Solar Energy without the Sun?

When the words “photovoltaic” or “solar energy” are brought up, what’s the first thing that people think of? Not surprisingly, the answer is the sun. This is unsurprising, as anything solar-related needs sunlight to produce energy. The sun may be our greatest asset in solar energy, but it’s also the biggest obstacle as well, because there is only sunlight for half the day, and sometimes an overcast or stormy day prevents any solar energy from being produced.

Now, imagine solar panels that aren’t reliant on the sun for power. The idea might sound farfetched, but that’s exactly what researchers at MIT have accomplished: sun-free photovoltaics. This new photovoltaic energy-conversion system can be powered solely by heat, generating electricity with no sunlight at all. It may come as a surprise to some people, but this concept is by no means new. More than half a century ago, researchers developed thermophotovoltaics (TPV), which couple a photovoltaic (PV) cell with any source of heat. While the idea was groundbreaking, the idea was impractical at the time due to insufficient technology.

However, with recent advances in solar technology, researchers at MIT have developed a novel way of engineering to allow for sun-free energy. Essentially, the surface of a material is specially modified so it converts heat into precisely tuned wavelengths of light, which are selected to match the wavelengths that photovoltaic cells can best convert to electricity, in order to maximize efficiency. What really makes this system effective is the surface of the material, which has billions of nanoscale pits etched on its surface, and when the material absorbs heat, the pitted surface radiates energy primarily at these carefully chosen wavelengths.

Researchers at MIT are not yet satisfied, and they have their sights set on making sun-free photovoltaics viable in everyday life. According to the U.S. Energy Information Administration, 92 percent of all the energy we use involves converting heat into mechanical energy, and then often into electricity. One such example is using fuel to boil water to turn a turbine, which is attached to a generator. However, these mechanical systems have relatively low efficiency, and can’t be scaled down to the small sizes needed for devices such as sensors, smartphones, or medical monitors.

“Being able to convert heat from various sources into electricity without moving parts would bring huge benefits, especially if we could do it efficiently, relatively inexpensively and on a small scale,” says Ivan Celanovic, a research engineer involved in MIT’s ongoing quest for efficient solar energy.

Even despite this hurdle, the future of solar energy is as bright as ever. The possibilities of photovoltaics that do not rely on the sun are endless. No longer will geography and location limit the scope of the solar frontier. Instead, with the potential to succeed in all areas of the world, sun-free photovoltaics are the future of solar energy, and it will be the leading component in solar energy within the next decade.

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