How Solar Battery Chargers Function

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Uh oh. The shortcut you decided to take through the forest has turned into a confusing maze. You're lost, somehow off the main road, and there's no way to get back. To make things worse, your car is nearly out of gas. You've also failed to inform anyone of your whereabouts, and now your phone is almost dead. The periodic beeps signaling its low battery feel like a reflection of your own dwindling energy.

Fortunately, there's a break in the dense forest canopy. Ahead, you spot a vast meadow bathed in sunlight, the rays illuminating the tall grass. You park your car and head toward the meadow. Once you're clear of the trees, you look up and see a flawless sky, without a cloud in sight. Everything is going to be alright. After searching through your glove compartment for a moment, you find your solar-powered battery charger. You connect the USB cable to your phone, flip the charger to expose its small solar panel to the sky, and place the entire setup on a nearby stump. Now, you can kick back, relax, and wait, knowing that help is on its way. This could be the perfect time to enjoy a book.

Before the turn of the 21st century, finding yourself in a situation like this would have left you stranded with no solution. However, in recent years, numerous companies have developed solar-powered battery chargers capable of harnessing the sun's energy to charge everything from cars to small gadgets and even AA batteries. Discover the inner workings of solar battery chargers in the next section.

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Mechanics of Solar Battery Chargers

The sun has been shining light and radiating heat to Earth for billions of years. However, it’s only in recent history that humanity has discovered how to capture and convert some of this energy into electricity. The first breakthrough came with the creation of the photovoltaic cell by Bell Laboratories researchers in 1954 [source: DOE]. Since then, solar cells have progressed from powering large, costly space equipment to more accessible devices such as battery chargers. But how exactly does this solar energy transform into usable electricity?

Here’s how it works: An electrical current is generated by the movement of free electrons, which carry a negative charge. Normally, electrons are bound in orbits around an atom's nucleus, composed of protons and neutrons. These atomic particles are the fundamental components of matter and are present in everything. Some substances hold their electrons more tightly, but with sufficient energy, an electron can be dislodged from its orbit.

One energy particle that’s particularly good at dislodging electrons from atoms is the photon. This is the subatomic energy unit that makes up light. Photons from sunlight possess enough energy to free electrons from their orbits within the silicon element, which is the primary material used in most solar cells. The process of photons freeing electrons is known as the photoelectric effect [source: ASU].

By introducing the impurities boron and phosphorus into silicon, an imbalance is created between positively and negatively charged particles. This imbalance generates an electrical field within the silicon. When photons hit the material and release electrons from their orbits, this electrical field pushes the electrons toward the front of the solar cell, creating a negatively charged side. The protons left behind on the opposite side of the cell form a positive charge [source: GE]. When these two sides are connected through an external load — like the terminals of a solar battery charger — the electrons flow through the load and generate electricity. Since a single solar cell produces only one or two watts of power, multiple cells are linked together to form modules that collectively generate enough energy to charge a battery [source: DOE].

Chemical batteries produce an electron flow through a chemical reaction. Lithium-ion batteries, commonly found in devices like cell phones and iPods, generate energy by transferring ions between lithium and carbon. In both types of batteries, electricity is created by the flow from negative to positive electrodes. When recharging a battery, the electron flow reverses, and the battery's electrical charge is restored.

Solar battery chargers don’t directly charge the lithium-ion battery in your device. Instead, they usually charge their own internal rechargeable batteries — either chemical or lithium-ion — through solar panels, then transfer the energy to your device. No external electrical source is needed.

Let’s delve into the numerous advantages of solar battery chargers in the next section.

Benefits of Solar Battery Chargers

The most obvious advantage of solar battery chargers is that they don’t require any external electrical sources for recharging. This means that they provide great freedom of movement. The sun shines almost everywhere on Earth during the day, so if you're ever lost in the woods with a dead phone, you only need sunlight to bring it back to life.

This independence from traditional electrical sources offers several additional benefits. Solar cells create no emissions, waste, or harmful byproducts; any photons that aren't absorbed simply pass through the silicon or reflect off, as they would from any other material. Remember, the energy transfer that generates electricity comes from photons liberating electrons, allowing them to flow. Electricity itself isn't energy, but an energy carrier, and generating it via the photoelectric effect is a harmless process.

However, the electricity generated around the globe is often far from environmentally friendly. For instance, nearly half of the electricity produced in the U.S. in 2008 was derived from burning coal [source: EIA]. While coal is an inexpensive and readily available way to generate power, it is also a significant source of pollutants. The Environmental Protection Agency (EPA) reports that coal-fired power plants contribute 59% of sulfur dioxide emissions and 50% of particulate pollutants in the U.S. Additionally, these plants are a major source of mercury contamination [source: EPA].

The two primary benefits of owning a solar battery charger are the freedom it offers and its environmental friendliness. That said, there are some downsides to solar charging. The biggest drawback is that for about half of any given day (except near the poles), the sun isn't available. Without sunlight, solar-powered devices are essentially useless at night. Bad weather and thick clouds also significantly affect solar cell performance. Even in full sunlight, most solar cells today are only about 10% efficient, meaning they’re slower than chargers that plug into a wall outlet [source: DOE].

If you ever find yourself stranded in the woods, you'll undoubtedly realize that a solar battery charger is indeed a brilliant invention.

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