A combination of inexpensive materials collects and concentrates heat from the Sun.
Heating water to its boiling point is an important first step not only for preparing a cup of tea or a bowl of pasta, but for a range of applications fundamental to an industrial society, including distillation, sterilization, and power generation. In a solar economy, one could boil water with an electric heater powered by a photovoltaic cell. But it would be far more efficient to use solar energy to heat the water directly.
That’s manifestly possible. For decades solar steam turbines in wide-open sunny spaces have used arrays of mirrors to concentrate sunlight from a large area onto a small volume of water. But those mirrors are expensive: They must be precisely machined to focus light over several hundred meters, and they must be mounted on motors to track the Sun’s position in the sky. Because the motors require that a powerful source of electricity already be available, optical concentrating arrays aren’t suitable to smaller-scale or off-the-grid applications, such as sterilizing medical instruments in a clinic in the developing world.
Now MIT’s Gang Chen, George Ni, and their colleagues have demonstrated a different approach: concentrating not the Sun’s light but its heat.1 Because their steam generator consists entirely of commonly available materials—a conscious choice on their part—they estimate that per unit area, it could be built for just 1–3% of the cost of an array of motorized mirrors.
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