The space program could not have existed without the solar cells and its twin, the transistor. Almost all satellites ever launched have relied on these two semiconductor devices to operate. Solar cells convert sunlight directly into electricity. No more than several hundred microns thick, they produce electricity without boilers, turbines, pipes and cooling towers. In fact, they work without moving parts. Photons, packets of energy from the sun, silently split loosely bound electrons in the solar material from their orbits. The solar cell's intrinsic voltage pushes those liberated electrons in its vicinity to contacts where they flow through as electricity. The modularity of the technology called photovoltaics allows technicians to exactly fit the amount of solar cells to the application at hand whether requiring a milliwatt or megawatts of power.
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