Iron Man has his arc reactor, the humans in "Avatar" have their unobtanium and what would "Star Trek" be without dilithium crystals? While these energy sources are impressive, they're also fictional. Humanity will eventually need to transition from a dependence on fossil fuels to other forms of energy, but what are they? And when can we have them?
Humanity needs a potent, dependable and sustainable energy source. Our planet already has one in the form of the sun, so it shouldn't come as a surprise that the biggest energy sources for the future all involve that fiery star.
First, there's the hydrogen fuel cell to consider: a battery that depends on oxygen and pure hydrogen gas and converts chemical energy into electrical energy. The real challenge is obtaining that pure hydrogen gas, but all Earth's hydrogen is already oxidized -- unless you obtain it from hydrocarbons in oil and natural gas, which puts the focus back on nonrenewable fossil fuels.
Since we can't harvest pure hydrogen from the rich reserves on Jupiter or the sun just yet, we're left with one option: produce it through the electrolysis of water. Sadly, this process currently demands more energy than it supplies. If we can overcome this technological hurdle, however, hydrogen fuel cells could have a major impact on global energy.
While nuclear fission produces a great deal of energy without relying on fossil fuels, it also produces nuclear waste. Nuclear fusion, the source of the sun's energy, generates significantly less waste without all the radiation. But again, it occurs in the sun, where powerful gravity and heat strip hydrogen atoms down to their nuclei and fuse them together. Scientists are getting closer to pulling off this effect on Earth, but the fusion reactors are still expected to expend more energy than they produce. As the technology improves, however, fusion will become an increasingly attractive option, assuming we can figure out how to contain it, too.
Finally, there's good old solar energy. The amount of solar energy we can harvest on Earth is somewhat limited by varying cloud cover and the cycle of night and day. Space-based solar power (SBSP) would allow us to work around these challenges. Solar harvesters in orbit, on the moon or elsewhere in space could collect solar energy and transmit it back to Earth. While the idea originated in the 1960s, SBSP gains more and more potential as solar technology improves and the cost of deployment decreases.
These three energy sources continue to tantalize us with their potential for clean, renewable energy. The question is, which will we figure out how to master first?
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