Multijunction Solar Cells - Technology Imitates Nature

Remember your basic Biology 101 and photosynthesis?

In case you need a refresher on the topic, photosynthesis is how a plant converts light into energy, which it uses to run its metabolic processes. Multijunction solar represent the mechanical, artificial analogue to this biological process. But before we get into that, let's take a look at your basic solar cell.

It's Been Around Longer Than You Think
The idea of generating electricity using sunlight dates back almost to the time people started using electricity. In fact, a photovoltaic effect was first produced around 1840 - not long after Queen

Victoria ascended to the British throne. However, it was another fifty years or so before someone actually created a working solar cell, and another twelve years before Einstein was able to explain how it worked (he won the 1921 Nobel Prize for that). The first modern multijunction solar were made just after World War II.

In simple terms, a solar produces electricity when sunlight (photons) hit the surface. This sunlight is absorbed by a semi-conductor, usually silicon. This causes electrons, the subatomic particles that carry a negative electrical charge, to come loose from the atom, which ultimately produces electrical current.

The Problem - and Solutions
The problem with those silicon flat-panel solar arrays is that they aren't terribly efficient. However, a cpv solar cell array can have an efficiency rate of over 40%, meaning that two-fifths of the light that hits the surface is converted into electrical current. This figure is going up, and within the next year or so, a cpv solar cell array will have what is called grid parity with today's fossil-fueled power plants, meaning that a grid of solar cells will produce the same amount of energy as an equivalent fossil fuel setup.

The secret is that new solar cells have multiple layers, each of which captures a different part of the light spectrum. As you probably know, sunlight contains several different colors, which we cannot perceive until that sunlight is broken up into its components by a prism, such as a crystal or water droplets. You see the different parts of the spectrum when a rainbow forms in the sky after a rainstorm.

Regular solar cells with a single layer are only able to capture part of the spectrum; CPV cell layers are "tuned" specifically to capture the entire spectrum.
Efficiency is further increased in an array using concentrated photovoltaic cells, in which various devices - such as mirrors and fresnel lenses - are employed to increase the intensity of the sunlight hitting the surface.

Wayne Hemrick writes about-- multijunction solar cells

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