifetimes

– Reliable power regardless of conditions

– No maintenance or refueling needed

– Compact and lightweight

– Proven technology for space missions

Disadvantages of RTGs

– Use of radioactive materials

– Low power output compared to size

– Thermal and radiation shielding required

– Limited fuel availability and high cost

– Not suitable for widespread commercial use


While no energy solution is perfectly infinite, some renewable technologies like nuclear fusion, geothermal, ocean thermal, space-based solar and tidal have tremendous longevity. Fusion has effectively unlimited potential if technical challenges can be overcome. Geothermal can provide stable baseload power for millions of years. Space-based solar exploits a truly endless resource in the Sun’s constant energy output. And ocean thermal and tidal energy rely on motions of the Earth, Sun and Moon that are predictable for eons into the future.

For specialized applications like deep space travel, radioisotope generators can keep running unmaintained for decades or centuries at a time. But for scalable energy production here on Earth, the best truly renewable sources are those driven indirectly by the Sun’s natural fusion reactor: geothermal, ocean thermal, biofuels and orbital solar arrays. While no energy solution will ever be perfectly endless, renewables like these offer the best chance of powering civilization for many millennia to come.