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A guide to the energy of Earth
Energy is neither created nor destroyed — and yet the global demand for it continues to increase. But where does energy come from, and where does it go? Joshua M. Sneideman examines the many ways in which energy cycles through our planet, from the sun to our food chain to electricity and beyond.

How do solar panels work?
The Earth intercepts a lot of solar power: 173,000 terawatts. That’s 10,000 times more power than the planet’s population uses. So is it possible that one day the world could be completely reliant on solar energy? Richard Komp examines how solar panels convert solar energy to electrical energy.

Can 100% renewable energy power the world?
Every year, the world uses 35 billion barrels of oil. This massive scale of fossil fuel dependence pollutes the earth, and it won’t last forever. On the other hand, we have abundant sun, water and wind, which are all renewable energy sources. So why don’t we exchange our fossil fuel dependence for an existence based only on renewables? Federico Rosei and Renzo Rosei describe the challenges.

Why aren’t we only using solar power?
Solar power is cheaper and more sustainable than our current coal-fueled power plants, so why haven't we made the switch? The real culprits here are the clouds, which make solar power difficult to control. Alexandros George Charalambides explains how solar towers and panels create electricity and how scientists are trying to create a system that can function even under cloud cover.

Why don’t perpetual motion machines ever work?
Perpetual motion machines — devices that can do work indefinitely without any external energy source — have captured many inventors’ imaginations because they could totally transform our relationship with energy. There’s just one problem: they don’t work. Why not? Netta Schramm describes the pitfalls of perpetual motion machines.

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