Fusion is the way our sun powers itself. It's clean, it's efficient, and all you need is hydrogen, which we've got a bunch of stashed away in the ocean. We've been having trouble making fusion happen here on Earth, because we don't have any suns lying around to do it for us, but this could be the year where we make it happen, efficiently, with giant lasers.
Nuclear power plants create energy using fission, where big atoms like uranium split into two or more smaller atoms, releasing a bunch of energy as they do. Fusion, on the other hand, takes two small atoms (hydrogen, nearly as small as they get) and sticks them together, releasing even more energy without any nasty radioactive byproducts. Getting two hydrogen atoms to form one helium atom is not easy: anywhere outside of the core of a star, you have to get creative, using magnetic fields or explosives or lasers to provide the temperatures and pressures necessary.
Fusion sounds all kinds of futuristic, but it's not. We can do fusion already, using those aforementioned magnetic fields or explosives or lasers. The trick that we haven't figured out is getting fusion to release more energy than we put in to make it happen. So like, we can fire a whole bunch of super powerful lasers at a little pellet of hydrogen to heat and compress it enough get it to fuse, but the energy that we put into the lasers is way higher than the energy that's released by the fusion, kinda defeating the whole point of a fusion power source.
The magical "break-even" point is where you get the same amount of energy out of a fusion reaction as you put into it, and once we hit that, we can start to get excited about cheap and clean fusion power. The National Ignition Facility, which uses a huge laser to compress little pellets of hydrogen to get them to fuse, has slowly been working up to break-even (what they call "ignition"), and it's optimistic that a 2.2 megajoule pulse from its laser system will be enough to ignite a pellet of hydrogen before the end of the year.
Getting from fusion ignition to a working power plant is another matter entirely. For fusion power to be practical, we'd need lasers igniting 15 hydrogen pellets per second, and each one of those pellets would have to produce 50 times more energy than went into fusing it. But, it's definitely possible to get a fusion power plant like this up and running, provided we're willing to invest in it: the National Ignition Facility says that with $4 billion, they'd be able to create a pilot laser fusion power plant that would be putting hundreds of megawatts into the grid by the early 2020s. LINK
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