Uh oh. That shortcut you took through the woods has led you into a maze. You're lost, and somehow you've ended up off the main road with no way back in sight -- and your car is running low on gas. To make matters worse, you've told no one where you're going and your phone is running out of juice. The measured beeps it issues to alert you of its imminent demise seem like a reminder of your own as well.
Luckily for you, there's a break in the forest canopy. You see a wide meadow full of sunshine streaming down into the tall grass up ahead. You park your car and walk to the meadow. Once clear of the trees, you look up, and there's not a cloud in the sky. Yes, you're going to be just fine. After rummaging around in your glove compartment for a bit, you retrieve your solar-powered battery charger. You plug the USB cable from the charger into your cell phone, flip the charger over so that its small solar panel faces skyward, find your cell phone signal, place the whole setup on a stump, kick back and wait. This is a probably a good time to relax and read a book, since you know that help is on the way.
Before the first decade of the 21st century, you would have been out of luck had you found yourself in a scenario like this one. Lately, however, a number of companies have created a spate of battery chargers that use the power of the sun to fuel everything from cars to gadgets to AA batteries. Find out about the mechanics behind solar battery chargers on the next page.
Mechanics of Solar Battery Chargers
The sun has been sending light and heat to the Earth for several billion years. Yet, only recently have we humans figured out how to capture and harness some of this energy as electricity. The first method was the photovoltaic cell created by researchers at Bell Laboratories in 1954 [source: DOE]. Since then, solar cells have evolved from transforming sunlight into usable electricity for huge, expensive space equipment to more down-to-earth devices like battery chargers. That's great, but how is this solar energy translated into electricity?
This is how it happens: An electrical current is created by the movement of free electrons, which carry a negative charge. Normally, electrons are entangled in an orbit around the nucleus of an atom, which is made of protons and neutrons. These atomic particles are the building blocks of matter and can be found in absolutely everything. Some matter holds its electrons more tightly than others, but given enough energy, an electron can be knocked loose from its orbit.
One particle of energy that does a fine job of knocking electrons loose from atoms is the photon. This is the subatomic energy packet that forms the basis for light. Photons from sunlight carry enough energy to jar electrons from their orbit in the element silicon, which is the material used in most solar cells. The photon's ability to disentangle electrons is called the photoelectric effect [source: ASU].
An imbalance between positively charged and negatively charged particles is created within the silicon by adding the impurities boron and phosphorus. This imbalance creates an electrical field in the silicon. When photons strike the material and break electrons free from their orbits, this electrical field pushes them toward the front of the solar cell, which creates a negatively charged side. The protons left behind on the other side of the cell surface create a positive charge [source: GE]. When these two sides are connected using an external load -- an indirect circuit like the terminals of this solar battery charger -- the electrons flow into the load and creates electricity. Since a single solar cell only produces one or two watts of electricity, multiple cells are combined to form modules that work together to produce enough power to charge a battery [source: DOE].
Chemical batteries generate electron flow through a chemical reaction. Lithium-ion batteries, like those found in cell phones and iPods, create energy through an exchange of ions from lithium to carbon. In both types of batteries, electricity is created by the flow from negative to positive electrodes. When a battery is recharged, the flow of electrons reverses itself, and the battery's electrical potential is replenished.
Solar battery chargers don't directly charge the lithium ion battery in your gadget. They usually maintain their own rechargeable batteries -- either chemical or lithium-ion -- that are charged through the solar modules and redistribute their charge to your gadget. No external electrical source is required.
Let's explore the many benefits of solar battery chargers on the next page.
Benefits of Solar Battery Chargers
It's pretty easy to determine the most important benefit that solar battery chargers provide: They don't require external electrical sources to recharge your batteries. This means that solar battery chargers offer freedom of movement. You can find the sun pretty much anywhere on Earth during the daytime. So, if you find yourself lost in the woods with a dead cell phone, you need only the sun's rays to get it up and running again.
This lack of a typical electrical source also offers some subtler benefits. Solar cells generate no emissions, waste or byproducts; those photons that aren't used simply pass through the silicon or bounce off of it as they would any other material. Remember, this electricity is produced by the transfer of energy from photon to electron, which frees the electron and allows it to flow. Electricity is not itself a form of energy, but an energy carrier. Producing it through the photoelectric effect is a benign way of generating an electrical charge.
However, the electricity that's produced around the world is often much less benign from an environmental standpoint. For example, in 2008, nearly half of the electricity generated in the United States came from the burning of coal [source: EIA]. While coal is a cheap and easy way to generate electricity, it's also a major source of pollutants. The Environmental Protection Agency (EPA) estimates that coal-fire power plants generate 59 percent of the sulfur dioxide in the air within the U.S., as well as 50 percent of the particulate pollutants. What's more, coal-fired power plants also contribute heavily to mercury pollution [source: EPA].
Freedom of movement and environmental friendliness are the two biggest reasons to own a solar battery charger. However, there are also a few drawbacks to solar charging. Chief among them is that for around half of any given day (outside of the Earth's polar regions), the sun is nowhere to be found. The absence of photons showering from space makes any solar power device all but useless at night. Bad weather and heavy cloud cover also have a big impact on how well a solar cell operates. Even in bright sunlight, most solar cells currently in production are only about 10 percent efficient, which makes them slower than chargers that plug into a wall outlet [source: DOE].
Still, if you find yourself trapped in the woods, you'll likely conclude that a solar battery charger was a great invention indeed.
For more information on gadgets and other related topics, visit the next page.
- "Dirty coal power." Sierra Club. Accessed February 5, 2009. http://www.sierraclub.org/cleanair/factsheets/power.asp
- "Electric power monthly." Energy Information Administration. January 15, 2009. http://www.eia.doe.gov/cneaf/electricity/epm/epm_sum.html
- "How solar cells work." General Electric. Accessed February 5, 2009. http://www.gepower.com/prod_serv/products/solar/en/how_solar_work.htm
- "Solar energy -- energy from the sun." Department of Energy. Accessed February 5, 2009. http://www.eia.doe.gov/kids/energyfacts/sources/renewable/solar.html
- "Solar tutorial." Battery Stuff. Accessed February 5, 2009. http://www.batterystuff.com/tutorial_solar.html
- "Solar battery charger." Solar Sphere. Accessed February 5, 2009. http://www.spheralsolar.com/solarbatterycharger.html
- "The photoelectric effect." Arizona State University. Accessed February 5, 2009. http://acept.asu.edu/PiN/rdg/photoelectric/photoelectric.shtml